Class II MHC molecules are recognized by which immune cells?

• A. CD4+ T cells
• B. CD8+ T cells
• C. Natural killer cells
• D. Neutrophils

Answer: (A)

Class II MHC molecules are presented by professional antigen-presenting cells and are specifically recognized by CD4+ T helper cells. The CD4 molecule on these T cells binds to the MHC II-peptide complex, enabling activation and the downstream helper functions that coordinate the immune response, such as assisting B cells in antibody production. In contrast, CD8+ T cells recognize peptides presented by MHC class I, which are found on most nucleated cells and drive cytotoxic responses. Natural killer cells don’t rely on TCR-MHC II recognition, and neutrophils aren’t T cells that recognize peptide-MHC II complexes.