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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 1,459 records · Page 81Linked to original sources
PubMed1987

Interferon-gamma synergizes with tumor necrosis factor and with interleukin 1 and requires the presence of both monokines to induce antitumor cytotoxic activity in macrophages.

Small concentrations of recombinant murine interferon-gamma (MuIFN-gamma), recombinant human interleukin 1 (HuIL-1), and recombinant murine tumor necrosis factor (MuTNF), added separately to cultures of thioglycolate-elicited peritoneal macrophages, produced no cytotoxic activity against L5178Y cells, a tumor cell line which is resistant to the direct toxic effects of these cytokines, either alone or in combination. However, small concentrations of MuIFN-gamma when combined with small concentrations of either HuIL-1 or MuTNF activated these macrophages to produce cytotoxic effects against L5178Y cells; small concentrations of HuIL-1 and MuTNF in combination had no macrophage activating activity. Specific antibody to MuTNF blocked the macrophage-activating synergistic effects of MuIFN-gamma + HuIL-1, and specific antibody to HuIL-1 blocked the macrophage-activating activity of MuIFN-gamma + MuTNF, indicating that MuTNF was induced in macrophage cultures treated with MuIFN-gamma + HuIL-1, and that murine IL-1 was induced in macrophage cultures treated with MuIFN-gamma + MuTNF. These results indicate that all three cytokines are required for induction of antitumor cytotoxic activation of macrophages. Experiments with a concentration of MuIFN-gamma which alone could activate macrophages revealed that both MuTNF and murine IL-1 were required for this activation. The demonstration that small concentrations of these three cytokines can act synergistically, but not separately, to activate macrophages indicates the importance of cytokine combinations in immunoregulation and in anti-tumor cell-mediated immune responses.

Animals↗
PubMed1987

Protein translocation into Escherichia coli membrane vesicles is inhibited by functional synthetic signal peptides.

A synthetic peptide corresponding to the signal sequence of wild type Escherichia coli lambda-receptor protein (LamB) inhibits in vitro translocation of precursors of both alkaline phosphatase and outer membrane protein A into E. coli membrane vesicles (half-maximal inhibition at 1-2 microM). By contrast, the inhibitory effect was nearly absent in a synthetic peptide corresponding to the signal sequence from a mutant strain that harbors a deletion mutation in the LamB signal region and displays an export-defective phenotype for this protein in vivo. Two peptides derived from pseudorevertant strains that arose from the deletion mutant and exported LamB in vivo were found to inhibit in vitro translocation with effectiveness that correlated with their in vivo export ability. Controls indicated that these synthetic signal peptides did not disrupt the E. coli membrane vesicles. These results can be interpreted to indicate that the presequences of exported proteins interact specifically with a receptor either in the E. coli inner membrane or in the cytoplasmic fraction. However, biophysical data for the family of signal peptides studied here reveal that they will spontaneously insert into a lipid membrane at concentrations comparable to those that cause inhibition. Hence, an indirect effect mediated by the lipid bilayer of the membrane must be considered.

Alkaline Phosphatase↗
PubMed1987

Spontaneous and induced interferon production by peripheral blood leucocytes from control population and patients with herpes genitalis.

The spontaneous and PHA induced levels of interferon were measured in peripheral blood leucocyte cultures of twenty-eight individuals diagnosed as positive for herpes genitalis, and in a group of control subjects. As reported by Cunningham and Merigan [1983] for herpes labialis, leucocytes from individuals with herpes genitalis produced low levels of interferon spontaneously; however, similar results were found for individuals within the control population. No statistically significant difference could be found for PHA induced interferon levels, antigen induced interferon levels, or helper/suppressor cell ratios between the herpes genitalis population and control population. Our results indicate that interferon does not play a major role in the latency or recurrence of herpes genitalis.

Antigens, Viral↗
PubMed1987

A training model for the stereomicroscopic evaluation of flap survival.

The stereomicroscopic appearance of the vasculature and circulation of groin flaps, with their epigastric pedicles divided at various time intervals, is an early diagnostic indication of flap viability. A simple and comprehensive training model, with characteristic vascular and flow changes within a single flap, is provided in rats, with pedicles transected at three to four days after the flap is raised.

Animals↗
PubMed1987

High-dose almitrine bismesylate inhibits hypoxic pulmonary vasoconstriction in closed-chest dogs.

The effect of almitrine bismesylate on the hypoxic pulmonary vasoconstrictor (HPV) response was studied in seven closed-chest dogs anesthetized with pentobarbital and paralyzed with pancuronium. The right lung was ventilated continuously with 100% O2, while the left lung was ventilated with either 100% O2 ("hyperoxia") or with an hypoxic gas mixture ("hypoxia": end-tidal PO2 = 50.1 +/- 0.1 mmHg). Cardiac output (CO) was altered from a "normal" value of 3.10 +/- 0.18 l . min-1 to a "high" value of 3.92 +/- 0.16 l . min-1 by opening arteriovenous fistulae which allowed measurements of two points along a pressure-flow line. These four phases of left lung hypoxia or hyperoxia with normal and high cardiac output were repeated in the presence and absence of almitrine. Almitrine bismesylate was administered as a constant infusion of 14.3 micrograms . kg-1 . min-1 for a mean plasma concentration of 219.5 +/- 26.4 ng . ml-1. Relative blood flow to each lung was measured with a differential CO2 excretion (VCO2) method corrected for the Haldane effect. With both lungs hyperoxic, the percent left lung blood flow (%QL-VCO2) was 44 +/- 1%. When the left lung was exposed to hypoxia, the %QL-VCO2 decreased significantly to 22 +/- 1%. However, with the administration of almitrine, the %QL-VCO2 during left lung hypoxia increased significantly to 36 +/- 2%. The arterial oxygen tension decreased significantly between hyperoxia (PaO2 = 633 +/- 6 mmHg) and hypoxia (271 +/- 31 mmHg). With the addition of almitrine, there was no change during hyperoxia; however, during hypoxia, the PaO2 decreased significantly to 124 +/- 15 mmHg. Cardiac output did not influence these findings. The pulmonary vascular conductance (G) is the slope of the pressure-flow line.(ABSTRACT TRUNCATED AT 250 WORDS)

Almitrine↗
PubMed1987

Effects of antibiotics and other inhibitors on ATP-dependent protein translocation into membrane vesicles.

The effects of several membrane antibiotics and other agents on ATP-dependent protein translocation were examined in membrane vesicles under conditions where no significant proton motive force was present. The membrane perturbants ethanol and procaine abolished ATP-dependent protein translocation. Phenethyl alcohol at low concentrations abolished translocation, whereas at high concentrations it allowed precursors to be translocated but inhibited their processing. Translocation of precursors promoted by phenethyl alcohol was temperature dependent and occurred without an added energy source but was enhanced by ATP. However, such precursors could not be further processed to mature forms upon removal of the alcohol. The membrane-active antibiotics polymyxin B and gramicidin S were strong inhibitors of translocation, whereas gramicidin D, cerulenin, and mycobacillin had no effect even at higher concentrations, indicating some specificity in interference with protein translocation. Duramycin, an antibiotic previously shown to affect protein-lipid interaction, severely impaired protein translocation. These results showed that membrane structures play important roles, either directly or indirectly, in protein translocation. Chelating agents 1,10-phenanthroline and EDTA, but not EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid], also abolished protein translocation.

Adenosine Triphosphate↗