Effects of theophylline on human natural killer cells

Theophylline has been shown previously to inhibit a number of cellular immune functions of granulocytes and T-lymphocytes. In the present report, we demonstrate that theophylline, in a dosedependent fashion, suppresses human natural killer (NK) cell activity in vitro. To determine if theophylline produces quantitative or qualitative alterations in NK cells in vivo we quantitated peripheral blood NK cells with three monoclonal antibodies and FACS analysis and measured NK cytolytic activity in eight normal volunteers who took theophylline for eight days. No change was noted in the number or cytolytic activity of NK cells over the eight days of monitoring. We conclude that theophylline does not alter NK cells in vivo when given in therapeutic doses.