Yuxin Lu

B cells can serve dual roles in modulating T cell immunity through their potent capacity to present Ag and induce regulatory tolerance. Although B cells are necessary components for the initiation of spontaneous T cell autoimmunity to beta cell Ags in nonobese diabetic (NOD) mice, the role of activated B cells in the autoimmune process is poorly understood. In this study, we show that LPS-activated B cells, but not control B cells, express Fas ligand and secrete TGF-beta. Coincubation of diabetogenic T cells with activated B cells in vitro leads to the apoptosis of both T and B lymphocytes. Transfusion of activated B cells, but not control B cells, into prediabetic NOD mice inhibited spontaneous Th1 autoimmunity, but did not promote Th2 responses to beta cell autoantigens. Furthermore, this treatment induced mononuclear cell apoptosis predominantly in the spleen and temporarily impaired the activity of APCs. Cotransfer of activated B cells with diabetogenic splenic T cells prevented the adoptive transfer of type I diabetes mellitus (T1DM) to NOD/scid mice. Importantly, whereas 90% of NOD mice treated with control B cells developed T1DM within 27 wk, <20% of the NOD mice treated with activated B cells became hyperglycemic up to 1 year of age. Our data suggest that activated B cells can down-regulate pathogenic Th1 immunity through triggering the apoptosis of Th1 cells and/or inhibition of APC activity by the secretion of TGF-beta. These findings provide new insights into T-B cell interactions and may aid in the design of new therapies for human T1DM.

Gamma-aminobutyric acid (GABA) is both a major inhibitory neurotransmitter in the CNS and a product of beta cells of the peripheral islets. Our previous studies, and those of others, have shown that T cells express functional GABAA receptors. However, their subunit composition and physiological relevance are unknown. In this study, we show that a subset of GABAA receptor subunits are expressed by CD4+ T cells, including the delta subunit that confers high affinity for GABA and sensitivity to alcohol. GABA at relatively low concentrations down-regulated effector T cell responses to beta cell Ags ex vivo, and administration of GABA retarded the adoptive transfer of type 1 diabetes (T1D) in NOD/scid mice. Furthermore, treatment with low dose of GABA (600 microg daily) dramatically inhibited the development of proinflammatory T cell responses and disease progression in T1D-prone NOD mice that already had established autoimmunity. Finally, GABA inhibited TCR-mediated T cell cycle progression in vitro, which may underlie GABA's therapeutic effects. The immunoinhibitory effects of GABA on T cells may contribute to the long prodomal period preceding the development of T1D, the immunological privilege of the CNS, and the regulatory effects of alcohol on immune responses. Potentially, pharmacological modulation of GABAA receptors on T cells may provide a new class of therapies for human T1D as well as other inflammatory diseases.

Islet transplantation offers a potential therapy to restore glucose homeostasis in type 1 diabetes patients. A method to image transplanted islets noninvasively and repeatedly would greatly assist studies of islet transplantation. Using recombinant adenovirus, we show that isolated rodent and human islets can be genetically engineered to express luciferase and then imaged after implantation into NOD-scid mice using a cooled charge-coupled device. The magnitude of the signal was dependent on the islet dose. Adenovirus-directed luciferase expression, however, rapidly attenuated. We next tested lentivirus vectors that should direct the long-term expression of reporter genes in transduced islets. Transplanted lentivirus-transduced islets restored euglycemia long term in streptozotocin-treated NOD-scid mice. The signal from implanted lentivirus-transduced islets was related directly to the implanted islet mass, and the signal did not attenuate over the observation period. Viral transduction, luciferase expression, and repeated imaging had no apparent long-term deleterious effects on islet function after implantation. These data demonstrate that the introduction of reporter genes into an isolated tissue allows the long-term monitoring of its survival following implantation. Such imaging technologies may allow earlier detection of graft rejection and the adjustment of therapies to prolong graft survival posttransplantation.