2. What is major histocompatibility complex
The major histocompatibility complex is a set of surface protein
essential for the acquired immune system to recognize foreign
MHC binds to antigen derived from pathogen and display them on
the cell surface for recognition by the appropriate T-cells
3. On the basis of their structure, cellular
distribution, and function, MHC gene
products are classified into two groups.
CLASS l MHC
CLASS ll MHC
4. CLASS l MHC
Class l MHC molecules are expressed on all nucleated cells and
6. Class l MHC and CD 8 cell
The 3 domain of class l MHC molecules has a binding site for CD8.
Since CD8+ T cells recognize peptides only if presented as a complex
with self-class l MHC molecule, CD8+ T cells are said to be class l
7. Class ll MHC
Class ll MHC molecules are mainly expressed on cells : macrophages, B
lymphocytes, and dendritic cells.
Class ll MHC molecules present antigen derived from extracellular microbes
and soluble proteins.
1. Organ transplantation : no two individuals are likely to express the same
MHC molecules, and therefore grafts exchanged between these
individuals are recognized and attacked by the immune systems
HLA matching has the greatest clinical impact in kidney and bone
marrow transplantation, where efforts are made to match at the HLA
matching, unless being transplanted in to vascularized (or inflamed) bed.
11. By segregating cytoplasmic and internalized antigens, MHC molecules
ensure that the correct immune response is mounted against different
CTLs against cytoplasmic microbes, and macrophages against extracellular
An individual mounts an immune response against a protein only if he or
she inherits the gene.
For example :-if the antigen is a peptide from ragweed pollen, the
individual who expresses class ll molecule capable of binding the antigen
would be genetically prone to allergic against pollen.