Purpose The relationship between B cells subsets distribution, clinical and laboratory parameters, therapeutic response and prognosis in lupus nephritis (LN) is still underestimated. The aim of our study is to investigate the value of B cells subsets as biomarkers in patients with active LN, in patients at the onset of renal manifestation or with renal flare, and finally in nephritic patients in relation to their clinical and laboratory characteristics at the baseline and during the course of the disease.

Methods 50 patients with active LN at disease onset or disease flare were enrolled and evaluated every tree months. Laboratory, immunological and disease activity data were collected at the baseline and at 6(T6), 12(T12), 24(T24), 36(T36) months and at the last follow-up(FU).Number of renal flares, time to renal remission and persistent proteinuria at the last FU were considered. B cell subsets were evaluated at baseline through cytofluorimetry and classified using C27/IgD classification. The characterisation of B cells subsets was realised in 50 LN patients and 37 healthy controls.

Results LN patients had a lower percentage of CD19 +cells than controls(9.2% vs 10.6%; p=0.01)as well as a lower percentage of memory unswitched cells CD27 +IgD+(10.7% vs 15.3%; p<0.001) while LN patients had an higher percentage of plasmablasts and double negative memory cells CD27-IgD-(respectively 5.9% vs 1%; p<0.001 and 10,9% vs 4,1%;p=001).

No significant differences regardless B cells subsets were found between early LN patients and long ones as well as between LN patients at the onset and LN patients during renal flare. We found a correlation between an higher disease activity (assessed with SLEDAI 2K) and lower percentage of memory B cells IgD-CD27+(p=0.02).Double negative B cells CD27-IgD- tended to be correlated with an higher disease activity. Of interest the correlation between persistent proteinuria detected during the follow-up and a lower percentage of plasmablasts at the baseline (p=0.015).

Conclusion The alteration of B cells subsets is an early event in LN without differences regardless the timing of renal involvement (nephritic onset or later LN development).The association between persistent proteinuria and a lower percentage of plasmablasts at the baseline could be a negative prognostic factor considering the correlation between persistent proteinuria and worse renal outcome.