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.

In the present study, we characterize a polymorphism in the CD93 molecule, originally identified as the receptor for the C1q complement component (i.e., C1qRp, or AA4.1) in non-obese diabetic (NOD) mice. This allele carries a coding polymorphism in the first epidermal growth factor-like domain of CD93, which results in an amino acid substitution from Asn→His at position 264. This polymorphism does not appear to influence protein translation or ecto-domain cleavage, as CD93 is detectable in bone-marrow-derived macrophage and B-cell precursor lysates and in soluble form in the serum. The NOD CD93 isoform causes a phenotypic aberrancy in the early B-cell developmental stages (i.e., pro-, pre-, immature, and transitional), likely related to a conformational variation. Interestingly, the NZB/W F1 strain, which serves as a murine model of Lupus, also expresses an identical CD93 sequence polymorphism. Cd93 is located within the NOD Idd13 locus and is also tightly linked to the NZB/W F1 Wbw1 and Nkt2 disease susceptibility loci, which are thought to regulate natural killer T (NKT) cell homeostasis. Consistent with this genetic linkage, we found B6 CD93−/− and B6.NODIdd13 mice to be susceptible to a profound CD4+ NKT cell deficient state. These data suggest that Cd93 may be an autoimmune susceptibility gene residing within the Idd13 locus, which plays a role in regulating absolute numbers of CD4+ NKT cells.