Tropism of bunyaviruses: evidence for a G1 glycoprotein-mediated entry pathway common to the California serogroup.

The California serogroup is composed of antigenically and biologically related viruses within the Bunyavirus genus of the Bunyaviridae. We used a large panel of murine cells to study their tissue tropisms and found virtually identical patterns of viral replication among all of the members of this serogroup, in contrast to other members of the family (Bunyamwera, Cache Valley, and Punta Toro viruses). By analyzing the nonpermissive infections with both an RNA dot-blot and a virus binding assay, we determined that tropism for cultured cells was determined at the level of entry. A truncated soluble form of the La Crosse G1 glycoprotein (sG1) was expressed in a baculovirus system and, despite slight differences in glycosylation, was shown to resemble native G1 by immunoprecipitation with six monoclonal antibodies. sG1 bound to permissive but not to nonpermissive cell lines, as demonstrated by flow cytometry. The sG1 effectively blocked infection of permissive cell lines with all of the California serogroup viruses, but did not block infection of two other bunyaviruses. These results indicate that the California serogroup bunyaviruses share a common receptor on vertebrate cells which may differ from the receptor used by other Bunyaviridae and demonstrate that the G1 glycoprotein is the virus attachment protein. sG1 will be a useful reagent in the search for a putative receptor molecule.