Differential effects of ouabain on human cell-mediated cytotoxicity. I. Inhibition of mitogen-induced cellular cytotoxicity and antibody-dependent cellular cytotoxicity against chicken red cell targets.

The effects of ouabain, a known inhibitor of lymphoproliferation, were studied in relation to the cytotoxic effector function of human peripheral blood mononuclear leukocytes (MNL) against chicken red blood cell (CRC) targets. MNL effectors lysed ⁵¹Cr-labeled CRC targets in the presence of PHA (mitogen-induced cellular cytotoxicity—MICC) or rabbit anti-CRC antibody (antibody-dependent cellular cytotoxicity—ADCC) in the absence of ouabain. The addition of ouabain to the cytotoxic reaction caused profound diminution of MICC with greater than 90% suppression of killing at ouabain concentrations of 5 × 10^?4M; ADCC was much more resistant to the effects of ouabain with only 60 to 70% inhibition of killing at similar ouabain concentrations (P < 0.01). Similar ouabain inhibition of MICC occurred whether the effector cell populations were unseparated MNL, depleted of monocytes, enriched for T cells, or depleted of T cells, suggesting a generalized activity by ouabain against all effector cells active in MICC. Ouabain inhibition of MICC could be overcome by increasing PHA concentrations, indicating that ouabain inhibition was not due to irreversible toxic effects on effector cells. Increasing the concentration of anti-CRC antibody resulted in increased killing in this ADCC system and, paradoxically, ADCC cultures with the highest antibody concentrations were more completely inhibited by ouabain. This enhanced inhibitory effect of ouabain on ADCC cultures with the highest antibody concentrations was not observed when the effector cell population was first depleted of phagocytic cells, suggesting a preferential inhibitory action by ouabain against monocyte effectors in ADCC. Thus, the differential inhibitory effects of ouabain on MICC and ADCC against CRC targets may be in part explained by the differing ouabain sensitivities of the various effector cell subpopulations involved in these cell-mediated cytotoxic events.     

Differential effects of ouabain on human cell-mediated cytotoxicity. II. Stimulation of monocyte-mediated, spontaneous cytotoxicity against chicken red cell targets.

We have previously shown that ouabain inhibits mitogen-induced cellular cytotoxicity (MICC) and antibody-dependent cellular cytotoxicity (ADCC) against chicken red cell (CRC) targets. We now report that ouabain increases spontaneous killing of CRC targets in the absence of mitogen or antibody. Spontaneous cytotoxicity by fresh mononuclear leukocytes (MNL) was enhanced by ouabain in a dose-dependent fashion and was maximal at a ouabain concentration of 5 × 10^?5M. Removal of phagocytic cells from the MNL effector cell population abrogated ouabain-induced spontaneous cytotoxicity, suggesting that the effector cell activated by ouabain was a monocyte. Ouabain-induced spontaneous cytotoxicity was relatively inefficient compared to MICC or ADCC and was only demonstrated consistently at effector:target cell ratios higher than those routinely employed for MICC and ADCC. Very low concentrations of ouabain (5 × 10^?9M) also enhanced spontaneous cytotoxicity of MNL precultured for 7 days, when added at either Day 0 or Day 6 of preculture. The cell effecting spontaneous cytotoxicity after 7 days of culture has been previously shown to be a monocyte. Thus, ouabain has opposing effects on cell-mediated cytotoxic functions: it inhibits MICC and ADCC against CRC targets, but stimulates spontaneous, monocyte-mediated cytotoxicity against the same targets.     

Preparation and crystal structure of [NEt4]3[Fe6W2S8(SEt)9]; structural and electrochemical comparisons with its molybdenum analogue

[NEt₄]₃[Fe₆M₂S₈(SEt)₉] (M = Mo or W) compounds are isomorphous and contain molybdenum and tungsten atoms in an essentially identical environment. These complexes undergo an irreversible one-electron oxidation at −0.46 V (Mo) and −0.51 V (W) and two one-electron reductions at −1.56 and −1.76 V (Mo) and −1.52 and −1.84 V (W), in DMSO solution versus (0.1 M). The only distinction between the behavior of these molybdenum and tungsten complexes identified thus far is that, for the former the reductions are reversible whereas for the latter they are irreversible. This difference may be relevant to the low activity found for nitrogenases reconstituted with tungsten in place of molybdenum.     

Studies on methemoglobin reductase. Immunochemical similarity of soluble methemoglobin reductase and cytochrome b5 of human erythrocytes with NADH-cytochrome b5 reductase and cytochrome b5 of rat liver microsomes.

An antibody preparation elicited against purified, lysosomal-solubilized NADH-cytochrome b₅ reductase from rat liver microsomes was shown to interact with methemoglobin reductase of human erythrocytes by inhibiting the rate of erythrocyte cytochrome b₅ reduction by NADH. The ferricyanide reductase activity of the enzyme was not inhibited by the antibody, suggesting that the inhibition of methemoglobin reductase activity may be due to interference with the binding of cytochrorme b₅ to the flavoprotein. Under conditions of limiting concentrations of flavoprotein, the antibody inhibited the rate of methemoglobin reduction in a reconstituted system consisting of homogeneous methemoglobin reductase and cytochrome b₅ from human erythrocytes. This inhibition was due to the decreased level of reduced cytochrome b₅ during the steady state of methemoglobin reduction while the rate of methemoglobin reduction per reduced cytochrome b₅ stayed constant, suggesting that the enzyme was not concerned with an electron transport between the reduced cytochrome b₅ and methemoglobin.An antibody to purified, trypsin-solubilized cytochrome b₅ from rat liver microsomes was shown to inhibit erythrocyte cytochrome b₅ reduction by methemoglobin reductase and NADH to a lesser extent than microsomal cytochrome b₅ preparations from rat liver (trypsin solubilized or detergent solubilized) and pig liver (trypsin solubilized). The results presented establish that soluble methemoglobin reductase and cytochrome b₅ of human erythrocytes are immunochemically similar to NADH-cytochrome b₅ reductase and cytochrome b₅ of liver microsomes, respectively.     

The action of proteolytic enzymes on chloroplast thylakoid membranes

Envelope- and stroma-free thylakoid membranes of Vicia faba chloroplasts were incubated with trypsin or pronase for several hours. The indigestible residue was analyzed by polyacrylamide gel electrophoresis. Trypsinization resulted in a complete digestion of all proteins with the exception of the pigment-protein complexes as well as a polypeptide not yet characterized. Yet, as compared with untreated material, Complex II was found to have higher electrophoretic mobility. Electron-microscopic studies illustrate that the indigestible residue still has a preserved membrane structure. Disintegration of the thylakoid membranes by sodium dodecyl sulfate followed by trypsinization also resulted in the two complexes while all the other proteins were found to be digested. However, after removal of the lipids the protein moieties of the complexes proved to be easily digestible. From these results it is concluded that pigment-protein interaction may be an important factor in maintaining a conformation rather resistant to perturbants and proteases. In contrast to trypsin, pronase completely digested the polypeptides of the thylakoid membranes including the protein moieties of the pigment-protein complexes leaving an amorphous lipid mass. The results support the assumption that the complexes are necessary to maintain the membrane structure.     

Mechanism of steroid action in inflammation: Inhibition of prostaglandin synthesis and release

Acute arthritis was induced by injection of cell-free extract of group A Streptococci into the knee joints of mature male rats. Slices of control and inflamed synovia were incubated for 30 to 240 minutes and the rate of prostaglandin E (PGE) released into the medium was measured by radioimmunoassay. PGE release from inflamed synovia was 5–8 fold higher than that in normal tissue. Incubation of inflamed synovia with corticosterone acetate, dexamethasone or prednisone (100 μg/ml) for one or four hours reduced PGE release by 33% and 55% respectively. Lower concentrations of corticosterone (10 – 30 μg/ml) were ineffective. Aldosterone and progesterone (100 μg/ml) had no effect on PGE release throughout the incubation period. Chloroquine (10 μg/ml) inhibited PGE release from inflamed synovia by 50%. Indomethacin (1 μg/ml) abolished PGE release by 90%. Corticosterone, dexamethasone and prednisone reduced PGE content of inflamed synovia by approximately 45% during a 4-h incubation period. Aldosterone and progesterone were ineffective, while indomethacin reduced PGE content by 70%. The suppressive action of corticosterone on PGE release was prevented by addition to the medium of arachidonic acid (2 μg/ml). By contrast, the inhibitory action of indomethacin was not affected by provision of exogenous substrate. We suggest that glucocorticosteroids reduce PGE release by limiting the availability of the substrate for prostaglandin biosynthesis, and this may well explain some of their anti-inflammatory properties.     

Synthesis of a cytosine nucleoside of 2-amino-2-deoxy-beta-D-xylofuranose.

1-(2-Amino-2-deoxy-beta-D-xylofuranosyl)cytosine (13) was synthesized by three routes: (a) coupling of 2-deoxy-3,5-di-O-p-nitrobenzoyl-2-(trifluoroacetamido)-D-xylofuranosyl chloride (5) with 2,4-dimethoxypyrimidine and subsequent treatment with methanolic ammonia, (b) coupling of 5 with 4-N-acetyl-2-O,4-N-bis(trimethylsilyl)cytosine followed by treatment with methanolic ammonia, and (c) thiation of 1-[3,5-di-O-acetyl-2-deoxy-2-(trifluoroacetamido)-beta-D-xylofuranosyl]uracil (6) by treatment with phosphorus pentasulfide in pyridine followed by amination of the resulting 4-thionucleoside 12 with metanolic ammonia. The best yield was obtained via route (a).     

Appearance of lymphocyte surface markers and functional responses in neonatal and young rabbit spleens

We examined spleen cells from newborn to 1-month-old rabbits for easily detectable surface immunoglobulin, complement receptors, and for in vitro proliferative responsiveness to anti-immunoglobulin antisera and several mitogens. From birth through the first month of life about 15% of the cells from rabbit spleens had easily detectable surface immunoglobulin while about 45% had C3 receptors. In adults as many as 77% of the spleen cells had easily detectable surface Ig but the proportion with C3 receptors remained about 45%. The proliferative response to anti-allotype antisera was present at birth, and was at adult levels by 1 month of age. The proliferative response to pokeweed mitogen was low when cells were obtained during the first week of life but was comparable in magnitude to the response of adult cells by 2 weeks of age. In vitro responsiveness to concanavalin A was present at low levels at birth and increased sharply during the first week. We did not observe significant stimulation of spleen cells from neonatal to 4-week-old rabbits by lipopolysaccharide from Salmonella typhosa. Our data suggest that lymphocyte surface markers and functional responses appear asynchronously in spleen cells of developing rabbits.     

Studies on plasma membranes. XXIII. Hormone-like action of concanavalin A on liver plasma membranes: inhibition of (Na+-K+)ATPase.

Concanavalin A inhibits the (Na+-K+)-ATPase activity of isolated rat-liver plasma membranes, while leaving the Mg2+-ATPase unaffected. Glucagon and cyclic AMP act supplementary to the lectin in the inhibition. The lectin effect is counteracted by insulin and L-epinephrine, and is completely abolished by the beta-adrenergic blocking agent propranolol. Results are discussed on the basis of the known interactions of concanavalin A with plasma membrane components, including its hormone-like action.