Toll-Like Receptor 4-Dependent Platelet-Related Thrombosis in SARS-CoV-2 Infection.

BACKGROUND: SARS-CoV-2 is associated with an increased risk of venous and arterial thrombosis, but the underlying mechanism is still unclear. METHODS: We performed a cross-sectional analysis of platelet function in 25 SARS-CoV-2 and 10 healthy subjects by measuring Nox2 (NADPH oxidase 2)-derived oxidative stress and thromboxane B2, and investigated if administration of monoclonal antibodies against the S protein (Spike protein) of SARS-CoV-2 affects platelet activation. Furthermore, we investigated in vitro if the S protein of SARS-CoV-2 or plasma from SARS-CoV-2 enhanced platelet activation. RESULTS: Ex vivo studies showed enhanced platelet Nox2-derived oxidative stress and thromboxane B2 biosynthesis and under laminar flow platelet-dependent thrombus growth in SARS-CoV-2 compared with controls; both effects were lowered by Nox2 and TLR4 (Toll-like receptor 4) inhibitors. Two hours after administration of monoclonal antibodies, a significant inhibition of platelet activation was observed in patients with SARS-CoV-2 compared with untreated ones. In vitro study showed that S protein per se did not elicit platelet activation but amplified the platelet response to subthreshold concentrations of agonists and functionally interacted with platelet TLR4. A docking simulation analysis suggested that TLR4 binds to S protein via three receptor-binding domains; furthermore, immunoprecipitation and immunofluorescence showed S protein-TLR4 colocalization in platelets from SARS-CoV-2. Plasma from patients with SARS-CoV-2 enhanced platelet activation and Nox2-related oxidative stress, an effect blunted by TNF (tumor necrosis factor) α inhibitor; this effect was recapitulated by an in vitro study documenting that TNFα alone promoted platelet activation and amplified the platelet response to S protein via p47phox (phagocyte oxidase) upregulation. CONCLUSIONS: The study identifies 2 TLR4-dependent and independent pathways promoting platelet-dependent thrombus growth and suggests inhibition of TLR4. or p47phox as a tool to counteract thrombosis in SARS-CoV-2.

Blood Myeloid Dendritic Cells and slanDC in Antiretroviral Therapy- Suppressed HIV-Infected Patients.

Myeloid dendritic cells (mDCs) play a complex role in HIV infection regardless of viral replication. The aim of our study was to analyse mDCs in long term antiretroviral therapy (ART)- suppressed HIV-infected patients. We evaluated the numbers of mDCs and slanDC in the context of different degree of CD4+ T cell recovery, persistent T cell activation (as HLA-DR+/CD3+ expression) and monocyte-macrophage activation assessed in terms of circulating levels of both sCD14 and sCD163. We enrolled 72 aviremic patients under effective ART and 34 healthy donors (HD). Patients were divided into two groups on the bases of ΔCD4, indicating the difference between the value of CD4 at the time of sampling and CD4 nadir. Higher levels of mDCs and slanDC were found in patients with ΔCD4>200/mmc in comparison to HD. In those patients also an increased level of sCD14 was found, whereas sCD163 seemed to be at normal levels. An augmentation of activated CD4 T lymphocytes was found, although less pronounced in patients with ΔCD4<200/mmc. In conclusion, our findings showed an expansion of mDCs with a shift to inflammatory slanDC that could sustain both microbial translocation and HIV latency in CD4 T cells.