title: Inhibition of natural killer cell activity by therapeutic levels of theophylline.
abstract: Theophylline, as used for the treatment of asthma and chronic obstructive pulmonary disease, may have several effects, including direct bronchodilation, improvement in diaphragmatic and ciliary function, and possibly immune modulation. In this study, we quantified the capacity for theophylline to inhibit natural killer (NK) cells and investigated the mechanism(s) that mediate this inhibition. Theophylline at 10 micrograms/ml and 20 micrograms/ml inhibited the tumoricidal activity of isolated peripheral blood lymphocytes (PBL) by 19 +/- 5% and 36 +/- 6%, respectively (n = 6). Using fluorescence-activated cell sorting, we purified NK cells from PBL and tested theophylline's effects on the kinetics of tumor lysis (Vmax) and on tumor binding. Theophylline at 20 micrograms/ml reduced Vmax by 40 +/- 9% but had no effect on tumor binding. We compared the effects of theophylline, which is both a phosphodiesterase (PDE) inhibitor and an adenosine receptor (AdR) antagonist, with agents that range from relatively pure AdR antagonists to pure PDE inhibitors. Inhibition of NK activity occurred only with PDE inhibitors. We also extracted lymphocyte PDE and observed a direct correlation (r2 = 0.99) between theophylline's activity as a PDE inhibitor and its capacity to inhibit NK activity. These results suggest that theophylline inhibits NK cytotoxicity through its activity as a PDE inhibitor. The clinical relevance of these findings awaits further study.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, UCLA School of Medicine 90024.
authors.forename: L A
authors.initials: LA
authors.lastname: Coskey
authors.forename: J
authors.initials: J
authors.lastname: Bitting
authors.forename: M D
authors.initials: MD
authors.lastname: Roth
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D006801:Humans; D007694:Killer Cells, Natural / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D008214:Lymphocytes / Q000737:chemistry; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D058915:Purinergic P1 Receptor Antagonists; D013806:Theophylline / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D010726:Phosphodiesterase Inhibitors; D058915:Purinergic P1 Receptor Antagonists; D013806:Theophylline; D015105:3',5'-Cyclic-AMP Phosphodiesterases