Cellular contributions to the pathogenesis of anti-platelet factor 4 disorders

PURPOSE OF REVIEW: Anti-platelet factor 4 (PF4) disorders, including heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombocytopenia and thrombosis (VITT), and emerging disorders such as VITT-like monoclonal gammopathy of thrombotic significance (MGTS), are monoclonal antibody-mediated and characterized by thrombocytopenia and thrombosis. Understanding the cellular and molecular mechanisms among these anti-PF4 disorders can help explain the variability in clinical presentations. RECENT FINDINGS: Recent work demonstrated that beyond platelets, immune and vascular cells serve a critical role in driving thrombosis and the severity of clinical outcomes. Neutrophils drive thrombosis via NETosis, monocytes release tissue factor-rich microparticles, and endothelial cells provide adhesive and immunogenic surfaces that sustain thromboinflammation. Thus, our understanding of the pathogenesis of anti-PF4 disorders is defined by complex interactions and effector functions of multiple cellular contributors working in parallel to create a highly prothrombotic environment. SUMMARY: A deeper understanding of these intercellular pathways will shed light on the role of innate immune cells, in addition to platelets, in creating variable clinical outcomes between anti-PF4 disorders and reveal novel therapeutic targets. This expands our understanding of unifying mechanisms between these disorders and informs future strategies to improve diagnosis and treatment.