Unstable antigenic variation of leptospiras.

The antigenic variants which were found in leptospiras, Leptospira interrogans serovar copenhageni Shibaura grown in a liquid medium containing a homologous antiserum were found to be unstable. The unstable variants showed decreased agglutinability against the homologous antiserum. The decreased agglutinability of the unstable variants reverted to the parent's level of agglutinability after 1 or 2 passages through the normal serum medium. The unstable variants differed antigenically from the parent in the agglutinin-absorption test; however, the agglutinin-absorption test was found to be inadequate for showing the antigenic difference between the parent and the unstable variants because their difference was diminished when the agglutinin-absorbed antigen was increased. The application of Laurell rocket immunoelectrophoresis (LRI) to the SDS-extracted antigens revealed the distinct difference between the parent and the unstable variants. Other findings presented herein indicated the difference between the antigens of the parent and the unstable variants to be one of quantity. The magnitude of the quantitative difference between the antigens could be modified by the medium containing various concentrations of the homologous antiserum. The clones of the unstable variant showed antigenic characteristics which were similar to the original unstable variant.