Objective To investigate the molecular size distribution and the structure of group B me-ningococcal capsular polysaccharides for the development of vaccines .Methods The molecular size distribution of group B meningococcal capsular polysaccharides was analyzed by chromatography on a Sepharose CL -4B col-umn.The molecular weight of repeat units were measured by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS).The structural characteristics of group B meningococcal capsular polysaccharides were analyzed by nuclear magnetic resonance ( NMR) based on the chemical shift of all charac-teristic protons by using group C meningococcal capsular polysaccharides and sialic acid as the controls .Results The KD value of group B meningococcal capsular polysaccharides extracted from 15 strains were ranged from 0.60 to 0.76.The molecular weight of repeat units was 284, which was identical to the theoretical value .The group B meningococcal capsular polysaccharides were 2→8 linked homopolymers of sialic acid lacking O-acetyl groups.Conclusion The group B meningococcal capsular polysaccharides had lower molecular weights , which might result in their poor immunogenicity .The structure of group B meningococcal capsular polysaccharides could be quickly and accurately analyzed by NMR technology .

Objective To re-evaluate the immunogenicity of meningococcal serogroups A and C polysaccharide vaccine among a healthy population of age 5 to 59.Methods Pre and post-vaccination ser-um samples were collected from the subjects involved in a randomized , controlled clinical trial conducted in 2005 at Hechi, Guangxi, China.Enzyme-linked immunosorbent assay (ELISA) was performed for the quan-titative detection of specific anti-capsule IgG antibody against meningococcal serogroups A and C in serum samples.Serum bactericidal assay ( SBA) was used to measure the bactericidal antibody activity against se-rougroups A and C bacterial strains .Results Geometric mean concentrations (GMCs) of specific anti-cap-sule IgG antibody were 23.66 μg/ml and 78.83 μg/ml for serogroup A (P<0.05), and 1.23 μg/ml and 51.25 μg/ml for serogroup C (P<0.05) in serum samples of pre and post-vaccination, respectively.Be-fore immunization , 99% of serum samples ( 97/98 ) showed serogroup A-specific IgG concentration ≥2μg/ml, which reached up to 100%(98/98) after vaccination (P>0.05).The percentage of serum sam-ples with serogroup C-specific IgG concentration ≥2 μg/ml rose from 20%to 99% after vaccination ( P<0.05).The ratio of positive serum samples with at least four times of increases in concentration of specific IgG against serogroup A and serogroup C after vaccine immunization were 34% and 100%, respectively . The rSBA geometric mean titers ( GMTs) for serogroups A and C in serum sample of post-vaccination were respectively elevated from 1164 to 5530 (P<0.05), and from 4 to 6225 (P<0.05).The percentage of se-rum samples with rSBA GMTs≥128 increased from 91% to 99% for serogroup A (P>0.05), and from 14%to 96%for serogroup C (P<0.05) after vaccination.The rSBA GMTs with at least four times of in-creases after vaccination were detected respectively in 53% and 100% of serogroups A and C vaccinated subjects.Pearson correlation coefficient between IgG concentration and rSBA GMTs was r=0.15 (pre) and r=0.23 (post) for serogroup A, and r=-0.14 (pre) and r=0.58 (post) for serogroup C (P<0.05). Conclusion This study has demonstrated an efficient and sustained immunogenicity with meningococcal sero -groups A and C polysaccharide vaccine as evidenced by the data from standardized assays of ELISA and SBA .

Objective To dynamically analyze the antibodies with regard to in vitro serum bacteri-cidal activity and the quantity of IgG in healthy adults received one dose of immunization with ACYW 135 me-ningococcal polysaccharide vaccine .To investigate the term of protection with polysaccharide vaccine and the correlation between bactericidal titer and IgG concentration .Methods Twenty healthy adults were given one dose of immunization with quadrivalent meningococcal polysaccharide vaccine .Serum samples were col-lected before and after vaccination at specific time points .Test for serum bactericidal activity ( SBA ) and quantitative ELISA were performed to detect bactericidal titers and IgG concentrations in serum samples .Re-sults Certain levels of antibodies against capsular polysaccharides of serogroup A , C, Y and W135 strains had already existed prior to immunization .Moreover, bactericidal titers against serogroup A , Y and W135 strains except serogroup C strain were relatively high .Specific IgG concentrations and bactericidal titers for all serogroup stains were significantly increased on day 15 after vaccination (P<0.05), and then sustained at a high level during a time period from day 30 to day 160.Both IgG concentrations and bactericidal titers dropped to the levels similar to that before preimmunization in about 3 years.No significant correlation was observed between bactericidal titers and IgG concentrations (r<0.3, P>0.05).However, a close correla-tion was demonstrated between GMTs and GMCs of serum samples (r>0.7, P<0.05).Conclusion The geometric mean titers ( GMTs) and geometric mean concentrations ( GMCs) of serum samples collected be-fore and after vaccination at different time points were reliable and consistent parameters for the evaluation of vaccine .The term of protection of quadivalent meningococcal polysaccharide vaccine was about 3 years upon a single dose of immunization .

Objective To prepare a human meningococcal reference serum and standardize IgG concentrations to capsular polysaccharides and in vitro bactericidal activities of the reference serum against serogroup A, C, Y and W135 strains.Methods Twenty healthy adults were recruited and given one dose of immunization with tetravalent (serogroups A, C, Y and W135) meningococcal polysaccharide vaccine . Plasma samples were collected and gone through a series of process treatments including defibrination , filtra-tion, and lyophilization to prepare the meningococcal reference serum Men 10.The IgG concentrations of Men10 to capsular polysaccharides of serogroups A , C, Y and W135 were calibrated by using an internation-al reference serum CDC1992 as the standard in enzyme-linked immunosorbent assay (ELISA).Provisional IgG concentrations of Men10 were intensively validated by testing a panel of 12 calibration serum samples from Centers for Disease Control and Prevention , USA ( US CDC) and a panel of 56 serum samples immu-nized with A, C, Y and W135 meningococcal polysaccharide vaccine from Lanzhou Institute of Biological Products Co., Ltd.(LIBP) with the assays using Men10 and CDC1992 as the standard and/or test sam-ples, respectively.The bactericidal titers against serogroup A , C, Y and W135 strains were measured by se-rum bactericidal assay (SBA).Results Four thousand vials (0.5 ml/vial)of lyophilized human meningo-coccal reference serum Men10 were successfully prepared with 2.5%of residual moisture .Reference serum Men10 was sterile and free from contamination by hepatitis B virus , hepatitis C virus , human immunodefi-ciency virus and syphilis .Provisional IgG concentration of Men 10 to capsular polysaccharide of serogroups A, C, Y and W135 was calibrated by using CDC1992 as the standard.Furthermore, IgG concentrations of both panels of 12 CDC calibration serum samples and 56 LIBP serum samples calibrated by using Men 10 as the standard correlated well with those by using CDC1992 as the standard (r=0.99,P<0.05).The IgG concentrations of CDC1992 as calibrated by using Men10 as the standard showed significant correlation with its previously determined values with variation <10%.SBA titers for serotype A , C, Y and W135 strains were established as well .Conclusion A panel of new human meningococcal reference serum Men 10 with accurately calibrated IgG concentration against capsular polysaccharide of serogroups A , C, Y and W135 as well as SBA titers was successfully established .