An inhibitor to rubella hemagglutination present in bovine albumin preparations: its removal by treatment with kaolin.

Certain commercial preparations of bovine albumin, fraction V, show inhibitory activity in the rubella hemagglutination (HA) and hemagglutination-inhibition (HI) tests. This does not appear to be due to albumin per se, but instead to a contaminant (or contaminants) with the properties of a lipoprotein. All inhibitory activity can be removed from albumin preparations by treatment with kaolin, gel filtration, or flotation ultracentrifugation. We have found that, even when there was no inhibition of HA titers, kaolin treatment of the albumins prior to their incorporation into the test diluent resulted in more clearly defined agglutination patterns. Reasons for and against including albumin in the test diluent are discussed. It is concluded that, although not essential, it is a worthwhile additive. Our data suggest, however, that each batch of albumin used for this purpose should be checked for the presence of inhibitor, and that treatment with kaolin might be considered as a routine step prior to its incorporation into the test diluent.