Spin membrane immunoassay for use in meningococcal serology.

A modified and improved spin membrane immunoassay has been developed for detecting complement-activating antibodies to Neisseria meningitidis capsular polysaccharide antigens. The polysaccharides were incorporated in the membranes of large unilamellar vesicles prepared by the reverse-phase evaporation method and filled with the water-soluble spin label tempocholine chloride. Upon addition of group-specific antisera and complement, the lipid membrane was damaged and the spin label leaked out. This process was monitored by electron spin resonance spectroscopy. A satisfactory assay was developed for polysaccharides of group A and C, whereas in the case of the B system the assay was more labile. The method is rapid and has a sensitivity comparable to that of radioimmunoassay. When studying paired sera from five recruits vaccinated with an A + C polysaccharide vaccine, significant rises in titers to both A and C polysaccharides were observed in all the postvaccination sera.