Background Severe immunopathology may drive the deleterious manifestations that are observed in the advanced stages of coronavirus disease 2019 (COVID-19) but are poorly understood. Objective Our aim was to phenotype leukocyte subpopulations and the cytokine milieu in the lungs and blood of critically ill patients with COVID-19 acute respiratory distress syndrome (ARDS). Methods We consecutively included patients less than 72 hours after intubation following informed consent from their next of kin. Bronchoalveolar lavage fluid was evaluated by microscopy; bronchoalveolar lavage fluid and blood were assessed by 10-color flow cytometry and a multiplex cytokine panel. Results Four mechanically ventilated patients (aged 40-75 years) with moderate-to-severe COVID-19 ARDS were included. Immature neutrophils dominated in both blood and lungs, whereas CD4 and CD8 T-cell lymphopenia was observed in the 2 compartments. However, regulatory T cells and T H 17 cells were found in higher fractions in the lung. Lung CD4 and CD8 T cells and macrophages expressed an even higher upregulation of activation markers than in blood. A wide range of cytokines were expressed at high levels both in the blood and in the lungs, most notably, IL-1RA, IL-6, IL-8, IP-10, and monocyte chemoattactant protein-1, consistent with hyperinflammation. Conclusion COVID-19 ARDS exhibits a distinct immunologic profile in the lungs, with a depleted and exhausted CD4 and CD8 T-cell population that resides within a heavily hyperinflammatory milieu.

Type I interferons (IFN-I) play a critical role in human antiviral immunity, as demonstrated by the exceptionally rare deleterious variants of IFNAR1 or IFNAR2. We investigated five children from Greenland, Canada, and Alaska presenting with viral diseases, including life-threatening COVID-19 or influenza, in addition to meningoencephalitis and/or hemophagocytic lymphohistiocytosis following live-attenuated viral vaccination. The affected individuals bore the same homozygous IFNAR2 c.157T>C, p.Ser53Pro missense variant. Although absent from reference databases, p.Ser53Pro occurred with a minor allele frequency of 0.034 in their Inuit ancestry. The serine to proline substitution prevented cell surface expression of IFNAR2 protein, small amounts of which persisted intracellularly in an aberrantly glycosylated state. Cells exclusively expressing the p.Ser53Pro variant lacked responses to recombinant IFN-I and displayed heightened vulnerability to multiple viruses in vitro—a phenotype rescued by wild-type IFNAR2 complementation. This novel form of autosomal recessive IFNAR2 deficiency reinforces the essential role of IFN-I in viral immunity. Further studies are warranted to assess the need for population screening.

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Activation of the complement system is initiated by the alternative, the classical, or the lectin pathway. As the complement system is involved in the pathophysiology of graft rejection after kidney transplantation, we investigated the possible role of mannose-binding lectin in kidney transplantation and the influence of human leukocyte antigen (HLA) immunization on this process. In a prospective study of 544 kidney transplant patients over a follow-up period of 5 years, low serum levels of this lectin at the time of transplantation were found to be significantly associated with decreased 5-year death-censored graft survival (hazard ratio 1.68). Subanalysis showed that this association was confined to non-HLA-immunized patients (hazard ratio 1.93). The strongest association was seen in non-HLA-immunized patients receiving a kidney from a deceased donor (hazard ratio 2.93). No significant association with mannose-binding lectin levels and graft survival were found in HLA-immunized patients. Variant MBL2 genotypes causing low mannose-binding lectin serum concentrations showed the same association pattern. Our findings demonstrate a clear protective role of mannose-binding lectin and thus innate immunity in maintaining kidney graft survival, but these are probably overruled by HLA immunization.