RESEARCH ARTICLE Immune Responses to HBsAg Conjugated to Protein D of Non-Typeable Haemophilus influenzae in Mice

Background Hepatitis B vaccine that contains an aluminum hydroxide adjuvant induces apoptotic death of Hepa 1–6 cells. Difficult-to-degrade chemical additives in vaccines effectively enhance vaccine immunogenicity, but also affect the host tissue. Identification of bio-molecules that are readily degraded and compatible in vivo as an adjuvant is important for vaccine re-search. The hapten–carrier effect suggests that stimulation of helper T (Th) cells by carrier adjuvants is feasible. Protein D (PD) of non-typeable Haemophilus influenzae covalently conjugated to some polysaccharide vaccines has been confirmed to convert T-cell indepen-dent (TI) antigens into T-cell dependent (TD) antigens, and elicit strong T-cell responses ul-timately. Herein, we would substitube PD for aluminum hydroxide adjuvant in Hepatitis B vaccine. Methods and results Truncated PD (amino acids 20–364) was expressed in Escherichia coli and purified by (NH4)2SO4 precipitation and DEAE chromatography. After evaluation of antigenicity b