The document discusses the major histocompatibility complex (MHC), which are surface proteins that play an important role in identifying antigens and presenting them to T cells. It covers the different classes of MHC molecules, their structures, functions in immunity, and examples in humans (HLA) and mice (H-2 complex). MHC molecules present peptide fragments on their surface and interact specifically with T cells through anchor residues on the peptides. They are essential for self/non-self discrimination, defense against infection, and transplantation compatibility.

1. S U B M I T T E D T O - S U B M I T T E D B Y -
M R . N A V I S H M A T H U R A D I T I B A G D I
A S S I S T A N T P R O F E S S O R A T M S B T 1 S T S E M .
L A C H O O M E M O R I A L C O L L E G E B I O T E C H N O L G Y
O F S C I E N C E A N D T E C H N O L O G Y
J O D H P U R
COLLEGE OF
SCIENCE AND
TECHNOLOGY

2. MAJOR HISTOCOMPATIBILITY
COMPLEX

3. Contents-
 Introduction
 History
 Types of MHC molecule
 Structure of MHC molecule
 HLA (Human Leukocyte Antigen)
 H-2 complex (MHC of mouse)
 Peptide MHC Interaction
 Function of MHC
 Summary of MHC molecule
 References

4. Introduction-
 Major Histocompactibility complex (MHC) is set of surface proteins located on
the cell membrane of nucleated cells.
 It plays more important work to indentify the antigen between self and non self
body, intracellular recognization and responsible for antigen presentation.
 Histo refers to tissues. Compatibility refers to living together harmoniously.MHC
molecules always recognize only T lymphocytes.
 The two types of MHC are worked in immunity. T helper (Th) cell recognized by
MHC molecules II, and T cytotoxic (TC) cells are recognized by MHC I
molecules.
 Definition• "Major Histocompactibility complex is membrane attached protein
which work on recognization of antigen between self and non self body and
antigen presentation"

5. History-
 George Snell(1903-1996) discovered the
first components of the MHC through their
role in rejecting transplants in mice, and
created the word “histocompatibility”.
 Around a decade later, Jean Dausset(1916-
2009)uncovered the first compatibility
antigen in humans.
 Experiments by Baruj Benacerraf (1920-
2011) in the 1970s provided the first
indication that immune reactions are
controlled by the MHC genes ('immune
response genes').

6. Classes of MHC molecule-
The MHC molecules are classified into four classes namely-
 Class I MHC molecules
 Class II MHC molecules
 Class III MHC molecules
 Class IV MHC molecules

7. Class I MHC molecule-
 Class I MHC (45 KD) molecule are a group of major histocompactibility
antigen.
 They are present the surface of all nucleated cells except nervous tissue
and platelets.
 It present antigen to Te cells.
 It bind with CD-8 adhesion molecules of Te cells.
 It brings about cell mediated immune response.

8. Structure of MHC I molecule-
 It consists two polypeptide chains namely a chain
and B2 - micro globulin.
 a chain which is non covalently attached with B2
microglobulin.
 a chain contain a transmembrane glycoprotein
which is encoded by A,B and C gene of grouped
HLA a chain is organized by three domains such as
a 1, a 2 and a 3 each domain containing 90 amino
acids sequences.B2 microglobulin is similar in size
of a 3 and it dose not contain trans membrane
proteins.
 When the antigen is internalized and processed
inside by proteosome (Ubiquitin, cytosolic
degradation), the peptides are produced.
 Peptide is further loaded on the groove of MHC I
molecules from endoplasmic reticulum.

10. Class II MHC molecule-
 Class II MHC molecule are present on the surface of antigen presenting cell and
cell which engulfed the foreign antigen.
 It binds with the exogenous (endocytic degradation ) antigens.
 It binds with CD4 adhesion molecules TH cells.• It also consist of two
polypeptide chains namely a chain and ß chain.
 Antigen is processed inside the endosome and peptide is further loaded on groove
of MHC II molecules.

11. Structure of MHC II molecule-
 The class II MHC Molecule consists of two
polypeptide chain namely a chain (33 kDa)
and B (28kDa) chain.
 The both chain are attached noncovelantly.
 Each chain contains two units. The two units
of a chain are called al and a2. The two
domains of B chains are called B1 and B2.
 32 and a2 are transmembrane domains
anchoring the MHC to plasma membrane.
 The al and B1 domains jointly bear a peptide
binding groove.

13. Class III MHC molecule
The molecules include complements like C2 and C4 and Bf (factor B).
Class IV MHC molecule
These molecule is present on T cells of leukemia (Tla) as well as on
immature thymocytes.

14. HLA- Human Leukocyte
Antigen-
 HLA is the human leukocyte antigen.
 HLA is the MHC molecules present in human beings.
 HLA is a set of surface protein present on the surface of all nucleated cells. They
are responsible for graft rejection, adaptive immunity, defense against infection,
some time it is expressed on cancer cell destruction, certain autoimmune diseases
and certain complements.
 MHC is the general term referring to the cell surface antigen of vertebrates.

15. HLA complex spans 3.5 million bp on the
short arm of chromosome 6

16. Classical HLA-
Class I
 HLA-A,-B and–C loci
 Encode the heavy chain (α chain) of HLA class I molecule.
Class II
 HLA-DP,- DQ, and DR
 Each has loci A and B, encode the α chain and β chain of HLA class II molecule,
respectively.

17. Function of HLA molecule-
Antigen presentation
 Process : endogenous antigen and exogenous antigen
 Presentation: TCR recognize MHC :peptide complex (double
recognition)
 MHC restriction of T cell : Any individual’s T cells respond to a specific
MHC allele expressed by that individual, that is to “self” MHC.
others
 Genetically regulator of immune response, so to predispose individuals
to particular susceptibility or disorders.
 Immune regulation.

18. H-2 complex of mouse-
 The major histocompactibility complex (MHC) of mouse is called H-2 complex.
 H-2 complex is a cluster of genes responsible for the production of antigens
located of nucleated cells and complement components.
 This complex is located in the short arm of the chromosome number 17.
 It consists of a set of structural genes.
 The genes, that make up a given histocompatibility complex, are called halotypes

19. Peptide MHC Interaction-
Peptide-binding groove of MHC Class I
 α 1 and α2 domains form peptide-binding
domains
 Anti parallel eight stranded β-pleated sheet form
the floor
 Two long α helices, oriented adjacent and roughly
parallel to each other form sides of the deep cleft.
 Closed ends, accommodate about 8-11 aa in a
flexible, extended conformation.

20. Peptide binding to
Class I MHC
Solvent Accessibility
About 80% Buried.
Size does matter.
( 9 mers best. )

21. Peptide-binding groove of MHC Class II
•Two long α helicesas sides and theβ sheet as bottom
•The ends of class II peptide-binding cleft are more open, bind longer and irregular
peptides (12-16 aa be optimal)

25. MHC-Peptide Interaction-
 There are about a dozen of types of classical HLA molecules on the cell surface
for one individual.
 However, there are much, much, much more kinds of antigen peptides would be
presented in one individual.
 So, one type of HLA molecule can present large number of different peptides?
• Some amino acid residues of peptide sanchor the peptide into the pockets within
the groove of the MHC molecule, called anchor residue.
So,
• A given MHC molecule binds a group peptides with same anchor residues
• The different MHC molecules bind different groups of peptides.

26. Class I MHC Elution of peptides.
Anchor Residues.

27. Function of MHC molecule-
 MHC molecules are loaded with a bit of sample peptide fragment derived from
the degradation of proteins present inside the cell. This peptide is the mirror
image of proteins present inside the cell.
 MHC molecules contain self as well as nonself (foreign)antigen.
 They bring about defense against infections and diseases. They mediate certain
autoimmune diseases.
 They are responsible for individual smell of people.
 Provide the strongest barrier for transplantation.
 Play a central role in generation and execution of immune response (presentation
of peptide antigen to T cells).
 Susceptibility to infectious diseases and development of autoimmune diseases.

28. Summary of MHC-
 The both MHC I and II molecule are responsible for antigen presentation and it
has application of antigen recognization between self and nonself recognization,
mostly they are located on T lymphocytes encoded by chromosome 6 of the
human. The two types of antigen degradated peptides (exogenous and
endogenous) are involved to complete these process of antigen neutralization.

29. References-
 Judy Owen, Jenni Punt, Sharon Stranford. 2013. Kuby immunology.
7th edition. W.H. Freeman & Company. New York. NY 10010. Page
no. 161-184.
 Fatima Dulsy & Arumugam N., Immunology (2013), 4th edition,
Saras Publication, Camp Road Periavilai, Kanyakumari. Page no-
481-502.2