Cytokines in the acquired immunodeficiency syndrome and other infectious diseases

The pathogenesis of several infectious diseases is frequently related not only to their etiological agents of viral, bacterial, or parasitic nature, but also to the host immune response. Both inflammatory responses and specific immune responses to the invading microorganisms are controlled by complex networks of intercellular signalling molecules, namely cytokines. This rapidly growing family of mediators includes lymphokines, interleukins, and molecules such as tumor necrosis factors and interferons. Patterns of cytokine production from antigen- or allergen-specific T lymphocytic cell clones have been identified, firstly in animal models and subsequently in man, and are commonly referred to as TH0, TH1, and TH2 profiles. The predominance of one of these profiles strongly influences the type of immune response (humoral versus cellular) and, at least in some experimental models, whether the immune response is protective or harmful. This is most convincingly demonstrated in models of parasitic diseases, but has also been hypothesized to be involved in the pathogenesis of human immunodeficiency virus infection and the acquired immunodeficiency syndrome. Earlier studies on human immunodeficiency virus infection revealed that the replicative capacity of this retrovirus, like the herpes viruses, is strongly influenced by the cytokine milieu of infected cells. Transcriptional and post-transcriptional regulation of human immunodeficiency virus expression by human cytokines are examples of the complex interdigitation of viruses with the host immune system.

IL-10 synergizes with multiple cytokines in enhancing HIV production in cells of monocytic lineage

Several cytokines, whose expression is increased in human immunodeficiency virus (HIV)-infected individuals, can enhance virus replication in CD4+ T lymphocytes and mononuclear phagocytes (MP). We have previously reported that interleukin (IL)-10 inhibited HIV replication in acutely infected monocyte-derived macrophages (MDM) at concentrations that completely blocked the production of endogenous tumor necrosis factor-alpha (TNF-alpha) and IL-6 from infected cells. In the present study, lower concentrations of IL-10, which were unable to completely suppress endogenous cytokines, paradoxically enhanced HIV replication in MDM induced by other cytokines. This synergistic induction of HIV expression by IL-10 in combination with TNF-alpha, IL-6, and other cytokines was also observed in the chronically infected promonocytic cell line, U1. The enhancing effect of IL-10 was correlated with an increase in HIV mRNA accumulation and potentiation of phorbol ester-induced long terminal repeat-driven transcription that was independent of the NF-kappa B and Sp1 transcription factors. Thus, IL-10 is a cytokine capable of exerting complex regulatory effects on HIV expression in MP as a function of its own concentration and of the presence of other HIV regulatory cytokines.

Cloning and characterization of a new isoform of the interleukin 1 receptor antagonist

By reverse transcriptase polymerase chain reaction on messenger RNA from human polymorphonuclear cells, we have isolated a sequence identical to the cDNA coding for intracellular interleukin 1 receptor antagonist (icIL-1ra), but containing an additional in-frame 63-bp sequence located three codons downstream of the translation start of icIL-1ra. This additional sequence is inserted between the first and second exon of the intracellular form, the latter of which is colinear with part of the first exon of the secreted form of IL-1ra. The additional sequence is coded by an extra exon located 2 kb downstream the first icIL-1ra-specific exon. The complementary DNA sequence of the alternatively spliced form of icIL-1ra shows that the predicted protein differs from classical icIL-1ra in the NH2 terminus by insertion of a leaderless sequence of 21 amino acids rich in glycine and glutamic acid residues. Transcripts coding for this new form of icIL-1ra were detected in activated fibroblasts, keratinocytes, and at low levels in myelomonocytic cells. The recombinant protein expressed in COS cells had an apparent molecular mass in sodium dodecyl sulfate polyacrylamide gel electrophoresis of 25 kD compared to 22 kD of classical icIL-1ra, and was mostly intracellular. The ability of this new form of icIL-1ra to inhibit IL-1 activity, in terms of induction of E-selectin and human immunodeficiency virus replication, was comparable to that of classical icIL-1ra. We propose to refer to this new form of icIL-1ra as icIL-1ra type II.

The "bystander effect": association of U-87 cell death with ganciclovir-mediated apoptosis of nearby cells and lack of effect in athymic mice

Cells expressing the herpes simplex-thymidine kinase (HS-TK) gene as a consequence of retroviral transduction, as well as TK-negative (TK-) bystander cells, can be killed by treatment with ganciclovir (GCV). In vitro, this "bystander effect," has been attributed to metabolic cooperation through gap junctions or to the uptake of apoptotic vesicles. We show that GCV treatment kills TK-negative U-87 glioma cells cocultured with cells that express TK (TK+) but that have lost the capacity for releasing retroviral particles. A photometric enzyme immunoassay identifies histone-associated DNA fragments, typical of apoptosis, in the cytosol of GCV-treated TK+ cells, and apoptotic features are also demonstrated by ultrastructural studies. Northern blot analysis and the reverse transcription polymerase chain reaction (PCR) show that connexin 43, a major constituent of gap junctions, is expressed in TK+ and U-87 cells. The size of U-87 tumors in nude mice subsequently injected with TK+ cells and GCV is not significantly different than in untreated animals; whereas, after injecting 1:1 mixtures of U-87 and TK+ cells, GCV treatment only causes a temporary regression of tumor growth. On the contrary, when the injected mixtures contain PA317.STK.SBA (a retroviral producer cell line that can transduce efficiently the HS-TK gene) and U-87 cells, tumors are destroyed effectively by GCV treatment. Thus, an experimental setting in which U-87 gliomas are matched with cells that are able to express, but not to transduce, the HS-TK gene indicates that the bystander effect kills U-87 cells in vitro by mechanisms associated with apoptotic death. In vivo, this effect is not sufficient to restrain the tumor growth taking place in immunodeficient animals.

Cytolysis does not per se induce lipid peroxidation: evidence in man

An increasing bulk of data counters the opinion that cell death and lysis necessarily trigger the formation and release of detectable amounts of molecules that are markers of lipid peroxidation. Plasma levels of thiobarbituric-acid-reacting compounds, protein-aldehyde fluorescent adducts, lipid peroxides, and endogenous antioxidant compounds were monitored versus controls, during intensive care treatment, in six patients seriously poisoned by ingestion of the mushroom Amanita Phalloides. All six patients showed cytolysis, and four of them massive tissue necrosis, as monitored in terms of serum transaminases. In all six patients, however, the blood parameters of redox equilibrium measured were within the normal range for the whole observation period.

Phylogeny inferred from codon usage pattern in 31 organisms

We employed the Codonusage database to analyze the codon usage pattern in 31 organisms from all the main biological taxa. We tested the similarity in codon usage pattern between each organism and all the others by the Pearson linear correlation coefficient. The 465 values obtained were located in a 31 x 31 triangular matrix from which a correlation distance matrix was calculated. An evolutionary dendrogram was then constructed from these distances. The results showed a fair correlation between codon usage patterns and phylogenetic relationships, at least for organisms which diverged in rather recent times (end of Jurassic--beginning of Cretaceous).

Effect of cellular differentiation on cytokine-induced expression of human immunodeficiency virus in chronically infected promonocytic cells: dissociation of cellular differentiation and viral expression

Cellular differentiation is thought to play an important role in the susceptibility of monocytic lineage cells to human immunodeficiency virus (HIV) infection as well as in their ability to support virus replication. In addition, virus replication in monocytes/macrophages has been demonstrated in vitro to be strongly modulated by several cytokines such as tumor necrosis factor alpha and granulocyte-macrophage colony-stimulating factor. The purpose of the present study was to investigate the interaction between cellular differentiation and cytokines in the regulation of HIV expression from chronically infected monocytic lineage cells. U1, a persistently HIV-infected promonocytic cell line, is characterized by low levels of virus expression which can be modulated by several cytokines. 1 alpha,-25-Dihydroxyvitamin D3 (Vit.D3), a well-known differentiating agent for myelomonocytic cells which has been previously reported to modulate HIV replication in other in vitro systems, induced maturation of U1 cells toward a macrophage-like phenotype, as demonstrated by the induction of the differentiation-associated cell surface markers CD14 and CD11b. Vit.D3-induced differentiation did not result in induction of HIV expression; however, when U1 cells were stimulated with tumor necrosis factor alpha in the presence of Vit.D3, a synergistic induction of cell differentiation and viral expression was demonstrated. In contrast, Vit.D3 suppressed the induction of HIV expression in U1 cells stimulated with gamma interferon, interleukin-6, and granulocyte-macrophage colony-stimulating factor, although synergy between Vit.D3 and these cytokines was observed in terms of cellular differentiation. These data suggest that differentiation of monocytic cells does not necessarily correlate with increased HIV expression.

HIV replication in IL-2-stimulated peripheral blood mononuclear cells is driven in an autocrine/paracrine manner by endogenous cytokines

Replication of HIV is regulated by virus-encoded regulatory proteins, as well as by a variety of cellular factors including cytokines. In the present study, we have investigated the autocrine/paracrine effects of endogenous cytokines on HIV replication in primary PBMCs of healthy HIV seronegative individuals. Addition of rIL-2 to cultures between 0 and 72 h after isolation of PBMCs allowed the replication of primary HIV isolates and laboratory-adapted HIV strains to levels comparable with or greater than those obtained in parallel cultures of autologous PHA-blasts. In this regard, both major cellular targets of HIV infection, CD4+ T lymphocytes and mononuclear phagocytes, were maintained for several weeks in IL-2-stimulated PBMC cultures and virion production was observed in both cell lineages. The kinetics of secretion of several cytokines (such as TNF-alpha, IL-1 beta, IL-6, and IFN-gamma), as well as expression of cellular activation markers, paralleled HIV replication in IL-2-stimulated PBMCs. Endogenous pro-inflammatory cytokines and IFN-gamma played a major role in the regulation of HIV replication in IL-2-stimulated PBMCs, as determined by the ability of several anti-cytokine Abs or antagonists to suppress HIV production; this was not the case in parallel cultures of autologous PHA-blasts. Thus, IL-2-stimulated PBMCs may represent a more physiologic in vitro system than PHA-blasts for the study of HIV infection and replication, and should prove useful in investigating the role of cytokines and other host factors in the regulation of HIV production.

HIV replication in IL-2-stimulated peripheral blood mononuclear cells is driven in an autocrine/paracrine manner by endogenous cytokines

Replication of HIV is regulated by virus-encoded regulatory proteins, as well as by a variety of cellular factors including cytokines. In the present study, we have investigated the autocrine/paracrine effects of endogenous cytokines on HIV replication in primary PBMCs of healthy HIV seronegative individuals. Addition of rIL-2 to cultures between 0 and 72 h after isolation of PBMCs allowed the replication of primary HIV isolates and laboratory-adapted HIV strains to levels comparable with or greater than those obtained in parallel cultures of autologous PHA-blasts. In this regard, both major cellular targets of HIV infection, CD4+ T lymphocytes and mononuclear phagocytes, were maintained for several weeks in IL-2-stimulated PBMC cultures and virion production was observed in both cell lineages. The kinetics of secretion of several cytokines (such as TNF-alpha, IL-1 beta, IL-6, and IFN-gamma), as well as expression of cellular activation markers, paralleled HIV replication in IL-2-stimulated PBMCs. Endogenous pro-inflammatory cytokines and IFN-gamma played a major role in the regulation of HIV replication in IL-2-stimulated PBMCs, as determined by the ability of several anti-cytokine Abs or antagonists to suppress HIV production; this was not the case in parallel cultures of autologous PHA-blasts. Thus, IL-2-stimulated PBMCs may represent a more physiologic in vitro system than PHA-blasts for the study of HIV infection and replication, and should prove useful in investigating the role of cytokines and other host factors in the regulation of HIV production.

Metabolism of 4-hydroxy-2-nonenal and aging

Hepatocytes isolated from male Wistar rats of 2-3 and 20-24 months of age were compared as regards concentration and metabolism of 4-hydroxy-2-nonenal, one of the major aldehyde products of n-6 fatty acid oxidative breakdown. A significant accumulation of fluorescent 4-hydroxy-2-nonenal-membrane lipid adducts was found in the cells from the old rats. The mechanism mainly responsible for such aldehyde accumulation was shown to be the impairment of its enzymatic metabolism. In fact, while endogenous, that is non-stimulated, aldehyde production was not impaired, the reductive pathway of 4-hydroxy-2-nonenal metabolism in hepatocytes from old rats was strongly depressed. The decrease of 4-hydroxy-2-nonenal consumption with age was confirmed in homogenates from liver and kidney, while there were no differences between young and old animals in heart, lung or brain.

Ethanol-induced potentiation of rat hepatocyte damage due to 1,2-dibromoethane

Low amounts of 1,2-dibromoethane (DBE), not able per se to exert pro-oxidant and cytotoxic activity on rat hepatocyte suspensions, become effective when administered with carbon tetrachloride (CCl4), due to impairment of the glutathione transferase detoxication pathway by CCl4. Treatment of rats with a single dose of ethanol (2.5 g/kg body wt) 2 h before liver cell isolation potentiates the effect of DBE alone on both malonaldehyde formation and lactate dehydrogenase release by the hepatocyte. The potentiation of the DBE effects by ethanol may be through a series of mechanisms, such as a strong inactivation of hepatocyte glutathione transferase similar to that caused by CCl4, an increased basal level of lipid peroxidation and a significant loss of total glutathione.

Aphidicolin inhibits in vitro the activity of pseudorabies virus (PRV) DNA polymerase and in vivo the viral proliferation

We have purified and characterized Pseudorabies virus (PRV) DNA polymerase from infected TK- mouse cells. PRV DNA polymerase has a 3'- > 5' exonuclease activity; it is stimulated by ionic strength, requires magnesium for optimal activity and it is more sensitive to aphidicolin than eukaryotic and HSV-1 replicative DNA polymerases. Aphidicolin inhibits in vitro PRV DNA polymerase competitively with respect to dCTP with a Ki of 0.06 microM and completely blocks viral growth in vivo at 4.4 microM. The high sensitivity to aphidicolin of animal herpesvirus DNA polymerases might allow a topical use of this drug in the treatment of animal herpesvirus keratitis and stomatitis.

Prevention of carbon tetrachloride-induced lipid peroxidation in liver microsomes from dehydroepiandrosterone-pretreated rats

Dehydroepiandrosterone (DHEA), a lipid soluble steroid, administered to rats (100 mg/kg b.wt) by a single intraperitoneal injection, increases to twice its normal level in the liver microsomes. Microsomes so enriched become resistant to lipid peroxidation induced by incubation with carbon tetrachloride in the presence of a NADPH-regenerating system: also the lipid peroxidation-dependent inactivation of glucose-6-phosphatase and gamma-glutamyl transpetidase due to the haloalkane are prevented. Noteworthy, the liver microsomal drug-metabolizing enzymes and in particular the catalytic activity of cytochrome P450IIE1, responsible for the CCl4-activation, are not impaired by the supplementation with the steroid. Consistently, in DHEA-pretreated microsomes the protein covalent binding of the trichloromethyl radical (CCl3 degrees), is similar to that of not supplemented microsomes treated with CCl4. It thus seems likely that DHEA protects liver microsomes from oxidative damage induced by carbon tetrachloride through its own antioxidant properties rather than inhibiting the metabolism of the toxin.

Interleukin 10 blocks HIV replication in macrophages by inhibiting the autocrine loop of tumor necrosis factor alpha and interleukin 6 induction of virus

Human interleukin 10 is a pleiotropic cytokine capable of suppressing cytokine production from macrophages and T cells; in addition, it exerts complex regulatory effects on CD8+ T cells, natural killer cells, vascular endothelial cells, and B lymphocytes. Levels of IL-10 are elevated in HIV-infected individuals, suggesting that this cytokine may play a role in the suppression of T cell and monocyte/macrophage function typical of HIV disease. In this article, IL-10 blocked HIV-induced tumor necrosis factor alpha and interleukin 6 secretion and inhibited HIV replication in monocyte-derived macrophages (MDMs). The inhibition by IL-10 was correlated with a block in endogenous TNF-alpha and IL-6 secretion from HIV-infected MDMs.

A family of serine proteases expressed exclusively in myelo-monocytic cells specifically processes the nuclear factor-kappa B subunit p65 in vitro and may impair human immunodeficiency virus replication in these cells

Two groups of U937 promonocytic cells were obtained by limiting dilution cloning which differed strikingly in their ability to support human immunodeficiency virus 1 (HIV-1) replication. "Plus" clones replicated the virus efficiently, whereas "minus" clones did not. We examined these clones for differences in nuclear factor (NF)-kappa B activity which might account for the observed phenomenon. Stimulation of plus clones liberated the classical p50-p65 complex from cytoplasmic pools, whereas minus clones produced an apparently novel, faster-migrating complex, as judged by electrophoretic mobility shift assays. It is surprising that the faster-migrating complex was composed also of p50 and p65. However, the p65 subunit was COOH-terminally truncated, as shown by immunoprecipitation. The truncation resulted from limited proteolysis of p65 during cellular extraction which released particular lysosomal serine proteases, such as elastase, cathepsin G, and proteinase 3. These specific proteases are coordinately expressed and were present exclusively in the minus U937 clones, but not in the plus clones, as demonstrated in the case of cathepsin G. In addition, these proteases were detected in certain subclones of THP-1 and HL-60 cells and in primary monocytes, in each case correlating with the truncated from of p65. We demonstrate in vitro cleavage of p65 by purified elastase and cathepsin G. It is possible that particular serine proteases may have inhibiting effects on the replication of HIV-1 in myelo-monocytic cells. The data also demonstrate that special precautions must be taken when making extracts from myelo-monocytic cells.

Oxidative stress in the development of human ischemic hepatitis during circulatory shock

An increasing number of studies support the involvement of free radical-mediated oxidative reactions in the pathogenesis of tissue injury following ischemia reperfusion. In particular, a condition of oxidative stress is evident in patients with circulatory shock, a disease process often complicated by progressive organ failure sustained by inflammatory reactions. In all shock patients without signs of organ failure, a consistent increase of intermediate and final products of lipid peroxidation (lipid peroxides and aldehydes respectively) was observed. Impairment of the redox equilibrium in the tissues of these patients was confirmed by a significant reduction of glutathione and vitamin E hematic concentrations. Moreover, a selective increase of plasma aldehyde-protein adducts, actual proof of oxidative damage of macromolecules, is only present in the shock patients who, in addition, show hepatic cytolysis (ischemic hepatitis) as estimated by plasma levels of LDH5 isoenzyme. Aldehyde adducts well mark the progression of the disease towards multiple organ failure. Finally, the good statistical correlation between aldehyde-modified proteins and LDH5, as well as their distinct behaviour in control and ischemic hepatitis, support the involvement of oxidative damage in the expression and worsening of circulatory shock.

Regulation of HIV expression by viral genes and cytokines

The human immunodeficiency virus (HIV) is the causative agent of the acquired immunodeficiency syndrome (AIDS), a leading cause of death among young individuals. As a complex pathogenic retrovirus, HIV is characterized in vitro and in vivo by the ability to establish either a latent or productive infection of CD4+ T lymphocytes and mononuclear phagocytes (MPs). Viral latency and expression are under the control of both viral genes and several host-related factors. Among these latter, several proinflammatory and immunoregulatory cytokines profoundly affect HIV replication in T lymphocytes and MPs in vitro. Because many of these cytokines have been found to be elevated in HIV-infected individuals, it is likely that they act as regulators of viral expression in vivo. Both viral genes and cytokines regulate transcriptional and posttranscriptional steps in HIV replication. Thus, it is likely that common regulatory pathways between these two distinct classes of regulator molecules will be identified in the near future and will provide potential targets for pharmacologic intervention and treatment of HIV disease.

NF-kappa B-dependent and -independent pathways of HIV activation in a chronically infected T cell line

J delta K cells were isolated as a chronically infected survivor cell line, following infection of Jurkat CD4+ T cells with dl-NF, a mutated strain of human immunodeficiency virus type 1 (HIV-1) containing a deletion of the long terminal repeat (LTR) NF-kappa B sites. J delta K cells exhibited very low levels of constitutive HIV production. HIV-1 expression was activated from J delta K cells by treatment with phorbol myristate acetate (PMA), sodium butyrate (NaB), or hexamethylene bisacetamide (HMBA), but not tumor necrosis factor alpha (TNF-alpha), confirming the role of NF-kappa B in mediating TNF-alpha induction of HIV transcription. The strong induction of HIV expression by NaB or HMBA in J delta K cells clearly demonstrates the existence of NF-kappa B-independent mechanisms of HIV activation in chronically infected cells. J delta K cells may provide a useful model for characterizing NF-kappa B-independent transcriptional activation of the HIV LTR.

Role of aldehyde metabolizing enzymes in mediating effects of aldehyde products of lipid peroxidation in liver cells

It is well established that many types of tumor cells have reduced lipid peroxidation capacity compared to their normal counterparts. Changes in the activity of enzymes metabolizing aldehydes produced by lipid peroxidation have also been reported in a variety of tumor cells. We have investigated the relationship between changes in lipid peroxidation and changes in aldehyde-metabolizing enzymes in normal hepatocytes and two representative rat hepatoma cell lines, McA-RH-7777 and JM2. Compared to hepatocytes, both 7777 and JM2 cells have significantly lower basal and prooxidant-induced levels of lipid peroxidation than normal hepatocytes. Using 4-hydroxynonenal (4-HNE) as substrate, both cell lines also have significantly reduced activities of alcohol dehydrogenase (ADH) and glutathione S-transferase (GST) compared to hepatocytes. JM2 cells have significantly increased aldehyde dehydrogenase (ALDH) and aldehyde reductase (ALRD) activities with 4-HNE. In 7777 cells the ALDH and ALRD activities are not different from hepatocytes. The changes in enzyme activity are inversely correlated with the sensitivity of cells to 4-HNE. JM2 cells, with increased ALDH and ALRD and decreased ADH and GST, are much more resistant to the toxic effects of 4-HNE than 7777 cells. Normal hepatocytes and JM2 cells are approximately equally resistant to 4-HNE even though hepatocytes rely primarily on GST-mediated aldehyde conjugation to metabolize 4-HNE. Coupled with previous results from our laboratories, the overall increased sensitivity of certain hepatoma cells to lipid aldehydes appears due to decreased ability of these hepatoma cells to remove toxic products of lipid peroxidation. Moreover, hepatoma cells with increased levels of aldehyde dehydrogenase and aldehyde reductase appear most like hepatocytes in their ability to metabolize lipid aldehydes.