ADENOSINE ACTS AS AN ENDOGENOUS MODULATOR OF IL-2-DEPENDENT PROLIFERATION OF CYTOTOXIC T-LYMPHOCYTES

CTLL-2 cells are a clone of CTL that are dependent on IL-2 for prolife ration. In addition to various cytokine receptors, we observed that th ese cells express three subtypes of adenosine receptors (ARs). In an i nitial attempt to delineate the functions of these receptors in CTLL-2 cells, we tested their role in proliferation. Elimination of endogeno us adenosine with adenosine deaminase (ADA) markedly suppressed IL-2-d ependent proliferation of these cells. This proliferative response was restored by addition of R-phenylisopropyladenosine (R-PIA), a nonhydr olyzable adenosine analogue. The stimulatory response to R-PIA was att enuated following blockade of ARs by 0.5 mM theophylline and 10 mu M B W-A1433, but not by blockade of the A(1)AR with 100 nM xanthine amine congener. The rank order of potency of adenosine analogues in prolifer ation assays was R-PIA greater than or equal to N-ethylcarboxamide ade nosine > S-PIA > PAPA-APEC (a substituted ethylamino-5'-N-ethylcarboxa midoadenosine). These data suggest a potential role of the A(3)AR in t he proliferative response. R-PIA stimulates production of 1,4,5-inosit ol trisphosphate in CTLL-2 cells, suggesting a role of the phospholipa se C signaling pathway in the proliferative response. A23187 (100 nM) and phorbol 12,13 dibutyrate (10 nM), but not 4 alpha-phorbol (10 nM), were able to restore IL-2-dependent CTLL-2 proliferation in the prese nce of ADA. Furthermore, inhibition of protein kinase C by staurospori ne (10 nM) and of phospholipase C by tricyclodecan-9-yl-xanthogenate ( D609) blocked R-PIA-mediated cell proliferation. These data demonstrat e an obligatory role of adenosine in IL-2-dependent proliferation of C TLL-2 cells and support the involvement of an AR-stimulated phospholip ase C signaling pathway in this process.