Skin IL-17A and IFN-γ Production Correlate with Disease Severity in Patients with Psoriasis and Streptococcal Infection

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-gamma production by T cells infiltrating skin lesions and PASI in 313 patients with psoriasis, compared with that in 252 healthy controls. The phenotype of beta-hemolytic Streptococci-specific infiltrating T cells in skin lesions was evaluated and characterized for IFN-gamma, IL-4, and IL-17A production. In addition, PBMCs were tested by ELISpot for IFN-gamma 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 beta-hemolytic Streptococci antigens. Most beta-hemolytic Streptococci-specific T cells displayed T helper 17 and T helper 1 phenotypes. The levels of IFN-gamma and IL-17A secreted by skin-infiltrating T cells of patients with psoriasis significantly correlated with PASI score. In beta-hemolytic Streptococci-positive patients, IFN-gamma 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.