This study first established conversion factors between different international units through absorption equivalence ELISA, enabling comparability of serum concentrations for anti-HBs, anti-SARS-CoV-2 RBD and NP, and anti-tetanus toxin IgG. It was found that anti-tetanus toxin IgG median concentrations were significantly higher than anti-HBs and anti-SARS-CoV-2 antibodies, while NP-specific IgG exceeded RBD-specific IgG in early post-infection phases. These findings are critical for evaluating humoral immunity induced by different vaccines.
Literature Overview
This study, 'Conversion Factors to Compare Serum Concentrations of Anti-HBs, Anti-SARS-CoV-2, and Anti-Tetanus Toxin IgG', systematically established conversion factors between international units using absorption equivalence ELISA, enabling cross-comparison of serum concentrations for anti-HBs, anti-SARS-CoV-2 RBD/NP, and anti-tetanus toxin IgG. The research also revealed dynamic antibody concentration changes after infections or vaccinations, offering new insights into plasma cell pool assessment.
Background Knowledge
In immunology, serum antibody concentrations are typically expressed in international units (IU or BAU) rather than mass concentrations (e.g., µg/mL), limiting comparisons between antibodies of different specificities. Although WHO provides standard sera for anti-HBs IgG, anti-SARS-CoV-2 IgG, and anti-tetanus toxin IgG, these units are arbitrarily defined and cannot be directly compared across standards. Therefore, standardizing these units to enable antibody concentration comparisons remains a critical challenge in vaccine immunogenicity assessment and humoral immunity research. This study introduced an absorption equivalence ELISA method using an influenza NP-specific monoclonal antibody (mAb SR2-NP66/67) as a reference standard, enabling systematic comparisons of serum IgG concentrations across antigens. The conversion factors revealed relative concentration differences between anti-HBs, anti-SARS-CoV-2, and anti-tetanus toxin IgG, advancing antibody detection standardization and offering new perspectives on vaccine-induced humoral immunity.
Research Methods and Experiments
The study coated high-binding microplates with HBs, SARS-CoV-2 RBD and NP, tetanus toxin (Ttx), and influenza NP proteins. Using absorption equivalence ELISA, international unit standards (e.g., WHO anti-HBs IgG 07/146, anti-SARS-CoV-2 IgG 20/136 and 21/340, anti-Ttx IgG 13/240) were compared against mAb SR2-NP66/67 by measuring OD values and constructing concentration-OD curves. Polynomial fitting calculated equivalence conversion factors between units. Serum samples from 54 SARS-CoV-2-infected or vaccinated individuals were analyzed for anti-HBs, anti-RBD, anti-NP, and anti-Ttx IgG concentrations, which were then standardized to µg/mL equivalents of mAb SR2-NP66/67 for cross-specificity comparisons.
Key Conclusions and Perspectives
Research Significance and Prospects
This study establishes the first cross-unit conversion framework for antibody concentrations, providing a foundation for serological test standardization. Future applications include evaluating additional vaccine- or infection-related antibodies, elucidating long-term humoral immunity dynamics, and plasma cell pool characteristics. Clinically, the method can enhance antibody deficiency monitoring in children and vaccine response assessments, improving comparability and practicality of antibody concentration measurements.
Conclusion
This research successfully established unit conversion factors between anti-HBs, anti-SARS-CoV-2 RBD/NP, and anti-tetanus toxin IgG using absorption equivalence ELISA, enabling standardized comparisons of serum antibody concentrations across specificities. The study demonstrates significantly higher median concentrations of anti-tetanus toxin IgG compared to anti-HBs and anti-RBD IgG, with NP-specific antibodies dominating in early SARS-CoV-2 infection. These findings underscore antigen-specific differences in humoral immune responses and provide standardized tools for vaccine immunogenicity assessment, humoral immunodeficiency analysis, and clinical antibody monitoring. Future work will expand this methodology to other vaccines/diseases, further characterizing plasma cell pool dynamics and secretion kinetics to enhance immunological assay accuracy and cross-comparability. Notably, serum antibody concentrations not only reflect vaccine immunogenicity but also indirectly indicate plasma cell numbers and antibody secretion levels, offering theoretical support for personalized immune monitoring and vaccine response optimization.
