Serotypes, reovirus

Fig. 10.18. Gel electrophoretic analysis in 2.5% acrylamide of the double-stranded RNA species present in three different reovirus serotypes. The molecular weights lie between 0.8 and 7.5 million (Shatkin et al. 1968).

During cellular entry via the endosomes, the cr3 protein is removed from virions by acid-dependent proteolysis [160, 161]. This is the first necessary step for penetration of reovirus into the cytoplasm [162-164]. This is hypothesized to facilitate a conformational change in crl to a more extended form [156]. Monoclonal antibodies to each of the reovirus outer capsid proteins have been isolated and characterized [158, 165]. crl-specific mAbs are serotype specific [158, 165] and some of these mAbs are effective at neutralizing infectivity in vitro [158, 165, 166]. 

The mammalian reoviruses are divided into three serotypes (1, 2, and 3) on the basis of hemagglutination inhibition and antibody neutralization tests (Rosen, 1960). Reovirions contain a segmented, double-stranded RNA (dsRNA) genome surrounded by two concentric icosahedral protein shells (Gomatos et ai, 1962). There is an internal core containing the genome and a closely applied inner capsid surrounded by an outer capsid shell (Smith et ai, 1969 Fig. 1). 

Using a genetic approach, Sharpe and Fields (1981) also investigated reovirus inhibition of cellular DNA synthesis. They found that while type 3 reovirus inhibits cellular DNA synthesis in mouse L cells, type 1 reovirus exerts little or no effect on L cell DNA synthesis (Fig. 2). The different effects of type 1 and 3 reovirus on L cell DNA synthesis could not be explained by differences in the growth characteristics of these viruses in mouse L cells because both serotypes grow to the same extent and at the same rate in these cells. Furthermore, no cytopathic effects were observed in L cells at the time of inhibition of DNA synthesis. 

In addition to the laboratory strains of type 1 and type 3, five field isolates collected by Rosen and co-workers of reovirus type 1 and 3 (Rosen and Abinanti, 1960 Rosen et al., 1963) were examined for their ability to inhibit L cell DNA synthesis. Two type 1 human isolates did not inhibit L cell DNA synthesis, whereas, three type 3 isolates (two bovine and one mouse) did inhibit L cell DNA synthesis (Sharpe and Fields, 1981). Thus, the capacity of type 3 reovirus to inhibit DNA synthesis is a serotype-specific property and not just peculiar to the laboratory strain of reovirus type 3 Dearing. This finding is consistent with the identification of the SI gene product as the determinant of serotype specificity (Weiner et al., 1977, 1978). 

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