title: B cell receptor-independent stimuli trigger immunoglobulin (Ig) class switch recombination and production of IgG autoantibodies by anergic self-reactive B cells.
abstract: In both humans and animals, immunoglobulin (Ig)G autoantibodies are less frequent but more pathogenic than IgM autoantibodies, suggesting that controls over Ig isotype switching are required to reinforce B cell self-tolerance. We have used gene targeting to produce mice in which hen egg lysozyme (HEL)-specific B cells can switch to all Ig isotypes (SWHEL mice). When crossed with soluble HEL transgenic (Tg) mice, self-reactive SWHEL B cells became anergic. However, in contrast to anergic B cells from the original nonswitching anti-HEL x soluble HEL double Tg model, self-reactive SWHEL B cells also displayed an immature phenotype, reduced lifespan, and exclusion from the splenic follicle. These differences were not related to their ability to Ig class switch, but instead to competition with non-HEL-binding B cells generated by VH gene replacement in SWHEL mice. When activated in vitro with B cell receptor (BCR)-independent stimuli such as anti-CD40 monoclonal antibody plus interleukin 4 or lipopolysaccharide (LPS), anergic SWHEL double Tg B cells proliferated and produced IgG anti-HEL antibodies as efficiently as naive HEL-binding B cells from SWHEL Ig Tg mice. These results demonstrate that no intrinsic constraints to isotype switching exist in anergic self-reactive B cells. Instead, production of IgG autoantibodies is prevented by separate controls that reduce the likelihood of anergic B cells encountering BCR-independent stimuli. That bacteria-derived LPS could circumvent these controls may explain the well-known association between autoantibody-mediated diseases and episodes of systemic infection.
authors.affiliation: Centenary Institute of Cancer Medicine and Cell Biology, Locked Bag Number 6, Newtown NSW 2042, Australia. r.brink@centenary.usyd.edu.au
authors.forename: Tri Giang
authors.initials: TG
authors.lastname: Phan
authors.forename: Michelle
authors.initials: M
authors.lastname: Amesbury
authors.forename: Sandra
authors.initials: S
authors.lastname: Gardam
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Crosbie
authors.forename: Jhagvaral
authors.initials: J
authors.lastname: Hasbold
authors.forename: Philip D
authors.initials: PD
authors.lastname: Hodgkin
authors.forename: Antony
authors.initials: A
authors.lastname: Basten
authors.forename: Robert
authors.initials: R
authors.lastname: Brink
mesh_terms: D000818:Animals; D001323:Autoantibodies / Q000096:biosynthesis*; D001324:Autoantigens / Q000502:physiology; D001402:B-Lymphocytes / Q000276:immunology*; D019070:Cell Lineage; D002465:Cell Movement; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000096:biosynthesis*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000235:genetics; D016130:Immunophenotyping; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009113:Muramidase; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D017634:Self Tolerance / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D008070:Lipopolysaccharides; D011947:Receptors, Antigen, B-Cell; C421864:hen egg lysozyme; D009113:Muramidase