The synthesis and storage of protein by isolated lymphoid cells, examined by autoradiography with the electron microscope

Autoradiography with the electron microscope was employed to locate sites of synthesis and storage of newly‐formed protein in cells isolated from lymph nodes of immunized rabbits and incubated with tritium‐labelled leucine. The chief object of the investigation was to locate the site of sequestration of newly‐formed antibody during the half‐hour that intervenes between its synthesis and release from the plasma cell. By making counts of grains over nuclei, Golgi complex and ergastoplasm, and relating these to the relative volume of each region, evidence was obtained that, during the latent period of secretion, antibody moves into the Golgi region from its site of synthesis in the ergastoplasm. In analyzing the data, some of the difficulties involved in quantitative autoradiography were considered and the statistical inappropriateness of using mean grain counts and their standard errors to estimate the concentration of isotope was discussed. As an alternative with a sounder theoretical basis, the ratio estimate was adopted, and Fieller's theorem was used to obtain conservative estimates of confidence limits. The results of statistical analysis supported the biological conclusion that newly‐formed antibody migrates to the Golgi region, but the role of the Golgi complex in secretion of antibody remains to be explained. The hypothesis that plasma cells originate by differentiation from large lymphocytes received circumstantial support from the observation that among those cells active in synthesis of protein, a series transitional in structure from large lymphocytes to mature plasma cells could be assembled.