Full text loading...
Chapter 14 : Quantitation of Anti-Pneumococcal Capsular Antibody in Ligand-Binding Assays
Category: Bacterial Pathogenesis; Immunology
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
This chapter provides a historical overview of the ligand-binding assays currently recommended by the World Health Organization (WHO) to evaluate immune responses to polysaccharide (PS)-based vaccines against Streptococcus pneumoniae. These assays are designed to quantitatively measure serotype-specific antibody concentrations in the sera of subjects participating in treatment and control groups in clinical trials. The chapter discusses the utility of other types of pneumococcal immunoassays and provides our perspective on critical parameters for maintaining a bridge to previously established serologic correlates associated with the vaccine efficacy. The first pneumococcal vaccines were introduced in the 1940s for adults and included serotype-defining capsular PSs purified from four to six serotypes. The use of highly purified water for injection is recommended for buffers to prevent background noise in the enzyme-linked immunosorbent assays (ELISAs). The accurate measurement of pneumococcal PS (PPS)-specific antibodies is challenging because naturally occurring antibodies in sera can bind to cell wall PS (CPS) as well as to other covalently bound and copurified antigens of S. pneumoniae. While the ELISA is well suited for screening large numbers of specimens against a single analyte, a separate assay is required for each pneumococcal serotype. The current ELISAs provide a solid foundation for the future development, validation, and interlaboratory standardization of new ligand-binding assays for such applications.
Comparison of anti-PPS antibody assignments for sera using two different CPS absorbents ( 90 ). Pre (n = 32)- and post (n = 31)-immunization sera from infants immunized with an experimental five-valent PCV were tested using either crude Wyeth PnA or purified CPS from the SSI to assess a comprehensive antibody concentration range. A representative comparison is shown here, for anti-PPS serotype 18C. The relatively crude PnA preparation performs equivalently to the purified CPS from SSI in the Quataert et al. assay for all five serotypes: 6B (y = 0.919x + 0.091; r = 0.981), 14 (y = 1.022x + 0.075), 19F (y = 0.972x + 0.037; r = 0.985), and 23F (y = 0.978x + 0.080; r = 0.997) (data not shown).
Scatter plot of antibody concentrations assigned by qualifying (WHO-designated) and Wyeth laboratories ( 102 ). Both laboratories ran on three separate occasions a panel of adult sera (n = 61) covering a broad range of antibody concentrations, using the same protocol but using independently obtained reagents, materials, equipment, and software. The most notable difference is that two different pneumococcal absorbents were used; Wyeth laboratory used PnA while the WHO laboratory used CPS (SSI). Scatter plots (those for serotypes 1 [PN1] and 23F [PN23F] are shown) of the antibody concentrations by serotype as determined by the WHO versus the Wyeth laboratory closely matched the line of congruence, with the regression line very close to 1 and the intercept close to 0. The R 2 value was greater than 0.96 for all serotypes tested (1, 4, 5, 6B, 9V, 14, 18C, 19F, and 23).
Validation of ELISAs for quantification of antibodies to multiple serotypes of S. pneumoniaea