Background and objectives There have been only several studies on the correlation between glomerular exostosin expression and membranous lupus nephritis. In this study, we validate the previous findings in Chinese patients with class V lupus nephritis.
Design, setting, participants, and measurements 165 class V cases and varying numbers of control cases were included. Exostosin1/exostosin2 staining was performed by immunohistochemistry and the staining intensity was quantified using an imaging analysis system. Between-group comparisons were tested for statistical significance using Pearson's chi-square test, Fisher's exact test, unpaired t-test, Mann-Whitney U test, or one-way ANOVA.
Results 46% of class V, 9% of class V+III/IV, and none of the other classes of lupus nephritis were exostosin positive. Only 3 cases were exostosin-positive among the 61 cases with other secondary membranous nephropathy. Exostosin-positive rate in cases with nephrotic syndrome was significantly higher than that without nephrotic syndrome(P<0.001) and the exostosin staining intensities of the exostosin- positive class V patients were positively correlated with proteinuria (r=0.53 P<0.001). Compared with the exostosin-negative cases, the exostosin-positive ones had higher proteinuria levels [3.9(IQR, 2.0-6.3)g/day vs 2.3 (IQR, 1.0-3.6)g/day] (P<0.001), lower scores of activity index [1(IQR, 1-2) vs 2 (IQR, 1-3)] (p=0.001), chronicity index [1(IQR, 0-2) vs 2(IQR, 1-2)] (P=0.02) and tubular atrophy score[0 (IQR, 0-1) vs 1 (IQR, 0-1)](P=0.008), a higher proportion of extensive subepithelial deposition [62% vs 27%](P<0.001), a similar treatment response and comparable time to kidney endpoint. Among the 47 class V cases who underwent repeat biopsy because of relapse or unresponsiveness to treatment, 97% of the exostosin-negative cases remained negative, while 44% of the exostosin-positive cases were still positive. The rate of histological transition in the exostosin-negative class V cases was significantly higher than that in the exostosin-positive class V cases (59% vs 22%, P=0.03).
Conclusions exostosin positivity occured frequently in patients with class V lupus nephritis, and the exostosin-positive cases have more severe proteinuria and a lower rate of histologic transition than the exostosin-negative patients.