The Effect of BAFF Inhibition on Autoreactive B-Cell Selection in Murine Systemic Lupus Erythematosus

Alexis Boneparth, Megan Woods, Weiqing Huang, Meredith Akerman, Martin Lesser, Anne Davidson

The goal of this study was to determine how BAFF availability influences selection of the autoreactive B cell repertoire in NZB/W and NZW/BXSB lupus prone mice bearing the site-directed heavy chain transgene 3H9 that encodes for anti-dsDNA and anti-CL autoantibodies. We used a bone marrow chimera system in which autoreactive 3H9 transgenic B cells were allowed to mature in competition with wild type cells and could be identified by GFP fluorescence. The light chain repertoire associated with the 3H9 heavy chain in naïve and antigen-activated B cell subsets was assessed using single cell PCR. We found that deletion of autoreactive transgenic B cells occurred in the bone marrow of both strains regardless of BAFF availability and there were only modest and physiologically non-relevant effects on the naïve B cell repertoire. BAFF inhibition had different effects on selection of the germinal center repertoire in the two strains. In the NZW/BXSB strain, BAFF inhibition phenocopied the loss of one TLR7 allele in that it influenced the selection of 3H9 encoded autoreactive B cells in the germinal center but did not prevent somatic mutation. In the NZB/W strain BAFF inhibition did not alter the selection of 3H9 encoded B cells in the germinal center but it influenced selection of a subset of germinal center cells into the plasma cell compartment. Our data underscore the complexity of regulation of the autoreactive B cell repertoire by BAFF and may help to explain the heterogeneity of responses observed after BAFF inhibition in humans.