Germinal Center Changes and Plasma Cell Reaction During the Primary Immune Response

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Abstract
Histologic and autoradiographic investigations were performed on the lymphatic tissue of the mouse spleen during the 1st 4 days after a primary sheep red blood cell (SRBC)-stimulation. Germinal center cells in the lymphatic tissue responded to antigenic stimulation by proliferation which was detected in 2 ways 1. within intact germinal centers (hyperplasia), and 2. in a dispersed manner with migration. Both of these responses are considered characteristic of the inductive phase of the primary immune response. An increase in germinal center volume and number of countable centers per longitudinal section occurred 2 h after SRBC-injection, followed by a rapid decrease in both parameters over the next 22 h. A recovery in both germinal center volume and number occurred between days 1 and 4 following injection. At day 4, a fourfold increase in germinal center volume was measured in the antigen stimulated group. In the SRBC-stimulated animals the increase in number of large pyronine-stained cells in the lymphocyte mass coincided closely with germinal center dissociation. Topographically, the time sequence of the increase in number of pyronine-stained cells was 1st in the area of the germinal center, 2nd in the edema-like region of the lymphatic nodule, and 3rd in the red pulp of the spleen. Coinciding with the increased number of pyronine-stained cells in the spleen red pulp was the formation of foci of plasma cells in which active plasmacytopoiesis could be observed. The fate of large pyronine-stained cells during early intervals of the primary immune response was studied with spleen imprint autoradio-grams. These studies suggested that the pyronine-stained cells of the dissociated germinal centers were precursors of immature plasma cells, the transformation beginning between days 1 and 2 after antigen injection.