The cellular dermal infiltrate in experimental immediate type cutaneous hypersensitivity

A previously developed guinea pig model for the study of the dermal inflammatory cell infiltrate of allergic, toxic, and irritant reactions was adapted to the study of the immediate intradermal reaction to ovalbumin. Comparison of qualitative and quantitative counts of infiltrating cells at three levels in the dermis showed that counting 20 subepidermal fields starting from the injection point of the allergen gave reliable figures. The reaction showed microscopically two phases. The first was of rapid onset and characterized by a high proportion of neutrophils, unlike the picture seen in the previously studied (allergic and toxic) reaction types. In the second phase, which can be termed "late phase" reaction, mononuclear cells and basophil granulocytes predominated. The late phase of the reaction bears similarities to the delayed allergic contact reaction at the same timepoint in that the response was rich in basophils. There were, however, other differences; e.g. eosinophils and neutrophils were more common.