Which cell type serves as the primary antigen-presenting cell for naive T cell activation?

• A. NK cells
• B. Eosinophils
• C. Dendritic cells
• D. B cells

Answer: (C)

Antigen presentation to naive T cells requires a professional presenting cell that provides both antigen signal and strong costimulation. Dendritic cells are specialized for this role: they constantly sample tissue antigens, migrate to draining lymph nodes, and mature to express high levels of MHC molecules and costimulatory proteins like CD80/86. This combination delivers the necessary 2-signal activation to naive CD4 T cells (and, via cross-presentation, to CD8 T cells) and is why they are the most potent initiators of T cell responses. B cells can present antigen to T helper cells, but they’re less efficient at priming naive T cells and usually rely on prior activation. NK cells and eosinophils are notPrimarily involved in initiating naive T cell responses; NK cells are cytotoxic innate effectors, and eosinophils are effector cells in parasitic defense and allergic responses. So, dendritic cells best explain the primary antigen-presenting cell for naive T cell activation.