Which cell type is primarily responsible for phagocytosis and microbial killing early in infection?

• A. B lymphocytes.
• B. CD8+ T cells.
• C. Neutrophils.
• D. Mast cells.

Answer: (C)

Neutrophils are the frontline phagocytes of the innate immune response. They rapidly migrate to sites of infection and, upon arrival, ingest (phagocytose) microbes and kill them inside phagolysosomes using potent antimicrobial weapons—reactive oxygen species from the NADPH oxidase system and granule enzymes, with myeloperoxidase generating strong oxidants. Their speed, abundance, and direct microbicidal activity make them the primary cells responsible for early clearance of bacteria.

B lymphocytes primarily produce antibodies and participate in humoral immunity; phagocytosis isn’t their main early function. CD8+ T cells target and kill infected host cells, not microbes directly. Mast cells release inflammatory mediators to recruit other immune cells, but they don’t perform phagocytosis as a primary role.