Background Incomplete systemic lupus erythematosus (iSLE) patients display symptoms typical for SLE but have insufficient criteria to fulfil the diagnosis. Biomarkers are needed to identify iSLE patients that will progress to SLE. Interferon (IFN) type I activation, B-cell activating factor (BAFF) and B-cell subset distortions play an important role in the pathogenesis of SLE. The aim of this cross-sectional study was to investigate whether B-cell subsets are altered in iSLE patients, and whether these alterations correlate with IFN scores and BAFF levels.

Methods iSLE patients (n =34), SLE patients (n =41) with quiescent disease (SLEDAI ≤ 4) and healthy controls (HCs; n =22) were included. Proportions of B-cell subsets were measured with flow cytometry, IFN scores with RT-PCR and BAFF levels with ELISA.

Results Proportions of age-associated B-cells were elevated in iSLE patients compared to HCs and correlated with IgG levels. In iSLE patients, IFN scores and BAFF levels were significantly increased compared to HCs. Also, IFN scores correlated with proportions of switched memory B-cells, plasma cells, IgG levels and correlated negatively with complement levels in iSLE patients.

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Abstract P100 Figure 1

Proportions of B-cells subsets, and levels of B-cells activating factor (BAFF) in HCs, isLE patients and SLE patients. Median and interquartile range are depicted for every group. Switched memory B-cells were elevated in SLE patients compared to healthy controls. Age-associated B-cells were elevated in iSLE and SLE patients compared to HCs. The dotted line in the left lower image represents the median IFN score of the iSLE group. The dotted line in the right lower image represents +2SD above the mean of the HC group, which was used as cut-off for BAFF positivity. *p< .05, **p< .01. HC = healthy controls, iSLE = incomplete SLE, ABC = age-associated B-cell, IFN = Interferon, BAFF = B-cell activating factor

Conclusions In this cross-sectional study, distortions in B-cell subsets were observed in iSLE patients and were correlated with IFN scores and IgG levels. Since these factors play an important role in the pathogenesis of SLE, iSLE patients with these distortions, high IFN scores, and high levels of IgG and BAFF may be at risk for progression to SLE.

Acknowledgement This study was funded by ReumaNederland