The Who, How and Where of Antigen

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The imme tem i high damic ad diere, hicheabe it to effectie protect a idiida from mer-o potetia pathogeic ecoter. Ear tdie thatcombied techiqe ch a eectro microcop adimmoforecece ieded aabe iformatio othe tatic ocatio ad orgaizatio of the ce of theimme tem, ad iferred their damic propertie(for a hitorica perpectie ad referece to origiaartice ee REFS 1–3). Hoeer, it i ecear to coiderthe deeopmet of imme repoe i term of bothitracear ad itercear iteractio i the appro-priate eiromet ad i rea time4–8. Ideed, the recetdeeopmet of high-reotio imagig techiqe,icdig cofoca microcop, total internal reflection

fluorescence microscopy ad intravital multiphoton micro-

scopy, ha proided iight ito the patio-tempora

damic of the moecar ad cear eet thatderie imme repoe to pathogeic ifectio. Oeexampe of ch a iight i the moecar decriptioof the immoogica ape, a trctre that i com-mo aociated ith mphocte actiatio fooigthe recogitio of a pecific atige9–12 (BOX 1).

B-ce actiatio i iitiated fooig egagemetof the B-ce receptor (BCR) b a pecific atige.B ce ca recogize ad repod to both obead membrae-aociated atige, athogh recetiight gget that membrae-aociated atigeare more importat for B-ce actiatio in vivo13,14.Fooig atigeic timatio, B ce ca proce

ad preet atige i aociatio ith MHC ca IImoece, thereb recritig pecific CD4+ T-cehep ad timatig B-ce proiferatio ad dif-feretiatio15,16 (BOX 2). Athogh the precie factorthat determie the fate of actiated B ce crret remai cear, B ce ca dif feretiate aog toditict patha. O the oe had, B ce ca dif-feretiate to form extrafoicar pamabat thatare eetia for rapid atibod prodctio ad ear protectie imme repoe. O the other had,actiated B ce ca eter germinal centres, here the ca differetiate ito plasma cells, hich ca ecretehigh-affiit atibod fooig affiit matratio,or memory B cells, hich cofer og-atig protectiofrom ecodar chaege ith atige17,18.

I thi Reie, e dic recet iight ito the

ite at hich B ce ecoter atige in vivo, a ea the mechaim b hich thee iteractio occr(for exceet reie that icde compreheiedecriptio of atige preetatio to T ce in vivo,ee REFS 2,19–21). It i o cear that B ce caecoter ad repod to atige throgh ma dif-feret mechaim depedig o the atre ad izeof the atige itef, a e a o the cear cotextad ocatio i hich atige preetatio occr.Thi proide great eratiit i term of iitiatigrepoe that are appropriate to the particar atigead are therefore the mot effectie for the protectioof the hot.

Lymphocyte Interaction

Laboratory, Cancer Research

UK London Research

Institute, Lincoln’s Inn Fields

Laboratories, 44 Lincoln’s Inn

Fields, London WC2A 3PX, UK.

Correspondence to F.D.B.

e‑mail: facundo.batista@

cancer.org.uk

doi:10.1038/nri2454

Published online

12 December 2008

Total internal reflection

fluorescence microscopy

A microscopy method that

allows for the identification

of fluorescence within

100–200 nm of the interface

between cells and their

substrate (for example, lipid

bilayers or glass coverslips),

thereby providing a high lateral

and axial resolution at the

cell–substrate interface and

the ability to observe

nanoscale movement of

signalling molecules during

cellular activation.

The who, how and where of antigenpresentation to B cellsFacundo D. Batista and Naomi E. Harwood

Abstract | A functional immune system depends on the appropriate activation of

lymphocytes following antigen encounter. In this Review, we summarize studies that

have used high-resolution imaging approaches to visualize antigen presentation to

B cells in secondary lymphoid organs. These studies illustrate that encounters of B cells

with antigen in these organs can be facilitated by diffusion of the antigen or by thepresentation of antigen by macrophages, dendritic cells and follicular dendritic cells.

We describe cell-surface molecules that might be important in mediating antigen

presentation to B cells and also highlight the key role of B cells themselves in antigen

transport. Data obtained from the studies discussed here highlight the predominance,

importance and variety of the cell-mediated processes that are involved in presenting

antigen to B cells in vivo.

REVIEWS

nATuRE REvIEws | Immunology vOluME 9 | jAnuARy 2009 | 15

© 2009 Macmillan Publishers Limited. All rights reserved

mailto:[email protected]






Intravital multiphoton

microscopy

A microscopy method that

combines the advanced

optical techniques of

laser-scanning confocal

microscopy with

long-wavelength multiphoton

fluorescence excitation to

capture high-resolution,

three-dimensional images of

living cells and/or tissues that

have been labelled with

fluorophores. It provides a

greater tissue imaging depth

(up to 350 µm depending

on the tissue) and less

photobleaching and

phototoxicity than

conventional imaging

methods.

Germinal centre

A highly specialized and

dynamic microenvironment

that gives rise to secondaryB-cell follicles during an

immune response. It is the

main site of B-cell maturation,

during which memory B cells

and plasma cells that produce

high-affinity antibody are

generated.

Plasma cell

A non-dividing, terminally

differentiated, antibody-

secreting cell of the B-cell

lineage.

Memory B cell

An antigen-experienced B cell

that expresses high-affinity

antibodies and quickly

differentiates into a plasma

cell during antigen-recall

responses.

Alymphoplastic (aly/aly)

mice

Mice that are characterized

by the absence of lymph

nodes and Peyer’s patches.

Alymphoplasia is caused by a

spontaneous mutation in the

gene that encodes nuclear-

factor-κB-inducing kinase.

Sites of antigen encounter

A ce of the imme tem ca repod to a hgerage of potetia pathogeic chaege throghot thehoe bod, thee repoe mt be tight coordiatedto cofer effectie protectio. Oig to thi great ati-geic dierit, the eet of atige ecoter ith aatige-pecific mphocte that ca mot a rapid adappropriate repoe od eem ike. To maximizethe probabiit of ch a iteractio, thee eet occri defied ite, ch a the mph ode ad pee,hich are coectie ko a ecodar mphoidorga (slO). Thee ite poe a high orgaizedmicroarchitectre that i ecear for the compartme-taizatio of mero cear iteractio ad there-fore proide the optima eiromet for the iitiatioof imme repoe, icdig the determiatio of ce fate22. Frthermore, ithi 24 hor mphoctethat hae bee ccef i their earch for atigerecircate throghot the bod ad betee slO todramatica icreae the probabiit of ecoterigcogate atige3.

slO are extreme e coected to the bood admphatic tem, aoig them to cotia ampead cocetrate atige that are circatig throgh-ot the bod. The importace of slO i orgaizigad coordiatig imme repoe i eidet fromthe eere impairmet i the actiatio of aie m-phocte i alymphoplastic (aly/aly) mice ad apeic(homebox 11-deficiet) mice23. Accordig, a mea-igf ietigatio ito the patio-tempora damicad the mechaim b hich mphocte ecoteratige in vivo mt be coidered ithi ch high orgaized eiromet.

Lymph nodes. It i o ide dertood thatbeeath the protectie oter coageo cape, amph ode i diided ito three dicrete (bt o-rigid) regio that are defied b the expreio of pecific chemokie3,24 (FIG. 1a). Direct beeath thebcapar i i a macrophage-rich heet that r-rod the B-ce zoe, hich i ao termed the cor-tex. B ce i thi regio are orgaized ito aggregate,

Box 1 | The immunological synapse

Lymphocyte activation is initiated following the recognition of specific antigen by clonotypic immunoreceptors, such

as the B‑cell receptor (BCR) and the T‑cell receptor (TCR). The recognition of specific antigen on a spatially constrained

surface is associated with membrane reorganization that results in the formation of an immunological synapse9–12.

The structure of the mature immunological synapse is characterized by the spatial segregation of immunoreceptors into

a central supramolecular activation cluster (cSMAC) from the surrounding peripheral SMAC (pSMAC), which contains integrins,

such as lymphocyte function‑associated antigen 1 (LFA1) (see the figure). The early molecular events that underlie the formation

of the immunological synapse have been revealed by high‑resolution imaging techniques and are highly coordinated and tightly

regulated. Following the recognition of specific antigen and before the formation of the immunological synapse, B cells rapidly

spread over the antigen‑containing surface in a manner that is dependent on intracellular signalling and cytoskeletal

rearrangements120. During B‑cell spreading, antigen–BCR microclusters are continually assembled at the periphery of the

contact area between the cells14. As similar microclusters are crucial for sustained signalling in T cells121–123, we have proposed

that these microclusters form functional signalling units that are common to both types of lymphocyte 14.A comprehensive genetic dissection of the requirements for B‑cell spreading identified an important role for the sequential

recruitment of the kinases LYN and spleen tyrosine kinase (SYK) to antigen–BCR microclusters in the initiation of

BCR‑induced signalling124. Furthermore, this study visualized the formation of microsignalosomes through the recruitment of

signalling molecules and adaptors to the antigen–BCR microclusters and showed the importance of cooperation between

VAV and phospholipase Cγ2 in mediating the spreading response. The role of LYN and SYK in the initiation of BCR signalling

has been further supported through

fluorescence resonance energy transfer

(FRET)‑based assays125. B‑cell spreading

facilitates the propagation of signalling

through microclusters by allowing the BCR

to engage more antigen, which promotes

further localized signalling and cytoskeleton

rearrangements120. The spreading response

is followed by a prolonged contraction

phase, which results in the accumulationof antigen–BCR microclusters in the

cSMAC of the mature immunological

synapse. The cSMAC functions as a site for

internalization of antigen12,120, before it is

processed and presented in association

with MHC class II molecules; presentation

of antigen–MHC molecules mediates the

recruitment of the CD4+ T‑cell help that is

necessary for full B‑cell activation15,16. APC,

antigen‑presenting cell; C3, complement

component 3; CR, complement receptor;

FcR, Fc receptor.

APC

Antigen

BCR

Antibody

B cellMicrosignalosome

APC

B cell

B-cell contact area with APC(APC not shown)

Mature immunological synapse:

top view

Immunological synapse: side view

cSMAC pSMAC

Antigen–BCR microcluster: side view

pSMAC cSMAC

B-cellcontact area

FcR CR

Integrinreceptor

C3fragment

R E V I E W S

16 | jAnuARy 2009 | vOluME 9 www.atr./riw/i




T-cell-dependent antigen

A protein antigen that needs to

be recognized by T helper cells

(in the context of MHC

molecules) and requires

cooperation between these

antigen-specific T cells and

B cells for a specific antibody

response to be generated.

Affinity maturation

A process whereby the

mutation of antibody

variable-region genes followed

by selection for higher-affinity

variants in the germinal centre

leads to an increase in average

antibody affinity for an antigen

as an immune response

progresses. The selection is

thought to be a competitive

process in which B cells

compete with free antibody

to capture decreasing amounts

of antigen.

µ mt − / − mice

A strain of mutant mice that

carry a stop codon in the first

membrane exon of the µ-chain

constant region. They lack

IgM+ B cells, and B-cell

development is arrested before

the differentiation stage at

which IgD can be expressed.

ko a foice, ad are the arget popatio of IgMmedIgDhiCD21medCD23hi B ce i the bod. Foiceare ao rich i radiatio-reitat foicar dedriticce (FDC) that expre high ee of the adheiomoece acar ce-adheio moece 1 (vCAM1)ad itercear adheio moece 1 (ICAM1), a ea compemet ad Fc receptor25–28. FDC are thoghtto be of meechma origi ad th form a pop-atio of ce that i ditict from caic DC29. Theprecie mechaim of FDC deeopmet i ot etf dertood, bt i ko to reqire the expre-io of ario chemokie receptor ad the preeceof B ce17,30. Fooig expore to atige, foicema ao cotai peciaized trctre, ko agermia cetre, hich coit of rapid proiferat-ig B ce ithi a etork of FDC. The formatioof germia cetre i importat drig the deeop-met of hmora imme repoe to T-cell-dependent

antigens, a the ere a ite for affinity maturation ad thegeeratio of og-atig memor B ce.

The T-ce zoe, or paracortex, hich i adacet to

the foice, cotai high edotheia ee (HEv)ad mero atige-preetig ce. The HEv arepeciaized capiarie that cotia pp the mphode ith ad drai it of mphocte from ad to theperipher. Frthermore, HEv i the paracortex ca oftemediate the recritmet of ce other tha mphocte,ch a atige-preetig ce that hae accmatedatige i the peripher. The paracortex ao cotaia etork of coageo codit fibre that ao thepaage of o-moecar-ma compoet of mphaticfid, icdig chemokie, from the bcapar ito HEv (reieed i REF. 31).

The meda, hich i the iermot area of themph ode, cotai both B ad T ce that are orga-ized ito medar cord ad i ao rich i DC admacrophage.

lmph ode are trategica poitioed at brachethroghot the mphatic tem to eabe exteieatigeic ampig of mphatic fid4. lmphatic fid,hich cotai ario chemokie ad atige thathae bee coected from the bod, eter the mphode throgh the afferet mph ee ad i be-qet fitered b the mph ode a it fo toardthe efferet mph ee. lmphatic fid i preetedfrom free diffig ito the iterior he it eterthe mph ode b the bcapar i; itead, ittrae to the meda throgh trctre ko atrabecar ie. I additio, compoet of m-phatic fid that hae a moecar eight of beo~70 kDa (eqiaet to a damic radi of ~5.5 m)are aoed to moe toard the HEv throgh the itri-cate mehork of fibrobatic reticar ce (FRC)-iedcoageo codit that are aociated ith DC32,33

(FIG. 1b). Accordig, ear oberatio idicated thatthe paracortex did ot cotai proceed atige,athogh ome atige cod be detected i DC34. Themphatic fid that exit the mph ode i erichedith mphocte35 ad therefore proide a mea forthee ce to retr to the circatio24.

Spleen. The orgaizatio of the mphoid tie of thepee i imiar to that of the mph ode, ith B-cefoice ad T-ce zoe that cotai etork of retic-ar ce (ao ko a the periarterioar mphoidheath) ad a imiar codit tem36 i the peic

Box 2 | B cells mediate antigen presentation to antigen-specific T cells

B cells can have a role in initiating T‑cell responses by functioning as antigen‑presenting cells (APCs). When compared

with dendritic cells, B cells are relatively poor APCs, and therefore the importance of B cells in antigen presentation to

T cells has been controversial. However, their presentation potential can be enhanced following specific recognition

of antigen126. Furthermore, it has been recently shown that reconstitution of chimeric µ mt –/– mice with B cells that lack

MHC class II molecules results in impairment of T‑cell responses following antigen stimulation 127, which suggests that

presentation of antigen by B cells does contribute to T‑cell activation.

Tracking and intravital microscopy of antigen‑specific lymphocytes in lymph nodes (see the figure) showed that

around 24 hours following antigen encounter, B cells (green) migrated towards the B‑cell–T‑cell boundary at the

edge of the follicles70 in a CC‑chemokine receptor‑7‑dependent manner48. When they reached this boundary, B cells

were found to engage antigen‑specific T cells (red) for up to 1 hour. A similar migration pattern to the B‑cell–T‑cell

boundary was observed in response to stimulation with particulate antigen or immune complexes following their

accumulation at the subcapsular sinus (SCS)64,67. B‑cell–T‑cell conjugates are suprisingly motile and migrate through

the lymph node at the same rate as unconjugated

B cells. The importance of these long‑lived B‑cell–T‑cell

conjugates in the generation of sustained immunity

has recently been highlighted through the investigation

of mice that are deficient in SLAM‑associated protein

(SAP)128. Although the CD4+ T cells from SAP‑deficient

mice exhibit typical dendritic‑cell‑mediated

activation, they cannot interact with cognate B cells,

resulting in severely impaired formation and function

of germinal centres. Thus, it seems that although the

number of naive antigen‑specific B cells in vivo is

probably low, this mechanism of antigen presentation

to T cells by B cells contributes to the initiation of T‑cell

responses in vivo.

Follicle

Follicle

T-cellzone

SCS

R E V I E W S



http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7412&ordinalpos=3&itool=EntrezSystem2.PEntrez.Gene.Gene_ResultsPanel.Gene_RVDocSum






T-cell-independent antigen

An antigen that directly

activates B cells.

hite pp37 (FIG. 1a). The pee ao cotai red pp,hich i rich ppied ith bood ad cotai arioatige-preetig ce, mphocte ad pama ce38.The oter imit of the hite pp i eparated from thered pp b a regio ko a the margia zoe 39.Thi area ha exteie acatre, ad bood thateter the pee throgh foicar arterioe brachei the margia i reache the margia zoe beforeit permeatio throgh the red pp40. The margiazoe ao cotai mero macrophage ad DC,ad a izabe popatio of o-recircatig B ce41.

Thee margia-zoe B ce form a popatio of cethat i ditict from foicar B ce, a arge propor-tio of hich are poreactie coe. Margia-zoeB ce hae a IgMhiIgDoCD21hiCD23o pheotpead are thoght to participate i the deeopmet of ear imme repoe to both T-ce-depedet adT-cell-independent antigens42. I cotrat to mph ode,the pee i ot ppied ith afferet mphatic fid(athogh it doe cotai efferet mphatic); itead,it i peciaized i motig imme repoe tobood-bore atige43.

Subcapsularsinus

Afferent lymph

Efferentlymph

HEV

Follicle

Arteriolebranch

Paracortex

PALS

Medulla

Conduit networkConduitnetwork

Conduit network

a

b c

Marginalzone

SpleenLymph node

Marginalsinus

Collagenbundles

FRC Associated DC

Red pulp

Whitepulp

Centralarteriole

T-cell zoneFollicle

Follicle

SCS

Trabecularsinus

Blood

Follicle

Figure 1 | T raizati ar pi ra. a | A schematic representation of secondary lymphoid organs

(SLOs). The lymph node is organized into three discrete (but non-rigid) regions: the medulla, the paracortex (also known as the

T-cell zone) and the follicles (also known as the B-cell zone). Antigen-laden lymphatic fluid flows from the afferent lymph vessel

into the subcapsular sinus and through the trabecular sinuses to the medulla, where it exits through the efferent lymph

vessel. Lymphatic fluid also flows through the conduit network in the paracortex, allowing passage of low-molecular-mass

components, including chemokines and antigen, from the subcapsular sinus to high endothelial venules (HEVs). HEVs in the

paracortex also allow for the entry and exit of lymphocytes to and from the lymph node. The white pulp of the spleen consists

of the paracortex (also known as the periarteriolar lymphoid sheath; PALS), B-cell follicles, a central arteriole and the marginal

zone. Blood arrives at the spleen at the marginal sinus through branches of the central arteriole and from there it flows to the

red pulp through the marginal zone or to the white pulp through the conduit network. b | The conduit network in the lymph

node is composed of a collagen core and is lined with fibroblastic reticular cells (FRCs). Dendritic cells (DCs) are often

associated with FRCs and can extend short protrusions into the conduits, possibly to sample the lymphatic fluid that is

transported through this network. | A snapshot of a video generated using multiphoton microscopy on the popliteal lymph

node. The distribution of seminaphtho-rhodafluor (SNARF)-labelled B cells (red) within the follicles (delineated by a dashed

line) beneath the subcapsular sinus (SCS; solid line) and of carboxyfluorescein diacetate succinimidyl ester (CFSE)-labelled

T cells (green) in the paracortex is shown in the absence of antigen. Scale bar represents 100 µm.

R E V I E W S





Lymphocyte behaviour in ‘resting’ SLOs

To etabih the ite ad mechaim of atige eco-ter ith mphocte in vivo, it i importat to dertadthe ocaizatio ad damic of thee ce i the retigmphoid orga. Athogh iformatio o ce dam-ic i the pat a iferred from tdie ig taticapproache1–3, iitia grodbreakig tdie that direct

iaized the patio-tempora damic of mphoctein vivo ere poibe becae of adace i the fied of mtiphoto microcop (reieed i REFS 5,19). Thimethod ao for the ietigatio of cear behaiori rea time ad to a depth i iig tie that i prohib-ited b techiqe ch a cofoca microcop 5. The ear-iet mtiphoto microcop ietigatio ere carriedot o expated or ioated mph ode44–46, ad ma of the origia oberatio hae ice bee cofirmed imph ode in vivo fooig miima rgica dirp-tio. Hoeer, high-reotio imagig of mphoctebehaior i peic tie i hampered b the techicachaege that are aociated ith the ioatio of thi

ita ad deep embedded orga6.

The firt rpriig oberatio from thee mti-photo microcop tdie a the high motie atreof mphocte ithi the retig mph ode45–48. B adT ce that ere high poarized i hape ere fodto moe ithi their retricted cear zoe (FIG. 1c) bt aog apparet radom traectorie, ith aerage

eocitie of arod 6 µm (for B ce) ad 12 µm (for Tce) per mite. Coer ipectio of thi moemet fo-oig the iaizatio of the codit etork proidedeidece for a order to thi proce. uig a eegattem ioig chimeric mice that expre gree fo-recet protei, Baéoff et al.49 cod iaize the FDCad FRC i the mph ode before the itrodctio of apopatio of abeed mphocte. Thi td hoedthat the T ce i the paracortex are i coe aociatioith FRC, hich ao the T ce to be gided aoga defied etork. A B ce eter the mph odethrogh HEv i the paracortex, it a ao ggetedthat thee ce cod migrate aog FRC i thi areabefore migratig i a chemokie-directed maer to thefoice, here a imiar etork compoed of FDC cabe ed to orchetrate their moemet. sch rapid moe-met acro thee etork gget that mphocte ithe mph ode are cotia caig their eiro-met ad are read to repod to atige a oo a iti ecotered. Iteretig, imiar ietigatio haeoffered iight ito the behaior of CD11c+ DC i the

paracortex50. I cotrat to mphocte, ad a expectedgie their potetia roe i trctra pport of the co-dit etork, thee DC ere fod to be eie, ho-ig moemet at a eocit of e tha 2 µm per mite.Hoeer, thi retrictio i motiit did ot preet therapid moemet of their dedritic procee, idicatigthat thee DC retai the capacit to ampe ad repodto eirometa iga.

Presentation of antigen to B cells

B ce ca prompt detect ad mot repoeto atige after immizatio. I the cae of ma obeatige, repoe ca be moted fooig a impe

diffio of atige ito the mphoid tie; ho-eer, thee ecoter are a mediated throghmacrophage, DC ad FDC (FIG. 2).

Encountering of soluble antigen. Atige ca be rap-id ppied to the mph ode throgh the afferetmph ee. Ideed, atige arria at the bcap-ar i ca be detected ithi mite of bctae-o admiitratio51. A mot B ce are mai ocatedi the foice, mph-bore atige mt gai acceto foicar B ce i a maer that i idepedetof the codit tem, hich i preet predomiat ithe paracortex.

Iteretig, eera eectro microcop td-ie hae idetified pore of ~0.1–1 µm diameter i theregio of the bcapar i that are adacet tothe mph-ode parechma52–54. Thee pore mightao ma obe atige, ch a o-moecar-matoxi, that eter the mph ode throgh the afferetmph ee to direct pa ito the foice ad gaiacce to B ce55 (FIG. 2a). Ideed, ig immohito-

chemitr of froze mph-ode ectio, it a hothat thi rapid diffio of atige a idepedet of DC ad did ot reqire migratio of B ce from theirfoicar ocatio. Thee oberatio are coitetith a preio td, hich hoed that immiza-tio of mice ith obe atige iitia reted i abtatia decreae i the motiit of atige-pecificB ce i the foice48. Frthermore, i the 24 horfooig immizatio thee B ce ere ho topreet atige i aociatio ith MHC ca II mo-ece o their rface (BOX 2) ad to migrate toardthe bodar betee the foice ad the paracortex.Therefore, ma o-moecar-ma atige ma gaiacce to ce i the foice ithot reqirig ce-mediated preetatio, throgh direct diffio frompore i the bcapar i. Hoeer the exiteceof thee pore remai cotroeria, a the ma imp be ite geerated b ce that hae recet migratedthrogh the i a. Frthermore, there i a dicrep-ac betee the dimeio of the obered poread the radi of the atige that hae bee excdedfrom acceig the foice b diffio. I ie of thi, iteem reaoabe to potate the exitece of a ater-atie mea of mediatig the moemet of maeratige ito the foice, perhap i a maer that iremiicet of diffio from the codit tem, aobered i the paracortex.

Macrophage-mediated presentation.Athogh diff-io of atige from the bcapar i proide oemechaim for expoig foicar B ce to ma obeatige, the acce of arger particate atige to B cei the foice i imited. It a therefore ggeted thatpeciaized ce, poib ocated i the bcapar i,might traport arge atige to the B-ce foice53,56–58.Ear microcop tdie reeaed a popatio of macro-phage that reide direct beeath the bcapari52,53 ad ca exted their procee throgh it to gaiacce to afferet mphatic fid53,56,58. A thee macro-phage hae bee ho to bid a obe recombiat

R E V I E W S





Metallophilic macrophage

A macrophage that is located

at the border of the white pulp

and the marginal zone of the

spleen. These macrophages

express high levels of CD169

but lack expression of the

mannose receptor.

protei that cotai domai of the maoe receptor,it ha bee ggeted that the ma captre ad coce-trate atige i a imiar a to metallophilic macrophages that reide i the peic margia zoe59–61.

The macrophage i the bcapar i are a di-tict popatio to thoe i the meda ad hae im-ited phagoctic actiit, hich eabe them to preet

itact atige o their ce rface56,58. Ideed, theemacrophage hae bee ho to captre ad retaiatige for p to 72 hor fooig the iitia atigeexpore62. Hoeer, hether thi ioe the imperetetio of atige o the macrophage rface or ati-ge iteraizatio ito o-degradatie itracearcompartmet before it i recced to the ce rface

Subcapsular sinus

SCS macrophage

HEV

Recentlymigrated DC

FRC

T cell

c

a

b

Resident DC

Antigen-specificB cell

Antigen-specificB cell

Folliculardendritic cell

Primary follicle

Small solubleantigen

Paracortex

Afferent lymph vessel

DC-SIGN

BCR

FcR

Antibody

Immunecomplex

C3 fragmentAntigen

SCS

Antigen-specific B cells

Antigen

Antigen non-specific B cells

MAC1

CR

Figure 2 | B- tr wit pii ati i t p . a | B cells in follicles have been found

to encounter small soluble antigens from the lymphatic fluid as they diffuse from the subcapsular sinus (SCS) to the

follicles55. Large antigens, immune complexes and viruses can be presented to follicular B cells at the macrophage-

rich SCS64,67,68. In addition, follicular B cells may recognize antigen that is presented on the surface of follicular dendritic

cells (FDCs). b | Snapshot of a video that was generated using multiphoton intravital microscopy on the popliteal lymph

node. The solid line identifies the position of the SCS. A magnified view of antigen–B-cell conjugates is shown, in which

conjugates appear yellow as a result of the merge of the red antigen-specific B cells and green antigen (P. Barral and F. B.,

unpublished observations). | Schematic view of the paracortex to illustrate where antigen-specific B cells encounter

antigen at this site. B cells entering the lymph node can encounter unprocessed antigen on the surface of resident or

recently migrated DCs, in close proximity to the high-endothelial venules (HEVs) 73,77–79. The conduit system, which is

lined with FRCs and DCs, transports low-molecular-mass components of the lymphatic fluid through the lymph node;B cells and T cells have been shown to migrate in association with the FRC network49. BCR, B-cell receptor; C3, complement

component 3; CR, complement receptor; DC-SIGN, DC-specific ICAM3-grabbing non-integrin; FcR, Fc receptor;

ICAM3, intercellular adhesion molecule 3; MAC1, macrophage receptor 1.

R E V I E W S





Clodronate-loaded liposome

A liposome that contains the

drug dichloromethylene

diphosphonate. These

liposomes are ingested by

macrophages, resulting in

cell death.

i ot cear. I additio, macrophage are ko to

expre a ide rage of ce-rface receptor thatcod participate i the preetatio of proceedatige, icdig compemet receptor, patter-recogitio receptor ad/or carbohdrate-bidigcaeger receptor63 (TABLE 1). Ideed, macrophagereceptor 1 (MAC1; ao ko a αMβ2 itegriad CD11b–CD18 dimer), hich i a receptor forcompemet compoet 3 (C3) that i expreed b macrophage, ha bee ggeted to cotribte to theretetio of atige o the ce rface64. Ateratie,the ihibitor o-affiit receptor for IgG (FcγRIIB)might mediate the iteraizatio ad reccig of IgG-cotaiig imme compexe to the macrophage cerface, a ha bee ho i DC65. Fia, the C-tpeecti DC-pecific ICAM3-grabbig o-itegri(DC-sIGn; ao ko a CD209) cod participatei the retetio of gcoated atige, hich i co-itet ith the oberatio that mice deficiet i themoe homooge of DC-sIGn, sIGnR1, fai to mothmora imme repoe fooig ifectio ithStreptococcus pneumoniae66.

A crcia ad e decribed roe for bcapar-i macrophage i the preetatio of atige tofoicar B ce ha bee recet etabihed b threeidepedet tdie64,67,68. Thee tdie idetified that,oo after atige admiitratio, bcapar-imacrophage are repoibe for the rapid accma-

tio of ario arger atige, ch a thoe fod iimme compexe (ith atibod ad/or compemetfragmet), particate, bacteria ad ire (FIG. 2a,b).Thee macrophage might faor the retetio of ati-ge o their rface throgh their expreio of -phated gcoprotei, ch a CD169, ad the ack of expreio of the maoe receptor, hich i a aociated ith phagoctoi of opoized atige68.Depetio of macrophage, icdig thoe i the b-capar i ad the meda, throgh treatmet ithclodronate-loaded liposomes redered mice abe tocaptre ad retai eicar tomatiti ir at the b-capar i, retig i temic diemiatio of

thi ir68. Frthermore, a the retetio of atige a

ot impaired fooig the depetio of C3, compemet-idepedet mechaim might ao cotribte to themaiteace of atige o the macrophage rface68.

The accmated atige i beqet preetedi it itact form b macrophage for recogitio b eighborig foicar B ce. Accordig, fooigadmiitratio of atige, it a ho that atige-pecific B ce i the foice exhibited redced migratiooer time ad made tabe cotact ith macrophagei the bcapar i64,67,68. A ICAM1 ad vCAM1are expreed i the bcapar i68, it i expectedthat the ma faciitate B-ce adheio i thi regio adthereb oer the threhod of atige that i reqiredfor B-ce actiatio13,69. Together, thee tdie proidethe firt cear demotratio of a roe for macrophagei the iitiatio of foicar B-ce repoe. The macro-phage–B-ce iteractio at the bcapar i aoatige-pecific B ce to acqire ad iteraize atigethrogh their BCR before their migratio to the B-ce–T-ce bodar 67, here the ma receie pecific T-cehep48,70 (BOX 2). Iteretig, it ha recet bee otedthat the repoe of B ce ad CD4+ T ce to arge irapartice i determiitica iked to their atige pe-cificitie71, ggetig that atige ptake b the B cema ot ioe iteraizatio of hoe ira pathogeat the bcapar i.

DC-mediated presentation. B ce eter the mph odethrogh the HEv, o the paracortex od eem the ideaite for the immediate preetatio of atige to theece. Frthermore, thi regio cotai both reidet DCi coe aociatio ith FRC ad recet migratedDC that hae coected atige from periphera ti-e. DC are ide coidered to be the mot efficietprofeioa atige-preetig ce ad therefore areparticar importat for the preetatio of peptidei a compex ith MHC moece to aie T ce72–74.Hoeer, B ce recogize atige i it proceedatie tate, ad coeqet preetatio to B ceod eceitate a mechaim hereb DC-accmated

Table 1 | Cell-surface molecules that are implicated in presenting antigen to B cells

Prti Rptr Ati prt Prtati trat

Macrophage MAC1 Complement-coated antigen Remains on the cell surface

FcγRIIB IgG-coated antigen Internalized in neutral endosomes and recycled?

DC-SIGN Carbohydrate-containing antigen Internalized in neutral endosomes and recycled?

DC FcγRIIB IgG-coated antigen Internalized in neutral endosomes and recycled?

DC-SIGN Carbohydrate-containing antigen Internalized in neutral endosomes and recycled?

FDC CR1 and CR2 Complement-coated antigen Remains on the cell surface


Marginal-zoneB cell

CR1 and CR2 Complement-coated antigen Remains on the cell surface

Follicular B cell CR1 and CR2 Complement-coated antigen Remains on the cell surface


CR, complement receptor; DC, dendritic cell; DC-SIGN, DC-specific ICAM3-grabbing non-integrin; FcγRIIB, low-affinity Fcreceptor for IgG; FDC, follicular DC; ICAM3, intercellular adhesion molecule 3; MAC1, macrophage receptor 1.

R E V I E W S











Endosome

A vacuolar compartment

where large molecules are

transported after being

engulfed by endocytosis. The

endosome can then mature

and fuse with lysosomes, which

contain degrading enzymes.

Endosomal and phagosomal

pathways are interconnected.

B-1 cell

An IgMhi

IgDlow

MAC1+

B220lowCD23– cell that is

dominant in the peritoneal and

pleural cavities. B-1-precursor

cells develop in the fetal liver

and omentum, and in adult

mice the size of the B-1-cell

population is kept constant

owing to the self-renewing

capacity of these cells. B-1

cells recognize self

components, as well as

common bacterial antigens,

and they secrete antibodies

that tend to have low affinity

and broad specificity.

atige i either tab dipaed o the ce rface or ireitat to itracear degradatio65,75 (TABLE 1). Ideed,it ha bee ho that FcγRIIB ca mediate the iter-aizatio of atige-cotaiig imme compexe itoo-degradatie itracear compartmet65, ad itha ao bee ggeted that DC-sIGn might ao theaccmatio of itact atige i etra endosomes iDC. Cocomitat ith thi hpothei, sIGnR1 habee impicated i the iteraizatio of HIv-1 ito ao-ooma compartmet of DC ad the beqetdeier of itact HIv-1 irio to slO76.

A popatio of DC i the paracortex that capreet itact atige to B ce ha bee idetified77–79.A detaied characterizatio of thi DC popatio b itraita mtiphoto microcop hoed that theece are mai ocated arod HEv o that migrat-ig B ce ca re their atigeic cotet79 (FIG. 2c).Fooig the admiitratio of atige-oaded DCto mice, recet migrated atige-pecific B ceho decreaed motiit ad a icreae i their rei-dec time o DC. Iteretig, thee DC retaied

the capacit to timate B ce fooig treatmetith proae (a mixtre of proteiae) to remoe ce-rface-expoed atige, ggetig that DC ca iter-aize ad the recce itact atige to their ce rface.The DC-mediated preetatio of atige to B cei the paracortex i the idea eiromet i hich toreceie the ecear T-ce hep for their maxima acti-

atio79. I pport of thi, DC, B ce ad T ce haebee ho to coocaize i thi regio of the mphode50. Thi DC-mediated actiatio of B ce ma gie rie to extrafoicar pama ce that mot ear atibod repoe to atige. Ateratie, fooigactiatio b CD4+ T ce, B ce might migrate to thefoice ad mediate germia-cetre formatio. It iao proe aabe to characterize the in vivo damicof a popatio of maoe-receptor-bidig DC thataccmate obe atige i the foice ad preet itto foicar B ce80.

Techica cotrait hae imited the appicatioof itraita mtiphoto microcop i the td of mphocte damic i the pee. Hoeer, a the co-dit tem i the hite pp36 ad the core orgaizatioof B- ad T-ce zoe i the pee are imiar to thoei the mph ode, the mechaim of atige pree-tatio to B ce might be imiar i both tie. Thepeic margia-zoe B-ce popatio ha bee hoto rapid prodce atibod i repoe to bood-bore

atige, ad therefore thee ce hae a importat roei the iitiatio of ear imme repoe81. Hoeer,the participatio of margia-zoe B ce at ater tageof the imme repoe ha bee e e character-ized. static in vitro imagig approache hae bee edto td DC-mediated atige preetatio to peicmargia-zoe B ce82 ad hae ho that thi actia-tio ead to the rapid geeratio of pama ce thatprodce IgM idepedet of T-ce hep, aoig forthe rapid ad ehaced formatio of atige-cotaiigimme compexe. Itrigig, a popatio of B ceith imiar characteritic to margia-zoe B ce habee detected i hma mph ode83.

FDC-mediated presentation. Caica, FDC haebee coidered to be the ce that are mai repo-ibe for atige preetatio to B ce i slO. Ear atoradiograph aai combied ith high-reotioeectro microcop hoed that extracear atige ia pama-membrae-aociated form i retaied i thefoice for prooged period after immizatio51,84.sbeqet, it a etabihed that FDC i the fo-ice are repoibe for mediatig the retetio of ati-ge i the form of imme compexe26,85,86. I additioto their roe i atige retetio ad preetatio, it iko that FDC fctio a potet acceor ce dr-ig B-ce actiatio, poib throgh mechaim thatioe the ecretio of chemokie ad/or the expre-io of FcγRIIB87.

The ditictie pheotpe of FDC pport theretetio of imme compexe i the foice throghto differet mechaim (TABLE 1). The firt mechaimdeped o the compemet tem85,88,89. FDC exprehigh ee of compemet receptor 1 (CR1) ad CR2 (ao ko a CD35 ad CD21, repectie), hich

bid to ario fragmet of C3. Chimeric mice that ack expreio of CR1 ad CR2 i the radioreitat troma-ce compartmet (icdig FDC) caot depoitatige o the rface of FDC90,91, ad FDC from micethat are abe to prodce CR2 igad caot preetatige to B ce92.

The ecod mechaim of atige depoitio ioethe retetio of imme compexe that cotai IgG fo-oig their bidig to Fc receptor, ch a FcγRIIB,that are expreed o the rface of FDC i germiacetre28,93. Coitet ith thi, FcγRIIB-deficiet miceho eere redced trappig of imme compexe ithe mph ode ad pee, ad FcγRIIB-deficiet micethat ere recotitted ith id-tpe, atige-pecificmphocte exhibit eere impaired reca repoeto imme compexe28.

Depoitio of atige o the rface of FDC throgheither or both of thee mechaim od therefore beexpected to icreae the iitiatio of imme repoe.Ideed, preformed imme compexe58,94 ad atigecoated ith C3d fragmet95 are both aociated ith thetimatio of B-ce actiatio, potetia a a ret of icreaed depoitio of atige o the rface of FDC96.Frthermore, fooig their bidig to atige, atraIgM atibodie that are prodced mai b peritoeaB-1 cells97 idce the formatio of imme compexead acceerate the depoitio of atige o the rface

of FDC27. Mice ith a targeted deetio i the carbox-termia tai of IgM fai to expre erm IgM ad hodeaed hmora imme repoe, ggetig a roefor FDC i the iitiatio of imme repoe98,99.

Depite the abiit of FDC to preet proceedatige, the importace of thi patha for the actiatioof aie B ce drig the iitiatio of primar immerepoe, a e a it derig mechaim, hae etto be firm etabihed. Iteretig, it ha bee pot-ated that FDC ma be particar importat for thepreetatio of microbia atige, i repoe to hichpre-exitig atra IgM atibodie cod faciitate therapid formatio of imme compexe, thereb retig

R E V I E W S









Somatic hypermutation

(SHM). A unique mutation

mechanism that is targeted

to the variable regions of rearranged immunoglobulin

gene segments. Combined with

selection for B cells that

produce high-affinity antibody,

SHM leads to affinity

maturation of B cells in

germinal centres.

Cobra venom factor

The complement-activating

glycoprotein component of

cobra venom, which is

functionally analogous to the

mammalian complement

factor C3b.

i microbia-atige preetatio b Fc receptor o therface of FDC100. Hoeer, it i ko that FDC iprimar foice do ot expre high ee of FcγRIIB28 ad therefore thi receptor caot hae a importatroe i atige retetio ad preetatio drig theiitiatio of imme repoe.

FDC ca ao act a atige ‘depot’ i the slOch that the ca preet atige ee after the iitia‘ae’ of atige ha paed26–28,101. Thi i importatfor the deeopmet of a effectie ad og-atigimme repoe, a the iitia ecoter of atigeith aie B ce i the slO i ike to be of oaffiit. uder thee coditio, actiated B ce theeter germia cetre, here the dergo affiit matratio17. Thi proce ao the eectio of B-cecoe ith higher affiit for atige drig a T-ce-depedet atibod repoe ad tart a fe da afterthe iitiatio of the repoe.

The caic mode that decribed the mechaim of atige preetatio to B ce i germia cetre abaed o eera biochemica ad hitoogica obera-

tio. I thi mode, the germia cetre a diidedito to fctioa ditict zoe17. The dark zoea thoght to cotai cetrobat ad to be the iteof rapid B-ce proiferatio, herea the FDC-rich ightzoe fctioed a the ite for the eectio of B-cecoe that expre BCR of the highet affiit foo-ig somatic hypermutation. Recet, three idepedettdie examiig the patio-tempora damic of B ce hae qetioed the origia mode ad the abo-te ‘diiio of abor’ betee the to zoe of thegermia cetre102–104. Iteretig, each of thee tdiehoed that 6 da after atige admiitratio B cemoed rapid ithi the germia cetre, hich idi-cated the did ot make prooged cotact ith atigepreeted o the rface of FDC. It a therefore g-geted that the mode of atige recogitio b B ceoccrrig drig the ater tage of a imme repoema operate differet to that obered drig ear atige ecoter. Ideed, thee tdie hoed thatgermia-cetre B ce adopted a a morphoog ith ma exteded procee102–104. Thee proceema be repoibe for mediatig atige iteraiza-tio a the B ce migrate aog the rface of the FDC.uder atige-imitig coditio, B ce expreigBCR ith higher affiit ca accmate more atigead coeqet compete more effectie to recritpecific T-ce hep for their deeopmet, ith o

the highet affiit coe beig eected for riai the germia cetre102,105. Hoeer, it i importat toote that CD4+ T ce reide excie ithi the ightzoe, o the compete abece of fctioa egregatioi the germia cetre i ike.

Atige preetatio b FDC throgh bidig of imme compexe to FcR or compemet receptor ma be importat for the deeopmet of high-affiit atibod ad og-atig memor repoe106. srpriig, ho-eer, the proce of affiit matratio ad the riaof memor B ce, athogh impaired, ca occr i theabece of detectabe atige depoitio o FDC107,108.Thi oberatio ed to the hpothei that i additio

to atige retetio, FDC might hae aother roedrig affiit matratio109. Hoeer, thee tdiedid ot excde the poibiit that competitio amogB ce for atige cod hae a roe i the eectio of high-affiit B-ce coe i the germia cetre. I

ie of thi, it od proe extreme iformatie tocharacterize the patio-tempora damic of ce thatretai atige ithi imme compexe, hich odetabih the precie roe of depoit of atige o FDCdrig the proce of affiit matratio.

How does antigen gain access to FDCs? A a coeqeceof the roe of FDC i mediatig atige preetatio toB ce, mch effort ha bee ieted i addreig theapparet aoma of ho atige i the form of immecompexe ca gai rapid acce to FDC, hich are co-fied to the B-ce foice. A the bcapar i adthe codit tem retrict the diffio of arge atigefrom the mphatic fid, a ce-mediated mechaimmt operate to traport atige to FDC.

I the pee, margia-zoe B ce hae bee impi-

cated i thi proce59,110 (FIG. 3a). The ocatio of B cei the margia zoe make them idea poitioedto ampe ad mot rapid repoe to bood-boreatige. Ideed, dipacemet of thee B ce b treat-met ith edotoxi, ch a ipopoaccharide, aaccompaied b impaired accmatio of immecompexe o the rface of FDC i the foice59,111,112.Moreoer, it ha bee ho that the accmatio of IgM-cotaiig imme compexe o FDC a abro-gated i the abece of fctioa margia-zoe B ce.Thi gget that margia-zoe B ce faciitate theadat actiit of IgM113.

Margia-zoe B ce expre compemet receptor(TABLE 1), ad thee ma be importat for their fctioi traportig atige to FDC. Ideed, ear ieti-gatio ig cobra venom factor ad atibodie agaitC3 hoed that the traport of imme compexefrom the margia zoe to the FDC deped o com-poet of the compemet tem85,89,114. I the abeceof CR2 expreio b margia-zoe B ce, immecompexe ere aociated predomiat ith macro-phage i the margia zoe, a the B ce faied totraport atige to the FDC115. The mechaim b hich margia-zoe B ce traport atige from themargia zoe to the foice a reeaed b a recettd ioig the treatmet of chimeric mice ith thephigoie 1-phophate receptor 1 (s1PR1) atagoit

FTy720 (REF. 116). Margia-zoe B ce ere fod tocotia htte to ad from the foice i a procethat depeded o the expreio of CXC-chemokiereceptor 5 (CXCR5) ad s1PR1, repectie. A mar-gia-zoe B ce ca bid imme compexe throghCR1 ad CR2, thi httig proce cod be the a i hich atige i effectie deiered from the boodto FDC. Iteretig, it ha bee potated that theacta trafer of imme compexe from margia-zoe B ce to FDC occr throgh proteoi of CR2o the rface of the margia-zoe B ce117. Hoeer,it i ot ko hether margia-zoe B ce ca pafree atige direct to foicar B ce.

R E V I E W S









simiar, it ha bee ggeted that foicar B cethemee fctio a atige traporter i the mphode ad pee89,118 (FIG. 3b). Thi actiit doe otdeped o atige-pecific recogitio ad thereforei mediated b receptor other tha the BCR (TABLE 1).It ha bee propoed that atige ca be acqired b other foicar B ce i the abece of atige-pecificB ce64,67, ad thi ma deped o the expreio of compemet receptor o the B-ce rface64. A FDCexpre higher ee of compemet receptor thafoicar B ce, it od be expected that the codcompete effectie ith B ce for atige bidig27.It remai to be determied hether other receptor of the iate imme tem hae a roe i the traportof atige b B ce ithi slO. CD23+ matre B cehae i fact bee ho to mediate the traport of IgE-cotaiig imme compexe ito the foice i aBCR-idepedet maer119. Athogh ch a itatioi ike to occr i phioogica coditio, it doeidicate that ateratie receptor might be ioed iatige traport.

Conclusions and perspectives

Oera, it i cear that B ce ca repod rapid toatigeic timatio throgh eera mechaim, adthe ao hae a iqe trategic roe i the traportof atige to FDC i the germia cetre. Thi ide

ariet i potetia atige-preetatio mechaim ipromoted b fctioa peciaizatio ithi slO adproide iaabe fexibiit i motig appropriateimme repoe to atige. A ch, the mechaimthat i ed to preet a pecific atige ca be effec-tie taiored both to the atige itef ad to the a the atige i deiered to the B ce. The predomiaceof ce-baed trategie for the preetatio of atige toB ce ao for exteie regatio ad coordiatioof the retig imme repoe.

I pite of igificat recet progre i character-izig the ite ad damic of atige preetatioto B ce in vivo, ome ie remai to be addreed.Thee icde a defiitie moecar decriptio of themechaim of atige preetatio to B ce, icd-ig the retetio ad iteraizatio trategie that are

Immunecomplex

Antigennon-specificBCR

CR

Marginal-zoneB cell

Marginal zone

a Splenic marginal-zone B cells transport antigen to FDCs b Follicular B cells in the lymph node transport antigen to FDCs

Primary follicle Primary follicle

SCSmacrophage

Folliculardendritic cell

FollicularB cell

?

?

Subcapsular sinusS1Phi

CXCL13low

S1Plow

CXCL13hi

C3fragment

FcR

DC-SIGN

Figure 3 | B iat ati traprt t iar riti i pt rptr.

a | Marginal-zone B cells in the spleen can bind to immune complexes that contain antigen and are coated in complement

fragments, using complement receptors (CR) in a manner that is independent of B-cell receptor (BCR) specificity. These

marginal-zone B cells can shuttle to the follicular region, which is rich in CXC-chemokine ligand 13 (CXCL13), in a CXC-

chemokine-receptor-5-dependent manner116. Follicular dendritic cells (FDCs) in the follicle, which express high levels of

CR, can then compete for binding to antigen that is presented by marginal-zone B cells. The marginal-zone B cells then

migrate back to the marginal zone, where there are high levels of sphingosine 1-phosphate (S1P), and this depends on

their expression of the receptors for S1P1 and S1P3. b | Follicular B cells in the lymph node can bind to particulate antigen

on the surface of subcapsular sinus (SCS) macrophages. This binding does not depend on the specificity of the BCR and is

mediated by CRs. It has been suggested that these follicular B cells can then mediate the transport of antigen to FDCs,

which express higher levels of CRs64,67. C3, complement component 3; DC-SIGN, DC-specific ICAM3-grabbing

non-integrin; FcR, Fc receptor; ICAM3, intercellular adhesion molecule 3.

R E V I E W S





ed b the atige-preetig ce. I additio, itod proe iformatie to track the fate of B ce fo-oig atigeic timatio, i term of the particardifferetiatio patha that i iitiated. sch progrema be poibe b improig the reotio that iachieabe b imagig techiqe, i combiatio iththe geeratio of aima mode that are deficiet i orhae atered expreio of the differet compoet thatma be ioed. Frthermore, adace i the fied of high-reotio itraita imagig ma ao for the

iaizatio of in vivo atige ecoter at greatertie depth ad for more exteded period of time.Thee deeopmet ma ao offer iight ito potetia

roe of the iteractio betee foicar B ce i theimme repoe ad ito the importace of FDC ithe preetatio of atige to aie B ce. Fia, it iimportat to etabih that the in vivo oberatio thathae bee coected o far i trageic aima-modetem refect thoe that occr drig the timatioof the atra repertoire of B ce drig ifectio orfooig acciatio.

Take together, a more compreheie decriptio of the mechaim b hich B ce ee ad repod toatige i hae impicatio for the ftre taiorig of

acciatio trategie ad ao i the ratioa deigof treatmet for ifectio ad atoimme dieae.

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AcknowledgementsWe thank members of the Lymphocyte Interaction Laboratory

for critical reading of the manuscript, particularly P. Barral for

providing multiphoton microscopy images.

DATABASESEntrez Gene: http://www.ncbi.nlm.nih.gov/entrez/query.

fcgi?db=gene

C3 | CR1 | CR2 | CXCR5 | DC-SIGN | ICAM1 | MAC1 | S1PR1 |

VCAM1

FURTHER INFORMATIONFacundo Batista’s homepage: http://science.cancerresearchuk.

org/research/loc/london/lifch/batistaf

All lInks ARe AcTIve In The onlIne Pdf

R E V I E W S

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene





















http://science.cancerresearchuk.org/research/loc/london/lifch/batistaf
















The Who, How and Where of Antigen

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