Fig. 6.

Natural surfactant and rSP-B reduce SARS-CoV-2 infection and cell death. (A) Immunofluorescence (via whole well scan) of Vero E6 cells 24 hpi with different variants of SARS-CoV-2 with or without the addition of poractant alfa. Wells were stained for intracellular viral NC to quantify degree of infection and quantified (FFU). (B) Quantification of data from (A) (all variants taken together). Surfactant dramatically diminishes infection. (C and D) Quantification of degree of infection of Vero E6 cells based on specific SARS-CoV-2 variant, with or without the addition of poractant alfa; (C) shows the results from variants Beta, Alpha, Gamma, WA1, and D614G; (D) shows the results from Delta. (E) Total infected Vero E6 cells 24 hpi after increasing dosages of poractant alfa; its antiviral actions increase with dose. (F–I) The addition of surfactant or rSP-B to SP-B-deficient PLOs and DLOs can rescue them from their otherwise higher susceptibility to infection and death. (F) Reiteration of the normal inhibition of infection of WT PLO cells with the addition of surfactant. The pivotal role of SP-B in this “rescue” is reinforced by showing that the otherwise higher rate of infection of SP-B-deficient DLO cells is diminished by the addition of surfactant (G) or rSP-B (H). Similarly, cell death (quantified using PI) of infected SP-B-deficient PLOs is reduced at 52 h by the addition of rSP-B (I). Significance calculated using two-way ANOVA: *P < 0.05, **P < 0.01, and ****P < 0.0001.