title: An in vitro model for T cell-independent induction of humoral immunity. A requirement for NK cells.
abstract: We previously established an in vitro polyclonal model for membrane Ig-mediated Ig secretion by B cells in response to T cell-independent type 2 (TI-2) Ags, by using dextran-conjugated anti-IgD Abs (alpha delta-dex). We demonstrated that resting B cells activated with alpha delta-dex plus IL-2 secreted large amounts of Ig only in the presence of NK cells. In this report we show that, in contrast to small B cell-enriched spleen cells that require activation with the combination of alpha delta-dex and IL-2 for induction of Ig secretion, large B cells were induced to secrete Ig in response to alpha delta-dex, alone. These responses were inhibited by previous depletion of asialo-Gm-1+ cells from the B cell-enriched population, and restored both by the addition of freshly explanted NK cells and by in vitro-activated NK cells, suggesting a requirement for NK cells. Small alpha delta-dex-activated B cells could, however, also be stimulated to secrete Ig in the absence of added cytokines but only after the addition of in vitro-activated NK cells and not freshly explanted splenic NK cells. When highly purified large B cells, obtained by electronic cell sorting, were cultured with in vitro-activated NK cells, Ig secretion was induced even in the absence of any other added B cell stimulus. Because the splenic marginal zone has been implicated in humoral immune responses to TI-2 Ags, we further fractionated large B cells into marginal zone (MZB) and follicular (FB) B cells by electronic cell sorting. In vitro-activated NK cells stimulated large MZB, but not FB, cells to secrete Ig in the absence of exogenous stimuli. These data establish a T cell-independent model for induction of Ig synthesis in the absence of any added cytokine and demonstrate a role for freshly explanted NK cells in stimulating Ab production in response to TI-2 Ags. Further, they show that pre-activated NK cells can induce Ig secretion from pre-activated B cells even in the absence of any added stimuli. These data also underscore a special role for the MZB cell in these responses.
authors.affiliation: Department of Pathology, Uniformed Services University of Health Sciences, Bethesda, MD 20814.
authors.forename: C M
authors.initials: CM
authors.lastname: Snapper
authors.forename: H
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: M A
authors.initials: MA
authors.lastname: Moorman
authors.forename: J J
authors.initials: JJ
authors.lastname: Mond
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000917:Antibody Formation; D002478:Cells, Cultured; D003911:Dextrans / Q000494:pharmacology; D005260:Female; D005677:G(M1) Ganglioside / Q000502:physiology; D007376:Interleukin-2 / Q000494:pharmacology; D007694:Killer Cells, Natural / Q000502:physiology*; D051379:Mice; D008811:Mice, Inbred DBA; D008954:Models, Biological; D013601:T-Lymphocytes / Q000502:physiology*
chemical_list: D000888:Antibodies, Anti-Idiotypic; D003911:Dextrans; D007376:Interleukin-2; C039951:anti-IgD; D005677:G(M1) Ganglioside; C018835:asialo GM1 ganglioside