Preparation and immunogenicity of serogroup B meningococcal OS-OMPC conjugates

The objective of the present study is to purify oligosaccharides (OSs) from serogroup B meningococci (3407 or 542852) with common lipooligosaccharide (LOS) immunotypes prevalent in China and to successfully conjugate them to their outer membrane protein complexes (OMPCs). Conjugates possessing broad cross-reactivity with different serogroup B meningococci were obtained. Both LOSs from the above two strains were purified on a Sephadex G75 column and hydrolyzed with acetic acid, and then the pure OSs were obtained by using a Sephadex G50 chromatographic column. The pure OSs were conjugated to corresponding OMPCs by carbodiimide mediated condensation. Mice were immunized with the OS-OMPC conjugates to produce antibodies. Immunogenicities of the conjugates were tested by ELISA, bactericidal test and Western-blotting. The titers of antibodies against OS and LOS elicited by the two OS-OMPC conjugates increased respectively by 2.5 and 2 to 10 times as compared with those of antibodies against unconjugated OS and LOS. The sera elicited by the conjugates possessed a stronger bactericidal activity to the strains (3407, 542852, 29021) with the same LOS immunotype than to the strain with different LOS immunotype (86155). The results determined by ELISA indicated that the sera against the conjugates showed strong response to the strains with the same or different LOS immunotypes. It was confirmed by western-blotting analysis that the sera elicited by the two conjugates reacted with 42, 39 and 26 kDa proteins from the OMPC. Among the reactive bands, the 42 kDa proteins were class 1 OMPs. The two serogroup B meningococcal OMPCs were strong immunogens and good carriers coupling with OSs as well. The immunogenicity of the conjugated OS was increased and the OS-OMPC conjugates of the serogroup B meningococci showed a broad antigenic response to the strains tested.