The proliferative capacity of pure red cell aplasia bone marrow cells.

Pure red cell aplasia (PRCA) is a heterogeneous disorder. Immunologic abnormalities have recently been uncovered suggesting that both cell-mediated and humoral immune mechanisms may be of etiological importance in PRCA. Utilizing a technique for the cloning of bone marrow erythroid precursors, we determined the in vitro proliferative capacity of erythroid cells obtained from 21 patients with PRCA. Bone marrow cells from one group of patients produced normal or increased numbers of erythroid colonies while the in vitro proliferative capacity of bone marrow cells from a second group was characterized by subnormal erythroid colony formation. Sera obtained from the former group was frequently associated with demonstrable serum inhibitors of erythropoiesis, while PRCA in the latter group was probably the consequence of intrinsic erythroid stem cell defects or pathologic cellular interactions with nonerythroid regulatory cells. This survey of a relatively large population of patients with PRCA provides evidence for the multiple causative mechanisms that can be operative in the production of PRCA.     

Pure red cell aplasia: review of treatment and proposal for a treatment strategy.

The management of pure red cell aplasia (PRCA) continues to challenge clinical investigators because the pathophysiology is heterogeneous and poorly understood. There are five treatment regimens that have established efficacy for patients with chronic PRCA. In patients with congenital hypoplastic anemia the best results have been reported using corticosteroids. Cyclosporine A is recommended as the treatment of choice in acquired PRCA. High-dose intravenous immunoglobulin therapy is highly effective in PRCA associated with parvovirus B19 infections and impaired IgG-antibody response. Treatment failures may be successfully managed with horse anti-human thymocyte globulin or cyclophosphamide plus corticosteroids. The potential of hematopoietic growth factors in the treatment of PRCA awaits further studies.     

Retrovirus-induced feline pure red cell aplasia: the kinetics of erythroid marrow failure

Cats viremic with feline leukemia virus subgroup C (FeLV-C) develop pure red cell aplasia (PRCA) characterized by the loss of detectable late erythroid progenitors (CFU-E) in marrow culture. Normal numbers of early erythroid progenitors (BFU-E) and granulocyte-macrophage progenitors (CFU-GM) remain, suggesting that the maturation of BFU-E to CFU-E is impaired in vivo. We have examined the cell cycle kinetics of BFU-E and their response to hematopoietic growth factor(s) to better characterize erythropoiesis as anemia develops. Within 3 weeks of FeLV-C infection, yet 6-42 weeks before anemia, the traction of BFU-E in DNA synthesis as determined by tritiated thymidine suicide increased to 43 +/- 4% (normal 23 +/- 2%) while there was no change in the cell cycle kinetics of CFU-GM. In additional studies, we evaluated the response of marrow to the hematopoietic growth factor(s) present in medium conditioned by FeLV-infected feline embryonic fibroblasts (FEA/FeLV CM). With cells from normal cats or cats viremic with FeLV-C but not anemic, a 4-fold increase in erythroid bursts was seen in cultures with 5% FEA/FeLV CM when compared to cultures without CM. However, just prior to the onset of anemia, when the numbers of detectable CFU-E decreased, BFU-E no longer responded to FEA/FeLV CM in vitro. BFU-E from anemic cats also required 10% cat or human serum for optimal in vitro growth. These altered kinetics and in vitro growth characteristics may relate to the in vivo block of BFU-E differentiation and PRCA. Finally, when marrow from cats with PRCA was placed in suspension culture for 2 to 4 days in the presence of cat serum and CM, the numbers of BFU-E increased 2- to 4-fold although no CFU-E were generated. By 4 to 7 days, CFU-E were detected, suggesting that conditions contributing to the block of erythroid maturation did not persist. The suspension culture technique provides an approach to study further the defect in erythroid differentiation characteristic of feline PRCA.     

An assay for serum cytotoxicity against erythroid precursor cells in pure red cell aplasia

Several reports have indicated that a circulating serum inhibitor (antibody) is involved in the pathogenesis of acquired pure red cell aplasia (PRCA). In the present study, the pathophysiologic significance of this inhibitor was assessed according to the status of erythroid progenitor cells in the bone marrow. So far, direct proof for the antibody acting against erythroid stemcells was lacking. Employing an "in vitro" assay, erythroid colony forming cell (CFU-e) numbers in PRCA marrow were quantified and the cytotoxic effect of PRCA serum on CFU-e was investigated. It was revealed that the CFU-e population size in the marrow of PRCA patients was severely reduced; at the same time the relative number of myeloid colony forming cells was normal. The serum was demonstrated to contain a factor cell which was cytotoxic to CFU-e, in the presence of complement. The results indicate that inhibition of erythropoiesis in PRCA is achieved by a complement dependent plasma factor which eliminates or inactivates CFU-e and which constitutes an effective block at the precursor cell level in the differentiation pathway of the erythroid line. The data present a practical assay for measuring cytotoxic factors affecting erythroid stem cells.     

Pure red cell aplasia and thymoma associated with high levels of the suppressor/cytotoxic T lymphocyte subset.

A 64 year old man admitted to hospital with increasing effort dyspnoea and lethargy was found to have a thymoma and pure red cell aplasia. Lymphocytes accounted for 20-30% of marrow cells, and numbers of T8 suppressor/cytotoxic cells in peripheral blood were greatly increased. He remained anaemic after removal of the thymoma despite blood transfusions, and immunosuppression with prednisolone 60 mg and cyclophosphamide 50 mg daily was started. The dose of prednisolone was reduced to 15 mg owing to steroid myopathy and the risk of opportunistic infection. He went into remission, and the dose was further decreased to 10 mg daily.     

Antibodies against interspecies erythrokaryocyte antigen in patients with partial red cell aplasia of the bone marrow

Immunofluorescense and cytotoxicity test in vitro were used to demonstrate specific antibodies in sera of 11 out of 19 patients with partial red cell aplasia (PRCA). The antibodies reacted with erythroblast cells from embryos and adult men, with bone marrow cells from a female patient suffering from acute erythroleukemia, with erythrokaryocytes of mouse embryos and cells of Rauscher's viral erythroleukemia. The results of cross adsorption and blockade of the immunofluorescent reaction of the sera of PRCA patients with antibodies against mouse erythroblast antigen bearing an interspecies determinant suggest that in the pathogenesis of PRCA there takes part an autoimmune reaction against specific interspecies antigen to erythrokaryocytes. This antigen is apparently similar to antigen against mouse erythroblast cells.     

Coalescing red algae exhibit noninvasive,reversible chimerism

Chimerism is produced by the somatic fusion of two or more genetically distinct conspecific individuals. In animals, the main cost of fusion is competition between genetically different cell lineages and the probability of original cell line replacement by more competitive invasive lines, which limits its natural frequency (3%–5%). In red and brown seaweeds, chimerism is widespread (27%–53%), seemingly without the negative outcomes described for animals. The rigidity of cell walls in macroalgae prevents cell motility and invasions. In addition, in moving waters, most somatic fusions involve the holdfast. Histological observations in laboratory‐built bicolor macroalgal chimeras indicated that upright axes emerge from the base of plants by proliferation and vertical growth of discrete cell groups that include one or just a few of the cell lineages occurring in the holdfasts. Laboratory experiments showed growth competition between cell lineages, thus explaining lineage segregation during growth along originally chimeric erect axes. Genotyping of the axes showed more heterogeneous tissues basally, but apically more homogeneous ones, generating a vertical gradient of allele abundance and diversity. The few chimeric primary branches produced, eventually became homogenous after repeated branching. Therefore, coalescing macroagae exhibit a unique pattern of post‐fusion growth, with the capacity to reverse chimerism. This pattern is significantly different from those in animals and land plants, suggesting chimerism is a biologically heterogeneous concept.     

Polyamines--sickling red blood cell interaction.

The binding of polyamine as a function of concentration to normal and sickling rcc'. blood cells is analyzed by Langmuir type binding isotherms, based on the Gouy-Chapman model for an electrical double Iayer, where the zeta potential is a function of only the normal distance coordinate. For normal erythrocytes, the apparent exotropic binding constants are found to be 103, 110, and 130 dl/g at normal distance coordinates of 4, 5, and 6 Å, iezpectively. The esotropic binding constant is determined to be 420 dl/g at a distance of 7 Å. For sickling red blood cells, the apparent exotropic binding constants are 3.3, 3.8, 4.6, and 6-7 dl/g at a distance of 4 to 7 Å. The esotropic binding constant at a distance of 8 Å is found to be 12-9 dl/g. The apparent binding affinity of polyamines to the normal red blood cell. therefore, is approximately 30 times greater than to the sickling erythrocyte.The Praxis pulse nuclear magnetic resonance spectrometer is used to determine the spin-lattice relaxation time (T₁) for water in the presence of normal and sickling red blood cells. The spin-lattice relaxation time is found to be 540 ms for normal erythrocytes and 445 ms for sickling red blood cells in the oxy state. Differences in the spin-spin relaxation time (T₂) for the two types of erythrocyte are negligible, being within the range of normal experimental error.     

Thermodynamics of red cell glycolysis.

1. Changes of Gibbs energy, enthalpy and entropy in red cells during steady-state glycolysis were discussed. 2. The heat production of red cells at various metabolic conditions was measured on a flow microcalorimeter with simultaneous analyses of lactate and other metabolites. The results were discussed in relation to enthalpy changes of the different metabolic steps in the glycolytic pathway.     

Thermoelasticity of red blood cell membrane.

The elastic properties of the human red blood cell membrane have been measured as functions of temperature. The area compressibility modulus and the elastic shear modulus, which together characterize the surface elastic behavior of the membrane, have been measured over the temperature range of 2-50 degrees C with micropipette aspiration of flaccid and osmotically swollen red cells. In addition, the fractional increase in membrane surface area from 2-50 degrees C has been measured to give a value for the thermal area expansivity. The value of the elastic shear modulus at 25 degrees C was measured to be 6.6 X 10(-3) dyne/cm. The change in the elastic shear modulus with temperature was -6 X 10(-5) dyne/cm degrees C. Fractional forces were shown to be only on the order of 10-15%. The area compressibility modulus at 25 degrees C was measured to be 450 dyne/cm. The change in the area compressibility modulus with temperature was -6 dyne/cm degrees C. The thermal area expansivity for red cell membrane was measured to be 1.2 X 10(-3)/degrees C. With this data and thermoelastic relations the heat of expansion is determined to be 110-200 ergs/cm2; the heat of extension is 2 X 10(-2) ergs/cm2 for unit extension of the red cell membrane. The heat of expansion is of the order anticipated for a lipid bilayer idealized as twice the behavior of a monolayer at an oil-water interface. The observation that the heat of extension is positive demonstrates that the entropy of the material increases with extension, and that the dominant mechanism of elastic energy storage is energetic. Assuming that the red cell membrane shear rigidity is associated with "spectrin," unit extension of the membrane increases the configurational entropy of spectrin by 500 cal/mol.