False positive rubella virus haemagglutination inhibition reactions: occurrence and disclosure

A floatation centrifugation procedure is described by which antibodies and non-specific rubella virus haemagglutination inhibitors can be completely separated. Using this method it was shown that false positive reactions occur with the conventional pretreatments of sera for removing inhibitors, especially with the heparin-McCl2 procedure. Other methods for removal of inhibitors were examined in view of recent knowledge about the chemical nature of the inhibitors. Treatment with phospholipase C proved useful for disclosure of false positive reactions, while floatation centrifugation was the most sensitive method for demonstration of low antibody concentrations.