Contribution of intraperitoneal immunization to the local immune response in the respiratory tract of sheep.

The contribution of gut-associated lymphoid tissue (GALT) to the local immune response in the respiratory mucosa of sheep has been investigated. Sheep were primed intraperitoneally (i.p.) with antigen in Freund's complete adjuvant, a procedure known to produce a large IgA-specific antibody-containing cell (ACC) response in intestinal lymph. ACC and their class specificity were then enumerated by double fluorochrome immunofluorescence in respiratory tissues after intratracheal (i.t.) antigen administration. This immunization procedure produced an enhanced IgA-specific ACC response in the upper respiratory tract mucosa compared with either i.t. or i.p. immunization alone and this was not reflected in the regional lymph nodes. Furthermore, chronic drainage of the intestinal efferent lymphatic duct for the duration of the immunization period abrogated the enhanced response in the respiratory mucosa. These data are consistent with the concept of an intermucosal cell circuit with respect to IgA cell precursors, and provide indirect evidence that IgA responses in the respiratory tract can be enhanced by harnessing the immune potential of GALT as a source of IgA precursors by appropriate immunization strategies.