Are Basophils Identifiable in Histological Sections of Cat Skin?

Abstract

The name ‘‘basophil’’ derives from the staining characteristics of the cell’s granules with Romanowsky stains such as Diff Quik. Basophils are routinely identified in blood smears but seldom in histologic sections from companion or farm animals, so how do the granules of basophils stain with hematoxylin and eosin (HE)? In a report of basophilic enterocolitis in a horse, the granules of the basophils were described as ‘‘slightly amphiphilic.’’ Basophils were detected in the skin of dogs in experimental flea allergy dermatitis; however, the authors used Karnovsky’s fixative and a special processing technique to demonstrate the basophils because they knew that basophils could not be distinguished from other granulocytes in HE sections of formalin-fixed canine skin. Here, we detail what we believe are the features of basophils in HE sections of skin from a cat. The 10-year-old Persian cat was presented with a 10-mmdiameter, ulcerated, pruritic lesion on the left pinna and a 20-mm-diameter similar lesion on the neck. An EDTA blood sample was drawn just before biopsy of both lesions. Imprints of the biopsy specimens were prepared before the biopsies were immersed in 10% neutral buffered formalin. The cat had peripheral blood basophilia (0.9 10/liter; reference range, 0–0.2 10/liter) without eosinophilia (0.5 10/liter; reference range, 0–1.5 10/liter). Imprints from both lesions, stained with Diff Quik (Fig. 1) had numerous basophils and only a few eosinophils (3–12 eosinophils per 100 basophils in five 400 fields). The histologic sections, stained with HE, had a marked dermal infiltration of granulocytes with eosinophilic granules that were assumed to be eosinophils. The remarkable disparity between the cytologic findings and the histologic interpretation suggested that most of the eosinophilic granulocytes in the histologic sections must be basophils. Upon closer examination of the histologic sections,