Development of a large scale human complement source for use in bacterial immunoassays.

Area of Science:

• Immunology
• Vaccinology

Background:

• The serum bactericidal assay is crucial for evaluating meningococcal vaccines.
• Assessing vaccine efficacy is complicated by the need for human complement, which is difficult to source due to widespread natural immunity.
• Variability in complement sources hinders inter-laboratory and inter-strain comparisons.

Purpose of the Study:

• To develop a standardized method for preparing human complement for immunological assays.
• To overcome challenges in sourcing consistent human complement for meningococcal vaccine assessment.
• To enable reliable comparisons of vaccine responses across different strains and in large clinical trials.

Main Methods:

• Developed an IgG-depletion method using Protein G sepharose affinity chromatography on pooled human plasma.
• Recovered and reconstituted C1q, which was co-depleted with IgG.
• Assessed retained complement activity, including alternative pathway activity and hemolytic activity, and complement component levels.

Main Results:

• Successfully prepared large batches of IgG-depleted human complement that retained significant alternative pathway (96.8%) and total hemolytic (84.2%) activity.
• Key complement components (C3, C5, properdin, factor H) were retained.
• The prepared complement was suitable for serum bactericidal activity and antibody-mediated complement deposition assays against Neisseria meningitidis serogroup B.

Conclusions:

• The developed method provides a consistent and reliable source of human complement for immunological assays.
• This standardization facilitates direct comparisons of meningococcal vaccine responses in large-scale clinical studies.
• Enables robust assessment of antibody-mediated immune responses to diverse meningococcal strains.