A re-examination of the single radial haemolysis technique for the assay of influenza anti-neuraminidase antibodies in human sera.

A new study is described of the use of single radial haemolysis (SRH) for the measurement of antibodies to influenza virus neuraminidase (NA). The technique is known to be consistently successful in the assay of anti-haemagglutinin (HA) antibodies, subject only to the condition that the indicator virus belongs to an appropriate serotype. Its adaptation to the measurement of anti-NA is, however, more difficult. The virus used must be a recombinant which contains a specific NA and an "irrelevant" HA. However the present experiments showed that the two recombinants MRC-3 and X-38, which contain the same NA but a different HA, gave different results. Other properties of recombinants, including rates of attachment to and elution from red cells, may affect the results. The chemical NA-inhibition test (NI), although requiring the use of antigenic hybrids, did not produce these discrepancies. However it appears possible to exploit the simplicity and convenience of SRH for mass survey of anti-Na, if individual hybrid recombinants can first be shown to yield results comparable to those obtained by NI.