Fig. 1

Serum levels of IgG recognizing MDA protein modifications directly correlate with more active SLE in independent cohorts. Serum immunoglobulin G (IgG) levels to malondialdehyde (MDA) protein modification were previously measured by ELISA in 125 healthy blood donors and compared to 120 SLE patients from the John Hopkins cohort [12] and 105 SLE patients from the New York University (NYU) Medical Center cohort [7], here combined and denoted as the US cohort (n = 225). In the current study, IgG anti-MDA levels were similarly quantified for 397 SLE patients from the Swedish Karolinska cohort. As a comparison, IgG to another oxidation-associated antigen, phosphorylcholine (PC), was determined in parallel. a IgG anti-PC and b IgG anti-MDA levels in the US cohort are compared to healthy blood donors. c IgG anti-MDA in the US cohort correlates with SLE disease activity by SELENA Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). d IgG anti-PC and e IgG anti-MDA in 287 SLE patients from the Karolinska cohort compared to sex- and age-matched population controls. f IgG anti-MDA serum levels in the Karolinska SLE cohort correlate with SLE disease activity by SLEDAI-2K. g Levels of IgG anti-PC,  h IgG anti-MDA, and i total IgG in 397 SLE patients in the Swedish KI cohort were also compared to the subset of 177 population controls without any chronic diseases, here termed healthy population (pop.) controls, based on medical examination, prescription medications, and self-reported conditions. j Meta-analysis of the combined data from the US SLE cohort and the Swedish Karolinska SLE cohort shows a significant association of elevated IgG anti-MDA levels with high disease activity (SLEDAI ≥ 6). Cutoff for high IgG anti-MDA was based on the 75th percentile of the corresponding control cohorts (10.5 NYU-RU/ml for the US cohort or 42 KI-RU/ml for the Karolinska cohort). P values are presented from Mann-Whitney analysis (comparing antibody levels in groups), Spearman correlation (correlations of antibody levels with SLEDAI), and the Mantel-Haenszel (M-H) method with fixed effects (meta-analysis). Note that although the assays were similar between the two SLE cohorts, they are not identical and use different relative units, denoted NYU-RU and KI-RU. CI confidence interval, NS not significant, RU relative units