Psoriasis is a multisystemic inflammatory disorder mainly involving the skin and joints, whose etiopathogenesis is still not completely understood. An association with streptococcal throat infection has been suggested. We aim to investigate a correlation between IL-17A and IFN-γ production by T cells infiltrating skin lesions and PASI in 313 patients with psoriasis, compared with that in 252 healthy controls. The phenotype of β-hemolytic Streptococci-specific infiltrating T cells in skin lesions was evaluated and characterized for IFN-γ, IL-4, and IL-17A production. In addition, PBMCs were tested by ELISpot for IFN-γ and IL-17A after streptococcal antigen exposure. A total of 64 of 313 (20.4%) patients with psoriasis had throat streptococcal infection. Of the 3,868 skin-derived T-cell clones from psoriasis with streptococcal infection, 66% proliferated in response to β-hemolytic Streptococci antigens. Most β-hemolytic Streptococci-specific T cells displayed T helper 17 and T helper 1 phenotypes. The levels of IFN-γ and IL-17A secreted by skin-infiltrating T cells of patients with psoriasis significantly correlated with PASI score. In β-hemolytic Streptococci-positive patients, IFN-γ and IL-17A production by peripheral blood T cells after stimulation with streptococcal antigens was quantified by ELISpot. The results obtained may suggest ELISpot as a useful diagnostic tool to identify patients with psoriasis that may deserve antibiotic treatment.
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