## 4 Discussion
To prevent artificial virus-cell interactions, in our study, we used a replication-competent rLCMV/LASV\({}_{\text{GP}}\) chimera, which incorporated LASV\({}_{\text{GP}}\) in the backbone of the close relative OW mmamarenavirus LCMV and faithfully recapitulated LASV infection in vitro and in vivo [66; 77]. Alternatively, it may be possible that exogenously expressed Axl RTK does not completely recapitulate the cellular factor functionality, which provides a possible explanation for both findings. Axl RTK activation is associated with reduction of the IFN-I response, resulting in increased viral replication of many viruses [51; 93; 94]. Nevertheless, our results show that, in our experimental settings, Axl RTK inhibition by R428 inhibits rLCMV/LASV\({}_{\text{GP}}\) entry without affecting IFN-I expression. It is conceivable that the well-known immunosuppressive capacity of LASV (REF) is potent enough to also prevent the effect of R428 on the innate immune response. Nevertheless, at late phases of the infection, the host can detect LASV presence, triggering a strong innate immune response [107]. Therefore, the inhibition of Axl RTK could play a relevant role at late infection times. Our time-of-addition and post-entry assays, as well as the virus visualization under confocal microscopy, instead, suggest that Axl RTK participates mainly during LASV transport, early after virion attachment. In summary, our study provides evidence for the participation of Axl and HGFR RTKs in LASV entry, but not in later steps, regardless of the presence or absence of functional, highly glycosylated DG. Furthermore, inhibition of both RTKs, Axl, and HGFR, resulted in reduced LASV entry by alteration of cytoplasmic macropinosome trafficking with vesicle retention and accumulation at the cellular membrane. The present results suggest that basal macropinocytosis, which involve Axl and HGFR RTKs, is necessary for LASV transportation upon viral internalization, and highlights the importance of additional host factors in the process of viral entry and their relevance as promising antiviral drug targets. The following are available online at [[http://www.mdpi.com/1999-4915/12/8/857/s1](http://www.mdpi.com/1999-4915/12/8/857/s1)]([http://www.mdpi.com/1999-4915/12/8/857/s1](http://www.mdpi.com/1999-4915/12/8/857/s1)), Figure S1: Surface expression of highly glycosylated DG and Axl RTK in A549 (A) and HT-1080 (B) cells. Figure S2: Numbers of infected cells per well (96-well plate) from (A) Figure 2B and (B) Figure 2C. (C) Entry assay for Rib in A549 cells. Figure S3: Threshold cycles (Ct) corresponding to Figure 4. Figure S4: (A) Numbers of infected cells per well (96-well plate) from Figure 5C. Figure S5: rLCMV/LASVGP co-localization with macropinosomes. Figure S6: (A,B) Numbers of infected cells per well (96-well plate) from Figure 7.  
**Author Contributions:** [PERSON]; [PERSON]; and S.K. conceptualized research; S.K. acquired funding; [PERSON]; [PERSON]; and S.K. administered and supervised the research project; [PERSON]; [PERSON]; and S.K. performed investigation and methodology; [PERSON]; [PERSON]; and S.K. analyzed data and contributed to discussion; [PERSON] and S.K. wrote the original draft; [PERSON] and [PERSON] discussed, reviewed, and edited the final version of the manuscript. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was supported by the Swiss National Science Foundation grants 310030_170108 and CRSII3_160780/1 to S.K. ; and funds to S.K. from the University of Lausanne. **Acknowledgments:** Sadly, the principal investigator, [PERSON] passed away during the writing process of this manuscript. We would like to express our deep gratitude to him for having shared with us his tremendous knowledge and passion for virology. He will be missed and always remains in our memory.