Final answer:
The major histocompatibility complex (MHC), or human leukocyte antigen (HLA) in humans, includes molecules essential for immune system function. MHC Class I molecules are on all nucleated cells to present endogenous peptides, while MHC Class II molecules are on antigen-presenting cells to present exogenous peptides to T cells.
Step-by-step explanation:
Function of the Major Histocompatibility Class (MHC)
The major histocompatibility complex (MHC), also known as human leukocyte antigen (HLA) in humans, is a group of genes that code for MHC molecules, which are transmembrane glycoproteins. These MHC molecules are present on the surface of all nucleated cells and play a crucial role in the immune response. MHC Class I molecules are found on all nucleated cells and indicate to the immune system that a cell is "self" by presenting endogenous peptides, typically from the normal degradation of proteins. On the other hand, class II MHC molecules are found only on antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. They present exogenous peptides, derived from extracellular pathogens, to T cells and are a key component of the adaptive immune response. Collectively, these molecules are involved in antigen presentation, an essential process for immune surveillance against pathogens and for the detection of abnormal or cancerous cells.