Apparent chorionic gonadotropin immunoreactivity in human non-placental tissues: reduction by protease inhibitors or...

Thirty-three of forty-one non-placental human tissue samples analysed by radioimmunoassay (RIA) appeared to contain immunoreactive hCG-like material. Tissues with apparent hCG in appreciable quantity were exposed to heat or protease inhibitors to ascertain the contribution of proteolytic enzyme activity to the observed immunoreactivity. Following incubation with protease inhibitor N-alpha-p-tosyl-L-lysine chloromethyl ketone-HCl (TLCK) at a dose that has no effect on the hCG standard curve and reduces the assayable hCG in term placenta by less than 20%, the hCG-like immunoreactivity of testicular and colon tissues was reduced by 39 to 90%. Similarly, heat treatment virtually eliminated hCG-like immunoreactivity of non-placental normal tissues, but had little effect on purified hCG or hCG present in term placenta. The factor present in normal non-placental human tissue giving positive results in the RIA for hCG is not identical to native hCG; it may be proteolytic in nature thus influencing the radioligand assay. The residual immunoreactivity measured following heat treatment of purified hCG increases when anti hCG-beta antiserum is used, but decreases when either anti hCG-alpha or anti-hCG is used.