Studies of hypersensitivity to low molecular weight substances. III. The 2,4-dinitrophenyl group as a determinant in the preciptin reaction.

Summary The 2,4-dinitrophenyl group, combined with proteins through azo linkage or by substitution in free amino groups, has been studied as a determinant in the precipitin reaction. The precipitin curves obtained resemble those encountered with purified antigens of high molecular weight with the chief exception that in the region of antibody excess antigen is not completely precipitated. Dinitrophenyl-azo-ovalbumin was a less effective precipitant than the conjugated ovalbumin in which dinitrophenyl groups were substituted in free amino groups. The former, however, was relatively more effective in precipitating antibody from antisera to dinitrophenyl-azo-proteins than from antisera prepared against amino-substituted dinitrophenyl-proteins. The globulin fraction of pooled antisera to dinitrophenyl-bovine γ globulin contained at least three species of antibodies—viz: those precipitated by bovine γ globulin; those precipitated by dinitrophenyl-ovalbumin and those precipitated only by dinitrophenyl-bovine γ globulin. These were present in the ratio of 1:1:1.3, respectively. After maximal precipitation with each of these antigens the supernates9 binding of e-N-dinitrophenyllysine, a hapten in which dinitrophenyl is combined with lysine in the same way as in the immunizing conjugate, was determined by the method of equilibrium dialysis. The binding in the three cases, relative to the binding by the unabsorbed immune globulin, was in the ratio of 1:0.6:0.25, respectively. Hence, the antibodies precipitated by bovine γ globulin had no detectable specificity for the dinitrophenyl group, and the antibodies precipitated by the heterologous conjugate (dinitrophenyl-ovalbumin) had a greater affinity for the dinitrophenyl determinant than those antihapten antibodies that required for precipitation the fully homolgous conjugate (dinitrophenyl-bovine γ globulin). Antibodies with dual specificity, i.e., with one specificity for the hapten and a distinctly different one for the protein of the immunizing conjugate, were not detected.