What do T-cells primarily recognize in immune responses?

T-cells primarily recognize antigens on infected cells, which is central to their function in the immune response. These antigens are typically presented by major histocompatibility complex (MHC) molecules on the surface of cells. Infected cells process and display fragments of pathogens, such as viruses or intracellular bacteria, on their surface using MHC class I molecules for CD8+ cytotoxic T-cells, or MHC class II molecules for CD4+ helper T-cells.

This recognition is crucial for T-cells to activate and proliferate in response to a threat. The CD8+ T-cells can directly kill infected host cells, while CD4+ T-cells can help orchestrate other parts of the immune response, including the activation of B-cells and other immune cells. Thus, the ability of T-cells to specifically target and respond to these presented antigens is vital for an effective immune response against infections.

While pathogens are indeed the source of these antigens and self-cells can be affected, T-cells do not exclusively recognize pathogens or self-cells independently; rather, their primary role is tied to the recognition of antigens that signal infection. Therefore, identifying and responding to antigens on infected cells is specifically