A DELTA-T-CELL RECEPTOR DELETING ELEMENT TRANSGENIC REPORTER CONSTRUCT IS REARRANGED IN ALPHA-BETA-T-CELLS BUT NOT GAMMA-DELTA-T-CELL LINEAGES

T cells can be divided into two groups on the basis of the expression of either alpha beta or gamma delta T-cell receptors (TCRs), Because t he TCR delta chain Locus lies within the larger TCR alpha chain locus, control of the utilization of these two receptors is important in T-c ell development, specifically for determination of T-cell type: rearra ngement of the a locus results in deletion of the delta coding segment s and commitment to the alpha beta lineage. In the developing thymus, a relative site-specific recombination occurs by which the TCR delta c hain gene segments are deleted. This deletion removes all D delta, J d elta, and C delta genes and occurs on both alleles, This delta deletio nal mechanism is evolutionarily conserved between mice and humans. Tra nsgenic mice which contain the human delta deleting elements and as mu ch internal TCR delta chain coding sequence as possible without allowi ng the formation of a complete delta chain gene were developed, Severa l transgenic lines showing recombinations between deleting elements wi thin the transgene were developed. These lines demonstrate that utiliz ation of the delta deleting elements occurs in cup T cells of the sple en and thymus. These recombinations are rare in the gamma delta popula tion, indicating that the machinery for utilization of delta deleting elements is functional in alpha beta T cells but absent in gamma delta T cells. Furthermore, a discrete population of early thymocytes conta ining delta deleting element recombinations but not V alpha-to-J alpha rearrangements has been identified. These data are consistent with a model in which delta deletion contributes to the implementation of a s ignal by which the TCR or chain locus is rearranged and expressed and thus becomes an alpha beta T cell.