Question

Immunology: Explain why there are ethnic/individual differences in susceptibility to infection (other than environmental factors). Use this same explanation to further explain why different ethnic groups/individuals have tendencies for autoimmune diseases. Be sure to discuss epitopes, antigens, infectious agents, MHC, functional domains on relevant proteins, protein structures, recognition, endoplasmic reticulum, phagolysosome, etc…..

Answer 1

Because MHC ( cluster of genes called Major Histocompatibility complex ) are highly polymorphic which means the genes encoding MHC molecules (which have a central role in generating cell mediated immunity by activatjon of T-helper and T-cytotoxic cells ) have multiple alleles and every individual / ethnic group is having different alleles which encode different MHC molecules among them. Generally , a cell has 6 different MHC - 1 molecules and more than 12 types of MHC-2 molecules. This leads to variability of immune response to different epitopes of antigen. MHC-1 present self antigen to T-cytotoxic cells via endogenous pathways. While MHC -2 display foreign antigen via exogenous pathways which involves endocytosis of antigen by APCs ( antigen presenting cells ) and fusion with lysosome to form phagolysome , therefore converting large antigen to smaller peptides and these peptides are carried by MHC-2 (synthesised by Endoplasmic Reticulum ) via promiscuous binding to surface of cells which helps in recognition of foreign antigen by T-helper cells.

Since an antigen which are generally having protein structure is having different epitopes ( functional domains of proteins ) which actually bind to the antigen binding portion of antibodies. Set of MHCs in an individual is responsible for which antigens are being recognised by the immune system.thereby producing difference in the susceptibility of infection.

Autoimmune disease occur when T-cells recognise self antigens as foreign or MHC-2 molcecule starts expressing self antigens as foreign to T-helper cells via endogenous pathways. Therefore T-helper cells initiate cell mediated immunity against self cells by releasing certain cytokines and activating T-cytotoxic and B-cells against self cells.