Inhibition of murine erythroid colony formation in vitro by interferon gamma and correction by interferon receptor immunoadhesin

It has been previously reported that inhibition of human erythroid colony-forming units (CFU-E) in vitro by interleukin-1 (IL-1) is an indirect effect, occurring through the production of interferon gamma (IFN gamma). IFN gamma, in turn, inhibits CFU-E colony formation directly, and its inhibitory effect can be overcome by exposure to high concentrations of erythropoietin (EPO). To develop an in vitro animal model for investigating inhibition of erythropoiesis by IFN gamma, the effects of recombinant murine (rm) IFN gamma on highly purified CFU-E from the spleens of mice infected with the anemia strain of the Friend virus (FVA) were studied. rmIFN gamma inhibited CFU-E colony formation in a dose-dependent manner. This inhibition occurred with large (> or = 8 cell) colonies only; smaller colonies were not affected. The inhibitory effect was corrected to 72% of control by high EPO concentrations of 64 U/mL. Murine CFU-E were then cultured with rmIFN gamma in the presence of a soluble murine IFN gamma receptor fused to the hinge and Fc domains of the human IgG1 heavy chain (mIFN gamma R- IgG). Inhibition of CFU-E colony formation by rmIFN gamma (100 U/mL) was corrected by mIFN gamma R-IgG in a dose-dependent manner, with an approximate IC50 of 0.05 nmol/L, and complete or near complete correction at 0.5 nmol/L. Similarly, a human IFN gamma R-IgG greatly reduced the inhibitory effect of recombinant human IFN gamma on human CFU-E. These experiments provide an in vitro animal model for studying the inhibitory effects of IFN gamma on erythropoiesis and indicate that IFN gamma R-IgG may be a useful agent for reducing the toxicity of IFN gamma in vivo.     

Loxoribine induces chronic lymphocytic leukemia B cells to traverse the cell cycle

Leukemic B cells from a majority of patients with chronic lymphocytic leukemia (CLL) enter the cell cycle upon stimulation in vitro with loxoribine, a potent 7,8-disubstituted guanine ribonucleoside immunostimulant. In the absence of added costimulants, a proportion of these cells become activated and undergo DNA synthesis and mitosis accompanied by a marked increase in expression of an array of cell surface activation antigens. The resultant activated B-CLL cells exhibit greatly enhanced sensitivity to cycle-active cytotoxic drugs. This approach may be of potential value in the therapy of CLL.     

Cytokine-specific regulation of urokinase receptor (CD87) expression by U937 mononuclear phagocytes

Mononuclear phagocytes concentrate urokinase-type plasminogen activator (uPA) at the cell surface by expressing membrane uPA receptors (uPAR). This study examines the ability of exogenous cytokines to alter expression of membrane-associated uPA and uPAR in U937 mononuclear phagocytes. Cells were stimulated with recombinant interferon gamma (IFN gamma) or tumor necrosis factor alpha (TNF alpha), followed by immunolabeling for uPA or uPAR and flow cytometry. IFN gamma increased surface uPA 2.2-fold relative to unstimulated controls (P < .001), whereas TNF alpha had no significant effect. Likewise, maximal uPA binding capacity was increased 2.8-fold by IFN gamma (P < .02), but was not affected by TNF alpha. In unstimulated cells, 50% of receptors were occupied by endogenously generated uPA, and this proportion was not affected by either cytokine. IFN gamma upregulated uPAR 2.1-fold relative to unstimulated controls (P < .001), whereas TNF alpha had no effect. In contrast to effects on surface protein, TNF alpha induced a substantial increase in uPAR mRNA, equaling the effect of IFN gamma. In addition, both cytokines doubled the intracellular uPAR pool (P < .01). By contrast, TNF alpha induced a 2.5-fold increase in the level of uPAR protein released into conditioned medium (compared with unstimulated cells), whereas IFN gamma had no effect. These results indicate that uPAR expression is regulated in a cytokine-specific fashion. Some stimuli, such as TNF alpha, may increase uPAR synthetic activity without a corresponding change in membrane expression, because of enhanced release of uPAR from the cell. Cytokine-specific modulation of uPAR may be important in regulating the function of mononuclear phagocytes in inflammation and tissue repair.     

Immediate results and long-term follow-up after repeat balloon aortic valvuloplasty.

Balloon aortic valvuloplasty (BAV) was performed in 219 elderly patients with aortic stenosis between December 1985 and April 1990. Forty-three patients underwent repeat BAV for symptomatic restenosis of the aortic valve 13 +/- 8 mo following initial BAV. To evaluate the outcome following initial and repeat BAV, hemodynamic results were analyzed according to the following subgroups: BAV 1--initial BAV for all patients (n = 219); BAV 1/1--initial BAV in those who had only one BAV (n = 176); BAV 1/2--the initial BAV in those who had repeat BAV (n = 43); and BAV 2--repeat BAV (n = 43). The mean age of patients undergoing BAV 2 was 82 +/- 6 yr compared to 78 +/- 10 yr for all patients undergoing BAV 1 (p = .01). At the time of BAV 1 there was no difference in baseline or post-valvuloplasty aortic valve area (AVA) or peak aortic valve gradient (AVG) for patients having BAV 1/1 compared to those having BAV 1/2. However, for patients having repeat BAV, although the magnitude of the hemodynamic improvement of BAV 1/2 (AVA increased from 0.6 to 0.9 cm2, AVG decreased from 68 to 34 mm Hg, p less than .001) was similar to the magnitude of the hemodynamic improvement of BAV 2 (AVA increased from 0.5 to 0.8 cm2, AVG decreased from 65 to 34 mm Hg, p less than .001), the baseline AVA (0.5 cm2 at BAV 2 vs. 0.6 at BAV 1/2) and the post-valvuloplasty AVA (0.8 cm2 at BAV 2 vs. 0.9 at BAV 1/2) were significantly smaller (p less than .004).(ABSTRACT TRUNCATED AT 250 WORDS)