antigénprezentálók

Antigen-presenting cells (APCs) are a group of immune cells that play a crucial role in initiating and regulating adaptive immune responses. They are characterized by their ability to capture, process, and present antigens to T cells, thereby activating them. The most well-known APCs are dendritic cells (DCs), macrophages, and B cells. These cells are strategically positioned in various tissues and organs, including the skin, lymph nodes, and mucosal surfaces, where they encounter and internalize pathogens and other foreign substances.

The process of antigen presentation involves several steps. First, APCs capture antigens through various mechanisms, such as phagocytosis, pinocytosis, or direct binding to antigen-presenting molecules on their surface. Once internalized, antigens are degraded into peptides by proteasomes and other enzymes within the cell. These peptides are then loaded onto major histocompatibility complex (MHC) molecules, which are transported to the cell surface for presentation to T cells.

APCs can present antigens to T cells in two main ways: via MHC class I molecules, which present endogenous antigens (derived from within the cell) to CD8+ T cells, or via MHC class II molecules, which present exogenous antigens (derived from outside the cell) to CD4+ T cells. This dual presentation capability allows APCs to activate both cytotoxic T cells and helper T cells, thereby initiating a robust adaptive immune response.

In addition to their role in initiating immune responses, APCs also play a regulatory role in maintaining immune homeostasis. They can modulate the activity of T cells through the production of cytokines and the expression of co-stimulatory molecules. APCs can also induce T cell tolerance, preventing the immune system from attacking self-tissues. This regulatory function is essential for preventing autoimmune diseases and maintaining a balanced immune response.

Overall, antigen-presenting cells are vital for the proper functioning of the adaptive immune system. Their ability to capture, process, and present antigens to T cells enables the immune system to mount an effective response against pathogens and other foreign substances while maintaining self-tolerance.