title: Complex formation of CD23/surface immunoglobulin and CD23/CD81/MHC class II on an EBV-transformed human B cell line and inferable role of tetraspanin.
abstract: CD23, a low-affinity IgE receptor, is a type II transmembrane protein having a C-type lectin domain and it associates noncovalently with MHC class II on B cells. The results of our immunoprecipitation analysis suggest that CD23 co-exists with at least two additional molecules, surface immunoglobulin (sIg) and CD81 (and/or CD9), on the cell surface of L-KT9 cells (an Epstein-Barr virus (EBV)-transformed human B cell line). When both CD23 and sIg molecules were stimulated simultaneously by the corresponding antibodies, a large increase in CD81 in the immunoprecipitation was observed as compared with the case of stimulation by only one antibody. Simultaneous stimulation by anti-CD23 and anti-Ig may mimic the situation of B cells stimulated by an antigen/IgE complex. In addition, a large increase in MHC class II in the immunoprecipitation was also observed by cross-linking of CD23 with anti-CD23 and its second antibody as compared with the case of stimulation by anti-CD23 alone. The cross-linking of CD23 with anti-CD23 and its antibody may mimic the situation of B cells stimulated by an IgE/antigen/IgE complex. Therefore, the complex formation among CD23, sIg, MHC class II, and CD81 on the cell surface of L-KT9 cells by the antigen/IgE or IgE/antigen/IgE complex is most likely to be closely related to B cell regulatory events by signaling through sIg or MHC class II. Tetraspanins such as CD81 and CD9 are thought to be involved in the formation and the preservation of various different membrane complexes consisting of several functional proteins.
authors.affiliation: Institute for Immunology/Genetic Medicine, Hokkaido University, Sapporo, Japan. koshigeko@hkg.odn.ne.jp
authors.forename: Shigeko
authors.initials: S
authors.lastname: Kijimoto-Ochiai
authors.forename: Atsutaka
authors.initials: A
authors.lastname: Noguchi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Ohnishi
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Araki
mesh_terms: D000936:Antigen-Antibody Complex / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism* / Q000821:virology; D002460:Cell Line; D002472:Cell Transformation, Viral; D004854:Herpesvirus 4, Human / Q000254:growth & development; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D007073:Immunoglobulin E / Q000378:metabolism; D008213:Lymphocyte Activation; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000378:metabolism; D011233:Precipitin Tests; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D017455:Receptors, IgE / Q000378:metabolism*; D060225:Tetraspanin 28; D060245:Tetraspanin 29
chemical_list: D000936:Antigen-Antibody Complex; D015703:Antigens, CD; C554798:CD81 protein, human; C554869:CD9 protein, human; D000949:Histocompatibility Antigens Class II; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D011947:Receptors, Antigen, B-Cell; D017455:Receptors, IgE; D060225:Tetraspanin 28; D060245:Tetraspanin 29; D007073:Immunoglobulin E