Cellepresentasjon

Cellepresentasjon, also known as cell presentation, is a fundamental biological process where a cell displays antigens on its surface for recognition by other cells, particularly immune cells. This mechanism is crucial for the immune system to distinguish between self and non-self entities, such as pathogens or cancerous cells.

The process involves specialized molecules called Major Histocompatibility Complex (MHC) proteins. MHC class I molecules are found on almost all nucleated cells and present endogenous antigens, meaning those originating from within the cell, such as viral proteins or mutated self-proteins. MHC class II molecules are primarily expressed on antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells, and they present exogenous antigens, which are derived from external sources, such as bacteria that have been engulfed by the APC.

When a cell encounters an antigen, it processes it into smaller peptide fragments. These fragments are then loaded onto MHC molecules within the cell's endoplasmic reticulum. The MHC-peptide complex is subsequently transported to the cell surface. Cytotoxic T lymphocytes (CTLs), a type of T cell, recognize the antigen presented on MHC class I molecules. If the presented antigen is foreign or abnormal, the CTL is activated to destroy the presenting cell. Helper T lymphocytes recognize antigens presented on MHC class II molecules. This recognition triggers the activation of helper T cells, which then orchestrate a broader immune response, including the activation of B cells to produce antibodies and other immune cells.

In essence, cell presentation acts as a signaling system, allowing immune cells to monitor the internal state of other cells and to identify and respond to threats. Aberrations in cell presentation can lead to autoimmune diseases or immunodeficiency.