COMPARISON OF NON PARALLEL IMMUNOASSAY CURVES RESULTING FROM MIXTURESOF COMPETING ANTIGENS

Relative potency is a measure that has been used for many years to sum marize the comparison of dose-response curves in parallel line bioassa ys. When response curves for two preparations are not parallel the tra ditional definition of relative potency no longer applies. We review t he concept of relative potency and show that, in some situations, it c an be given meaning for non-parallel curves as the ratio of biological activity in full strength assay preparations. Under an assumption tha t non-parallel curves result from the competition of mixtures of antig ens for receptor binding sites, estimation of relative potency for non -parallel curves can be accomplished. We show that estimation of model s for both parallel curve and response attenuation situations may be a ccomplished within the framework of generalized linear models. This es timation depends on the ability to deal with non-linear parameters app earing in the link function, and an iterative algorithm depending on d irect parameter updates is outlined. The topics discussed are illustra ted with the analysis of data from two immunoassays conducted with vet erinary vaccines. The models developed here depend in an essential way on the assumption of response attenuation by competing antigens. Our methods may not be appropriate for non-parallel curves caused by other phenomena. (C) 1997 by John Wiley & Sons, Ltd.