Evidence against the induction of immunological tolerance by feeding antigens to chickens

A series of studies was conducted to determine whether oral tolerance shown to be inducible in rodents can be induced in chickens. A preliminary study was performed with male juvenile Sprague-Dawley rats to ascertain the ability of ELISA to detect oral tolerance induction. Two groups of six rats were provided water with or without 2 mg/mL BSA for 14 consecutive d to induce tolerance. Eight days following water treatment, the rats were challenged i.m. with 1 mg BSA. Serum collected from the rats 20 d later showed decreased (P < .01) anti-BSA ELISA titers in the group given BSA in the water relative to those given ordinary water. Three experiments were conducted to determine whether oral tolerance could be induced in chickens. Birds were given daily oral doses of 25 mg BSA for 14 d (Experiment 1), or fed 5% casein in their diet for 14 d (Experiment 2), or 1 mL of a 50% suspension of SRBC for 10 d (Experiment 3). All birds were challenged with the same antigen after oral dosing. Birds orally dosed with BSA prior to challenge with BSA had titers similar to birds not fed BSA prior to challenge with BSA. When chickens were fed casein (P < .05) or orally gavaged with SRBC (P < .1), titers were enhanced. These observations suggest that feeding antigens prior to injection with the same antigen leads to an enhanced humoral immune response in birds and not tolerance.