Tag: covid immunology

To the Editor — As the COVID Human Genetic Effort consortium (https://www.covidhge.com/), we have studied genetic and immunological determinants of life-threatening COVID-19 pneumonia¹, multisystem inflammatory syndrome (MIS-C)², resistance to SARS-CoV-2 infection³ and ‘COVID toes’⁴, and here we present our efforts to investigate post-acute COVID-19 syndrome, or ‘long COVID’.

Most people infected with SARS-CoV-2 experience a mild to moderate acute infection, while ~10% develop hypoxemic pneumonia and 3% develop critical illness, which are outcomes associated with older age and male sex. Inborn errors of type I interferon immunity involving the viral sensors TLR7 or TLR3 can explain critical disease in 1–5% of people less than 60 years of age, whereas neutralizing autoantibodies to the type I interferons IFN-α, IFN-β and IFN-ω are seen in 15–20% of people over 70 years of age¹, which highlights the importance of type I interferon immunity for protective immunity against acute SARS-CoV-2 infection in the respiratory tract.

Although hypoxemic pneumonia typically occurs 2 weeks after infection, a small fraction of children and young adults develop MIS-C at about 4 weeks after infection. This disorder overlaps Kawasaki disease and superantigen-mediated toxic shock syndrome. Immunological analyses have revealed hyperinflammatory immune responses, distinct from those of acute COVID-19 and Kawasaki disease⁵, and activation of T cells, possibly by a SARS-CoV-2 superantigen⁶. There is massive expansion of T cells expressing the T cell receptor (TCR) β-chain variable region TRBV11-2 in combination with variable TCR α-chains and broadly reactive autoantibodies². Intriguingly, the delayed presentation of MIS-C after infection is at odds with other superantigen-mediated disorders, which might be explained by viral persistence specifically in the intestine and repeated superantigen-mediated activation through a leaky gut. Viral persistence has been proposed to be associated with the degree of activation of the immune system during acute infection with SARS-CoV-2⁷.

Signs and symptoms after SARS-CoV-2 infection have been reported to also persist even longer in some children and adults. The World Health Organization defines the ‘post COVID’ condition as one that “occurs in individuals with a history of probable or confirmed SARS CoV-2 infection, usually 3 months from the onset of COVID-19 with symptoms and that last for at least 2 months and cannot be explained by an alternative diagnosis” (https://www.who.int/publications/i/item/WHO-2019-nCoV-Post_COVID-19_condition-Clinical_case_definition-2021.1). Long COVID spans from very mild to severely debilitating disease with objective organ damage, but sometimes the distinction between recovery from post–intensive care unit syndrome and ongoing pathology is not clearly defined or reported in studies.

Interestingly, an acute multi-organ phenotype encompassing multiple neurological, neuropsychological–neurocognitive, cardiopulmonary, gastrointestinal and dermatological complaints during acute COVID-19 correlates with longer persistence of signs and symptoms⁸.

The World Health Organization’s definition of long COVID is vague, which leads to concerns that a variety of conditions, including psychosomatic complaints, become intermixed with more severe, post-infectious organ dysfunction. To maximize our chances of identifying the human genetic immunological determinants of disease, we will focus our efforts on the most severe cases of long COVID available through our international network of collaborators and clinics. We will include patients with over 3 months of persistent signs and symptoms after PCR-verified SARS-CoV-2 infection. We will also limit our studies to patients with severe organ damage or dysfunction that can be objectively verified by imaging and physiological or biochemical–molecular tests (Fig. 1a). Finally, to distinguish these patients with severe long COVID from patients with post–critical illness syndromes, we will include only patients whose persistent organ dysfunction cannot be explained by the severity of the preceding SARS-CoV-2 infection or by the treatments or medical interventions experienced.

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Source: Brodin P, Casari G, Townsend L, O’Farrelly C, Tancevski I, Löffler-Ragg J, Mogensen TH, Casanova JL; COVID Human Genetic Effort. Studying severe long COVID to understand post-infectious disorders beyond COVID-19. Nat Med. 2022 Apr 5. doi: 10.1038/s41591-022-01766-7. Epub ahead of print. PMID: 35383311. https://www.nature.com/articles/s41591-022-01766-7 (Full article)