IN MLS-1(A) MICE, FETAL-TYPE BETA-GENE REARRANGEMENTS ARE FREQUENT AMONG SELF-ANERGIC-V(BETA)6 T-CELLS

T lymphocytes generated in the fetal and neonatal period are character ized by T cell receptor (TCR) gene rearrangements that lack N region n ucleotides (fetal-type TCR). Using fetal-type TCR as a lineage marker, we show that such T cells are long-lived and persist in the periphery of adult mice. Moreover, in both neonatal and adult environments, upo n encounter with self-antigens, they are less likely to be deleted. In efficient clonal deletion could be due to the intrinsic properties of the T cells generated during this period, or to yet unknown properties of the perinatal thymus. Such anergic T cells constitute a subset tha t can further expand in vivo in an antigen-independent fashion, leavin g open the possibility for self-aggression under the appropriate trigg ering conditions.