First response in bacterial infections. Able to leave the circulation and enter the tissues to phagocytize invaders. L ast only about 7 hours in circulation, few days in tissues.
Granules contain histamine.
Can leave the circulation and produce toxins which destroy invaders such as helminths. Increased in circulation in allergic reactions and systemic fungal infections. Macrophages wander throughout the body. Secondary, clean-up in bacterial infections, but primary in viral and fungal infections. Histiocytes macrophages fixed usually to mast cells where they are involved in localized histamine release.