Quantitation of a highly immunogenic leukocyte antigen (L1) by radioimmunoassay: methodological evaluation

This paper describes a radioimmunoassay (RIA) for the quantitation of a major protein antigen (L1) released from human granulocytes. A protein A-carrying strain of Staphylococcus aureus was used as a solid phase IgG-binding reagent for the separation of antigen-antibody complexes from free antigen in the assay. A two-step version of the RIA may be completed in 2.5 h and has a detection limit of about 5 ng/ml. The sensitivity may be increased by minor modifications. A single step version takes 1.5 h and has adequate sensitivity to cover clinically important plasma levels. Selection and optimal use of reagents for the two-step procedure is described and their storage discussed. The simplicity of the procedure combined with high sensitivity and satisfactory accuracy, precision and reproducibility makes this assay suitable for quantitation of L1 in various body fluids.