ABSTRACT
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 (P0.05).The percentage of serum sam-ples with serogroup C-specific IgG concentration ≥2 μg/ml rose from 20%to 99% after vaccination ( P0.05), 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 .
ABSTRACT
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 .
ABSTRACT
Objective To analyze the levels of human serum antibody against Neisseria meningitidis serogroup C measured by serum bactericidal assay (SBA) and ELISA.Methods SBA and a modified ELISA were applied to measure the serum bactericidal titer and the specific concentration of immunoglobulin G (IgG) against meningoeoccal serogroup C in sera samples.Seventy-five sera were from healthy adults without undertaking vaccination while another 429 and 388pre- and post- vaccinated sera were from 143 infants and 194 young children immunized with conjugate vaccine or polysaccharide vaccine,respectively.Correlation between serum bactericidal titer and the concentration of specific IgG against meningococcal serogroup C was analyzed.Results The concentration of meningococcal serogroup C specific IgG in healthy adults showed a strong correlation (r=0.814 33,P＜0.001 ) with serum bactericidal titer through linear regression analysis.Weak correlation was observed between SBA titers and IgG concentration in pre vaccinated sera of infants and children ( conjugate/polysaccharide vaccine ) ( infants:r =0.140 64,P ＞ 0.100/r =0.2899,P＜0.05; children:r=0.540 40,P＜0.05/r=0.194 36,P＜0.05).After immunization with 2-dose conjugate vaccine in infants and 1-dose in children,a strong correlation between the two panels of results was observed (r=0.809 38,P＜0.001 and r=0.837 23,P＜0.001 respectively).However after immunization with polysaccharide vaccine,the correlation between serum bactericidal titer and concentration of specific IgG was weak (r＜0.500 00).Conclusion Among healthy adults and post vaccinated infants or young children immunized with conjugate vaccine,the concentration of specific IgG was comparable to the serum bactericidal titer against meningococcal serogroup C.However,it was not unfavorable to use ELISA as the principal means of measuring serum antibody responses to polysaccharide vaccine for infants under 1 year old.