Background: The affinity of an antibody to its antigen is a crucial parameter in its biological activity and performance of an immunoassay such as ELISA. Affinity of most IgG specific MAbs are often determined by methods which require labeling of either antigen or antibody, and are sometimes difficult to control, do not always lead to the expected signal and often result in immunological modification of the molecules. Moreover, direct solid phase binding assays pose some problems such as diffusion effects and difficulties in reaching equilibrium due to heterogeneous binding and co-operativity.
Objective: To employ a rapid and simple ELISA-based method for measuring affinity constants of two pan-h-IgG specific MAbs (3F2D8 and 5F19G11) established in our laboratory.
Methods: The method is based on the effect of antibody affinity on the sigmoidal dose response curve. In this method, the binding of anti-human IgG (anti-h-IgG) MAbs with their corresponding antigen was measured using serial concentrations of both antigen and antibody. The amount of antibody bound to the antigen on the plate is represented as a sigmoidal curve of OD versus the logarithm of antibody concentration added to each well.
Results: Based on the data obtained from this study, the affinity constants of 3F2D8 and 5F19G11 MAbs were 0.74 x 10 8 Mol –1 and 0.96 x 10 7 Mol –1, respectively.
Conclusion: 3F2D8 MAb with reasonably high affinity is suggested as a candidate for quantitative measurement of IgG by ELISA, whereas 5F19G11 MAb could be considered as a suitable tool for immunoaffinity chromatography.