Immune complex diseases complement activation

CH50 determinations can be used to analyze the total serum complement and are useful for monitoring immune complex diseases (Sullivan, 1989) activation of complement (Table 15.13) in the presence of autoantibodies is indicative of immune complex diseases and autoimmunity. The various components of the complement system (C3, C4) can also be measured to assess the integrity of the system. For instance, low serum concentrations of C3 and C4, with a concomitant decrease in CH50 may indicate activation of complement, while a low C4 alone is a sensitive indicator of reduced activation of the complement system. Since C3 is used as an alternate complement pathway, it usually measures high. Therefore, a low C3 with a normal C4 may indicate an alternate pathway of activation. 

Whereas complement and its role in immune complex diseases have been described above (Sect. D.1.2), there appears to be a number of instances of untoward reactions to drugs in which complement activation may play a major role. Anaphylactic reactions have been described following the development of drug-specific antibodies of the IgG type capable of activating complement. In some cases, such as an immediate-type reaction following the intravenous injection of protamine sulfate (Lakin et al. 1978), homocy to tropic antibodies of IgG type capable of passively transferring the reaction have been demonstrated. Such antibodies have a short sensitization period, are stable to heating at 56 °C and seem to require complement to induce the anaphylactic reaction. 

Type III reactions (immune-complex reactions) In type III reactions, formation of an immune complex and its deposition on tissue surface serve as primary initiators. Occasionally, immune complexes bind to endothelial cells and lead to immune-complex deposition with subsequent complement activation in the linings of blood vessels. Circumstances that govern immune formation or immune-complex disease remain unclear to date, and it usually occurs without symptoms. The clinical symptoms of a type III reaction include serum sickness (e.g. 3-lactams), drug-induced lupus erythematosus (e.g. quinidine) and vasculitis (e.g. minocycline). Type III reactions can result in acute interstitial nephritis or serum sickness (fever, arthritis, enlarged lymph nodes, urticaria and maculopapular rashes) [1-3]. 

H14. Harkiss, G. D., Hazleman, B. L., and Brown, D. L., A longitudinal study of circulating immune complexes, DNA antibodies, and complement in patients with systemic lupus erythematosus. An analysis of their relationship to disease activity. ]. Clin. Lab. Immunol. 2, 275-283 (1979). 

Systemic lupus erythematosus is a systemic inflammatory disease with formation of autoantibodies against DNA, wide spread immune complex deposition and complement activation. Symptoms include arthritis, a characteristic butterfly rash on the face, myalgia, glomerulonephritis, vasculitis, pericarditis and inflamed and fibrosed lungs. 

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