Kidney glomerulosclerosis commonly progresses to end-stage kidney failure, but pathogenic mechanisms are still poorly understood. Here, we show that podocyte expression of decay-accelerating factor (DAF/CD55), a complement C3 convertase regulator, crucially controls disease in murine models of adriamycin (ADR)-induced focal and segmental glomerulosclerosis (FSGS) and streptozotocin (STZ)-induced diabetic glomerulosclerosis. ADR induces enzymatic cleavage of DAF from podocyte surfaces, leading to complement activation. C3 deficiency or prevention of C3a receptor (C3aR) signaling abrogates disease despite DAF deficiency, confirming complement dependence. Mechanistic studies show that C3a/C3aR ligations on podocytes initiate an autocrine IL-1β/IL-1R1 signaling loop that reduces nephrin expression, causing actin cytoskeleton rearrangement. Uncoupling IL-1β/IL-1R1 signaling prevents disease, providing a causal link. Glomeruli of patients with FSGS lack DAF and stain positive for C3d, and urinary C3a positively correlates with the degree of proteinuria. Together, our data indicate that the development and progression of glomerulosclerosis involve loss of podocyte DAF, triggering local, complement-dependent, IL-1β–induced podocyte injury, potentially identifying new therapeutic targets.

IL-17–producing CD4 ⁺ (Th17) cells are pathogenically linked to autoimmunity and, specifically, to autoimmune kidney disease. The newly recognized immunoregulatory functions of erythropoietin (EPO) and its predominant intrarenal source suggested that EPO physiologically regulates Th17 cell differentiation, thereby serving as a barrier to development of autoimmune kidney disease. Using in vitro studies of human and murine cells and in vivo models, we show that EPO ligation of its receptor (EPO-R) on CD4 ⁺ T cells directly inhibits Th17 cell generation and promotes transdifferentiation of Th17 cells into IL-17 ^– FOXP3 ⁺ CD4 ⁺ T cells. Mechanistically, EPO/EPO-R ligation abrogates upregulation of SGK1 gene expression and blocks p38 activity to prevent SGK1 phosphorylation, thereby inhibiting RORC-mediated transcription of IL17 and IL23 receptor genes. In a murine model of Th17 cell–dependent aristolochic acid–induced interstitial kidney disease associated with reduced renal EPO production, we demonstrate that transgenic EPO overexpression or recombinant EPO (rEPO) administration limits Th17 cell formation and clinical/histological disease expression. EPO/EPO-R ligations on CD4 ⁺ T cells abrogate, while absence of T cell–expressed EPO-R augments, Th17 cell induction and clinical/histological expression of pristane-induced glomerulonephritis (associated with decreased intrarenal EPO). rEPO prevents spontaneous glomerulonephritis and Th17 cell generation in MRL- lpr mice. Together, our findings indicate that EPO physiologically and therapeutically modulates Th17 cells to limit expression of Th17 cell–associated autoimmune kidney disease.

Vitamin D belongs to the group of liposoluble steroids mainly involved in bone metabolism by modulating calcium and phosphorus absorption or reabsorption at various levels, as well as parathyroid hormone production. Recent evidence has shown the extra-bone effects of vitamin D, including glucose homeostasis, cardiovascular protection, and anti-inflammatory and antiproliferative effects. This narrative review provides an overall view of vitamin D’s role in different settings, with a special focus on chronic kidney disease and kidney transplant.

Immune disorders, involving both innate and adaptive response, are common in patients with end-stage renal disease under chronic hemodialysis. Endogenous and exogenous factors, such as uremic toxins and the extracorporeal treatment itself, alter the immune balance, leading to chronic inflammation and higher risk of cardiovascular events. Several studies have previously described the immune effects of chronic hemodialysis and the possibility to modulate inflammation through more biocompatible dialyzers and innovative techniques. On the other hand, very limited data are available on the possible immunological effects of a single hemodialysis treatment. In spite of the lacking information about the immunological reactivity related to a single session, there is evidence to indicate that mediators of innate and adaptive response, above all complement cascade and T cells, are implicated in immune system modulation during hemodialysis treatment. Expanding our understanding of these modulations represents a necessary basis to develop pro-tolerogenic strategies in specific conditions, like hemodialysis in septic patients or the last session prior to kidney transplant in candidates for receiving a graft.

Donor-specific (d-sp) interferon gamma enzyme-linked immunosorbent spot (d-sp ELISPOT) and Panel of reactive T-cell (PRT) ELISPOT assays have been developed to detect alloreactive memory T (Tmem) cells in order to estimate the risk of acute rejection after kidney transplantation. Adding IL15 to the PRT assay (PRT+IL15) may uncover the presence of pathogenic alloreactive CD28^-Tmem. Face-to-face comparisons of these assays have not been done yet. We performed pre-transplant d-sp ELISPOT and PRT assays (±IL15, against six B-cell lines) in 168 consecutive kidney transplant recipients and evaluated the multivariable-adjusted associations with biopsy-proven acute rejection (BPAR), de novo donor-specific antibodies (DSA), and eGFR decline over a 48-month follow-up period. D-sp ELISPOT was positive in 81 (48%) subjects, while 71 (42%) and 81 (48%) subjects displayed positive PRT and PRT+IL15, respectively. Their median [interquartile range] numerical test result was 23 [6–65], 18 [8–37], and 26 [10–45] spots/3x10⁵ PBMCs, respectively. The number of PRT spots were weakly correlated with those of d-sp ELISPOT, but highly correlated with PRT+IL15 (rho = 0.96, P<0.001). d-sp ELISPOT, but not PRT (±IL15) was independently associated with BPAR (adjusted Odds Ratio of BPAR associated with d-sp ELISPOT positivity: 4.20 [95%CI: 1.06 to 21.73; P = 0.041]). Unlike d-sp ELISPOT, median PRT and PRT+IL15 were independently associated with higher Δ3-48month eGFR decline post-transplantation (for both assays, about -3mL/min/1.73m2 per one standard deviation unit increase in the spot number). Pre-transplant T-cell immune-monitoring using d-sp ELISPOT and PRT assays identifies kidney transplant candidates at high risk of BPAR and worse kidney allograft progression.

Significance Statement: Better understanding of the regulation of auto- and alloantibody production is essential to develop hypothesis-driven therapies for autoimmune kidney diseases and graft rejection. Murine studies demonstrate that erythropoietin (EPO), a kidney-produced hormone, inhibits primary, T cell–dependent humoral immunity. EPO also diminishes autoantibodies and disease severity in murine models of lupus, and significantly reduces secondary humoral immunity in an allogeneic organ transplant model. A direct, STAT5-dependent, inhibitory effect of EPO through its receptor (EPOR) on T follicular helper (T_FH) cells that is crucial for B cell maturation mediates these effects. In vitro experiments document that EPO inhibitory effects on T_FH formation apply to human cells, providing a rationale for further testing how EPOR activation affects autoimmune kidney diseases and antibody-mediated graft rejection. Background: Although high-affinity IgG auto- and alloantibodies are important drivers of kidney inflammation that can result in ESKD, therapeutic approaches that effectively reduce such pathogenic antibodies remain elusive. Erythropoietin (EPO) has immunomodulatory functions, but its effects on antibody production are unknown. Methods: We assessed the effect and underlying mechanisms of EPO/EPO receptor (EPOR) signaling on primary and secondary, T cell–dependent and T–independent antibody formation using in vitro culture systems, murine models of organ transplantation and lupus nephritis, and mice conditionally deficient for the EPOR expressed on T cells or B cells. Results: In wild-type mice, recombinant EPO inhibited primary, T cell–dependent humoral immunity to model antigens and strong, polyclonal stimuli, but did not alter T–independent humoral immune responses. EPO also significantly impaired secondary humoral immunity in a potent allogeneic organ transplant model system. The effects required T cell, but not B cell, expression of the EPOR and resulted in diminished frequencies of germinal center (GC) B cells and T follicular helper cells (T_FH). In vitro and in vivo experiments showed that EPO directly prevented T_FH differentiation and function via a STAT5-dependent mechanism that reduces CD4⁺ T cell expression of Bcl6. In lupus models, EPO reduced T_FH, GC B cells, and autoantibody production, and abrogated autoimmune glomerulonephritis, demonstrating clinical relevance. In vitro studies verified that EPO prevents differentiation of human T_FH cells. Conclusions: Our findings newly demonstrate that EPO inhibits T_FH-dependent antibody formation, an observation with potential implications for treating antibody-mediated diseases, including those of the kidney.