REGULATION OF THE IMMUNE-RESPONSE TO ORAL-ADMINISTRATION OF ANTIGENS IN FOOD ALLERGIC EXPERIMENTAL-ANIMALS

Immunological tolerance normally develops early in life against, foods to avoid that the immune system induces inflammatory reactions agains t food components. In an experimental model in rats they can be made a llergic to ovalbumin (OA) by colonisation with a transgenic E. coli wh ich produces OA. The sensitised animals have IgE and IgG antibodies as well as T cells directed against OA and may develop diarrhoea when fe d OA. They also have IgE-carrying mast cells, eosinophils and goblet c ells in their intestinal mucosa. In contrast animals which have been t olerised by feeding OA have few IgE-covered mast cells, eosinophils an d goblet cells. Instead they have a CD4(+) T cell population with CD25 (IL-2R alpha-chain) centrally in the villi, but no signs of inflammat ory reactivity. These CD25(+) T cells are found in the draining lymph nodes of orally tolerised animals after parenteral immunisation with t he antigen. These cells seem to effectively down-regulate both T and B cell responses to fed antigen but also to an unrelated antigen given simultaneously and handled by the same lymph node - so called ''bystan der tolerance''. Recently we have shown that such regulatory T cells a re also involved in the control of the response to the normal bacteria l flora. This model may be used to study in detail the mechanisms behi nd the normal appearance of tolerance to food components and the comme nsal bacterial flora. (C) 1998 Elsevier Science Inc.