Dissecting signaling parameters in autoreactive B cells

Abstract In systemic lupus erythematosus (SLE), IgG antibodies (Abs) directed against nuclear antigens (ANA) are pathogenic. Healthy individuals (HC) harbor a similar frequency of ANA+ mature B cells without producing pathogenic IgG Abs. Differences in behavior between ANA+/- B cells in SLE patients and HC have not been explored. The aim of this study was to measure the response to BCR activation in the ANA+/- B cell subpopulations in SLE patients and HC. B cells from 7 SLE patients and 5 HC were isolated and activated with F(ab)'2 fragments of anti-IgG Abs. Calcium flux was measured using indo-1 AM. The response was quantified by area under the curve (AUC), using the bound/unbound ratio of the marker for 5 minutes after activation. Values were compared using Wilcoxon rank sum test. In SLE patients, ANA+ IgG memory cells have a stronger calcium influx than ANA- (AUC for ANA + vs -: 89.46±18.51 vs 76.17±12.65; p=0.05). This difference is not present in HC (AUC for ANA + vs -: 88.02±16.51 vs 89.52±14.49; p=ns). In both HC and SLE patients, ANA+ naïve B cells are less responsive to BCR activation, suggesting anergy. IgM+ B cells overall, irrespective of ANA status, seem to be less responsive in patients with SLE. These results show that ANA+ IgG memory B cells are hyperreactive in SLE patients. The data also suggests a mechanism for the breach in tolerance that is observed in SLE. Further studies are warranted to explore the mechanism and effects on autoantibody generation in SLE.