How do T cells recognize antigens?

T cells recognize antigens primarily through the interaction with antigens that are presented on the surface of other cells by Major Histocompatibility Complex (MHC) molecules. This is a crucial aspect of the adaptive immune response.

MHC molecules play a key role in the immune system by displaying peptide fragments derived from proteins within the cell to T cells. There are two main classes of MHC molecules: Class I MHC molecules present antigens from intracellular pathogens, such as viruses, to CD8+ cytotoxic T cells, while Class II MHC molecules present antigens from extracellular sources to CD4+ helper T cells.

When a T cell encounters an antigen presented by an MHC molecule that matches its specific T-cell receptor (TCR), it binds to this complex. This recognition is essential for activating T cells, leading to their proliferation, differentiation, and execution of their immune functions, such as helping other immune cells or directly killing infected cells.

This mechanism of antigen recognition is fundamental for the specificity and adaptability of the immune response, allowing T cells to effectively target and destroy infected or abnormal cells in the body.