Immunologic aspects of eosinophilia.

There is compelling investigative data to indicate that the eosinophil may be more than just coincidentally involved in immune system function. In concert with IgE and the mast cell it is likely that eosinophil actions evolved as an early host defense mechanism against helminth parasites. Thus, a reasonable basis exists for the concept that in the evolutionary scheme there emerged genetically endowed humans with the potential for mounting immediate hypersensitivity responses to multicellular and complex antigenic particulates and animal and plant products, e.g., pollens and danders; hence the atopic state, allergic reactivity and the eosinophil. In many instances there is reason to interpret and ascribe a benign nature to eosinophil accumulations. In other circumstances, associations with hypersensitivity inflammation, for better or for worse, are viewed with special interest by eosinophil watchers as the unraveling of allergic phenomena continues.