The relative rates of formation of new leukocytes in patients with acute and chronic leukemias measured by the uptake of radioactive phosphorus in the isolated desoxyribosenucleic acid

Reduction of B cell turnover in chronic lymphocytic leukaemia

Whether chronic lymphocytic leukaemia (CLL) is a latent or a proliferating disease has been intensively debated. Whilst the dogma that CLL results from accumulation of dormant lymphocytes is supported by the unresponsiveness of leukaemic cells to antigens and polyclonal activators, recent in vivo kinetic measurements indicate that B lymphocytes do divide at significant rates in CLL. However, an important and still unanswered question is whether CLL cells proliferate faster or slower compared with their normal counterparts. This report addressed directly this point and compared B-cell kinetics in CLL subjects and healthy controls, using a pulse-chase approach based on incorporation of deuterium from 6,6-(2)H(2)-glucose into DNA. We confirmed that B cells proliferated at significant levels in CLL but found that the proliferation rates were reduced compared with healthy subjects (mean 0.47 vs. 1.31%/d respectively, P = 0.007), equivalent to an extended doubling time of circulating B cells (147 d vs. 53 d). In conclusion, CLL B cells proliferate at reduced levels compared with healthy controls. CLL is thus characterized by an aberrant B-cell kinetics with a decrease in cell turnover, an observation that may impact on elaboration of efficient therapeutic strategies.

PROLIFERATIVE ACTIVITY OF THE LYMPHATIC TISSUES OF RATS AS STUDIED WITH TRITIUM-LABELED THYMIDINE

Cytokinetic data are presented, employing quantitation of H³DNA in the lymphatic tissues of normal rats serially sacrificed after H³Tdr administration. A marked difference in the patterns of initial labeling and label loss was observed between the thymus and peripheral lymphatic tissue. The data are compatible with other indications of rapid cell renewal in the thymus. There is suppression of initial uptake of H³Tdr into the DNA of each large lymphocytic progenitor cell in the thymus, apparently because of a feedback of thymidine containing material from small lymphocytes in the thymus. Depletion of the thymus of small cells, as by operative stress or whole body x-ray, leads to a marked increase in the uptake of H³Tdr into the DNA of large thymocytes. This finding, which is in agreement with the previous findings of Sugino et al. (33, 34) suggesting transfer of thymine nucleotides from small thymus lymphocytes to precursor cells, may or may not be related to the apparent transfer of DNA label between thymic cells. The evidence for the latter consists of the curvilinear dilution of the DNA label in the thymus proliferating cell population and the relationship between the rate of DNA label dilution in large cells and the H³DNA in the small cells in the thymus. After the DNA label in progenitor cells in the thymus and lymph nodes has entered the small cell population, the subsequent dilution of grains in these dividing cells follows the same slope as the loss of radioactivity from the entire lymph node. There is a long retention of some H³DNA label in the dividing lymph node cell population. This suggests that the loss of radioactivity from the dividing cells and from the small cell population as a whole occurs equally. This pattern prevails regardless of whether the percentage of large and small cells is altered experimentally. These findings can be explained by an interchange of the DNA nuclear label between small lymphocytes and large lymphocytes. This could occur by some process such as phagocytosis or pinocytosis, or by transformation of the small lymphocyte into a large, dividing cell. The data fit best with the latter possibility. All or any of these mechanisms would lead to an equilibration of the DNA label between large and small cells. This finding prevents the assignment of a finite life span to lymphocytes on the basis of DNA labeling kinetics. Nevertheless, there appear to be at least two different types of lymphocytes. One, the "thymus-type" lymphocyte, is found in the thymus cortex, bone marrow and germinal centers of lymphoid follicles. The other type, found abundantly in the widespread peripheral lymphatic tissue, shows a very prolonged retention of DNA label and is believed to be the recirculating, "immunologically committed" cells described by others. These cells do not appear to enter the thymus cortex.

Regional differences in renewal rates of fibroblasts in young adult female mice

Young adult female mice were given a total of 90 intraperitoneal injections each of (methyl-3H)thymidine (3HTdR) at intervals of 8 h over 30 days to establish renewal rates of fibroblasts in various locations. Radioautographs prepared from punch biopsy material of the ears, taken repeatedly during the labeling procedure, revealed an approximately linear increase of labeling indices of dermal fibroblasts with time. Labeling indices of fibroblasts at the end of repetitive injections of 3HTdR differed depending on the site and/or type of connective tissues examined. Low values were obtained for fibroblasts in the leptomeninx (3.9%), the tracheal wall (4.4%), the achilles tendon (5.8%) and the dermis of the ear (6.5%), while higher values were registered for fibroblasts located in the lower half of the abdominal dermis (12.3%), peritendinous sheaths (12.6%), the interstitial connective tissue of the thigh muscles (12.9%), the submucosa of the colon (23%), the fibrous capsule of the adrenals (25.7%), and the upper half of the abdominal dermis (26%). These regional differences, with the exception of the skin and possibly of the tracheal wall, did not correlate with local temperature. Possible additional factors influencing fibroblast renewal rates may include the type of connective tissue, the degree of vascularization, mechanical stress and hormonal action. Estimated turnover times, based on the assumptions of a DNA synthesis time of 6 h or more and a linear increase of labeling indices as a function of time of repetitive labeling, range from about 90 to more than 700 days. The higher values approximate the median life span of the mouse strain used.

Chronic lymphocytic leukemia: a proliferative or accumulative disorder?

In two untreated patients with progressive CLL, quantitative 14C autoradiography of lymph nodes and, subsequently, continuous infusion of [3H] thymidine over eight and nine days, respectively, were performed in order to analyse the lymph node cell kinetics. Simultaneously, the turnover of labelled lymphocytes in the peripheral blood was evaluated. From another CLL patient a regional lymph node was removed 6 h after an intralymphatic flash injection of [3H] thymidine and sectioned for autoradiographic study of the distribution of labelled cells within the lymph node tissue. While the durations of DNA synthesis were found to be normal, the labelling indices were reduced. The relative cell production rate was far lower than normal. Very small growth fractions were calculated, amounting to less than 1% in one patient, and to 2.4% in the other. The distribution of labelled cells in the lymph nodes was focal, which supports the finding of low growth fractions. According to the present data, CLL is a disorder in which a very small number of cells cycle at a roughly normal rate. A kinetic definition of accumulative and proliferative tumour growth is introduced. Tumour growth is termed accumulative if growth appears to result from a decreased relative cell loss rate rather than an increased relative cell production rate. According to this definition, the kinetics in CLL may be classified as accumulative. In absolute terms, however, the number of lymphoid cells produced per unit of time was found to be far higher in CLL than in the healthy state.

Membrane permeability in normal human lymphocytes and lymphocytes from patients with chronic lymphatic leukaemia

The rate of release of intracellular enzymes from the lymphocytes of patients with chronic lymphatic leukaemia has been shown to be slower than that from normal lymphocytes, despite their lower enzyme contents. Addition of ATP, ADP and AMP to the medium reduces enzyme efflux in a manner similar to that in normal lymphocytes. Iodoacetate, however, causes a marked increase in enzyme leakage from both normal and leukaemic cells. It appears therefore that the membrane permeability of leukaemic lymphocytes is at least partly dependent upon the intracellular energy content. Since the ATP contents of the leukaemic cells were lower than those of normal lymphocytes, however, it is concluded that some additional factor is concerned in reducing permeability to enzymes in chronic lymphatic leukaemia. The possibility that the immunoglobulin associated with the cell membrane of leukaemic cells may play a part in reducing its permeability has been explored, but washed and unwashed cells were found to lose enzymes at similar rates. The lower permeability of the membranes of such cells may partly explain their longer lifespan in chronic lymphatic leukaemia.

The characteristics of thoracic duct lymph in man

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