title: A fail-safe mechanism for negative selection of isotype-switched B cell precursors is regulated by the Fas/FasL pathway.
abstract: In B lymphocytes, immunoglobulin (Ig)M receptors drive development and construction of naive repertoire, whereas IgG receptors promote formation of the memory B cell compartment. This isotype switching process requires appropriate B cell activation and T cell help. In the absence of T cell help, activated B cells undergo Fas-mediated apoptosis, a peripheral mechanism contributing to the establishment of self-tolerance. Using Igmicro-deficient microMT mouse model, where B cell development is blocked at pro-B stage, here we show an alternative developmental pathway used by isotype-switched B cell precursors. We find that isotype switching occurs normally in B cell precursors and is T independent. Ongoing isotype switching was found in both normal and microMT B cell development as reflected by detection of IgG1 germline and postswitch transcripts as well as activation-induced cytidine deaminase expression, resulting in the generation of IgG-expressing cells. These isotype-switched B cells are negatively selected by Fas pathway, as blocking the Fas/FasL interaction rescues the development of isotype-switched B cells in vivo and in vitro. Similar to memory B cells, isotype-switched B cells have a marginal zone phenotype. We suggest a novel developmental pathway used by isotype-switched B cell precursors that effectively circumvents peripheral tolerance requirements. This developmental pathway, however, is strictly controlled by Fas/FasL interaction to prevent B cell autoimmunity.
authors: Department of Immunology, Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel. melamedd@techunix.technion.ac.il
authors: Jane
authors: J
authors: Seagal
authors: Efrat
authors: E
authors: Edry
authors: Zohar
authors: Z
authors: Keren
authors: Nira
authors: N
authors: Leider
authors: Ofra
authors: O
authors: Benny
authors: Marcelle
authors: M
authors: Machluf
authors: Doron
authors: D
authors: Melamed
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D002454:Cell Differentiation / Q000276:immunology; D017637:Clonal Deletion / Q000276:immunology*; D053222:Fas Ligand Protein; D017578:Immunoglobulin Class Switching / Q000276:immunology; D008562:Membrane Glycoproteins / Q000276:immunology*; D051379:Mice; D019014:fas Receptor / Q000235:genetics / Q000276:immunology*
chemical_list: D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D019014:fas Receptor