Eosinophils constitute only 1-4% of the circulating leukocytes in healthy adults. They may leave the bloodstream by diapedesis, spread out, and move about in the connective tissues. They are capable of only limited phagocytosis, showing a preference for antigen antibody complexes. The number of circulating eosinophils typically increases during allergic reactions and in response to parasitic infections and rapidly decreases in response to treatment with exogenous corticosteroids in blood.