Recombinant Protein D from Haemophilus influenzae Induces Mouse Bactericidal Antibodies Against Typeable and Non-Typeable Haemophilus influenzae, which Partially Protect Infant Rats Against Serotype b Bacteraemia
Authors:   Bacteriology Division, National Institute for Biological Standards and Control, MHRA, Potters Bar, Hertfordshire EN6 3QG, UK and Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, 138673 Singapore, Palmer Nathan , Tan Yajun ,   National Institutes for Food and Drug Control, No.31, Huatuo Road, Bio-Pharmaceutical Industrial Base, Daxing District, Beijing, 102629, P. R. China, Saydam Manolya ,   Bacteriology Division, National Institute for Biological Standards and Control, MHRA, Potters Bar, Hertfordshire EN6 3QG, UK, Felek Arif ,   Bacteriology Division, National Institute for Biological Standards and Control, MHRA, Potters Bar, Hertfordshire EN6 3QG, UK, Zhang Huajie ,   National Institutes for Food and Drug Control, No.31, Huatuo Road, Bio-Pharmaceutical Industrial Base, Daxing District, Beijing, 102629, P. R. China, Zhang Shumin ,   National Institutes for Food and Drug Control, No.31, Huatuo Road, Bio-Pharmaceutical Industrial Base, Daxing District, Beijing, 102629, P. R. China, Fang Min ,   Bacteriology Division, National Institute for Biological Standards and Control, MHRA, Potters Bar, Hertfordshire EN6 3QG, UK, Wheeler Jun X. ,   Bacteriology Division, National Institute for Biological Standards and Control, MHRA, Potters Bar, Hertfordshire EN6 3QG, UK, Hou Qiming ,   National Institutes for Food and Drug Control, No.31, Huatuo Road, Bio-Pharmaceutical Industrial Base, Daxing District, Beijing, 102629, P. R. China, Ma Xiao ,   National Institutes for Food and Drug Control, No.31, Huatuo Road, Bio-Pharmaceutical Industrial Base, Daxing District, Beijing, 102629, P. R. China, Wang Junzhi ,   National Institutes for Food and Drug Control, No.31, Huatuo Road, Bio-Pharmaceutical Industrial Base, Daxing District, Beijing, 102629, P. R. China, Mawas Fatme ,   Bacteriology Division, National Institute for Biological Standards and Control, MHRA, Potters Bar, Hertfordshire EN6 3QG, UK
Published: February 2022

Aim To evaluate the immunogenicity of a recombinant protein D from Haemophilus Influenzae (Hi) and the functional activities of the induced protein D antibodies in a mouse model. Methods Female Balb/c mice were immunised subcutaneously with recombinant protein D in the presence or absence of adjuvants and the serum immunoglobulin G (IgG) response to protein D was assessed by ELISA. The functional activity of the immune sera was evaluated in vitro using bactericidal assay against typeable Hi serotype b (Hib) and non-typeable Hi (NTHi) clinical isolates and in vivo using an infant rat bacteraemia model and a Hib clinical isolate. Results A dose-dependent IgG response was induced in mice immunised with the recombinant protein D and this response was further increased by the adjuvants used [CPG, AlPO4 and Al(OH)3], with the latter showing the greatest effect on the antibody response. Immune sera were very effective in bactericidal assay against several Hib and NTHi clinical isolates, with a higher serum bactericidal titre against the NTHi than against the Hib isolates. This is possibly due to the lower expression of protein D on the Hib isolates used in our study, compared to the NTHi isolates. In addition, anti-protein D antibodies were partially protective in vivo infant rat bacteraemia model against a challenge with Hib Eagan strain. Conclusion Our results suggest that recombinant protein D is a good vaccine candidate against Hi and should be given in combination with other vaccine candidates to ensure complete protection against Hib and NTHi.