ROLE OF ADENOSINE-DEAMINASE IN LYMPHOCYTE-PROLIFERATION

Abstract

Activity of adenosine deaminase (ADA), an enzyme known to be deficient in some patients with severe combined immunodeficiency, increased 3-fold within a 24 h exposure of human peripheral blood lymphocytes to phytohemagglutinin (PHA) in culture. This increase took place before the onset of DNA synthesis. Increased levels of ADA activity were also observed in lymphocytes incubated with pokeweed mitogen (PWM) for 60 h. DNA synthesis induced by PHA, PWM or mixed lymphocte cultures (MLC) was strongly inhibited by adenosine at concentrations of 10-4 M or higher when human peripheral blood lymphocytes were cultured in a medium supplemented with horse serum, which lacks ADA. Coformycin (10-6-10-8 M), a potent inhibitor of ADA, inhibited PHA-, PWM- and MLC-induced DNA synthesis to a variable extent; thymidine incorporation induced by Salmonella marcescens lipopolysaccharide in mouse spleen cell cultures was strongly inhibited (by 75% or more) by 10-6 M coformycin. Combination of 10-7-10-8 M coformycin and 10-4-10-5 M adenosine synergistically inhibited mitogen- or MLC-induced DNA synthesis in human and mouse lymphocyte cultures. These results, together with observations on children with ADA deficiency, suggest that ADA is highly important for lymphocyte proliferation. Human peripheral blood lymphocytes incubated with PHA, 10-5 M adenosine and 10-7 M coformycin showed some cytotoxicity; the rate of 51Cr release from normal lymphocytes was not modified by the drugs. In vivo clones of lymphocytes responding to specific antigens might be eliminated by coformycin. Coformycin may be useful as a specific immunosuppressive agent.