Interaction of Alphaviruses with the serum complement system is a function of method of purification

The interaction of Sindbis and Ross River viruses with the serum complement system in vitro was influenced by the type of density gradient used to purify them. Sindbis virus purified on sucrose gradients activated the alternate serum complement pathway while Ross River virus prepared in an identical manner had no effect on C3 turnover in non-immune serum. Both viruses purified on tartrate gradients inhibited the spontaneous cleavage of C3 in normal serum. At least some of this inhibition appeared to be due to the presence of tartrate adsorbed to the surface of virions.