THE HEMAGGLUTININ ENVELOPE PROTEIN OF CANINE-DISTEMPER VIRUS (CDV) CONFERS CELL TROPISM AS ILLUSTRATED BY CDV AND MEASLES-VIRUS COMPLEMENTATION ANALYSIS

Measles virus (MV) and canine distemper virus (CDV) are morbilliviruse s that cause acute illnesses and several persistent central nervous sy stem infections in humans and in dogs, respectively, Characteristicall y, the cytopathic effect of these viruses is the formation of syncytia in permissive cells. In this study, a vaccinia virus expression syste m was used to express MV and CDV hemagglutinin (HA) and fusion (F) env elope proteins. We found that cotransfecting F and HA genes of MV or F and HA genes of CDV resulted in extensive syncytium formation in perm issive cells while transfecting either F or HA alone did not, Similar experiments with heterologous pairs of proteins, CDV-F with MV-HA or M V-F with CDV-HA, caused significant cell fusion in both cases, These r esults indicate that in this expression system, cell fusion requires b oth F and HA; however, the functions of these proteins are interchange able between the two types of morbilliviruses. Human-mouse somatic hyb rids were used to determine the human chromosome conferring susceptibi lity to either MV and CDV, Of the 12 hybrids screened, none were sensi tive to MV. Two of the hybrids containing human chromosome 19 formed s yncytia following CDV infection, In addition, these two hybrids underw ent cell fusion when cotransfected,vith CDV-F and CDV-HA (but not MV-F and MV-HA) glycoproteins by using the vaccinia virus expression syste m, To discover the viral component responsible for cell specificity, c omplementation experiments coexpressing CDV-HA with MV-F or CDV-F with MV-HA in the CDV-sensitive hybrids were performed, We found that sync ytia were formed only in the presence of CDV-HA, These results support the idea that the HA protein is responsible for cell tropism, Further more, while the F protein is necessary for the fusion process, it is i nterchangeable with the F protein from other morbilliviruses.