Which immune cells are primarily responsible for antigen presentation to naive T cells?

• A. Macrophages
• B. Dendritic cells
• C. B cells
• D. Neutrophils

Answer: (B)

Antigen presentation to naive T cells requires professional antigen-presenting cells that provide both an MHC-peptide complex and the necessary second signal for T cell activation. Dendritic cells specialize in this role. They capture antigen in tissues, migrate to lymph nodes, and express high levels of MHC class II along with co-stimulatory molecules (like CD80/86), delivering the crucial second signal that activates naive T cells and initiates their clonal expansion. They’re also capable of cross-presenting to CD8+ T cells, broadening their priming capability.

Macrophages can present antigen and activate T cells, but they’re more involved in sustaining and modulating responses once T cells are already activated, not in priming naive T cells. B cells can present antigen to helper T cells, particularly during ongoing antibody responses, but this occurs after B cells have been activated themselves and is not the primary route for initiating naive T cell responses. Neutrophils do not serve as antigen-presenting cells for naive T cells.