Flagellar antigens from S. adelaide bacteria were labelled with carrier-free 125I so as to achieve a substitution rate of 0.1 to 2.1 radioactive iodine atoms per flagellin molecule. Lymph nodes from rats injected with small amounts of these antigens were teased into a single cell suspension. Single antibody-forming cells were identified and submitted individually to autoradiography so as to measure their content of iodine 125I. The study was confined to the 7S phase of the primary response.
Grain counts over 216 single antibody-forming cells were no higher than counts over equivalent background areas in the emulsion. This finding suggested that the cells contained little or no macromolecular antigen, and it was considered very unlikely that there were sufficient macromolecules of antigen in a plasma cell to act as a direct template on polysomes for the formation of antibody. The question of the possible presence, in such cells, of fragments of antigen was considered. This possibility, while not supported by the present results, cannot be excluded at present.