Background: The basis for the efficacy of theophylline in the treatment of asthma remains enigmatic. Although commonly classified as a bronchodilator, its ability to dilate smooth muscle is considered fairly poor and clinical responses are often independent of bronchodilation. Recent studies have suggested that immunomodulatory activities may contribute to the therapeutic benefit mediated by theophylline.
Objective: We performed these preliminary studies to determine whether theophylline modulates cytokine production by peripheral blood mononuclear cells.
Methods: Peripheral blood mononuclear cells were obtained from 24 asthmatic subjects and were left in a resting state or stimulated with either mitogens (phytohemagglutinin, lipopolysaccharide) or antigen (tetanus, cat) with or without the additional presence of theophylline (15 micrograms/dL). Supernatants were collected and evaluated for cytokine concentration by ELISA.
Results: Theophylline neither inhibited production of allergenic cytokines such as IL-4 nor modulated the repertoire of cytokines produced by TH cells. A statistically significant inhibition of spontaneous interferon-gamma synthesis was observed (24.5 +/- 8.6 to 13.4 +/- 4.2; P < .05). Theophylline did have anti-inflammatory effects on cytokines primarily produced by mononuclear phagocytic cells. Theophylline mediated a slight inhibition of TNF-alpha production (0.26 +/- 0.08 to 0.21 +/- 0.06; P < .05). Theophylline was also associated with a 2.8-fold increase in spontaneous production of the anti-inflammatory cytokine IL-10 (0.35 +/- 0.08 to 0.98 +/- 0.16 ng; P < .01).
Conclusions: A relative absence of IL-10 characterizes the asthmatic airways and may contribute to the development and severity of allergic inflammation. Induction of IL-10 production by theophylline may therefore mitigate inflammation and contribute to the clinical efficacy of this class of medications.