Critical role for mouse marginal zone B cells in PF4/heparin antibody production

Abstract

Heparin-induced thrombocytopenia (HIT) is an immune-mediated disorder that can cause fatal arterial or venous thrombosis/thromboembolism. Immune complexes consisting of platelet factor 4 (PF4), heparin, and PF4/heparin-reactive antibodies are central to the pathogenesis of HIT. However, the B-cell origin of HIT antibody production is not known. Here, we show that anti-PF4/heparin antibodies are readily generated in wild-type mice on challenge with PF4/heparin complexes, and that antibody production is severely impaired in B-cell-specific Notch2-deficient mice that lack marginal zone (MZ) B cells. As expected, Notch2-deficient mice responded normally to challenge with T-cell-dependent antigen nitrophenyl-chicken g globulin but not to the T-cell-independent antigen trinitrophenylFicoll. In addition, wild-type, but not Notch2-deficient, B cells plus B-cell-depleted wild-type splenocytes adoptively transferred into B-cell-deficient mMT mice responded to PF4/heparin complex challenge. PF4/heparin-specific antibodies produced by wild-type mice were IgG2b and IgG3 isotypes. An in vitro class-switching assay showed that MZ B cells were capable of producing antibodies of IgG2b and IgG3 isotypes. Lastly, MZ, but not follicular, B cells adoptively transferred into B-cell-deficient mMT mice responded to PF4/heparin complex challenge by producing PF4/heparin-specific antibodies of IgG2b and IgG3 isotypes. Taken together, these data demonstrate that MZ B cells are critical for PF4/heparin-specific antibody production. (Blood. 2013;121(17):3484-3492)

MZB1 is a GRP94 cochaperone that enables proper immunoglobulin heavy chain biosynthesis upon ER stress

“…1E,F). MZ B cells also generate significant levels of IgG3 during a TI-2 response (Guinamard et al 2000;Zheng et al 2013) and are capable of switching to IgG3 upon in vitro stimulation with LPS and IL-4 (Oliver et al 1997). Indeed, we detected reduced amounts of anti-TNP-specific antibodies of the IgG3 isotype in Mzb1 À/À mice compared with Mzb1 +/+ mice throughout the TI-2 response (Fig.…”

Critical role of CD4 T cells in PF4/heparin antibody production in mice

“…9 Typically, MZ B cells participate in T-cell-independent antibody responses. [10][11][12] However, human patients with severe HIT possess T cells that are responsive to PF4/heparin.…”

“…9 G. Arepally (Duke University) provided mouse PF4. T-cell-dependent and -independent antigen immunizations were performed as described.…”

“…T-cell-dependent and -independent antigen immunizations were performed as described. 9 The T-cell-dependent antigen was nitrophenyl-chicken g globulin (NP-CGG; Biosearch Technologies) and the T-cellindependent antigen was trinitrophenyl-Ficoll (TNP-Ficoll; Biosearch Technologies).…”

“…7,8 The MZ subset has been shown to be critical for production of PF4/heparin-specific antibodies. 9 Typically, MZ B cells produce IgM or IgG antibodies independent of T-cell help. [10][11][12] Indeed, HIT patients have features of a T-cell-independent humoral immune response, characterized by rapid onset and decline of antibodies and apparent absence of immunologic memory.…”