Question

1. Please discuss the purpose of the Major Histocompatibility Complex. What are the two distinct classes found? What purpose do they serve? How does this relate to clonal selection theory and immune tolerance?

Answer 1

Answer :

1)

Major Histocompatibility Complex are group of genes that encode proteins on cell surface that have an important role in immune response. Their main role is in antigen presentation where MHC molecule display peptide fragments for recognition by appropriate T cells.

Two distinct classes are MHC 1 and 2.

MHC class II are for CD4+ T lymphocytes.

MHC class I for CD8+ T cells.

MHC class I is in all nucleated cells. MHC class II are in specialized antigen presenting cells as dendritic cells, macrophages and B lymphocytes.

Clonal selection theory postulates that antigen selectively expands B cells expressing antibodies on their surface to which it can bind. Subsequently T helper cells recognize the antigen loaded MHC molecules and signal B cells into its pathway of proliferation and differentiation.

Immune tolerance is unresponsiveness of the immune system. Immunological tolerance to antigens presented on MHC II molecules begins at selection stage of T cell development. By this means immune system is tolerant to self antigens.