What is a primary function of macrophages?

• A. Produce antibodies
• B. Phagocytize foreign substances and help activate T cells
• C. Transport oxygen
• D. Regulate blood pressure

Answer: (B)

Macrophages are phagocytic cells that clear foreign substances and cellular debris and also help start the adaptive immune response by presenting antigens to T cells. They specialize in engulfing pathogens through phagocytosis, breaking them down with lysosomal enzymes, and then displaying peptide fragments on MHC class II molecules to helper T cells. This antigen presentation is what helps activate T cells and coordinate a more targeted immune response. They also secrete cytokines to recruit and activate other immune cells, reinforcing the defense. This fits best because antibodies are produced by B cells and plasma cells, not macrophages; oxygen transport is the job of red blood cells; and regulating blood pressure is a function of the circulatory system.