The role of adenosine receptor engagement in murine fetal thymocyte development

The role of adenosine receptor engagement in murine T-cell development was evaluated by culturing day 15-16 fetal thymic lobes in the presence of vari ous concentrations of the adenosine receptor agonist 5'-(N-ethyl)-carboxami doadenosine (NECA) or the adenosine receptor antagonist 8-phenyltheophyllin e (8-PT) using the fetal thymic organ culture (FTOC) system. Before and 8 d ays after culture, thymocytes were isolated, counted, and analyzed for the expression of CD4 and CD8 T-cell differentiation molecules. Analysis of fre sh thymocytes prior to culture showed that the majority of cells were of th e CD4 single-positive or CD4(+) CD8(+) immature phenotype. Eight days after culture with media alone, 44% of cells were CD4(+) and 23% were CD8(+), an d the number of viable thymocytes had increased from 1.7X10(5) to 2.2X10(5) cells per thymic lobe. A dose-dependent inhibition of maturation was obser ved in cultures with 8-PT, with greater than 85% inhibition at 50 mu M. The double-positive thymocyte subset was most severely depleted. The number of cells obtained from cultures with NECA was also reduced, with about 65% in hibition at 50 mu M, especially the CD8(+) subset that was most severely af fected. These results suggest that adenosine receptor engagement is require d for normal T-cell differentiation and that adenosine receptor agonists an d antagonists have distinct effects on thymocyte differentiation. An unders tanding of the cell-type-specific and developmental expression of adenosine receptors will help elucidate the mechanisms by which adenosine receptor e ngagement influences T-cell development.