Oncornavirus lytic activity in the serum of gibbon apes.

Fresh blood serum from normal gibbon apes (Hylobates lar) contained heat-sensitive lytic activity for various mammalian oncornaviruses. Lytic activity quantitatively similar to that in gibbon serum was demonstrated in serum from three other primate species, including man; it was demonstrated to be low or absent in lower mammalian species with the exception of domestic cats, which had intermediate levels of serum lytic activity. Gibbons that acquired infectious gibbon ape leukemia virus, either naturally by exposure to a virus-shedding ape or experimentally by deliberate virus inoculation, had the same levels of serum lytic activity as did unexposed gibbons that had no detectable antibodies to gibbon ape leukemia virus. A leukemic-viremic gibbon had low or absent serum oncornavirus lytic activity. These results indicated that serum lytic activity does not necessarily protect against infection by oncornaviruses, although it may limit virus replication and/or dissemination.

Effects of deoxynucleosides on cultured human leukemia cell growth and deoxynucleotide pools.

We investigated the mechanism of cell growth inhibition caused by the deoxyribonucleosides thymidine (dThd), deoxyguanosine (dGuo), deoxyadenosine (dAdo), and deoxycytidine (dCyd). Growth of the cultured human leukemic cells HL-60 and K-562 was measured by cloning in soft agar. Of the deoxyribonucleosides, dGuo was the most potent cell growth inhibitor; however, the potency of added dAdo was probably attenuated by the presence of adenosine deaminase in the tissue culture growth medium. The concentrations of nucleoside causing 50% inhibition of HL-60 cloning were: dCyd, greater than 10,000 microM; dAdo, 500 microM; dThd, 5,000 microM; and dGuo, 80 microM. For K-562 cloning, the concentrations causing 50% inhibition of cloning were dCyd, greater 10,000 microM; dAdo, 1,600 microM; dThd, 880 microM;' and dGuo, 100 microM. Measurement of deoxycytidine 5'-triphosphate (dCTP) pool size in HL-60 cells following incubation with 750 microM deoxyribonucleosides revealed that dGuo caused the greatest reduction of dCTP pools, both in early (passage 10)- and late (passage 71)-passage-derived HL-60 cell cultures (35 and 19% of control, respectively), compared to dThd (61 and 26% of control, respectively) and dAdo (39% of control of HL-60 passage 10). In K-562 cells, reductions in dCTP pool size caused by dAdo, dThd, and dGuo were 68, 46, and 35% of control, respectively. Incorporation of [3H]dCyd into DNA of HL-60 and K-562 cells was enhanced by dThd and dGuo, but the degree of enhancement was greater for dThd than for dGuo. Despite its effect in reducing HL-60 dCTP pool size, dAdo failed to enhance [3H]dCyd incorporation in either HL-60 or K-562 cells. Addition of dCyd to the cultures could only partially rescue the inhibition of HL-60 cloning caused by dThd or dGuo, suggesting that inhibition of cytidine 5'-diphosphate reduction by ribonucleotide reductase is not the only mechanism whereby these nucleosides inhibit leukemic cell cloning. These data suggest that, in addition to inhibiting de novo dCTP production via ribonucleotide reductase, these nucleosides may affect other processes in the salvage pathway such as cellular uptake and phosphorylation or the DNA polymerase reaction itself.

Improved determination of beta-glucuronidase in serum.

With phenolphthalein beta-glucuronide as the substrate in the serum beta-glucuronidase assay, centrifugation at high speed after addition of alkali was required to minimize blanks. Optimal substrate concentration was 3--6 mM. Excess substrate was inhibitory.

Effect of macrophage activation by immunoadjuvants on serum levels of lysosomal hydrolases in mice.

The effect of pyran copolymer, injected into mice bearing the M109 Madison lung carcinoma, on serum concentrations of lysozyme, beta-glucuronidase, and N-acetyl-beta, D-glucosaminidase was studied and compared with that of other immunoadjuvants. Increases in lysozyme levels ranging from 50 to 100% were observed after injection of pyran, BCG and Bru-Pel; increases in the levels of the other enzymes were less consistent. Other immunoadjuvants were less effective in raising serum concentrations of lysosomal enzymes. The findings were correlated with the results of previous studies on macrophage activation and antineoplastic action produced by these immunoadjuvants and suggest that serum levels of lysozyme can serve as indices of these effects.