| BackgroundPrimary Sjogren Syndrome (pSS) is a systemic autoimmune disease involving multiple organs, among which the renal involvement mainly manifests as interstitial nephritis and renal tubular acidosis. There is lack of data among literature on glomerulonephritis in pSS patients along with its clinicopathologic features. Mechanisms underlying renal damage in pSS remain to be elucidated but have been believed to involve local lymphocyte infiltration, T cell subset dysregulation and autoantibody formation. Recent studies revealed that ectopic germinal center (EGC) formation and epithelial cell-mediated antigen presentation might play a pivotal role in tissue inflammatory injury in pSS. Given that the costimulatory molecule B7-1 (CD80), classically expressed on professional antigen-presenting cells (APCs), is also upregulated on epithelial cells-including both the renal tubular epithelial cells and the podocytes-under pathogenic conditions, we hypothesize that B7-1 might link the tubular and glomerular damage in pSS. The phenomenon of tubular injury-mediated glomerular injury is featured in Heymann nephritis, an animal model of membranous nephropathy (MN), which is due to in situ deposition of autoantibodies against podocytes; although it is unclear how these autoantibodies are formed. Therefore, we retrospectively studied the clinicopathologic features of 42 pSS patients with MN (pSS-MN) from Peking Union Medical College Hospital. Their EGC formation, B7-1 expression and IL-17 pathway were also evaluated, aiming to explore the mechanisms underlying pSS-MN and the crosslink between tubular and glomerular injury.Purpose1. To analyze the clinical and pathological features and the prognosis of pSS-MN patients, and identify the factors correlated with its clinicopathologic parameters and prognosis.2. To evaluate lymphocyte infiltration and EGC formation in pSS-MN patients, and their association with the clinicopathologic parameters and prognosis.3. To study the expression of B7-1 and IL-17 pathway on renal pathology, and their possible correlation with clinicopathologic features and prognosis.MethodThe medical records and follow-up data of 42 patients with pSS-MN confirmed by renal biopsy in Peking Union Medical College Hospital from January 1993 to December 2014 were reviewed. The pSS activity was evaluated, and pathological features including glomerular sclerosis, tubular injury and interstitial fibrosis were evaluated semi-quantitatively. The lymphocyte infiltration grade and germinal center (GC) formation were evaluated by immunohistochemical (IHC) staining of CD21, a specific marker of follicular dendritic cells. T cell subsets were also explored along with their clinical implication in two patients using IHC or immunofluorescence of CD3 (T cell marker), Foxp3 (Treg marker) and IL-17A(Th17 marker). IHC staining of B7-1 and IL-17A in all available cases and IL-17RD in a subset of cases were performed to evaluate their expression on infiltration inflammatory cells, tubular epithelial cells and podocytes; their correlation with clinicopathologic parameters and prognosis were also studied. Continuous variables are displayed as mean ± standard deviation and compared using student’s t-test or Mann-Whitney test, one-way analysis of variance, Pearson or Spearman’s correlation coefficients. Categorical variables are expressed as percentage and compared with Fisher exact test and Spearman’s correlation coefficients. Kaplan-Meier analysis were also used. A P-value of <0.05 was considered significant. Statistical analysis was performed using the SPSS software (version 19.0 for Windows).Results1. Clinical and pathological features of pSS-MN patientsAmong 154 pSS patients with a renal biopsy,94 (61.0%) were diagnosed with glomerulonephritis, including 42 (44.6%) cases of MN. Clinically, the majority were female (76.2%), with an average age of 52.3±19.0 years. Half of the patients had onset of pSS prior to MN (50.0%), while 31.0% never had symptoms of pSS. At the time of renal biopsy, the patients presented with nephrotic syndrome (85.7%), microscopic hematuria (81.0%), proteinuria (4.6±3.1g/24h), hypoalbuminemia (26.5±7.3 g/L) with normal eGFR (92.8±26.3 ml/min). Hypergammaglobulinemia and hypocomplementemia were present in 26.8% and 20.0% patients respectively. Nine (21.4%) cases had concomitant Hashimoto thyroiditis, whose serum IgG level was significantly higher than that of the others (28.6±6.9 g/L vs.19.8±7.3 g/L, p<0.001). Of the 15 cases who had serum anti-PLA2R antibody tested,8 (53.3%) were positive and 7 (46.7%) were negative. Pathologically,18 (42.9%) cases had atypical MN, featured by mesangial electron-dense deposit or C1q staining. On immunofluorescent study, C3 was positive in 43.9% cases and C1q positive in 34.1%. IgG subtype staining showed positivity of IgG4 (95%), IgG1 (55%), IgG3 (50%) but not IgG2. On follow-up,97.6% of patients received immunosuppressive treatment, including full-dose corticosteroid (GCS) plus cyclophosphamide (54.8%) or other immunosuppressants (7.1%), half-dose GCS plus calcineurin inhibitors (19.0%), and full-dose GCS alone (14.3%). Twenty-five cases were followed-up more than 6 months, with an average of 39.0 ± 49.5 months and a median time of 24 months. Partial or complete remission of nephrotic syndrome was reached in 52% cases. Most (76.0%) patients had stable renal function; 16% had mild progression or fluctuation; only two patients had progression of CKD with persistent or recurrent proteinuria.2. Ectopic germinal center structures in pSS-MN patientsCD21 staining on 35 available biopsy samples revealed the presence of GC-like structures in 11 (31.4%) cases, and EGCs were notably abutting or surrounding the glomeruli in 7 cases. Grading of interstitial lymphocyte infiltration revealed the percentage of GO (absent), G1 (scattered), G2 (focal) and G3 (formation of GC-like structures) to be 5.7%,34.3%,28.6% and 31.4%, respectively, which was positively correlated with glomerulosclerosis index (p=0.007); and there was a trend toward higher eGFR in the severely infiltrating group (G2-G3,85.7±26.7 ml/min) than mildly infiltrating group (G0-G1,100.6±23.2 ml/min, p=0.068). T cell subset staining in 2 clinically distinct cases showed prominent difference in the composition of their GC-like structures.3. Evaluation of B7-1 and IL-17 pathway as potential mechanism in pSS-MN patientsThe B7-1 expression in pSS-MN patients was elevated compared with patients with minor glomerular lesion (GML) and mainly expressed in the interstitium and tubular epithelium and rarely in the glomeruli. B7-1 was not correlated with proteinuria or renal function at the time of biopsy, but was significantly higher in those with persistent or recurrent proteinuria vs. those with remission of proteinuria (p=0.044). IL-17 expression was also elevated in pSS-MN patients compared with GML patients, and its intensity was positively correlated with B7-1 expression (p=0.048). IL-17RD was widely expressed in both tubular epithelia and glomeruli.Conclusion1. MN is the most common type of glomerulonephritis among pSS patients; nearly half patients has atypical MN on pathology, and meanwhile nearly half patients has negative serum anti-PLA2R antibodies, but they are not significantly correlated.2. Interstitial lymphocyte infiltration varies in degree, with approximately one third forming EGCs, and correlates with glomerulosclerosis and renal function. Clinically distinct cases showed prominent difference in the composition of their EGCs.3. B7-1 expression in kidney is elevated in pSS-MN patients and may predict outcome of proteinuria. IL-17 expression is also elevated and is positively correlated with the expression of B7-1. IL-17 and IL-17RD might together contribute to local B7-1 expression and tubular-glomerular damage. |
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