Abstract: 　Objective To investigate the role of cytokines interferon gamma (IFN γ) and interleukin 4 (IL 4) in host defense to Pneumocystis carinii infection. Method Two different murine models (IFN γ or IL 4 gene knockout C57BL/6 mice,15 mice each strain) were contagiously infected with P.carinii by cohousing with P.carinii positive mice for 3,5,7 weeks as well as 15 gene un knockout C57BL/6 mice for infection control group. Another 15 non contagious C57BL/6 mice were as the normal control group. The number of P.carinii ,the CD4 + and CD8 + T cells, and specific IgG were detected. Results The number of P.carinii differed in different groups of mice cohabited with P.carinii infected mice. The number of the organisms in the lungs of IFN γ knockout mice increased significantly ( P < 0.05),showed a slight increase in the lungs of IL 4 knockout mice as well as the gene un knockout mice ( P > 0.05). The CD4 +and CD8 + T cells response was in parallel to the burden of cysts in the lungs but specific lgG increased gradually in 3 groups after co housing. Conclusion IFN γ is important in host for defense from P.carini infection. Absence of IL 4 does not affect the resistance of mice against P.carinii infection.

Key words: IFN γ, IL 4, Pneumocystis carinii infection, Resistance