An immunohistochemical study of the lesions of demodicosis in the dog.

Histopathological and immunohistochemical examination of skin biopsies from 32 dogs with demodicosis is reported. There was no association between the different clinical presentations of the disease and the histopathological character of the biopsies, which included absence of inflammation (n = 2), dominant perifolliculitis (n = 11), interface mural folliculitis (n = 7), mural folliculitis (n = 1), furunculosis (n = 10) and nodular dermatitis (n = 1). In eight of 32 biopsies colonies of coccoid bacteria or Malassezia pachydermatis-like yeasts were observed. IgG-bearing plasma cells were found in similar numbers in the inflammatory infiltrates of all types of histological lesion, and were invariably more numerous than IgM or IgA plasma cells. The IgG plasma cells were largely IgG4 in lesions of perifolliculitis, but consisted of a mixture of IgG2 and IgG4 where folliculitis or furunculosis was present. CD3+T lymphocytes were prominent within the interface infiltrates of follicular epithelium and also within the lesions of furunculosis. Dermal inflammatory cells and epidermal Langerhans cells expressing MHC Class II were observed in similar number in all types of lesion. The study demonstrated an active local cutaneous immune response in canine demodicosis, which increased as the dermal pathology progressed from perifolliculitis to furunculosis.