Abstract
While making serological studies of several transplanted rabbit cancers by the methods that disclosed a distinctive substance in the Brown-Pearce carcinoma, 1 we have noted that the blood serum of normal rabbits will fix complement in mixture with saline extracts of normal rabbit tissues in dilutions far beyond any anticomplementary or summative effects. This phenomenon appears to be due to a natural antibody that reacts with sedimentable constituents of normal tissues.
The antibody can be detected by means of a standardized complement fixation test in which 2 units of complement are employed and 2 hours at room temperature allowed for fixation. Antigens are prepared by extracting normal rabbit tissues (liver, kidney, brain, etc.—either fresh or preserved frozen at −22°C) with sand in a mortar, suspending the ground paste in physiological saline (1:10 to 1:40 or more) and centrifuging at 4400 rpm for 20 minutes. The unheated supernatant liquids, opalescent but free from gross particles, have proved notably effective in the tests.
When the sera of 22 normal adult rabbits were mixed with antigens consisting of 1:20 or 1:40 saline extracts of normal rabbit livers, fixation invariably occurred, and it was complete with many of the sera in dilutions as high as 1:16 to 1:64. No fixation was got when the sera of 13 rabbits less than 4 weeks old from 7 litters were tested concurrently with the same antigens. None of the sera proved anticomplementary in dilutions of 1:2 or more in concurrent tests though a few showed slight anticomplementary effect when a double volume of the 1:2 dilution was tested, and the antigens were not anticomplementary when 4 and 8 times the standard amount were employed in control tests.
Experiments were next undertaken to ascertain some of the properties of the substance present in the serum of normal adult rabbits which is responsible for the fixation.
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