Problems with radiolabelling egg albumin for the Farr ammonium sulphate technique for antibody estimation.

High concentrations of passive haemagglutinating antibodies were raised in sheep immunised with egg albumin (Ea) in Feund's adjuvant. Further attempts to study the antigen binding capacities and avidities of these antisera by the Farr ammonium sulphate technique were hindered by unsuccessful attempts to label Ea with 125Iodine by either the chloramine T or sodium nitrite-HCl methods. This problem was attributed to the unavailability of tyrosine in the native protein. This was solved by labelling Ea with the Bolton-Hunter reagent which does not require the presence of tyrosine. However labelled Ea binds non-specifically to normal serum to give high control values of circa 40% binding. Despite this it was possible to estimate antibody concentrations and avidities of lamb sera.