#1257 Complement system is overactivated in patients with IgA nephropathy after COVID-19
Authors: Guo Weiyi , Wang Guoqin , Kong Lingqiang , Sun Lijun , Xu Xiaoyi , Cheng Wenrong , Dong Hongrui , Cheng Hong 
Published: May 2024

Abstract

Background and Aims
Since the coronavirus disease of 2019 (COVID-19) pandemic swept across the world, the flare of immune-mediated disease following SARS-CoV-2 infection has emerged rapidly. IgA nephropathy (IgAN), which has been confirmed as a complement mediated autoimmune disease, is also one of the common glomerulonephritis associated with COVID-19. Here, we aim to investigate the clinical and immunological characteristics of patients with IgAN after COVID-19.

Method
From December 2022 to April 2023, 33 patients with renal biopsy-proven IgAN (Group CoV) at Beijing Anzhen hospital who had experienced COVID-19 before renal biopsy were enrolled. Meanwhile, 44 patients with IgAN (Group non-CoV) diagnosed from December 2018 to April 2019 (the same period in the previous year, with no COVID-19) were enrolled as control. Plasma FHR-5, MBL, C5a, soluble C5b-9, serum Gd-IgA1 and IgA immune complex were detected by enzyme-linked immunosorbent assay. Glomerular staining for FHR-5, C3c, MAC and Gd-IgA1 were detected by immunofluorescence. SARS-CoV-2 nucleocapsid was detected by immunohistochemistry. Clinicopathological and immunological features between the two groups were analyzed.

Results
The median time between onset of COVID-19 symptoms and the time of renal biopsy was 12 (6, 18) weeks, ranging from 1 to 26 weeks. SARS-CoV-2 nucleocapsid antigen expression in the renal tubular epithelial cells were observed in 11/33 (33.3%) patients. Compared with Group non-CoV, the level of eGFR was significantly lower in Group CoV[67.30 (52.94, 96.43) ml/min per 1.73 m2 vs. 101.04 (74.35, 120.98) ml/min per 1.73 m2, p = 0.010]. Histologically, compared with Group non-CoV, Group CoV presented with more percentages of segmental glomerulosclerosis/adhesion (p = 0.003) and less percentages of mesangial hypercellularity (p = 0.017). The level of plasma level of C5a [16.45 (10.48, 22.07) ng/ml vs. 3.68 (2.70, 4.47) ng/ml], soluble C5b-9 [614.43 (481.66, 770.02) ng/ml vs. 358.08 (304.83, 471.77) ng/ml], FHR5 [4.01 (3.51, 4.48) ug/ml vs. 2.73 (2.25, 3.21) ug/ml]were all significantly higher in Group CoV compared with Group non-CoV, respectively (p &lt; 0.001). Although the plasma level of MBL showed no difference in Group CoV and Group non-CoV, the proportion of high levels of MBL in Group CoV was higher than in Group non-CoV (p = 0.025). Compared with Group non-CoV, the intensity of glomerular MAC deposition was much stronger in Group CoV. There were no significant differences in serum levels of IgA, Gd-IgA1, IgA immune complex between two Groups. However, a greater intensity of Gd-IgA1 deposition in glomerular mesangial and capillary areas has been exhibited in Group CoV than those in Group non-CoV (p = 0.005).

Conclusion
For IgAN after COVID-19, mucosal immune responses to SARS-CoV-2 infection may result in the overactivation of systemic and renal local complement system, which is the first hit, and increased glomerular deposition of Gd-IgA1 is the second hit. We think that these two hits may lead to renal dysfunction and promote renal progression in IgAN patients. It is crucial to emphasize the necessity for long term follow-up in these patients of IgAN after COVID-19. Additionally, we propose that inhibitors targeting the mediators of complement activation might be a promising therapy for these IgAN patients after SARS-CoV-2 infection.