MHC Molecules

What exactly are MHC molecules and what role do they play in the immune response?

MHC molecules, or Major Histocompatibility Complex molecules, are a set of proteins that play a crucial role in the immune system's ability to recognize foreign substances. MHC molecules are encoded by MHC genes and are found on the surface of most cells. There are two major classes: MHC I and MHC II. MHC I molecules present antigen fragments to cytotoxic T cells (also known as CD8+ T cells), triggering an immune response. MHC II molecules work with antigen presenting cells, such as dendritic cells, macrophages, and B cells, to present antigen fragments to CD4+ T cells, also leading to immune response.

What is the difference between MHC I and MHC II molecules?

MHC I molecules are present on all nucleated cells and present endogenous or self-antigens. They primarily interact with cytotoxic T cells. On the other hand, MHC II molecules are mostly found on antigen presenting cells, such as B-cells, dendritic cells, and macrophages and present exogenous antigens, primarily to CD4+ helper T cells.

What is the significance of the human leukocyte antigen (HLA) locus in MHC molecules?

The human leukocyte antigen (HLA) locus is a specific region on the human genome where the MHC genes are located. These genes are responsible for the production of MHC molecules. HLA-A, HLA-B, HLA-C are associated with MHC I molecules, while HLA-D relates to MHC II molecules. Variations in these genes can significantly affect the immune response.

How do MHC molecules interact with T cells to stimulate immune response?

MHC molecules display pieces of proteins, or antigen fragments, from within the cell to the surface. T cells survey these presented antigen fragments. If a T cell, either CD4+ or cytotoxic, recognizes the presented fragment as foreign, it triggers an immune response. MHC I molecules present antigens to cytotoxic T cells, which can destroy the infected cell. MHC II molecules present antigens to CD4+ T cells, which produce substances like interferon gamma to boost immune response.

What role does beta2 microglobulin play in the function of MHC I molecules?

Beta2 microglobulin is a component of MHC I molecules. It is non-covalently bonded to the alpha chain of the MHC I molecule and plays a critical role in stabilizing the structure of the molecule. Without beta2 microglobulin, MHC I molecules cannot properly present antigens to cytotoxic T cells, significantly compromising the immune response.