Association of Autoantibody Concentrations and Trajectories With Lupus Nephritis Histologic Features and Treatment Response

Abstract

Objective: Autoantibodies are a hallmark of lupus nephritis (LN), but their association with LN classes and treatment response are not adequately known. In this study, we quantified circulating autoantibodies in the Accelerating Medicines Partnership LN longitudinal cohort to identify serological biomarkers of LN histologic classification and treatment response and how these biomarkers change over time based on treatment response.

Methods: Peripheral blood samples were collected from 279 patients with systemic lupus erythematosus undergoing diagnostic kidney biopsy based on proteinuria. Of these, 268 were diagnosed with LN. Thirteen autoantibody specificities were measured by bead-based assays (Bio-Rad Bioplex 2200) and anti-C1q by enzyme-linked immunosorbent assay at the time of biopsy (baseline) and at 3, 6, and 12 months after biopsy. Clinical response was determined at 12 months.

Results: Proliferative LN (International Society of Nephrology/Renal Pathology Society class III/IV±V, n = 160) was associated with higher concentrations of anti-C1q, anti-chromatin, anti-double-stranded DNA (dsDNA), and anti-ribosomal P autoantibodies compared to nonproliferative LN (classes I/II/V/VI, n = 108). Anti-C1q and-dsDNA were independently associated with proliferative LN. In proliferative LN, higher baseline anti-C1q levels predicted complete response (area under the curve [AUC] 0.72; P = 0.002) better than baseline proteinuria (AUC 0.59; P = 0.21). Furthermore, all autoantibody levels except for anti-La/SSB decreased over 12 months in patients with proliferative, but not membranous, LN with a complete response.

Conclusion: Baseline levels of anti-C1q and anti-dsDNA may serve as noninvasive biomarkers of proliferative LN, and anti-C1q may predict complete response at the time of kidney biopsy. In addition, tracking autoantibodies over time may provide further insights into treatment response and pathogenic mechanisms in patients with proliferative LN.

Figure 1.. Prevalence and heterogeneity of autoantibody expression in lupus nephritis (LN) patients.

(A) Overall prevalence (any positive titer) of autoantibodies at the time of kidney biopsy in SLE patients with (class I-VI; n=268) or without LN (non-LN; n=11). Statistical significance was determined using Fisher’s exact test. **p<0.01, ***p<0.001, ****p<0.0001. (B) Heatmap of baseline autoantibody concentrations in LN patients (n=268). Values were scaled using Min-Max normalization, and clustering was performed using Ward’s minimum variance method. RiboP, ribosomal P

Figure 2.. Concentrations of anti-C1q, -chromatin, -dsDNA, and –ribosomal P are associated with proliferative LN.

(A) Prevalence of baseline autoantibodies in mesangial (class I/II; n=24), pure proliferative (class III/IV; n=90), mixed proliferative (class III/IV+V; n=70), membranous (class V; n=72), and advanced sclerosis (class VI; n=25) LN patients. Statistical significance determined using Fisher’s exact test. (B-E) Baseline autoantibody concentrations that significantly differ between proliferative (prolif; class III/IV+/−V; n=160) and non-proliferative (non-prolif; class I/II/V/VI; n=108) LN. Dashed lines represent the assay maximum and positive cutoff. Statistical significance determined using the Kruskal-Wallis test with Dunn’s multiple comparisons. (F) Heatmap of Spearman’s rank correlation coefficients for autoantibody concentrations and NIH activity and chronicity indices and subindices. Clustering was performed using Ward’s minimum variance method. *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001. RiboP, ribosomal P.

Figure 3.. Diagnostic implications of baseline autoantibody concentrations for predicting proliferative lupus nephritis (LN).

(A) Volcano plot displaying the area under the curve (AUC) for the ability of baseline autoantibody concentrations or number of positive autoantibodies to predict proliferative LN. (B) Forest plot of associations between autoantibody concentrations and proliferative, membranous, and other LN classes (class I/II/VI; n=36). Undiluted concentrations were divided by the assay positivity cutoff. Dots represent the odds ratio per fold change over the positivity cutoff, and horizontal lines represent the 95% confidence interval. (C) Sensitivity, specificity, positive (PPV) and negative predictive values (NPV), and likelihood ratios (LR) of baseline autoantibody levels for predicting proliferative LN. Autoantibodies were classified as any (any positivity), mid/high (out of range pre-dilution), or high (out of range pre-dilution and positive post-dilution). (D) PPV of a combination of baseline anti-dsDNA and –C1q levels. Anti-dsDNA autoantibodies were classified as negative, low (within range pre-dilution), moderate (out of range pre-dilution and negative post-dilution), or high (out of range pre-dilution and positive post-dilution). Anti-C1q positivity was determined using the manufacturer’s instructions for both A and B. The baseline rate (prior probability) of proliferative lupus nephritis was 57% (160/279). RiboP, ribosomal P.

Figure 4.. Autoantibody baseline concentrations and trajectories associate with complete response in proliferative lupus nephritis (LN) patients.

Autoantibody concentrations were measured at the time of kidney biopsy (V0) and 3 (V1), 6 (V2), and 12 (V3) months post-kidney biopsy in patients with (A-D) proliferative or (E-H) membranous LN. Treatment response was determined at 12 months as complete (proliferative, n=21; membranous, n=5), partial (proliferative, n=17; membranous, n=9), or no response (proliferative, n=33; membranous, n=18). (A-H) Dashed lines represent the positive cutoff for each assay. Statistical significance was determined using a 2-way ANOVA with Tukey’s multiple comparisons. *p<0.05, **p<0.01 relative to non-responders. ^#p<0.05, ^##p<0.01 relative to partial responders. (I) Volcano plot displaying the area under the curve (AUC) for the performance of baseline autoantibody concentrations to predict complete treatment response in proliferative LN patients. The dashed line indicates the significance threshold. (J) ROC curves comparing the predictive performance of baseline anti-C1q, -SmRNP, and –dsDNA autoantibodies with baseline urine protein creatinine ratio (UPCR) levels in proliferative LN patients. (K) Forest plot of associations between autoantibody concentration Z-scores and complete response in proliferative LN patients. Dots represent the odds ratio, and horizontal lines represent the 95% confidence interval. RiboP, ribosomal P.