Macrophages express abundant amounts of MHC class II upon which antigens are displayed for activation of T helper cells. Macrophages secrete cytokines when activated. These cytokines trigger inflammation, complement activation, T helper cell activation, call other cells to the site of infection, promote increased hematopoiesis, and induce nearby cells to gear up their intracellular antiviral defenses. Neutrophils, basophils and eosinophils are granulocytes. Their numbers increase greatly during infection due to increased synthesis of them in the bone marrow in response to cytokines.
Basophils are present in blood.
They contain granules of histamine and other inflammatory mediators. In response to infection or allergens, basophils degranulate , meaning that they release the granule contents by exocytosis. The release of histamine and other factors leads to smooth muscle contraction, increased mucus, and other symptoms associated with allergic reactions. Figure 2-10C . Eosinophils are granulocytes that play a role in defending against parasitic worms.