antigénpresentációban

Antigénprezentáció is a fundamental process in immunology where fragments of antigens are displayed on the surface of cells. This display is crucial for initiating adaptive immune responses. Antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells, are specialized in this function. They engulf or phagocytose foreign particles, pathogens, or even self-components. Within the APC, these antigens are broken down into smaller peptides through a process called antigen processing.

These processed peptides are then loaded onto specialized molecules called Major Histocompatibility Complex (MHC) molecules. There are two main classes of MHC molecules: MHC class I and MHC class II. MHC class I molecules typically present peptides derived from intracellular antigens, such as viral proteins or abnormal self-proteins, and are found on almost all nucleated cells. MHC class II molecules primarily present peptides derived from extracellular antigens, which have been taken up by phagocytosis or endocytosis, and are predominantly expressed on professional APCs.

Once loaded onto MHC molecules, the peptide-MHC complexes are transported to the cell surface and presented to T lymphocytes. Helper T cells (CD4+) recognize antigens presented by MHC class II molecules, while cytotoxic T lymphocytes (CD8+) recognize antigens presented by MHC class I molecules. This recognition event is the first step in T cell activation, leading to the development of a specific immune response tailored to eliminate the presented antigen. Antigénprezentáció is therefore essential for distinguishing self from non-self and for mounting effective defense against pathogens.