Aggregation and anticomplementary activity of an antigen used in the complement fixation test for Johne's disease.

Exhaustive lipid extraction of the Johne's bacilli before preparing the Maltaner-Wadsworth antigen removed both the anticomplementary activity of the preparation and its ability to fix complement. Gel filtration temporarily removed anticomplementary activity but tended to reduce the antigenic activity of the extract. Sonication significantly reduced the anticomplementary activity of the antigen without affecting its capacity to fix complement but the effects were only temporary. It is suggested that the antigen exists as micelles which gradually aggregate and re-arrange thereby exposing anticomplementary sites hitherto masked in the dispersed micelles.