Binding parameters of antibodies reacting with multivalent antigens: functional affinity or pseudo-affinity

Area of Science:

• Immunology
• Biochemistry
• Biophysics

Background:

• Bivalent antibodies binding multivalent antigens, like cell surface targets, are often assessed using 'functional affinity'.
• However, the underlying equations for affinity are strictly applicable only to monovalent interactions.
• This discrepancy raises concerns about the validity of 'functional affinity' in complex biological systems.

Discussion:

• 'Functional affinity' is shown to be an invalid metric because it fails to accurately represent antibody-antigen interactions.
• A key issue is that the dissociation of bivalent antibodies from multivalent antigens is typically not a first-order reaction.
• This non-first-order dissociation complicates direct comparisons based on traditional affinity calculations.

Key Insights:

• 'Functional affinity' does not accurately describe the complex binding dynamics of bivalent antibodies to multivalent antigens.
• Dissociation kinetics, particularly over extended periods until near-complete dissociation, provide a more reliable method for comparing antibody efficacy.
• Focusing on dissociation rates offers a more scientifically rigorous approach to understanding antibody-antigen interactions.

Outlook:

• Future research should prioritize the characterization of dissociation kinetics over 'functional affinity' for antibody evaluation.
• Developing standardized methods for measuring long-term dissociation will be crucial for advancing antibody-based therapeutics and diagnostics.
• This shift in methodology promises more accurate comparisons and a deeper understanding of antibody binding mechanisms.