Aberrant IL-4 production by SOCS3-over-expressing T cells during infection with Leishmania major exacerbates disease manifestations

Suppressor of cytokine signaling (SOCS) 3 is a major negative feedback regulator of signal transducer and activator of transcription 3-activating cytokines. Studies using T-cell-specific SOCS3-deficient mice indicate that the absence of SOCS3 in T cells results in exacerbation of disease progression after infection by Leishmania major due to skewing of the T_h3 cell phenotype accompanied by hyper-production of IL-10 and transforming growth factor β (TGF-β). Here we show that transgenic mice over-expressing the SOCS3 gene in T cells (Lck-SOCS3 Tg mice) are also susceptible to infection by L. major. Forced expression of SOCS3 in T cells did not affect the production of the anti-inflammatory cytokines IL-10 and TGF-β or that of the protective T_h1 type cytokine IFN-γ, which is required for parasite clearance. CD⁴1 T cells isolated from infected-Lck-SOCS3 Tg mice produced much higher levels of IL-4 when they were restimulated with L. major antigen in vitro. Exacerbation of disease progression in Lck-SOCS3 Tg mice was completely reversed by administration of a neutralizing antibody against IL-4. These data suggest that tight regulation of SOCS3 expression in T_h cells is crucial for disease control during infection by L. major.