Which cells act as antigen-presenting cells (APCs) to initiate the adaptive immune response?

• A. B cells produce antibodies
• B. Neutrophils
• C. Dendritic cells process and present antigens on MHC molecules to T cells
• D. Red blood cells

Answer: (C)

Antigen presentation to naive T cells by professional antigen-presenting cells initiates the adaptive immune response. Dendritic cells are the most effective at this role: they patrol for pathogens, take up antigens, then migrate to lymphoid tissues where they process those antigens and display peptide fragments on MHC molecules. This peptide-MHC display, along with essential co-stimulatory signals, activates naive T cells and starts the specificity-driven expansion that characterizes the adaptive response. B cells can present antigens too, but their primary role is antibody production, while neutrophils and red blood cells do not function as antigen-presenting cells to T cells.