All-trans retinoic acid directly inhibits granulocyte colony- stimulating factor-induced proliferation of CD34+ human hematopoietic progenitor cells

In this study we examine the effects of retinoids on purified CD34+ human hematopoietic progenitor cells. All-trans retinoic acid inhibited granulocyte colony-stimulating factor (G-CSF)-induced proliferation of CD34+ cells in short-term liquid cultures in a dose-dependent fashion with maximal inhibition of 72% at a concentration of retinoic acid of 1 mumol/L. Although no significant effects were observed on granulocyte- macrophage CSF (GM-CSF)--interleukin-3--or stem cell factor (SCF)- induced proliferation, the combinations of G-CSF and each of these cytokines were all inhibited. Moreover, retinol (3 mumol/L) and chylomicron remnant retinyl esters (0.1 mumol/L) in concentrations normally found in human plasma also had inhibitory effects. Single-cell experiments showed that the effects of retinoic acid were directly mediated. Retinoids also significantly inhibited G-CSF-induced colony formation in semisolid medium, with 88% inhibition observed at a concentration of retinoic acid of 1 mumol/L. However, we did not observe any effects of retinoic acid on G-CSF-induced differentiation as assessed by morphology and flowcytometry. Similar to previous findings using total bone marrow mononuclear cells, we observed a stimulation of GM-CSF-induced colony formation after 14 days. We also observed a stimulatory effect of low doses of retinoic acid (30 nmol/L) on blast-cell colony formation on stromal cell layers. Taken together, the data indicate that vitamin A present in human plasma has inhibitory as well as stimulatory effects on myelopoiesis.     

A quantitative method to measure human platelet chemotaxis using indium- 111-oxine-labeled gel-filtered platelets

Human blood platelets have been shown to migrate directionally and specifically toward collagen in plasma in vitro. We have developed a new system to monitor this behavior using a linear 7-compartment chamber with 111In-oxine-labeled gel-filtered platelets. The compartments are separated by various Nuclepore and Millipore filter membranes. Radiolabeled platelets suspended in plasma are placed in the central compartment and the other compartments are filled with platelet- free plasma. When collagen is added to an end compartment, platelets migrate toward that end. The degree of this directed movement or chemotaxis can be measured by counting the radioactivity of the contents of each compartment and then comparing the counts from radiolabeled platelets that have moved to the end that holds the chemotactic inducer with those that have randomly migrated to the opposite end, containing only plasma. This assay system allows quantitative comparisons between the chemotaxis-inducing abilities of different substances and permits the study of soluble materials. Experiments to determine the optimal conditions for the procedure are reported, and the advantages of this new method for the investigation of platelet chemotaxis and the identification of chemotaxins are discussed.     

Elevated platelet-bound IgG associated with an episode of thrombotic thrombocytopenic purpura

The level of platelet-associated IgG (PAIgG) were measured during the successful treatment of a patient with thrombotic thrombocytopenic purpura. Prior to therapy. PAIgG was found to be markedly elevated to 195 fg/cell (normal range 0--3.5 fg/cell). The institution of combined therapy with intensive plasma exchange transfusions, high-dose steroids, and antiplatelet drugs resulted in a complete recovery and a decline in PAIgG to the normal range. The possible role of platelet antibody in the pathogenesis of this disorder is discussed.     

The secretion of plasminogen activators by human myeloid leukemic cells in vitro

Peripheral blood cell preparation from 23 normal subjects and 72 patients with acute and 32 patients with chronic myeloid leukemia were cultured in vitro and released plasminogen activators were analyzed. The quantity of plasminogen activator secreted by leukemic cells varied widely and could not be correlated with the clinical severity of the disease. Immunochemical and electrophoretic techniques have been used to show that normal peripheral blood granulocytes released exclusively urokinase-like plasminogen activator, whereas leukemic cells secreted either urokinase or a tissue activator-like enzyme. The molecular species of enzyme released by acute myeloid leukemic cells may serve as a diagnostic marker of relevance to the management of this disease, since patients with acute myeloid leukemia whose cells released only tissue plasminogen activator did not respond to combination chemotherapy. Tissue plasminogen activators released by leukemic cells may display an unusual electrophoretic pattern that resembles that shown by urokinase. Immunochemical procedures are therefore essential for the correct identification of these enzymes.     

P-selectin glycoprotein ligand-1 (PSGL-1) is a ligand for L-selectin in neutrophil aggregation

In inflammation, activated neutrophils adhere to endothelial cells and aggregate with one another. While beta 2-integrin and L-selectin are essential for aggregation, their ligands remain to be identified. We have previously shown that L-selectin mediates a carbohydrate-dependent interaction in aggregation (Simon et al: J Immunol 149:2765, 1992; Rochon et al: J Immunol 152:1385, 1994). We have suggested that the L- selectin counter-structure is a mucinlike protein and proposed that aggregation occurs through a two-step process involving L-selectin, beta 2-integrin, and their distinct counter-structures (Bennett et al: J Leuk Biol 58:510, 1995). A candidate ligand for L-selectin is P- selectin glycoprotein ligand-1 (PSGL-1), a mucinlike protein on neutrophils that binds P-and E-selectin. Using flow cytometry we show that the number and size of neutrophil aggregates is reduced with Fab fragments of PL1, an anti-PSGL-1 monoclonal antibody that blocks the interaction between P-selectin and PSGL-1 (Moore et al: J Cell Biol 128:661, 1995). In addition, monoclonal antibodies to L-selectin and PSGL-1 were used simultaneously to modulate the availability of these adhesion molecules on individual cell populations. The inhibition of aggregation by these antibodies is consistent with L-selectin and PSGL- 1 being counter-structures. We suggest that L-selectin and PSGL-1 support a collisional cell-cell interaction that represents the first step in neutrophil aggregation.     

Allogenic transplant of canine peripheral blood stem cells mobilized by recombinant canine hematopoietic growth factors

We have studied graft-versus-host disease (GVHD) after transplantation of allogeneic peripheral blood stem cells (PBSC) mobilized by either recombinant canine granulocyte colony-stimulating factor (rcG-CSF) alone or combined with stem cell factor (rcSCF). These studies were prompted by the observation of extremely rapid and sustained engraftment of growth factor-mobilized PBSC in the autologous setting using genetically marked cells and changes in function of T lymphocytes from donors that had undergone mobilization. Specifically, lymphocytes from growth factor-treated donors were hyporesponsive in mixed leukocyte culture and in response to Con A, raising hopes that GVHD in dogs given growth factor mobilized allogenic PBSC might be altered in a beneficial way. Eighteen dogs were given a median of 17.1 x 10(8) PBSC/kg from littermate donors after 920 cGy of total body irradiation without postgrafting immunosuppression. Donors were either genotypically DLA-identical (n = 9) or DLA-haploidentical (n = 9). The median number of colony-forming unit-granulocyte macrophage (CFU-GM) infused was 27 x 10(4)/kg, and the number of CD34+ cells in the transplant was on the order of 4.6 x 10(6)/kg. The dogs received a median of 52.8 x 10(7) CD4 cells/kg and 13.7 X 10(7) CD8 cells/kg. All 18 dogs had prompt hematopoietic engraftment of donor cells as assessed by chimerism studies using variable number tandem repeat, as well as cytogenetic markers. Three of the nine dogs given grafts from DLA- identical littermates had fatal GVHD, five had transient GVHD, and one had no GVHD. All nine DLA-haploidentical recipients of PBSC developed fatal hyperacute GVHD. In conclusion, the expectation about rapid engraftment was fulfilled. However, incidence and severity of acute GVHD after transplantation of mobilized PBSC were not different than previously reported for nonmobilized PBSC or marrow. This model will allow for further studies, including T-cell depletion to minimize GVHD without increasing graft rejection.     

Sleep apnoea caused by rheumatoid arthritis

Sleep apnoea syndrome (SAS) is a rarely documented, but possibly lethal, complication of the instability of the cervical spine in rheumatoid arthritis. Five patients with SAS of a central or peripheral origin are presented, and the problems of recognizing and diagnosing the syndrome are discussed. We hope that clinicians will become more aware of the existence and the different aetiologies of SAS, thus improving early recognition and appropriate treatment. Adequate treatment has proven to increase survival in peripheral SAS and seems to be successful in doing so in central SAS.      

Comparative evidence for a link between Peyer's patch development and susceptibility to transmissible spongiform encephalopathies

Background  

Epidemiological analyses indicate that the age distribution of natural cases of transmissible spongiform encephalopathies (TSEs) reflect age-related risk of infection, however, the underlying mechanisms remain poorly understood. Using a comparative approach, we tested the hypothesis that, there is a significant correlation between risk of infection for scrapie, bovine spongiform encephalopathy (BSE) and variant CJD (vCJD), and the development of lymphoid tissue in the gut.