[Fractionation of serum by gel filtration: contamination of IgM fractions by non-specific inhibitors of hemagglutination of the rubella virus].

Rubella virus hemagglutination non-specific inhibitors, in sera fractionated on Bio-Gel A 5 m, elute in IgM containing fractions. In addition, in heparin-MnCl2 treated sera, the same inhibitors display a different chromatographic behaviour on Bio-Gel A 5m, being eluted earlier than IgM. Therefore, in order to avoid false-positive results due to the presence of non-specific inhibitors in IgM containing fractions it is necessary to verify the disappearance of hemagglutination-inhibition activity after 2-ME reduction.