HUMAN LYMPHOCYTE TRANSFORMATION FOLLOWING INHIBITION OF PURINE NUCLEOSIDE PHOSPHORYLASE

Abstract

The genetic absence of purine nucleoside phosphorylase (NP) is associated with an isolated T-cell immune deficiency in humans. NP is responsible for the conversion of inosine to hypoxanthine and guanosine to guanine. We have synthesized a non-metabolizable compound, 6-hydroxy-9-p-aminobenzylpurine (HABP), an inhibitor of NP that has a Ki of 250 μM. The presence of HABP reduced the incorporation of 3H-thymidine into DNA in phytohemagglutinin stimulated human lymphocytes from healthy volunteers to 30% of control values. Patients with NP deficiency have increased levels of inosine and guanosine in their plasma. The addition of inosine to the culture medium of stimulated lymphocytes at 4 mM had no inhibitory effect on DNA synthesis as measured by thymidine incorporation. The addition of 2 mM guanosine, however, reduced thymidine incorporation to 4% of control lymphocytes. The inhibitory effect of guanosine could be partially corrected by the addition of hypoxanthine to the medium at 500 μM concentrations. The addition of uridine to the medium at concentrations to 1 mM did not reverse the inhibition induced by guanosine. These studies indicate that the T-cell abnormality observed in NP deficiency can be mimicked by two related mechanisms, 1) by inhibiting NP in normal lymphocytes, or 2) by increased concentration of guanosine in the culture medium.