Radioautographic Studies of Reticular and Lymphoid Cells in Germinal Centers of Lymph Nodes

Abstract

Earlier studies from our laboratory have shown that there are two populations of small lymphocytes in the rat with respect to rate and site of formation and circulating life span (Caffrey et al., 1962). One of these has a rapid turnover rate with a circulating life span of about 5 days. The other is produced at a slow and rather constant rate which is roughly proportional to the growth rate of young adult animals. It is the latter population which has a long circulating life span and recirculates from blood to lymph. It is believed that at least some of these may have a life span commensurate with that of the animal since heavily labeled small lymphocytes have been recovered for as long as one year after labeling with Thymidine-³H. Subsequent studies have shown the percentages of the two populations in blood, thoracic duct lymph, and in each of the major lymphoid organs. It was determined that approximately 75% of the small lymphocytes of the mesenteric lymph node were of the long-lived variety and approximately 25% were short-lived (Everett et al., 1964 a). From attempts to assess the respective functions of the two varieties of small lymphocytes, evidence was obtained which suggested that the long-lived lymphocyte has an active role in immune response mechanisms. For example, these cells evidenced enlargement, both nuclear and cytoplasmic, in animals treated with pertussis vaccine (Everett et al., 1964 a). Additionally, as an indirect response to total body irradiation (Everett et al, 1964 b), many long-lived cells enlarged and showed a pronounced increase in the rate of protein synthesis (Everett et al., 1965).