In order to explore the role of activator protein-1 (AP-1) in the transcription of interleukin-5 (IL-5) gene regulated by protein kinase C (PKC) signal in peripheral blood T lymphocytes from asthmatic patient, T lymphocytes were isolated and purified from peripheral blood of each asthmatic patient. The T lymphocytes were randomly divided into 4 groups: group A (blank control), group B (treated with PKC agonist phorbol 12-myristate 13-acetate (PMA)), Group C (treated with PMA and AP-1 cis-element decoy oligodeoxynucleotides (decoy ODNs)), and group D (treated with PMA and AP-1 mutant decoy ODNs). The ODNs were transfected into the T cells of group C and D by cation liposome respectively. Reverse transcription-polymerase chain reaction (RT-PCR) was employed to assess IL-5 mRNA expression, and electrophoretic mobility shift assays (EMSA) for the activation of AP-1. The results showed that the activation of AP-1 (88 003. 58+/-1 626.57) and the expression of IL-5 mRNA (0.8300+/-0.0294) in T lymphocytes stimulated with PMA were significantly higher than these in blank control (20888.47 +/- 1103.56 and 0.3050 +/- 0.0208, respectively, P< 0.01), while the indexes (23219.83 +/- 1024.86 and 0.3425 +/- 0.0171 respectively) of T lymphocytes stimulated with PMA and AP-1 decoy ODNs were significantly inhibited, as compared with group B (P< 0.01). The indexes (87107.41 +/- 1342.92 and 0. 8225 +/- 0.0222, respectively) in T lymphocytes stimulated with PMA and AP-1 mutant decoy ODNs did not exhibit significant changes, as compared with group B (P>0.05). The significant positive correlation was found between the activation of AP-1 and the expression of IL-5 mRNA (P< 0.01). It was concluded that AP-1 might participate in the signal transduction of PKC-triggered transcription of IL-5 gene in asthmatic T lymphocytes. This suggests the activation of PKC/AP-1 signal transduction cascade of T lymphocytes may play an important role in the pathogenesis of asthma.