Preprints were being uploaded at a fierce rate. Faced with this tsunami of information, Associate Professor Ashley St John from Duke-NUS and then-Postdoctoral Research Scholar Abhay PS Rathore from Duke University published a review of various immune responses in the lung during and after SARS-CoV-2 infection, synthesising what was known at that point and drawing out deeper insights.
The insights of this review, which was published in The Journal of Immunology, could assist in developing a vaccine that protects from SARS-CoV-2 infection without triggering inflammatory immune reactions, the authors hoped. Excessive inflammatory reactions can lead to severely — or even fatally — damaged lungs.
St John and Rathore further described how recovery from SARS-CoV-2 may also be associated with persistent immunological changes. Some patients continued to have reduced numbers of lymphocytes and eosinophils — a type of white blood cell that curbs infection and boosts inflammation — in the weeks after hospital discharge. Others experienced inflammatory symptoms persisting even after recovery. They also reported that pre-existing antibodies against coronaviruses did not necessarily work against SARS-CoV-2.
Unlike other coronaviruses which typically infect cells in the airways, SARS-CoV-2 could also infect endothelial cells, the single-layer cell lining of blood vessels. The review noted that data showed virus particles observed within endothelial cells of the kidney, highlighting that inflammatory immune responses could be far-reaching and trigger organ damage well beyond the lungs. SARS-CoV-2 was also observed to infect secondary lymphoid organs, which, in turn, could cause the white pulp of the spleen, which contains immune cells, to wither.
The review found that the collated risk factors for more severe SARS-CoV-2 infection outcomes included low blood oxygen during a patient’s initial admission for treatment, hypertension, smoking, coronary heart disease, cerebrovascular disease, diabetes, and pre-existing lung diseases. Chronic infections, such as hepatitis B and tuberculosis, were other factors associated with worse infections. Men generally exhibited more severe SARS-CoV-2 infections than women.