Heparin-induced thrombocytopenia immune complexes activate the inflammasome pathway in a complement-dependent manner

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction to heparin caused by pathological immunoglobulin G (IgG) antibodies targeting platelet factor (PF) 4/heparin antigenic complexes. Immune complexes (ICs) consisting of IgG antibodies and PF4/heparin bind to cellular FcγRIIA receptors to initiate prothrombotic cell signaling, including cytokine production and release.

This study sought to investigate the role of inflammasome cytokine production and release of interleukin (IL)-1β following HIT IC challenge.

Inflammasome cytokine release of IL-1β was measured in a whole blood assay, where healthy donor whole blood was incubated with PF4/heparin antigen and ICs consisting of the monoclonal HIT-like antibody, KKO, or HIT patient plasma. Corresponding studies were conducted in peripheral blood mononuclear cells (PBMCs). Requirements for cellular FcγRIIA, complement pathway, and inflammasome were determined with respective inhibitors. FcγRIIA transgenic mice with or without a genetic deletion of Nlrp3 were subjected to an FcγRIIA-dependent thrombosis model.

Whole blood or PBMCs incubated with HIT ICs or HIT patient plasma elicited a significant increase in IL-1β secretion, which was dependent on FcγRIIA. IL-1β secretion required complement, as heat-inactivated plasma or incubation with terminal complement inhibitors prevented cytokine release. Pretreatment of whole blood or PBMCs with the NLRP3 inhibitor MCC950 markedly reduced IL-1β secretion. Furthermore, transgenic mice given an FcγRIIA-dependent thrombotic challenge demonstrated a requirement for Nlrp3 to experience severe thrombocytopenia and thrombosis.

These data demonstrate that HIT ICs activate the inflammasome pathway in an FcγR/complement-dependent manner leading to IL-1β secretion, which is a positive regulator of HIT pathology.