Which cell is a leukocyte derived from a myeloid lineage and is among the early responders to infection?

• A. Neutrophil
• B. Lymphocyte
• C. Erythrocyte
• D. Platelet

Answer: (A)

In the immune system, white blood cells (leukocytes) come from two main branches of hematopoiesis: myeloid and lymphoid. Neutrophils are produced from the myeloid lineage and are classic early responders to bacterial infection. They rapidly migrate to the infection site, engulf and kill bacteria (phagocytosis), and release antimicrobial substances to control the invaders. Lymphocytes, in contrast, arise from the lymphoid lineage and are key players in adaptive immunity, not immediate innate responses. Erythrocytes and platelets are also derived from the myeloid lineage but are not leukocytes. Neutrophils fit the description as the initial, rapid responders among leukocytes.