Which cells are professional antigen presenting cells that prime naive T cells?

• A. Macrophages
• B. Dendritic cells
• C. B cells
• D. Red blood cells

Answer: (B)

Dendritic cells are professional antigen-presenting cells that prime naive T cells by capturing antigens in tissues, then migrating to lymph nodes to present peptide fragments on MHC class II with strong co-stimulatory signals (such as B7 engaging CD28). This dual signal—antigen presentation plus co-stimulation—drives naive T cell activation, clonal expansion, and differentiation. They’re also adept at cross-presentation to CD8+ T cells via MHC I, broadening their role in initiating cytotoxic responses.

Macrophages can present antigens, but they typically do so to already-activated T cells rather than efficiently priming naive ones. B cells can present antigen as well, but mainly in the context of helping antibody responses and require antigen-specific uptake via the B cell receptor. Red blood cells do not present antigens at all.

So, the cells that best fit as professional APCs that prime naive T cells are dendritic cells.