Histologic and Clinical Factors Associated with Kidney Outcomes in IgA Vasculitis Nephritis

BACKGROUND

Nephritis is a common manifestation of IgA vasculitis and is morphologically indistinguishable from IgA nephropathy. While MEST-C scores are predictive of kidney outcomes in IgA nephropathy, their value in IgA vasculitis nephritis has not been investigated in large multiethnic cohorts.

METHODS

Biopsies from 262 children and 99 adults with IgA vasculitis nephritis ( N =361) from 23 centers in North America, Europe, and Asia were independently scored by three pathologists. MEST-C scores were assessed for correlation with eGFR/proteinuria at biopsy. Because most patients ( N =309, 86%) received immunosuppression, risk factors for outcomes were evaluated in this group using latent class mixed models to identify classes of eGFR trajectories over a median follow-up of 2.7 years (interquartile range, 1.2-5.1). Clinical and histologic parameters associated with each class were determined using logistic regression.

RESULTS

M, E, T, and C scores were correlated with either eGFR or proteinuria at biopsy. Two classes were identified by latent class mixed model, one with initial improvement in eGFR followed by a late decline (class 1, N =91) and another with stable eGFR (class 2, N =218). Class 1 was associated with a higher risk of an established kidney outcome (time to ≥30% decline in eGFR or kidney failure; hazard ratio, 5.84; 95% confidence interval, 2.37 to 14.4). Among MEST-C scores, only E1 was associated with class 1 by multivariable analysis. Other factors associated with class 1 were age 18 years and younger, male sex, lower eGFR at biopsy, and extrarenal noncutaneous disease. Fibrous crescents without active changes were associated with class 2.

CONCLUSIONS

Kidney outcome in patients with biopsied IgA vasculitis nephritis treated with immunosuppression was determined by clinical risk factors and endocapillary hypercellularity (E1) and fibrous crescents, which are features that are not part of the International Study of Diseases of Children classification.

CADHERIN-11 regulation of myeloid phagocytes and autoimmune inflammation in murine lupus

BACKGROUND AND OBJECTIVE

Understanding the regulation of efferocytosis by myeloid phagocytes is important in identifying novel targets in systemic lupus erythematosus (SLE). Cadherin-11 (CDH11), a cell adhesion molecule, is implicated in inflammatory arthritis and fibrosis and recently been shown to regulate macrophage phagocytosis. The extent and mechanism of this regulation is unknown. Our objective was to examine the extent to which CDH11 regulates myeloid phagocytes and contributes to autoimmunity and tissue inflammation.

METHODS

We analyzed efferocytosis in macrophages and dendritic cells (DCs) from WT and Cdh11-/- mice and investigated the mechanisms in vitro. We investigated the role of CDH11 in disease development in vivo using the pristane induced lupus model. To translate the clinical relevance of CDH11 in human disease, we measured serum CDH11 levels in two independent pediatric SLE (pSLE) cohorts and healthy controls.

RESULTS

Using bone marrow derived macrophages (BMDMs) and DCs (BMDCs), we found impaired efferocytosis in phagocytes from Cdh11-/- mice, mediated by downregulated efferocytosis receptor expression and RhoGTPase activation. Specifically, loss of CDH11 downregulated Mertk expression and Rac1 activation in BMDMs, and integrin αVβ3 expression and Cdc42 activation in BMDCs, highlighting distinct pathways. In vivo, Cdh11-/- mice displayed defective efferocytosis and increased accumulation of apoptotic debris in pristane-induced lupus. Further, Cdh11-/- mice had enhanced systemic inflammation and autoimmune inflammation with increased anti-dsDNA autoantibodies, splenomegaly, type I interferons, and inflammatory cytokines. Paradoxically, at the tissue level, Cdh11-/- mice were protected against glomerulonephritis, indicating a dual role in murine lupus. Finally, SLE patients had increased serum CDH11 compared to controls.

CONCLUSION

This study highlights a novel role of CDH11 in regulating myeloid cells and efferocytosis and its potential as a contributor to development in autoimmunity murine lupus. Despite the increase in autoimmunity, Cdh11-/- mice developed decreased tissue inflammation and damage.

SAT0234 SERUM AXL, FERRITIN, IGFBP4 AND STNFR2 AS BIOMARKERS OF PEDIATRIC SLE

Background:

Proteomic screening is an efficient approach for identifying protein biomarkers in various inflammatory diseases. Our preliminary proteomic analysis revealed elevated levels of serum Axl, Ferritin, IGFBP4 and sTNFR2 in adult patients with active lupus nephritis (LN) (1). However, the role of these serum biomarkers in pediatric systemic lupus erythematosus (SLE) patients has not been examined.

Objectives:

To evaluate the performance of 4 serum protein markers for detecting disease activity in pediatric patients with SLE.

Methods:

83 pediatric patients who fulfilled ≥4 ACR criteria for SLE and 25 healthy controls were recruited for serological testing of 4 protein markers identified by antibody-coated microarray screen, namely Axl, ferritin, IGFBP4 and sTNFR2. SLE disease activity was assessed using the SLEDAI-2k score, renal disease activity was assessed by the renal SLEDAI (range 0-16; 0= inactive LN, ≥ 8= active renal). 57 patients had clinically active SLE (SLEDAI score ≥ 4 or having a flare) (28 active renal and 29 active non-renal SLE patients). In active renal patients, concurrent renal biopsy was performed, unless contraindicated. The ISN/RPS criteria were used to assess the histopathologic features of LN. Those Patients were further subcategorized into 2 groups; active proliferative (ISN/RPS classes III/IV) and non-proliferative (classes I/II/V).

Results:

The serum concentrations of Axl and ferritin were significantly higher in patients with active SLE than inactive SLE (3765±235 vs. 2513±130 pg/ml,P= 0.001) and (111±26 vs. 18±4 ng/ml,P =0.0001) respectively. Serum Axl levels were significantly higher in active renal versus active non-renal SLE patients (3765±235.3 vs. 2825±200.7 pg/ml,P= 0.04). In the active renal patients with paired kidney tissue and blood samples, none of the biomarkers tested discriminated classes of LN, although serum Axl, ferritin and IGBPB4 levels were higher in the proliferative subgroup. The levels of Axl, ferritin and IGFBP4 correlated significantly with SLEDAI scores (Axl, r= 0.58,P<0.0001; ferritin, r= 0.53,P<0.0001; IGFBP4, r= 0.229,P= 0.03). However, only serum Axl levels correlated significantly with the renal SLEDAI (r= 0.46,P= 0.01). The levels of Axl, IFGBP4 and sTNFR2 correlated with decreased C3 levels (r= - 0.54,P<0.0001; r= - 0.29,P= 0.007; r= - 0.29,P= 0.007) respectively. Only serum Axl and ferritin correlated with urinary PCR (r= 0.42,P<0.0001; r= 0.22,P=0.04) respectively. These markers were more specific, but less sensitive, in detecting concurrent SLE activity than elevated anti-dsDNA or decreased C3. The specificity values of serum ferritin and IGFBP4 for concurrent active lupus nephritis were higher than anti-dsDNA or C3. Serum ferritin was the best predictor of global SLE activity (AUC 0.81,P<0.0001), followed by C3 (AUC 0.79,P<0.0001) then Axl (AUC 0.71,P= 0.002), while both Axl and C3 were the best predictors of lupus nephritis activity (AUC 0.72, both).

Conclusion:

In pediatric SLE patients, serum ferritin and Axl perform better than traditional yardsticks in identifying disease activity, either global or renal. The performance of these serum markers should be explored further in a longitudinal cohort of pediatric SLE patients.

References:

[1]Wu T, Ding H, Han J, et al. Antibody-Array-Based Proteomic Screening of Serum Markers in Systemic Lupus Erythematosus: A Discovery Study. J Proteome Res. 2016 Jul 1;15 (7): 2102-14.

Disclosure of Interests:

None declared

Renal cell carcinoma harboring somatic TSC2 mutations in a child with methylmalonic acidemia

Pediatric renal cell carcinoma (RCC) is a rare cancer that can be associated with inherited diseases including tuberous sclerosis complex (TSC) caused by germline mutations in TSC1 or TSC2. Somatic mutations in TSC1 and TSC2 have also been reported in adult RCC, which predict response to mTOR inhibitors. Here, we present the first case of RCC in a child with methylmalonic acidemia (MMA). Clinical whole exome sequencing of blood and tumor samples confirmed the diagnosis of MMA and revealed two somatic inactivating mutations in TSC2, suggesting the potential consideration of an mTOR inhibitor in the event of tumor recurrence.

Abstract 004: Aberrant CD4 + T Cell Function in Stroke-prone Hypertensive Rats Due to a Mutation in Stim1

The genetic mechanism of end organ injury in hypertension may involve gene variation in genes participating in inflammation and its regulation. We identified a novel truncating mutation in the hypertensive end organ injury-prone spontaneously hypertensive rat (SHR-A3/SHRSP) line affecting the C-terminus of STIM1, a protein involved in the store-operated Ca 2+ entry (SOCE) pathway. The genomes of injury-resistant SHR lines, including SHR-B2 used here, encode the ‘wild-type’ STIM1. SOCE is required by T cells to activate the transcription factor NFAT and regulate T cell proliferation and cytokine production. T cell receptor (TCR) stimulation depletes intracellular Ca 2+ stores, activates the ER Ca 2+ -sensor STIM1 and results in SOCE. We tested the effect of STIM1 mutation on lymphocyte SOCE and found it was dramatically reduced in SHR-A3, but not in SHR-B2 (maximal [Ca 2+ ] i : 150.5±34.9 vs 521.5±42.6 nM, p<0.0001). Flow cytometric analysis of circulating T cell subsets revealed comparable levels of CD4 + and CD8 + T cells in both lines, however circulating CD4 + CD25 + FoxP3 + T regs were reduced in SHR-A3 compared to SHR-B2 (4.34±0.59 vs 7.12±0.33%, p=0.01). TCR-induced lymphocyte proliferation was similar in both SHR-A3 and SHR-B2. T cell cytokine production in response to TCR stimulation was markedly impaired CD4 + T cells from SHR-A3 compared with SHR-B2 (IL-2: 168 ±83.4 vs 1385±377.0 pg/mL, p=0.01; IFNγ: 235±69.5 vs 2119±434.7 pg/mL, p=0.002). IL-2 and IFNγ production was completely inhibited by Pyr6, an inhibitor of Stim1-dependent SOCE. However, circulating levels of IL-2 and IFNγ were not different between the two lines. Based on our findings, we conclude that TCR-mediated effector signaling is impaired due to defective SOCE in SHR-A3 rats. Defects in SOCE in SHR-A3 attributable to STIM1 mutation alter T cell function, reduce T reg numbers and may disturb regulatory interactions between T cells and other immune cells involved in end organ injury.

Renal Mast Cell recruitment in MRL/lpr mice (173.28)

Mast cells (MC) are key effectors cells of the immune system. MC infiltration has been reported in a variety of renal diseases including lupus nephritis. Recently it has been argued that MCs are key contributors to a common pathway of progressive renal injury, however, the chemotaxic mechanism of renal MC recruitment are largely unknown. We observed a progressive age-depended MC infiltrate in kidneys of MRL/lpr mice. MRL/lpr bone marrow-derived MC (BMMC) had a high chemotatic capacity in response to MRL/lpr serum. In order to characterize the factors involved in MCs recruitment in MRL/lpr mice we performed expression array analysis in stimulated and un-stimulated MRL/lpr MCs. Serum stimulation increased BMMC expression of the integrin alpha E and chemokine receptors CCR5 and CXCR4. Kidney immunofluorescence staining confirmed these finding in situ. BMMC chemotaxis in vitro was enhanced in response to CCR5 ligands (MIP-1α and RANTES) and CXCR4 ligand (SDF-1) and was blocked by using a non-peptide chemokine receptor antagonist TAK-779. In vivo, TAK-779 significantly blocked the accumulation of renal MC in MRL/lpr mice. Our study indicate that the chemokine receptors CCR5 and CXCR4 and the integrin alpha E are important mediators of renal MC recruitment.

Endothelial Cells Bind Immune Complexes in the Kidney (172.39)

Inflammatory kidney diseases often involve the deposition of antibodies (Ab) or antibody-antigen immune complexes (IC). The glomerulus is a highly evolved vascular system which filters blood to produce urine. Ab-mediated glomerular injury can lead to bleeding into the urine, protein wasting, hypertension, decreased urine output, edema, and kidney failure. However, the mechanisms by which IC deposit and the means by which they are cleared remain unclear. In order to model endothelium-Ab interactions, kidney endothelial cells (KEnCs) were isolated from C57BL/6 mice and cultured in vitro. Immuno-phenotyping was performed to assess expression of CD31, VEGF receptors, von Willebrand factor (vWF), and alpha smooth muscle actin. CD31+ vWF+ VEGF-R2+ KEnCs displayed a phenotype in culture similar to other microvascular cells. Monomeric and heat aggregated Ig (HA-IgG) and peroxidase-antiperoxidase IC (PAP-IC) were used for binding and stimulation assays. Effects of stimulation of KEnCs were identified using PCR arrays and multiplex cytokine analysis. KEnCs stained brightly with HA-IgG and PAP-IC, but only dimly with monomeric IgG. KEnCs responded to IC with robust chemokine and cytokine responses in a dose dependent manner. Competitive binding studies mapped the interaction to the Fc-portion of IgG, but suggest that the KEnCs bind independently of classical Fc-receptors. Results support an important role for KEnCs in the pathogenesis of IC kidney diseases.