A double antibody radioimmunoassay for mouse hemoglobins: Use of polyethylene glycol in conjunction with the second antibody

Abstract

A double antibody radioimmunoassay (RIA) system is described for detection of small quantities of hemoglobins. Mouse (C57BL/6) hemoglobin and horse anti-mouse hemoglobin antiserum were used to develop the system. The first phase of the RIA, i.e., the initial reaction between the antigen and the antibody, was found to be complete within 24 h. The reaction proceeded better at 4°C than at 25°C. The second phase, i.e., separation of bound from unbound antigen, was achieved by precipitation with a second antibody (goat anti-horse IgG) and polyethylene glycol (PEG). A 50 g/l concentration of PEG was found to be best suited for the assay. Mixing of all the reagents together was found to decrease the binding as compared to the system in which second antibody and PEG were added after completion of the first phase. Maximum precipitation of the complex took place within 30 min after the addition of the second antibody and 1 h after the addition of 50 g/l PEG. The RIA system described here combines the conventional double antibody RIA with the PEG method. This method has decreased the amount of time necessary for precipitation from 24 h (or longer) to 1 h. Large molecular weight antigens could not be estimated in the conventional PEG method because of their insolubility in 200 g/l PEG utilized in the assay. The use of a low concentration of PEG along with the second antibody in the method described here allows the estimation of large molecular weight antigens. This double antibody-PEG method has a general applicability for small as well as large molecular weight antigens.