Cutaneous allergic response in atopic dogs: relationship of cellular and histamine responses.

We studied the cutaneous response to intradermal antigen using clinical, histologic, and physiologic criteria in ragweed-sensitized dogs. The clinical response was measured early (the wheal at 20 minutes) and late (induration at 6 hours). We assessed cutaneous responsiveness to histamine before and 6 hours after injection (intradermally) of ragweed (n = 5, antigen group) and diluent (n = 4, 10% glycerin in 0.9% NaCl, sham group); we measured the wheal in response to histamine (1.0 ng to 0.1 mg, intradermally), constructed a dose-response curve, and interpolated the provocative dose (milligrams) of histamine required to create a wheal 10 mm larger than the response to saline control. Skin biopsy specimens were obtained before and after injection of either ragweed or diluent. Consistent with the human late-phase response, neutrophils and eosinophils were present in the dermis at 1 hour, maximal at 6 hours, and decreased at 24 hours. Mononuclear cells increased significantly at 6 hours and were the predominant cells present at 24 hours after antigen. The late clinical response correlated only with influx of eosinophils (rs = 0.85; p less than 0.005). Histamine responsiveness increased markedly after antigen (p less than 0.0001), did not change after glycerin diluent (sham), and was correlated with the intensity of neutrophil influx at 6 hours (rs = 0.69; p less than 0.05), and to a much greater degree with mononuclear cell influx at 6 hours (rs = 0.85; p less than 0.005).