EXTRATHYMIC AND THYMIC ORIGIN OF MURINE IEL - ARE MOST IEL IN EUTHYMIC MICE DERIVED FROM THE THYMUS

Although an abundance of literature supports the hypothesis that murin e intestinal intraepithelial lymphocytes (IEL) can develop extrathymic ally, whether most IEL in euthymic mice are extrathymically derived is unknown. Recent evidence, however, suggests that the development of m ost IEL in euthymic mice is influenced either directly or indirectly b y the thymus. While some evidence suggests that the thymus can influen ce the extrathymic development of IEL through thymus-derived factors, clearly a substantial portion (if not most) of the IEL in euthymic mic e are derived directly from the thymus. The ability of the thymus to g enerate IEL depends on the age of the thymus, as fetal/neonatal thymus up to approximately 2 weeks of age generates a totally different subs et of IEL than the adult thymus. These results suggest that the IEL ge nerated from the fetal early neonatal thymus recognize a different ant igen than the IEL generated from the adult thymus. The former probably recognizes self-antigen and the later recognizes bacterial antigen.