The quantitative relation between complement and complement fixing antibody

In the course of investigation on precipitin and complement fixing antibodies produced by injections of edestin, it was observed that, while the serum of a rabbit immunized with this protein showed the presence of precipitin antibodies, it did not show any complement fixing antibodies when employing the usual 2 units of complement in the fixation tests. It appeared reasonable at first to accept this finding as evidence of the lack of relation between these two types of antibodies. It seemed, however, that possibly the employment of 2 units of complement in the tests might give a sufficient excess of this ingredient to render a serum negative for complement fixing antibodies, although a reasonable number of such antibodies might still be present in the serum. With this possibility in mind, a series of complement fixation tests were carried out, using complement gradations of 1¼ units, 1½ units, 1¾ units and 2 units. The quantity of serum employed was 0.01 c.c. It was observed that the same serum which gave negative results when 2 units of complement were employed, gave weak positive results with 1¾ units of complement; stronger positive results with 1½ units; and still stronger with 1¼ units of complement. In the last case the serum showed slight anticomplementary properties, which disappeared after about 10 minutes' incubation in the water bath. This work is still being continued, but the results obtained thus far indicate that the employment of 2 units of complement in complement fixation tests is too great an excess of this ingredient for correct results in some cases, and that the employment of lesser quantities of complement, properly controlled, would serve as a finer measure of the complement fixing power of a given serum.