ABSTRACT
Objective To investigate the distribution and sequence conservation of genes encoding the outer membrane lipoprotein D(LPD)of nontypeable Haemophilus influenzae(NTHi)isolates and to ana-lyze the immunogenicity and the immunoprotective effects of the expressed recombinant LPD(rLPD). Meth-ods PCR analysis was used to detect the genes encoding LPD of NTHi isolates. The PCR products were se-quenced after T-A cloning. A prokaryotic expression system for genes encoding LPD was established to ex-press the rLPD. Ni-NTA affinity chromatography was used for purification. SDS-PAGE and Bio-Rad Gel Im-age Analyzer were used to detect the expression and the yield of rLPD. The antigenicity and immunoreactivity of rLPD were detected by ELISA and Western blot assay. The immunoprotective effects of rLPD against lethal dose of NTHi were evaluated in a mouse model. Results All of the tested NTHi isolates were positive for the genes encoding LPD. They shared 98. 0% -99. 4% homologies in nucleotide sequences and 98. 5% -100% homologies in amino acid sequences. The established prokaryotic expression system expressed rLPD with a high yield. High levels of antibody in rabbits were induced by the rLPD. The anti-NTHi antiserum samples from rabbits and children could recognize and react with the rLPD. The result of ELISA indicated that 93. 6%(58 / 62)and 53. 2%(32 / 62)of the serum samples from children with NTHi infection were positive for rLPD-IgM and rLPD-IgG,respectively. The rLPD at concentrations of 100 μg and 200 μg could respectively protect 60. 0% and 73. 3% of mice from lethal NTHi infection. Conclusion The genes enco-ding LPD were extensively distributed in NTHi isolates with high sequence conservation. The expressed rLPD could be used as a potential candidate antigen in the development of genetic engineering vaccine against NTHi infection considering its high immunogenicity and immunoprotective effects.