Signaling through FcγRIIA and the C5a-C5aR pathway mediates platelet hyperactivation in COVID-19

Patients with COVID-19 present with a wide variety of clinical manifestations. Thromboembolic events constitute a significant cause of morbidity and mortality in patients infected with SARS-CoV-2. Severe COVID-19 has been associated with hyperinflammation and pre-existing cardiovascular disease. Platelets are important mediators and sensors of inflammation and are directly affected by cardiovascular stressors. In this report, we found that platelets from severely ill, hospitalized COVID-19 patients exhibit higher basal levels of activation measured by P-selectin surface expression, and have a poor functional reserve upon in vitro stimulation. Correlating clinical features to the ability of plasma from COVID-19 patients to stimulate control platelets identified ferritin as a pivotal clinical marker associated with platelet hyperactivation. The COVID-19 plasma-mediated effect on control platelets was highest for patients that subsequently developed inpatient thrombotic events. Proteomic analysis of plasma from COVID-19 patients identified key mediators of inflammation and cardiovascular disease that positively correlated with in vitro platelet activation. Mechanistically, blocking the signaling of the Fc{gamma}RIIa-Syk and C5a-C5aR pathways on platelets, using antibody-mediated neutralization, IgG depletion or the Syk inhibitor fostamatinib, reversed this hyperactivity driven by COVID-19 plasma and prevented platelet aggregation in endothelial microfluidic chamber conditions, thus identifying these potentially actionable pathways as central for platelet activation and/or vascular complications in COVID-19 patients. In conclusion, we reveal a key role of platelet-mediated immunothrombosis in COVID-19 and identify distinct, clinically relevant, targetable signaling pathways that mediate this effect. These studies have implications for the role of platelet hyperactivation in complications associated with SARS-CoV-2 infection. Cover illustration O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY One-sentence summaryThe Fc{gamma}RIIA and C5a-C5aR pathways mediate platelet hyperactivation in COVID-19

Erythrocytes Reveal Complement Activation in Patients with COVID-19

COVID-19, the disease caused by the SARS-CoV-2 virus, can progress to multi-organ failure characterized by respiratory insufficiency, arrhythmias, thromboembolic complications and shock 1-5. The mortality of patients hospitalized with COVID-19 is unacceptably high and new strategies are urgently needed to rapidly identify and treat patients at risk for organ failure. Clinical epidemiologic studies demonstrate that vulnerability to organ failure is greatest after viral clearance from the upper airway 6-8, which suggests that dysregulation of the host immune response is a critical mediator of clinical deterioration and death. Autopsy and pre-clinical evidence implicate aberrant complement activation in endothelial injury and organ failure 9,10. A potential therapeutic strategy warranting investigation is to inhibit complement, with case reports of successful treatment of COVID-19 with inhibitors of complement 10-13. However, this approach requires careful balance between the host protective and potential injurious effects of complement activation, and biomarkers to identify the optimal timing and candidates for therapy are lacking. Here we report the presence of complement activation products on circulating erythrocytes from hospitalized COVID-19 patients using flow cytometry. These findings suggest that novel erythrocyte-based diagnostics provide a method to identify patients with dysregulated complement activation.

Deep immune profiling of COVID-19 patients reveals patient heterogeneity and distinct immunotypes with implications for therapeutic interventions

COVID-19 has become a global pandemic. Immune dysregulation has been implicated, but immune responses remain poorly understood. We analyzed 71 COVID-19 patients compared to recovered and healthy subjects using high dimensional cytometry. Integrated analysis of [~]200 immune and >30 clinical features revealed activation of T cell and B cell subsets, but only in some patients. A subgroup of patients had T cell activation characteristic of acute viral infection and plasmablast responses could reach >30% of circulating B cells. However, another subgroup had lymphocyte activation comparable to uninfected subjects. Stable versus dynamic immunological signatures were identified and linked to trajectories of disease severity change. These analyses identified three "immunotypes" associated with poor clinical trajectories versus improving health. These immunotypes may have implications for therapeutics and vaccines.