The differential immune response in mild versus fatal SARS-CoV2 infection.

This study compared the immune response in mild versus fatal SARS-CoV2 infection. Forty nasopharyngeal swabs with either productive mild infection (n = 20) or negative for SARS-CoV2 (n = 20) were tested along with ten lung sections from people who died of COVID-19 which contained abundant SARS-CoV2 and ten controls. There was a 25-fold increase in the CD3+T cell numbers in the viral positive nasopharyngeal swabs compared to the controls (p < 0.001) and no change in the CD3+T cell count in the fatal COVID-19 lungs versus the controls. CD11b + and CD206+ macrophage counts were significantly higher in the mild versus fatal disease (p = 0.002). In situ analysis for SARS-CoV2 RNA found ten COVID-19 lung sections that had no/rare detectable virus and also lacked the microangiopathy typical of the viral positive sections. These viral negative lung tissues when compared to the viral positive lung samples showed a highly significant increase in CD3+ and CD8 T cells (p < 0.001), equivalent numbers of CD163+ cells, and significantly less PDL1, CD11b and CD206+ cells (p = 0.002). It is concluded that mild SARS-CoV2 infection is marked by a much stronger CD3/CD8 T cell, CD11b, and CD206 macrophage response than the fatal lung disease where viral RNA is abundant.