Antigen requirements, sensitivity, and specificity of enzyme immunoassays for measles and rubella viral antibodies

Enzyme immunoassay (EIA) systems for measles virus and rubella virus were studied from the standpoints of requirements for suitable viral antigens and control antigens, and the sensitivity and specificity of the tests for detecting antibody elicited by past infection (determination of immunity status), and for serodiagnosis of currenet infections. Crude or semipurified measles virus antigens were satisfactory for EIA, but antigens derived by pelleting virus from infected cell culture fluids were slightly more specific in their reactivity than were antigens produced from lysates of infected cells. However, reliable rubella EIA antigens could be produced only from infected cell culture fluids, and they required density gradient purification to render them suitably specific. Even with gradient-purified rubella antigens, it was necessary to use antigen prepared in an identical fashion from uninfected cell culture fluids as a control on the specificity of reactions obtained with test sera. With appropriate viral antigens and control antigens, both measles and rubella EIA systems were highly sensitive and specific for determination of immunity status and for serodiagnosis of current infections. Antibody was detectable earlier in the course of infection by EIA than by hemagglutination inhibition or complement fixation, but this did not limit the diagnostic value of the test, since titer increases demonstrable by EIA were usually greater than those detectable by hemagglutination inhibition or complement fixation tests.