RELATIONSHIP OF GERMINAL CENTERS IN LYMPHOID TISSUE TO IMMUNOLOGICAL MEMORY I. EVIDENCE ]~OR THE FORMATION OF SMALL LYMPHOCYTES UPON TRANSFER OF P~rM~D SPLENIC WHITE PULP TO SYlqGENEIC

Active germinal centers are recognized as areas of rapidly proliferating blast cells in the white pulp of the spleen and in the cortex of lymph nodes. The origin and life history of these cells, their relationship to the surrounding mantle zone of small lymphocytes and, in particular, the functional significance of these two groups of cells is still unknown. Flemming (1) has proposed that germinal centers are a major site of production of small lymphocytes, but this interpretation has been disputed by others (2, 3). Hellman (4) has suggested that these structures are a reaction site against invading organisms. This is consistent with the fact that germinal centers appear specifically after exposure to antigen (5, 6). Rapid proliferation of blast cells in the germinal centers develops later than the peak of the primary response and coincides with development of primed cells after exposure to antigen (7, 8). Moreover, it can be shown by microdissection methods that the cells capable of giving a secondary response develop in the splenic white pulp at this time (9, 10). I t is therefore important to determine the life history and immunological properties of the cell types arising in the white pulp after intravenous injection of antigen.