Antibodies in the intestinal secretions of rats. Primary and secondary responses to polymeric flagellin.

ABSTRACT

The antibody responses in serum and secretions obtained from the mucosal surfaces of the small intestine of rats immunized by a parenteral and intestinal route have been compared. Though no significant differences in the mean serum titres were found, the responses of animals immunized via the latter route to large doses of antigen were far less uniform. Apart from the first few days of the primary response, antibody activity was found in three major immunoglobulin classes (IgG2, IgA and IgM), irrespective of the route of immunization. Significant antibody activity appeared in the intestinal surface secretions only after two injections of antigen. In rats immunized parenterally the activity was found only in the IgG2 component. Whilst activity was found in both IgG2 and IgA fractions of the secretions obtained from intestinally immunized rats, it was predominantly of the IgG2 class. The possible significance of this observation is discussed.