antigenspresentation

Antigen presentation is a crucial process in the immune system that involves the display of foreign substances, known as antigens, on the surface of cells to activate T cells. This process is essential for the body's ability to recognize and respond to infections and other foreign invaders. There are two main types of antigen presentation: MHC class I and MHC class II.

MHC class I presentation occurs in all nucleated cells and is responsible for presenting antigens derived from intracellular pathogens, such as viruses, to cytotoxic T cells. These antigens are processed within the cell and presented on the cell surface by MHC class I molecules, which are heterodimers consisting of a polymorphic heavy chain and a non-polymorphic light chain. The presented antigen is recognized by the T cell receptor (TCR) on the cytotoxic T cell, leading to the activation of the cell and the initiation of an immune response.

MHC class II presentation occurs primarily in professional antigen-presenting cells (APCs), such as dendritic cells and macrophages, and is responsible for presenting antigens derived from extracellular pathogens, such as bacteria, to helper T cells. These antigens are taken up by the APC, processed in an endosomal compartment, and presented on the cell surface by MHC class II molecules, which are also heterodimers consisting of a polymorphic heavy chain and a non-polymorphic light chain. The presented antigen is recognized by the TCR on the helper T cell, leading to the activation of the cell and the initiation of an immune response.

Antigen presentation is a highly regulated process that involves the coordinated action of numerous molecules and pathways. Dysregulation of antigen presentation can lead to immune disorders, such as autoimmune diseases and immunodeficiency disorders. Understanding the mechanisms of antigen presentation is therefore crucial for the development of new therapies for these conditions.