Immunization with Protein D from Non-Typeable Haemophilus influenzae (NTHi) Induced Cytokine Responses and Bioactive Antibody Production

BACKGROUND: Outer membrane protein D (PD) is a highly conserved and stable protein in the outer membrane of both encapsulated (typeable) and non-capsulated (non-typeable) strains of Haemophilus influenzae. As an immunogen, PD is a potential candidate vaccine against non-typeable H. influenzae (NTHi) strains. OBJECTIVES: The aim of this study was to determine the cytokine pattern and the opsonic antibody response in a BALB/c mouse model versus PD from NTHi as a vaccine candidate. METHODS: Protein D was formulated with Freund’s and outer membrane vesicle (OMV) adjuvants and injected into experimental mice. Sera from all groups were collected. The bioactivity of the anti-PD antibody was determined by opsonophagocytic killing test. To evaluate the cytokine responses, the spleens were assembled, suspension of splenocytes was recalled with antigen, and culture supernatants were analyzed by ELISA for IL-4, IL-10, and IFN-γ cytokines. RESULTS: Anti-PD antibodies promoted phagocytosis of NTHi in both immunized mice groups (those administered PD + Freund’s and those administered PD + OMV adjuvants, 92.8% and 83.5%, respectively, compared to the control group). In addition, the concentrations of three cytokines were increased markedly in immunized mice. CONCLUSIONS: We conclude that immunization with PD protects mice against NTHi. It is associated with improvements in both cellular and humoral immune responses and opsonic antibody activity.