Which cell type is the primary source of macrophages after migrating into tissues to fight infection?

Which cell type is the primary source of macrophages after migrating into tissues to fight infection?

• A. Lymphocytes
• B. Neutrophils
• C. Monocytes
• D. Eosinophils

Answer: (C)

Macrophages in tissues come from monocytes that leave the bloodstream and differentiate after migrating to the site of infection. Monocytes are produced in the bone marrow and circulate in the blood; when an infection occurs, they exit into tissues and mature into macrophages, which then carry out phagocytosis, antigen presentation, and cytokine signaling to coordinate the immune response. Other options don’t serve this role: lymphocytes are part of the adaptive immune system, not precursors to macrophages; neutrophils are rapid responders that phagocytose bacteria but do not become macrophages; eosinophils handle parasitic infections and allergic responses and similarly do not differentiate into macrophages.

Macrophages in tissues come from monocytes that leave the bloodstream and differentiate after migrating to the site of infection. Monocytes are produced in the bone marrow and circulate in the blood; when an infection occurs, they exit into tissues and mature into macrophages, which then carry out phagocytosis, antigen presentation, and cytokine signaling to coordinate the immune response. Other options don’t serve this role: lymphocytes are part of the adaptive immune system, not precursors to macrophages; neutrophils are rapid responders that phagocytose bacteria but do not become macrophages; eosinophils handle parasitic infections and allergic responses and similarly do not differentiate into macrophages.