RESUMEN
Objective To investigate the distribution and sequence conservation of Hap adhensin encoding gene (hap) in clinical isolates of nontypeable Haemophilus influenzae (NTHi), to screen out and identify the predominant T-and B-cell (T-B) combined antigenic epitopes on Hap protein and to analyze their immunogenicity.Methods Sequence conservation of hap genes in NTHi strains and T-B combined antigenic epitopes were predicted using bioinformatic softwares.PCR was used to amplify the 156 bp segment at 5′-end and the 855 bp segment at 3′-end of hap gene (hap-5′-156 and hap-3′-855) and the amplified products were sequenced.Phage display systems of seven T-B combined antigenic epitopes located on the 55 aa segment at N-terminal and the 285 aa segment at C-terminal of Hap protein (Hap-N52 and Hap-C285) were constructed.Western blot assay and ELISA were performed to detect the antigenicity and immunoreactivity of different T-B combined epitopes displayed by recombinant phage PⅢ protein (rPⅢ).Results Hap protein encoded by the hap gene in NTHi was located on membrane surface.Sequences of the 156 bp segment at 5′-end and the 855 bp segment at 3′-end of hap genes extracted from different NTHi strains were relatively conservative, but many mutations were found in sequences at the middle regions of these hap genes.All of the 56 NTHi strains carried hap-5′-156 and hap-3′-855 segments and shared 92.3％-100％ identities in nucleotide and amino acid sequences of these segements.Hap-N5-24 in the Hap-N52 segment as well as Hap-C4-27, Hap-C28-47, Hap-C114-129, Hap-C150-173, Hap-C200-227 and Hap-C241-267 in the Hap-C285 segment was predicted as the T-B combined antigenic epitope with a higher score and less mutations.Results of Western blot assay and ELISA confirmed that the rPⅢ-displayed Hap-C4-27 and Hap-C150-173 epitopes presented clear hybridization bands with NTHi antisera, and 96.9％ (63/65) and 92.3％ (60/65) of serum samples from children with NTHi infection were positive for antibodies against Hap-C4-27 and Hap-C150-173 epitopes, respectively.Conclusion The gene of hap is widely distributed in clinical isolates of NTHi.Moreover, sequences of the 156 pb segment at 5′-end and the 855 bp segment at 3′-end of hap gene are conservative.Hap-C4-27 and Hap-C150-173 are the predominant T-B combined antigenic epitopes on Hap protein, suggesting that they can be used as epitope candidates for developing multiple antigenic peptide vaccines against NTHi.
RESUMEN
Objective To measure the concentrations of antibodies against outer membrane protein P6 and its T-and B-combined antigenic epitopes of nontypeable Haemophilus influenzae ( NTHi) in children and adults of different ages and to evaluate the differences among different subjects for further investigation on NTHi multiple antigenic peptide vaccine .Methods A prokaryotic expression system was established to ex-press the recombinant outer membrane protein P 6 of NTHi.The expressed protein was purified by using Ni-NTA affinity chromatography .T-and B-cell epitopes in protein P6 were predicted with Epitope prediction software 1.0 and ANTIGENIC program and were used to synthesize T-and B-combined antigenic epitopes .A total of 605 subjects aged from 1 day to 103 years old were recruited from October 2013 to March 2014 .Ser-um concentrations of antibodies against protein P 6 and its T-and B-combined antigenic epitopes were meas-ured by using ELISA .Mann-Whitney U test was used to analyze the differences between groups .Pearson product-moment correlation coefficient was used for correlation analysis .Results Four T-and B-combined antigenic epitopes including P 6-2, P6-61, P6-95 and P6-122 were predicted and synthesized .The levels of antibodies against NTHi P6 and P6-2, P6-61, P6-95 and P6-122 were significant lower in the <1 months group than those in the 1-6 months group (all P<0.001) and 7 months-3 years group (all P<0.001).Three groups including 7 months-3 years group , 4-6 years group and 7-14 years group showed significant differ-ences regarding to the antibodies levels , among the 7 months-3 years group showed the highest levels , fol-lowed by the 4-6 years group and the 7-14 years group.However, no significant difference was found be-tween other adjacent groups .Concentrations of antibodies against P 6-2, P6-61, P6-95 and P6-122 were pos-itively correlated with the level of antibody against P 6 (P<0.0001).Conclusion The distribution of anti-bodies against T-and B-combined antigenic epitopes in P6 was highly in accord with those against P6, which indicated good immunogenicity of those epitopes .The highest antibodies levels were found in subjects aged 7 months to 3 years old , which might correlate with the high risk of NTHi infection at that stage .