Protection against mortality due to Vibrio cholerae infection in infant rabbits caused by immunization of mothers with cholera protective antigen.

Vaccination of female rabbits with cholera protective antigen (CPA) protected their F1 progeny from lethal challenge with Vibrio cholerae. Protection was determined by the choleragenic score and survival rates. Serum and milk IgG, IgM, IgA titres to CPA, cholera toxin, and LPS were determined. At 8 and 20 weeks post-immunization, mothers' milk, sera, and infants' sera showed elevated CPA-specific IgG and IgA, and infants were protected. Mothers' serum and milk antibody remained elevated for 36 weeks. At 26 weeks, mothers were re-bred, but their progeny were swapped and cross-fed. Infants born to the placebo-vaccinated mothers and nursed by CPA-immune nannies were partially protected from challenge. Infants born to CPA-immune mothers and cross-fed by the placebo-vaccinated nannies were less protected. CPA stimulated both transplacental and milk antibody, but passive immunity was primarily milk-derived. A 36-week booster vaccine stimulated an anamnestic serological response that did not provide protection equivalent to the original vaccine. CPA provided partial protective immunity to the milk-fed infant rabbits that suggests that CPA may be important in the development of a cholera vaccine.