The major histocompatibility complex (MHC) is a collection of genes located on chromosome 6 in humans that encode MHC molecules. MHC molecules present peptide fragments on the cell surface to help the immune system identify infected or damaged cells. There are two main classes of MHC molecules: class I molecules present peptides from intracellular proteins on most nucleated cells to cytotoxic T cells, while class II molecules present peptides from extracellular proteins on antigen-presenting cells to helper T cells. MHC molecules play a key role in immune system functions like regulating T cell development and activating immune responses against pathogens.

1. NAREN
MHC- STRUCTURE & FUNCTION.

2. MAJOR HISTOCOMPACTIBILITY COMPLEX
STRUCTURE AND FUNCTION

3. INTRODUCTION
 The major histocompactibily complex is a collection of genes .
 Arrayed within a long continuous stretch of DNA on choromosomes
6 in humans & on chromosome 17 on the mice.
 The MHC is reffered to as HLA (Human leukocyte antigen) complex
humans & as H-2 complex in mice.

4.  Viruses, many bacteria, protozoan parasites, such as those
infection inside the host cell, where the antibodies cannot
reach.
 To rebuff these organisms, another arm of the immune system
comes into play.
 The host cells carry MHC molecules on their surface, which
are associated with self peptides.
 In an infected cell, these MHC molecules bind to & display
small peptides, or fragment of proteins that come from the
parasites. Which can be recognized by the antigen receptor
on cytotoxic T lymphocytes or Tc cells.

5. STRUCTURE OF MHC

6. MHC CLASS1
 Consist of a large ALPHA chain
noncovalently associated with a
small BETA2 macroglobulin
molecules.
 ALPHA chain- human HLA complex
encodes ALPHA chain, it is a
polymorphic transmembrance
glycoprotein of 45KD.
 BETA2 microglobulin is coded by
gene located on different
choromose and it is invariant
protein of 12KD.

7.  ALPHA chain is anchored in the plasma membrane by inserting its hydrophobic
transmembrane segment and hydrophilic cytoplasmic tail.
 ALPHA chain- alpha1, alpha2, alpha3. are the three external domain.
 Each containg approximately 90 amino acid. Transmembrane domain has 40 amino
acid. Cytoplasmic anchor segment has 30 amino acid.
 Peptides that bind to peptide-binding cleft are usually 8-10 amino acid residue long.
 Peptide binding cleft is situated on the top of the MHC molecules and it is made up of
apha 1 & alpha 2 domains.
 The alpha 3 domain appears to be highly conserved amoung class1 MHC molecules and
contain sequence that is recognized by CD8 membrane receptor of Tc cells.

8. MHC CLASS 2
Is a heterodimer consisting of 2
different polypeptide chain, of
alpha chain of 33KD and beta
chain of 28KD.Which associate
with each other noncoventely.
Class 2 MHC molecules also
contain an 1.external domain 2.
transmembrane segment, 3.
cytoplasmic tail.
The external domain contain
alpha1 and alpha 2 domain and
beta1 and beta2 domain.
The alpha 1 and beta 1 domain
forms antigen binding cleft for
process antigen.

9. FUNCTIONS OF MHC
 The function of MHC molecules is to bind peptide fragments derived
from pathogens and display them on the cell surface for recognition
by the appropriate T cells.
 Regulate Tcell development, by positive negative selection.

10.  The consequences are almost always deleterious to the pathogen—
virus-infected cells are killed, macrophages are activated to kill
bacteria living in their intracellular vesicles, and B cells are
activated to produce antibodies that eliminate or neutralize
extracellular pathogens.
 MHC class 2 molecules helps in binding of the peptide derived from
exogenous antigen which are endocystosed by APC .

11.  Class I MHC itself can serve as an inhibitory ligand for natural killer
cells (NKs).
 The function of the class I MHC is to display intracellular proteins to
cytotoxic Tcells(CTLs). However, class I MHC can also present
peptides generated from exogenous proteins ,in a process known
as cross-presentation.

12. THANK YOU