Determination of relative antigen-antibody avidities by radial immunodiffusion

Radial immunodiffusion can be used to determine relative antigen-antibody avidities in exactly the same way as demonstrated previously for quantitative immunoelectrophoresis (Birkmeyer et al., 1981). Antigen-antibody interactions of greater avidity result in a greater value of (delta Area/delta [Antigen]) in plots of immunoprecipitin circle area versus antigen concentration while interactions of equal avidity will yield equal values of (delta Area/delta [Antigen]). This was demonstrated using antigens of different weight ranging from 8000 to 66,000.