Quantitative Studies of the Reaction of Complement Fixation with Tuberculous Immune Serum and Antigen

Abstract

Summary and Conclusions: Studies of the fixation of complement by tubercle antigen and immune serum have been extended to include observations with more widely varying quantities of each reagent. In experiments covering a wide range of concentration of complement, there was a linear relation, on the one hand, between complement and immune serum when antigen was present in sufficient amount to give the maximal reaction obtainable with the quantities of serum tested and, on the other hand, between antigen and complement when immune serum was present in sufficient amount to give the maximal reaction with quantities of antigen tested. By determining the ratios of the slopes of the straight-line graphs representing these relationships, constant values for the specific reactive capacity of antigen with immune serum were obtained. The normal horse serum used in diluting the immune serum had no appreciable effect upon the results. Comparisons of complement activity were made in relation to the point of 50 per cent hemolysis because the form of the hemolytic curve may vary with experimental conditions which necessitate different volumes of complement, without, however, appreciably affecting the region near 50 per cent hemolysis. The 50 per cent point may be determined by interpolation. These quantitative studies provide a basis for the accurate determination of the activity of immune serum and antigen in relation to each other and to complement and appear to be applicable both to experimental studies of the reactions of immune sera and antigens and to the development of practical tests for the diagnosis of disease.