title: Deletion or inhibition of Fc gamma receptor 2B (CD32) prevents FVIII-specific activation of memory B cells in vitro.
abstract: Development of inhibitory antibodies against factor VIII (FVIII) is a severe complication of replacement therapy in haemophilia A. Patients with inhibitors are treated with high FVIII doses in the context of immune tolerance therapy (ITT). Data from haemophilia A mouse model suggest that high FVIII concentrations prevent the formation of antibody secreting cells (ASCs) from memory B cells (MBCs) by inducing apoptosis. Fc gamma receptor 2B (CD32) is an important regulator of B cell function, mediating inhibitory signals after cross-linking with the B cell receptor. Here, the role of CD32 in the regulation of FVIII-specific MBCs was investigated using F8-/- and F8-/-CD32-/- knockout mice and monoclonal antibodies (mAbs). The initial immune response was similar between F8-/- and F8-/-CD32-/- mice, including concentration of anti-FVIII antibodies and number of FVIII-specific ASCs in spleen and bone marrow. In contrast, formation of ASCs from MBCs upon rhFVIII re-stimulation in vitro was abolished in F8-/-CD32-/- mice, whereas FVIII/anti-FVIII immune complexes significantly enhanced ASC formation in F8-/- mice. Inhibition of CD32 by mAbs or F(ab)2 fragments prevented ASC formation in a dose-dependent manner. Transfer of B cell-depleted splenocytes using CD45R (B220) depletion from CD32-competent mice did not restore ASC formation in F8-/-CD32-/- cells confirming that CD32 is required on B cells. We conclude that CD32 is a crucial regulator of FVIII-specific B cells and is required for the differentiation of MBCs into ASCs. Inhibition of CD32 could potentially improve the efficacy of FVIII in the context of ITT.
authors.affiliation: Sonja Werwitzke, MD, PhD, Department of Haematology, Haemostasis,, Oncology and Stem Cell Transplantation, Hannover Medical School, D-30625 Hannover, Germany, Tel.: + 49 511 532 8377, Fax: + 49 511 18524, E-mail: werwitzke.sonja@mh-hannover.de.
authors.forename: Sonja
authors.initials: S
authors.lastname: Werwitzke
authors.forename: Nadine
authors.initials: N
authors.lastname: Vollack
authors.forename: Marcus
authors.initials: M
authors.lastname: von Hornung
authors.forename: Katy
authors.initials: K
authors.lastname: Kalippke
authors.forename: Julia
authors.initials: J
authors.lastname: Kutzschbach
authors.forename: Arne
authors.initials: A
authors.lastname: Trummer
authors.forename: Arnold
authors.initials: A
authors.lastname: Ganser
authors.forename: Andreas
authors.initials: A
authors.lastname: Tiede
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D000910:Antibodies, Heterophile / Q000096:biosynthesis / Q000276:immunology; D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing / Q000096:biosynthesis / Q000276:immunology; D000936:Antigen-Antibody Complex / Q000032:analysis; D017209:Apoptosis; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D001853:Bone Marrow / Q000276:immunology; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004306:Dose-Response Relationship, Immunologic; D005169:Factor VIII / Q000235:genetics / Q000276:immunology* / Q000494:pharmacology / Q000627:therapeutic use; D006467:Hemophilia A / Q000276:immunology; D007156:Immunologic Memory / Q000276:immunology*; D017493:Leukocyte Common Antigens / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D017452:Receptors, IgG / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000276:immunology / Q000494:pharmacology / Q000627:therapeutic use; D013154:Spleen / Q000276:immunology
chemical_list: D000910:Antibodies, Heterophile; D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D000936:Antigen-Antibody Complex; C499172:Fcgr2b protein, mouse; D017452:Receptors, IgG; D011994:Recombinant Proteins; C078147:F8 protein, human; D005169:Factor VIII; D017493:Leukocyte Common Antigens
keywords: CD32; Haemophilia A mouse model; inhibitor; memory B cells; recall response