Particle-induced erythropoietin-independent effects of erythroid precursor cells in murine bone marrow.

A possible regulatory action of phagocytic cells on erythropoiesis was investigated by infusion of inert polystyrene latex particles (LAT). LAT appeared to induce changes in the femoral content of erythroid progenitor cells. These changes were most pronounced in primitive erythroid progenitor cells (BFUe) and appeared to be gradually damped in more differentiated populations (CFUe and erythroblasts). LAT did not influence granulocyte/macrophage progenitor cells (CFUc). The effects of LAT could not be attributed to changes in the systemic erythropoietin (EP) concentration. Administration of dexamethason nullified the effect of low doses of LAT, suggesting that phagocytosis of the particles is essential to the observed effects. Erythroid burst formation was previously found to be dependent on a bone marrow associated activity, termed BFA (burst feeder activity). BFA acts as an in vitro inducer of EP-responsiveness in BFUe. In this study it was found that LAT-induced changes in femoral erythroid progenitor cell content were characteristically preceded by corresponding changes in BFA. It was concluded that BFA-associated cells probably play a role in vivo in the early differentiation of erythroid progenitor cells. The present data are interpreted as direct in vivo evidence supporting a two-step regulatory model operating in erythropoiesis and provide evidence that phagocytic cells are a component of the erythroid haemopoietic inductive micro-environment.

The specificity of heterologous antiserum against brain of nude mice.

Serum prepared in rabbits against brain of nude mice was tested for its T-cell specificity by immunoperoxidase staining. The difference in activity of this anti-brain serum against early precursors and more differentiated precursors of the haemopoietic cell lines was investigated by CFU-s and CFU-c determination after serum incubation. The results showed that the activity of the anti-nude brain serum is completely comparable to serum prepared against brain of normal mice.

Influence of interferon preparations on the proliferative capacity of human and mouse bone marrow cells in vitro.

The toxicity of interferon to bone marrow was studied by the use of in vitro colony forming assays for hemopoietic cells. In the same study the relative inhibitory effects of two clinically common interferon preparations, leukocyte and fibroblast interferons, were compared with regard to their effect on both myeloid [colony-forming unit, culture (CFUc)] and erythroid [colony-forming unit, erythroid (CFUe)] progenitor cells. CFUe formation in human bone marrow cells in vitro appeared to be fairly resistant to both interferons. Only high doses of both interferons gave a marked inhibition of CFUe. However, the toxicity of leukocyte and fibroblast interferon was divergent for CFUe in human bone marrow. Leukocyte interferon appeared to be considerably more inhibitory for CFUe than was fibroblast interferon. The effects of mouse interferon, induced in L929 cells, on the growth of CFUc and CFUe in murine bone marrow cells were comparable with those of fibroblast interferon on human cells. The toxicity of human and murine interferon was species specific. Except for the toxicity of leukocyte interferon to CFUc in human bone marrow, the toxicity of interferon was marked only with concentrations on interferon far exceeding the amount necessary to produce an antiviral state in vitro.

Studies of the hemopoietic microenvironments: effects of acid mucopolysaccharides and dextran sulphate on erythroid and granuloid differentiation in vitro.

The effects of acid mucopolysaccharides (AMPS) on in vitro erythrocytic and granulocytic colony formation of murine bone marrow cells have been studied. High concentrations of chondroitin sulphate A, B and C and heparitin sulphate partly or completely inhibited the response of CFU-E to erythropoietin stimulation whereas addition of heparin, hyalyronic acid and keratan sulphate II in concentrations up to 100 microgram/ml did not elicit an inhibition of erythrocytic colony formation. The granulocytic colony formation was not significantly affected by AMPS-addition under these circumstances. Low concentrations of chondroitin sulphate A and B evoked a stimulatory effect on the CFU-E number. The synthetic polyanion dextran sulphate did not affect the erythrocytic and granulocytic colony formation. It is concluded that AMPS can affect the in vitro erythrocytic proliferation and differentiation in concentrations which do not affect the granulocytic maturation. Since stromal cells, i.e. macrophages and reticular cells, in bone marrow in vivo have the ability to produce and remove AMPS in the extravascular matrix we postulate that stomal cells may be involved in the regulation of erythroid progenitor cell maturation.

The relation between the proliferative activity and the differentiation pattern of bone marrow cells from Rauscher leukemia virus infected BALB/c mice.

The proliferative activity of bone marrow from Rauscher Leukemia Virus infected mice was studied during the course of the disease. Spleen colony assay and thin-layer agar technique, both presumably reflecting the number of pluripotent hemopoietic stem cells, showed a 2.6 times increase in colony forming units (CFU-S resp. CFU-A) at 12 days after infection. The Bradley method of culturing colonies in agar, which is stated to reflect the number of myeloid precursor cells, resulted in a slower rise in colony forming units (CFU-C) with a maximum of 2.3 times increase at 19 days after infection. These results were compared to the differentiation patterns of the bone marrow at similar intervals after infection. The course of the CFU-C curve parallelled the rise in the number of the myeloblasts in the bone marrow. The pattern of CFU-A and CFU-S curves preceded the rise in number of CFU-C by 7 days. It was found, that RLV infection apart from causing an erythroblastosis in the spleen and a severe anemia is followed by a disappearance of neutrophil granulocytes from the bone marrow. The latter phenomenon is probably the primary cause of the increase of hemopoietic stem cells.