CTSB and infection: With a TMPRSS2 inhibitor, the extent of infection decreased, but the fraction unaffected, now denoted fu(DT), plateaued at values that increased with the mean Cathepsin B/L expression level– fu(DT)~0.13 at low and fu(DT)~0.88 at high expression levels–indicating again that the apparent activity of the TMPRSS2 inhibitor decreased as the Cathepsin B/L pathway became increasingly preferred (Fig 2J).