Apoptosis of antigen-specific T cells induced by oral administration of antigen: comparison of intestinal and non-intestinal immune organs

Oral-tolerance induction in diet-induced obese mice

OBJECTIVE

It is known that immune functions are altered in various ways by obesity. However, changes in the intestinal immune system resulting from obesity remain poorly understood. Oral tolerance is a system that suppresses antigen specific immune responses to orally administrated antigens. The intestinal immune system is intimately associated with the oral tolerance system, that acts to prevent allergic and inflammatory diseases. In this study we investigated the effect of obesity on induction of oral tolerance to ovalbumin (OVA) in an animal model of obesity.

RESEARCH METHODS AND PROCEDURES

Obese mice induced by a high fat diet and control mice were allowed free access for 3 days to a 1%-ovalbumin (OVA) solution in drinking water. After continuous feeding of the antigen, all the mice were immunized by two intraperitoneal injections of OVA administered 7 days apart.

RESULTS

In the control mice, induction of oral tolerance caused an increase in antigen specific IgG1 levels and a decrease in IgG2a levels. In contrast, the IgG1/IgG2a ratio was reversed in obese mice. OVA-specific IL-2 production was suppressed by antigen feeding in both the control and obese mice; however, suppression of OVA-specific IL-10 was observed only in the control mice. Although OVA-specific IgA and IgM were not affected by antigen feeding, the obese groups of mice had significantly lower titers of antibodies.

DISCUSSION

These findings suggest that obesity may affect induction of oral tolerance following antigen feeding and that these changes may be related to the inflammatory reaction.

Maternal antibodies block induction of oral tolerance in newly hatched chicks

Oral antigens administered to newly hatched chicks induce oral tolerance. Some of the antigens encountered via the gut during this period are pathogen-derived, and should not be tolerogenic. As chicks are protected in early life by maternal antibodies, we assumed that the same antibodies also served to prevent tolerance by blocking the relevant antigen. We used bovine serum albumin (BSA) as a model antigen, and initially showed that tolerance was invariably generated in chicks younger than 3 days of age. We then showed that tolerance and its prevention were due to circulatory BSA: intravenous BSA induced tolerance, BSA was present in serum of previously fed chicks, and tolerance was completely blocked in chicks containing high levels of maternal anti-BSA. These findings indicate that tolerance in the young chick is probably generated in central lymphoid organs, and that maternal antibodies block access of antigen to these organs, thereby preserving immune competence.