A PUTATIVE MECHANISM FOR THE NONSPECIFIC UPTAKE OF INTACT RADIOLABELED MONOCLONAL-ANTIBODIES IN THE TESTES AND PROSTATE

Non-specific testicular accumulation of radiolabelled intact anti-CEA monoclonal antibody (MAb), (A431/26, Behringwerke AG) was observed in 11 out of 12 patients with the testes and prostate included in the exa mination field at radioimmunoscintigraphy (RIS), Previous studies have shown that placental alkaline phosphatase (PLAP) serves as an Fc-rece ptor, mediating IgG transport through the placenta, A closely related protein, the germ cell alkaline phosphatase (GCAP), is expressed in th e testes, The testicular uptake of IgG is observed only when intact bu t not fragmented MAbs are used, indicating involvement of Fc-receptors , MDCK cells (dog kidney cell line) transfected with the plasmid pSVT7 containing the GCAP gene were shown to acquire the capacity to both e xpress membrane bound GCAP and to bind Ige on the cell surface, This m ight indicate that GCAP is responsible for the non-specific accumulati on of intact MAb in the testes and prostate often observed when intact murine MAbs are used for radioimmunolocalization (RIL).