Exposure to low doses of IL-5 specifically primes eosinophils for later actions by other stimulants. Once activated, the eosinophils present in certain pathological conditions associated with eosinophilia have enhanced generation of reactive oxygen species, enhanced glucose utilization and transport, increased oxygen consumption, a reduced cell surface charge, and activation of acid phosphatases in specific granules. Accompanying these changes is a decrease in cell density. Eosinophils enhance the immune response to helminths. Although the release of these proteins similarly damages tumor cells, the interaction between eosinophils and tumor cells is less well understood.
Eosinophils perform an immunosuppressive function in immediate hypersensitivity reactions.
The prostaglandins E 1 and E 2 released from the membranes of activated eosinophils are capable of suppressing basophil degranulation. Other granule contents, such as histaminase and phospholipase B, inactivate histamine and the PAF of mast cells, respectively. Eosinophils also mediate tissue damage through the effects of MBP, ECP, and superoxide and the other reactive oxygen species enhanced by the eosinophil peroxidase system. The balance between eosinophilic stimulation of and inhibition of inflammation is delicate and easily disrupted. Even after a patient with eosinophilia has been thoroughly evaluated, sometimes an explanation for the eosinophilia cannot be found.