The effect of excess antigen on the enzyme-linked immunosorbent assay of onco-placental proteins.

The time course of the antigen-antibody reaction between human chorionic gonadotrophin, pregnancy specific beta 1 glycoprotein and pregnancy associated plasma protein A and their respective immobilised antibodies has been investigated. All 3 antigens showed enhanced binding with increasing length of incubation up to a maximum value, followed by a decrease. It is suggested that the diminution in binding at high antigen concentration is caused by the solubilisation of the immobilised antigen-antibody complex and that this is promoted by the high concentration of antigen.