Measurement of endotoxin. I. Fundamental studies of radioimmunoassay of endotoxin.

A method for estimating endotoxin by radioimmunoassay was recently introduced. The present paper describes improvements in the speed and sensitivity on this endotoxin measurement. Antigen was purified from E. coli O111: B4 (B) lipopolysaccharide by centrifugation and dialysis. Purified anti-endotoxin antibody was prepared from immunized rabbit serum. A radioimmunoassay system was established with the antigen and antibody. Dextran-coated charcoal was used to separate the antibody-bound antigen from free antigen. Experimental studies were also performed on possible factors related to the antigen-antibody reaction. Accurate measurements on quantities as low as 100 pg/ml (10ng/ml in the plasma) were performed by the dextran-coated charcoal method, and the reaction time was reduced to 2 hr at 4 degrees C. This new method does not require strict sterilization or aseptic handling, and therefore is quite practical for quantitative measurements of endotoxin.