Increased numbers of CD4+ and CD8+ T cells in lesional skin of cats with allergic dermatitis

The aim of this study was to characterize T cells in the skin of cats with an allergic dermatitis histologically compatible with atopic dermatitis, si nce T cells play an important role in the pathogenesis of atopic dermatitis in humans. We observed a significantly greater number of T cells in lesion al skin of domestic short-haired cats with allergic dermatitis (n = 10; med ian age 5.8 years) than in the skin of healthy control animals (n = 10; med ian age 5.0 years). In the skin of the healthy control animals, one or two CD4+ cells and no CD8+ cells were found. A predominant increase of CD4+ T c ells and a CD4+/CD8+ ratio (mean +/- SD: 3.9 +/- 2.0) was found in the lesi onal skin of 10 cats with allergic dermatitis. The CD4+/CD8+ cell ratio in the skin of healthy control animals could not be determined because of the absence of CD8+ cells. The CD4+/CD8+ cell ratio in the peripheral blood of 10 cats with allergic dermatitis (mean +/- SD: 1.9 +/- 0.4) did not differ significantly from that in 10 healthy control animals (2.2 +/- 0.4). The CD 4+/CD8+ cell ratio and predominance of CD4+ T cells in the lesional skin of cats with allergic dermatitis is comparable to that found in atopic dermat itis in humans. In addition, the observed increase of CD4+ T cells in the n onlesional skin of cats with allergic dermatitis compared to the skin of he althy cats is similar to what is seen in humans. Cytokines produced by T ce lls and antigen-specific T cells are important mediators in the inflammator y cascade resulting in atopic dermatitis in humans. This study is a first s tep to investigate their role in feline allergic dermatitis.