AbstractMurine norovirus (MNoV) is an important model of human norovirus (HNoV) and mucosal virus infection more broadly. Viral receptor utilization is a major determinant of cell tropism, host range, and pathogenesis. Thebona fidereceptor for HNoV is unknown. Recently, we identified CD300lf as a proteinaceous receptor for MNoV. Interestingly, its paralogue CD300ld was also sufficient for MNoV infectionin vitro. Here we explored whether CD300lf is the sole physiologic receptorin vivoand whether HNoV can use a CD300 ortholog as an entry receptor. We report that both CD300ld and CD300lf are sufficient for infection by diverse MNoV strainsin vitro. We further demonstrate that CD300lf is essential for both oral and parenteral MNoV infection and to elicit anti-MNoV humoral responsesin vivo. In mice deficient in STAT1 signaling, CD300lf is required for MNoV-induced lethality. However, after high dose intraperitoneal challenge with MNoV inCd300lf−/−Stat1−/−mice a single amino acid mutation in the MNoV capsid protein emerged. This substitution did not alter receptor utilizationin vitro. Finally, we demonstrate that human CD300lf (huCD300lf) is not essential for HNoV infection, nor does huCD300lf inhibit binding of HNoV virus-like particles to glycans. Thus, we report huCD300lf is not a receptor for HNoV.Author SummaryHuman norovirus is the leading cause of non-bacterial gastroenteritis causing up to 200,000 deaths each year. How human norovirus enters cells is unknown. Because human norovirus is difficult to grow in the laboratory and in small animals, we use mouse or murine norovirus as a model system. We recently discovered that murine norovirus can use the either CD300ld or CD300lf as a receptorin vitro. We also showed that CD300lf deficient mice were resistant to oral challenge with a single virus strain. Here we determined that CD300lf is essential for infection of diverse murine norovirus strains in cell lines and in mice with normal immune systems demonstrating it’s the primary physiologic receptor for diverse murine norovirus strains independent of infection route. However, in immunodeficient mice injected with high dose virus directly into the abdominal cavity, we observed a norovirus mutant that enabled CD300lf-independent infection. Finally, we demonstrated that human CD300lf is not the elusive receptor for human norovirus.