P2 receptors in the thymus: expression of P2X and P2Y receptors in adult rats, an immunohistochemical and in situ hybridisation study

The expression of the seven P2X receptor subtypes and of two P2Y receptors was examined immunohistochemically and by in situ hybridisation in thymi of adult male rats. P2X(4), P2Y(2 and 4) receptor mRNA colocalisation studies combining in situ hybridisation and immunohistochemistry were also carried out. P2X and P2Y receptors were found on thymocytes. P2X receptors were al so abundant in cells of the thymic microenvironment, involved in control of T-cell maturation in vivo. We are the first to describe the expression of P2X(4) receptors on thymocytes and confirm the finding of P2X(1) and P2Y(2) receptors on subpopulations of lymphocytes. P2X(1,2,3,4 and 5) receptors w ere present in blood vessels of the thymus. P2X(1,2 and 4) receptors were d etected in vascular smooth muscle, while P2X(3) receptors appeared to be as sociated with endothelial cells; some small arteries were positive for P2X( 5), possibly labelling vascular smooth muscle or fibroblasts in the adventi tia. P2X(2,3,6) (and 7) receptors were found on thymic epithelial cells. P2 X(2 and 3) receptors were abundant on medullary epithelial cells, whilst P2 X(6) receptors were prominent in Hassall's corpuscles. P2X(2) receptors wer e found on subcapsular and perivascular epithelial cells. P2X(2,6 and 7) re ceptors were detected in epithelial cells along the thymic septa. Expressio n of P2X receptors was also investigated by Western blotting of crude thymi c tissue extracts under reducing conditions. All seven P2X receptor subtype s were found to be dimers of approximately 70 kDa and 140 kDa molecular wei ght. ATP-mediated apoptosis and cell proliferation of thymocytes are discus sed.