B Cell Selection Defects Underlie the Development of Diabetogenic APCs in Nonobese Diabetic Mice

Abstract

One mechanism whereby B cells contribute to type 1 diabetes in nonobese diabetic (NOD) mice is as a subset of APCs that preferentially presents MHC class II-bound pancreatic β cell Ags to autoreactive CD4 T cells. This results from their ability to use cell surface Ig to specifically capture β cell Ags. Hence, we postulated a diabetogenic role for defects in the tolerance mechanisms normally blocking the maturation and/or activation of B cells expressing autoreactive Ig receptors. We compared B cell tolerance mechanisms in NOD mice with nonautoimmune strains by using the IgHEL and Ig3-83 transgenic systems, in which the majority of B cells recognize one defined Ag. NOD- and nonautoimmune-prone mice did not differ in ability to delete or receptor edit B cells recognizing membrane-bound self Ags. However, in contrast to the nonautoimmune-prone background, B cells recognizing soluble self Ags in NOD mice did not undergo partial deletion and were also not efficiently anergized. The defective induction of B cell tolerance to soluble autoantigens is most likely responsible for the generation of diabetogenic APC in NOD mice.

Enhanced responsiveness to T‐cell help causes loss of B‐lymphocyte tolerance to a β‐cell neo‐self‐antigen in type 1 diabetes prone NOD mice

“…5). This difference supported the previous study from our laboratories in which we had shown that in vitro stimulation of purified HEL-specific B lymphocytes derived from IgHEL Â sHEL Dbl-Tg donors with anti-IgM and anti-CD40 Ab (mimicking Ag and T-cell encounter), resulted in reversal of anergy in those cells when derived from donors with the NOD, but not the B6 background [8]. These in vitro experiments also suggested that anergic B lymphocytes on the NOD background were intrinsically more susceptible to a breakdown in self-tolerance upon provision of T-cell help than anergic B lymphocytes from B6 mice.…”

“…According to our previous studies in which IgHEL-Tg B lymphocytes were placed in an environment where HEL was expressed as a ubiquitous neo-self-Ag, the loss of self-tolerance in the B-lymphocyte repertoire of NOD mice occurred in peripheral lymphoid tissues, whereas central tolerance in the BM, manifest by deletion and receptor editing, remained intact [8]. Nevertheless, these studies did not tell us how autoimmune B-lymphocyte responses to b-cell-specific Ag per se occur.…”

“…NOD and B6 mice carrying IgHEL or sHEL Tg, as well as B6.insHEL and NOD.H2 k .insHEL mice, have been described previously [3,8,12,13,31]. NOD.H2 k .insHEL mice were backcrossed to NOD/Lt mice to replace the H2 k congenic region with the H2 g7 haplotype.…”

“…Lower avidity encounters cause B lymphocytes to undergo maturation arrest in a non-responsive anergic state. In the event that the self-Ag is inaccessible or present at very low concentrations, self-reactive B lymphocytes remain in an ''ignorant'' nontolerant state.In the first reported analysis of mechanisms of B-lymphocyte tolerance in NOD mice, Tg encoding hen-egg lysozyme (HEL) as a ubiquitous neo-self-Ag in high avidity multivalent membrane-bound form (mHEL) or a lower avidity oligovalent-soluble form (sHEL) were introduced into NOD.IgHEL-Tg mice, whose B-lymphocyte repertoire is largely composed (490%) of HEL-specific B lymphocytes [8]. HEL-specific B lymphocytes encountering mHEL on the NOD background underwent deletion and receptor editing as efficiently as those on the non-autoimmune prone C57BL/6 (B6) background.…”

“…Triplicate aliquots of 1 Â 10 5 B lymphocytes were seeded into 96-well plates in 200 mL complete RPMI alone or containing 10 mg/mL anti-IgM F(ab 0 ) 2 (Jackson ImmunoResearch) with or without 5 mg/mL anti-CD40 mAb (HM40-3, BD Biosciences) or 10 mg/mL LPS (Sigma-Aldrich). Proliferation of cells in the final 24 of a 72-h culture was assessed by [ 3 H]-thymidine (GE Healthcare) incorporation as described previously [8]. …”