Modulating T cell functions does not alleviate chronic inflammatory skin lesions in K5.TGF beta 1 transgenic mice

To use mice with chronic hyperproliferative skin inflammation as psoriasis models, their thorough phenotypic and functional characterization is indispensable. Mice with keratin 5 promoter-controlled overexpression of latent human Transforming Growth Factor (TGF)beta1 within the basal epidermis (K5.TGF beta 1 mice) show a psoriasiform phenotype, but the underlying pathogenic mechanisms are not entirely clear. To elucidate the contribution of T lymphocytes to the pathogenesis in K5.TGF beta 1 mice, we used three complementary approaches: first, peripheral T cells were eradicated via systemic treatment with CD3- or CD4-depleting antibodies. However, this elimination did not alleviate the chronic inflammatory disorder. Second, bone marrow transplantation from transgenic mice into wildtype recipients and vice versa resulted in the expected reconstitution of both adaptive and innate immune system but had little effect on the cutaneous phenotype both in wildtype and transgenic chimeras. Third, based on the hypothesis that the disease course could be modulated by regulatory T cells (Tregs), we expanded Tregs in vivo using a superagonistic anti-CD28 antibody. While this treatment achieved a threefold increase in Foxp3-expressing Tregs, there was little, if any, effect on the chronic skin inflammation. We conclude from our findings that T cells play little, if any, role in the skin lesions of K5.TGF beta 1 mice.