Michael C. Braun

C3 glomerulopathy: consensus report

C3 glomerulopathy is a recently introduced pathological entity whose original definition was glomerular pathology characterized by C3 accumulation with absent or scanty immunoglobulin deposition. In August 2012, an invited group of experts (comprising the authors of this document) in renal pathology, nephrology, complement biology, and complement therapeutics met to discuss C3 glomerulopathy in the first C3 Glomerulopathy Meeting. The objectives were to reach a consensus on: the definition of C3 glomerulopathy, appropriate complement investigations that should be performed in these patients, and how complement therapeutics should be explored in the condition. This meeting report represents the current consensus view of the group.

Selective Suppression of IL-12 Production by Chemoattractants

We investigated the ability of chemoattractants to affect IL-12 production by human monocytes and dendritic cells. We found that pretreatment of monocytes with macrophage chemoattractant proteins (MCP-1 to -4), or C5a, but not stromal-derived factor-1, macrophage inflammatory protein-1α, RANTES, or eotaxin, inhibited IL-12 p70 production in response to stimulation with Staphylococcus aureus, Cowan strain 1 (SAC), and IFN-γ. The production of TNF-α and IL-10, however, was minimally affected by any of the chemoattractants. The degree of inhibition of IL-12 p70 production by MCP-1 to -4 was donor dependent and was affected by the autocrine inhibitory effects of IL-10. In contrast, C5a profoundly suppressed IL-12 production in an IL-10-independent fashion. Neither TGF-β1 nor PGE2 was important for the suppression of IL-12 by any of the chemoattractants tested. The accumulation of mRNA for both IL-12 p35 and p40 genes was inhibited by chemokine pretreatment. Interestingly, MCP-1 to -4 and C5a did not suppress IL-12 production by monocyte-derived dendritic cells (DC) stimulated with CD40 ligand and IFN-γ or by SAC and IFN-γ, suggesting that these factors may act at the site of inflammation to suppress IL-12 and IFN-γ production rather than in the lymph node to affect T cell priming. Despite the inability of C5a to inhibit IL-12 production by DCs, the receptor for C5a (CD88) was expressed by these cells, and recombinant C5a induced a Ca2+ flux. Taken together, these results define a range of chemoattractant molecules with the ability to suppress IL-12 production by human monocytes and have broad implications for the regulation of immune responses in vivo.

Recurrence of Membranoproliferative Glomerulonephritis Type II in Renal Allografts: The North American Pediatric Renal Transplant Cooperative Study Experience

Membranoproliferative glomerulonephritis type II (MPGN II) is an uncommon form of complement-dependent acquired renal disease. Although it has been recognized since the 1970s that MPGN II recurs almost universally in renal transplants, data regarding the long-term consequences of disease recurrence are limited. Therefore, a retrospective comparative analysis of 75 patients with MPGN II contained in the North American Pediatric Renal Transplant Cooperative Study transplantation database was performed. Five-year graft survival for patients with MPGN II was significantly worse (50.0 +/- 7.5%) compared with the database as a whole (74.3 +/- 0.6%; P < 0.001). Living related donor organs had a significantly better 5-yr survival (65.9 +/- 10.7%) compared with cadaveric donor organs (34.1 +/- 9.8%; P = 0.004). The primary cause of graft failure in 11 (14.7%) patients was recurrent disease. Supplemental surveys were obtained on 29 (38%) of 75 patients. Analysis of these data indicated that recurrent disease occurred in 12 (67%) of the 18 patients with posttransplantation biopsies. Although there was no correlation between pretransplantation presentation, pre- or posttransplantation C3 levels, and either disease recurrence or graft failure, there was a strong association between heavy proteinuria and disease recurrence. The presence of glomerular crescents in allograft biopsies had a significant negative correlation with graft survival. At last follow-up, patients with recurrent disease had significantly higher serum creatinine and qualitatively more proteinuria than patients without biopsy-proven disease. These data indicate that recurrent MPGN II has a significant negative impact on renal allograft function and survival.

Regulation of interleukin-12 production byG-protein-coupled receptors

G-protein-coupled receptors have long been known to play a critical role in the recruitment and migration of leukocytes to areas of inflammation. This review will focus, however, on emerging data that G-protein-coupled receptors can modulate cytokine production by antigen-presenting cells including interleukin-12 and tumor necrosis factor-alpha and may therefore play a significant role in the regulation of innate and acquired immunity.

C5a Receptor Deficiency Attenuates T Cell Function and Renal Disease in MRLlpr Mice

The development and progression of systemic lupus erythematosus (SLE) is strongly associated with complement activation and deposition. To characterize the role of C5a and its receptor (C5aR) in SLE, C5aR-deficient mice were backcrossed nine generations onto the lupus-like MRL(lpr) genetic background. Evidence is presented that C5aR modulates both renal injury and T cell responses in MRL(lpr) mouse. C5aR-deficient MRL(lpr) mice had prolonged viability, with a mean survival time of 33.0 wk compared with 22.6 wk in control mice. Renal injury was also attenuated in the C5aR-/- MRL(lpr) mice. At 20 wk of age C5aR-/- MRL(lpr) mice had a complete absence of glomerular crescents and marked reductions in glomerular hypercellularity. There was no difference in the degree of glomerular C3 deposition; however, IgG deposits were reduced in the C5aR-/- MRL(lpr) mice. The reduction in glomerular injury was also associated with a four-fold decrease in renal CD4+ T cell infiltrates. Whereas there were modest differences in total IgG anti-dsDNA antibody titers, C5aR-deficient mice had 3.5-fold higher levels of IgG1 and 15-fold lower levels of IgG2a anti-dsDNA antibody titers compared to controls. The differences in anti-dsDNA IgG subclasses were associated with reduced CD4+ Th-1 responses in the C5aR-/- MRL(lpr) mice, including diminished production of IL-12p70, IFN-gamma, and increased expression of the Th-2 transcription factor GATA-3. These findings indicate that the C5aR plays a major role in modulating complement-dependent renal injury and T helper cell Th-1 responses in the MRL(lpr) mouse.

The C5a receptor is expressed by human renal proximal tubular epithelial cells.

The C5a receptor is expressed by a variety of cell types. These studies demonstrate by immunohistochemistry that the receptor is present on the surface of proximal and distal tubular epithelial cells from normal kidney. In addition, the receptor was detected on transitional epithelial cells of the ureter and bladder. Primary proximal tubular cultures and a proximal tubular cell line both also expressed the C5a receptor, as demonstrated by immunofluorescence and by FACS analysis. The presence of mRNA encoding the receptor was confirmed by reverse transcriptase‐polymerase chain reaction analysis. As opposed to its effect on glomerular mesangial cells, the receptor did not mediate a proliferative response by the proximal tubular cells. C5a also did not enhance the synthesis/secretion of transforming growth factor‐beta 1, monocyte chemoattractant protein‐1, platelet‐derived growth factor‐AB or tumour necrosis factor‐alpha by cultured proximal tubular cells. Therefore, although the C5a receptor clearly is expressed by proximal tubular cells, clarification of its functional relevance on this cell type awaits further studies.

Renal Expression of the C3a Receptor and Functional Responses of Primary Human Proximal Tubular Epithelial Cells

Although complement activation and deposition have been associated with a variety of glomerulopathies, the pathogenic mechanisms by which complement directly mediates renal injury remain to be fully elucidated. Renal parenchymal tissues express a limited repertoire of receptors that directly bind activated complement proteins. We report the renal expression of the receptor for the C3 cleavage product C3a, a member of the anaphylatoxin family. C3aR is highly expressed in normal human and murine kidney, as demonstrated by immunohistochemistry and in situ hybridization. Its distribution is limited to epithelial cells only, as glomerular endothelial and mesangial cells showed no evidence of C3aR expression. The C3aR is also expressed by primary renal proximal tubular epithelial cells in vitro as demonstrated by FACS, Western blot, and RT-PCR. In vitro C3aR is functional in terms of its capacity to bind 125I-labeled C3a and generate inositol triphosphate. Finally, using microarray analysis, four novel genes were identified and confirmed as transcriptionally regulated by C3aR activation in proximal tubular cells. These studies define a new pathway by which complement activation may directly modulate the renal response to immunologic injury.

Cholera toxin inhibits IL-12 production and CD8α+ dendritic cell differentiation by cAMP-mediated inhibition of IRF8 function

Prior studies have demonstrated that cholera toxin (CT) and other cAMP-inducing factors inhibit interleukin (IL)-12 production from monocytes and dendritic cells (DCs). We show that CT inhibits Th1 responses in vivo in mice infected with Toxoplasma gondii. This correlated with low serum IL-12 levels and a selective reduction in the numbers of CD8α+ conventional DCs (cDCs) in lymphoid organs. CT inhibited the function of interferon (IFN) regulatory factor (IRF) 8, a transcription factor known to positively regulate IL-12p35 and p40 gene expression, and the differentiation of CD8α+ and plasmacytoid DCs (pDCs). Fluorescence recovery after photobleaching analysis showed that exposure to CT, forskolin, or dibutyryl (db) cAMP blocked LPS and IFN-γ–induced IRF8 binding to chromatin. Moreover, CT and dbcAMP inhibited the binding of IRF8 to the IFN-stimulated response element (ISRE)–like element in the mouse IL-12p40 promoter, likely by blocking the formation of ISRE-binding IRF1–IRF8 heterocomplexes. Furthermore, CT inhibited the differentiation of pDCs from fms-like tyrosine kinase 3 ligand–treated bone marrow cells in vitro. Therefore, because IRF8 is essential for IL-12 production and the differentiation of CD8α+ cDCs and pDCs, these data suggest that CT and other Gs-protein agonists can affect IL-12 production and DC differentiation via a common mechanism involving IRF8.

Increased survival and reduced renal injury in MRL/lpr mice treated with a novel sphingosine-1-phosphate receptor agonist

Agonists of the type 1 sphingosine-1-phosphate (S1P) receptor inhibit lymphocyte migration, causing their sequestration in lymphoid tissue. The S1P agonist FTY720 prolongs the survival of organ allografts and blocks T-cell mediated autoimmune diseases in experimental models; however, it is a non-selective agonist of four of the five S1P receptors. In this study female MRL/lpr mice, which develop an aggressive form of spontaneous autoimmune kidney disease, were treated with a more selective agonist of the type 1 receptor (KRP-203) or vehicle at 12 or 16 weeks of age. Eighty percent of the mice treated at 12 weeks, before the onset of visible disease, survived to the 24 weeks end point with decreased tubulointerstitial disease and significantly fewer infiltrating CD4(+) and CD8(+) T-cells. Only half of the control vehicle-treated mice survived. All of the mice treated at 16 weeks survived with reduced proteinuria. Mice in both groups had significant reductions in circulating lymphocytes. Mice receiving KRP-203 for 8-12 weeks had significant reductions in T-cells and consequently less adenopathy. Ex vivo treatment of lymphocytes from MRL/lpr mice with KRP-203 enhanced their apoptosis. Our study indicates that KRP-203 attenuates kidney injury in MRL/lpr mice, in part, by reducing T-cell infiltrates.

Consensus Expert Recommendations for the Diagnosis and Management of Autosomal Recessive Polycystic Kidney Disease: Report of an International Conference

Autosomal-recessive polycystic kidney disease (ARPKD; MIM 263200) is a severe, typically early-onset form of cystic disease that primarily involves the kidneys and biliary tract. Phenotypic expression and age at presentation can be quite variable. 1 The incidence of ARPKD is 1 in 20000livebirths, 2 anditspleotropicmanifestationsarepotentially life-threatening. Optimal care requires proper surveillance to limit morbidity and mortality, knowledgeable approaches to diagnosis and treatment, and informed strategies to optimize quality of life. Clinical management therefore isideallydirected by multidisciplinary care teams consisting of perinatologists, neonatologists, nephrologists, hepatologists, geneticists, and behavioral specialists to coordinate patient care from the perinatal period to adulthood. In May 2013, an international team of 25 multidisciplinary specialists from the United States, Canada, Germany, and the United Kingdom convened in Washington, DC, to review the literature published from 1990 to 2013 and to develop recommendations for diagnosis, surveillance, and clinical management. Identification of the gene PKHD1, and the significant advances in perinatal care, imaging, medical management, and behavioral therapies during the past decade provide the foundational elements to define diagnostic criteria and establish clinical management guidelines as the first steps towards standardizing the clinical care for patients with ARPKD. The key issues discussed included recommendations regarding perinatal interventions, diagnostic criteria, genetic testing, management of renal and biliary-associated morbidities, and behavioral assessment. The meeting was funded by the National Institutes of Health and an educational grant from the Polycystic Kidney Disease Foundation. Here we summarize the discussions and provide an updated set of diagnostic, surveillance, and management recommendations for optimizing the pediatric care of patients with ARPKD. Specialist care of ARPKD-related complications, including dialysis, transplantation, and management of severe portal hypertension (HTN), will be addressed in a subsequent report. Given the paucity of information regarding targeted therapies in ARPKD, this topic was not addressed in this conference.