Comparison of several in vitro assay methods for the quantitative determination of complement consumption ('binding')...

Unspecifically induced activation of Complement (C) in solution can be caused either by denatured Ig molecules and by polymeric aggregates of same or more specifically by antigen-antibody complexes. As a quality criteria, e.g. for i.v.-IgG preparations, it is agreed by the majority of people concerned that the activation of C via the classical pathway might not be unspecifically initiated. Therefore, the generally used assay systems are based on quantitating the degree of consumption of C undergoing an antigen-independent, 'frustrated' activation via the classical pathway. There are principally two different types of test modifications which were investigated: a) C is being kept constant and protein is diluted or b) protein is being kept constant and C is titrated. When a group of differing IgG preparations or IgG fragments was assayed for its so-called 'anticomplementary' activity in various already described test methods, the particular test results from the individual test methods could not unequivocally be compared with each other because some of the methods had not been optimized with regard to the amount of reagents or test substance used; only a rough estimate of the data was obtained. The value of the not standardized assays remains, therefore, questionable reasonably good and reproducible results are obtained when the amount in particular of C added as well as its quality have been adequately optimized and standardized. This allows a refined differentiation of various IgG preparations by a reliable and unadjusted quantitation of C consumption. If for example, inappropriate and not optimized rations of C amboceptor (e.g. slight C excess) was used, a suppressed C consumption was found. It seems advisable to accept prophylactic testing of anticomplementary activity for quality control as one out of several other in vitro and in vivo parameters which potentially might predict safety for the patient, the physician, and also for the producer. However, it is agreed that, irrespective of in vitro tests, in vivo testing in animals and clinical proof of safety is undoubtedly needed.