antigénfeldolgozásban

Antigénfeldolgozás, often translated as antigen processing, is a crucial step in the adaptive immune response. It involves the breakdown of antigens, which are foreign substances that can trigger an immune reaction, into smaller peptide fragments. This process prepares these fragments to be presented on the surface of cells, primarily through MHC (Major Histocompatibility Complex) molecules.

There are two main pathways for antigen processing: the endogenous pathway and the exogenous pathway. The endogenous pathway deals with antigens originating within the cell, such as viral proteins or abnormal self-proteins. These are degraded by the proteasome and the resulting peptides are transported into the endoplasmic reticulum, where they are loaded onto MHC class I molecules. These MHC class I-peptide complexes are then displayed on the cell surface, signaling to cytotoxic T lymphocytes (CTLs) that the cell is infected or cancerous.

The exogenous pathway handles antigens that enter the cell from the outside, such as bacteria or allergens. These antigens are taken up by antigen-presenting cells (APCs) like dendritic cells, macrophages, or B cells through processes like phagocytosis or endocytosis. Inside the APC, these antigens are enclosed in vesicles called endosomes or phagosomes, which fuse with lysosomes. Here, they are degraded by acidic enzymes. The resulting peptides are then loaded onto MHC class II molecules within the endosomal pathway. These MHC class II-peptide complexes are also transported to the cell surface, where they are recognized by helper T lymphocytes (Th cells), initiating a broader immune response. This coordinated antigen processing and presentation is fundamental for the effective activation of T cells and the subsequent clearance of pathogens or abnormal cells.