Final answer:
T cells recognize foreign antigens on cells by their association with the major histocompatibility (MHC) molecule on the surface of infected cells. This is facilitated by the T cell receptors (TCRs) binding to the antigen-MHC complex. CD4 and CD8 molecules on T cells differentiate the interaction between TCRs and MHC molecules.
Step-by-step explanation:
T cells recognize foreign antigens on cells of the body by their association with the major histocompatibility (MHC) molecule on the surface of the infected cells. The major histocompatibility complex (MHC) is a cluster of genes that encode the antigen-presenting molecules. T cells have receptors called T cell receptors (TCRs) that bind to the antigen-MHC complex, allowing them to recognize and respond to foreign antigens.
For example, extracellular antigens, like those of bacteria, are brought into the endomembrane system of the cell and presented on MHC class II molecules. Antigen processing enzymatically cleaves the antigens into smaller pieces, which are then brought to the cell's surface and associated with MHC molecules. When a T cell encounters an antigen-MHC complex that matches its TCR, it triggers an immune response.
The CD4 and CD8 molecules on T cells differentiate whether the TCR will engage an MHC II or an MHC I molecule, respectively. These molecules are coreceptors that help in binding specificity and regulating the T cell's interaction with antigen-presenting cells.