AIM: To investigate the effect of theophylline on the naive T cell differentiation and the probable role of interleukin- 12 (IL-12). METHODS: Naive cord blood T cells were treated with theophylline 10 mg/L for 3 d after stimulation with PHA 100 mg/L. Differentiation of Tcells was analyzed by flow cytometry. Theophylline 10 mg/L and IL-12- mAb 0.025 mg/L were added in cord blood mononuclear cell (CBMC) cultures primed with LPS 1 mg/L to detect the levels of IL-12 and IL-12P40. The whole blood cultures were obtained from twelve health volunteers with or without administration of theophylline (200 mg). Cytokines were measured by enzyme linked immuno-sorbent assay. RESULTS: Theophylline promoted T helper 1 (Th1) cells differentiation from naive T cells (21.9 %±10.3 % vs 9.4 %±5.6 %, P<0.05), but had no significant effect on Th2 deviation. But theophylline inhibited the production of IL-12 and IL-12P40 by CBMC in vitro (28±6 ng/L vs 57±14 ng/L and 88±34 ng/L vs 214±82 ng/L, P<0.01) and reduced IL-12 and IL-12P40 levels in whole blood cultures from healthy subjects (19±11 ng/L vs 31±15 ng/L and 92±13 ng/L vs 196±49 ng/L, P<0.01). CONCLUSION: Theophylline promoted the differentiation of Th1 cells. IL- 12 seemed not to be involved in this process. AIM: To investigate the effect of theophylline on the naive T cell differentiation and the probable role of interleukin-12 (IL-12). METHODS: Naive cord blood T cells were treated with theophylline 10 mg / L for 3 d after stimulation with PHA 100 mg / L. Differentiation of Tcells was analyzed by flow cytometry. Theophylline 10 mg / L and IL-12-mAb 0.025 mg / L were added in cord blood mononuclear cell (CBMC) cultures primed with LPS 1 mg / L to detect the Levels of IL-12 and IL-12P40. The whole blood cultures were obtained from twelve health volunteers with or without administration of theophylline (200 mg). Cytokines were measured by enzyme linked immuno-sorbent assay. RESULTS: Theophylline promoted T helper 1 ( Th1) cells differentiation from naive T cells (21.9% ± 10.3% vs 9.4% ± 5.6%, P <0.05) but had no significant effect on Th2 deviation. But theophylline inhibited the production of IL- 12 and IL- 12P40 by CBMC in vitro (28 ± 6 ng / L vs 57 ± 14 ng / L and 88 ± 34 ng / L vs 214 ± 82 ng / L, P < 0.01) and reduced IL-12P40 levels in whole blood cultures from healthy subjects (19 ± 11 ng / L vs. 31 ± 15 ng / L and 92 ± 13 ng / L vs 196 ± 49 ng / L, P < 0.01). CONCLUSION: Theophylline promoted the differentiation of Th1 cells. IL- 12 seemed not to be involved in this process.