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.