TMPRSS2 and infection: Here, we show that the N-terminus of LF contributes to the defense against SARS-CoV-2 infection via blockade of TMPRSS2: both the N-terminal synthetic peptide (designed by us and termed pLF1) and the natural N-terminal peptide, produced by controlled pepsin cleavage of LF, inhibit the proteolytic priming of the viral spike protein by TMPRSS2, and subsequently, cell infection by SARS-CoV-2.