Immunology of the gut: role of the eosinophil.

The gut wall is one of the conspicuous sites of eosinophil accumulation, presumably because of local chemotactic stimuli. It is reasonable to assume that one chemotactic factor is released by the mast cell, which is often found in proximity to the eosinophil. The association of eosinophils and eosinophilia with allergic disorders has long been recognized, and recent work has shown that increased eosinophil production is mediated by the lymphocyte. That process shares characteristics with other immunological actions. An increased rate of eosinophil tissue accumulation and destruction may be the factor which initiates the mechanism for increased production. None of many hypotheses about the 'function' of the eosinophil is substantiated; nevertheless it seems likely that this member of the immunological apparatus, which tends to be distributed in the front line (mucosal and cutaneous tissues), fulfils some normal protective or homeostatic function. Aside from that assumed normal function, there is growing clinical evidence that eosinophils can at times cause host injury, for example in such states as eosinophilic gastroenteritis and endomyocarditis.