Antigen-Presenting Cell (Arc)

An antigen presenting cell (APC) is a macrophage that acts on antigen and then delivers it to T lymphocytes. APC captures foreign antigens from the environment by phagocytosis or endocytosis. The antigens are then broken down inside the cell to form peptides. These peptides, in complex with MHC class II molecules, are transported to the surface of APCs and presented to T-helper receptors. Helper T cells recognize the peptide-MHC complex and are activated, triggering an immune response against that antigen. Thus, APCs play a key role in the initiation of adaptive immunity, providing a link between innate and acquired immunity.

Antigen presenting cells (APCs) are a special class of cells that are involved in the presentation of antigen to killer T cells or regulatory T cells. They are capable of expressing antigens on their surface, which are perceived by immunocompetent cells as “their” foreign or, as immunologists say, antigenic epitopes. This allows them to create a genetic memory of a past infection or the immune system's interaction with an infection. Antigen cells also deliver to areas of inflammation, where T-cell activation and proliferation occurs, a complex of cytokines, inflammatory mediators and adhesion molecules necessary for the development of the immune response.

Antigenis cells present T cells to the membrane covering the antigens of a foreign, that is, harmful cell. Lysis by neutrophils is the first step of antibody-dependent phagocytosis. In these cases, only those areas of the cell that contained foreign protein structures were lysed.

Antigens are substances that can cause an immune response, as well as recognize the native or altered form of these antigens. Antigens can exist everywhere: in blood plasma, lymph, saliva, lymphoid tissues of various organs, in the same place where they are produced - lymph nodes, thymus (thymus gland), paraconal bursae, tonsils, intestinal epithelium. Those antigens or peptides of foreign cells that enter the body are called haptens.