A variety of cell-mediated hypersensitivity reactions in experimental animals include a prominent infiltrate of basophilic leukocytes. This form of reactivity has been designated cutaneous basophil hypersensitivity and is favored when sensitization to several types of antigen is accomplished without the use of complete Freund's adjuvant.

A similar type of hypersensitivity response was sought in man using morphologic techniques which permit identification of basophilic leukocytes. Eight individuals with allergic contact dermatitis to a variety of allergens were studied and six of these developed typical contact reactions with erythema, edema, and epidermal vesicles. The microscopic findings in 3-day biopsies from these individuals differed significantly from classic descriptions of tuberculin hypersensitivity and showed, in addition to mononuclear cells and the characteristic epidermal changes, a substantial infiltrate of basophilic leukocytes and evidence of altered vascular permeability with vascular compaction, dermal edema, and fibrin deposition. Serial biopsies from one individual permitted analysis of the microscopic pathology as it unfolded at successive intervals after patch test. The initial lesion consisted of perivascular accumulations of lymphocytes; this was followed by an influx of basophils and, subsequently, of eosinophils.

These findings associate contact allergy in man with the parallel reactions of cutaneous basophil hypersensitivity in animals and provide further evidence for the heterogeneity of the cellular immune response. The data are consistent with the hypothesis that interaction between sensitized lymphocytes and antigen, at a local test site, is responsible for the attraction of basophils. They also directly implicate the clotting system in delayed-type reactions and suggest the possibility of a synergistic relationship between cellular immunity and reactions mediated by basophil-bound, homocytotrophic antibody.

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