Active immunity or tolerance to foods in patients with celiac disease or inflammatory bowel disease

Administration of exogenous interleukin-18 and interleukin-12 prevents the induction of oral tolerance

Interleukin-18 (IL-18), a pro-inflammatory member of the IL-1 family, has been associated with autoimmunity and allergic disease. This type of pathology is thought to be the result of a defect in immunological tolerance and is often observed in inflammatory disorders of the gut such as coeliac disease, Crohn's disease and ulcerative colitis. IL-18 has been implicated in a number of mucosal immune disorders, where it synergizes with IL-12 to induce the production of interferon-gamma (IFN-gamma). We have therefore investigated the effects of IL-18 and IL-12 administration on the induction of oral tolerance to ovalbumin. The suppression of specific Ig G2a production, delayed-type hypersensitivity responses and IFN-gamma production by antigen-specific T cells were all abrogated by the presence of exogenous IL-12 and IL-18, suggesting that oral tolerance was broken. The expression of the co-stimulatory molecule CD80 on dendritic cells was also shown to be increased by this combination of cytokines. As dendritic cells are thought to be of major importance in the induction of tolerance, this suggests a mechanism by which tolerance to mucosal antigens may be broken in vivo.

Mechanisms of immune tolerance to food antigens in humans

Immune responses and the mechanisms of tolerance to the common dietary antigens bovine gamma globulin (BGG), ovalbumin (OVA), and soybean protein were evaluated in normal human volunteers. Humoral and T cell proliferative responses to these antigens were measurable but low, consistent with immune tolerance. There were limited correlations between responses in the systemic and mucosal compartments, and in general the responses to one dietary antigen could not predict the response to another. T cell proliferation to dietary antigens increased significantly by addition of recombinant human interleukin-2 (rhuIL-2). Peripheral blood mononuclear cells stimulated with BGG or OVA expressed IL-2Ralpha chain but not IL-2 mRNA, consistent with T cell anergy. Incubation with exogenous IL-2 alone did not restore T cell proliferation to BGG or OVA. In some individuals T cell proliferation to an unrelated vaccine antigen was suppressed by addition of BGG or OVA, but could be reversed with low doses of rhuIL-2. We conclude that in humans anergy is the major mechanism of tolerance to chronic antigen feeding, and we propose that such anergic, antigen-specific T cells actively contribute to maintenance of homeostasis in the intestine in the face of massive antigen challenge.

Oral tolerance elicited in mice by beta-lactoglobulin entrapped in biodegradable microspheres

Oral administration of antigen is known to be appropriate for some vaccine purposes as well as oral tolerance induction. In the present study, oral administration of beta-lactoglobulin (BLG) loaded poly(D,L-lactide-co-glycolide) (D,L-PLG) microspheres induced tolerance was evaluated. A single feeding of 5 micrograms of encapsulated BLG tolerized BALB/c mice to subsequent BLG parenteral challenge, suppressing the specific humoral, intestinal and cellular responses. The tolerogenic efficient dose was then reduced 10,000 times, compared to oral administration of soluble BLG. This suggests that loading food proteins into D,L-PLG microspheres might be a potential tool for inducing oral tolerance with allergens.