Comparative in Vitro Analysis of Proliferation, Ig Secretion, and Ig Class Switching by Murine Marginal Zone and Follicular B Cells
NAVAL MEDICAL RESEARCH INST BETHESDA MD
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We have previously demonstrated that activation of murine B cells by dextran-conjugated anti-IgD antibodies may serve as a polyclonal, in vitro model system for studying immune responses to T cell-independent type 2 Tl-2 Ag, as exemplified by the bacterial polysaccharides. Because in vivo lg responses to Tl-2 Ag are mediated primarily by B cells resident in the splenic marginal zone, we wished to determine whether this reflected an intrinsic difference in the responsiveness of marginal zone B cells MZB compared with follicular B cells FB to this class of Ag. In this report we demonstrate that highly purified MZB, isolated by electronic cell sorting, exhibit a lower proliferative response in vitro response to unconjugated anti-lg antibody as well as to dextran- or Sepharose-conjugated anti-lgM or anti-lgD antibodies, whereas they proliferate equal to or better than FB when stimulated by other B cell mitogens including LPS, Salmonella typhimurium mitogen, or an anti-CD3-activated CD4 Th2 cell clone. Despite the different proliferative responses of MZB and FB induced by anti-lg, Ag receptor cross-linkage stimulates comparable increases in intracellular free calcium concentrations in both of these B cell populations. Furthermore, MZB secrete lg and undergo lg isotype switching to a comparable degree, relative to FB, in response to both T cell-dependent and T cell- independent stimuli. This suggests that the compartmentalization of zone reflects something other than the intrinsic responsiveness of the B cells from these two sites.
- Genetic Engineering and Molecular Biology
- Medicine and Medical Research