Abstract Objective Asthma is a chronic non-specific inflammatory of the airways induced by Th2 type cells. IL-12 can inhibit Th2 immune response in the allergen sensitization stage. But whether it can inhibit the established Th2 immune responses is in question. In this study, the effect of IL-12 on the established Th2-type immune responses in asthma was examined in order to provide evidence for the clinical use of IL-12. Methods Experiment 1: Ovalbumin(OVA) and aluminium hydroxide were intraperitonearly injected into 25 female BALB/c mice of 6 - 8 weeks old to induce sensitization. Five mice were sacrificed before sensitization, and a further 5 more were sacrificed on 7, 14, 21 and 28 days after sensitization. The levels of Th2 cytokines IL-4 and IL-5 in the splenic mononuclear cells (MNCs) cultured supernatants were measured using ELISA to evaluate the time of Th2 immune response establishment. Experiment 2: Another 40 female BALB/c mice of 6 - 8 weeks old were sensitized by OVA and aluminium hydroxide intruperitonear injection. Then asthma was induced by OVA inhalation. Twenty asthmatic mice were selected randomly to receive recombinant IL-12 treatment ( 0.5 μg was dissolved in 1 mL PBS once daily for 5 days) from 25 days post-sensitization. The rest of the asthmatic mice (n=20) just received a PBS injection. The 40 asthmatic mice were sacrificed at 30 days post-sensitization. The levels of Th2 cytokines IL-4, IL-5, and Th1 cytokines INF-γ in the splenic MNCs cultured supernatants and in bronchoalveolar lavage fluid (BALF) were measured by ELISA. Results Experiment 1 showed that the concentrations of IL-4 and IL-5 in the splenic MNCs cultured supernatants in mice increased on the 14th day post-injection, which suggested that a Th2 immune response had been established. Experiment 2 showed that the concentrations of IL- 4 and IL-5 in BALF significantly decreased in the IL-12-treated asthmatic mice when compared with the untreated asthmatic mice (19± 5 pg/mL vs 192±19 pg/mL,141±15 pg/mL vs 328±71 pg/mL,P<0.001).The concentration of INF-γ remained unchanged, so the ratio of IL-4/INF-γ in BALF decreased in the IL-12-treated asthmatic mice. The concentrations of IL-4 and IL-5 in the splenic MNCs cultured supernatants were significantly decreased in the IL-12-treated mice (139±54 pg/mL and 98±18 pg/mL) compared with the untreated-asthmatic mice (341±64 pg/mL and 411±108 pg/mL,P< 0.001). In contrast, the INF-γ concentration increased (1 403±185 pg/mL vs 317±55 pg/mL,P< 0.001). Conclusions IL-12 can inhibit established Th2-type immune responses and can restore the Th1/Th2 balance.
