The relationships between serum complement activity and the development of allergic lesions in rabbits.

Total serum hemolytic complement activity is consistently reduced in animals undergoing accelerated "serum sickness". The time of maximum reduction in complement titer invariably coincides with the time of complete antigen disappearance. This temporal relationship supports the belief that the reduction in complement titer is brought about by in vivo antigen-antibody combination. The intravenous administration of a single daily large dose of BGG-precipitated complexes produces a marked but temporary reduction in total complement hemolytic activity. On the other hand, multiple injections of soluble BGG immune complexes prepared in antigen excess failed to even temporarily alter complement titers. Animals undergoing the development of accelerated "serum sickness" treated by either type immune complex showed a significantly reduced incidence of arterial lesions. Apparently, this inhibiting effect on the development of arterial lesions was independent of variations in total complement hemolytic activity.