Major histocompatibility complexes (MHCs) are a group of proteins that play crucial roles in the immune system by presenting antigens to T-cells. MHCs are divided into two classes, MHC class 1 and MHC class 2.
MHC class 1 antigens are presented mainly on the surface of cells that are infected with viruses or cancerous. Antigens presented on MHC class 1 molecules are recognized by cytotoxic T cells (CD8+ T cells) which respond by attacking and killing the infected cell.
MHC class 2 antigens on the other hand are presented exclusively on antigen-presenting cells (APCs). APCs present antigens to T helper cells (CD4+ T cells) which help the body recognize the pathogen or antigen and respond appropriately.
T helper cells are a type of immune cell that play a crucial role in the body’s immune response. There are three main types of T helper cells: Th1, Th2 and Th17. Th1 cells help the body fight off viruses, bacteria and fungi by secreting cytokines that activate macrophages and activate cytotoxic T cells. Th2 cells help the body fight parasites and allergens by secreting cytokines that activate B-cells to produce antibodies. Th17 cells also help the body fight bacterial and fungal infections by secreting cytokines that activate neutrophils and phagocytes.