To further elucidate the effect of the different a 1 -AT variants on multicycle replication, viral titers were determined. To this end, cells were infected with VSVDG/LASVGP at an MOI of 0.02 in the presence or absence of doxycycline. Cell culture supernatants were collected 24 h and 48 h post-infection and virus titers were determined by plaque assay. As shown in Table 1 , non-induced S1P-specific a 1 -AT cell lines permitted unaffected growth of Effect of S1P Inhibition on LASV Replication www.plosntds.org VSVDG/LASVGP to comparable titers, whereas virus titers were reduced in cells expressing the S1P-specific a 1 -AT variant. At 24 h post-infection virus production decreased about 100 fold in cells expressing the a 1 -AT variant RRIL compared to non-induced control cultures. The presence of a 1 -AT variant RRLL reduced the virus titer in the supernatant about 10 fold, followed by a 6.2 fold reduction of virus production in a 1 -AT variant RRVL expressing cells. The presence of the a 1 -AT variant RRYL only exhibited a very moderate inhibitory effect on viral replication (inhibition ,2 fold). Again, the presence of the furin-adapted a 1 -AT variant RVKR did not affect VSVDG/LASVGP replication compared to non-induced control cells. Our results indicate that the various S1P-adapted a 1 -antitrypsins exhibit different inhibitory potentials, due to their different recognition motifs. However, the degree of inhibition of virus replication correlated well with the inhibitory potential of the various S1P-adapted a 1 -antitrypsin variants to block LASV GP processing. Interestingly, following the inhibition of virus progeny over a time period of 48 h only the S1P-adapted a 1 -AT variants RRIL and RRLL sustained their inhibitory capacity, whereas in cells expressing a 1 -antitrypsin variants RRVL and RRYL virus production was found to recover although the initial expression levels of a 1 -antitrypsin variants were similar (Table 1 ). These data indicate that the inhibitory potential of the a 1 -AT variants RRVL and RRYL is not sufficient to efficiently suppress the formation of infectious particles by effectively blocking LASV GP-C cleavage, whereas the a 1 -AT variants RRIL and RRLL seem to be appropriate candidates for efficient inhibition of LASV propagation.