TGF-β1 down-regulates induced expression of both class II MHC and B7-1 on primary murine renal tubular epithelial cells

Abstract

Background. We examined the immunomodulatory effects of transforming growth factor-β1 (TGF-β1) on the regulation of class II MHC and costimulatory molecule expression in a primary renal tubular epithelial cell line, called F1K. Methods. Class II major histocompatibility complex (MHC), class II transactivator, B7-1, intercellular adhesion molecule-1 (ICAM-1) and interferon-γ (IFN-γ) receptor β chain were evaluated in untreated and cytokine-treated F1K by Northern hybridization analysis and flow cytometry. T cell activation studies were performed to assess TGF-β1-mediated effects on antigen presenting cell function of F1K. Results. Pretreatment of F1K with TGF-β1 markedly inhibited IFN-γ-induced class II MHC expression, by both FACS and Northern analysis. Total class II transactivator mRNA levels were also diminished by TGF-β1, indicating that class II MHC modulation in F1K results from inhibition of this intermediate protein. As previous studies demonstrated that cotreatment of F1K cells with IFN-γ + lipopolysaccharide (LPS) induces B7-1, we evaluated the potential regulatory effects of TGF-β1 exposure on B7-1 expression. Our studies revealed that B7-1 mRNA and cell- surface expression in IFN-γ + LPS-treated F1K were decreased by TGF-β1 pretreatment. Functional studies evaluating TGF-β1-mediated effects were performed with IFN-γ + LPS-treated F1K and MR1.3, a nephritogenic CD4+ Th2 clone derived from kidneys of animals with autoimmune glomerulonephritis. Interleukin (IL)-4 production assays demonstrated activation of MR1.3 by IFN- γ + LPS-treated cells, but not by IFN-γ + LPS-treated cells previously exposed to TGF-β1, indicating that TGF-β1-mediated inhibition of class II MHC and B7-1 expression alters the antigen presenting cell function of F1K. Conclusions. These studies describe the proscriptive influence of TGF-β1 on class II MHC and B7-1 expression in renal tubular epithelial cells. Such findings indicate that TGF-β1 alters the antigen presenting cell function of renal tubular epithelial cells in vitro, and suggest a potential mechanism for immunosuppression of T cell-mediated renal immune responses in vivo.