In the bone marrow, basic stem cells develop and differentiate into red blood cells, platelets, and WBCs. Two types, neutrophils and eosinophils , are phagocytes, meaning they defend the body by engulfing foreign invaders and destroying them. The third type, basophils , play a role in hypersensitivity reactions. Agranulocytes lack granules in their cytoplasm. Monocytes , the largest WBCs, are phagocytes.
Lymphocytes help govern immunity and are responsible for antibody production.
Phagocytic WBCs recognize invaders, then track and pursue them. At the same time, the blood vessel walls become porous, allowing the phagocytes easier access to the affected tissue. Enzymes within the phagocyte help digest and neutralize them. When digestion is complete, some debris may leak from the phagocyte into the extracellular fluid. This WBC migration, phagocytosis, and leakage all contribute to inflammation.