#3053 CORRELATION OF SYSTEMIC AND IN SITU BIOMARKERS OF COMPLEMENT ACTIVATION WITH HISTOPATHOLOGICAL FEATURES AND PROGNOSIS IN C3 GLOMERULOPATHY
Authors: Meuleman Marie-Sophie , Petitprez Florent , Duval Anna , Bacchi Veronique Fremeaux , Van Huyen Jean-Paul Duong , Chauvet Sophie 
Published: June 2023

Abstract

Background and Aims
C3 glomerulopathy is a rare complement mediated disease, resulting from complement alternative pathway (AP) activation. In addition to AP activation, there are emerging evidence for terminal pathway (TP) implication in kidney damage. A C3G histopathologic index has recently been proposed to evaluate both activity and chronicity parameters. Only a chronicity index &gt; 4 has been independently validated as prognosis factor for end stage kidney disease. We aimed to determine the impact of local activation of the TP on disease phenotype.

Method
C3G histopathological index grading were evaluated via central review of 53 kidney biopsies from 43 patients carrying C3G. C5b-9 staining was performed on 53 FFPE kidney sections and quantified (scoring from grade 0 to 3 for C5b-9 deposits in glomeruli and from 0 to 2 in the tubulointerstitial compartment). Clinical data, C3 and sC5b-9 levels at the time of KB were retrospectively collected.

Results
KB were performed at diagnosis for n = 31. In 22 cases, KB was performed during follow up, under specific treatment (n = 10), without treatment (n = 7), or at disease relapse (n = 5). Twenty-five (47%) were children. Median[Q1-Q3] C3 level at KB was 623 mg/l [236-931]mg/l. Median[Q1-Q3] sC5b-9 level at KB, available in 16, was 374 ng/ml [203-1295]. Median [Q1-Q3] activity and chronicity index were respectively 9[6-12] and 1[0-6]. We confirmed the prognostic impact of chronicity index (p = 0.03) (Figure 1A) without impact of the activity index. Glomerular C5b-9 staining was positive in 47/53 (87%) (grade 1: n = 16 (30%); 2: n = 17 (32%); 3: n = 14 (26%)) and n = 40 (75%) had interstitial C5b-9 staining (grade 1: n = 28 (53%); 2: n = 12 (23%)). Soluble C5b-9 measurement correlated with intensity of C5b-9 glomerular deposit (coef corr = 0.69). As compared to patients with normal C3 level, patients with AP activation had higher proteinuria but kidney function at KB was similar. We found distinct histological features according to C3 plasmatic level (Table 1): patients with low C3 level had higher histological activity index (p = 0.03) and higher glomerular and tubulointerstitial C5b-9 staining (p = 0.001 and p = 0.002 respectively). C5b-9 glomeruli staining allows the identification of 3 groups of KB (1: no or low, 2: medium and 3: high C5b-9 staining) with distinct histological and clinical features. Activity index were higher in groups 2 & 3 (p = 0.05) and chronicity index in groups 1 & 3 (p = 0.003) (Table 2). Renal prognosis was poorer in patients with higher glomerular C5b-9 deposits (Figure 1B). Patients with chronicity index &gt;4 and high C5b-9 staining had the poorest renal survival (Figure 1C).

Conclusion
Our results suggest that TP activation in glomeruli may have an impact on histological features, contributing therefore to renal prognosis. Deeper exploration of correlation between systemic and in situ complement activation and histological features could allow to better identify patients with worst prognosis or who could benefit from emerging complement inhibition therapeutics.