Characterization of connexin 30.3 and 43 in thymocytes.

During maturation, thymocytes interact directly and indirectly with different cell types of the thymic microenvironment. Such a cellular communication has been basically ascribed to soluble factors and surface receptors. However, little attention has been given to cellular communication mediated by gap junctions. The existence of these intercellular channels in the immune system remained a controversial issue since the 1970s until recently, when a growing body of evidence has indicated their presence and physiological roles in the immune system. In this work, we investigated whether thymocytes express gap junction-forming proteins (connexins, Cx) and are capable of forming functional intercellular channels. Using RT-PCR, we demonstrated that thymocytes express the mRNA for two Cx isoforms: Cx30.3 and Cx43, but not for Cx26, Cx30, Cx31, Cx31.1, Cx32, Cx33, Cx36, Cx37, Cx40, Cx45, Cx46, and Cx50. In addition, the presence of Cx30.3 and Cx43 was confirmed using different techniques (RNase protection assay, western blot and immunofluorescence). However, despite the expression of these two Cxs, we did not detect functional homocellular coupling between thymocytes or between EL-4 cells (a Cx43 expressing thymic lymphoma-derived cell line) or heterocellular coupling between thymocytes and thymic epithelial cells (TEC) or between EL-4 and TEC in unstimulated conditions. Concluding, in this study, we described for the first time the expression of connexins in thymocytes, which may constitute a new molecule having a functional role in thymocytes maturation.