title: Elevated levels of intracellular cAMP sensitize resting B lymphocytes to immune complex-induced unresponsiveness.
abstract: The ability of immune complexes (IC) to regulate B lymphocyte differentiation was investigated. Using an in vitro model, we previously demonstrated that macrophages (M phi) or lymphoid dendritic cells pulsed with IC differentially regulated B cell function, inducing unresponsiveness or stimulation, respectively. The capacity of M phi to induce unresponsiveness was dependent upon two signals, an antigen-specific one supplied by the IC and M phi-secreted prostaglandin (PG)E2. Total inhibition of antibody production was never achieved as a small percentage of B lymphocytes were resistant to IC-induced unresponsiveness. In this study, utilizing an accessory cell-free system, we demonstrate that splenic B cell fractions separated on Percoll density gradients are heterogeneous in their sensitivity to IC-mediated unresponsiveness. Small resting B lymphocytes are exquisitely sensitive to IC-mediated negative signaling and exhibit virtual total ablation of antibody responses. Conversely, large activated B cells are more refractory to this inhibitory pathway. PGE2 and other agents which elevate cAMP potentiate IC-induced unresponsiveness in resting, but not activated B lymphocytes. In addition treatment of resting B cells with PGF2 alpha, which did not elevate cAMP, failed to sensitize these cells to IC-mediated negative signaling. Unresponsiveness induced by IC is selective for specific aspects of B lymphocyte activation, since B cell differentiation but not proliferation is affected. Furthermore, pre-treatment of resting B lymphocytes with interleukin 4 prevents the IC-induced ablation of IgM antibody responses. Overall, our results indicate that the binding of IC by resting B lymphocytes provides a potent mechanism for inhibiting differentiation without affecting proliferation. These observations suggest that in vivo, IC play an important role in regulating the memory B lymphocyte pathway.
authors.affiliation: Immunology Division of the Cancer Center, University of Rochester School of Medicine and Dentistry, NY 14642.
authors.forename: S H
authors.initials: SH
authors.lastname: Stein
authors.forename: R P
authors.initials: RP
authors.lastname: Phipps
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D002454:Cell Differentiation / Q000276:immunology; D002469:Cell Separation; D000242:Cyclic AMP / Q000502:physiology*; D015232:Dinoprostone / Q000502:physiology; D007108:Immune Tolerance / Q000276:immunology*; D007075:Immunoglobulin M / Q000096:biosynthesis; D015847:Interleukin-4 / Q000502:physiology; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D015398:Signal Transduction / Q000276:immunology
chemical_list: D000936:Antigen-Antibody Complex; D007075:Immunoglobulin M; D015847:Interleukin-4; D000242:Cyclic AMP; D015232:Dinoprostone