Cell-Cycle-Dependent and -Independent Damage to Rat Haemopoiesis By Hydroxyurea

The generally accepted cell-killing effect of hydroxyurea (HU) on S-phase cells, as well as its potential to arrest cells at the G₁/S boundary, hardly explain its benefit for application in human chronic myelogenous leukaemia. Studies were therefore performed in rat haemopoiesis in order to quantify the cell-killing effect on various phases of the cell cycle. For this purpose, the [³H]thymidine ([³H]TdR) labelling index and the specific activity of [³H]TdR in the DNA-synthesizing fraction of cells were determined after a non-cytoreductive dose of 25 mg/kg HU, as well as a medium cytoreductive dose of 100 mg/kg. Furthermore, flow cytometric DNA histograms and absolute as well as differential cell counts of femoral bone marrow were performed after 100 mg/kg HU. The results indicate a predominant cell kill in G₁ encompassing almost all 2c cells in the proliferative pool, while the S-phase fraction is not even reduced to half its initial value. the specific activity of [³H]TdR in cells synthesizing DNA, as well as the labelling index after HU show an initial dip and a tendency to recovery, as has been observed in many other cell systems. Instead of a complete restoration, however, there is a second depression of these parameters lasting for at least one cell cycle. the results are interpreted as a partly cell-cycle-dependent and partly independent action of HU in this cell system. the independent component may be attributed to the repeatedly described direct interference of HU with DNA. In rat haemopoiesis, therefore, this direct effect of HU on the DNA strands appears to be much more pronounced than in cell-culture systems and other mammalian tissues. In view of these findings, some caution should be taken in using HU for the determination of the S-phase fraction by way of a suicide experiment.     

Toxicity of Trimethoprim-Sulphamethoxazole in Patients with Megaloblastic Haemopoiesis

Four consecutive patients with megaloblastic anaemia who also received therapy with trimethoprim-sulphamethoxazole all showed poor responses to specific haematinic therapy. This was attributed to trimethoprim, which suppressed reticulocyte responses in three cases and produced a pancytopenia in two and a falling haemoglobin with neutropenia in a third. A fourth patient, with pernicious anaemia, had a satisfactory reticulocyte response but experienced no clinical benefit until after withdrawal of trimethoprim.Trimethoprim seems not to be a safe form of therapy in patients with a megaloblastic process; many of the toxic reactions reported with this drug may be on the basis of an unrecognized megaloblastic form of haemopoiesis.     

Haemopoiesis in the beagle foetus after in utero irradiation

On day 33 of gestation, foetal beagles were irradiated in utero (0.9 Gy of 60Co gamma-irradiation, 0.4 Gy/min). Foetal haematocytopoiesis was studied during the third trimester of gestation (days 42-55). Peripheral blood nucleated cell counts were 33 per cent lower than normal on day 44 and continued to be lower until day 49, when values became higher than normal. Splenic cellularities of irradiated pups on day 44 were more than 3 times those of the nonirradiated, but thereafter they were similar to normal. Differences in haemopoietic progenitor cell activity between irradiated and normal foetuses were observed. In comparison with the other foetal tissues, the foetal liver appeared to experience greater radiation injury. For example, on day 44, the irradiated liver BFU-E, CFU-E, and GM-CFC per 10(5) cells were almost fivefold lower than normal values. Spleens of irradiated foetal beagles contained a marked increase in all haemopoietic progenitor cells (BFU-E, CFU-E, and GM-CFC) and recognizable proliferative granulocytic cells and nucleated erythroid cells. The haemopoietic activity of the irradiated bone marrow during days 42-44 was similar to that of the irradiated spleen, and compensated for the damaged liver. However, unlike the irradiated spleen, the irradiated bone marrow had decreased BFU-E activity compared with the values for the nonirradiated bone marrow during days 48-55. Until day 50, the irradiated marrow contained fewer recognizable proliferative granulocytic cells but more nucleated erythroid cells.     

Pluripotent Stem Cells Do Not Completely Maintain Normal Human Steady-State Haemopoiesis

Since the classical work on the regulation of canine erythropoiesis by Alpen & Cranmore (1959), it has been generally accepted that recognizable bone-marrow cells are continuously replaced from sources of unrecognizable precursors. Although many features of pluripotent stem cells (PSC) and committed haemopoietic precursors have been determined, direct demonstration of a continuous influx, under normal steady-state conditions, from PSC into the recognizable bone-marrow cell compartments is still lacking. There is abundant evidence that PSC, in a number of species, including primates, resemble atypical or immature (‘transitional’) lumphocytes. By utilizing the technique of quantitative ¹⁴C-autoradiography, we have measured the activities of DNA and protein synthesis in individual bone-marrow cells of two healthy humans. A positive relationship was established between the protein synthesis rate and rate of movement through the cell cycle in all proliferative compartments. Lymphoid cells, considered to contain the fraction of PSC, were found in the lower range of this relationship. These low metabolic rates exclude fast growth as well as short cell-cycle times. In view of the low frequency of the potential PSC in the human bone marrow, amounting to less than 2%, these cells cannot be considered to represent a source continuously supplying the pool of rapidly proliferating, recognizable blast cells in the bone marrow under steady-state conditions. Some self-maintenance of a subcompartment within the pool of recognizable normal bone-marrow blast cells is therefore suggested.     

Haemopoiesis in mice genetically lacking granulocyte-macrophage colony stimulating factor during chronic infection with Mycobacterium avium

In order to test the role of granulocyte-macrophage colony stimulating factor (GM-CSF) in haemopoiesis during chronic infection, mice with a targeted disruption of the gene for GM-CSF were infected intraperitoneally with the facultative intracellular pathogen, Mycobacterium avium. The bacteria spread to lungs, liver and spleen and persisted for more than 10 weeks at levels between 105 and 106 CFU. Bacterial numbers did not differ significantly between infected GM-CSF-/- and wild-type mice, making this an excellent model in which to study the effects of GM-CSF deficiency on haemopoietic cells without complications of interpretation relating to differences in bacterial load. Haemopoietic colony forming cells (CFC) in the bone marrow of GM-CSF-/- mice before infection were not different from wild-type. However, whereas CFC in wild-type mice increased 1.5-fold with infection, GM-CSF-/- mice were unable to increase their CFC and numbers were significantly lower than in infected wild-type mice. Cells attracted to the peritoneal cavity of the GM-CSF-/- mice following i.p. injection of bacteria were notably lacking in the large, granular macrophages of activated appearance, which were a feature in wild-type mice. Nitric oxide production by peritoneal cells from GM-CSF-/- mice was deficient. Thus, GM-CSF is not critical for haemopoiesis during chronic infection, but in its absence the mice are unable to increase their output of haemopoietic cells and there are deficiencies in macrophage activation.     

Revisione delle specie: Actinomyces albus,A. chromogenus,A. odorifer,A. thermophylus,A. viridis,A. viridochromogenes,A. hominis,A. innominatus

Riassunto Lo studio comprende una revisione critico-sperimentale della specie Actinomyces albus, della quale vengono considerati come sinonimi circa 30 nomi speeifici, fra i quale A. chromogenus, A. odorifer, A. thermophylus p.p.; della specie é data una diagnosi ed una particolareggiata descrizione.Sono inoltre studiate le specie A. viridis, (= A. viridochromogenus) e A. innominatus, n. nomen. Quest'ultima é preceduta da una breve discussione sulla specie A. homini.

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Summary Twenty-six strains of Actinomyces albus are studied redescribed from morphological, cultural and biochemical standpoints. Many biological activities of A. chromogenus, A. odorifer and A. thermophilus are in common with other species of the same genus, so that they may be considered for sub-specific, (not specific) differentiation. A discussion on A. farcinicus, A. albidoflavus and A. aureus has been originated from mislabeling as A. albus; the group including the two last named species (flavus group) must be revised. A few strains classified A. farcinicus are in no doubt true A. albus, but this real specific entity remains to be revised from Nocard's strain. A. viridis, for the first time described by Lombardo-Pellegrino, has been redescribed three times as a new species under the same binomial, and the fourth as A. viridochromogenes. A. hominis Bostroem is an uncorrect determination for the species originally described by Waksmann and Curtiss, and it is renamed A. innominatus, the binomial A. (Streptothrix) hominis Auct. being a nomen ambiguum. In conclusion, 30 bionmial are appended in sinonimy to A. albus, including Cladothrix dichotoma Macé (1888) non Cohn, G. invulnerabilis Acosta et G. Rossi, C. odorifera Rullm. Actinomyces chromogenus Gasp., A. thermophilus Auct., p.p., A. (Streptothrix) Sanninii (Cif.) Westerd., A. Almquisti Duché, A. Gougeroti Duché, and so on.