0.05).The concentration of IL-6 in sputum of multi-virus infection group(122.51?39.86)ng/L was higher than in single virus infection group(65.30?34.92)ng/L.The concentration of IL-6 in sputum of bacteria-virus mixed infection group(120.31?46.62)ng/L was higher than in bacteria or virus single infection group(83.61?47.83)ng/L.Conclusion Streptococcus pneumonia and influenza virus A infection are important factors in AECOPD at early stage.Virus infection would prolong recovery time,increase inflammation of the airway and even induce bacteria infection.Therefore,we should pay more attention to the virus infection in COPD patients,especially A-type influenza virus.

Objective To screen a Madin-Darby canine kidney (MDCK) cell line for H5N1 influ-enza virus isolation and to evaluate its safety in vaccine production. Methods MDCK cells were cloned by the method of limiting dilution. Hemagglutination test was used to screen MDCK cells that were suitable for H5N1 influenza virus production. Tests for analyzing the characteristics, extraneous agents, endogenous agents and tumorigenicity of MDCK cells were performed according to Chinese Pharmacopeia Volume Ⅲ. Results A total of 108 MDCK cell lines were obtained and three of them were selected after hemagglutina-tion test. G1 cells were chosen following further screening with tumorigenicity test and receptor abundance analysis. The average number of chromosomes of the MDCK-G1 cells was 78±4. No bacteria, fungi or myco-plasma contamination was detected. In experimental group, each nude mouse was injected with 1×107/ml viable cells to observe their tumorigenicity. Twelve weeks after cell injection, no node was found at injection sites or in gross anatomy. There was no significant difference between the experimental and negative control groups. The result of the tumorigenicity test was negative. No node formation was found after injecting nude mice with cell lysate or cellular DNA collected from equivalent amount of cells. It was indicated that the MDCK-G1 cells were of low-oncogenic potential. Conclusions The MDCK-G1 cell line could be used as a substrate to produce H5N1 influenza virus vaccine.