Intestinal Antibody Secretion in the Young Pig in Response to Oral Immunization with <em>Escherichia coli</em>.

Intestinal immunoglobulins and antibodies in the local immune response to E. coli O somatic antigens have been studied in young fistulated pigs. Antibody levels in intestinal secretion were raised for approximately 2-3 weeks following a single local antigenic challenge with a heat-killed aqueous suspension of E. coli. A second challenge provoked a similar response suggesting a lack of immunological memory. Antibody activity in the secretions was predominantly associated with IgA and immunofluorescent studies of biopsy specimens from young fistulated animals indicated that intestinal synthesis and secretion of IgA had commenced by the 10th day of life. Studies of piglets reared with the sow indicated that oral immunization with E. coli antigen after 10 days of age stimulated intestinal antibody secretion before weaning at 3 weeks. The response of gnotobiotic pigs to oral immunization and infection was evaluated by immunofluorescent histology of the intestinal mucosa. Repeated oral administration of heat-killed E. coli O8 resulted in an immunocyte response in the lamina propria numerically comparable with that produced by infection with the live organism. The early response was dominated by cells of the IgM class whereas after 3 weeks IgA cells predominated. In the germ-free animal very few immunoglobulin-containing cells were detected. In vitro studies of antibacterial activity indicated that the most probable mechanism of immunological control in the alimentary tract is bacteriostasis. [ABSTRACT FROM AUTHOR]