What is the role of antigen-presenting cells (APCs) in the immune response?

• A. APCs produce antibodies directly.
• B. APCs are only in the innate immune system.
• C. APCs phagocytose pathogens but do not present antigens.
• D. APCs process and present antigens on MHC molecules to T cells, initiating adaptive immunity.

Answer: (D)

Antigen-presenting cells serve as the crucial bridge between innate detection and the adaptive immune response. They capture pathogens, break down their proteins, and display the resulting peptide fragments on MHC molecules on their surface. This presentation is what alert and activate T cells, especially helper T cells, to the presence of a threat and to coordinate a targeted immune response. Once T cells recognize these peptide-MHC complexes, they become activated and help drive the adaptive response, including enabling B cells to produce antibodies and supporting cytotoxic T cell responses when needed. Some APCs can also present antigens on MHC class I molecules in a process called cross-presentation, further expanding the adaptive response. Antibodies, on the other hand, are produced by B cells (plasma cells), not by antigen-presenting cells, so that option isn’t correct.