In vitro effects of adenosine deaminase inhibitors on lymphocyte mitogen responsiveness in the mouse

The effects of two adenosine deaminase (ADA) enzyme inhibitors, EHNA and 2′dCF, were examined on mitogen-induced lymphocyte blastogenesis in mice. The proliferative response of spleen cells stimulated with PHA was more sensitive to the inhibitory effect of 2′dCF than was the proliferative response to Con A, 78 and 39% inhibition, respectively. The inhibitory effect increased with increasing concentrations of 2′dCF up to a concentration of 1.0 μ M and then plateaued. A dose-related inhibitory effect of EHNA was observed with both PHA and Con A-induced spleen cell mitogenesis. No differences in the susceptibility to EHNA were observed for the two mitogens. EHNA had little inhibitory effect on the LPS-induced mitogenic response of spleen cells. Moreover, at low concentrations of EHNA (0.1–20 μ M), an augmentation in the proliferative response to LPS was observed which was eliminated by removing T cells from the spleen cell suspension by treatment with anti-Thy 1.2 and complement. In contrast, 2′dCF produced 50% inhibition at 50 μ M concentrations. The effect of these ADA inhibitors was also tested on thymocyte subpopulations separated by peanut agglutination (PNA) and cortisone treatment (CRT). The less mature cortical thymocytes (PNA +) were more susceptible to ADA inhibition by 2′dCF and EHNA than the more mature medullary thymocytes (PNA −, CRT). These results demonstrate that the susceptibility of thymocyte subpopulations to ADA inhibitors changes with different stages of maturation. The spleen cell studies suggest that there are two subpopulations of mitogen responsive T cells, one which is relatively sensitive and the other resistant to the inhibitory effects of 2′dCF. ADA inhibitors, especially 2′dCF, may be useful tools to better define lymphocyte subpopulations and to study lymphocyte differentiation and cellular interactions.