Defective immune response and failure to induce oral tolerance following enterai exposure to antigen in broilers afflicted with stunting syndrome.

Infectious stunting syndrome (SS) in broilers is a multi-symptomatic disease that includes lesions in the intestinal tract. We investigated whether these lesions impeded functions of the intestinal immune system. Two functions were studied: the capacity to generate 1) immune responses to a resident pathogen .(E. coli) of the gut and to a parenterally administered antigen (ss-casein), and 2) tolerance to an orally administered antigen (ss-casein). SS was induced in day-old broilers by an inoculum prepared from SS afflicted broilers. After onset of SS, immune responses (or absence of, in the case of tolerance) were studied by specific antibody production and T lymphocyte proliferation. Immune responses were induced by subcutaneous immunization of broilers against ss-casein or following natural exposure to enteric .E. coli. Oral tolerance was induced by a single feeding of ss-casein in gelatine capsules. Both enterai anti-E. .coli and parenteral anti-ss-casein responses were significantly reduced in SS birds. SS afflicted broilers did not develop ss-casein-specific oral tolerance. These results indicate dysfunction of both the intestinal immune system and that of systemic acquired immune responses in SS.