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1.  Avidity Determinations for Haemophilus influenzae Type b Anti-Polyribosylribitol Phosphate Antibodies 
Determination of antibody avidity measurements can be difficult in human serum depending on the population evaluated. We evaluated three approaches for the determination of antibody avidity for immunoglobulin G (IgG). These approaches were (i) elution of bound antibody with increasing concentrations of a chaotropic agent using a single serum dilution, (ii) binding interference of multiple serum dilutions by a single concentration of a chaotrope, and (iii) elution of multiple serum dilutions by a single concentration of a chaotrope. Parameters that affect the determination of avidity measurements and their limitations were evaluated with pre- and post-Haemophilus influenzae type b conjugate vaccination sera (n = 89). We determined that elution of low-avidity antibodies present in multiple dilutions of the serum sample by a single concentration of a chaotrope (0.15 M sodium thiocyanate [NaSCN]) was optimal for the determination of avidity measurements throughout a wide range of IgG concentrations (0.94 to 304.6 μg/ml). The percent reduction in concentration as determined by the elution assay with 0.15 M NaSCN correlated highly (r = 0.84) with weighted averages obtained by an elution assay with multiple solutions of NaSCN. The correlation (r = 0.57) between elution and binding interference, when a single concentration of a chaotrope was used, was lower than the correlation between the two elution methods (r = 0.84). We found that the serum dilution, the heterogeneity of the antibody population, and the concentration of the chaotrope were the primary variables affecting avidity determinations. In this study, we present multiple analysis methods depending on the methodology used. We also present the factors that affect the analysis of avidity determinations given the polyclonal nature of human sera. This experimental approach should benefit the evaluation of similar antibodies induced by other bacterial polysaccharide vaccines.
PMCID: PMC1235792  PMID: 16148167
2.  Specificity of the Antibody Response to the Pneumococcal Polysaccharide and Conjugate Vaccines in Human Immunodeficiency Virus-Infected Adults 
Nonspecific antibodies, which are thought to be nonprotective, have been shown to contribute a substantial proportion of the measured concentration in the standardized immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) for pneumococcal polysaccharide capsular antibodies. The presence of such antibodies in human immunodeficiency virus (HIV)-infected persons has not been evaluated. The amount of nonspecific antibodies is proportional to the reduction in IgG antibody concentration that occurs with serum absorption with the heterologous polysaccharide 22F. We measured the amount of nonspecific antibodies before and after vaccination with the pneumococcal conjugate vaccine (PCV; n = 33) or the pneumococcal polysaccharide vaccine (PPV; n = 34) in HIV-infected adults with CD4 counts of ≥200 cells/mm3. Blood was drawn before and 2 months after vaccination. For prevaccination sera, we found a substantial amount of nonspecific antibodies for serotypes 4, 6B, 9V, and 23F (23 to 47% of measured IgG concentration), but not for serotype 14. There tended to be proportionately less nonspecific antibodies in postvaccine sera than prevaccine sera for PCV, but not for PPV. Subjects with a low HIV viral load (≤400 copies/ml) had proportionately more nonspecific antibodies than those with higher viral load before and after both vaccines. After 22F absorption, the geometric mean concentrations of antibodies were significantly higher post-PCV than post-PPV for the high viral load group for all five serotypes, but for no serotypes in the low viral load group. These findings confirm that absorption with a heterologous pneumococcal polysaccharide (e.g., 22F) is necessary to remove nonspecific antibodies in a standardized IgG ELISA for pneumococcal capsular antibodies in HIV-infected adults.
PMCID: PMC321324  PMID: 14715560
3.  Specific, Sensitive, and Quantitative Enzyme-Linked Immunosorbent Assay for Human Immunoglobulin G Antibodies to Anthrax Toxin Protective Antigen 
Emerging Infectious Diseases  2002;8(10):1103-1110.
The bioterrorism-associated human anthrax epidemic in the fall of 2001 highlighted the need for a sensitive, reproducible, and specific laboratory test for the confirmatory diagnosis of human anthrax. The Centers for Disease Control and Prevention developed, optimized, and rapidly qualified an enzyme-linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) antibodies to Bacillus anthracis protective antigen (PA) in human serum. The qualified ELISA had a minimum detection limit of 0.06 µg/mL, a reliable lower limit of detection of 0.09 µg/mL, and a lower limit of quantification in undiluted serum specimens of 3.0 µg/mL anti-PA IgG. The diagnostic sensitivity of the assay was 97.8%, and the diagnostic specificity was 94.2%. A competitive inhibition anti-PA IgG ELISA was also developed to enhance diagnostic specificity to 100%. The anti-PA ELISAs proved valuable for the confirmation of cases of cutaneous and inhalational anthrax and evaluation of patients in whom the diagnosis of anthrax was being considered.
PMCID: PMC2730307  PMID: 12396924
Bacillus anthracis; anthrax; antibody; assay; toxin; bioterrorism; ELISA; serology
4.  An Analytical Model Applied to a Multicenter Pneumococcal Enzyme-Linked Immunosorbent Assay Study 
Journal of Clinical Microbiology  2000;38(6):2043-2050.
Pneumococcal conjugate vaccines will eventually be licensed after favorable results from phase III efficacy trials. After licensure of a conjugate vaccine for invasive pneumococcal disease in infants, new conjugate vaccines will likely be licensed primarily on the basis of immunogenicity data rather than clinical efficacy. Analytical methods must therefore be developed, evaluated, and validated to compare immunogenicity results accurately within and between laboratories for different vaccines. At present no analytical technique is uniformly accepted and used in vaccine evaluation studies to determine the acceptable level of agreement between a laboratory result and the assigned value for a given serum sample. This multicenter study describes the magnitude of agreement among 12 laboratories quantifying an identical series of 48 pneumococcal serum specimens from 24 individuals (quality-control sera) by a consensus immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) developed for this study. After provisional or trial antibody concentrations were assigned to the quality-control serum samples for this study, four methods for comparison of a series of laboratory-determined values with the assigned concentrations were evaluated. The percent error between assigned values and laboratory-determined concentrations proved to be the most informative of the four methods. We present guidelines that a laboratory may follow to analyze a series of quality-control sera to determine if it can reproduce the assigned antibody concentrations within an acceptable level of tolerance. While this study focused on a pneumococcal IgG ELISA, the methods that we describe are easily generalizable to other immunological assays.
PMCID: PMC86724  PMID: 10834951

Results 1-4 (4)