Effect of oestradiol on the secretory immune system in the rat: an increase in biliary IgM antibodies against a T-cell independent antigen.

The effect of sex hormones on the secretory immune system was studied in rats ooforectomized and substituted with oestradiol in permeable capsules deposited subcutaneously. Ooforectomized rats and sham-operated rats without oestradiol substitution served as controls. Two weeks after the ooforectomy the rats were immunized in the Peyer's patches with Escherichia coli O6 carrying type 1 fimbriae. Some rats were given a booster dose with the same antigen at the same site 3 weeks later. Bile and serum were taken 7 days after the last immunization. The oestradiol treatment did not influence the total level of IgA or IgG or the level of specific IgA or IgG antibodies in bile or serum. Instead there was a specific increase in biliary IgM antibodies against lipopolysaccharide (LPS) as well as a rise in the total IgM concentration in the bile in the oestradiol-treated rats. Despite this there was no difference in the biliary IgM anti-fimbrial antibody level between the different groups. The oestradiol treatment did not change the levels of total immunoglobulins or antibodies against fimbriae and LPS in serum. An oestradiol-induced increase similar to the one seen in biliary IgM anti-LPS antibodies in primary immunized animals was not seen during the secondary response in booster immunized rats. Thus it seemed as if the effect of oestradiol on the secretory immune system in the bile was mainly due to an influence on primary stimulated B-cell clones in the liver, producing IgM antibodies against a T-cell-independent antigen. The effect may be mediated through a direct action of oestradiol on the B lymphocytes.