Affinity diffusion. I. Method for measuring dissociation constants of precipitating antibodies

Area of Science:

• Immunochemistry
• Biophysical Chemistry

Background:

• Antigen-antibody interactions are fundamental in immunology and diagnostics.
• Quantifying the dissociation constant (Kd) is crucial for understanding binding affinities.
• Gel precipitation methods offer a visual approach to studying these reactions.

Purpose of the Study:

• To determine the dissociation constant (Kd) of antigen-antibody reactions.
• To investigate the relationship between diffusion rates and precipitate formation in gels.
• To compare results using whole antiserum versus purified IgG fractions.

Main Methods:

• Monodimensional single diffusion in antibody-containing gels.
• Measurement of precipitate front progression over time.
• Varying antibody concentrations to analyze diffusion rates.
• Utilized bovine serum albumin (BSA) and rabbit anti-BSA system.

Main Results:

• Determined a dissociation constant (Kd) of approximately 1.0 x 10-5 moles per liter.
• Observed that the precipitate front progression rate was significantly faster than the antigen's molecular diffusion coefficient.
• Consistent results were obtained using both whole antiserum and purified IgG.

Conclusions:

• Gel diffusion methods can effectively determine antigen-antibody dissociation constants.
• The observed faster precipitate front progression suggests complex interactions beyond simple diffusion.
• The study validates the use of purified IgG for accurate Kd determination.