In order to express recombinant human interleukin 6 (rhIL 6) in Salmonella typhimurium x4550,a recombinant expression plasmid pYA3333 IL6 was constructed by using PCR amplification,site specific mutagenesis and DNA recombination in vitro.Hybridoma growth factor (HGF) activity of rhIL 6 was measured with an IL 6 dependent B cell hybridoma line B9.Results showed that the expressed rhIL 6 relative molecular weight 2 1×10 4 was accounted for 17.6%...