Relationship of Germinal Centers in Lymphoid Tissue to Immunological Memory

The fate, proliferation, and developmental potentialities of cell suspensions made from white pulp containing large germinal centers have been studied in the mouse by transfer of cells labeled with thymidine-(3)H to lethally irradiated, syngeneic recipients. Radioautographic analyses were made using both smears and sections of a variety of tissues. Thymidine-(3)H-labeling patterns of white pulp showed that, initially, labeling occurred in a majority of blast and "intermediate cells" but in very few or no small lymphocytes. After intravenous transfer, most of the labeled cells localized in the lymphoid tissues of spleen, lymph nodes, and Peyer's patches. Few cells migrated to the thymus, lung, liver, and intestinal mucosa. Both after intravenous and after intraperitoneal transfer there was a rapid increase in the incidence of labeled small lymphocytes and a decrease of labeled blasts and intermediate cells. This was accompanied by an increase in the grain count of the small lymphocytes and a progressive decrease in the grain counts of the blast cells. Exposure of nonlabeled donor cells to thymidine-(3)H at various time intervals after transfer indicated that dividing cells were present early after transfer but that their incidence progressively decreased. Between 24 and 48 hr, very little cell division was detectable.