Impaired intracellular calcium mobilization and NFATc1 availability in tolerant anti-insulin B cells.
B lymphocytes that recognize soluble self-Ags are routinely found in normal individuals in a functionally inactive or anergic state. Current models indicate that this tolerant state is maintained by interactions with self-Ags that uncouple the BCR from downstream signaling pathways and increase levels of free calcium. Contrary to this expectation, B cells that harbor anti-insulin Ig transgenes (125Tg) are maintained in a tolerant state even though free calcium levels remain normal and tyrosine kinase substrate phosphorylation is preserved following BCR stimulation. Under basal conditions, intracellular levels of inositol 1,4,5-trisphosphate are increased and NFATc1 levels are reduced in 125Tg B cells. The 125Tg B cells are markedly impaired in their ability to mobilize calcium upon stimulation with ionomycin, and BCR-induced calcium mobilization from internal stores is decreased. In contrast, poisoning intracellular calcium pumps with thapsigargin increases calcium mobilization in 125Tg B cells. Changes in calcium signaling are accompanied by a failure of 125Tg B cells to translocate NFATc1 into the nucleus following stimulation with either anti-IgM or ionomycin. Thus, disassociation of BCR from multiple signaling pathways is not essential for maintaining tolerance in anti-insulin 125Tg B cells. Rather, BCRs that are occupied by autologous insulin deliver signals that induce changes in intracellular calcium mobilization and maintain tolerance by preventing activation of key transcription factors such as NFAT.
Acevedo-Suárez
Carlos A
CA
Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Kilkenny
Dawn M
DM
Reich
Martha B
MB
Thomas
James W
JW
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020013:Calcium Signaling / Q000235:genetics / Q000276:immunology*; D002478:Cells, Cultured; D007108:Immune Tolerance / Q000235:genetics; D007075:Immunoglobulin M / Q000502:physiology; D007328:Insulin / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D050778:NFATC Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*
D007075:Immunoglobulin M; D007328:Insulin; D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D002118:Calcium