REAPPRAISAL OF MODIFIED NEUTRALIZATION TEST FOR INOUE-MELNICK VIRUS

Ito et al. (1992) reported an improved modification of the neutralizat ion (NT) test for Inoue-Melnick Virus (IMV) by prolonged 90 min incuba tion of the mixture of the virus and serum. For confirmation, we compa red the results of the NT test by 90 and 60 min incubation. Against hu man sera, the NT test by 90 min incubation was significantly more sens itive than the test by 60 min incubation. By 90 min incubation, the NT titers increased by 3 to 6 times and approximately 6% of antibody-neg ative adult sera previously determined in the tests by 60 min incubati on turned to positive (more than 1:10). However, antibody-negative ser a of Japanese children examined previously in the tests by 60 min incu bation remained negative after the 90 min tests. On the other hand, ag ainst rabbit immune sera, no significant difference of NT titers was o bserved between the two NT tests for 90 and 60 min incubation. Also we reinvestigated Japanese adult sera for type 2 IMV infection by the NT test for 90 min incubation, but did not find any serum of type 2 or i ntermediate type infection. Therefore, it is not necessary to change t he previous conclusion that in Japan IMV infections are mostly of type 1.