Since the early experiments of Fagraeus (1), the role of plasma cells in antibody formation has been extensively studied and reviewed (2-7). Plasma cells have been found to contain (8-15) and produce (16-23) antibody, and apparently are the chief mediators of a humoral immune response. After the second injection of an antigen, far more plasma cells appear than after the first; this appears to be the main reason for the characteristic booster serum antibody response (18). Burnet and Fenner (2) first suggested that the secondary response might represent the proliferation of cells specifically altered by the primary immunization. Since the development of the clonal selection theory of acquired immunity (6, 24--27), there has been renewed interest in the nature of the plasma cell ancestor, the carrier of specific immunological memory.The present experiments have used autoradiographic labeling techniques to study this question. They are predicated on the uptake of tritiated (H*-) thymidine as an index of desoxyribonucleic acid (DNA) synthesis (28-30), and the validity of our conclusions depends on a number of premises which are widely held, but still the subject of active discussion (31-33). The premises most directly relevant to our experiments are: (a) the tritium label on thymidine is stable and does not exchange; nor does thymine base exchange after incorporation into DNA; (b) DNA itself is metabolically stable and turnover is insignificant in resting mammalian cells; (c) HS-thymidine injected intravenously is rapidly distributed throughout the body, and either promptly incorporated into DNA or eliminated; (d) thymidine or H3-thymidine does not affect the normal behavior of the cells that have taken it up. This last premise has recently been challenged (34).
All antibody-forming tissues contain a varied population of cells of different types and in various stages of differentiation, obviously engaged in a variety of different tasks. Plasma cells, the chief formers of circulating antibody (1-3), constitute a minority of the population. The results of biochemical studies on antibody synthesis will thus frequently be influenced by the behavior of the more numerous cells, not directly involved in antibody synthesis. Several techniques are now available for studying antibody formation by single cells in vitro (2-5), and we now report a technique whereby such single antibodyforming cells can be studied biochemically using autoradiography. A high rate of desoxyribonucleic acid (DNA) synthesis in the over-all cell population of immunized lymph nodes has been reported (6). The present studies deal with DNA synthesis by individual antibody-forming cells and the age of antibodyforming cells at the height of a secondary response to purified Salmonella flagellin. Materials and MethodsExcept where stated, the techniques used were identical with those described in the accompanying paper (7). DNA synthesis in these studies is defined as the uptake of Ha-thymidine into the nucleus.Antigen.--Flagellin, the protein purified from flagella, has been shown to cause the production of a higher proportion (though perhaps a lower absolute number) of detectably active plasma cells, than the flagella from which it was derived (8). In these experiments, rats were primarily immunized with an injection of 25/zg of Salmonella adelaide (SW 1338, XKXV, fg) flageUin into each hind foot-pad; 4 to 12 weeks later, each rat was secondarily immunized with a similar pair of injections, and killed 2 to 7 days later.
Aryl hydrocarbon hydroxylase activity in lymphoblasts from normal Finnish adults and from patients with pulmonary carcinomas and other types of malignancy has been studied by a modification of previously used techniques. High absolute induced aryl hydrocarbon hydroxylase activity was found in 39% of patients with untreated lung cancer but only in 15% of normal people. No increased frequency was found in the control group comprising other malignancies. The diagnosis of pulmonary carcinoma was made at a lower mean age (4.9 years younger) in the individuals with high aryl hydrocarbon hydroxylase activity than in those with low activity. High absolute aryl hydrocarbon hydroxylase activity was dominantly inherited in normal individuals, and the frequency of athe Ahb gene in the Finnish population was 8%.
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