Regulation of thymocyte proliferation and survival by deoxynucleosides. Deoxycytidine produced by thymic accessory cells protects thymocytes from deoxyguanosine toxicity and stimulates their spontaneous proliferation

Abstract

Deoxyguanosine (dGuo) inhibits thymic blast DNA synthesis and then induces thymocyte cell death. The dGuo inhibitory action, measured with four different assays (spontaneous thymidine incorporation, immunofluorescent detection of 5-bromodeoxyuridine incorporation, dye exclusion, tetrazolium salt cleavage), was suppressed in the presence of supernatants from cultures containing phagocytic cells. In particular, we studied the anti-dGuo activity in supernatants from thymic reticulum cultures (TRS) and in those from phagocytic cells isolated from TR cultures (P-TR). The anti-dGuo substance was identified as deoxycytidine (dCyd) by high performance liquid chromatography and other physicochemical studies. Secretion of dCyd by P-TR is accompanied by thymidine but not by purine nucleoside secretion. A dual mechanism of thymocyte rescue by dCyd was demonstrated by a study of the dose-dependencies of dCyd-mediated prevention and reversal, respectively, of the dGuo inhibition. In addition to this exogenously added anti-dGuo action, dCyd and dCyd-containing TRS induced significant stimulation of spontaneous thymic blast proliferation, and the kinetics of both effects were identical. These findings might suggest that a major role of thymic phagocytic cells is the supply of pyrimidine nucleosides to thymocytes resulting in the maintenance of proliferation and protection of at least some thymic blasts from the toxic effects of dGTP accumulation. The role of this system in the intrathymic selection process is discussed.

In vivo dynamics of CD4–8– thymocytes. Proliferation, renewal and differentiation of different cell subsets studied by DNA biosynthetic labeling and surface antigen detection

“…Due to endogenous thymidine competition [26], BrdUrd is not reutilized in the thymus and can thus be used for precursor product studies which were not possible with tritiated thymidine. We have already used this method to study thymocyte dynamics and differentiation in the normal and regenerating murine thymus [27-301.…”

“…The recent development of anti-bromodeoxyuridine (BrdUrd) antibodies [24,251 gives the opportunity to study the proliferative kinetics of cells in relation to their surface phenotype. Due to endogenous thymidine competition [26], BrdUrd is not reutilized in the thymus and can thus be used for precursor product studies which were not possible with tritiated thymidine. We have already used this method to study thymocyte dynamics and differentiation in the normal and regenerating murine thymus [27-301. We have shown that the main thymocyte differentiation pathway in vivo is DN + double-positive (DP)-+ single-positive (SP) cells, making CD4' 8' DP cells an important intermediary stage, and not a pure dead end, despite the death of the majority of DP cells in the cortex, The DN+ DP transition happens in cycling cells [30].…”

Only dull CD3+ thymocytes bind to thymic epithelial cells. the binding is elicited by both CD2/LFA‐3 and LFA‐1/ICAM‐1 interactions

“…Thymic epithelial cells (TEC) are believed to play an important role in the process by which immature lymphoid cells differentiate into immunocomponent T cells in the thymus [1][2][3][4]. TEC have been shown to express antigen-presenting activity, and it has been suggested that immature T cells interact with self Ag presented by TEC during their maturation process, and are educated to distinguish self Ag from nonself Ag through this interaction [5].…”

Molecular Imaging of Deoxycytidine Kinase Activity Using Deoxycytidine-Enhanced CEST MRI

“…Hence, the dose used in our study corresponds to 153 mg/kg in the human. In fact, doses of dC have been used to antagonize the toxicity of gemcitabine and ara-C (42,43), thymidine (44), and deoxyguanosine (45), which would be sufficient for generating detectable CEST MRI contrast. Although the exact dC concentrations in the plasma or tissues were not measured in these studies, we still speculate that a mmol/L concentration level of dCTP is achievable based on previously reported values of gemcitabine.…”