Which cell type is primarily responsible for defending against bacteria and viruses?

Monocytes play a critical role in the immune response by acting as a type of white blood cell that is key in defending the body against bacterial and viral infections. Upon entering tissues, monocytes can differentiate into macrophages and dendritic cells. Macrophages are highly effective at engulfing and destroying pathogens, while dendritic cells are essential for processing and presenting antigens to T cells, which activates the adaptive immune response.

This functionality sets monocytes apart from the other cell types listed. Granulocytes, for example, are important in the immune response, especially in fighting off certain infections, but they have specific roles in responding to and mediating allergic reactions, as well as responding to parasitic infections, rather than directly engulfing pathogens like monocytes do.

Basophils primarily participate in inflammatory responses and the allergic reaction process, rather than directly attacking pathogens. Platelets, on the other hand, are involved in blood clotting and do not play a direct role in the immune response against viruses or bacteria.

Overall, the primary function of monocytes in differentiating and presenting antigens to other immune cells underscores their critical role in both immediate and adaptive immune defense against pathogens.