Phosphatidylserine-positive extracellular vesicles boost effector CD8+ T cell responses during viral infection.

CD8+ T cells are crucial for the clearance of viral infections. During the acute phase, proinflammatory conditions increase the amount of circulating phosphatidylserine+ (PS) extracellular vesicles (EVs). These EVs interact especially with CD8+ T cells; however, it remains unclear whether they can actively modulate CD8+ T cell responses. In this study, we have developed a method to analyze cell-bound PS+ EVs and their target cells in vivo. We show that EV+ cell abundance increases during viral infection and that EVs preferentially bind to activated, but not naive, CD8+ T cells. Superresolution imaging revealed that PS+ EVs attach to clusters of CD8 molecules on the T cell surface. Furthermore, EV-binding induces antigen (Ag)-specific TCR signaling and increased nuclear translocation of the transcription factor Nuclear factor of activated T-cells (NFATc1) in vivo. EV-decorated but not EV-free CD8+ T cells are enriched for gene signatures associated with T-cell receptor signaling, early effector differentiation, and proliferation. Our data thus demonstrate that PS+ EVs provide Ag-specific adjuvant effects to activated CD8+ T cells in vivo.

Serum of Post-COVID-19 Syndrome Patients with or without ME/CFS Differentially Affects Endothelial Cell Function In Vitro.

A proportion of COVID-19 reconvalescent patients develop post-COVID-19 syndrome (PCS) including a subgroup fulfilling diagnostic criteria of Myalgic encephalomyelitis/Chronic Fatigue Syndrome (PCS/CFS). Recently, endothelial dysfunction (ED) has been demonstrated in these patients, but the mechanisms remain elusive. Therefore, we investigated the effects of patients' sera on endothelia cells (ECs) in vitro. PCS (n = 17), PCS/CFS (n = 13), and healthy controls (HC, n = 14) were screened for serum anti-endothelial cell autoantibodies (AECAs) and dysregulated cytokines. Serum-treated ECs were analysed for the induction of activation markers and the release of small molecules by flow cytometry. Moreover, the angiogenic potential of sera was measured in a tube formation assay. While only marginal differences between patient groups were observed for serum cytokines, AECA binding to ECs was significantly increased in PCS/CFS patients. Surprisingly, PCS and PCS/CFS sera reduced surface levels of several EC activation markers. PCS sera enhanced the release of molecules associated with vascular remodelling and significantly promoted angiogenesis in vitro compared to the PCS/CFS and HC groups. Additionally, sera from both patient cohorts induced the release of molecules involved in inhibition of nitric oxide-mediated endothelial relaxation. Overall, PCS and PCS/CFS patients' sera differed in their AECA content and their functional effects on ECs, i.e., secretion profiles and angiogenic potential. We hypothesise a pro-angiogenic effect of PCS sera as a compensatory mechanism to ED which is absent in PCS/CFS patients.