Human alpha beta and gamma delta thymocyte development: TCR gene rearrangements, intracellular TCR beta expression, and gamma delta developmental potential--differences between men and mice.

To evaluate the role of the TCR in the alphabeta/gammadelta lineage choice during human thymocyte development, molecular analyses of the TCRbeta locus in gammadelta cells and the TCRgamma and delta loci in alphabeta cells were undertaken. TCRbeta variable gene segments remained largely in germline configuration in gammadelta cells, indicating that commitment to the gammadelta lineage occurred before complete TCRbeta rearrangements in most cases. The few TCRbeta rearrangements detected were primarily out-of-frame, suggesting that productive TCRbeta rearrangements diverted cells away from the gammadelta lineage.

Regulation of adenosine receptor engagement by ecto-adenosine deaminase.

Adenosine deaminase (ADA) can localize to the cell surface through its interaction with CD26. Using CD26-transfected cells, we demonstrate that cell surface ADA (ecto-ADA) can regulate adenosine receptor engagement by degrading extracellular adenosine (Ado) to inosine. This ability was dependent upon CD26 expression, the extent of CD26 saturation with ecto-ADA, and the kinetics of the cAMP response.