Protective Milk O Antibodies Induced in Guinea Pigs by Parenteral <i>Shigella </i>Ribosomal Vaccine

IgG and IgA O antibodies were studied in milk and sera of guinea pigs subcutaneously immunized at various stages of pregnancy with Shigella ribosomal vaccines (SRV) from Shigella sonnei and Shigella flexneri. Both vaccines induced O antibodies in milk, the level of IgA antibodies being significantly higher than that of IgG antibodies. The immune milk provided a clear-cut protection against experimental Shigella-induced keratoconjunctivitis. These results are consistent with the previously shown ability of parenteral SRV to stimulate gut-associated lymphoid tissue and confirm the involvement of secretory IgA O antibodies in the protection induced by the parenteral SRV. The high level of milk antibodies in vaccinated guinea pigs suggests the possibility to use the parenteral SRV for developing lactogenic immunity.