title: Positive selection of B cells expressing low densities of self-reactive BCRs.
abstract: B cell tolerance or autoimmunity is determined by selective events. Negative selection of self-reactive B cells is well documented and proven. In contrast, positive selection of conventional B cells is yet to be firmly established. Here, we demonstrate that developing self-reactive B cells are not always highly sensitive to the deletion mechanisms imposed by membrane-bound self-antigens. At low amounts, membrane-bound antigens allow survival of B cells bearing a single high affinity self-reactive B cell receptor (BCR). More importantly, we show that forced allelic inclusion modifies B cell fate; low quantities of self-antigen induce the selection and accumulation of increased numbers of self-reactive B cells with decreased expression of antigen-specific BCRs. By directly measuring antigen binding by intact B cells, we show that the low amounts of self-antigen select self-reactive B cells with a lower association constant. A fraction of these B cells is activated and secretes autoantibodies that form circulating immune complexes with self-antigen. These findings demonstrate that conventional B cells can undergo positive selection and that the fate of a self-reactive B cell depends on the quantity of self-antigen, the number of BCRs engaged, and on its overall antigen-binding avidity, rather than on the affinity of individual BCRs.
authors.affiliation: Lymphocyte Population Biology Unit, Institut Pasteur, 75015 Paris, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Gaudin
authors.forename: Yi
authors.initials: Y
authors.lastname: Hao
authors.forename: Maria Manuela
authors.initials: MM
authors.lastname: Rosado
authors.forename: Richard
authors.initials: R
authors.lastname: Chaby
authors.forename: Robert
authors.initials: R
authors.lastname: Girard
authors.forename: António A
authors.initials: AA
authors.lastname: Freitas
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000276:immunology*; D015551:Autoimmunity; D001402:B-Lymphocytes / Q000276:immunology / Q000502:physiology*; D001973:Bromodeoxyuridine; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D007108:Immune Tolerance; D007457:Iodine Radioisotopes; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009113:Muramidase / Q000276:immunology / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000276:immunology* / Q000378:metabolism
chemical_list: D001324:Autoantigens; D007457:Iodine Radioisotopes; D011947:Receptors, Antigen, B-Cell; C421864:hen egg lysozyme; D009113:Muramidase; D001973:Bromodeoxyuridine