RESUMO
Forty-five vesiculovirus isolates were systematically compared for their capacity to induce interferon (IFN) in chick embryo cells under conditions such that the maximum (quantum) yield of IFN per cell and the titer of IFN-inducing particles (IFP) could validly be determined. Twelve isolates of the New Jersey (NJ) serotype of vesicular stomatitis virus (VSV) were good inducers, yielding amounts of IFN that ranged in a continuum from 300 to more than 8,000 units per 10(7) cells. These must reflect genetic differences between the closely related viruses. These differences were not reflected in the nucleotide sequence of the viral 3' leader RNA, for analysis of eight of the NJ isolates showed no correlation with the IFN yields. As found in previous smaller surveys, 28 out of 32 VSV isolates of the Indiana (IN) serotype produced little or no IFN, or even suppressed its induction. However, four exceptional IN strains were isolated during 1984 and 1985 from cattle within a relatively circumscribed geographical area in Costa Rica and Panama; all belonged to Indiana virus, type 1, subtype IV, in the proposed G-protein gene evolutionary tree. This is the first example of an IFN-inducing phenotype serving as a phylogenetic marker.