Serum IgG1 and IgG2a responses to SaoA or Eno. Serum IgG2a and IgG1 responses to SaoA or Eno were measured by ELISA. The data represent IgG2a and IgG1 subclass antibody titers to SaoA or Eno in sera from ten mice orally immunized with the indicated S. Choleraesuis strains 3 weeks after the first immunization and 2 weeks after boosting. Serum from individual mice were serially diluted to obtain titers, starting from 1:50. Error bars represent variation between mice. ns not significant. *P < 0.05; **P < 0.01.