The Antigen-Antibody Reaction

Summary

1. 1. A quantitative study of the precipitin reaction has been made as a function of NaCl concentration. The system used was chicken ovalbumin and the homologous rabbit antibody separated into its eu- and pseudoglobulin fractions and the same antibody fractions and duck ovalbumin as the heterologous system.

2. 2. Using pseudoglobulin antibody, it was shown that in the virtual absence of salt the precipitin reaction not only persists but gives larger amounts of precipitate N in the equivalence and antigen excess zones than when NaCl was added. Furthermore, antigen excess inhibition occurs at much lower antigen concentrations in 9.0 and 0.9% than in 0.09% NaCl. In the 0.00% NaCl series about seven times the antigen N concentration of the equivalence zone is needed for partial inhibition, compared with about twice the equivalence zone antigen N needed for almost complete inhibition with 0.9% NaCl.

3. 3. Some of the possible causes for these differences are discussed. It is suggested and evidence is presented that rabbit pseudoglobulin antibody may contain at least two antibody fractions. One of these precipitates preferentially at the lowest sodium chloride concentration and only to a very small extent in 0.9% or higher salt concentration. For want of further defining criteria this fraction is tentatively called “salt sensitive” antibody. The rest of the pseudoglobulin antibody appears to be much less “salt sensitive.”

4. 4. In the precipitin reaction with euglobulin antibody less nitrogen is precipitated throughout the course of the reaction at the higher salt concentration than at the lower salt concentration.

5. 5. The heterologous reaction between duck ovalbumin and eu- and pseudoglobulin antibody fractions differs somewhat from the homologous reaction. Decreased amounts of precipitation, greater inhibition of the reaction at the higher salt concentrations, and less inhibition in antigen excess were observed.