Abstract
Precipitin is identical with the antibody effective in passive sensitization. This is demonstrated by injecting a guinea-pig with the precipitate formed by a mixture of horse serum with the serum of a rabbit immunized thereto. This guinea-pig, if tested after an interval of three days by the intravenous injection of horse serum, presents a violent, at times a fatal anaphylactic response.
If the precipitating antibody is heated at 72° for one half hour, it loses its precipitating functions, but retains its sensitizing power, though somewhat diminished. Such heated precipitin, sometimes described as “precipitinoid,” is known to retain its combining power with antigen. One may conclude, therefore, that the combining power, but not the precipitating power, of antibody is essential in anaphylaxis.
Precipitating antibody heated at 72° for one half hour has lost its capacity to bind complement in the presence of antigen. However, it still retains its sensitizing value. These facts are illustrated by the following experiment.
The serum of a rabbit, immunized to crystallized egg albumen, is diluted with three volumes of salt solution. Part of this diluted serum is heated at 56° for one half hour to destroy complement, and part of it is heated at 72° for one half hour to destroy the precipitating function. In the following table the amounts of diluted serum employed are reduced to correspond to the amount of serum therein contained. The method employed is that of complement fixation.
After incubation for one hour, one C.C. of well-sensitized cells was added to each of the tubes. Hemolysis was complete in tubes 2 to 6 after one half hour, but had not even begun in I. On the following day tube I showed slight hemolysis. The test was made with the usual additional controls.
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