Use of the direct linear plot to estimate, in an immunoglobulin solution, the proportion which is specific monoclonal antibody against an unknown cell surface antigen.

A Cornish-Bowden direct linear plot was used to assess the level of specific monoclonal antibody in a protein A preparation from mouse ascitic fluid. With this method, experimental observations are plotted directly as lines in parameter space and estimates of kinetic parameters are read directly from the plot without need for further calculation. This method is particularly well suited for the analysis of systems, such as the one outlined here, where conventional kinetic analysis is not possible because the preparation contains both specific and non-specific antibody. Results obtained with the direct linear plot showed that estimates of the level of specific immunoglobulin present in a given protein A preparation are consistent, not only within individual experiments, but also throughout a series of experiments using more than one labelled antibody preparation.