title: B-cell proliferation initiated by Ia cross-linking and sustained by interleukins leads to class switching but not somatic mutation in vitro.
abstract: Somatic mutations that are acquired by antibody V genes of antigen-stimulated B cells ultimately provide the clonal diversity from which memory B cells are selected during immune responses to T-cell-dependent antigens. Somatic mutations apparently are not acquired when B cells are stimulated by mitogens nor when they participate in immune responses to T-cell-independent antigens. Since the basis of T-cell-dependent humoral immunity is T-cell recognition of processed antigen in the context of class II major histocompatibility glycoproteins (Ia) on the B-cell surface, we sought to determine whether the ligation of Ia on B cells induces somatic mutation. B cells were stimulated in vitro by a procedure in which their proliferation was dependent upon ligation of surface Ia with antibody. Sequences of hybridoma V genes derived from these B cells revealed no somatic mutations despite prolonged stimulation in vitro and the induction of immunoglobulin secretion and switching to isotypes characteristic of T cell-dependent humoral immunity. We infer that Ia-mediated signalling and isotype switching are not causally related to somatic mutation. The avenue of differentiation that leads to somatic mutation in memory B cells is apparently separable from that leading to proliferation, immunoglobulin secretion and switching.
authors.affiliation: Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
authors.forename: L J
authors.initials: LJ
authors.lastname: Wysocki
authors.forename: G
authors.initials: G
authors.lastname: Creadon
authors.forename: K R
authors.initials: KR
authors.lastname: Lehmann
authors.forename: J C
authors.initials: JC
authors.lastname: Cambier
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA / Q000737:chemistry; D005803:Genes, Immunoglobulin / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D007132:Immunoglobulin Isotypes / Q000032:analysis*; D015847:Interleukin-4 / Q000276:immunology*; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D009154:Mutation / Q000276:immunology*; D016133:Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology
chemical_list: D000949:Histocompatibility Antigens Class II; D007132:Immunoglobulin Isotypes; D015847:Interleukin-4; D004247:DNA