Search

The peripheral B cell prosurvival cytokine BAFF/B lymphocyte stimulator (BLyS) has been proposed to participate in the regulation of immunological tolerance. Selective elimination or reconstitution of B cells expressing transgene-encoded, autoreactive BCRs upon systemic BLyS depletion or supplementation, respectively, was observed in two separate studies. Such findings led to a model positing a higher dependency of autoreactive B cells on BLyS. We tested this model by exploiting two targeted IgH transgenic mice (H chain knock-in [HKI]) that produce large numbers of follicular (FO) B cells that are either weakly or strongly autoreactive with nuclear autoantigens. Even though HKI B cells do not exhibit classical features of anergy, we found that mature, naive, autoreactive HKI B cells are outcompeted for representation in the periphery by a polyclonal B cell population. However, this is not due to a higher dependency of HKI B cells on BLyS for survival. Additionally, excess BLyS does not rescue HKI B cells from selective elimination. These findings suggest that some autoreactive FO B cells can fully develop while in competition with non-autoreactive cells for BLyS, but remain at a competitive disadvantage for other trophic factors that regulate peripheral stability. As such, our data indicate the existence of peripheral tolerance mechanisms that regulate the frequency of autoreactive FO B cells independent of the BLyS pathway.

B lymphocytes are required for the pathogenesis of autoimmune diabetes in NOD mice. Previous studies established that a lymphopenic transitional (TR) B cell compartment reduces the competitive constraint on the entry of newly emerging TR B cells into the splenic follicle (FO), thereby disrupting a peripheral negative selection checkpoint in NOD mice. Thus, development of clinically feasible immunotherapeutic approaches for restoration of appropriate negative selection is essential for the prevention of anti-islet autoimmunity. In this study we hypothesized that in vivo neutralization of the B lymphocyte stimulator (BLyS/BAFF) may enhance the stringency of TR-->FO selection by increasing TR B cell competition for follicular entry in NOD mice. This study demonstrated that in vivo BLyS neutralization therapy leads to the depletion of follicular and marginal zone B lymphocytes. Long-term in vivo BLyS neutralization caused an increased TR:FO B cell ratio in the periphery indicating a relative resistance to follicular entry. Moreover, in vivo BLyS neutralization: 1) restored negative selection at the TR-->FO checkpoint, 2) abrogated serum insulin autoantibodies, 3) reduced the severity of islet inflammation, 4) significantly reduced the incidence of spontaneous diabetes, 5) arrested the terminal stages of islet cell destruction, and 6) disrupted CD4 T cell activation in NOD mice. Overall, this study demonstrates the efficacy of B lymphocyte-directed therapy via in vivo BLyS neutralization for the prevention of autoimmune diabetes.

BLyS and APRIL are two members of the TNF superfamily that are secreted by activated myeloid cells and have costimulatory activity on B cells. BLyS and APRIL share two receptors, TACI and BCMA, whereas a third receptor, BAFF-R, specifically binds BLyS. Both BLyS and APRIL have been described as homotrimeric molecules, a feature common to members of the TNF superfamily. In this study, we show that APRIL and BLyS can form active heterotrimeric molecules when coexpressed and that circulating heterotrimers are present in serum samples from patients with systemic immune-based rheumatic diseases. These findings raise the possibility that active BLyS/APRIL heterotrimers may play a role in rheumatic and other autoimmune diseases and that other members of the TNF ligand superfamily may also form active soluble heterotrimers.