Preparation of a human meningococcal reference serum and standardization of IgG concentrations to capsular polysaccharides and bactericidal activities against serogroup A, C, Y and W135 strains

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 , filtration, 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 international 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 immunized 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 samples, respectively.The bactericidal titers against serogroup A , C, Y and W135 strains were measured by serum bactericidal assay （SBA）.Results Four thousand vials （0.5 ml/vial）of lyophilized human meningococcal 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 immunodeficiency 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 . Key words: Human meningococcal reference serum; Antibody concentration; Enzyme-linked immunosorbent assay （ELISA） ; Serum bactericidal assay （SBA）