A combination of double immunofluorescent technique and radioautographic localization of radioactive antigens was used to investigate the question whether single antibody-producing cells can make antibodies of more than one specificity after immunization with antigens bearing more than one determinant. When guinea pig γ2-globulins, containing the F(ab')2 and Fc determinants, were used to immunize rabbits, a small percentage of cells (3.7%) were stained with both the anti-F(ab')2 and anti-Fc reagents. These results were shown to be due to the lack of absolute specificity of the detecting antigen and antibody reagents which can be obtained for use in this system.
However, when immunological systems such as hapten-protein conjugates were used, and where completely specific antigen and antibody reagents could be prepared, the results were unequivocal. The individual lymph node cells from rabbits or guinea pigs immunized with hapten-protein conjugates produced antibodies against the hapten or antibodies against the antigenic determinants of the carrier molecule, never antibodies against both specificities.