Membrane filtration enzyme immunoassay, a novel, rapid method for measurement of virus-specific immunoglobulins G and M and detection of viral antigens

Measurement of IgM responses to a subunit influenza A vaccine by sucrose-gradient centrifugation and membrane-filtration enzyme immunoassays

IgM responses to a deoxycholate-split influenza vaccine containing the surface antigens of the H3N2 virus A/Philippines/2/82 were studied in five volunteers, three of whom were seronegative by haemagglutination inhibition (HI) tests. Responses were measured by a sucrose-gradient centrifugation technique, in which IgM-specific HI activity was computed as a proportion of total IgM and IgG-specific HI activity, and by a membrane filtration-enzyme immunoassay (MF-EIA). Responses could be detected in all volunteers when measured by sucrose-gradient centrifugation within 1-2 weeks, and the IgM induced was 5-40% of total HI-specific activity. The response was also observed in the presence of low levels of pre-existing antibody. Levels of IgM antibody, when measured by MF-EIA, could be easily detected in two of the volunteers, while those of two others were very low and there was no response in a fifth. No biphasic virus-specific response to vaccination, involving first IgM and then IgG, could be measured by either technique. From these studies, the sucrose-gradient fractionation technique appears to be the more sensitive procedure.

An improved membrane-filtration enzyme immunoassay for the rapid serological diagnosis of viral infections

A one-step modification of the membrane-filtration enzyme immunoassay (MF EIA) (Barnett et al., J. Clin. Microbiol., 23:385-399, 1987), for estimation of virus-specific antibody is described. The modified MF EIA allowed serum, antigen and enzyme-conjugated anti-globulin to be incubated together in membrane-based 96-well plates to enable the formation of immune complexes in solution at 37 degrees C. The assay required only 45 min for completion and polyethylene glycol was shown to be an essential component in reaction mixtures for IgG assays to enhance immune complex formation. The modified MF EIA was as sensitive as the previous two-step method for monitoring responses to influenza vaccine, and control antigen backgrounds were significantly reduced. The one-step procedure was also shown to be suitable for the rapid serodiagnosis of naturally acquired influenza A and B infections. However, MF EIA detected cross-reactive H1N1 responses in 57.7% of naturally-acquired H3N2 infections, suggesting that responses to common internal antigens were being measured. Cross-reactive responses to influenza A viruses could not be detected in volunteers receiving subunit vaccines.