Final answer:
Cytotoxic T cells recognize infected cells by binding to major histocompatibility complex class I (MHC I) molecules presenting pathogenic peptides. This interaction activates the cytotoxic T cell to release toxic substances, inducing apoptosis in the infected target cell.
Correct option is a) MHC I
Step-by-step explanation:
Cytotoxic T cells, or CD8+ T cells, play a pivotal role in immune defense by recognizing and binding to major histocompatibility complex class I (MHC I) molecules on the surface of nucleated cells. These MHC I molecules present endogenous antigens derived from within the cell, such as viral proteins during infection. Upon T cell receptor (TCR) engagement, cytotoxic T cells are activated to release cytotoxic molecules, initiating the destruction of the infected cell. This direct cell-killing ability is crucial for eliminating intracellular pathogens.
In contrast, helper T cells, specifically CD4+ T cells, interact with MHC II molecules on antigen-presenting cells. They facilitate immune responses by coordinating and activating various immune cells, linking innate and adaptive immunity. Together, CD8+ cytotoxic T cells and CD4+ helper T cells contribute to a coordinated and effective immune defense against diverse pathogens.