Lymphocytes

LYMPHOCYTES

DR. SHILPA SONI

MGMCH, JAIPUR

BASICS OF IMMUNE SYSTEM

LympRetic syst

Lymphoid sys

Lymphoid cells

Lymphd organs

Retic sys

Phagocytic cells

LYMPHOID ORGANS

Central(1*)lympd organs

(precursor Lmpc proliferates,dev

& mature)

•Thymus•BM

Peripheral (2*) lympd

organs

•LN,spleen•Mucosa associated lympd tissue

SITES OF LYMPHOCYTIC CELLS

CELLS OF LYMP.RETIC SYST Lymphocytes- T- lymph B- “ Null cells/large granular lymphocytes -ADCC-antibody dependent cell mediated cytotoxic lymp. -NK cells Reticular sys cells-Phagocytic cells- macrophages & microphages Macrophg -monocytes(in Bd) largest of lymp cells. -Histiocytes(in tissues)-microglia in CNS -Kupffer cells in liver -alveolar macrophages in lungs -osteoclasts in bone -sinushistiocytes in spleen. LN Microphg -polymorphnuc cells of Bd- N,E & B.

Dendritic cells-dentritic, langerhans, follicular dendritic cells

MHC Located at short arm of Chr-6, codes for

histocompatibility (transplantation )Ag. Binds peptide fragments of foreign Pr.

for presentation to appr. Ag specific T cell.

Classified as-Class-I•Gps,on all nuc. Cells & plt•Presn Ag to CD 8•Graft rejectn & cytolysis

Class-II•Gps, on APCs-macrophg,Dcs,B cells•Ag to CD 4•Graft vs host rxn & mixed leukocyte rxn

Class-III•Soluble prt of complement sys•Heat shock prt•TNF α•TNF β

LYMPHOCYTES Human body

contains 10¹² lymphocytes out of which 10^9 are renewed daily.

Mature B & T cells before encountering Ag are K/A Naïve cells.

Types- T lymphocytes - B “

NormalPercentage Lymphocytes: 15-40% of White Blood Cells

Total Lymphocytes: 800-2600/mm³ Total T Lymphocytes: 800-2200/mm³

T helper Cells: >400/mm³T suppressor Cells: 250-750/mm³Helper Cell to Suppressor Cell ratio: >0.9CD2 Percentage of Lymphocytes: 65-85%CD4 Percentage of Lymphocytes: 45-75%

T CELLS Thymus derived lympc- 60-70% of periph lymphoc. Found in- paracortical areas of LN. - periarteriolar sheeths of spleen. Ag + TCR -> signal 1 All T cells contain CD 3 molecule->signal 1 Surface mol or receptors of T cells- CD 2 CD 4 – 60% of T cells CD 8 – 30% of T cells (cytotoxic) CD 11a CD 28 – binds to B 7-1(CD 80) & 7-2(CD 86) of

APCs -> signal 2 CD 40

T CELL SUBSETS CD8/CTL CD4/TH cells

1) TH1 - inflammatory response

2) TH2 - anti-inflammatory, B cell response3) Treg - inhibit immune responses

T-LYMPHOCYTES

T cells:

Development in thymus

Migration out of thymus into blood(Naïve T cells)

Priming phase: Antigen-dependent differentiation in lymphoid tissues(to become memory and effector T cells)

Effector phase: Migration to sites of infection and effector function

Human:

Fetal development

Birth

School

Job

Immunology’s Secret”

1) Early experiments demonstrated that antigen-derived (i.e. TCR-mediated) signals alone are insufficient to initiate an immune response

2) A second substance - an “adjuvant” - is required to prevent the induction of tolerance

3) In vitro, triggering the TCR alone also leads to a tolerant state (known as “anergy”)

4) “Two-Signal Hypothesis”: Activation of a naïve T cell requires signals from both the TCR (antigen-specific) and a second, co-stimulatory receptor (antigen-independent)

5) Adjuvants work in part by inducing antigen presenting cells to express ligands for co-stimulatory receptors

FIGURE 6-1

FIGURE 6-2

Green: MHC class IIRed: Lysosomal protein

Polarization of T Cells Part I: The Cytoskeleton

1) T cell responses are directed at the APC/target cell, not in all directions

2) This requires reorganization of the cell to have a “front” (toward the APC) and a “back” - induced by signals from the TCR and costimulatory molecules

3) Result: Reorganization of the cytoskeleton causes reorientation of cytosolic organelles toward APC - Golgi, secretory vessicles, and microtubule organizing center (MTOC). The MTOC connects actin cytoskeletal changes with the tubulin cytoskeleton

Fig. 8.29 The polarization of T cells during specific antigen recognition

Polarization of T Cells Part II: Lipid Rafts

1) Lipid rafts - also called GEMs (glycolipid enriched microdomains) and DIGs (detergent-insoluble glycolipid-rich domains) - are plasma membrane microdomains

2) Enriched in cholesterol, glycolipids, and sphingolipids (i.e. lipids that are not glycerol-based), making them more rigid than the surrounding membrane

3) Some membrane proteins are segregated - selectively enriched or depleted in rafts. Many key signaling molecules (esp. src-family kinases) are constitutively localized to lipid rafts.

4) Dynamic structures - small rafts can condense to form larger rafts

5) During T cell activation, TCR, CD28, and many adhesion molecules are recruited into lipid rafts, where they can interact with signaling molecules

The T cell antigen receptor

Va Vb

Ca Cb

Carbohydrates

Hinge

Transmembrane regionCytoplasmic tail

+++

Antigencombining site

The Immunologic Synapse - Putting it Together1) The combination of cytoskeletal rearrangement and lipid raft

redistribution leads to the formation of a Supramolecular Activation Complex (SMAC) - a highly ordered arrangement of receptors, adhesion molecules, and signaling molecules

Th2

Additional Figures

T CELLS AND THEIR CYTOKINES

T cells

CD 4 (60%)also k/a Th/inducers/TH 0 cells.binds

MHC II

TH1Secretes IL-2,IFN-γFacilitates delayed

hypersens,macroph. Activatn,synth of IgG2 Abs

TH2Secretes IL4,IL5

Facilitates synth of all Abs except IgG2

CD8(30%) cytotoxic T cells

Or suppressor cellsBinds to MHC I

Secretes IL2, INFγFacilitates type 2 hypersensitivity.

T - LYMPHOCYTE IN VARIOUS

DERMATOSIS

PPPPPPPPPP PSORIASIS The disorder is

mediated largely by CLA(cutaneous lymphocyte associated antigen)-positive, CD8+ T cells with type 1 cytokines (interferon-g, interleukin-2, and lymphotoxin); these cells may be activated by an autoantigen in skin

ALLERGIC CONTACT DERMATITIS

It is mediated by CLA-positive,

CD8+ effector T cells that recognize contact-sensitizing antigens.

The activated T cells have a variable cytokine profile (e.g., both type 1 and type 2 cytokines).

ATOPIC DERMATITIS

initiated by CLA-positive, CD4+ T cells with type 2

cytokines (interleukin-4, 5, 10, and 13). T cells that produce type 1 cytokines may be

involved in persistent lesions

CUT. T CELL LYMPHOMA The transformed T

cells are found throughout the dermis and in the epidermis. Many reactive (nontransformed) CLA-positive T cells are also present in lesions.

GRAFT .VS. HOST RXN

CLA-positive T cells producing type 1

cytokines (in acute disease) or type 2

cytokines (in chronic disease)

are present in lesions.

Other T cell- skin disorders-LP-Eczemas-Pneumocystis jiroveci pneumoniaand cryptosporidiosis.

DEFFECTS OF T CELLS T-cell defects-Wiskott–Aldrich syndrome (WASP gene

mutations)-Ataxia telangiectasia (ATM mutations)-Chronic mucocutaneous candidiasis (AIRE,

FoxP3 deficiency)-X-linked hyper-IgM (CD40 ligand deficiency);

autosomal hyper-IgM syndrome(multiple defects)-Cartilage–hair hypoplasia-Idiopathic CD4+ T-cell lymphopenia

B LYMPHOCYTES10%- 20% Of periph

lymphoc

Humoral immunity

Presents in BM, peripherallymphoid tissues-

superficialcortex of LN, white pulp ofSpleen, tonsils & extraLymphatic organs e.g GIT

Responds to free Ag

Acts as APC

Ag binding compon-IgM

CONT.. Other molecules are complement

receptor, Fc receptors, CD 21 – recept for EBV, CD 40-essential for intraction of T & B cell -> B cell maturation (mutation in CD 40 ligand cause immunodeficiency called X-linked hyper IgM syndrome.

B cell development in the bone marrow

BRegulates construction of an antigen receptor

Bone Marrow provides aMATURATION & DIFFERENTIATION MICROENVIRONMENT

for B cell development

Ensures each cell has only one specificityB

Checks and disposes of self-reactive B cells

B

Exports useful cells to the peripheryB

Provides a site for antibody production

B

B-LYMPHOCYTESin bone marrow

* The lymphoid stem cells differentiate into B cells

* B-cells precursors mature, differentiate into immunocomptent B-cells with a single antigen specificity

* Immature B-cells that express high affinity receptors for self antigens, die or fail to mature

i.e negative selection or clonal deletion

* This process induces central self tolerance and reduces autoimmune diseases

B

B

Stromal cell

Bone marrow stromal cell

Maturing B cells

Stages of differentiation in the bone marrow aredefined by Ig gene rearrangement

B CELL STAGE

IgH GENECONFIGURATION

Stem cell Early pro-B Late pro-B Large pre-B

Germline DH to JH VH to DHJH VHDHJH

Pre-B cellreceptor

expressed

Ig light chain gene has not yet rearranged

B-LYMPOCYTES

* Immature B cells - IgM receptors on the surface

* Mature B cells - IgM, IgD molecules on surfaces

IgM and IgD molecules serve as receptors for antigens

* Memory B-cells - IgG or IgA or IgE on the surface

* B-cells bear receptors for Fc portion of IgG and a receptor for C3 component of the complement

* They express an array of molecules on their surfaces that are important in B-cells interactions with other cells such as MHC II, B7 and CD40

ACTIVATION OF B CELLS TO MAKE ANTIBODY

ANTIBODIES OR IMMUNOGLOBULINS Structure & functions Definition: Glycoprotein molecules that are produced by

plasma cells in response to an immunogen and which function as antibodies.

* Produced by:

B-lymphocytes in response to exposure to antigen

* React specifically with antigen

* Five classes of Antibodies: IgG IgM IgA IgD IgE

ANTIBODY STRUCTURE Immunoglobulins are glycoproteins made up of - Four polypeptide chains (IgG): a- Two light (L) polypeptide chains b- Two heavy (H) polypeptide chains - The four chains are linked by disulfide bonds

- Terminal portion of L-chain contains part of antigen binding site

- H-chains are distinct for each of the five immunoglobulins

- Terminal portion of H-chain participate in antigen binding site

- The other (Carboxyl) terminal portion forms Fc fragment

VARIABLE(V) AND CONSTANT (C) REGIONS - Each H-chain and each L-chain has V-region and C-region

- V-region lies in terminal portion of molecule

- V-region shows wide variation in amino a. sequences

- Hypervariable region form region complementary to Ag determinant

- It is responsible for antigen binding

- C-region lies in carboxyl or terminal portion of molecule

- C-region shows an unvarying amino acid sequence

- It is responsible for biologic functions

AB FRAGMENTS & THEIR FUNCTIONS

Fab fragment: antigen binding site

Fc (crystallizable fragment): a- Complement fixation (IgM and IgG) b- Opsonization (IgG) C- Placental attachment (IgG) d- Mucosal attachment (IgA) e- Binding to mast cells (IgE)

STRUCT OF DIFF. IMUNOG.

PROPERTIES OF IMMUNOGLOBULINS

Property

IgG

IgA IgM IgE IgD

Heavy chain symbol

γ α µ ε δ

Molecular weight

150 KDa

170-400 KDa

900 KDa

190 KDa

180 KDa

Percentage in serum

75 % 15 % 10 % 0.004 % % 0.2

Complement fixation

Yes No Yes No No

Transplacental passage

Yes No No No No

Opsonization Yes No No No No

PRIMARY AND SECONDARY ANTIBODY RESPONSE

Primary antibody respone Secondary antibody response

* first exposure to antigen * Subsequent exposure

* lag period: days or weeks * Lag period: hours

* Small amount immunogl. * large amount immunogl.

* in Weeks then decline * Persist for long periods

* Antibody is IgM * Antibody is IgG

B - CELL DEFFECTS

-X-linked agammaglobulinaemia-μ-chain deficiency; surrogate light-chain

deficiency-SWAP-70 deficiency-Hyper-IgE syndrome (includes secondary

neutrophil disorder)-CD79a (Igα chain) deficiency-BLNK deficiency-ICOS deficiency-TACI deficiency

B CELL LYMPHOMA

DIFFERENCES BETWEEN T & B LYMPHOCYTES.

T cells B cells

•Ab binding site Ag rec (TCR with CD3)

Surface Ig

•Fc receptor — +

•Complement receptor

- +

•EAC rosette-C 3, CR 2, EBV rec

- +

•E/SRBC rosette-Cd 2, measles rec

+ -

•Microvilli on surface

- +

•Thymus specific Ag

+ -

•Blast transformation

Occurs by anti CD 3, phytohemagglutinin, concanavalin

Occurs by anti Ig endotoxin, staph aureus, EBV

COMBINED DEFFECTS

-Severe combined immunodeficiency (RAG-1/RAG-2 mutations, common γ-chain deficiency; CD3ε deficiency)

-Adenosine deaminase deficiency-Purine nucleoside phosphorylase deficiency DNA repair defects (DNA ligase IV); Bloom’s

syndrome; xeroderma pigmentosum-Canale–Smith syndrome (autoimmune

lymphoproliferative syndromes; fas, fas-ligand, caspase deficiencies)

-X-linked lymphoproliferative syndrome (SAP deficiency; includes NK disorder)

Thank you

Increased (Lymphocytosis)Increased Absolute Lymphocyte Count (>4500/mm3) Non-activated Lymphocytes

Influenza Pertussis Tuberculosis Mumps Varicella Herpes Simplex Virus Rubeola Brucellosis Chronic Lymphocytic Leukemia Acute Lymphoblastic Leukemia

Activated Lymphocytes (Atypical lymphocytes)Cytomegalovirus Infection Infectious Mononucleosis Infectious HepatitisToxoplasmosisPost-transfusionMedication

Mephenytoin Dilantin Para-aminosalicylic acid

Increased Relative Lymphocyte CountNormal finding in children under age 2

yearsAcute stage of viral infectionConnective tissue diseaseHyperthyroidismAddison's DiseaseSplenomegaly

DecreasedAIDSBone Marrow suppressionAplastic AnemiaNeoplasmsSteroidsAdrenocortical hyperfunctionNeurologic Disorders

Multiple Sclerosis Myasthenia Gravis Gullain Barre Syndrom