α-2,6-sialic acid/IgG anti-dsDNA ratios correlate with human lupus disease activity and possible mechanisms: A pilot study

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Objective To study the association of α2,6-sialic acid (SIA) content in serum IgG anti-dsDNA with human systemic lupus erythematosus disease activity index (SLEDAI) and the effect of sialylated and desialylated (deSIA) IgG anti-dsDNA on lupus B cells. Methods Blood from lupus patients was collected to determine the ratio of SIA in isolated IgG anti-dsDNA over serum IgG anti-dsDNA (SIA/IgG anti-dsDNA) ratios, which were plotted against SLEDAI using a receiver-operating-characteristics curve. Lupus B cells were cultured in vitro with chimeric sialylated IgG anti-dsDNA and its deSIA form. Culture supernatants were assayed for anti-inflammatory IL-10 and SIA/IgG anti-dsDNA ratios, which were compared among different pre-treatment groups using t-tests. Results The area-under-the-curve (AUC) for anti-dsDNA levels against SLEDAI was 0.791 positively (95% confidence interval [C.I.]: 0.699–0.884) and SIA/IgG anti-dsDNA ratios against SLEDAI yielded an AUC of 0.705 inversely (95% C.I: 0.601–0.809): not significantly different. SIA/IgG anti-dsDNA ratios discriminated significantly between patients without and patients with proteinuria ( p = .046). SIA/IgG anti-dsDNA ratios correlated significantly and positively with serum C3c and C4 levels. Pre-treatment with IgG anti-dsDNA and its immune complexes (dsDNA/IgG anti-dsDNA IC) induced higher IL-10 from lupus B cells than medium pre-treatment (most p < .01 from day 2 to day 5 culture). DeSIA IgG anti-dsDNA IC induced lower IL-10 ( p < .05) and lower SIA/IgG anti-dsDNA ratios ( p < .001) from lupus B cells than medium and dsDNA pre-treatment. Conclusion α2,6-SIA/IgG anti-dsDNA ratios inversely forecasted SLEDAI scores. Possible mechanisms may be due to the different effects of sialylated and deSIA IgG anti-dsDNA on lupus B cells in terms of IL-10 secretion and SIA/IgG anti-dsDNA ratios.