Establishment and verification of a quantitative ELISA assay for detection of human serotype specific IgG against Streptococcus pneumoniae

  Objective   To establish a quantitative enzyme-linked immunosobent assay (ELISA) recommended by World Health Organization (WHO) for the detection of human serotype specific immunoglobulin G (IgG) against Streptococcus pneumoniae (Sp).

  Methods  According to WHO′s operation manual for Enzyme linked immunosobent assay ELISA for the quantitative of Streptococcus pneumoniae serotype specific IgG (Pn PS ELISA), we established a ELISA method to detect serotype specific IgG against Sp in human serum specimens by using Sp capsular polysaccharide 4, 6B, 9V, 14, 18C, 19F, and 23F (purchased American Type Culture Collection, ATCC) as coating antigens and pneumococcal capsular polysaccharide antibody standard serum 007 sp (from National Institute for Biological Standards and Control, NIBSC) as standard serum. The accuracy and stability of the established method were evaluated using WHO′s calibration serum panel and internal quality control serum PnG.

  Results  The concentration of 7 serotype specific coating antigens of Sp capsular polysaccharide (4, 6b, 9V, 14, 18C、19F and 23F) were determined and serotype specific IgG against Sp in human serum specimens were detected with the quantitative ELISA method established. More than 75% of measurements for 7 serotype specific Sp capsular polysaccharide IgG antibodies for 12 WHO calibration sera were within ± 40% of the measurement values assigned by reference laboratories of WHO, with an overall consistency rate of 86.9%, a correlation curve slope of 0.94, and an R² of 0.99, respectively. In addition, the results of 20 consecutive internal quality control serum test showed that the coefficient of variation (CV) of different batches were less than 15%, which met the requirements of WHO intra-laboratory evaluation.

  Conclusion   A quantitative ELISA method recommended by WHO for detection of serotype-specific Streptococcus pneumoniae IgG antibody in human serum was successfully established and verified. The accurate and stable method meet the requirements of disease surveillance and vaccine effect evaluation.