What role do granulocytes play in the human body?

Granulocytes have a life span of only a few days and are continuously produced from stem cells (i.e., precursor cells) in the bone marrow. They enter the bloodstream and circulate for a few hours, after which they leave the circulation and die. Granulocytes are mobile and are attracted to foreign materials by chemical signals, some of which are produced by the invading microorganisms themselves, others by damaged tissues, and still others by the interaction between microbes and proteins in the blood plasma. Some microorganisms produce toxins that poison granulocytes and thus escape phagocytosis, and other microbes are indigestible and are not killed when ingested. As a result, granulocytes are of limited effectiveness by themselves and require reinforcement by the mechanisms of specific immunity (e.g., antibody-mediated immunity).