An important part of the nonspecific immune response is (are)

• A. B cells
• B. Dendritic cells
• C. Polymorphonuclear cells (PMNs)
• D. Cytotoxic T lymphocytes (CTLs)

Answer: (C)

Nonspecific, or innate, immunity acts quickly and targets general features of pathogens rather than specific antigens. The most representative effectors here are neutrophils, or polymorphonuclear cells. These cells are the first responders to infection and roam into tissues in large numbers in response to chemotactic signals. They perform rapid phagocytosis of bacteria, release antimicrobial granules containing enzymes and reactive oxygen species, and can form extracellular traps to trap pathogens. This all happens without prior exposure or antigen-specific receptors, hallmarking innate defense.

In contrast, what B cells and cytotoxic T lymphocytes do relies on recognizing specific antigens and expanding clonally after activation, which is the domain of adaptive immunity. Dendritic cells bridge innate and adaptive immunity by presenting antigens to T cells, rather than acting as primary effectors of nonspecific defense, though they are important in kickstarting the adaptive response. Therefore, the best answer is the polymorphonuclear cells, reflecting their central role as rapid, nonspecific responders.