T-CELL MIGRATION DURING DEVELOPMENT - HOMING IS NOT RELATED TO TCR V-BETA-1 REPERTOIRE SELECTION

T cell precursors enter the chick thymus in three waves during embryonic life. Each wave of thymocyte precursors colonizing the thymus gave rise to a similar TCR V-beta repertoire in thymus, spleen and intestine both in terms of V(beta)1 and J(beta) usage as well as in the length of V-beta-D-beta-J(beta) junctions. Seventeen V(beta)1s were utilized, and a new J(beta) segment was found. In the progeny of the third wave, more nucleotides were deleted at the 5' end of the J(beta) segment, but the overall size of the CDR3 was conserved by a concomitant increase of N nucleotide addition at the V-beta-D-beta-J(beta) junctions during rearrangement. This CDR3 modification was observed in the spleen but not in the intestine, implying that progeny of the third wave migrate preferentially to the spleen, a possibility that was confirmed by adoptive cell transfers into congenic chickens. Very low frequencies of non-productive rearrangements in the intestine suggested that negative selection may occur in this organ. The present analysis indicates that V(beta)1(+) T cells in spleen and intestine are primarily of thymic origin, this colonization of both organs occurs in waves and is not characterized by preselection of the TCR V(beta)1 repertoire.