A gene transfer system establishes interleukin-6 neither promotes nor suppresses renal injury

IL-12 Drives IFN-γ-Dependent Autoimmune Kidney Disease in MRL-Fas lpr Mice

IL-12 is secreted by kidney tubular epithelial cells in autoimmune MRL-Faslpr mice before renal injury and increases with advancing disease. Because IL-12 is a potent inducer of IFN-γ, the purpose of this study was to determine whether local provision of IL-12 elicits IFN-γ-secreting T cells within the kidney, which, in turn, incites injury in MRL-Faslpr mice. We used an ex vivo retroviral gene transfer strategy to construct IL-12-secreting MRL-Faslpr tubular epithelial cells (IL-12 “carrier cells”), which were implanted under the kidney capsule of MRL-Faslpr mice before renal disease for a sustained period (28 days). IL-12 “carrier cells” generated intrarenal and systemic IL-12. IL-12 fostered a marked, well-demarcated accumulation of CD4, CD8, and double negative (CD4−CD8− B220+) T cells adjacent to the implant site. We detected more IFN-γ-producing T cells (CD4 > CD8 > CD4−CD8− B220+) at 28 days (73 ± 14%) as compared with 7 days (20 ± 8%) after implanting the IL-12 “carrier cells;” the majority of these cells were proliferating (60–70%). By comparison, an increase in systemic IL-12 resulted in a diffuse acceleration of pathology in the contralateral (unimplanted) kidney. IFN-γ was required for IL-12-incited renal injury, because IL-12 “carrier cells” failed to elicit injury in MRL-Faslpr kidneys genetically deficient in IFN-γ receptors. Furthermore, IFN-γ “carrier cells” elicited kidney injury in wild-type MRL-Faslpr mice. Taken together, IL-12 elicits autoimmune injury by fostering the accumulation of IFN-γ-secreting CD4, CD8, and CD4−CD8− B220+ T cells within the kidney, which, in turn, promote a cascade of events culminating in autoimmune kidney disease in MRL-Faslpr mice.

IFN-γ Limits Macrophage Expansion in MRL-Fas lpr Autoimmune Interstitial Nephritis: A Negative Regulatory Pathway

IFN-γ is capable of enhancing and limiting inflammation. Therefore, an increase in IFN-γ in autoimmune MRL-Faslpr mice could exacerbate or thwart renal injury. We have established a retroviral gene transfer approach to incite interstitial nephritis in MRL-Faslpr mice that is rapid, enduring, and circumscribed. Renal tubular epithelial cells (TEC) were genetically modified to secrete macrophage (Mφ) growth factors (CSF-1-TEC, GM-CSF-1-TEC) and infused under the renal capsule. To determine the impact of IFN-γ in Mφ growth factor-incited renal injury, we constructed a MRL-Faslpr IFN-γ-receptor (IFN-γR)-deficient strain. Gene transfer of CSF-1 or GM-CSF incited more severe interstitial nephritis in IFN-γR-deficient than in IFN-γR-intact MRL-Faslpr mice, consisting of an increase of Mφ. To determine the mechanism responsible for the increase in Mφ in IFN-γR-deficient MRL-Faslpr mice, we evaluated Mφ proliferation, apoptosis, and recruitment. Proliferation of bone marrow Mφ from IFN-γR-intact MRL-Faslpr costimulated with CSF-1 or GM-CSF and IFN-γ was reduced twofold, while the IFN-γR-deficient MRL-Faslpr bone marrow Mφ remained stable. Furthermore, we detected more proliferating and fewer apoptotic Mφ within the interstitium in IFN-γR-deficient MRL-Faslpr mice. Using unilateral ureteral ligation we established that IFN-γR signaling does not alter Mφ recruitment into the kidney. Thus, the increase in Mφ elicited by Mφ growth factors in IFN-γR-deficient MRL-Faslpr mice is a result of enhanced proliferation and decreased apoptosis, and is independent of recruitment. Taken together, we suggest that IFN-γ provides a negative regulatory pathway capable of limiting Mφ-mediated renal inflammation.