AFFINITY OF MONOCLONAL-ANTIBODIES - INTERPRETATION OF THE POSITIVE COOPERATIVE NATURE OF ANTI-HCG/HCG INTERACTIONS

The interaction of some individual MAbs and human chorionic gonadotrophin (hCG) showed apparent positive cooperativity as observed by equilibrium binding studies. This form of cooperative interaction has now been further characterized. The main results were: (1) the apparent positive cooperativity was strongly dependent upon concentration and temperature; (2) the cooperativity was strongly reduced by using peptic F(ab')2 fragments of IgG and became undetectable when the MAb was replaced by the corresponding Fab fragment; (3) the molecular weight of the complex changed from 226 kDa to 450 kDa upon increasing the hCG/MAb ratio. From these and additional results it is hypothesized that the apparent positive cooperativity results from self (Fc-Fc) associations mediated or facilitated by prior antigen binding.