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Lymphocytes and macrophages act as effector immune cells in the initiation and progression of renal injury. Recent data have shown that subpopulations of these immune cells (regulatory T lymphocytes and alternately-activated or regulatory macrophages) are potent modulators of tissue injury and repair in renal disease. Recent animal studies examining the therapeutic effect of these cells raise the exciting possibility that strategies targeting these cell types may be effective in treating and preventing kidney disease in humans. This review will describe their biological role in experimental kidney disease and therapeutic potential in clinical nephrology. regulatory T lymphocytes; FoxP3; macrophages; dendritic cells; immunotherapy

Matrix accumulation in the renal tubulointerstitium is predictive of a progressive decline in renal function. Transforming growth factor-β1 (TGF-β1) and, more recently, connective tissue growth factor (CTGF) are recognized to play key roles in mediating the fibrogenic response, independently of the primary renal insult. Further definition of the independent and interrelated effects of CTGF and TGF-β1 is critical for the development of effective antifibrotic strategies. CTGF (20 ng/ml) induced fibronectin and collagen IV secretion in primary cultures of human proximal tubule cells (PTC) and cortical fibroblasts (CF) compared with control values (P < 0.005 in all cases). This effect was inhibited by neutralizing antibodies to either TGF-β or to the TGF-β type II receptor (TβRII). TGF-β1 induced a greater increase in fibronectin and collagen IV secretion in both PTC (P < 0.01) and CF (P < 0.01) compared with that observed with CTGF alone. The combination of TGF-β1 and CTGF was additive in their effects on both PTC and CF fibronectin and collagen IV secretion. TGF-β1 (2 ng/ml) stimulated CTGF mRNA expression within 30 min, which was sustained for up to 24 h, with a consequent increase in CTGF protein (P < 0.05), whereas CTGF had no effect on TGF-β1 mRNA or protein expression. TGF-β1 (2 ng/ml) induced phosphorylated (p)Smad-2 within 15 min, which was sustained for up to 24 h. CTGF had a delayed effect on increasing pSmad-2 expression, which was evident at 24 h. In conclusion, this study has demonstrated the key dependence of the fibrogenic actions of CTGF on TGF-β. It has further uniquely demonstrated that CTGF requires TGF-β, signaling through the TβRII in both PTCs and CFs, to exert its fibrogenic response in this in vitro model. [ABSTRACT FROM AUTHOR]

Tranilast (N-[3,4-dimethoxycinnamoyl]anthranilic acid) is a synthetic compound that we have recently reported to inhibit transforming growth factor-β1 (TGF-β1)-induced tubulointerstitial fibrosis in the kidney. Connective tissue growth factor (CTGF) is recognized as a potent downstream mediator of TGF-β1. Both proximal tubule cells (PTCs) and cortical fibroblasts (CFs) are considered to be responsible for the production of tubulointerstitial extracellular matrix (ECM). These studies were undertaken to assess the profibrotic effects of CTGF in an in vitro model of the human PTCs and CFs, and to determine whether tranilast is effective in limiting the in vitro matrix responses induced by CTGF. Primary cultures of PTCs and CFs were exposed to CTGF (20 ng/ml)±tranilast (100 μM). Cell hypertrophy and the secretion of the ECM proteins fibronectin and collagen IV were determined. The effects of tranilast on TGF-β1-induced CTGF mRNA expression and on phosphorylation of Smad2 were determined. CTGF significantly induced cell hypertrophy, increased fibronectin, and collagen IV secretion in PTCs and CFs. In all cases, the CTGF-induced increase in ECM protein was inhibited in the presence of tranilast. Tranilast reduced CTGF mRNA and phosphorylation of Smad2, which were induced by TGF-β1 in PTCs and CFs. These results suggest that tranilast is a potential effective antifibrotic compound in the kidney, exerting its effects via inhibition of TGF-β1-induced CTGF expression and downstream activation of the Smad2 pathway in both PTCs and CFs.Kidney International (2006) 69, 989–995. doi:10.1038/sj.ki.5000189; published online 22 February 2006 [ABSTRACT FROM AUTHOR]

CD39 is an ecto-enzyme that degrades extracellular nucleotides, such as ATP, and is highly expressed on by the vasculature and circulating cells including Foxp3+ regulatory T (Treg) cells. To study the role of purinergic regulation in renal disease, we used the adriamycin nephropathy (AN) mouse model of chronic renal injury, using human CD39-transgenic (hCD39Tg) and wild-type (WT) BALB/c mice. Effects of CD39 expression by Treg cells were assessed in AN by adoptive transfer of CD4(+) CD25(+) and CD4(+) CD25(-) T cells isolated from hCD39Tg and WT mice. hCD39Tg mice were protected from renal injury in AN with decreased urinary protein and serum creatinine, and significantly less renal injury compared with WT mice. While WT CD25(+) and hCD39Tg CD25(-) T cells conferred some protection against AN, hCD39Tg CD25(+) Treg cells offered greater protection. In vitro studies showed direct pro-apoptotic effects of ATP on renal tubular cells. In conclusion, hCD39 expressed by circulating leukocytes and intrinsic renal cells limits innate AN injury. Specifically, CD39 expression by Treg cells contributes to its protective role in renal injury. These findings suggest that extracellular nucleotides mediate AN kidney injury and that CD39, expressed by Treg cells and other cells, is protective in this model., (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Regulatory T cells (Tregs) help protect against autoimmune renal injury. The use of agonist antibodies and antibody/cytokine combinations to expand Tregs in vivo may have therapeutic potential for renal disease. Here, we investigated the effects of administering IL-2/IL-2Ab complexes in mice with adriamycin nephropathy, a model of proteinuric kidney disease that resembles human focal segmental glomerulosclerosis. Injecting IL-2/IL-2Ab complexes before or, to a lesser extent, after induction of disease promoted expansion of Tregs. Furthermore, administration of this complex was renoprotective, evidenced by improved renal function, maintenance of body weight, less histologic injury, and reduced inflammation. IL-2/IL-2Ab reduced serum IL-6 and renal expression of IL-6 and IL-17 but enhanced expression of IL-10 and Foxp3 in the spleen. In vitro, the addition of IL-2/IL-2Ab complexes induced rapid STAT-5 phosphorylation in CD4 T cells. In summary, these data suggest that inducing the expansion of Tregs by administering IL-2/IL-2Ab complexes is a possible strategy to treat renal disease.

Autoreactive T cells play a pivotal role in the pathogenesis of autoimmune kidney disease. T cell vaccination (TCV) may limit autoimmune disease and induce CD8+ regulatory T cells (Tregs). We used Heymann nephritis (HN), a rat model of human membranous nephritis, to study the effects of TCV on autoimmune kidney disease. We harvested CD4+ T cells from renal tubular antigen (Fx1A) -immunized rats and activated these cells in vitro to express the MHC Class Ib molecule Qa-1. Vaccination of Lewis rats with these autoreactive Fx1A-induced T cells protected against HN, whereas control-primed T cells did not. Rats that underwent TCV had lower levels of proteinuria and serum creatinine and significantly less glomerulosclerosis, tubular damage, and interstitial infiltrates. Furthermore, these rats expressed less IFN-γ and IL-6 in splenocytes, whereas the numbers of Tregs and the expression of Foxp3 were unchanged. In vitro cytotoxicity assays showed CD8+ T cell-mediated elimination of Qa-1-expressing CD4+ T cells. In vivo, TCV abrogated the increase in Qa-1-expressing CXCR5+ TFH cells observed in HN compared with controls. Taken together, these results suggest that TCV protects against autoimmune kidney disease by targeting Qa-1-expressing autoreactive CD4+ cells.

Regulatory T cells (Tregs) have a key role in immune homeostasis and in suppressing unwanted inflammatory responses toward self-antigens. Tregs have been implicated in the control of initial activation events, and play roles in limiting proliferation, differentiation and effector functions of T helper cells. However, the activities of Tregs in the development and progression of kidney disease are not fully elucidated. We have demonstrated the potency of Tregs in animal models of kidney disease. In this review, we summarise mechanistic information from rodent models on the roles of Tregs in glomerular immunopathology and discuss the function of Tregs in diverse kidney diseases. Further studies of Tregs should provide important insights into designing of therapeutic strategies to prevent human kidney disease.

Matrix accumulation in the renal tubulointerstitium is predictive of a progressive decline in renal function. Transforming growth factor-beta(1) (TGF-beta(1)) and, more recently, connective tissue growth factor (CTGF) are recognized to play key roles in mediating the fibrogenic response, independently of the primary renal insult. Further definition of the independent and interrelated effects of CTGF and TGF-beta(1) is critical for the development of effective antifibrotic strategies. CTGF (20 ng/ml) induced fibronectin and collagen IV secretion in primary cultures of human proximal tubule cells (PTC) and cortical fibroblasts (CF) compared with control values (P < 0.005 in all cases). This effect was inhibited by neutralizing antibodies to either TGF-beta or to the TGF-beta type II receptor (TbetaRII). TGF-beta(1) induced a greater increase in fibronectin and collagen IV secretion in both PTC (P < 0.01) and CF (P < 0.01) compared with that observed with CTGF alone. The combination of TGF-beta(1) and CTGF was additive in their effects on both PTC and CF fibronectin and collagen IV secretion. TGF-beta(1) (2 ng/ml) stimulated CTGF mRNA expression within 30 min, which was sustained for up to 24 h, with a consequent increase in CTGF protein (P < 0.05), whereas CTGF had no effect on TGF-beta(1) mRNA or protein expression. TGF-beta(1) (2 ng/ml) induced phosphorylated (p)Smad-2 within 15 min, which was sustained for up to 24 h. CTGF had a delayed effect on increasing pSmad-2 expression, which was evident at 24 h. In conclusion, this study has demonstrated the key dependence of the fibrogenic actions of CTGF on TGF-beta. It has further uniquely demonstrated that CTGF requires TGF-beta, signaling through the TbetaRII in both PTCs and CFs, to exert its fibrogenic response in this in vitro model.

Postprandial hyperglycemia is implicated as a risk factor predisposing to vascular complications. This study was designed to assess recurrent short-term increases in glucose on markers of renal fibrogenesis. Human renal cortical fibroblasts were exposed to fluctuating short-term (2 h) increases to 15 mM d-glucose, three times a day over 72 h, on a background of 5 mM d-glucose. To determine whether observed changes were due to fluctuating osmolality, identical experiments were undertaken with cells exposed to l-glucose. Parallel experiments were performed in cells exposed to 5 mM d-glucose and constant exposure to either 15 or 7.5 mM d-glucose. Fluctuating d-glucose increased extracellular matrix, as measured by proline incorporation (P < 0.05), collagen IV (P < 0.005), and fibronectin production (P < 0.001), in association with increased tissue inhibitor of matrix metalloproteinase (MMP) (P < 0.05). Sustained exposure to 15 mM d-glucose increased fibronectin (P < 0.001), in association with increased MMP-2 (P = 0.01) and MMP-9 activity (P < 0.05), suggestive of a protective effect on collagen matrix accumulation. Transforming growth factor-beta(1) (TGF-beta(1)) mRNA was increased after short-term (90 min) exposure to 15 mM glucose (P < 0.05) and after 24-h exposure to 7.5 mM ? (P < 0.05). Normalization of TGF-beta(1) secretion occurred within 48 h of constant exposure to an elevated glucose. Fluctuating l-glucose also induced TGF-beta(1) mRNA and a profibrotic profile, however, to a lesser extent than observed with exposure to fluctuating d-glucose. The results suggest that exposure to fluctuating glucose concentrations increases renal interstitial fibrosis compared with stable elevations in d-glucose. The effects are, in part, due to the inherent osmotic changes.