The secretory antibody response in milk and bile against fimbriae and LPS in rats monocolonized or immunized in the Peyer's patches with Escherichia coli.

The homing of lymphoid cells to mucosa-associated lymphoid tissue is, amongst other factors, influenced by the nature of the antigen used to induce an immune response. To study this phenomenon we have monocolonized rats with a type 1 fimbriated Escherichia coli O6K13H1 strain and compared the secretory antibody response to colonization with the primary and secondary response obtained in rats immunized in the Peyer's patches (PP). Samples were tested with respect to the titres of antibodies against two antigens present on the E. coli strain: O6 lipopolysaccharide (LPS) and type 1 fimbrial antigen. In the primary immunized animals, IgA anti-fimbrial antibodies were mainly seen in milk and IgA anti-LPS antibodies mostly found in bile. In the booster immunized, and in the monocolonized, animals there was a shift of the antibody response towards the bile. Thus anti-fimbrial antibodies appeared in milk at approximately the same or at a lower level than in bile and the IgA anti-LPS antibodies were almost completely absent in the milk. The IgG antibody response of the animals immunized in the PP was primarily confined to milk for both anti-LPS and anti-fimbrial antibodies, while the colonized animals responded with higher levels in bile than in milk. IgM antibodies were only seen in the milk, except in primary immunized animals in which biliary IgM antibodies also were found. The data illustrate that: (i) primary stimulated cells predestined to produce IgA anti-LPS antibodies home mainly to the intestine, while cells predestined to anti-fimbrial antibody production have a greater tendency to populate the mammary gland; (ii) after repeated antigen stimulation and maturation of the immune response the cells are directed from the mammary gland to the intestine. We thus conclude that the nature of the antigen and the stage of lymphocyte maturation influences the homing of the cells and the appearance of various antibodies in different secretions.