FIG. 3.

Anti-OMP IgG values in pregnant ewes immunized with vaccine strain SU304 (solid circles), plasmid-cured strain SU40 (squares), or crp cdt cya strain SSM189 (triangles) and in nonimmunized ewes (open circles). All animals were challenged with wild-type SS44 10 weeks after the second vaccine administration. Arrows indicate times of first immunization, second immunization, and challenge with wild-type strain SS44. Values are expressed as means and standard deviations of OD readings at 450 nm. The horizontal line represents the cutoff value (0.254), calculated as described in Materials and Methods.