EXPRESSION OF THE P2Y6 PURINERGIC RECEPTOR IN HUMAN T-CELLS INFILTRATING INFLAMMATORY BOWEL-DISEASE

The human P2Y6 receptor is a member of the G-protein-coupled P2Y purin ergic receptor family that responds to extracellular uridine diphospha te (UDP). In previous work, we cloned the human P2Y6 receptor from an activated T-cell library, and others have shown that it is expressed a s a 1.9-kb transcript in several lymphoid tissues. This suggests a rol e for P2Y6 in T-cell function. However, the precise cellular expressio n pattern and regulation of P2Y6 in immune cells have not yet been est ablished. In this study, we have examined the expression of P2Y6 in a range of tissues containing leukocytes by a combination of in situ hyb ridization (ISH), Northern blot analysis, and RT-PCR. Northern hybridi zation revealed that activated peripheral T cells show increased level s of P2Y6 mRNA. Furthermore, RT-PCR analysis of CD4(+) and CD8(+) subs ets illustrated strong expression in both activated GD4(+) and CD8(+) T cells. Stimulation of resting and activated T cells with the P2Y6 li gand UDP caused a rise in the intracellular free calcium concentration in only the activated subset, indicating the presence of functional r eceptor. By ISH, P2Y6 expression was detected in the T cells of the th ymic medulla and spleen, whereas no signal was detected in the bane ma rrow, fetal liver, or lymph nodes. T cells are thought to play an impo rtant role in the pathogenesis of inflammatory bowel disease (IBD), an d because a recent finding has suggested a role for extracellular nucl eotides in mediating colonic epithelial cell damage in IBD, we specula ted that the P2Y6 nucleotide receptor may be expressed in the T cells infiltrating IBD. ISH results reveal that P2Y6 is highly expressed in the T cells infiltrating active IBD, whereas P2Y6 expression was absen t from the T cells of unaffected bowel. These results demonstrate expr ession and regulation of P2Y6 expression in T cells, and suggest a rol e for P2Y6 in the pathogenesis of IBD-mediated intestinal damage.