A screening assay for rapid and quantitative measurement of immunoglobulins and anti-immunoglobulins in unknown sera

Abstract

A radioimmunoassay which can measure serum levels of antibody and antigen when both species are immuloglobulins (Igs) is described. The technique is based on competition between insolubilized Ig (bound to Sepharose) and serum Ig for radiolabeled Ig. For measurement of anti-Ig antibodies, labeled Ig antigen is added to a mixture of antibody-Sepharose and unknown or standard antibody solution. For measurement of antigen, labeled, purified antibody is added to a mixture of antigen-Sepharose and unknown or standard antigen solution. Although both assays can detect either Ig antigen or Ig antibody in a given unknown, the antibody assay requires 10-20 times as much antigen as antibody to achieve the same degree of inhibition, and the antigen assay is 100 times more sensitive for antigen than for antibody. By titrating the same unknown in both assays, one can determine whether inhibitory activity is due to antigen or antibody. The routine assay readily detects 1 microgram/ml of antibody or of antigen. A modified assay was also developed which detects levels of antibody as low as 5-10 ng/ml. The technique is simple and allows rapid screening of hundreds of serum samples in a short period of time. The assay can also be modified for measurement of anti-idiotype antibodies.