NEUTRALIZATION ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR EVALUATION OF IMMUNITY TO MEASLES-VIRUS

A neutralization enzyme-linked immunosorbent (Nt-ELISA) assay for dete rmination of protective immunity to measles virus was developed and ev aluated. This procedure uses the same initial steps as performed to de termine antibody titers by seroneutralization (Nt) test. However, a re duction in virus infectivity by neutralizing antibody was determined b y quantitation of viral antigen using ELISA. The serum dilution that r esulted in neutralization of 50% of infectious virus could be determin ed from the absorbance values. To be able to screen a large number of specimens, the conditions of the Nt-ELISA test were adjusted such that negative sera for measles antibodies and the positive ones were clear ly distinguished on the basis of a single dilution (1:4). This test sh owed similar sensitivity (88.3%) and equal specificity as the Nt test when screening 136 serum samples from normal subjects. The estimation of protective antibody titers by Nt and Nt-ELISA methods was strongly correlated (correlation coefficient = 0.91). Thus, the measles Nt-ELIS A test is rapid, reproducible, sensitive, and specific for detection o f protective measles antibodies.