AN IMPROVED SANDWICH ELISA METHOD FOR THE DETERMINATION OF IMMUNOREACTIVE SCHIZOPHYLLAN (SPG)

As it is important to determine the optimal serum concentration of sch izophyllan (SPG) when it is used as an anti-cancer drug, we devised a solid-phase ELISA. We also developed a sandwich ELISA using murine ant i-SPG monoclonal antibody as the first antibody and rabbit anti-SPG se rum as the second antibody in order to improve the detection sensitivi ty. This assay was able to determine SPG concentrations over 1.0 ng/ml and the absorbance at 490 nm was directly proportional to the SPG con centration. SPG in rabbit serum, obtained after intravenous and intram uscular injection (SPG; 10 mg/kg), was determined by this sandwich ELI SA. Furthermore, the sensitivity of this ELISA method was compared wit h that of the Limulus test. The Limulus test is able to detect SPG in physiological saline (pH 6.3) at concentrations greater than 1.0 mu g/ ml, but the sensitivity increased when SPG was dissolved in alkaline s olution (pH 12.0), enabling SPG to be measured almost down to 1.0 ng/m l. These data suggest that our sandwich ELISA may be used for the meas urement of SPG in blood or tissue.