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Some Factors Influencing the Selection of a Complement-Fixation Method

I. A Comparison of Two Quantitative Technics, and an Alternative Method of Expressing Serum-Dilution Titer

Division of Animal Pathology, Science Service, Dominion Department of Agriculture, Animal Diseases Research Institute, Hull, Quebec (Canada)

Abstract

Requirements in regard to accuracy and the difficulties likely to be encountered in evaluation of the results are the two major factors governing the selection of a quantitative complement-fixation method. In this paper, two quantitative complement-fixation procedures are evaluated on these bases.

If only a rough estimate of antibody activity is needed, the serum dilution titer determined by method 1 is adequate. If however a more precise measurement of antibody content is required, method 2 will prove more satisfactory. Especially will this be the case in comparison of the relative efficiency of different methods of preparing antigen, in determination of antigenic relationships or in measurement of the relative specific, non-specific and cross-activities of a serum.

When antigens are crude containing relatively large amounts of extraneous material, method 1, which employs a lower antigen dose may be preferable. If so, calculation of the increment ratio titer as indicated in the second section of this paper, may give a more precise estimate of titer than the usual method of recording serum-dilution titers in terms of the dilution factor. Not only do the increment ratios provide a sharper differentiation in relative titers than the latter, but they enable the reactions of anticomplementary sera to be recorded in numerical terms. Furthermore, it is possible to introduce a correction factor for variation in the stability of different lots of complement during preliminary incubation. The use of increment ratios in defining the relative "specific" and "nonspecific" activities of sera is also described.