ABSTRACT
Development of neutralising antibodies (inhibitors) against factor VIII (FVIII) is a frequent and severe complication of replacement therapy in haemophilia A. Previous data from haemophilia A mouse model demonstrates that both CD32 inhibition and high doses of rhFVIII prevent the differentiation of FVIII-specific memory B cells (MBCs) into antibody secreting cells (ASCs). Here, cellular targets responsible for the suppression of ASC formation by means of CD32 inhibition and high dose of rhFVIII were analysed. We investigated apoptosis on FVIII-specific MBCs using a pan caspases inhibitor, and screened for defects in rhFVIII presentation by analysing T cell release of Th1- and Th2-cytokines in vitro. Although high dose of rhFVIII suppressed ASC formation, cytokine response was not affected. Upon re-stimulation of splenocytes with high dose of rhFVIII, prevention of apoptosis fully restored the FVIII-specific recall response. In contrast, genetic deletion or inhibition of CD32 significantly altered Th1- and Th2-response. CD32 blockade and inhibition of apoptosis resulted in a partial rescue of FVIII-specific ASCs. Normal cytokine secretion could not be restored. In conclusion, suppression of FVIII-specific recall response by CD32 and high doses of rhFVIII is mediated by distinct mechanisms. High dose of rhFVIII induces apoptosis in FVIII-specific MBCs but does not influence FVIII-specific T cell response. CD32 blockade, however, may suppress the FVIII-specific recall response by two ways: i) increasing apoptosis of FVIII-specific MBCs and ii) disturbing FVIII-specific T cell response by modulating presentation of rhFVIII to CD4+ T cells in vitro.
Subject(s)
Antibodies, Neutralizing/immunology , B-Lymphocytes/immunology , Coagulants/administration & dosage , Factor VII Deficiency/drug therapy , Factor VIII/administration & dosage , Immunologic Memory , Receptors, IgG/metabolism , Animals , Antibodies, Monoclonal/pharmacology , Antibodies, Neutralizing/blood , Apoptosis , B-Lymphocytes/drug effects , B-Lymphocytes/metabolism , B-Lymphocytes/pathology , Cells, Cultured , Coagulants/immunology , Cytokines/immunology , Cytokines/metabolism , Disease Models, Animal , Factor VII Deficiency/blood , Factor VII Deficiency/genetics , Factor VII Deficiency/immunology , Factor VIII/genetics , Factor VIII/immunology , Genetic Predisposition to Disease , Immunologic Memory/drug effects , Mice, Knockout , Phenotype , Receptors, IgG/antagonists & inhibitors , Receptors, IgG/deficiency , Receptors, IgG/genetics , T-Lymphocytes, Helper-Inducer/immunology , T-Lymphocytes, Helper-Inducer/metabolism , Time FactorsABSTRACT
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.
Subject(s)
B-Lymphocyte Subsets/immunology , Factor VIII/immunology , Immunologic Memory/immunology , Lymphocyte Activation/immunology , Receptors, IgG/physiology , Adoptive Transfer , Animals , Antibodies, Heterophile/biosynthesis , Antibodies, Heterophile/immunology , Antibodies, Monoclonal , Antibodies, Neutralizing/biosynthesis , Antibodies, Neutralizing/immunology , Antigen-Antibody Complex/analysis , Apoptosis , Bone Marrow/immunology , Cells, Cultured , Disease Models, Animal , Dose-Response Relationship, Immunologic , Factor VIII/genetics , Factor VIII/pharmacology , Factor VIII/therapeutic use , Hemophilia A/immunology , Leukocyte Common Antigens/immunology , Lymphocyte Activation/drug effects , Mice , Mice, Knockout , Receptors, IgG/antagonists & inhibitors , Receptors, IgG/deficiency , Receptors, IgG/genetics , Recombinant Proteins/immunology , Recombinant Proteins/pharmacology , Recombinant Proteins/therapeutic use , Spleen/immunologyABSTRACT
During oogenesis, the egg prepares for fertilization and early embryogenesis. As a consequence, vesicle transport is very active during vitellogenesis, and oocytes are an outstanding system to study regulators of membrane trafficking. Here, we combine zebrafish genetics and the oocyte model to identify the molecular lesion underlying the zebrafish souffle (suf) mutation. We demonstrate that suf encodes the homolog of the Hereditary Spastic Paraplegia (HSP) gene SPASTIZIN (SPG15). We show that in zebrafish oocytes suf mutants accumulate Rab11b-positive vesicles, but trafficking of recycling endosomes is not affected. Instead, we detect Suf/Spastizin on cortical granules, which undergo regulated secretion. We demonstrate genetically that Suf is essential for granule maturation into secretion competent dense-core vesicles describing a novel role for Suf in vesicle maturation. Interestingly, in suf mutants immature, secretory precursors accumulate, because they fail to pinch-off Clathrin-coated buds. Moreover, pharmacological inhibition of the abscission regulator Dynamin leads to an accumulation of immature secretory granules and mimics the suf phenotype. Our results identify a novel regulator of secretory vesicle formation in the zebrafish oocyte. In addition, we describe an uncharacterized cellular mechanism for Suf/Spastizin activity during secretion, which raises the possibility of novel therapeutic avenues for HSP research.
