Innate immune sensing of viral molecular patterns is essential for development of antiviral responses. Like many viruses SARS CoV-2 has evolved strategies to circumvent innate immune detection including low CpG levels in the genome, glycosylation to shield essential elements including the receptor binding domain, RNA shielding and generation of viral proteins that actively impede anti-viral interferon responses. Together these strategies allow widespread infection and increased viral load. Despite the efforts of immune subversion SARS-CoV-2 infection does activate innate immune pathways inducing a robust type I/III interferon response, production of proinflammatory cytokines, and recruitment of neutrophils and myeloid cells. This may induce hyperinflammation or alternatively, effectively recruit adaptive immune responses that help clear the infection and prevent reinfection. The dysregulation of the renin-angiotensin system due to downregulation of angiotensin converting enzyme 2, the receptor for SARS-CoV-2, together with the activation of type I/III interferon response, and inflammasome response converge to promote free radical production and oxidative stress. This exacerbates tissue damage in the respiratory system but also leads to widespread activation of coagulation pathways leading to thrombosis. Here, we review the current knowledge of the role of the innate immune response following SARS-CoV-2 infection, much of which is based on the knowledge from SARS-CoV and other coronaviruses. Understanding how the virus subverts the initial immune response and how an aberrant innate immune response contributes to the respiratory and vascular damage in COVID-19 may help explain factors that contribute to the variety of clinical manifestations and outcome of SARS-CoV-2 infection.
Although most autoimmune diseases are considered to be CD4 T-cell or antibody-mediated, many respond to CD20-depleting antibodies that have limited influence on CD4 and plasma cells. This includes rituximab that is used in cancer, rheumatoid arthritis and off-label in a large number of other autoimmunities, notably multiple sclerosis, where ofatumumab is in late stage development and ocrelizumab is approved for use. Recently, the COVID-19 pandemic created concerns about immunosuppression in autoimmunity, leading to cessation or a delay in immunotherapy treatments. However, based on the known and emerging biology of multiple sclerosis and COVID-19, it was hypothesised that whilst B-cell depletion should not necessarily expose people to severe SARS-CoV-2-related issues, it may inhibit protective immunity following infection and vaccination. As such, drug-induced B-cell subset inhibition that controls multiple sclerosis and other autoimmunities, would not influence innate and CD8 T-cell responses, which are central to SARS-CoV-2 elimination, nor the hyper-coagulation and innate inflammation causing severe morbidity. This is supported clinically, as the majority (mortality rate n=~5/392) of SARS-CoV-2 infected, CD20-depleted people with multiple sclerosis have recovered. However, protective neutralising-antibody and vaccination responses are predicted to be blunted, until naïve B-cells repopulate, based on B-cell repopulation-kinetics and vaccination responses, from published rituximab and unpublished ocrelizumab (NCT00676715, NCT02545868) trial data, shown here. This suggests that it may be possible to undertake dose-interruption to maintain inflammatory disease control in MS and other autoimmune diseases, whilst allowing effective vaccination against SARS-CoV-29, if and when an effective vaccine is available.