Hypoxia induces lytic replication of Kaposi sarcoma-associated herpesvirus.

There is substantial evidence that Kaposi sarcoma-associated herpesvirus (KSHV) plays an important role in the pathogenesis of all forms of Kaposi sarcoma (KS). It has been noted that KS commonly occurs in locations, such as the feet, where tissue may be poorly oxygenated. On the basis of this observation, the potential role of hypoxia in the reactivation of KSHV replication was explored by studying 2 KSHV-infected primary effusion lymphoma B-cell lines (BC-3 and BCBL-1) latently infected with KSHV. Acute and chronic exposure of these cells to hypoxia (1% O(2)) induced KSHV lytic replication, as indicated by an increase in intracellular lytic protein expression and detection of virus in cell supernatants by Western immunoblotting. In addition, hypoxia increased the levels of secreted viral interleukin-6. Moreover, hypoxia enhanced the lytic replication initiated by the viral inducer 12-O-tetradecanoylphorbol-13-acetate. Desferoxamine and cobalt chloride, 2 compounds that increase the intracellular levels of hypoxia-inducible factor 1, were also able to induce KSHV lytic replication. These studies suggest that hypoxia is an inducer of KSHV replication. This process may play an important role in the pathogenesis of KS.

HLA-DR is involved in the HIV-1 binding site on cells expressing MHC class II antigens.

The primary interaction of HIV-1 with the target cell involves the viral large envelope protein (gp120) and the cellular CD4 molecule. mAb reacting with portions of CD4 have been shown to block HIV-1 attachment and infection. In one of the early reports describing HIV-1 cell interaction, some mAb reacting with MHC class II Ag were also found to block infection. To investigate further a possible role for MHC class II in HIV-1 binding, a cultured T lymphocyte cell line (H-9) that expresses MHC class II molecules and PHA-stimulated PBL was exposed for various time periods to concentrated viral particles and individual HIV-1 proteins. A decrease in the ability to detect the CD4a epitope and HLA-DR was observed after the cells were exposed to virus for 15, 30, and 60 min whereas HLA-DP and HLA-DQ Ag increased or remained unchanged. After 120 min of virus exposure, the CD4a epitope remained diminished whereas HLA-DR was detected at levels found on cells not exposed to virus. mAb detecting the CD4a epitope and HLA-DR, as well as alloantisera detecting the specific HLA-DR Ag on the target cell, blocked HIV-1 binding. When immunopurified gp120 was added to PHA-stimulated and unstimulated PBL, the CD4a epitope decreased in the same manner as was observed with whole virus preparations. In contrast to exposure to the intact virus, HLA-DR expression appeared to increase. Other viral proteins, p17, p24, and a portion of the small envelope protein, gp41, had no effect on the ability to detect cell surface Ag. Thus, although CD4 is the primary receptor for HIV-1 binding, HLA-DR appears to be involved in the binding site, probably by virtue of its close proximity to the CD4 molecule on the cell surface.

The distribution of peroxide regulating enzymes in the canine eye.

The retina and rod outer segments (ROS), rich in unsaturated lipids, are highly susceptible to autoxidation via free radical mechanisms. In the canine eye, four enzymes, i.e.; p-phenylenediamine (PPD) peroxidase, glutathione peroxidases, catalase and superoxide dismutase which are involved in the production or degradation of peroxides, were measured. All enzymes were present in the retina, ciliary body and iris, but differed in concentration. Superoxide dismutase showed high activity in the ROS. In the retinal pigment epithelium (RPE) a peroxidase utilizing PPD as cosubstrate and superoxide dismutase were both present. The former enzyme was found equally distributed between soluble and insoluble forms. A pigment granule fraction from the RPE only contained PPD-peroxidase. The compartmentalization of peroxide regulating enzymes in the eye is striking. Whereas the retina seems well protected against superoxide free radicals and hydrogen peroxide by virtue of superoxide dismutase, peroxidases and catalase activities, the ROS are only protected by superoxide dismutase. Therefore, after phagocytosis of the ROS, any peroxidized lipids, organic peroxides, or unconverted superoxide radicals contained within the ROS, must be detoxified by a specific RPE peroxidase and superoxide dismutase. Hydrogen peroxide or other peroxidized compounds apparently are not degraded by glutathione peroxidases or catalase, since these enzymes were not measurable in our RPE preparations. The role of antioxidative enzymes in the eye, which retard peroxide and free radical information, appears to be specific and regional.

Studies on the retina and the pigment epithelium in hereditary canine ceroid lipofuscinosis, I. The distribution of enzymes in the whole retina and pigment epithelium.

The massive accumulation of autofluorescent lipopigments, representative of autoxidation, is a key morphological feature in canine ceroid lipofuscinosis (CCL). In the eye peroxidase, catalase, and four acid hydrolases were compared with regard to aged and clinical condition in a series of English setters affected with CCL. In unaffected English setters "soluble" peroxidase increased in the RPE to adult levels at 2 yr of age. Affected dogs had higher RPE peroxidase activity earlier in life, which then decline with age. The soluble retinal peroxidase of both unaffected and CCL dogs increased steadily with age, but the latter group of dogs were much lower in activity. By 2 yr of age, RPE and retinal peroxidase values were only 25% and 47% of unaffected dog levels. Although the soluble enzyme of unaffected dogs exhibited a maturational profile, membrane-bound RPE peroxidase showed a hyperbolic curve reaching a maximum at 10 mo of age. By 2 yr of age, the "bound" enzyme in affected dogs was below unaffected levels in the RPE and retina. Three acid hydrolases were slightly increased in the RPE and retina of affected dogs. Acid lipase activity, however, was similar in both unaffected and CCL dogs. Catalase was not found in the RPE of either group of dogs. The catalase activity in the retina of both affected and unaffected dogs was at similar levels. Since catalase is not present in the RPE, the major defense against peroxidase accumulation and peroxide toxicity probably depends upon peroxidase. The present study indicates that a decrease in this key regulating enzyme may be related to the formation of lipopigments in the retina and RPE of dogs with CCL.

Studies on the retina and the pigment epithelium in hereditary canine ceroid lipofuscinosis. II. The subcellular distribution of lysosomal hydrolases and other enzymes.

Observations on the progressive course of retinal degeneration in canine ceroid lipofuscinosis (CCL) showed dramatic changes in enzyme activity and subcellular compartmentation. Thus, in affected animals, a new particle containing high levels of hexosaminidase and galactosidase was found in fractions lighter than seen in controls. In the later stages of disease and in normal aging, a progressive increase in dense fractions with high titers of acid lipase and acid phosphatase was observed. Peroxidase was found predominantly in the heavier fractions (1.24 to 1.28 gm/ml) and was lower than normal in affected retina and RPE. These fractions were located above the pigment granule fraction. Changes of peroxidase activity in the pigment granules were age dependent in controls, but a decrease of similar magnitude occurred much earlier in affected dogs. The accumulation of large numbers of dense bodies in the retina and RPE in CCL may indicate an impairment of intracellular digestive mechanisms. The early and marked reduction of peroxidase activity in affected dogs is an important indicator for major changes in the biochemistry of the entire eye in this disease. Therefore the initial pathogenic event seems to be the inability of affected cells to cope with peroxidative damage at an early stage, followed by an exaggerated attempt by the cells to digest accumulating lipopigments.