Vaccination boosts protective responses and counters SARS-CoV-2-induced pathogenic memory B cells

Much is to be learned about the interface between immune responses to SARS-CoV-2 infection and vaccination. We monitored immune responses specific to SARS-CoV-2 Spike Receptor-Binding-Domain (RBD) in convalescent individuals for eight months after infection diagnosis and following vaccination. Over time, neutralizing antibody responses, which are predominantly RBD specific, generally decreased, while RBD-specific memory B cells persisted. RBD-specific antibody and B cell responses to vaccination were more vigorous than those elicited by infection in the same subjects or by vaccination in infection-naïve comparators. Notably, the frequencies of double negative B memory cells, which are dysfunctional and potentially pathogenic, increased in the convalescent subjects over time. Unexpectedly, this effect was reversed by vaccination. Our work identifies a novel aspect of immune dysfunction in mild/moderate COVID-19, supports the practice of offering SARS-CoV-2 vaccination regardless of infection history, and provides a potential mechanistic explanation for the vaccination-induced reduction of “Long-COVID” symptoms.

SARs-CoV-2 Infection Impacts the Function and Phenotype of Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDC) are innate immune cells and potent producers of interferon alpha (IFN-α). Sars-CoV-2, an RNA virus that causes Coronavirus Disease 2019 (COVID-19), has taken the lives of more than 400,000 people in the United States. Reports indicate that COVID-19 patients have reduced plasma IFN-α, suggesting a potential use of IFN-α as a disease therapeutic. However, investigations on pDC function and phenotype in COVID-19 patients are needed. We isolated peripheral blood mononuclear cells from fifty hospitalized COVID-19 patients. PBMC were stimulated with HSV-1 or Influenza A virus and IFN-α production and phenotype were assessed by flow cytometry. After stimulation, there were fewer IFN-α+ pDC from COVID-19 patients compared to controls. To reduce inflammation, COVID-19 patients may be treated with dexamethasone, a corticosteroid that has negative effects on pDC function. Although there was more impairment of pDC numbers and function in dexamethasone-treated subjects, the pDC dysregulation was also seen prior to dexamethasone treatment. Phenotypically, we identified reduced expression of pDC markers BDCA2 and CD123, and an upregulation of co-stimulatory markers on pDC from COVID-19 patients. We also observed an increased proportion of Ki67+ pDCs, which indicates increased turnover of pDCs during moderate to severe COVID-19 disease. In summary, pDC from COVID-19 patients produce significantly less IFN-α, express costimulatory ligands used to stimulate adaptive immunity, and may be undergoing rapid turnover. Overall, these changes may compromise the antiviral and adaptive immune response or represent pDC exhaustion during SARS-CoV-2 infection.

Frontline Science: AMPK regulates metabolic reprogramming necessary for interferon production in human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play a crucial role in innate viral immunity as the most potent producers of type I interferons (IFN) in the human body. However, the metabolic regulation of IFN production in such vast quantity remains poorly understood. In this study, AMP-activated protein kinase (AMPK) is strongly implicated as a driver of metabolic reprogramming that the authors and others have observed in pDCs after activation via TLR7/9. Oxygen consumption and mitochondrial membrane potential (MMP) were elevated following stimulation of pDCs with influenza or herpes simplex virus. Blocking these changes using mitochondrial inhibitors abrogated IFN-α production. While it appears that multiple carbon sources can be used by pDCs, blocking pyruvate metabolism had the strongest effect on IFN-α production. Furthermore, we saw no evidence of aerobic glycolysis (AG) during pDC activation and blocking lactate dehydrogenase activity did not inhibit IFN-α. TLR7/9 ligation induces a posttranslational modification in Raptor that is catalyzed by AMPK, and blocking TLR7/9 before virus introduction prevents this change. Finally, it is demonstrated that Dorsomorphin, an AMPK inhibitor, inhibited both IFN-α production and MMP in a dose-dependent manner. Taken together, these data reveal a potential cellular mechanism for the metabolic reprogramming in TLR 7/9-activated pDCs that supports activation and IFN-α production.