Haemolysis by two alphaviruses: Semliki Forest and Sindbis virus.

Purified preparations of Semliki Forest (SFV) and Sindbis virus haemolyse red blood cells from several species of animals and birds. The optimal haemolysis by SFV was obtained at pH 5.8 with 1-day-old chick erythrocytes incubated at room temperature. Considerable variation in haemolytic activity was observed between different virus preparations purified by different methods. The haemolytic activity of SFV was inhibited by antisera against whole virus or isolated envelope proteins but not with antiserum against virus capsid protein. Neither lipid and detergent-free envelope protein octamers with high haemaggluinating titre, nor isolated nucleocapsids caused haemolysis. Fresh, unpurified SFV and Sindbis virus preparations did not haemolyse unless they were exposed for repeated cycles of freezing and thawing. It appears that the haemolytic activity resides in the virus glycoproteins(s) but can only be manifested in slightly damaged whole virus particles.