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term used to describe a form of immunity that is only effective if the parasite persists in the host and wanes rapidly when all parasites are eliminated


-constitute 1-5% of the total circulationg leukocytes
-normally present in peripheral tissues, esp mucosal lining of the resp, gI and genitourinary tracts
-most abundant at sites of parasitic, allergic, or some types of fungal inflammatory disease
-respond to many of the same stimuli and chemotaxins as neutrophils, as well as eosinophil-specific chemotaxins

Growth and differentiation of eosinophils

dependent on 3 cytokines:
IL-5 (most significant eosinophil differentiation factor)
GM-CSF - granulocyte macrophage-colony stimulating factor

Eosinophil cell membrane receptors

-include Fc receptors for IgG, IgA and IgE and complement receptors


-eosinophil-specific chemotaxins
-CC chemokines

Granular contents of Eosinophils

-Major basic protein (parasite killing, neutralizes heparin)
-Eosinophilic cationic protein (parasite killing)
-Arylsulfatase B. (inactivates leukotrienes)
-Histaminase (inactivates histamine)
-Phospholipase D. (incativates platlet activating factor)
-Peroxidase, collagenase, elastase etc
-Platelet activating factor

Major basic protein

-constitutes about 50% of eosinophil granule proteins
-strongly cationic, therefore interacts readily with negatively charged surface of the parasite
-toxic to helminths

Eosinophil cation protein

-pore forming protein that is toxic to helminths

Evasion of immune mechanisms by parasites

-antigenic variation
-secretion of proteases which cleaves Igs, resulting in shortened half-lives
-evasion of lysosomal enzymes

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