antigénpresentálás

Antigénpresentálás, often translated as antigen presentation, is a crucial process in the adaptive immune system. It is the mechanism by which immune cells, primarily antigen-presenting cells (APCs), display fragments of antigens on their surface to T lymphocytes. This presentation is essential for initiating an immune response.

The main types of antigen-presenting cells include dendritic cells, macrophages, and B cells. These cells engulf pathogens or foreign substances, break them down into smaller peptide fragments, and then associate these fragments with molecules called Major Histocompatibility Complex (MHC) proteins. There are two main classes of MHC molecules: MHC class I and MHC class II.

MHC class I molecules present antigens that originate from within the cell, such as viral proteins or tumor-specific antigens. Cells infected with viruses, for example, will display viral peptides on their surface via MHC class I molecules. This presentation signals to cytotoxic T lymphocytes (CTLs) that the cell is infected and should be eliminated.

MHC class II molecules, on the other hand, present antigens that are taken up from outside the cell. APCs that have phagocytosed or endocytosed foreign material will display these processed antigens on MHC class II molecules. This presentation is recognized by helper T lymphocytes (Th cells), which then orchestrate a broader immune response, including B cell activation and antibody production, as well as enhancing the activity of CTLs and macrophages. The interaction between the T cell receptor on the T lymphocyte and the antigen-MHC complex on the APC is highly specific, ensuring that immune responses are directed only against relevant threats.