Concentration dependence of the binding constant of antibodies

By simultaneous dilution of the antigen (AG) and the antibody (AB) used in an immune precipitation reaction, at the equivalence AG/AB ratio, it was found that the association constant, K_a, increased from 1.7 × 10⁷ l/M at the highest concn of AG and AB, to 6.5 × 10¹¹ l/M at 100-fold dilution of both. An important (but not the only) reason for this increase is taken to be the fact that the AB solution was polyclonal.