The Major Histocompatibility Complex (MHC) is a set of surface proteins located on nucleated cells that play an important role in the immune system. MHC molecules present antigen fragments to T cells and are responsible for self/non-self recognition. There are two main classes of MHC molecules - Class I molecules present intracellular antigens to CD8 T cells on nearly all nucleated cells, while Class II molecules present extracellular antigens to CD4 T cells and are found primarily on antigen presenting cells. Together, MHC molecules help the immune system distinguish between self and foreign antigens.

2. • MAJOR HISTOCOMPACTIBILITY COMPLEX (MHC) IS SET OF SURFACE PROTIENS LOCATED ON THE CELL
MEMBRANE OF NUCLEATED CELLS.
• IT PLAY MORE IMPORTANT WORK TO IDENTIFY THE ANTIGEN BETWEEN SELF AND NON-SELF BODY,
INTRACELLULAR RECOGNIZATION AND RESPIONSIBLE 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 CLASS 2 MOLECULES, AND T CYTOTOXIC (TC) CELLS ARE
RECOGNIZED BY CLASS 1 MHC MOLECULES.

3. •“ MAJOR HISTOCOMPATIBILITY COMPLEX IS MEMBRANE
ATTACHED PROTIEN WHICH WORK ON RECOGNIZATION
OF ANTIGENS BETWEEN SELF AND NON-SELF BODY AND
ANTIGEN PRESENTATIONS”.

4. • PETER GORER (1930) FOUND THAT FOUR GROUP OF MHC MOLECULES HE USED THE BLOOD SAMPLE OF
MICE TO IDENTIFIED THE BLOOD GROUP ANTIGEN WHICH DESIGNATED BY CLASS 1 TO CLASS 4 GROUP OF
MHC.
• GEORG SNELL, JEAN DAUSSET AND BARIY RECEIVED NOBEL PRIZE IN 1980 FOR THEIR CONTRIBUTION TO
THE DISCOVERY OF MHC MOLECULE.

5. • THE MHC MOLECULES ARE CLASSIFIED IN TO FOUR CLASSES NAMELY:-
• CLASS 1 MHC MOLECULES
• CLASS 2 MHC MOLECULES
• CLASS 3 MHC MOLECULES
• CLASS 4 MHC MOLECULES
• THE CLASS 1 AND CLASS 2 MHC MOLECULES ARE WORKED IN IMMUNITY.

6. CLASS 1 MHC GENES EXPRESS GLYCOPROTEINS CALLED CLASS 1 MHC MOLECULES, ON NEARLY ALL
NUCLEATED CELLS. EACH CLASS 1 MHC GENE CODES FOR A TRANSMEMBRANE GLYCOPROTEIN OF
APPROXIMATELY 43 KDA, WHICH IS REFFERED TO AS THE ALPHA ( OR HEAVY CHAIN). IT COMPRISES THREE
EXTRACELLULAR DOMAINS: ALPHA 1, ALPHA 2, AND ALPHA 3. THE ALPHA 3 DOMAIN IS HIGHLY CONSERVED
AND INTRACTS WITH THE GLYCOPROTEIN CD8 PRESENT ON TC CELLS. EVERY CLASS 1 MHC MOLECULES
EXPRESSED ON THE SURFACE OF A CELL FORMS NONCOVALENT ASSOCIATION WITH A SMALL INVARIENT
POLYPAPTIDE CALLED BETA 2- MICROGLOBULIN (APPROXIMATELY 12 Kda), which is encoded by gene present on
other chromosome ( in human, chromosome 15). In the absence of beta-2-macroglobulin; the mhc class 1 molecules is not
expressed on the cell membrane.

7. IN GENERAL, CLASS 1 MHC MOLECULES ARE EXPRESSED ON MOST NUCLEATED CELLS, BUT THE LEVEL OF
EXPRESSION DIFFERS AMONG DIFFERENT CELL TYPES. THE HIGHEST LEVELS OF CLASS 1 MHC MOLECULES
ARE EXPRESSED BY LYMPHOCYTES WHEREAS FIBROBLAST, LIVER HEPATOCYTES, AND NEURAL CELLS
EXPRESS VERY LOW LEVELS OF CLASS 1 MHC MOLECULES. A FEW CELL TYPES (E.G. NEURONS AND SPERM
CELls at certain stages of differentiation ) appear to lack class 1 mhc molecules altogether.

9. CLASS 2 MHC GENES CODE FOR ALPHA AND BETA-POLYPEPTIDE CHAINS OF APPROXIMATE MOLECULAR
MASS 35 KDA AND 28 kda, respectively. Class 2 mhc molecules, like class 1 mhc molecules, are transmembrane
glycoprotein molecules with cytoplasmic tails and extracellular ig-like domains; the domains are referred to as alpha 1,
alpha 2, beta 1 and beta 2. class 2 mhc molecules are also members of the ig superfamily. Glycoprotein cd4 present on th
cells interacts with the invariant portion of all class 2 mhc molecules.
Class 2 mhc gene express mhc molecule constitutively (i.e. under all conditions ) only on specialized antigen presenting
cells (apcs). Apcs are classified as professional and non-professional antigen-presenting cells.

10. PROFESSIONAL ANTIGEN-PRESENTING CELLS (PAPCS) ARE DENTRIC CELLS, MACROPHAGES AND B CELLS.
THESE CELLS DIFFER FROM ONE ANOTHER IN THEIR MECHANISMS OF ANTIGEN UPTAKE. DENTRIC CELLS ARE
CONSIDERD THE MOST POWERFUL AND MOST EFFICIENT OF THE PAPCS. THESE CELLS CONSTITUTIVELY
EXPRESS HIGH LEVELS OF CLASS 2 MHC MOLECULES. B CELLS CONSTITUTIVELY EXPRESS CLASS 2 MHC
MOLECULES, ALTHOUGH AT LOW LEVELS, AND POSSESS ANTIGEN-SPECIFIC SURFACE RECEPTORS.
PROFESSIONAL APCS DIFFER BY LOCATION AND MIGRATORY BEHAVIOR. SOME CIRCULATE ACTIVELY AND
OTHERS RESIDE FOR LONG PERIODS OF TIME IN SPECIFIC TISSUES AND ORGANS. NON-PROFESSIONAL
ANTIGEN-PRESENTING CELLS LIKE FIBROBLAST, THYMIC EPITHELIAL CELLS, GLIAL CELLS AND PANCREATIC
BETA CELLS CAN BE INDUCED TO EXPRESS CLASS 2 MHC MOLECULES.

11. IN GENERAL, IN THE ABSENCE OF INDUCING FACTORS, MOST CELLS EXPRESS LAST CLASS 1 MHC MOLECULES
WITHOUT EXPRESSING CLASS 2 MHC MOLECULES. CERTAIN CELLS, SUCH AS B CELLS, CONSTITUTIVELY
EXPRESS BOTH CLASS 1 AND CLASS 2 MHC MOLECULES. BY CONVENTION, CELL THAT DISPLAY PEPTIDE
ANTIGENS ASSOCIATED WITH CLASS 1 MHC MOLECULES TO TC CELLS ARE REFERRED TO AS TARGETS CELLS
AND CELLS THAT DISPLAY PEPTIDES ASSOCIATED WITH CLASS 2 MHC TO TH CELLS ARE CALLED ANTIGEN
PRESENTING CELLS ( BUT SOMETIMES WE USE APC FOR BOTH).

13. • MHC CLASS 1
• HAVE 8-10 AMINO ACID
• PEPTIDE BINDING DOMAIN ALPHA 1 OR ALPHA 2
• PRESENT ANTIGEN TO CD8 T CELLS
• FOUND AN ALL SURFACE OF NUCLEATED CELLS
• COMPOSED OF ONE PEPTIDE ENCODED IN HLA
LOCUS ON BETA 2 MICROGLOBULIN
• MHC CLASS 2
• HAVE 13-18 AMINO ACID
• PEPTIDE BINDING DOMAIN ALPHA 1 OR BETA 1
• PRESENT ANTIGEN TO CD4 T CELLS
• FOUND ON SURFACE OF APCS AND ACTIVATED T
CELLS
• COMPOSED OF TWO PEPTIDE ENCODED BY HLA
LOCUS

14. • BIND WITH ENDOGENOUS ANTIGEN
• HAS NO INVARIENT CHAIN
• AFTER BINDING TO CD8 T CELLS CYTOKINES ARE
PRODUCT THAT LEAD TO THE LYSIS OF ENTIRE
CELL.
• BIND WITH EXOGENOUS ANTIGENS
• HAS INVARIENT CHAIN
• AFTER BINDING TO CD4 T CELLS IT TRIGGERS B
CELL RESPONSES WHICH RESULT IN ANTIBODY
FORMATION.

16. THE HUMAN LEUKOCYTES ANTIGEN (HLA) SYSTEM ( THE MAJOR HISTOCOMPATIBILITY COMPLEX [MHC] IN
HUMANS ) IS AN IMPORTANT PART OF THE IMMUNE SYSTEM AND IS CONTROLLED BY GENES LOCATED ON
CHROMOSOME 6. IT ENCODED CELL SURFACE MOLECULES SPECIALIZED TO PRESENT ANTIGNIC PEPTIDES TO THE
T-CELL RECEPTOR (TCR) ON T CELLS.
• 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, DEFENCE AGAINST INFECTION, SOME TIME IT IS
EXPRESSED ON CANCER CELL DESTRUCTION CERTAIN AUTOIMMUNE DISEASE AND CERTAIN COPLEMENTS.
• MHC IS THE GENERAL TERM REFERRING TO THE CELL SURFACE ANTIGEN OF VERTIBRATES.

18. • THE MHC OF MOUSE IS CALLED H-2 COMPLEX.
• H-2 COMPLEX IS A CLUSTER OF GENES RESPONSIBLE
FOR THE PRODUCTION OF ANTIGEN LOCATED OF
NUCLEATED CELLS AND COMPLEMENT
COMPONENTS
• THIS COMPLEX IS LOCATED IN THE SHORT ARM OF
THE CHROMOSOME N.17
• IT CONSISTS A SET OF STRUCTURAL GENES.

19. • MHC MOLECULES ARE LOADED WITH A BIT OF SAMPLE PEPTIDE FRAGMENTS DERIVED FROM THE
DEGREDATION 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.
REFERENCE
Pathfinder book (7th edition) AND www.slideshare.com