In vivo activation of C3 revealed by crossed immunoelectrophoresis as a parameter of immunological activity in disease.

A technique suitable for the demonstration of in vivo activation of the third component of complement (C3) is described, and the results of detailed methodological studies are presented. The technique is a useful tool for monitoring the activity of the humoral immune system in disease states. The serum levels of complement components reflect a balance between synthesis and catabolic rates, while the present method gives a more dynamic picture of the state of the complement system. The results of the application of the technique to different groups of patients are presented.