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Standardization of a rapid modified micro-neuraminidase-inhibition test (Essen-NIT) for influenza virus-neuraminidase antibody assay and comparison with the W.H.O. method

1976; Academic Press; Volume: 4; Issue: 3 Linguagem: Inglês

10.1016/s0092-1157(76)80007-8

1878-2329

O. Thraenhart, E. Kuwert,

Respiratory viral infections research

A micro test (Essen-NIT) for the demonstration of neuraminidase antibodies (NI-AB) based on enzyme-antienzyme kinetic studies has been developed, which, in comparison with the W.H.O. method (Aymard-Henry, Coleman, Dowdle, Laver, Schild & Webster, 1973), has the following advantages: only one serum dilution is investigated for the quantitative NI-AB determination (one-point method) instead of serial serum dilutions; only micro-volumes (0·8 ml instead of 7·8 ml) are required; a standardized micro-system (Eppendorf) is applied; the overall reaction time is reduced from 20 h to 2 h 10 min; at least 50–100 quantitative NI-AB determinations may be performed by one technician each day instead of a few sera in 2 days; a computerized automatic evaluation of a weighted mean titer value from duplicates with variance as a parameter for the validity of the test result improves the reliability of the NI-AB titer. The NI-AB titer obtained by the Essen-NIT was independant of (a) substrate concentration when substrate excess was used, (b) enzyme concentration and (c) virus-serum incubation times between 15 and 60 min. When the results obtained with the same sera by the W.H.O. method and the Essen-NIT were compared, a statistically significant correlation of the titers was demonstrated. The titers of the Essen-NIT, however, were about four to six times lower than those obtained by the W.H.O. method which might be due to the longer incubation time of the enzyme-substrate and the lower enzyme concentration of the latter procedure but the specificity of this has to be re-evaluated. Based on 2000 NI-AB determinations (using N2 of A/Hong Kong 1/68 and A/Port Chalmers 1/73 viruses), it was shown by variance analysis that a ⩾ 1·5 increase in NI-AB titer is significant.