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Biomedical subjects

B I Lord

Publications and source records attributed to B I Lord.

At least 73 records · Page 4Linked to original sources
PubMed1989

The development of spatial distributions of CFU-S and in-vitro CFC in femora of mice of different ages.

The radial distributions of spleen colony forming units (CFU-S) and in-vitro colony forming cells (in-vitro-CFC) were measured in the diaphyseal marrow cavity of femora removed from 3-, 5- and 11-week-old mice. The distributions observed in 11-week-old mice confirm earlier findings that the highest concentrations of CFU-S exist near bone surfaces whereas the concentration of in-vitro-CFC increases to a peak value approximately 300 microns from the femoral axis with a low value at the bone surface. The gradients of the distributions in all three age groups are very similar suggesting that spatial organization in marrow is established by 3 weeks at the latest and, as the marrow cavities grow, so the distributions extend into the new space following their respective gradients. The peak of CFU-S concentration at the bone surfaces in all age groups coincides with increased rates of DNA synthesis and a low self-renewal capacity. Conversely, CFU-S nearer the centre of the cavity maintain a low turnover but have a high self-renewal capacity. Measurements made on 1-week-old mice show that the marrow contains a lower average concentration of CFU-S in the femoral cavity compared to older mice. However, these CFU-S have both a high rate of turnover and a high self-renewal capacity. It appears that these better quality CFU-S remain in a central location while the rest of the population ages and expands in association with growing bone regions.

Aging↗
PubMed1989

On the late seeding of CFU-S to the spleen: 8- vs 12-day CFU-S.

Marrow from 5-fluorouracil- or cyclophosphamide-treated mice, injected into lethally irradiated recipients, gives an increasing number of spleen colonies between days 7 and 14. It has been suggested that the later-forming colonies result from the more primitive spleen colony-forming units (CFU-S), which first seed into the marrow, only later to be recirculated and form colonies in the spleen. Strontium 89 (89Sr), a bone-seeking radionuclide, was injected into recipient mice to block such putative recirculation. A dose of 89Sr, which killed at least 99.8% of CFU-S in, or entering, the bone cavities, was incapable of preventing the increase in spleen colony numbers. Similarly, the splenic environment, modified by the presence of spleen colonies and able to provide a better bed for trapping CFU-S from the peripheral circulation, yielded the same number of further CFU-S, whether or not the animal had received 89Sr. Thus, it was concluded that the 12-day CFU-S does not seed initially into the marrow spaces. Direct observation of the quality of CFU-S initially seeding into the bone marrow and spleen showed, by retransplantation into secondary irradiated mice, that a similar spectrum of CFU-S types had seeded both organs.

Animals↗
PubMed1988

Haemopoietic growth factors: their relevance in osteoclast formation and function.

The major recent advance in our knowledge of the haemopoietic system has been the purification and characterization of a family of haemopoietic growth factors, and their availability in recombinant form. In the bone marrow the sequences of differentiation and proliferation leading to the production of mature cells that these factors regulate may be determined by the relative availability of the factors in microenvironmental domains. The observation that growth factor-producing cells and haemopoietic progenitor cells are not evenly distributed in the bone marrow leads us to expect that the overall effect of growth factors (and other regulatory molecules) on the production and function of macrophages and osteoclasts may differ when in vivo or in vitro assays are used as end-points and, in the latter case, when whole marrow or purified cell populations are tested. The availability of an in vitro assay in which osteoclast-like cells are generated will allow these concepts to be tested.

Animals↗
PubMed1988

Production of a multipotential cell (CFU-S) proliferation inhibitor by various populations of mouse and human macrophages.

Some bone marrow macrophages from a variety of animal species synthesize a proliferation inhibitor which specifically inhibits the flow of murine CFU-S into DNA-synthesis. Macrophages from other sources have now been assayed for their capacity to produce this inhibitor. Macrophages from mouse blood, marrow, spleen and peritoneum and human blood were cultured and their ability to produce inhibitor assayed against proliferating CFU-S by the tritiated thymidine suicide assay. Inhibitor was observed in all mouse and most human preparations though with varying degrees of activity, showing functional heterogeneity in the development of macrophages in different tissues. Peripheral blood from both mouse and human showed activity approaching that of fresh marrow. This confirms that mouse assay systems can be used to study the human counterpart of the mouse CFU-S proliferation inhibitor and that blood is a convenient source of material for purification and characterization studies.

Animals↗
PubMed1988

Long-term haemopoietic injury in mice after repeated irradiation: precursor-cell cycling and its regulation.

The cycling rate of haemopoietic stem cells (day 9 CFU-S) and granulocyte-macrophage colony forming cells (GM-CFC) in mouse femora was, in response to reduced numbers, elevated at all times of sampling between 3 weeks and 10 months after 4 repeated doses of 4.5 Gy X-rays (3 wk between doses). The level of a stimulator of CFU-S cycling was also elevated, and this was observed in both axial and marginal regions of the marrow inside the shaft. However, the rate of production of the stimulator was low; lower than previously reported in marrow regenerating after a single dose of 4.5 Gy, indicating damage to the regulatory stromal cells. The distribution of CFU-S across the axial and marginal zones of femoral marrow was changed from that in normal mice, where higher concentrations were found near the bone surface, to a more uniform distribution.

Animals↗
PubMed1988

Feedback regulators in normal and tumour tissues.

Regulation of cell behaviour and population size is presumed to be not unlike classical regulation in non-biological systems, i.e. it is controlled by the cybernetic principle of negative feedback whereby the performance of progenitor cells depends inversely on a signal from their product, the size of which is proportional to the mass of the product. This signal may be inhibitory, acting directly on the progenitor cells. Alternatively, it may operate via an indirect and integrated inhibitor/stimulator feedback loop in which the one influences the production of the other. Illustrations taken from the various phases of haemopoietic development show the operation of these loops. Haemopoietic stem cells are under the direct influence of both inhibitor and stimulator but it is a feedback signal from the stem cell population that dictates the production of the one rather than the other. A second inhibitor acting at the stem cell level is a low molecular weight tetrapeptide which blocks the entry of cells into DNA synthesis, thus protecting them during a regimen of treatment with an S-phase cytotoxic drug. Proliferation of the maturing cells is also inhibited by feedback products of their fully mature descendants. Here, the effect is one of cell cycle modulation, whereas in the stem cell population the inhibitor and stimulator effect an on/off switch. Attempts to characterize the molecules involved have been limited. A series of tri- to pentapeptides has been described for haemopoietic or epithelial cell inhibitors. A common feature of several is a pGlu-Glu end though whether this has any significance is not known. In tumours it has been shown that some ascites are self-limiting and treatment of small tumours with cell-free fluid from a mature growth blocks their further growth. It appears that many tumour cells produce the feedback signals characteristic of their normal counterparts but are themselves less sensitive to it. The same is true of transforming growth factor-beta which is produced and detected by virtually all cell types. In this case, the factor, inhibiting in most cases, is produced in inactive form and achieves its target specificity by a localized capacity to activate it. Some tumours, while responding to exogenous active TGF-beta are incapable of activating the latent molecule. It is concluded that the differential sensitivity of normal and neoplastic tissues to physiological feedback regulators is a potentially exploitable property in cancer therapy.

Cell Division↗
PubMed1987

Metabolically inactive 3T3 cells can substitute for marrow stromal cells to promote the proliferation and development of multipotent haemopoietic stem cells.

When highly enriched multipotential spleen colony forming cells (CFU-S) obtained following fluorescence activated cell sorting (FACS-CFU-S) are cultured on marrow stromal cells, they undergo proliferation and development to produce mature haemopoietic cells (Spooncer et al., Nature, 316:62-64, 1985). We now show that FACS-CFU-S behave in a similar way when cultured on monolayers of 3T3 cells, indicating that the 3T3 cells can supply at least part of the environment which is representative of marrow stromal cells and provide, therefore, a system for studying stromal cell: haemopoietic cell interactions. We also demonstrate that IL-3-dependent multipotential stem cell lines (FDCP-Mix), but not a variety of other "committed" IL-3-dependent cell lines, resemble FACS-CFU-S in terms of their ability to proliferate and differentiate when cultured on 3T3 cells in the absence of IL-3. In this system, attachment of the FDCP-Mix to the 3T3 cells is critical for the subsequent maintenance of viability and stimulation of development of the cells. When the FDCP-Mix cells are physically separated from the 3T3 cells, they die and their death cannot be prevented by using 3T3-cell-conditioned medium. The extracellular matrix generated by 3T3 cells is not sufficient for promoting attachment or viability of the FDCP-Mix cells, indicating the importance of integral membrane components. However, attachment and development of FDCP-Mix cells occurs on 3T3 cells that have been lightly fixed with glutaraldehyde indicating that active metabolism is not essential for the effects promoted by the 3T3 cells. We suggest that the ability of FACS-CFU-S and FDCP-Mix cells to respond to 3T3 cells involves specific ligand/receptor interactions.

Animals↗
PubMed1986

Comparison of haemopoiesis in young and old mice.

Haemopoietic status and functions have been compared in young (2-3-month-old) and old (2-2.5-year-old) BDF1 mice. The parameters measured include total marrow cellularity, CFU-S, CFU-mix, GM-CFC, BFU-E and CFU-F. In all cases the numbers of these cells in the femoral marrow of the old mice was equal to or greater than those in the femoral marrow of young mice. In addition to these parameters we have compared the ability of marrow from young and old mice to repopulate the marrow of recipient mice whose marrow had been eliminated by radiation; to grow in long-term bone marrow cultures; to produce ectopic grafts of marrow beneath the renal capsule of normal recipients; and to supply inhibitor and stimulator of stem cell proliferation in the marrow and to resynthesise these substances. We could detect no differences in any of these functions with the exception of that of resynthesis of the stem cell regulator substances, which appears to be somewhat slower in the old mice. This, however, does not impose any limitation upon the ability of the marrow to function either under normal conditions or in conditions requiring rapid proliferation. Therefore we can find no evidence whatsoever to suggest that aging of the haemopoietic system plays any part in aging of the individual or influencing the life-span.

Aging↗
PubMed1986

Controls on the cell cycle.

The control of cell proliferation, in physiological terms, depends not so much on our understanding of the sequence of biochemical events unfolding as a cell progresses through its proliferation cycle, as upon the recognition by a tissue of the demands for functional cells of a particular type. After considering the modes of control possible, i.e. by recruitment of resting G0-state cells into cycle or by modifying the proliferative behaviour of already proliferating cells, haemopoietic tissue is used as a model to illustrate how the principles of proliferation control in specific cell lineages can be effected. Although the mode of stem cell control is different from that in the maturing populations, all depend on a co-ordination of negative feedback loops for inhibitor and stimulator which are specific to that cell population. The concept of a 'quantal' cell cycle is considered but its application to control in an adult steady-state tissue must be modified to take account of microenvironmental influences which are shown, by their cellular organization, to be an important feature in haemopoietic and probably all other tissues.

Animals↗
PubMed1986

Effects of plutonium-239 on haemopoiesis. I. Quantitative and qualitative changes in CFU-S in different regions of the mouse femur and vertebrae.

Mice were injected with plutonium-239 (960 Bq/mouse) and, over a period of four months, the response of haemopoietic tissue and the self-renewal capacity of its stem cells was monitored. Cellularity, CFU-S concentration and self-renewal capacity were measured in five different regions of bone and marrow--axial and marginal marrow of the femoral shaft, femur shaft, proximal and distal ends of the femur shaft and vertebrae. Cellularities were little affected by plutonium but CFU-S were reduced in all regions, most severely in the bone shaft and marginal marrow due to the initial deposition of plutonium on the bone surface, by four days. The reduction in axial CFU-S, however, was due probably to a relatively long plasma half-life resulting from the tendency of plutonium to combine with plasma proteins. The capacity of CFU-S for self-renewal was reduced and remained low in all zones. Thus, although the highly self-renewing axial CFU-S were depleted, and remained so, due probably to a longer term redistribution of plutonium throughout the marrow, additional proliferation of the more mature CFU-S in the other zones kept their self-renewal low while replenishing their numbers and maintaining a normal cell output.

Alpha Particles↗
PubMed1986

The sensitivity of G0-state haemopoietic spleen colony-forming cells to a stimulus for proliferation.

Haemopoietic spleen colony-forming units (CFU-s) close to the axis (axial CFU-s) of the long bones have a high probability of self-renewal. They are pluripotent cells and are largely in a G0-State. By contrast, CFU-s close to the bone surface (marginal CFU-s) have a lower probability of self-renewal and are probably more mature, though still pluripotent. Most CFU-s proliferation arises in this zone. As a consequence, marginal CFU-s tend to have shorter G0 histories than do axial CFU-s. Femoral marrow was, therefore, divided into axial and marginal populations and the sensitivity of the CFU-s to an endogenous CFU-s-specific proliferation-stimulating factor was assessed and compared by the tritiated thymidine suicide technique. It was found that axial CFU-s are considerably more resistant to stimulation than are marginal CFU-s in that larger doses for longer periods of exposure are required to increase the proliferative activity of the cells. This behaviour is consistent with the suggestion that cells with a low division probability exist in deeper levels of the quiescent G0-state. Although this hypothesis was developed from the behaviour of cells maintained in culture under sub-optimal physiological conditions, this phenomenon appears, in vivo, to be a characteristic of the stem cell population of haemopoietic tissue; their high resistance to stimulation maintaining the axial CFU-s in a quiescent state.

Animals↗
PubMed1986

The kinetic response of haemopoietic precursor cells, in vivo, to highly purified, recombinant interleukin-3.

Interleukin-3 is a murine haemopoietic cell growth factor which has now been prepared in recombinant form, rIL-3. This purified material has been shown to act, in vitro, in a comparable manner to the native material and has recently been shown to have an in vivo effect on the committed, in vitro colony-forming cells. We have examined the effects, in vivo, of low acute and chronic infusion doses on the pluripotent haemopoietic spleen colony-forming cells, CFU-S, (stem cells). The proliferation rate of CFU-S is rapidly increased after administration of rIL-3. This is followed by a migration of the more mature CFU-S to the spleen where, particularly under chronic rIL-3 treatment there is a large increase in CFU-S numbers. The increased proliferation of CFU-S is accompanied by increased differentiation in the form of a large increase in in vitro IL-3 responsive cells. The changes observed were not the result of endotoxin contamination in the rIL-3 preparation. Significantly, however, larger doses of lipopolysaccharide, did mimic the effects of rIL-3 in vivo. IL-3 was not detected in the blood following LPs treatment but it is suggested that LPS acts indirectly on haemopoietic precursor cells by eliciting local production of IL-3, perhaps from adjacent T cells or stromal cells.

Animals↗
PubMed1986

Isolation of haemopoietic spleen colony forming cells.

A simplified and more widely applicable modification of the recently developed methodology for sorting and collecting purified populations of the pluripotent haemopoietic spleen colony-forming cell, CFU-S, is described. Based on their relatively low density and high affinity for wheat germ agglutinin, CFU-S are collected using a fluorescence activated cell sorter. Normal bone marrow cells are labelled with flurorescein labelled wheat germ agglutinin (WGA - FITC) and then subjected to a density cut on metrizamide. Cells with density less than 1.080 gm. ml-1 are sorted on a FACS-IV instrument. Highly fluorescent cells with medium forward and low perpendicular light scatters are collected. These cells are then re-sorted to the same criteria as for the first sort. This double sorting procedure gives a population of cells which, corrected for spleen seeding efficiency, contains about 90% CFC-S. Mixed CFC, in vitro, are also enriched but from the ratios of mixed to spleen CFC, and of 11 to 8 day spleen colony forming ability, there is a clear selection for the earlier, more primitive and/or non-cycling Go-phase CFC-S. This is confirmed by direct observation of autoradiographic labelling indices.

Animals↗
PubMed1985

Regulators of stem cell proliferation in the haemopoietic tissues of W/Wv and S1/S1d mice.

The presence of CFU-S proliferation stimulatory and inhibitory activities in the bone marrow and spleens of normal mice (+/+) and mice with mutations affecting the proliferative behaviour of stem cells (S1/S1d and W/Wv) has been investigated. S1/S1d and +/+ bone marrow and spleen contain virtually no detectable stimulator but the corresponding tissues from W/Wv mice are both strongly stimulatory. S1/S1d marrow in particular, but also +/+ marrow are strongly inhibitory whilst +/+ spleen, S1/S1d spleen, W/Wv marrow and W/Wv spleen all contain inhibitory activity but at a lower specific activity. The data are compatible with studies of cell and tissue grafts that have indicated an intrinsic haemopoietic stem cell defect in W/Wv mice and an extrinsic, microenvironmental defect in S1/S1d mice. It is suggested that they are also compatible with defective regulatory interactions between stem cells and regulator-producing cells and that the W and S1 loci may code for products involved in the production of, or response to, CFU-S proliferation regulators.

Animals↗
PubMed1985

Effect of haemopoietic stem-cell proliferation regulators on early and late spleen colony-forming cells.

An inhibitor and stimulator of CFU-s proliferation can be obtained from haemopoietic tissue containing, respectively, relatively quiescent CFU-s (e.g. normal bone marrow) and proliferating CFU-s (e.g. regenerating bone marrow). Their effects on the proliferative behaviour of steady-state and regenerating marrow CFU-s, which produce colonies 7, 10 and 12 days post-transplantation have been investigated. The results demonstrate changing sensitivities of CFU-s to inhibitor and stimulator as they progress through a developmental age structure, 'Older' CFU-s (producing early spleen colonies) are more sensitive to stimulator, 'Younger' CFU-s (producing late spleen colonies) are more sensitive to inhibitor.

Animals↗