Binding and structural diversity among high-affinity monoclonal anti-digoxin antibodies

Area of Science:

• Immunology
• Biochemistry
• Structural Biology

Background:

• Monoclonal antibodies targeting digoxin are valuable tools for structure-function studies.
• Understanding antibody-antigen interactions is crucial in immunology and drug development.

Purpose of the Study:

• To generate and characterize high-affinity monoclonal antibodies against the cardiac glycoside digoxin.
• To investigate the structure-function relationships between antibody-combining sites and digoxin's antigenic determinants.
• To explore the diversity of immune responses to a single hapten.

Main Methods:

• Production of monoclonal antibodies using hybridoma technology (spleen cells fused with myeloma cells).
• Radioimmunoassay (RIA) to determine antibody affinity constants (10^9 to 10^12 M-1).
• Inhibition RIA using digoxin analogs to assess antibody binding specificities.
• N-terminal amino acid sequence analysis of monoclonal antibody heavy (H) and light (L) chains.

Main Results:

• Fifteen high-affinity monoclonal anti-digoxin antibodies were successfully produced.
• Antibodies exhibited diverse binding specificities, with some targeting the aglycone and others the sugar moiety of digoxin.
• Antibodies were classified into eight sets based on binding specificities and into several sequence homology sets for H- and L-chains.
• Homologous antibody sequences did not consistently correlate with similar antigenic specificities or affinities, indicating complexity beyond VH- and VL-encoded sequences.

Conclusions:

• The study highlights the significant diversity of immune responses elicited by a single hapten, even in inbred mice.
• Antibody fine specificity for digoxin is not solely determined by VH- and VL-encoded sequences.
• Monoclonal anti-digoxin antibodies provide a model system for dissecting antibody-antigen interactions.