Upregulation of SOCS3 in lung CD4+ T cells in a mouse model of chronic PA lung infection and suppression of Th17-mediated neutrophil recruitment in exogenous SOCS3 transfer in vitro

Neutrophilic airway inflammation in chronic lung infections caused by Pseudomonas aeruginosa (PA) is associated with T helper (Th) 17 responses. Suppressor of cytokine signaling 3 (SOCS3) is the major negative modulator of Th17 function through the suppression of signal transducer and activator of transcription (STAT) 3 activation. The aim of the present study was to investigate the expression of SOCS3 in lung CD4(+) T cells in a mouse model of chronic PA lung infection and the effect of exogenous SOCS3 on Th17-mediated neutrophil recruitment in vitro. A mouse model of chronic PA lung infection was established and the activation of STAT3 and Th17 response in lung tissues and lung CD4(+) T cells was assessed. The protein and mRNA expression of SOCS3 in lung CD4(+) T cells was analyzed by western blotting and reverse transcription-quantitative polymerase chain reaction. The authors constructed a recombinant lentivirus carrying the SOCS3 gene and transferred it into lung CD4(+) T cells isolated from a mouse model. These transfected cells were stimulated with interleukin (IL) -23 in vitro and the protein level of p-STAT3 and retinoid-related orphan receptor (ROR).t was determined by western blotting. The expression of IL-17A(+) cells was analyzed by flow cytometry and the level of IL-17A in cell culture supernatant was measured by ELISA. The mouse lung epithelial cell line, MLE-12, was cocultured with lung CD4(+) T cells that overexpressed the SOCS3 gene and the culture supernatant was harvested and used for a chemotaxis assay. Compared with control mice, mice with chronic PA lung infection had significantly higher level of p-STAT3 and Th17 response in both lung tissues and lung CD4(+) T cells. The protein and mRNA level of SOCS3 in lung CD4(+) T cells increased as the chronic PA lung infection developed. Exogenous SOCS3 gene transfer in PA-infected lung CD4(+) T cells decreased p-STAT3 and ROR.t expression and suppressed the level of IL-17A(+) cells in vitro. MLE-12 cells cocultured with SOCS3-overexpressing lung CD4(+) T cells expressed a significantly lower level of neutrophil chemoattractants chemokine (C-X-C motif) ligand (CXCL) 1 and CXCL5, and recruited significantly smaller numbers of migrating neutrophils than those cocultured with control cells. SOCS3 was upregulated in lung CD4(+) T cells following the activation of STAT3/Th17 axis in a mouse model of chronic PA lung infection. Exogenous SOCS3 transfer in PA-infected lung CD4(+) T cells suppresses Th17-mediated neutrophil recruitment in vitro.