T-LYMPHOCYTES RECOGNIZE ANTIGEN-DERIVED PROTEIN FRAGMENTS (PEPTIDES) EXPRESSED ON THE SURFACE OF SELF ANTIGEN PRESENTING CELLS VIRUS-INFECTED CELLS ARE.

T-LYMPHOCYTES RECOGNIZE ANTIGEN-DERIVED PROTEIN FRAGMENTS (PEPTIDES) EXPRESSED ON THE SURFACE OF SELF

ANTIGEN PRESENTING CELLS

VIRUS-INFECTED CELLS ARE RECOGNIZED BY T-LYMPHOCYTES IN MHC-DEPENDENT MANNER

TISSUE TRANSPLANTATION IS RESTRICTED BY MHC MOLECULES

THE IMMUNE RESPONSE TO PROTEIN ANTIGENS IS REGULATED BY INDIVIDUALLY POLYMORPHIC MHC GENES

ANTIGEN PRESENTING CELLSANTIGEN PRESENTING CELLS

Synthesize antigens – endogenous antigensendogenous antigens (virus, tumor)

Internalize antigens – exogenous antigensexogenous antigens (any protein)

Degrade protein antigens to peptides – processingprocessing

Protein – derived peptides are presented by MHC (HLA) membrane proteins – antigen presentationantigen presentation

MHC molecules present both self and non-self protein MHC molecules present both self and non-self protein – derived peptides– derived peptides

MHC class I molecules are expressed in all nucleated MHC class I molecules are expressed in all nucleated cellscells

MHC class II molecules are expressed by professional MHC class II molecules are expressed by professional antigen presenting cellsantigen presenting cells

ANTIGEN RECOGNITION BY T-CELLS REQUIRESPEPTIDE ANTIGENS AND ANTIGEN PRESENTING CELLS

THAT EXPRESS MHC MOLECULES

YT

No T-cell response

soluble Ag

Native membrane Ag

Peptide antigen

Cell surface MHC-peptide complex

T-cell response

Cell surfacepeptides APC

THE STRUCTURE OF MHC GENES AND PROTEINS

s s

s s

s

s

s s

ss s

s s

s

s

s s

s

s ss s

s

s

s

s

s

s

s

s

s ss s

L

H HL

s ss s

s ss s

ss

s

s

s

s

ss

s

s

s

s

s

s

ssss

gde

ss

ss

a b

s

s

s

s

ss

s

s

s

s

s

s

ss

ss

s

s

s

s

s

s

ss

s

s

s

s

IgM CD79 TCR MHCI MHCIIThy-1 ICAM-1

CD2 B-7CD28CD8CD4CD3

ss

ss

s s

Fc RII

Poly-Ig

MEMBERS OF THE IMMUNOGLOBULIN SUPERGENE FAMILY

FUNCTION

RECOGNITION

Ig, TCR, MHC-I, MHC-II

ADHESION

ICAM-1, ICAM-2, VCAM-1, NCAM

BINDING

CD4, CD8, CD28, B7, IL-1RI, PDGFR, FcRII, poly-IgR

MOLECULES CONTAINING ONE OR MORE Ig DOMAIN(S)

V or C domain related

COOHNH2

TM CCOOHNH2

MHC class II

TM

NH2NH2

COOHCOOH

HOOCC

COOHNH2 COOHNH2

TM C

Transmembrane region (TM)

Cytoplasmic region ©

– carbohydrate

NH2

Peptide binding site

MHC class II

THE STRUCTURE OF MHC GENE PRODUCTS

3 2m

2

1 1

2 2

1

1 2 3 1 2 1 2

3 and 2m Ig supergene family 2 and 2

3,838,986 bp224 genes

on chromosome 6

http://webace.sanger.ac.uk/cgi-bin/ace/pic/6ace?name=MHC&class=Map&click=400-1

The MHC sequencing consortium

Nature 401, 1999

MAP OF THE HUMAN MHC FROM THE HUMAN GENOME PROJECT

TNF

LMP TAP

21-hydroxilase

Class III Non polymorphic genesClass II Class I

E G F

HSP

Class II

DMA/B

MICA/B

B C A

C2/C4

DQDP DN DR

B2 B2 B2A2 A2 B3B1 B1 (B4)A1 A1 AB B1A

DO

Classical MHC genes POLYMORPHIC

HLA – Human Leukocyte Antigen

HLA –A,B, C class I

EXPRESSED IN ALL NUCLEATED CELLS

HLA – DR, DP, DQ class II

EXPRESSED IN PROFESSIONAL APC

Non- classical MHC genes

E, G, F

Chromosome 6 short arm MHC

Chromosome 15 2m

LOCALIZATION OF MHC GENES

Class III genes

Differential distribution of MHC molecules

Tissue MHC class I MHC class II

T cells +++ +/-B cells +++ +++Macrophages +++ ++Other APC +++ +++

Epithelialcells of thymus + +++

Neutrophils +++ -Hepatocytes + -Kidney + -Brain + -Erythrocytes - -

Cell activation affects the level of MHC expressionThe pattern of expression reflects the function of MHC molecules

Class I is involved in anti-viral immune responsesClass II involved in activation of other cells of the immune system

A24A1

A24A11

A1A2

A11A2

A11A1

A24A2

1. 2. 3. 4.

INHERITANCE OF MHC CLASS I AND CLASS II GENES

HUMAN LEUKOCYTE ANTIGEN

HLA

α1β1 α2β2

PROFESSIONAL APC

transz

A24

A24

C1

C1

B8

B8

B27

B27

C6

C6

A1

A1

b2b1a1

transz

a2

DQ1cisz

cisz

transz

DQ2

EVERY CELL

CLASS ICLASS II

EVERY CELL

CLASS ICLASS II

POSTULATION

• every individual has 6 MHC class I molecules• alleles of all MHC types are distributed randomly in the population• every one of the 1 200 different alleles can be expressed with any

other allele

POLYMORPHISM OF MHC MOLECULES IN THE HUMAN POPULATION

~6 x 1015 individual combinations

Only monozygous twins are identical at the HLA locus

The human population is extensively outbred

MHC genetics in humans is extremely complex

PPOOLYGENIC & POLYMORPHICLYGENIC & POLYMORPHIC

Alleles are not distributed evenly in the population

Alleles are segregated among races

SELECTION

15.18

28.65

13.38

4.46

0.02

5.72

18.88

8.44

9.92

1.88

4.48

24.63

2.64

1.76

0.01

CAU AFR ASI

Frequency (%)

HLA-A1

HLA- A2

HLA- A3

HLA- A28

HLA- A36

Allelic groups

A B C

Po

lym

orp

his

m (

nu

mb

er o

f al

lele

s) Class I

657 alleles185

91

381

Class II492 alleles

2

317

1989

2045

DR DP DQ

DISTRIBUTION OF MHC ALLELES IN THE HUMAN POPULATION

Inheritance of MHC haplotypes

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

X

ParentsDP-1,2DQ-3,4DR-5,6B-7,8C-9,10A-11,12

DP-9,8DQ-7,6DR-5,4B-3,2C-1,8A-9,10

DP-1,8DQ-3,6DR-5,4B-7,2C-9,8A-11,10

DP-1,9DQ-3,7DR-5,5B-7,3C-9,1A-11,9

DP-2,8DQ-4,6DR-6,4B-8,2C-10,8A-12,10

DP-2,9DQ-4,7DR-6,5B-8,3C-10,10A-12,9

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

B C ADP DQ DR

Children

FUNCTIONS OF MHC MEMBRANE PROTEINS

PEPTIDE

1

3

2

2m

STRUCTURE OF CLASS I MHC MOLECULES

EXPRESSED BY ALL NUCLEATED CELLS

2

1

2

1

PEPTIDE

EXPRESSED BY PROFESSIONAL ANTIGEN PRESENTING CELLS

CAN BE INDUCED IN OTHER CELLS (endothel, microglia, astocyte)

STRUCTURE OF CLASS II MHC MOLECULES

MEMBRANE RECEPTORSMEMBRANE RECEPTORS

Intracellular peptide binding Intracellular peptide binding capacitycapacity

One binding site can One binding site can accomodate multiple peptidesaccomodate multiple peptides

MHC – PEPTIDE COMPLEXESMHC – PEPTIDE COMPLEXES

1

3

2

2m 2

1

2

1

Allelic polymorphism is concentrated inthe peptide antigen binding site

Polymorphism in the MHC affects peptide antigen binding

Allelic variants may differ by 20 amino acids

Class II(HLA-DR)

Class I

MHC class I accommodatepeptides of 8-10 amino acids

Cleft geometry

MHC class II accommodatepeptides of >13 amino acids

-M

-chain

Peptide

-chain

-chainPeptide

DPB1*01011 TAC GCG CGC TTC GAC AGC GAC GTG GGG GAG TTC CGG GCG GTG ACG GAG CTG GGG CGG CCT GCT GCG GAG TAC TGG AAC AGC CAG AAG GAC ATC CTG GAG GAG DPB1*01012 --- --- --- --- --- --- --- --- --A --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*02012 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*02013 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AC -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*0202 CT- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AG --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*0301 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- C-- --- --- --- DPB1*0401 -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*0402 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*0501 CT- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AG --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*0601 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- C-- --- --- --- DPB1*0801 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*0901 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- --- --- --- --- DPB1*1001 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*11011 --- --- --- --- --- --- --- --- --A --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- C-- --- --- --- DPB1*11012 --- --- --- --- --- --- --- --- --A --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- C-- --- --- --- DPB1*1301 --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*1401 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- C-- --- --- --- DPB1*1501 --- --- --- --- --- --- --- --- --A --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- C-- --- --- --- DPB1*1601 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*1701 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- --- --- --- --- DPB1*1801 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*1901 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AG --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*20011 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- C-- --- --- --- DPB1*20012 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --C --- --- --- --- --- --- --- C-- --- --- --- DPB1*2101 CT- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AG --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*2201 CT- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AG --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*2301 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*2401 -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -AG --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*2501 -T- -T- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- -A- -A- --- --- --- --- --- --- --- --- C-- --- --- --- DPB1*26011 --- --- --- --- --- --- --- --- --A --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- DPB1*26012 --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

30 HLA-DP allele sequences betweenNucleotides 204 and 290

(amino acids 35-68)

Most polymorphisms are point mutations

Y-F A-V Silent A-D A-EE-A

I-L

Polymorphic nucleotides encode amino acids associated with the peptide binding site

MHCI

P1P2P3P4P5P6P7P8P9Octapeptide

Decapeptide

anchoringamino acids

NH2 COOH

MHCII

P1

NH2

NH2

COOH

COOH

-1 1011-2 P4 P6 P9

anchoringamino acids

STRUCTURE OF THE PEPTIDE BINDING SITESTRUCTURE OF THE PEPTIDE BINDING SITE

P2 & P9 interact with hydrophobic pockets

Amino acid side chains of the ‘core’ region occupy evenly distributed pockets

Peptides can be eluted from MHC molecules

Acid elute peptides

Eluted peptides from MHC molecules have different sequences but contain motifs

Peptides bound to a particular type of MHC class I molecule have conserved patterns of amino acids

P E IYS F H I

A V TYK Q T L

P S AYS I K I

R T RYT Q L VN C

Tethering amino acids need not be identical but must be related

Y & F are aromaticV, L & I are hydrophobic

Side chains of anchor residues bind into POCKETS in the MHC molecule

S I I FN E K L

A P G YN P A L

R G Y YV Q Q L

Different types of MHC molecule bind peptides with different patterns of conserved amino acids

A common sequence in a peptide antigen that binds to an MHC molecule is called a MOTIF

Amino acids common to many peptides tether the peptide to structural features

of the MHC moleculeANCHOR RESIDUES

PEPTIDE MOTIFS IN SELF AND FOREIGN PROTEINSPEPTIDE MOTIFS IN SELF AND FOREIGN PROTEINS

MHC MOLECULES ARE EXPRESSED IN THE CELL SURFACE MEMBRANE WITH BOUND PEPTIDES DERIVED FROM SELF OR NON-

SELF PROTEINS

B-cell, macrophage, dendritic cell

Kidney epithelial cell

Liver cell

Present intracellular environment

Present intra- and extracellular environment

Class I MHC – code of 6Immunological ID

Peptides of restricted size, which derive from cytosolic or nuclear

proteins

Class II MHC

Overlapping peptides of various sizes, which derive from

membrane/exogeneous proteins

70% derives from MHC molecules

BENEFITS OF MHC POLYMORPHISM IN THE POPULATIONBENEFITS OF MHC POLYMORPHISM IN THE POPULATION

A DQB1DRB1Loci:

Person 1 Person 2

Haplotype

Alle

les

Alle

les

Gen

etic

pol

ymor

hism

of t

he p

opul

atio

n

Gen

otyp

e

Haplotype

21

2625

23113

271813

7

743

1824 2 3

B

138

32

113735

18

32

321

271 4 1

38 987

A DQB1DRB1

2

1

24

23

25

38

37

27

18

13

4

3

2

3511

3

2

1

1 3

B

138

32

113735

18

3

21

271 3 21

38 874

39

COMBINATION OF MHC ALLOTYPES IN INDIVIDUALS AND IN THE POPULATION

* * * *

* *

Populations need to express variantsof each type of MHC molecule

• The rate of replication by pathogenic microorganisms is faster than human reproduction

• In a given time a pathogen can mutate genes more frequently than humans and can easily evade changes in MHC molecules

• The number of types of MHC molecules are limited

To counteract the flexibility of pathogens

• The MHC has developed many variants of each type of MHC molecule

• These variants may not necessarily protect all individuals from every pathogen, but will protect the population from extinction

THE OUTCOME OF INFECTION IN A POPULATION WITH POLYMORPHIC MHC GENES

MHC-GenMHC-Gen

vv

vv

vv

v

vv

v

v

v

v

v v v

v

vv

v

vv

v

vv

Example: If MHC X was the only type of MHC molecule

Population threatenedwith extinction

Pathogen that evades MHC

X

MHCXX

Population is protected

Molecular basis of MHC types and variants

POLYMORPHISMVariation >1% at a single genetic locus in a

population of individualsMHC genes are the most polymorphic known

The type and variant MHC molecules do not vary in the lifetime of the individual

The diversity in MHC molecules exists at the population levelThis sharply contrast diversity in T and B cell antigen receptors which

exists within the individual

POLYGENISM

Several MHC class I and class II genes encoding different types of MHC molecule

with a range of peptide-binding specificities.

Foreign peptidesForeign peptides

Peptides Peptides recognized by an recognized by an

individualindividual

CHANGES OF GENETIC POLYMORPHISM IN THE POPULATIONCHANGES OF GENETIC POLYMORPHISM IN THE POPULATION

Multiple heterozygous alleleMultiple heterozygous allele

HomozygousHomozygous

FUNCTIONS OF MHC

• CLASSICAL MHC GENE PRODUCTS– Presentation of peptides derived from self proteins – continuos presentation

of self for the immune system– Determination of immunological self

• Self MHC + self peptides– Presentation of peptides derived from foreign (antigenic) proteins– Determination of non-self

• Self MHC + non-self peptides– Allogeneic immune response against non-self MHC (transplantation)

• Recognition of non-self MHC + peptide combinations – consequence of MHC-restricted T-cell recognition

– NK cell recognition– T-lymphocyte differentiation and selection in the thymus– T-lymphocyte survival in the periphery

• NON CLASSICAL MHC GENES– Specialized functions

• PROTEINS STRUCTURALLY RELATED TO CLASSICAL MHC MOLECULES

OTHER GENES IN THE MHC – not polymorphicMHC Class 1b genes

Encoding MHC class I-like proteins that associate with -2 microglobulinRestricted tissue expression

HLA-G trophoblast, interacts CD94 (NK-cell receptor). Inhibits NK cell attack of foetus/ tumours

HLA-E in the membrane of certain cells, binds conserved leader peptides from HLA-A, B, C. Interacts with CD94

HLA-F fetal liver, eosinophil surface, function unknown

MHC Class II genesEncoding several antigen processing genes

HLA-DMand in professional APC, proteasome components (LMP-2 & 7), peptide transporters (TAP-1 & 2), HLA-DO and DO

Many pseudogenes

MHC Class III genesEncoding complement proteins C4A and C4B, C2 and FACTOR B

TUMOUR NECROSIS FACTORS-

Immunologically irrelevant genesGenes encoding 21-hydroxylase, RNA Helicase, Caesin kinase

Heat shock protein 70, Sialidase