Assay of measles virus hemolysin and its antibody

Summary An assay method of measles virus hemolysin (HL) was developed utilizing spectrophotometric measurement of released hemoglobin. The method was based on the linear relationship, in a certain range of HL dilution, between the percentage of hemolyzed erythrocytes and the HL dilution as expressed in a logarithmic scale, and a HL unit was defined. The hemolysis inhibition (HLI) by measles immune serum was represented by an S-shaped symmetric curve with a constant amount of HL when the per cent HLI was plotted against the serum dilution expressed in a logarithmic scale, and the HLI antibody titer was expressed by the serum dilution showing 50% inhibition. The results of HLI test on children, though preliminary in nature, seemed to show that the test is satisfactory enough for routine use. These assay methods will be obviously very useful in studies of measles, in particular enable us to perform rational studies of HL and its activity, which would in turn contribute to the understanding of the nature of the virus and its infection.