PLASMA FACTORS INFLUENCING LEUKOCYTE RELEASE IN RATS*

A mathematical model of neutrophil production and control in normal man

A comprehensive mathematical model of neutrophil production in normal man is presented. The model incorporates three control elements which regulate homeostatically the rates of release of marrow cells to proliferation, maturation, and to the blood. The steady state properties of the model are demonstrated analytically. The basic equations of the model, which are nonlinear, have been integrated numerically. The solutions so obtained display graphically the dynamical response of the system to various perturbations, which simulate experimental investigations that have been made in the past of granulocytopoiesis. By an appropriate choice of values of the parameters characterizing the system, it is shown how most of the principal kinetic properties of the neutrophil production and control system are represented in a quantitative manner.

Hematopoietic growth factors: overview and clinical applications, Part I

The growth and differentiation of blood cells is regulated by a group of at least 12 glycoproteins, collectively known as hematopoietic growth factors. Advances in protein biochemistry and molecular genetics have provided the tools for the bulk production of these hormones for clinical application. Clinical trials of macrophage colony-stimulating factor, granulocyte macrophage colony-stimulating factor, granulocyte colony-stimulating factor, and interleukin-3 have all demonstrated significant effects on the peripheral blood counts of the recipients. The clinical usefulness of these agents in ameliorating post-chemotherapy myelosuppression, in the treatment of other cytopenias, and in enhancing engraftment after bone marrow transplantation has already been demonstrated. Potential applications to the therapy and diagnosis of other clinical disorders is under study. The history of the elucidation of these growth factors, our current understanding of their properties, interactions, and clinical effects, and the potential prospects for their future use in the manipulation of human blood cell production are the subject of this review.

Neutrophilic granulocytosis following lead acetate in female mice

Lead induces an abrupt neutrophilic granulocytosis with the peak response detected 4 days after treatment. Using the incorporation of tritiated thymidine as an index of neutrophil production, autoradiographic analysis revealed that only about 16% of the total neutrophil increase is associated with a stimulatory effect on production. The remainder of the increase appears to be linked to the panhistotoxic action of lead, promoting migration of neutrophils from reserve sites in the wake of tissue damage.

Perturbations of granulocyte counts induced by procedural, chemical and physiological events occurring during filtration leukapheresis in rats

During filtration leukapheresis a factor(s) is produced, released or extracted into rat blood which causes a transient granulocytosis in pheresed animals and in recipients of homologous plasma from these animals. To identify which factors contribute to this granulocytosis, the procedural steps involved in filtration leukapheresis as well as a number of chemical agents which are potentially extracted from of produced by the procedure, were tested for their ability to stimulate granulocytosis. Procedural steps tested included the depth of anesthesia, effect of the anticoagulant and possible interactions of blood cells with the plastic tubing in the system (sham-pheresis). Chemical agents tested included common mediators of inflammation and proteinases released by polymorphonuclear leukocytes (PMNs), extracts of nylon fibers and Tygon tubing, nylon monomers and solvents used in the manufacture of nylon, oxidized and decomplemented plasma and lysates of PMNs or microorganisms. Our findings demonstrate that several of these agents contribute to the granulocytosis seen during filtration leukapheresis of rats.

[Humoral factors in the regulation of cell proliferation in haematopoiesis. I. Granulopoiesis and lymphopoiesis (author's transl)]

Humoral Factors obviously play an important role in the maintenance of the steady state in haematopoiesis. There has been work on stimulators and inhibitors for several years. Colony-stimulating factor is the best characterized chemically and biologically. Interest in more or less cell-line-specific stimulators and inhibitors of lymphopoiesis is now growing. Various tissue extracts and cell culture supernatants have been partially purified and characterized biologically and chemically. Monocytes, producing stimulators and inhibitors, have a central function in the regulation of cell proliferation in haematopoiesis. Experiments performed in vitro can help better to understand data so far difficult to explain regarding patients with disturbed haematopoiesis. The in vivo relevance of these experiments, however, remains unclear.

Simulation of murine granulopoiesis

A mathematical model of granulocyte formation and its regulation has been made, using three negative feedback loops (i.e., two "chalone loops" and one "leucocytosis-inducing factor loop", as well as a short-lasting signal to cell division, induced by cell death. Experimental regeneration curves obtained after treating mice with two injections of cyclophosphamide or with one injection of vinblastine were reasonably well simulated. The simulations suggested that (i) immature granulocytes have a considerable capacity for additional mitoses (self-renewal); (ii) if an inhibitor of cell multiplication (chalone) is an important regulatory factor, it may be produced not only by mature, but also by immature granulocytes; and (iii) chalone may affect maturation times as well as generation times. It is possible to test experimentally these and other deductions mode from the model.

The effects of endotoxin on CFU-C clonogenic capacity of marrow and spleen cells from RLV-A infected mice

Bacterial endotoxin was used as a granulopoietic stressor in the RLV-A infected mouse as a means of studying the marrow and spleen CFU-C response to this agent. A control group of phenylhydrazine (PHZ)-treated mice was also employed to induce a reduction in hematocrit levels equivalent to that observed in the early and mid-stage of the disease course and was used to determine whether the cloning observed was a manifestation of RLV-A disease or could be attributed solely to the resulting anemia. Both RLV-A infected and PHZ marrow from mice maintained at a hematocrit of 40% exhibited similar but higher than normal clonogenic capacities, whereas RLV-A (hematocrit 40%) spleen had an expanded number of CFU-C's when compared to PHZ treated (hematocrit 40%) mice. Examination of spleens of endotoxin-treated RLV-A (hematocrit 30%) infected mice indicated a 6 to 7-fold increase in splenic CFU-C numbers compared to endotoxin-treated normal mice. PHZ plus endotoxin-treated normal animals (hematocrit 30%) had splenic CFU-C values which were approximately half those of RLV-A infected (hematocrit 30%) endotoxin-treated animals. Results of this experiment suggest a fully operable but greater than normal CFU-C storage pool in the RLV-A infected mouse spleen which does not seem to be due entirely to the anemia.

Lead-induced leukocytosis in female mice

Lead acetate was shown to stimulate a striking leukocytosis in young adult female mice. The effect was manifest 4 days after lead injection and continued throughout the following 4 days. At the higher treatment level, lead induced an increase of 300% for both monocytes and neutrophils. The leukocytosis was due primarily to the elevated levels of neutrophils as suggested by a decrease in the ratios of peripheral agranulocytes to granulocytes. No differences from normal leukocyte cytology were observed in blood samples collected from animals receiving lead.

Eosinophilopoietin. A circulating low molecular weight peptide-like substance which stimulates the production of eosinophils in mice

In earlier studies, methods were developed to raise specific antibodies in rabbits against purified suspensions of mouse or human eosinophils. On administration of antieosinophil serum (AES) to mice, the mature eosinophils in tissues, peripheral blood, and bone marrow were depleted, while the immature eosinophil pool in the bone marrow was observed to proliferate. The current investigations explore the generation of eosinophilopoietic factors during AES-induced eosinophilopenia. Mice received three injections of AES, one every other day. As the peripheral eosinophil counts started to recover after the last AES injection, the serum was collected and transferred to normal animals. Within 2 days the recipients showed an increase in peripheral blood as well as in bone marrow eosinophils. The rise in bone marrow eosinophils was due to newly formed cells as evidenced by increased uptake of [(3)H]thymidine. The generation of eosinophilopoietic activity was specifically related to depletion of eosinophils but not neutrophils. The eosinophilopoietic activity was: (a) dependent on the volume of serum transferred, (b) lost on dialysis, and (c) largely heat labile. The activity eluted as a low molecular weight substance on G-25 Sephadex and was digested by pronase but not by trypsin. Active fractions collected from G-25 columns were not chemotactic for the eosinophils in vitro. Thus, specific depletion of mature eosinophils generates a low molecular weight peptide which stimulates eosinophilopoiesis in vivo. It is suggested that this substance be named eosinophilopoietin.

Stimulation of granulocytic colony formation in agar diffusion chambers implanted in cyclophosphamide pretreated mice

The growth of mouse bone marrow colonies in agar diffusion chambers (ADCs) was evaluated using host mice injected with saline or with cyclophosphamide (CY) before chamber insertion. The mice pretreated with cyclophosphamide proved more effective hosts than control (saline pretreated) mice, indicating that cyclophosphamide causes the elaboration of a stimulating factor acting on colony precursor cells. Assays of the factor for colony stimulating activity against mouse bone marrow cells in agar culture in vitro suggest that potentiation may be due to a slight temporary increase in the level of colony stimulating factor (CSF) in the chamber environment, although a parallel increase was not detected in the serum. Stem cell recovery from the ADCs, measured by spleen colony formation, suggests that the stimulus may act by increasing differentiation at the level of the pluripotential stem cell.

Leukokinetic studies. 13. A non-steady-state kinetic evaluation of the mechanism of cortisone-induced granulocytosis

The mechanism by which adrenocortical steroids induce granulocytosis in man has been investigated using granulocytes labeled with radioactive diisopropylfluorophosphate. After an intravenous injection of 200 mg of cortisol was given to five normal subjects, the mean value for the total blood granulocyte pool increased from 79 to 138 x 10(7) cells per kg of body weight and reflected an increase in the size of both the circulating granulocyte pool and the marginal granulocyte pool. When granulocytes in the circulation were labeled with diisopropylfluorophosphate and granulocytosis was induced later by the intravenous administration of cortisol, the rate of decline of granulocyte specific activity was increased, indicating that the blood pool was being diluted at an accelerated rate by unlabeled cells entering from the bone marrow. The rate of egress of granulocytes from the blood pool to an inflammatory exudate was studied by the "skin window" technique. After the administration of cortisol, there was a mean reduction in the cellularity of induced inflammatory exudates of 75%. However, this reduction in cellularity varied considerably from subject to subject (45-98%). From these studies we can infer that steroids induce an absolute granulocytosis by decreasing the rate of egress of cells from the total blood granulocyte pool as well as by increasing the influx of cells from the bone marrow. By model simulation studies of the non-steady state induced by cortisol injection, it has been possible to quantitate these rate changes. In the present studies cortisol injection resulted in a mean decrease in blood granulocyte egress of 74% (1-99%) and a mean increase in cell inflow of 450% (300-750%).