s influenced by host tissue sialic

Recent studies have shown that the sialic acid content of Sindbis virus influences both its ability to activate the alternative pathway in vitro and its susceptibility to complement dependent clearance from the bloodstream in vivo. Other studies have shown that the sialic acid content of Sindbis virus is deter- mined by the host in which it is propagated. Because individuals vary in their cell surface sialic acid content, it is possible they also vary in their ability to defend themselves against Sindbis virus in- fection by virtue of their ability to modify the virus sialic acid con- tent and thereby the capacity of the virus to activate the alternative pathway. To test this hypothesis, outbred Swiss mice were injected subcutaneously with Sindbis virus. There was a significant positive correlation between the level of viremia 18 hr after infection and the sialic acid content of the host's erythrocytes. In addition, an- imals with erythrocyte sialic acid levels equal to or greater than the mean had a higher level of viremia than animals with eryth- rocyte sialic acid levels less than the mean. Finally, animals that had muscle sialic acid levels equal to or greater than the mean had a higher incidence of viremia than animals with muscle sialic acid levels less than the mean. These studies suggest that the amount of tissue sialic acid in an individual host influences its ability to resist Sindbis virus infection.