Elevated serum cytokine production in COVID-19 patients is associated with disease progression and severity. However, the stimuli that initiate cytokine production in patients remain to be fully revealed. Virus-infected cells release virus-associated exosomes, extracellular vesicles of endocytic origin, into the blood to deliver viral cargoes able to regulate immune responses. Researchers from Case Western Reserve University School of Medicine report that plasma exosomes of COVID-19 patients contain SARS-CoV-2 double stranded RNA (dsRNA) and stimulate robust production of interleukin-6 (IL-6), IL-8, tumor necrosis factor-α (TNF-α), and other inflammatory cytokines and chemokines by human peripheral mononuclear cells. Exosome depletion abolished these stimulated responses. COVID-19 plasma exosomes induced proinflammatory responses in CD4+ T cells, CD8+ T cells, and CD14+ monocytes but not significantly in regulatory T cells, Th17 T cells, or central memory T cells. COVID-19 plasma exosomes protect the SARS-CoV-2 dsRNA cargo from RNase and deliver the dsRNA into recipient cells. These exosomes significantly increase expression of endosomal toll-like receptor 3 (TLR3), TLR7, TLR8, and TLR9 in peripheral T cells and monocytes. A pharmacological inhibitor of TLR3 considerably reduced cytokine and chemokine production by CD4+ and CD8+ T cells but not by CD14+ monocytes, highlighting divergent signaling pathways of immune cells in response to COVID-19 plasma exosomes. These results identify a novel model of intercellular crosstalk following SARS-CoV-2 infection that evoke immune responses positioned to contribute to elevated cytokine production associated with COVID-19 progression, severity, and long-haul symptoms.
Profiles of cytokine production in PBMCs treated with COVID-19 plasma exosomes
Heatmap of inflammatory cytokine antibody arrays (a, G7 slide; b, G8 slide, RayBiotech Inc.) using culture supernatants from PBMC treated with COVID-19 plasma exosomes derived from patients early in their admission (Pt0001E to Pt1620E) and the same patients later in their hospitalization (Pt0001L to Pt1620L). The average age of the patients was 70.4. PBMC were treated with exosomes (4 × 109 ml−1) for 16 h at 37 °C in RPMI media. (c) Principal components analysis plot of antibody array results. (d) Volcano plot of significantly expressed cytokines and chemokines based on the antibody arrays.