Distinct and overlapping genomic profiles and antiviral effects of Interferon-λ and -α on HCV-infected and noninfected hepatoma cells

Recently, several SNPs in the region of the IL28B (IFN-λ) gene have been associated with spontaneous clearance of hepatitis C virus (HCV) and enhanced cure rates for IFN-alfa-based therapies, suggesting a potential correlation between IFN-λ and the ability to clear HCV. To understand the mechanism of IFN-λ's as compared to IFN-α's antiviral activity, we performed a comprehensive analysis of their anti-HCV effects, whole genome transcriptome profiling with validation, and signalling of IFN-α and IFN-λ using J6/JFH-1 and Huh7.5 cells in vitro. IFN-λ and IFN-α exhibited comparable anti-HCV activity and gene expression profiles in Huh7.5 cells. While the majority of genes induced by IFN-α and IFN-λ were similar, IFN-λ exhibits profound, but delayed kinetics of IFN-stimulated genes (ISG) induction, while IFN-α induced more rapid induction of ISGs. Furthermore, the increased induction of ISG expression by IFN-λ correlated with up-regulation of IFN-λ receptor (IL-28RA) expression and more prolonged activation of the Jak-STAT signalling pathway. The findings from our comparative analysis of IFN-α and IFN-λ in HCV-infected and noninfected cells support the clinical use of IFN-λ as a potential alternative to IFN-α in the treatment of chronic hepatitis C.

Suppressor of cytokine signaling-1 is an IL-4-inducible gene in macrophages and feedback inhibits IL-4 signaling

Interferon-gamma and interleukin-4 (IL-4) induce distinct gene expression profiles in macrophages by differentially activating signal transducers and activators of transcription (STAT)1 and STAT6, respectively. The role of suppressor of cytokine signaling (SOCS)-1 as a negative regulator of IFN-gamma signaling is well established. However, its potential role as a negative regulator of IL-4 signaling has not been explored. We found that IL-4, like IFN-gamma, induces rapid de novo expression of SOCS-1 in primary macrophages. Induction of SOCS-1 gene expression by IL-4 is STAT6-dependent, whereas induction of SOCS-1 by IFN-gamma is STAT1-dependent. Unlike their common ability to induce expression of SOCS-1, IL-4 also induced expression of SOCS-2 but not SOCS-3 in macrophages, whereas IFN-gamma induced expression of SOCS-3 but not SOCS-2. Forced expression of SOCS-1 or SOCS-3, but not SOCS-2, inhibited activation of STAT6 by IL-4. Moreover, SOCS-1 appears to serve as an endogenous regulator of IL-4 signaling in macrophages because the magnitude and duration of STAT6 activation as well as IL-4-mediated gene expression were much greater in SOCS-1-deficient (SOCS-1(-/-)) macrophages than in wild-type macrophages. Our findings demonstrate that, like IFN-gamma, IL-4 also induces expression of SOCS-1 in macrophages, and SOCS-1 feedback inhibits expression of STAT6-responsive genes.

Identification, cloning, and characterization of a novel soluble receptor that binds IL-22 and neutralizes its activity

With the use of a partial sequence of the human genome, we identified a gene encoding a novel soluble receptor belonging to the class II cytokine receptor family. This gene is positioned on chromosome 6 in the vicinity of the IFNGR1 gene in a head-to-tail orientation. The gene consists of six exons and encodes a 231-aa protein with a 21-aa leader sequence. The secreted mature protein demonstrates 34% amino acid identity to the extracellular domain of the IL-22R1 chain. Cross-linking experiments demonstrate that the protein binds IL-22 and prevents binding of IL-22 to the functional cell surface IL-22R complex, which consists of two subunits, the IL-22R1 and the IL-10R2c chains. Moreover, this soluble receptor, designated IL-22-binding protein (BP), is capable of neutralizing IL-22 activity. In the presence of the IL-22BP, IL-22 is unable to induce Stat activation in IL-22-responsive human lung carcinoma A549 cells. IL-22BP also blocked induction of the suppressors of cytokine signaling-3 (SOCS-3) gene expression by IL-22 in HepG2 cells. To further evaluate IL-22BP action, we used hamster cells expressing a modified IL-22R complex consisting of the intact IL-10R2c and the chimeric IL-22R1/gammaR1 receptor in which the IL-22R1 intracellular domain was replaced with the IFN-gammaR1 intracellular domain. In these cells, IL-22 activates biological activities specific for IFN-gamma, such as up-regulation of MHC class I Ag expression. The addition of IL-22BP neutralizes the ability of IL-22 to induce Stat activation and MHC class I Ag expression in these cells. Thus, the soluble receptor designated IL-22BP inhibits IL-22 activity by binding IL-22 and blocking its interaction with the cell surface IL-22R complex.

Identification of the functional interleukin-22 (IL-22) receptor complex: the IL-10R2 chain (IL-10Rbeta ) is a common chain of both the IL-10 and IL-22 (IL-10-related T cell-derived inducible factor, IL-TIF) receptor complexes

Interleukin-10 (IL-10)-related T cell-derived inducible factor (IL-TIF; provisionally designated IL-22) is a cytokine with limited homology to IL-10. We report here the identification of a functional IL-TIF receptor complex that consists of two receptor chains, the orphan CRF2-9 and IL-10R2, the second chain of the IL-10 receptor complex. Expression of the CRF2-9 chain in monkey COS cells renders them sensitive to IL-TIF. However, in hamster cells both chains, CRF2-9 and IL-10R2, must be expressed to assemble the functional IL-TIF receptor complex. The CRF2-9 chain (or the IL-TIF-R1 chain) is responsible for Stat recruitment. Substitution of the CRF2-9 intracellular domain with the IFN-gammaR1 intracellular domain changes the pattern of IL-TIF-induced Stat activation. The CRF2-9 gene is expressed in normal liver and kidney, suggesting a possible role for IL-TIF in regulating gene expression in these tissues. Each chain, CRF2-9 and IL-10R2, is capable of binding IL-TIF independently and can be cross-linked to the radiolabeled IL-TIF. However, binding of IL-TIF to the receptor complex is greater than binding to either receptor chain alone. Sharing of the common IL-10R2 chain between the IL-10 and IL-TIF receptor complexes is the first such case for receptor complexes with chains belonging to the class II cytokine receptor family, establishing a novel paradigm for IL-10-related ligands similar to the shared use of the gamma common chain (gamma(c)) by several cytokines, including IL-2, IL-4, IL-7, IL-9, and IL-15.

Interleukin-12 differentially regulates expression of IFN-gamma and interleukin-2 in human T lymphoblasts

Interleukin-12 (IL-12) is known to upregulate expression of interferon-gamma (IFN-gamma) by activated T cells. However, the effects of IL-12 on production of other Th1-type cytokines are less well defined. In this study, we examined the effects of IL-12 on expression of several cytokines, including IFN-gamma, IL-2, tumor necrosis factor-alpha (TNF-alpha), and IL-10, by primary human CD3(+) T cells. Although purified resting T cells were largely nonresponsive to IL-12 stimulation, anti-CD3-activated T cell blasts were strongly responsive, as demonstrated by the ability of IL-12 to induce Stat4 DNA-binding activity. Restimulation of T lymphoblasts on immobilized anti-CD3 monoclonal antibodies (mAb) induced rapid expression of TNF-alpha mRNA and more gradual increases in mRNA levels for IL-2, IFN-gamma, and IL-10. IL-12 markedly upregulated expression of IFN-gamma and IL-10 but downregulated expression of IL-2 in a dose-dependent and time-dependent manner. The levels of IL-2 produced by IL-12-treated T cells correlated inversely with the levels of IL-10. Moreover, neutralization of IL-10 activity with anti-IL-10 antibodies normalized IL-2 production by IL-12-treated T cells, confirming that the inhibition of IL-2 production by IL-12 was IL-10 mediated. Thus, IL-12 amplified expression of IFN-gamma and IL-10 and, via its ability to upregulate production of IL-10, inhibited expression of IL-2. These findings demonstrate that IL-12 differentially regulates expression of the Th1-type lymphokines, IFN-gamma and IL-2, in T lymphoblasts.

Cloning, expression and initial characterization of interleukin-19 (IL-19), a novel homologue of human interleukin-10 (IL-10)

Interleukin-10 (IL-10) is a pleiotropic cytokine with important immunoregulatory functions whose actions influence activities of many of the cell-types in the immune system. We report here identification and cloning of a gene and corresponding cDNAs encoding a novel homologue of IL-10, designated IL-19. IL-19 shares 21% amino acid identity with IL-10. The exon/intron structure of IL-19 is similar to that of the human IL-10 gene, comprising five exons and four introns within the coding region of the IL-19 cDNA. There are at least two distinct IL-19 mRNA species that differ in their 5'-sequences, suggesting the existence of an intron in the 5'-sequences of coding portion of the IL-19 gene. The longer 5'-sequence contains an alternative initiating ATG codon that is in-frame with the rest of the coding sequence. The expression of IL-19 mRNA can be induced in monocytes by LPS-treatment. The appearance of IL-19 mRNA in LPS-stimulated monocytes was slightly delayed compared to expression of IL-10 mRNA: significant levels of IL-10 mRNA were detectable at 2 h post-stimulation, whereas IL-19 mRNA was not detectable until 4 h. Treatment of monocytes with IL-4 or IL-13 did not induce de novo expression of IL-19, but these cytokines did potentiate IL-19 gene expression in LPS-stimulated monocytes. In addition, GM-CSF was capable of directly inducing IL-19 gene expression in monocytes. IL-19 does not bind or signal through the canonical IL-10 receptor complex, suggesting existence of an IL-19 specific receptor complex, the identity of which remains to be discovered.

Inhibition of IL-12 production in human monocyte-derived macrophages by TNF

IL-12 is a pivotal cytokine that links the innate and adaptive immune responses. TNF-alpha also plays a key role in orchestrating inflammation and immunity. The reciprocal influence of these two inflammatory mediators on each other may have significant impact on the cytokine balance that shapes the type and extent of immune responses. To investigate the relationship between TNF-alpha and IL-12 production, we analyzed the effects of exposure of human monocyte-derived macrophages to TNF-alpha on LPS- or Staphylococcus aureus-induced IL-12 production in the presence or absence of IFN-gamma. TNF-alpha is a potent inhibitor of IL-12 p40 and p70 secretion from human macrophages induced by LPS or S. aureus. IL-10 is not responsible for the TNF-alpha-mediated inhibition of IL-12. TNF-alpha selectively inhibits IL-12 p40 steady-state mRNA, but not those of IL-12 p35, IL-1alpha, IL-1beta, or IL-6. Nuclear run-on analysis identified this specific inhibitory effect at the transcriptional level for IL-12 p40 without down-regulation of the IL-12 p35 gene. The major transcriptional factors identified to be involved in the regulation of IL-12 p40 gene expression by LPS and IFN-gamma, i.e., c-Rel, NF-kappaB p50 and p65, IFN regulatory factor-1, and ets-2, were not affected by TNF-alpha when examined by nuclear translocation and DNA binding. These data demonstrate a selective negative regulation on IL-12 by TNF-alpha, identifying a direct negative feedback mechanism for inflammation-induced suppression of IL-12 gene expression.

Differential responses of human monocytes and macrophages to IL-4 and IL-13

The primary interleukin-4 (IL-4) receptor complex on monocytes (type I IL-4 receptor) includes the 140-kDa alpha chain (IL-4R alpha) and the IL-2 receptor gamma chain, gamma(c), which heterodimerize for intracellular signaling, resulting in suppression of lipopolysaccharide (LPS)-inducible inflammatory mediator production. The activity of IL-13 on human monocytes is very similar to that of IL-4 because the predominant signaling chain (IL-4R alpha) is common to both receptors. In fact, IL-4R alpha with IL-13R alpha1 is designated both as an IL-13 receptor and the type II IL-4 receptor. When the anti-inflammatory activities of IL-4 and IL-13 were investigated on synovial fluid macrophages and compared with the responses by monocytes isolated from the patients at the same time as joint drainage, the response profiles differed with some responses similar in the two cell populations, others reduced on the inflammatory cells. Similar differences were recorded in the response profiles to IL-4 and IL-13 by monocytes and monocytes cultured for 7 days in macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage CSF (GM-CSF) (monocyte-derived macrophages, MDMac). MDMac have reduced gamma(c) mRNA levels and reduced expression of the functional 64-kDa gamma(c). There was a similar loss of IL-13R alpha1 mRNA on monocyte differentiation. In turn, there was a significant reduction in the ability of IL-4 and IL-13 to activate STAT6. These findings suggest that different functional responses to IL-4 and IL-13 by human monocytes and macrophages may result from reduced expression of gamma(c) and IL-13R alpha1.

Interferons inhibit activation of STAT6 by interleukin 4 in human monocytes by inducing SOCS-1 gene expression

Interferons (IFNs) inhibit induction by IL-4 of multiple genes in human monocytes. However, the mechanism by which IFNs mediate this inhibition has not been defined. IL-4 activates gene expression by inducing tyrosine phosphorylation, homodimerization, and nuclear translocation of the latent transcription factor, STAT6 (signal transducer and activator of transcription-6). STAT6-responsive elements are characteristically present in the promoters of IL-4-inducible genes. Because STAT6 activation is essential for IL-4-induced gene expression, we examined the ability of type I and type II IFNs to regulate activation of STAT6 by IL-4 in primary human monocytes. Pretreatment of monocytes with IFN-beta or IFN-gamma, but not IL-1, IL-2, macrophage colony-stimulating factor, granulocyte/macrophage colony-stimulating factor, IL-6, or transforming growth factor beta suppressed activation of STAT6 by IL-4. This inhibition was associated with decreased tyrosine phosphorylation and nuclear translocation of STAT6 and was not evident unless the cells were preincubated with IFN for at least 1 hr before IL-4 stimulation. Furthermore, inhibition by IFN could be blocked by cotreatment with actinomycin D and correlated temporally with induction of the JAK/STAT inhibitory gene, SOCS-1. Forced expression of SOCS-1 in a macrophage cell line, RAW264, markedly suppressed trans-activation of an IL-4-inducible reporter as well as IL-6- and IFN-gamma-induced reporter gene activity. These findings demonstrate that IFNs inhibit IL-4-induced activation of STAT6 and STAT6-dependent gene expression, at least in part, by inducing expression of SOCS-1.

Diminished responses to IL-13 by human monocytes differentiated in vitro: role of the IL-13Ralpha1 chain and STAT6

The primary IL-13 receptor complex on human monocytes is believed to be a heterodimer comprised of the IL-4R alpha chain and the IL-2R gamma chain (gamma(c))-like molecule, IL-13R alpha1. mRNA levels for IL-13R alpha1, but not IL-4R alpha, were markedly decreased in in vitro monocyte-derived macrophages (MDMac), and with increasing time of monocytes in culture correlated with the loss of IL-13 regulation of lipopolysaccharide-induced TNF-alpha production. Analysis of cell lines Daudi and THP-1 that differentially express gamma(c) and IL-13R alpha1 showed that IL-13 can activate STAT6 in IL-13R alpha1-positive THP-1 cells but not in gamma(c)-positive, IL-13R alpha1-negative Daudi cells. IL-13 activation of STAT6 was reduced in MDMac which was associated with diminished IL-13-induced expression of CD23 and MHC class II. However, with reduced IL-13R alpha1 expression and low nuclear STAT6 activity, some IL-13-induced responses were unaltered in magnitude in MDMac. In the absence of functional IL-13R alpha1 and gamma(c), IL-13 must signal through an alternative receptor complex on MDMac. Experiments with a blocking antibody to IL-4R alpha showed that this chain remains an essential component of the IL-13 receptor complex on MDMac.

The interleukin-10 signal transduction pathway and regulation of gene expression in mononuclear phagocytes

Interleukin-10 (IL-10) activates a diverse array of functional responses in mononuclear phagocytes. Functional IL-10 receptor (IL-10R) complexes are tetramers consisting of two IL-10R1 polypeptide chains and two IL-10R2 chains. Binding of IL-10 to the extracellular domain of IL-10R1 activates phosphorylation of the receptor-associated Janus tyrosine kinases, JAK1 and Tyk2. These kinases then phosphorylate specific tyrosine residues (Y446 and Y496) on the intracellular domain of the IL-10R1 chain. Once phosphorylated, these tyrosine residues (and their flanking peptide sequences) serve as temporary docking sites for the latent transcription factor, STAT3 (signal transducer and activator of transcription-3). STAT3 binds to these sites via its SH2 (Src homology 2) domain, and is, in turn, tyrosine-phosphorylated by the receptor-associated JAKs. It then homodimerizes and translocates to the nucleus where it binds with high affinity to STAT-binding elements (SBE) in the promoters of various IL-10-responsive genes. One of these genes, SOCS-3 (Suppressor of Cytokine Signaling-3) is a member of a newly identified family of genes that inhibit JAK/STAT-dependent signaling. Moreover, the ability of IL-10 to induce de novo synthesis of SOCS-3 in monocytes correlates with its ability to inhibit expression of many genes in these cells, including endotoxin-inducible cytokines such as tumor necrosis factor-alpha (TNF-alpha) and IL-1. Thus, the ability of IL-10 to inhibit gene expression in monocytes is associated with its ability to rapidly induce synthesis of SOCS-3.

Interleukin-10 inhibits expression of both interferon alpha- and interferon gamma- induced genes by suppressing tyrosine phosphorylation of STAT1

Interleukin-10 (IL-10) helps maintain polarized T-helper cells in a T-helper lymphocyte 2 (Th2) phenotype. Part of this process involves the prevention of the development of Th1 cells, which are a primary source of interferon gamma (IFNgamma), a potent activator of monocytes and an inhibitor of Th2 proliferation. Because monocytes and macrophages are important mediators of Th1-type responses, such as delayed-type hypersensitivity, we sought to determine if IL-10 could directly mediate inhibition of IFNgamma- and IFNalpha-induced gene expression in these cells. Highly purified monocytes were incubated with IL-10 for 60 to 90 minutes before the addition of IFNgamma or IFNalpha. IL-10 preincubation resulted in the inhibition of gene expression for several IFN-induced genes, such as IP-10, ISG54, and intercellular adhesion molecule-1. The reduction in gene expression resulted from the ability of IL-10 to suppress IFN-induced assembly of signal transducer and activator of transcription (STAT) factors to specific promoter motifs on IFNalpha- and IFNgamma-inducible genes. This was accomplished by preventing the IFN-induced tyrosine phosphorylation of STAT1, a component of both IFNalpha- and IFNgamma-induced DNA binding complexes. Therefore, IL-10 can directly inhibit STAT-dependent early response gene expression induced by both IFNalpha and IFNgamma in monocytes by suppressing the tyrosine phosphorylation of STAT1. This may occur through the ability of IL-10 to induce expression of the gene, suppressor of cytokine signaling 3 (SOCS3).

Inhibition of IL-4-inducible gene expression in human monocytes by type I and type II interferons

The Th2-type cytokines, interleukin-4 (IL-4) and interleukin-13 (IL-13), induce expression of a distinct subset of genes in human monocytes, including FcepsilonRIIb (CD23), 15-lipoxygenase, IL-1 receptor antagonist (IL-1ra), and type I and type II IL-1 receptors (IL-1R). Type I interferons (IFN-alpha and IFN-beta) and type II interferon (IFN-gamma) inhibit induction of these genes by IL-4 and IL-13. However, the mechanism by which IFNs mediate this inhibition has not been defined. In this overview, we discuss the role of the transcription factor, STAT6 (signal transducer and activator of transcription-6) in mediating IL-4- and IL-13-induced gene expression in monocytes. We also discuss our recent findings that type I and type II IFNs suppress IL-4/IL-13-inducible gene expression by inhibiting tyrosine phosphorylation and nuclear translocation of STAT6. The ability of type I and type II IFNs to inhibit IL-4/IL-13-induced STAT6 activity is dose- and time-dependent, and is not unique to monocytes because IFNs induce the same effects in fibroblasts. Inhibition of STAT6 activity is not evident unless cells are preincubated with IFN for at least 1 h before IL-4 stimulation. Furthermore, inhibition can be blocked by actinomycin D, indicating a requirement for de novo transcription. We propose a model in which stimulation of monocytes by IFN activates de novo synthesis of an inhibitory factor, possibly one or more members of the SOCS/ SSI/CIS gene family, capable of suppressing activation of STAT6 by IL-4 and IL-13. Because STAT6 activation plays an essential role in IL-4/IL-13-induced gene expression, the ability of IFN-beta and IFN-gamma to inhibit STAT6 activity provides an explanation for how IFNs can suppress IL-4/IL-13-inducible gene expression.

Involvement of the IL-2 receptor gamma-chain (gammac) in the control by IL-4 of human monocyte and macrophage proinflammatory mediator production

IL-4 has potent anti-inflammatory properties on monocytes and suppresses both IL-1beta and TNF-alpha production. Well-characterized components of the IL-4 receptor on monocytes include the 140-kDa alpha-chain and the IL-2R gamma-chain, gammac, which normally dimerize 1:1 for signaling from the receptor. However, mRNA levels for gammac were very low in 7-day-cultured monocytes. As mRNA levels for gammac declined with culture, so too did the ability of IL-4 to down-regulate LPS-induced TNF-alpha production. In contrast, IL-4 consistently down-regulated IL-1beta production by cultured monocytes. Immunoprecipitation and Western blot analyses demonstrated that 7-day-cultured monocytes do not express the functionally active 64-kDa gammac protein. This was associated with decreased STAT6 activation by IL-4. Studies with Abs to gammac and an IL-4 mutant that is unable to bind to gammac showed that IL-4 can suppress IL-1beta but not TNF-alpha production by LPS-stimulated monocytes in the presence of little or no functioning gammac. IL-4 also suppressed IL-1beta but not TNF-alpha production by Mono Mac 6 cells, which express minimal levels of gammac. For gammac-expressing LPS/PMA-activated U937 cells, IL-4 decreased both TNF-alpha and IL-1beta production. These results suggest that functional gammac is not present on in vitro-derived macrophages, and that while some anti-inflammatory responses to IL-4 are lost with this down-regulation of functional gammac, others are retained. We conclude that different functional responses to IL-4 by human monocytes and macrophages are regulated by different IL-4 receptor configurations.

Production of IL-10 by human natural killer cells stimulated with IL-2 and/or IL-12

Human NK cell activity can be augmented in vitro by stimulation with IL-2 or IL-12, both of which also induce the production of IFN-gamma, TNF-alpha, and granulocyte-macrophage CSF by NK cells. For the first time, we demonstrate that freshly purified NK cells stimulated with IL-2 proliferated and produced IL-10 in a dose-dependent manner. IL-10 mRNA expression, as detected by semiquantitative reverse transcription-PCR, reached peak levels at 24 h. IL-10 protein was detectable on day 2 and further increased on days 3 and 6 as measured by ELISA. However, IL-12 alone induced neither substantial proliferation nor detectable IL-10 production by fresh NK cells, but it synergized with IL-2 in inducing IL-10 mRNA expression and protein synthesis. IL-10 production by activated NK cells was confirmed by intracytoplasmic cytokine staining by three-color immunofluorescence of CD16+ and/or CD56+ NK cells with anti-IL-10 antibody. IL-10 production by NK cells was further confirmed in the NK-like cell line, YT, which constitutively expressed IL-10 mRNA and protein. IL-12 alone did not induce NK proliferation, but it inhibited IL-2-induced proliferation. Neutralization of endogenously produced IL-10 with anti-IL-10 antibodies did not overcome the inhibition of IL-2-induced proliferation by IL-12. Together, these results demonstrate that IL-2 and IL-12 synergize to induce IL-10 production by human NK cells and that IL-12 inhibits IL-2 induced NK cell proliferation by an IL-10-independent mechanism.

IFN-gamma and IL-10 inhibit induction of IL-1 receptor type I and type II gene expression by IL-4 and IL-13 in human monocytes

The Th2-type cytokines IL-4 and IL-13 induce expression of a distinct subset of genes in human monocytes. These include Fc epsilonRII (CD23), 15-lipoxygenase, IL-1 receptor antagonist (IL-1ra), and type I and type II IL-1 receptors (IL-1R). IFN-gamma has been shown to inhibit induction of CD23 and 15-lipoxygenase in monocytes; however, the effects of IFN-gamma on type I and type II IL-1R gene expression have not been defined. We examined the effects of IFN-gamma on both basal and IL-4/IL-13-induced IL-1R gene expression in primary monocytes. IL-4 and IL-13 induced dose- and time-dependent increases in IL-1RI and IL-1RII mRNA levels. IFN-gamma decreased basal expression as well as the induction of these genes by IL-4 and IL-13. Inhibition of IL-1RI and IL-1RII mRNA levels by IFN-gamma was transcriptionally mediated, and correlated directly with decreased production of soluble IL-1RII. Furthermore, the ability to suppress IL-1RI and IL-1RII mRNA levels was not unique to IFN-gamma because IL-10 also inhibited expression of these genes in IL-4/IL-13-stimulated monocytes. Inhibition of IL-1R gene expression by IFN-gamma and IL-10 was not due to down-regulation of surface IL-4R because pretreatment with these cytokines did not decrease the number of IL-4 binding sites per cell. However, suppression of IL-1R gene expression by IFN-gamma and IL-10 was associated with decreased tyrosine phosphorylation and nuclear translocation of the IL-4/IL-13-inducible transcription factor, Stat6, suggesting a potential mechanism by which IFN-gamma and IL-10 may mediate their suppressive effects. These findings demonstrate that certain cytokines, including IFN-gamma and IL-10, antagonize the ability of IL-4 and IL-13 to induce increased expression of the IL-1RI and IL-1RII genes in monocytes.

IFN-gamma and IL-10 inhibit induction of IL-1 receptor type I and type II gene expression by IL-4 and IL-13 in human monocytes

The Th2-type cytokines IL-4 and IL-13 induce expression of a distinct subset of genes in human monocytes. These include Fc epsilonRII (CD23), 15-lipoxygenase, IL-1 receptor antagonist (IL-1ra), and type I and type II IL-1 receptors (IL-1R). IFN-gamma has been shown to inhibit induction of CD23 and 15-lipoxygenase in monocytes; however, the effects of IFN-gamma on type I and type II IL-1R gene expression have not been defined. We examined the effects of IFN-gamma on both basal and IL-4/IL-13-induced IL-1R gene expression in primary monocytes. IL-4 and IL-13 induced dose- and time-dependent increases in IL-1RI and IL-1RII mRNA levels. IFN-gamma decreased basal expression as well as the induction of these genes by IL-4 and IL-13. Inhibition of IL-1RI and IL-1RII mRNA levels by IFN-gamma was transcriptionally mediated, and correlated directly with decreased production of soluble IL-1RII. Furthermore, the ability to suppress IL-1RI and IL-1RII mRNA levels was not unique to IFN-gamma because IL-10 also inhibited expression of these genes in IL-4/IL-13-stimulated monocytes. Inhibition of IL-1R gene expression by IFN-gamma and IL-10 was not due to down-regulation of surface IL-4R because pretreatment with these cytokines did not decrease the number of IL-4 binding sites per cell. However, suppression of IL-1R gene expression by IFN-gamma and IL-10 was associated with decreased tyrosine phosphorylation and nuclear translocation of the IL-4/IL-13-inducible transcription factor, Stat6, suggesting a potential mechanism by which IFN-gamma and IL-10 may mediate their suppressive effects. These findings demonstrate that certain cytokines, including IFN-gamma and IL-10, antagonize the ability of IL-4 and IL-13 to induce increased expression of the IL-1RI and IL-1RII genes in monocytes.

Interleukin-10 upregulates tumor necrosis factor receptor type-II (p75) gene expression in endotoxin-stimulated human monocytes

Interferon-gamma (IFN-gamma) upregulates expression of certain genes in monocytes, including cell-surface molecules such as HLA class II, B7, and ICAM-1. IFN-gamma also potentiates production of cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and IL-12. Conversely, IL-10 downregulates expression of many of these same genes and often antagonizes the effects of IFN-gamma. IL-10 is known to inhibit TNF-alpha production in lipopolysaccharide (LPS)-stimulated monocytes; however, the effects of IL-10 on TNF receptor (TNF-R) expression are not well defined. We examined the effects of IL-10 on production of both membrane-associated (m) and soluble (s) TNF-R type II (sTNF-RII) by purified human CD14(+) monocytes. We also compared the effects of IFN-gamma and IL-10 on production of TNF-alpha and sTNF-RII by these cells. Monocytes constitutively expressed low levels of TNF-RII mRNA and mTNF-RII protein. LPS stimulation induced rapid, but transient loss (shedding) of mTNF-RII molecules and a delayed, but marked increase in TNF-RII mRNA levels. IL-10 increased expression of both mTNF-RII and sTNF-RII by LPS-stimulated monocytes, whereas IFN-gamma decreased their expression. The increased levels of sTNF-RII in cultures of IL-10-treated monocytes correlated directly with increased levels of TNF-RII mRNA and inversely with the levels of TNF-alpha mRNA. The ability of IL-10 to upregulate TNF-RII gene expression was transcriptionally mediated because actinomycin D blocked this effect. Furthermore, IL-10 treatment did not alter the half-life of TNF-RII mRNA transcripts in LPS-stimulated monocytes. To further examine the mechanism by which IL-10 potentiates TNF-RII gene expression, a 1.8-kb fragment of the human TNF-RII promoter cloned into a luciferase expression vector (pGL2-basic) was transfected into the IL-10-responsive macrophage cell line, RAW264.7. Although IL-10 alone induced only minimal promoter activity in these cells, it markedly increased the LPS-induced response, providing further evidence that the ability of IL-10 to amplify TNF-RII gene expression is transcriptionally controlled. Together, these findings demonstrate that IL-10 coordinately downregulates expression of TNF-alpha and upregulates expression of TNF-RII, particularly the soluble form of this receptor, in monocytes.

Interleukin-10 inhibits interferon-gamma-induced intercellular adhesion molecule-1 gene transcription in human monocytes

Interleukin-10 (IL-10) is a potent monocyte regulatory cytokine that inhibits gene expression of proinflammatory mediators. In this study, we investigated the mechanism by which IL-10 downregulates expression of intercellular adhesion molecule-1 (ICAM-1) on the cell surface of normal human monocytes activated with interferon-gamma (IFN-gamma). IL-10 inhibition of IFN-gamma-induced ICAM-1 expression was apparent as early as 3 hours and was blocked by an anti-IL-10 antibody but not by an isotype-matched control antibody. Northern blot analysis showed that IL-10 reduced the accumulation of ICAM-1 mRNA in IFN-gamma-stimulated monocytes. IL-10 inhibition of ICAM-1 steady-state mRNA was detected at 3 hours and remained at 24 hours. Nuclear run-on transcription assays showed that IL-10 inhibited the rate of IFN-gamma-induced transcription of the ICAM-1 gene, and mRNA stability studies showed that IL-10 did not alter the half-life of IFN-gamma-induced ICAM-1 message. Thus, IL-10 inhibits IFN-gamma-induced ICAM-1 expression in monocytes primarily at the level of gene transcription. Activation of IFN-gamma-responsive genes requires tyrosine phosphorylation of the transcriptional factor STAT-1alpha (signal transducer and activator of transcription-1alpha). However, IL-10 did not affect IFN-gamma-induced tyrosine phosphorylation of STAT-1alpha or alter STAT-1alpha binding to the IFN-gamma response element (IRE) in the ICAM-1 promoter. Instead, IL-10 prevented IFN-gamma-induced binding activity at the NF-kappaB site of the tumor necrosis factor alpha (TNF-alpha)-responsive NF-kappaB/C-EBP composite element in the ICAM-1 promoter. These data indicate that IL-10 inhibits IFN-gamma-induced transcription of the ICAM-1 gene by a regulatory mechanism that may involve NF-kappaB.

Motor pool organization of the external gastrocnemius muscle in the turtle, Pseudemys (Trachemys) scripta elegans

The spinal cord of the adult turtle, Pseudemys (Trachemys) scripta elegans, is now considered a promising model for the study of the segmental motor system in the generalized tetrapod. To facilitate such studies we have examined the location, soma geometry, soma size, and number of motoneurons innervating the external gastrocnemius (EG) muscle in this species, as this muscle is ideally suited to the study of interrelations between the neuronal and muscular components of the segmental motor system. Motoneurons were retrogradely labeled following application of horseradish peroxidase to the EG muscle nerve. In both horizontal and transverse planes, labeled motoneurons innervating the EG muscle were concentrated in the S1 lumbosacral segment, and extended rostrally and caudally as far as the exists of the D10 and S2 spinal nerves, respectively. In the transverse plane, motoneurons were arranged in a longitudinal column which occupied the dorsolateral quadrant of the ventral horn. EG motoneurons are fusiform in shape and present their largest dimension in the transverse plane with their long axis oriented in the ventromedial to dorsolateral plane. The soma diameters of EG motoneurons were normally distributed, reflecting the absence of separate fusimotor innervation in reptilian species. In individual turtles, there was a two- to threefold range in soma diameter while soma surface area extended over a seven- to tenfold range. Based on cell counts from five animals, the EG motor pool was composed of approximately 75 motoneurons. Taken together, the results of this study provide valuable information for interpreting the results of future studies on the segmental motor system of this species under both normal and pathophysiological conditions.

Inhibition of IL-10 expression by IFN-gamma up-regulates transcription of TNF-alpha in human monocytes

Stimulation of human monocytes with LPS induces expression of multiple cytokines, including TNF-alpha, IL-1 beta, IL-6, and IL-10, IL-10 expression is delayed relative to that of TNF-alpha, IL-1 beta, and IL-6. Furthermore, IL-10 feedback inhibits expression of TNF-alpha, IL-1 beta, and IL-6, thus providing an efficient autocrine mechanism for controlling proinflammatory cytokine production in monocytes. The Th1-type lymphokine, IFN-gamma, markedly up-regulates TNF-alpha production in monocytes. However, the precise mechanism by which IFN-gamma mediates this effect is unknown. We examined the effects of IFN-gamma on IL-10 expression in LPS-stimulated monocytes, and the relationship between IL-10 and TNF-alpha production in these cells. LPS stimulation induced rapid, ordered expression of multiple cytokines. Steady-state mRNA levels for TNF-alpha increased rapidly, reached maximal levels by 2 to 3 h poststimulation, and then declined sharply. IL-1 beta and IL-6 mRNA levels also increased markedly following stimulation with LPS, but decreased more slowly than did TNF-alpha. Down-regulation of mRNA for TNF-alpha, IL-1 beta, and IL-6 coincided with a delayed and more gradual increase in IL-10 mRNA levels. Furthermore, neutralization of IL-10 with anti-IL-10 Abs prolonged TNF-alpha mRNA expression, and significantly increased net TNF-alpha production. IFN-gamma suppressed expression of IL-10 mRNA and protein in a dose-dependent manner. Moreover, inhibition of IL-10 production correlated with a marked increase in both the magnitude and duration of TNF-alpha expression. Thus, potentiation of TNF-alpha production by IFN-gamma in monocytes is coupled to inhibition of endogenous IL-10 expression.

Inhibition of IL-10 expression by IFN-gamma up-regulates transcription of TNF-alpha in human monocytes

Stimulation of human monocytes with LPS induces expression of multiple cytokines, including TNF-alpha, IL-1 beta, IL-6, and IL-10, IL-10 expression is delayed relative to that of TNF-alpha, IL-1 beta, and IL-6. Furthermore, IL-10 feedback inhibits expression of TNF-alpha, IL-1 beta, and IL-6, thus providing an efficient autocrine mechanism for controlling proinflammatory cytokine production in monocytes. The Th1-type lymphokine, IFN-gamma, markedly up-regulates TNF-alpha production in monocytes. However, the precise mechanism by which IFN-gamma mediates this effect is unknown. We examined the effects of IFN-gamma on IL-10 expression in LPS-stimulated monocytes, and the relationship between IL-10 and TNF-alpha production in these cells. LPS stimulation induced rapid, ordered expression of multiple cytokines. Steady-state mRNA levels for TNF-alpha increased rapidly, reached maximal levels by 2 to 3 h poststimulation, and then declined sharply. IL-1 beta and IL-6 mRNA levels also increased markedly following stimulation with LPS, but decreased more slowly than did TNF-alpha. Down-regulation of mRNA for TNF-alpha, IL-1 beta, and IL-6 coincided with a delayed and more gradual increase in IL-10 mRNA levels. Furthermore, neutralization of IL-10 with anti-IL-10 Abs prolonged TNF-alpha mRNA expression, and significantly increased net TNF-alpha production. IFN-gamma suppressed expression of IL-10 mRNA and protein in a dose-dependent manner. Moreover, inhibition of IL-10 production correlated with a marked increase in both the magnitude and duration of TNF-alpha expression. Thus, potentiation of TNF-alpha production by IFN-gamma in monocytes is coupled to inhibition of endogenous IL-10 expression.

IFN-gamma priming of monocytes enhances LPS-induced TNF production by augmenting both transcription and MRNA stability

The induction of cytokine expression in monocytes/macrophages by bacterial endotoxin or lipopolysaccharide is a critical, highly regulated host defence response. The augmentation of LPS responses by interferon gamma (IFN-gamma), referred to as priming, is well established. However, the mechanism(s) by which priming occurs is poorly defined. Using tumour necrosis factor (TNF) induction as a model, experiments were designed to analyse in detail the priming effect on the LPS response in human monocytes. Priming by IFN-gamma was primarily manifested at the level of TNF mRNA accumulation. IFN-gamma pre-treatment affected the magnitude rather than the sensitivity of the LPS response. Priming occurred after several hours of treatment, and the primed state was induced by either IFN-gamma or GM-CSF, but not M-CSF. Primed monocytes transcribed TNF mRNA at a higher rate than freshly isolated monocytes upon activation with LPS. The increased transcriptional rate correlated with a marked increase in nuclear factor-kappa B activity in these cells as determined by electrophoretic mobility shift assay using a consensus NF-kappa B oligonucleotide. An additional significant finding was than TNF mRNA induced in primed cells was much more stable than in unprimed cells (T1/2 increased 6-8-fold). Consistent with the increased mRNA stability, the duration of mRNA accumulation was longer following LPS stimulation in primed monocytes, in addition to being of greater magnitude. Finally, primed and unprimed cells possessed a differential sensitivity to the kinase inhibitor H-89. H-89 substantially suppressed LPS-induced TNF mRNA accumulation in unprimed cells, but had no effect on primed monocytes following LPS stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue-specific regulation of IL-6 production by IL-4. Differential effects of IL-4 on nuclear factor-kappa B activity in monocytes and fibroblasts

IL-4 inhibits production of certain proinflammatory cytokines, including IL-1 beta, TNF-alpha, and IL-6, by activated monocytes. Although monocytes are a major source of IL-6, other cell types such as fibroblasts and endothelial cells can also express this cytokine. To determine whether IL-4 inhibits IL-6 expression in non-hemopoietic cells, we investigated the effects of IL-4 on IL-6 production in both primary human fibroblasts and fibroblast lines. Rheumatoid synovial fibroblasts were evaluated in these studies because, like monocytes, they produce high levels of IL-6 when stimulated with IL-1. Although peripheral blood monocytes did not constitutively express IL-6 mRNA or protein, stimulation with IL-1 or LPS induced de novo IL-6 expression in these cells. In contrast, synovial fibroblasts displayed a significant basal level of IL-6 production, which was markedly increased after stimulation with IL-1. IL-4 suppressed IL-6 expression in monocytes, but did not inhibit IL-6 production in synovial fibroblasts. The inability of IL-4 to suppress IL-6 synthesis in rheumatoid synovial fibroblasts was not caused by a lack of IL-4R and was not unique to these cells because IL-4 also failed to inhibit IL-6 production in normal fibroblast lines derived from other tissues. Inhibition of IL-6 production by IL-4 in monocytes was associated with decreased nuclear NF-kappa B levels. However, IL-4 does not globally suppress the activity of all DNA-binding proteins because IL-4 treatment did not reduce the levels of NF-IL-6 or NF-IL-1 beta B in the same cells. Because NF-kappa B activation is required for transcription of many cytokine genes, including IL-6, the ability of IL-4 to suppress NF-kappa B activity in monocytes suggests a potential mechanism by which this molecule may inhibit the expression of multiple cytokines.

Tissue-specific regulation of IL-6 production by IL-4. Differential effects of IL-4 on nuclear factor-kappa B activity in monocytes and fibroblasts

IL-4 inhibits production of certain proinflammatory cytokines, including IL-1 beta, TNF-alpha, and IL-6, by activated monocytes. Although monocytes are a major source of IL-6, other cell types such as fibroblasts and endothelial cells can also express this cytokine. To determine whether IL-4 inhibits IL-6 expression in non-hemopoietic cells, we investigated the effects of IL-4 on IL-6 production in both primary human fibroblasts and fibroblast lines. Rheumatoid synovial fibroblasts were evaluated in these studies because, like monocytes, they produce high levels of IL-6 when stimulated with IL-1. Although peripheral blood monocytes did not constitutively express IL-6 mRNA or protein, stimulation with IL-1 or LPS induced de novo IL-6 expression in these cells. In contrast, synovial fibroblasts displayed a significant basal level of IL-6 production, which was markedly increased after stimulation with IL-1. IL-4 suppressed IL-6 expression in monocytes, but did not inhibit IL-6 production in synovial fibroblasts. The inability of IL-4 to suppress IL-6 synthesis in rheumatoid synovial fibroblasts was not caused by a lack of IL-4R and was not unique to these cells because IL-4 also failed to inhibit IL-6 production in normal fibroblast lines derived from other tissues. Inhibition of IL-6 production by IL-4 in monocytes was associated with decreased nuclear NF-kappa B levels. However, IL-4 does not globally suppress the activity of all DNA-binding proteins because IL-4 treatment did not reduce the levels of NF-IL-6 or NF-IL-1 beta B in the same cells. Because NF-kappa B activation is required for transcription of many cytokine genes, including IL-6, the ability of IL-4 to suppress NF-kappa B activity in monocytes suggests a potential mechanism by which this molecule may inhibit the expression of multiple cytokines.

IL-4 reciprocally regulates IL-1 and IL-1 receptor antagonist expression in human monocytes

Activation of human monocytes with LPS induces coordinate expression of a number of cytokine genes, including IL-1 alpha, IL-1 beta, TNF-alpha, IL-6, and IL-8. The T cell-derived lymphokine, IL-4, inhibits expression of these genes in monocytes, suggesting that it may be an important physiologic regulator of cytokine production. We have previously shown that IL-4 reduces steady state messenger RNA (mRNA) levels for IL-1 beta in human monocytes by decreasing both IL-1 beta transcription and the t1/2 of newly formed IL-1 beta mRNA transcripts. In the present study, we extend these findings to show that IL-4 similarly accelerates the turnover of IL-6 mRNA in LPS-stimulated monocytes. However, this inhibition of cytokine expression and dramatic increase in the decay rate of cytokine mRNA does not extend to all LPS-inducible genes because IL-4 treatment did not inhibit the expression or accelerate the turnover of mRNA for the IL-1 receptor antagonist (IL-1ra) in the same cells. Although IL-1 beta and IL-1Ra are both LPS-inducible genes, they displayed distinct temporal patterns of expression. Peak steady state mRNA levels for IL-1ra lagged significantly behind that of IL-1 beta, suggesting a possible endogenous mechanism for limiting IL-1 biologic activity. Furthermore, although IL-4 suppressed expression of both IL-1 beta and IL-6, it up-regulated synthesis of IL-1ra mRNA and protein. Thus, IL-4 inhibits production of the proinflammatory cytokine, IL-1 beta, while concomitantly enhancing synthesis of the IL-1ra in activated human monocytes.

IL-4 reciprocally regulates IL-1 and IL-1 receptor antagonist expression in human monocytes

Activation of human monocytes with LPS induces coordinate expression of a number of cytokine genes, including IL-1 alpha, IL-1 beta, TNF-alpha, IL-6, and IL-8. The T cell-derived lymphokine, IL-4, inhibits expression of these genes in monocytes, suggesting that it may be an important physiologic regulator of cytokine production. We have previously shown that IL-4 reduces steady state messenger RNA (mRNA) levels for IL-1 beta in human monocytes by decreasing both IL-1 beta transcription and the t1/2 of newly formed IL-1 beta mRNA transcripts. In the present study, we extend these findings to show that IL-4 similarly accelerates the turnover of IL-6 mRNA in LPS-stimulated monocytes. However, this inhibition of cytokine expression and dramatic increase in the decay rate of cytokine mRNA does not extend to all LPS-inducible genes because IL-4 treatment did not inhibit the expression or accelerate the turnover of mRNA for the IL-1 receptor antagonist (IL-1ra) in the same cells. Although IL-1 beta and IL-1Ra are both LPS-inducible genes, they displayed distinct temporal patterns of expression. Peak steady state mRNA levels for IL-1ra lagged significantly behind that of IL-1 beta, suggesting a possible endogenous mechanism for limiting IL-1 biologic activity. Furthermore, although IL-4 suppressed expression of both IL-1 beta and IL-6, it up-regulated synthesis of IL-1ra mRNA and protein. Thus, IL-4 inhibits production of the proinflammatory cytokine, IL-1 beta, while concomitantly enhancing synthesis of the IL-1ra in activated human monocytes.

IL-1 expression in human monocytes is transcriptionally and posttranscriptionally regulated by IL-4

The T cell-derived lymphokine, IL-4, inhibits production of IL-1 beta by normal human monocytes. To determine whether IL-4 suppresses IL-1 expression by a transcriptional and/or posttranscriptional mechanism, we evaluated the half-life of LPS-induced IL-1 beta message and transcriptional rate of the pro-IL-1 beta gene in human monocytes after treatment with IL-4. Although the initial steady-state IL-1 mRNA levels in control and IL-4-treated monocytes were comparable during the first 2 h after stimulation with LPS, IL-1 message levels subsequently decreased at a significantly greater rate in the IL-4-treated cells. Thus, IL-4 did not prevent the initial expression of IL-1 message, but did accelerate down-regulation of IL-1 mRNA in LPS-stimulated monocytes. The initial 2 to 3 h lag period may be necessary for production of a protein(s) that mediates this inhibitory effect because treatment with the protein synthesis inhibitor, cycloheximide, blocked the marked reduction of IL-1 message levels induced by IL-4. Nuclear run-on analyses demonstrated that IL-4 decreases IL-1 mRNA levels, in part, by repressing IL-1 gene transcription. Furthermore, mRNA half-life studies showed that IL-4 also significantly increases the rate of IL-1 message turnover in these cells. Together, these findings demonstrate that IL-4 inhibits IL-1 production in human monocytes by suppressing the formation of new IL-1 transcripts as well as by decreasing IL-1 message stability. In addition, the kinetics of inhibition and the fact that cycloheximide blocks this process suggest that IL-4 induces or enhances synthesis of a protein(s) that mediates these effects.

IL-1 expression in human monocytes is transcriptionally and posttranscriptionally regulated by IL-4

The T cell-derived lymphokine, IL-4, inhibits production of IL-1 beta by normal human monocytes. To determine whether IL-4 suppresses IL-1 expression by a transcriptional and/or posttranscriptional mechanism, we evaluated the half-life of LPS-induced IL-1 beta message and transcriptional rate of the pro-IL-1 beta gene in human monocytes after treatment with IL-4. Although the initial steady-state IL-1 mRNA levels in control and IL-4-treated monocytes were comparable during the first 2 h after stimulation with LPS, IL-1 message levels subsequently decreased at a significantly greater rate in the IL-4-treated cells. Thus, IL-4 did not prevent the initial expression of IL-1 message, but did accelerate down-regulation of IL-1 mRNA in LPS-stimulated monocytes. The initial 2 to 3 h lag period may be necessary for production of a protein(s) that mediates this inhibitory effect because treatment with the protein synthesis inhibitor, cycloheximide, blocked the marked reduction of IL-1 message levels induced by IL-4. Nuclear run-on analyses demonstrated that IL-4 decreases IL-1 mRNA levels, in part, by repressing IL-1 gene transcription. Furthermore, mRNA half-life studies showed that IL-4 also significantly increases the rate of IL-1 message turnover in these cells. Together, these findings demonstrate that IL-4 inhibits IL-1 production in human monocytes by suppressing the formation of new IL-1 transcripts as well as by decreasing IL-1 message stability. In addition, the kinetics of inhibition and the fact that cycloheximide blocks this process suggest that IL-4 induces or enhances synthesis of a protein(s) that mediates these effects.

Aberrant regulation of IL-1 expression in macrophages from young autoimmune-prone mice

IL-1 is a multifunctional, immunoregulatory polypeptide produced by many cell types. Because activated macrophages are a major source of IL-1 and have also been implicated in the pathogenesis of autoimmune disease, we investigated the regulation of IL-1 expression in several autoimmune-prone strains of mice. Peritoneal macrophages derived from the autoimmune-prone strains MRL/lpr, MRL/+, NZB, and NZB/W F1, as well as NZW, displayed transient expression of IL-1 in contrast to the stable expression characteristic of control normal strains including A. Thy, A/J, B10, B10.A, B10.D2, C57BL/6, BALB/c, and C3H/HeN. The down-regulation of IL-1 by macrophages from the autoimmune-prone mice was not attributable to inherently defective signal transduction because macrophages from both the normal and autoimmune-prone strains displayed substantial initial levels of cell-associated and secreted IL-1. However, during the first 2 to 3 days in culture, macrophages from autoimmune-prone mice became progressively refractory to both induction and maintenance of IL-1, a pattern that correlated with changes in the levels of IL-1 alpha and beta mRNA. The progressive reduction in IL-1 expression by macrophages from these autoimmune-prone strains was not due to a reduction in general metabolism or viability, because expression of cell surface antigens, including MHC class I and II Ag and LFA-1, was comparable to that of control macrophages. Because IL-1 plays a critical role in the homeostasis of a variety of cell lineages, defective expression, and maintenance of IL-1 (and perhaps other cytokines) by macrophages from the autoimmune-prone strains may contribute to the immune dysregulation that develops in these mice. Alternatively, cytokine dysregulation might not contribute directly to disease, but rather reflect a more basic defect related to specific signal transducing or gene regulatory pathways.

Aberrant regulation of IL-1 expression in macrophages from young autoimmune-prone mice

IL-1 is a multifunctional, immunoregulatory polypeptide produced by many cell types. Because activated macrophages are a major source of IL-1 and have also been implicated in the pathogenesis of autoimmune disease, we investigated the regulation of IL-1 expression in several autoimmune-prone strains of mice. Peritoneal macrophages derived from the autoimmune-prone strains MRL/lpr, MRL/+, NZB, and NZB/W F1, as well as NZW, displayed transient expression of IL-1 in contrast to the stable expression characteristic of control normal strains including A. Thy, A/J, B10, B10.A, B10.D2, C57BL/6, BALB/c, and C3H/HeN. The down-regulation of IL-1 by macrophages from the autoimmune-prone mice was not attributable to inherently defective signal transduction because macrophages from both the normal and autoimmune-prone strains displayed substantial initial levels of cell-associated and secreted IL-1. However, during the first 2 to 3 days in culture, macrophages from autoimmune-prone mice became progressively refractory to both induction and maintenance of IL-1, a pattern that correlated with changes in the levels of IL-1 alpha and beta mRNA. The progressive reduction in IL-1 expression by macrophages from these autoimmune-prone strains was not due to a reduction in general metabolism or viability, because expression of cell surface antigens, including MHC class I and II Ag and LFA-1, was comparable to that of control macrophages. Because IL-1 plays a critical role in the homeostasis of a variety of cell lineages, defective expression, and maintenance of IL-1 (and perhaps other cytokines) by macrophages from the autoimmune-prone strains may contribute to the immune dysregulation that develops in these mice. Alternatively, cytokine dysregulation might not contribute directly to disease, but rather reflect a more basic defect related to specific signal transducing or gene regulatory pathways.

Differential regulation of IL-1 production in human monocytes by IFN-gamma and IL-4

We have demonstrated that IL-4 markedly inhibits IL-1 production by highly purified normal human monocytes. When added to monocyte cultures, IL-4 suppressed LPS-induced IL-1 production in a time- and dose-dependent manner. Concentrations of IL-4 as low as 100 pg/ml reduced IL-1 production by approximately 50%, and doses of 1 ng/ml or higher suppressed IL-1 production by more than 90%. Maximal inhibition required that IL-4 be added before or simultaneous with LPS. Northern dot blot analyses revealed that IL-4 not only dramatically reduced the steady-state IL-1 beta mRNA levels in LPS-stimulated monocytes, but also those of TNF-alpha and IL-6. The inhibitory effect was not stimulus-specific because IL-4 suppressed IL-1 production induced by a variety of monocyte activation stimuli, including LPS, PMA, and Staphylococcus aureus Cowan strain. Monocytes expressed a relatively small number of high affinity IL-4R (approximately 150/cell; Ka = 3.15 +/- 1.13 x 10(10) M-1) indicating that relatively few receptors are necessary to generate the inhibitory effect. IL-4 enhanced monocyte MHC class II Ag (HLA-DR) expression in a manner similar to that of IFN-gamma. However, although both IFN-gamma and IL-4 up-regulated HLA-DR expression, they exhibited opposite effects on IL-1 production: IFN-gamma significantly enhanced monocyte IL-1 production induced by submaximal concentrations of LPS; whereas, IL-4 suppressed IL-1 production. Moreover, IL-4 largely neutralized the potentiating effect of IFN-gamma suggesting that IL-4 may be an effective antagonist of certain IFN-gamma-induced effects. Together these findings demonstrate that the relative levels of IFN-gamma and IL-4 may profoundly influence the state of monocyte activation by differentially regulating the expression of IL-1.

Differential regulation of IL-1 production in human monocytes by IFN-gamma and IL-4

We have demonstrated that IL-4 markedly inhibits IL-1 production by highly purified normal human monocytes. When added to monocyte cultures, IL-4 suppressed LPS-induced IL-1 production in a time- and dose-dependent manner. Concentrations of IL-4 as low as 100 pg/ml reduced IL-1 production by approximately 50%, and doses of 1 ng/ml or higher suppressed IL-1 production by more than 90%. Maximal inhibition required that IL-4 be added before or simultaneous with LPS. Northern dot blot analyses revealed that IL-4 not only dramatically reduced the steady-state IL-1 beta mRNA levels in LPS-stimulated monocytes, but also those of TNF-alpha and IL-6. The inhibitory effect was not stimulus-specific because IL-4 suppressed IL-1 production induced by a variety of monocyte activation stimuli, including LPS, PMA, and Staphylococcus aureus Cowan strain. Monocytes expressed a relatively small number of high affinity IL-4R (approximately 150/cell; Ka = 3.15 +/- 1.13 x 10(10) M-1) indicating that relatively few receptors are necessary to generate the inhibitory effect. IL-4 enhanced monocyte MHC class II Ag (HLA-DR) expression in a manner similar to that of IFN-gamma. However, although both IFN-gamma and IL-4 up-regulated HLA-DR expression, they exhibited opposite effects on IL-1 production: IFN-gamma significantly enhanced monocyte IL-1 production induced by submaximal concentrations of LPS; whereas, IL-4 suppressed IL-1 production. Moreover, IL-4 largely neutralized the potentiating effect of IFN-gamma suggesting that IL-4 may be an effective antagonist of certain IFN-gamma-induced effects. Together these findings demonstrate that the relative levels of IFN-gamma and IL-4 may profoundly influence the state of monocyte activation by differentially regulating the expression of IL-1.

Lymphokine-independent induction of macrophage membrane IL-1 by autoreactive T cells recognizing either class I or class II MHC determinants

Here we report that autoreactive T cell clones and T cell hybridomas that recognize class I or class II MHC determinants can induce IL-1 expression on cultured macrophages in an MHC-restricted manner. This genetic restriction of membrane IL-1 (mIL-1) induction is not absolute, however; it is manifest only in macrophages that have been cultured for several days before stimulation. Macrophages that are evaluated within 24 h after adherence display a basal level of mIL-1, and the T cell-induced augmentation of basal mIL-1 expression is not MHC-restricted. It appears that T cells of both Th1 and Th2 type have the capacity to induce mIL-1, suggesting that this function is not limited to the T cell subset (Th2) that is able to use IL-1. Most importantly, the ability of T cells to induce IL-1 on macrophages seems to occur by virtue of direct cellular interactions, and is independent of lymphokine secretion. The induction event is rapid enough (2 to 4 h) to allow T cells to interact with both antigen and IL-1 during the initial T cell/macrophage contact. These findings thus reveal an efficient mechanism for the induction of IL-1 during Ag presentation to T cells.

Lymphokine-independent induction of macrophage membrane IL-1 by autoreactive T cells recognizing either class I or class II MHC determinants

Here we report that autoreactive T cell clones and T cell hybridomas that recognize class I or class II MHC determinants can induce IL-1 expression on cultured macrophages in an MHC-restricted manner. This genetic restriction of membrane IL-1 (mIL-1) induction is not absolute, however; it is manifest only in macrophages that have been cultured for several days before stimulation. Macrophages that are evaluated within 24 h after adherence display a basal level of mIL-1, and the T cell-induced augmentation of basal mIL-1 expression is not MHC-restricted. It appears that T cells of both Th1 and Th2 type have the capacity to induce mIL-1, suggesting that this function is not limited to the T cell subset (Th2) that is able to use IL-1. Most importantly, the ability of T cells to induce IL-1 on macrophages seems to occur by virtue of direct cellular interactions, and is independent of lymphokine secretion. The induction event is rapid enough (2 to 4 h) to allow T cells to interact with both antigen and IL-1 during the initial T cell/macrophage contact. These findings thus reveal an efficient mechanism for the induction of IL-1 during Ag presentation to T cells.

Specificity of anti-lymphocyte antibodies in sera from patients with AIDS-related complex (ARC) and healthy homosexuals

The presence and specificity of anti-lymphocyte antibodies (ALA) was investigated in sera from male homosexuals with AIDS-Related Complex (ARC) as well as healthy homosexuals. Individuals in the healthy homosexual group had no detectable antibodies to human immunodeficiency virus (HIV). Antibodies reactive with normal peripheral blood mononuclear cells were detected by Western blot analysis in sera from both groups of homosexuals. Of those individuals whose sera contained ALA, 71% of ARC patients and 83% of healthy homosexuals had antibodies recognizing a 73 kilodalton (kD) molecule. ALA present in ARC sera reacted with CD3+, CD4+ and CD8+ lymphocytes while little reactivity with B cells was observed. Our results indicate that ALA appear in homosexuals prior to HIV infection and are reactive primarily with T lymphocytes. A 73 kD structure associated with the T cell membrane is frequently the target for these antibodies.

Humoral-mediated suppression of interleukin 2-dependent target cell proliferation in acquired immune deficiency syndrome (AIDS): interference with normal IL-2 receptor expression

Sera from patients with acquired immune deficiency syndrome (AIDS) were analysed for effects on normal lymphocyte interleukin 2 (IL-2) production, IL-2 receptor (IL-2R) expression and levels of IL-2 dependent T cell proliferation. The presence of AIDS serum appeared to reduce significantly IL-2 production by cultures of mitogen-activated normal human peripheral blood mononuclear cells (PBMC). However, dilution analyses of the culture supernatants indicated that the primary inhibitory effect occurred at the level of the IL-2 responsive target cell. Furthermore, eight of nine AIDS sera, but none of the normal human sera (NHS) tested, suppressed the capacity of IL-2-dependent CTL-20 cells to proliferate in response to human IL-2. Fractionation of AIDS sera by gel filtration on Sephacryl S-200 revealed that inhibitory activity coeluted with the immunoglobulin fraction. Pretreatment of human IL-2R+ lymphoblasts with AIDS serum did not interfere with the binding of monoclonal antibody (anti-Tac) specific for the human IL-2R; however, significant reductions in the levels of phytohaemagglutinin-induced IL-2R expression were observed when normal human PBMC were cultured in the presence of AIDS serum. These findings indicate that the inhibitor present in many AIDS sera does not suppress lymphocyte proliferation by interfering directly with the IL-2 receptor, and suggest that inhibition occurs at a later stage of the cell cycle. One of the primary consequences of the activity of this serum inhibitory factor is a decline in the levels of lymphocytic IL-2R expression.

Kinetic analysis of the immunopotentiating effect of the hypoxanthine analogue, NPT-15392, on the interleukin-2 production potential of human lymphocytes

Previous studies have shown that NPT-15392 (9-erythro-(2-hydroxy, 3-nonyl) hypoxanthine) enhances a variety of lymphoid functional activities including proliferative responses to various antigenic and mitogenic stimuli. In order to account at least partially for this immunopotentiation by NPT-15392, we examined the effects of this compound on interleukin-2 (IL-2) production by cultures of mitogen-activated human peripheral blood mononuclear cells (PBMC). Coculture of PBMC with NPT-15392 and concanavalin A (Con A) for 24 h resulted in significant increase of IL-2 in the supernatants of such cultures as compared with the IL-2 levels of control, non-NPT-treated, Con A-activated cultures. This enhancing effect was demonstrable with final culture concentrations of NPT-15392 ranging from 0.1 to 0.5 microgram/ml. Doses of NPT-15392 in excess of 5.0 micrograms/ml resulted in modest suppression of net IL-2 production. Pretreatment of PBMC with NPT-15392 for 2-4 h prior to activation with Con A was sufficient to achieve maximum enhancement of IL-2 production (20-40% average increase). Exposure of PBMC to NPT-15392 for longer periods (i.e. 24 h) did not result in higher levels of IL-2 production. NPT-15392 alone did not induce IL-2 synthesis at any of the doses employed and did not induce proliferation of the IL-2-dependent target cells used to quantitate IL-2 activity. Because of the multipotential role of IL-2 in the immune system, enhancement of IL-2 production by NPT-15392 may be a central pathway whereby this compound augments many lymphoid effector functions.

Inhibition of interleukin-2-induced T-cell proliferation by sera from patients with the acquired immune deficiency syndrome

Sera from 22 patients with either lymphadenopathy syndrome (LAS), acquired immune deficiency syndrome (AIDS)-related complex (ARC), or acquired immune deficiency syndrome were examined for their effect on the interleukin-2 (IL-2)-induced proliferative response of an IL-2-dependent cytotoxic T-cell line, CTL-20. All of the patient sera included in this study were positive for the presence of antibodies against human T-cell lymphotropic virus type III (HTLV-III) as determined by an HTLV-III-specific enzyme-linked immunosorbent assay (ELISA). Eighteen of the 22 patient sera examined (81.8%) exhibited at least a modest suppressive effect on the proliferative response of CTL-20 cells. The inhibitory effect was dose-dependent and varied in intensity for each individual serum. In many cases, the magnitude of suppression was absolute in that it totally abrogated IL-2-induced DNA synthesis. Normal human serum (NHS) exerted no suppressive influence on the IL-2-induced proliferative response of identical control cultures. This same panel of 22 patient sera exhibited no significant inhibitory effects on the levels of protein synthesis in cultures of a non-IL-2-dependent human T-cell line, CCRF-HSB-2, indicating that the suppressive effect was not mediated by nonspecific serum cytotoxicity. The inhibitory effect of patient sera in the IL-2-dependent target cell assay correlated with the ability of these same sera to suppress the mitogen-induced proliferative response of normal human peripheral blood lymphocytes (PBL). These observations are particularly striking in view of the recognized defects of IL-2-dependent effector T-cell functions in AIDS.

Isoprinosine effects on interleukin-1 production in acquired immune deficiency syndrome (AIDS)

The in vitro effects of isoprinosine (ISO) on the production of IL-1 in AIDS patients and normal controls were investigated in this study. IL-1 production from adherent cells was measured by an indirect method using EL-4 cells. Five of eleven AIDS patients had depressed IL-1 production. Various concentrations of ISO were used to treat the adherent cells in vitro and the optimal concentration for stimulating IL-1 production was determined to be 100 micrograms/ml/10(6) cells. IL-1 production was augmented to normal or to near normal levels in four of five AIDS patients. Our results indicate that depressed immunity seen in some AIDS patients may be partly due to the depressed in IL-1 production and also that ISO can act as an immune potentiation in enhancing the production of this lymphokine in vitro.

Partial restoration of impaired interleukin-2 production and Tac antigen (putative interleukin-2 receptor) expression in patients with acquired immune deficiency syndrome by isoprinosine treatment in vitro

The in vitro effects of isoprinosine (ISO) on interleukin-2 (IL-2) production, the expression of Tac antigen (IL-2 receptor) on lymphocytes, and the ability of Leu 3(+) cells to absorb interleukin-1 (IL-1) were investigated in 10 patients with acquired immune deficiency syndrome (AIDS). In 9 of the 10 patients, production of IL-2 from mononuclear cells and Leu 3(+) cells was depressed; expression of Tac antigen on mononuclear cells and Leu 2(+) cells was found to be depressed in 9 of 10 patients. The ability of the Leu 3(+) lymphocytes to absorb IL-1 was depressed in all (four of four) patients studied. After ISO treatment, IL-2 production, Tac antigen expression and IL-1 absorption were restored to normal or near normal levels in most of the patients. These results suggest that ISO has an immunostimulating capacity in AIDS patients and that the potential of ISO in immune response restoration in AIDS patients deserves critical consideration.

Suppression of B-cell and T-cell responses by the prostaglandin-induced T-cell-derived suppressors (PITS)--III. Production of PITS beta factors from T-cell hybridomas

Previous studies have shown that the prostaglandin-induced T-cell-derived suppressors (PITS) are actually a mixture of at least seven distinct factors. These factors may be reproducibly resolved by size-exclusion chromatography followed by high-pressure liquid chromatography (HPLC). Results are presented here which suggest that two T-lymphocyte hybridoma clones are capable of constitutive synthesis of three of these suppressor factors. Results show that clone Hyb-7SC2 produces factors which co-elute (by HPLC) with the PITS beta2 and PITS beta3 factors, while clone Hyb-9SC2 produces a factor which co-elutes with PITS beta1. These results suggest the possibility that the seven PITS beta factors are not the product of a single cell population.

Suppression of B-cell and T-cell responses by the prostaglandin-induced T-cell-derived suppressor (PITS). II. Resolution of multiple PITS beta factors

It has been shown that T cells cultured with prostaglandin E2 are induced to release at least two peptide-containing lymphokines (PITS). Both the high-molecular-weight (35,000; PITS alpha) and the low-molecular-weight (2000 to 5000; PITS beta) factors were shown to be potent inhibitors of both T-cell- and B-cell-dependent mitogen responses. Data are reported here which show that the PITS beta factor may be reproducibly resolved into seven components by high-pressure liquid chromatography. Although each of these components is capable of suppressing the phytohemagglutinin-induced blastogenic response, not all of these factors will suppress the in vitro antibody response to sheep erythrocytes, or a mixed lymphocyte reaction. Nevertheless, the broad-range suppressive effects previously reported for PITS beta now seem to be mediated by multiple low-molecular-weight PITS factors.

Inhibitors of prostaglandin synthesis block the induction of staphylococcal enterotoxin B-activated T-suppressor cells

A variety of arachidonic acid metabolites possess the ability to modulate immune cell function. Various inhibitors of arachidonic acid metabolism were compared with regard to their effects on T-suppressor (Ts) cell function. Using staphylococcal enterotoxin B (SEB) to activate Lyt-2+ Ts cells, it was shown that indomethacin and 5,8,11,14-eicosatetraynoic acid (ETYA) inhibit the induction phase, but not the expression phase, of suppressor cell activity. Agents which inhibit thromboxane synthetase or lipoxygenase activities (imidazole, nordihydroguaiaretic acid, and pyrogallol) were not found to affect Ts cell induction. Since inhibitors of prostaglandin synthesis are thought to induce lower levels of cyclic adenosine monophosphate, an attempt to overcome the indomethacin inhibition of Ts cell induction by modulating cyclic adenosine monophosphate levels was made. It was found that theophylline and isoproterenol are not able to overcome the inhibition by indomethacin of Ts cell activity. These results strongly suggest that induction of Ts cells by SEB is dependent on the synthesis of products of the prostaglandin synthetase pathway.