Which statement describes the role of monocytes in forming macrophages?

Which statement describes the role of monocytes in forming macrophages?

• A. Monocytes mature into macrophages in tissues after migrating from bone marrow
• B. They are the primary producers of antibodies
• C. They circulate only in the bloodstream
• D. They differentiate into erythrocytes in the spleen

Answer: (A)

Monocytes serve as circulating precursors that, after leaving the bone marrow, migrate into tissues where they differentiate into macrophages. In the tissues these cells become the main phagocytes, engulfing pathogens and debris and presenting antigens to help drive the immune response. That maturation in the tissue is why this statement is correct. The other ideas don’t fit: antibody production is done by B cells/plasma cells; monocytes are not restricted to the bloodstream but move into tissues to act; and they do not become erythrocytes—the red blood cells arise from the erythroid lineage in the bone marrow.

Monocytes serve as circulating precursors that, after leaving the bone marrow, migrate into tissues where they differentiate into macrophages. In the tissues these cells become the main phagocytes, engulfing pathogens and debris and presenting antigens to help drive the immune response. That maturation in the tissue is why this statement is correct. The other ideas don’t fit: antibody production is done by B cells/plasma cells; monocytes are not restricted to the bloodstream but move into tissues to act; and they do not become erythrocytes—the red blood cells arise from the erythroid lineage in the bone marrow.