Detection of complement activation in immune complex diseases: six methods compared.
We compared the performance of six complement tests: electrophoresis, immunofixation, immunoelectrophoresis, and nephelometric quantifications of C3, C4, and C3d. We used 123 blood samples from 60 control subjects and 63 patients with immune complex diseases: systemic lupus erythematosus, idiopathic thrombocytopenic purpura, rheumatoid arthritis, acquired immunodeficiency syndrome, renal diseases, vasculitis, cryoglobulinemia, Gram-negative bacteremia, Hashimoto's thyroiditis, rheumatic heart disease, malaria, and chronic active hepatitis. Immunofixation and quantification of C3d were better for detecting complement activation, their sensitivity rates (90.5% and 89.3%, respectively) being higher than those of the other tests studied. Immunofixation is a relatively simple and inexpensive test, provides good resolution of protein bands, and yields results that are easily quantified with a densitometer. Nephelometry of C3d provides more rapid and accurate quantitative results than immunofixation, but commercial reagents are not yet available. The causes of false-positive results in complement tests and the mechanisms of complement activation in AIDS are also discussed.
D000163:Acquired Immunodeficiency Syndrome / Q000276:immunology; D001798:Blood Proteins / Q000032:analysis; D003167:Complement Activation; D003176:Complement C3 / Q000032:analysis; D015933:Complement C3d; D004586:Electrophoresis / Q000379:methods; D005189:False Positive Reactions; D006801:Humans; D007105:Immune Complex Diseases / Q000175:diagnosis / Q000276:immunology*; D007120:Immunochemistry; D009391:Nephelometry and Turbidimetry
D001798:Blood Proteins; D003176:Complement C3; D015933:Complement C3d