Background SLE is characterized by a loss of B cell tolerance resulting in expansion of autoreactive B cell and plasma cell populations. The key B cell cytokine BAFF/BLyS, and its concerted binding to BAFF-binding receptors (BBR: BAFF-R, TACI and BCMA) is crucial to B cell survival and maturation. High serum levels of BAFF have been reported in SLE and correlated with more active or resistent disease. Changes of expression of BBR, in particular BCMA have also been reported. BCDT is an effective therapy for many patients with SLE but the effect on BAFF/BBR immunoregulation, and the possible contribution to clinical response has not been explored.
Objectives To characterise expression of BBR in B cell subsets in patients with SLE in patients before and following BCDT, in relation to serum BAFF/BLyS levels.
Methods 21 Patients with SLE on conventional therapy and 12 post RTX were included with 9 age matched healthy controls. Phenotypic analyses of B-cell subsets and BAFF-R, TACI and BCMA expression on were performed using combinations of CD19, CD27, CD38 and IgD (% positive) on a FACS-Fortessa flow cytometer. FlowJo and Prism software were used to analse the data. BAFF/BlyS levels analysed using commercial ELISA from R and D systems. Analysis of significance was for non-parametric data using Mann Whitney U test.
Results Phenotype: Pretreatment, % B cells in phenotypically defined subsets in SLE patients showed a wide range of percentages compared with HC, contributing to the finding of relatively few significant differences between groups. Double negative B cells (IgD-CD27-) were expanded in SLE patients both before and after BCDT compared with HC (p<0.05).
BAFF-R: Expression of BAFF-R on the transitional/naïve subset (IgD+CD38++) was significantly lower both pre- and post-BCDT (p<0.05). BAFF-R expression on plasmablasts (IgD-CD38+++) was higher pre-BCDT compared to HC (p<0.05) but post-BCDT was not different from HC or pre-BCDT levels. There was a tendency for % BAFF-R+ve CD19 B cells to be inversely correlated with disease activity, which was less evident post-BCDT.
TACI: General profiles of %TACI positive cells in SLE B cell subsets showed a strong tendency to be higher than HC and for levels to have an inverse correlation with disease activity both pre- and post-BCDT.
BCMA and CD86: There was no clear disturbance in expression of BCMA and CD86 in SLE patients in our study in any particular subset, it also seems not be affected by BCDT.
Soluble BAFF: BAFF levels were significantly higher in SLE patients pre-BCDT vs HC (p<0.05) and rose higher after BCDT (p<0.01) vs HC. There was an inverse correlation between BAFF levels and BAFF-R (CD19) expression in patients pre-BCDT (R2=0.493, p<0.05) but not post-BCDT.
Conclusions The main finding was that pre-RTX, BAFF serum concentrations had a weak inverse correlation with % BAFF-R positive CD19+ cells and with disease activity especially on IgD+CD27-. BAFF levels after BCDT were not associated with disease activity or BAFF-R levels. Changes in TACI expression as well as BAFF-R may also contribute to high BAFF levels. However, low TACI expression but normal BAFF-R expression is associated with reduced TI-2 responses – but changes in BAFF-R (lower in active disease) may also be contributing to “fate” of B cell subsets towards plasma cell differentiation.
Disclosure of Interest G. Martin-Garcia: None Declared, E. Becerra: None Declared, M. Leandro: None Declared, I. Ortega: None Declared, D. Isenberg: None Declared, G. Cambridge Grant/Research support from: Supported by GSK, UK