Radioautographic and Electron-Microscopic Evidence of Rapid Uptake of Antigen by Lymphocytes

Iodine-125-labeled ferritin molecules were detected by radioautography in the sinuses of the rat popliteal lymph node shortly after injection into the foot pad; they appeared to be taken up by macrophages and phagocytic reticular cells. Electron microscopic examination of the same tissue also revealed ferritin molecules within small lymphocytes as early as 5 minutes after injection. The antigen appeared to be taken up by the process of pinocytosis and was distributed throughout the cytoplasm and nucleus. While the number of ferritin molecules observed in the lymphocyte was much less than that taken into the macrophage, the observation is significant in understanding the role lymphocytes play during the early phase of antibody response.