A salt-dependent hemagglutinating particle from measles-infected cells

Abstract

A salt-dependent agglutinin (SDA) has been isolated from measles-infected cells which adsorbs to erythrocytes only in hypertonic salines. SDA appears to agglutinate only those red blood cells already shown to be susceptible to measles hemagglutination, and receptors are resistant to receptor-destroying enzyme. In contrast to other measles hemagglutinating particles, SDA can be recovered from agglutinated red blood cells by elution into isotonic saline. SDA hemagglutination is specifically inhibited by measles convalescent sera. SDA contributes up to 50% of measles complement-fixing antigen activity of infected cell extracts. It induces the production of HI and neutralizing antibodies when injected into guinea pigs. SDA titers are highly dependent upon temperature, although adsorption to erythrocytes is not. Titers at 37° increase as a function of charge and concentration of anion and of pH. There was no dissociation or aggregation of SDA in activating salt concentrations as shown by zonal sedimentations. SDA sediments with a coefficient of 22 S and has a buoyant density in CsCl of 1.30 g/ml. Chemically it appears to be a protein with characteristics similar to those associated with the hemagglutinating activity of the measles envelope. The possibility that SDA represents a precursor of the measles envelope is discussed.