Expression and role of p75 interleukin 2 receptor on human monocytes

IFNs Drive Development of Novel IL-15-Responsive Macrophages

Disruption in homeostasis of IL-15 is linked to poor maternal and fetal outcomes during pregnancy. The only cells described to respond to IL-15 at the early maternal-fetal interface have been NK cells. We now show a novel population of macrophages, evident in several organs but enriched in the uterus of mice and humans, expressing the β-chain of the IL-15R complex (CD122) and responding to IL-15. CD122+ macrophages (CD122+Macs) are morphologic, phenotypic, and transcriptomic macrophages that can derive from bone marrow monocytes. CD122+Macs develop in the uterus and placenta with kinetics that mirror IFN activity at the maternal-fetal interface. M-CSF permits macrophages to express CD122, and IFNs are sufficient to drive expression of CD122 on macrophages. Neither type I nor type II IFNs are required to generate CD122+Macs, however. In response to IL-15, CD122+Macs activate the ERK signaling cascade and enhance production of proinflammatory cytokines after stimulation with the TLR9 agonist CpG. Finally, we provide evidence of human cells that phenocopy murine CD122+Macs in secretory phase endometrium during the implantation window and in first-trimester uterine decidua. Our data support a model wherein IFNs local to the maternal-fetal interface direct novel IL-15-responsive macrophages with the potential to mediate IL-15 signals critical for optimal outcomes of pregnancy.

IL-2/anti-IL-2 mAb immunocomplexes: A renascence of IL-2 in cancer immunotherapy?

The in vivo biological activity of IL-2 can be dramatically increased by complexing with anti-IL-2 mAb. Moreover, IL-2/anti-IL-2 mAb immunocomplexes selectively stimulate different subsets of immune cells, depending on the clone of anti-IL-2 mAb that is used. Thus, IL-2/S4B6 mAb complexes strongly stimulate CD122^high populations, namely NK and memory CD8⁺ T cells. They also intermediately stimulate T_reg cells. Conversely, IL-2/JES6.1 mAb immunocomplexes have no stimulatory activity for CD122^high populations. However, they potently and highly selectively stimulate CD25⁺ cells (i.e., T_reg and activated T cells). IL-2/S4B6 mAb immunocomplexes have also been shown to possess antitumor activity in various mouse tumor models.

Emerging immunopharmacological targets in multiple sclerosis

Inflammatory demyelination of the central nervous system (CNS) is the hallmark of multiple sclerosis (MS), a chronic debilitating disease that affects more than 2.5 million individuals worldwide. It has been widely accepted, although not proven, that the major pathogenic mechanism of MS involves myelin-reactive T cell activation in the periphery and migration into the CNS, which subsequently triggers an inflammatory cascade that leads to demyelination and axonal damage. Virtually all MS medications now in use target the immune system and prevent tissue damage by modulating neuroinflammatory processes. Although current therapies such as commonly prescribed disease-modifying medications decrease the relapse rate in relapsing-remitting MS (RRMS), the prevention of long-term accumulation of deficits remains a challenge. Medications used for progressive forms of MS also have limited efficacy. The need for therapies that are effective against disease progression continues to drive the search for novel pharmacological targets. In recent years, due to a better understanding of MS immunopathogenesis, new approaches have been introduced that more specifically target autoreactive immune cells and their products, thus increasing specificity and efficacy, while reducing potential side effects such as global immunosuppression. In this review we describe several immunopharmacological targets that are currently being explored for MS therapy.

Expression of CD11b and CD18 on polymorphonuclear neutrophils stimulated with interleukin-2

Background

Interleukin-2 (IL-2) is a lymphocyte-activating and growth-promoting factor, and has been widely studied on T-cells and NK-cells. However, the interaction of polymorphonuclear neutrophils (PMNs) with IL-2 is poorly studied and thus, this study aimed at defining IL-2 participation in the expression of CD11b and CD18 on PMNs.

Material and methods

PMNs were isolated from heparinized whole blood of healthy donors. Purified cells were incubated with IL-2 (10 ng/ml) for 24 hours at 37°C in a humidified incubator with 5% CO₂. After 24 hours’ incubation, surface molecules (CD11b and CD18) were measured by flow cytometry.

Results

Interestingly, the antibodies of IL-2Rβ chain (CD122-FITC) were found in all observed cells. The induction of CD11b mean fluorescence intensity (MFI) in highly purified PMNs stimulated with IL-2 was clearly increased recording 43% in comparison to the freshly isolated PMNs and the un-stimulated PMNs which were found to be 23% and 28% of CD11b, respectively. Furthermore, flow cytometry analysis demonstrated that the highly purified PMNs exposed to IL-2 showed an increase in CD18 MFI, recording 47% with respect to that of the freshly isolated PMNs and PMNs cultured with the medium alone which showed a small amount of 38% and 27%, respectively.

Conclusions

Results demonstrated that CD11b and CD18 had been acquired on the surface of the IL-2-in vitro-activated PMNs. These findings indicated that IL-2 may play a crucial role in PMNs migration.

The IL-2/CD25 pathway determines susceptibility to T1D in humans and NOD mice

Although the interleukin-2 (IL-2)/IL-2R signaling pathway has been the focus of numerous studies, certain aspects of its molecular regulation are not well characterized, especially in non-T cells, and a more complete understanding of the pathway is necessary to discern the functional basis of the genetic association between the IL-2-IL-21 and IL-2RA/CD25 gene regions and T1D in humans. Genetic variation in these regions may promote T1D susceptibility by influencing transcription and/or splicing and, hence, IL-2 and IL-2RA/CD25 expression at the protein level in different immune cell subsets; thus, there is a need to establish links between the genetic variation and immune cell phenotypes and functions in humans, which can be further investigated and validated in mouse models. The detection and characterization of genetically determined immunophenotypes should aid in elucidating disease mechanisms and may enable future monitoring of disease initiation and progression in prediabetic subjects and of responses to therapeutic intervention.

Anti-CD25 antibodies affect cytokine synthesis pattern of human dendritic cells and decrease their ability to prime allogeneic CD4+ T cells

Anti-CD25 monoclonal antibodies are widely used in clinical transplantation to prevent acute allograft rejection. Although their effects on T lymphocytes have been extensively studied, their impact on human dendritic cells (DC) has never been reported. Furthermore, the role of the IL-2 in DC functions has not yet been fully elucidated. In this study, we confirm that the stimulation of human monocyte-derived DC with LPS strongly induced the expression of CD25 and that LPS-matured DC also expressed the beta and gamma chain of the IL-2R. We also showed that adding anti-CD25 monoclonal antibodies to LPS induced a decrease in IL-12, IL-1, TNF-alpha, IL-6, and IFN-gamma production and an increase in IL-10 synthesis by DC compared with stimulation with LPS alone. Furthermore, we showed that these modifications diminished the T helper priming ability of DC and polarized the alloimmune response toward TH2. In contrast, humanized anti-CD25 monoclonal antibodies did not affect the up-regulation of CD86, CD80, CD83, HLADR, or CD40 induced upon LPS stimulation. Taken together, this study discloses some previously unrecognized effects of anti-CD25 monoclonal antibodies on DC that may contribute to their clinical efficacy. In addition, this study also shed some light on the role of the IL-2 in human DC activation.

Identification of the DNA binding element of the human ZNF300 protein

The human ZNF300 gene is a member of the KRAB/C₂H₂ zinc finger gene family, the members of which are known to be involved in various developmental and pathological processes. Here, we show that the ZNF300 gene encodes a 68-kDa nuclear protein that binds DNA in a sequence-specific manner. The ZNF300 DNA binding site, C(t/a)GGGGG(c/g)G, was defined via a random oligonucleotide selection assay, and the DNA binding site was further confirmed by electrophoretic mobility shift assays. A potential ZNF300 binding site was found in the promoter region of the human IL-2Rβ gene. The results of electrophoretic mobility shift assays indicated that ZNF300 bound to the ZNF300 binding site in the IL-2Rβ promoter in vitro. Transient co-transfection assays showed that ZNF300 could activate the IL-2Rβ promoter, and that the activation was abrogated by the mutation of residues in the ZNF300 binding site. Identifying the DNA binding site and characterizing the transcriptional regulation property of ZNF300 would provide critical insights into its potential as a transcriptional regulator.

Effect of DAB(389)IL-2 immunotoxin on the course of experimental autoimmune encephalomyelitis in Lewis rats

Activated T cells express the high affinity interleukin 2 receptor (IL-2R also CD25) that binds interleukin 2 (IL-2) and transduces signals important for the proliferation and survival of these cells. We investigated the effect of the genetically engineered immunotoxin DAB(389)IL-2 on experimental autoimmune encephalomyelitis (EAE), an autoimmune disease of the central nervous system (CNS) mediated by activated myelin-reactive T cells. EAE is the most commonly used animal model of the human disease multiple sclerosis (MS). DAB(389)IL-2 is a recombinant fusion product made of a portion of diphtheria toxin, which contains binding and translocation components of the toxin linked to IL-2. The diphtheria toxin targets and kills cells expressing the high affinity IL-2 receptor and has been successfully used in several autoimmune and neoplastic conditions. We observed a significant suppression of guinea-pig spinal cord homogenate (gpSCH)-MBP induced active EAE in Lewis rats at 2 x 1,600 kU of DAB(389)IL-2 given on days 7 and 9 post-immunization and complete suppression with the same dose on days 7, 8 and 9 or 7, 8, 9 and 10 after immunization during the active disease period. There were reduced mononuclear cell infiltrates of CD4(+), CD8(+), CD25(+) and alphabetaTCR(+) T cells in the spinal cord of treated rats. However, treatment at day 11 or 12 post-immunization led to severe, fatal disease. The toxin added to cultures in vitro or injected in vivo suppressed antigen- and mitogen-induced T cell proliferation. DAB(389)IL-2 treatment in vivo or exposure of encephalitogenic T cells in vitro prior to transfer did have a significant inhibitory effect on adoptive transfer EAE. Our data demonstrate that DAB(389)IL-2 immunotoxin can suppress active and passive EAE if applied at specific, early time points, but can have negative consequences at later time points.

Serum level of soluble interleukin-2 receptor alpha correlates with the clinical course and activity of Wilms' tumour and soft tissue sarcomas in children

Wilms' tumour (WT) and soft tissue sarcomas (SA) in children lack reliable biochemical markers. This study was carried out to determine the clinical significance of serum soluble interleukin-2 receptor alpha (sIL-2Ralpha) in the diagnostics and treatment monitoring of children with WT and SA. The study included 48 children: ten with WT, eight with SA and 30 healthy controls. The sIL-2Ralpha levels (ELISA) and rates of elevated sIL-2Ralpha values were estimated prospectively at diagnosis and in complete remission during treatment and after therapy. As the dependence on age was determined, the levels of sIL-2Ralpha were expressed as multiplications of the upper value of the normal range for a particular age ( xN). Median pretreatment levels of sIL-2Ralpha in patients exceeded those of healthy controls (1.79 xN for WT and 1.53 for SA vs. 0.61 for controls; p < 0.001) as did the rates of elevated sIL-2Ralpha values (80% of WTand 87.5% of SA patients vs. 0% of controls). Good response to therapy was paralleled by a significant decline of pretreatment sIL-2Ralpha levels and its elevated rates. Thus, sIL-2Ralpha determination may be of some value in the diagnostics and treatment monitoring of childhood WT and SA.

Identification of a novel G245R polymorphism in the IL-2 receptor beta membrane proximal domain associated with human visceral leishmaniasis

Binding of the interleukin-2 (IL-2) to the IL-2 receptor (IL-2R) triggers a series of intracellular events culminating in lymphocyte proliferation and differentiation. We report here the identification of a novel G245R polymorphism in the membrane proximal domain of the IL-2 receptor beta chain (IL-2Rbeta). Present at a frequency of 7.2%, the IL-2-Rbeta G245R was identified in a population of Eastern Sudan exposed to a severe outbreak of visceral leishmaniasis (VL), a disease associated with a marked depression of T-cell antigen-specific responses. The location of the G245R polymorphism next to the box1/box2 proximal cytokine receptor homology segment and suggestive genetic association with the development of disease (P=0.043), suggest that it may affect Janus kinase (JAK) association and impair growth signal transduction. However, additional genetic association with a synonymous single nucleotide polymorphism (IL2RB+8777T) suggests that other variations of IL2RB or nearby genes participate in the highly significant linkage with VL at 22q12 previously reported for this population.

Characterization of surface interleukin-2 receptor expression on gated populations of peripheral blood mononuclear cells from manatees, Trichechus manatus latirostris

An in vitro system to determine surface interleukin-2 receptor (IL-2R) expression on mitogen-stimulated peripheral blood mononuclear cells (PBMC) from free-ranging manatees, Trichechus manatus latirostris was developed. Human recombinant IL-2, conjugated with a fluorescein dye was used in conjunction with flow cytometric analysis to determine changes in surface expression of IL-2R at sequential times over a 48-h period of in vitro stimulation. Surface expression of IL-2R was detected on manatee PBMC, which also cross-reacted with an anti-feline pan T-cell marker. An expression index (EI) was calculated by comparing mitogen-activated and non-activated PBMC. Based on side- and forward-scatter properties, flow cytometric analysis showed an increase in the number of larger, more granular "lymphoblasts" following concanavalin A (Con A) stimulation. The appearance of lymphoblasts was correlated with an increase in their surface expression of IL-2 receptors. Surface IL-2R expression, in Con A-stimulated PBMC, was detected at 16 h, peaked at 24-36 h, and began to decrease by 48 h. Characterization of the IL-2R expression should provide additional information on the health status of manatees, and the effect of their sub lethal exposure to brevetoxin.

Priming by recombinant chicken interleukin-2 induces selective expression of IL-8 and IL-18 mRNA in chicken heterophils during receptor-mediated phagocytosis of opsonized and nonopsonized Salmonella enterica serovar enteritidis

Heterophils, the principal avian polymorphonuclear leukocytes (PMNs) equivalent to the mammalian neutrophil, function as professional phagocytes against bacterial infections, mediate acute inflammation, and respond to cytokine stimulation to aid in regulation of innate host defenses. Interleukin-2 (IL-2) has been found to exercise an array of biological effects on other cell types besides T lymphocytes, including NK cells, B cells, monocytes, and neutrophils. In the present experiments, using real-time quantitative RT-PCR, we evaluated the role of rChIL-2 as a priming mediator controlling heterophil responses at the level of gene transcription by examining the expression of mRNA for pro-inflammatory (IL-1beta, IL-6, IL-8) and Th1 (IL-18 and IFN-gamma) cytokine genes following stimulation with phagocytosis agonists; i.e., opsonized and nonopsonized Salmonella enteritidis. Peripheral blood heterophils were isolated and incubated with rChIL-2 from transfected COS cells. rChIL-2 selectively primed the heterophils for an increase in transcription of the pro-inflammatory cytokine IL-8 and of the Th1 cytokine IL-18 induced by all three phagocytic agonists. Although rChIL-2 priming modulated the expression of specific cytokine mRNA in heterophils stimulated by different phagocytic agonists, the rChIL-2 by itself did not directly induce gene expression of either the pro-inflammatory or Th1 cytokines. We propose that rChIL-2 could be priming heterophils solely to function as more efficient innate effector cells to limit bacterial growth through the selective increase of IL-8 and IL-18 gene expression.

Immune effects of escalating doses of granulocyte-macrophage colony-stimulating factor added to a fixed, low-dose, inpatient interleukin-2 regimen: a randomized phase I trial in patients with metastatic melanoma and renal cell carcinoma

Previous studies in cancer patients demonstrated that granulocyte-macrophage colony-stimulating factor (GM-CSF) upregulated the interleukin (IL)-2 receptor on T lymphocytes and monocytes suggesting that subsequently administered IL-2 would produce greater immune effects. The authors treated 21 patients with metastatic renal cell carcinoma and melanoma on a randomized phase I study to test this hypothesis. All 21 patients received a fixed dose of IL-2 (72,000 IU/kg every 8 hours for 5 days) administered intravenously as an inpatient. Patients were randomized to receive IL-2 alone or in combination with GM-CSF at a dose of 125 or 250 mcg/m /d (Sargramostim; Immunex Corporation, WA, U.S.A.) daily for 7 days by subcutaneous injection starting on day 1, the day before IL-2 treatment. The results from this study demonstrated that GM-CSF did not worsen the toxicities produced by IL-2 alone. Grade 3 confusion occurred in four patients, three who received IL-2 alone. No partial or complete tumor responses were seen. Assays of serum soluble IL-2 receptor (sIL2R) and neopterin, measures of T cell and monocyte activation, respectively, demonstrated a significant increase in sIL2R but not neopterin, 24 hours after the first dose of GM-CSF. In combination with IL-2, the higher dose of GM-CSF (250 mcg/m ) produced higher sIL2R levels on days 3 and 7 than the 125-mcg/m dose of GM-CSF or IL-2 alone. Although neopterin levels did not increase after 1 day of GM-CSF, the addition of IL-2 resulted in a significantly increased neopterin level on day 3 at the higher dose of GM-CSF. On day 7, neopterin levels in all three groups were similarly increased over baseline. Ten days after treatment, neopterin levels had returned to normal, but sIL2R levels remained markedly increased (12 fold) over baseline in the higher GM-CSF dose group. The authors conclude that 1) monocyte activation was not significantly enhanced by 1 day of GM-CSF treatment; 2) the 250-mcg/m GM-CSF dose plus IL-2 produced superior T cell activation compared with a lower dose of GM-CSF plus IL-2 or to IL-2 alone; and 3) the combination of GM-CSF and IL-2 was safe and tolerable but was not associated with any clinical responses.

Differential effects of age on chicken heterophil functional activation by recombinant chicken interleukin-2

Interleukin-2 (IL-2) exercises an array of biological effects on many cells including the functional activation of cells of the innate immune response. Heterophils, the avian equivalent of the neutrophil, function as professional phagocytes to aid in regulation of innate host defenses. The objective of the present studies was to examine the effects of recombinant chicken IL-2 (rChIL-2) on functional activities of heterophils from chickens during the first 3 weeks after hatch. Peripheral blood heterophils were isolated and incubated with either COS cell-derived rChIL-2 or supernatants from mock-transfected COS cells. rChIL-2 had no effect on the functional activities of heterophils from day-of-hatch chickens, but significantly increased the phagocytosis and bactericidal activity of heterophils from 7- and 14-day-old chickens. rChIL-2 induced no direct stimulation of the respiratory burst by heterophils, but primed heterophils from 7- and 14-day-old birds for an enhanced respiratory burst in response to phorbol ester stimulation. Lastly, rChIL-2 had neither direct nor priming effects on heterophil degranulation. The enhancing effects on heterophil functional activity by rChIL-2 were abated by a neutralizing anti-chicken IL-2 mAb and were therefore specific for this cytokine. These results show that rChIL-2 can directly activate chicken heterophils to exert effector functions, and that heterophil activation by rChIL-2 is also an age-dependent event.

Critical role of IL-15-IL-15R for antigen-presenting cell functions in the innate immune response

Activation of dendritic cells (DCs) and macrophages by infectious agents leads to secretion of interleukin 12 (IL-12), which subsequently induces interferon-gamma (IFN-gamma) production by multiple cell types that include DCs and macrophages. In turn, IFN-gamma acts on macrophages to augment IL-12 secretion and to produce nitric oxide (NO), which eradicates infected microbes. We show here that in cytokine common gamma subunit-deficient and/or IL-2 receptor beta-deficient mice, production of IL-12, IFN-gamma and NO by DCs and macrophages was severely impaired, as was up-regulation of major histocompatibility complex class II and CD40. Similar phenotypes were observed in DCs and macrophages from IL-15-deficient mice but not in those from IL-2-deficient mice. This shows that the IL-15-IL-15R interaction is critical in early activation of antigen-presenting cells and plays an important role in the innate immune system.

IL-2 signaling in human monocytes involves the phosphorylation and activation of p59hck

The activating properties of IL-2 and the structure of the IL-2R on human monocytes are well characterized. However, relatively little is known about the biochemical mechanisms involved in IL-2 signal transduction in these cells. We investigated the role of protein tyrosine kinases (PTKs) in the activation of monocytes by IL-2. Incubation of monocytes with the PTK inhibitor herbimycin A (HA) resulted in the dose-dependent suppression of IL-2-induced monocyte tumoricidal activity. This inhibition was rather potent, as a concentration of HA as low as 0.5 microM caused a complete abrogation of cytolytic activity. Furthermore, HA markedly suppressed the ability of IL-2 to induce IL-1 beta, TNF-alpha, IL-6, and IL-8 mRNA expression and protein secretion by monocytes. Anti-phosphotyrosine immunoblotting demonstrated that IL-2 induced a rapid and time-dependent increase in tyrosine phosphorylation of several cellular proteins of molecular masses ranging from 35 to 180 kDa. Interestingly, IL-2 caused a significant up-regulation of the constitutive levels of hck PTK mRNA and protein relative to medium-treated cells as well as an increase in p59hck tyrosine phosphorylation. Finally, we demonstrated by in vitro kinase assay that the specific activity of p59hck PTK was also induced by IL-2 in monocytes. Thus, these data show that the activation of PTKs is required for the triggering of monocyte effector and secretory functions by IL-2 and strongly suggest that p59hck is a key participant in IL-2 signaling in human monocytes.

Efficacy of cancer gene therapy in aging: adenocarcinoma cells engineered to release IL-2 are rejected but do not induce tumor specific immune memory in old mice

Numerous studies have demonstrated the efficacy of cytokine gene-engineered tumor cells to induce tumor rejection and specific memory acquisition into syngeneic immunocompetent mice by activation of host-dependent antitumor responses. A progressive immune dysfunction, mainly involving thymus-dependent specific immunity, occurs during aging. In this study we evaluated whether the injection of IL-2 gene-transfected tumor cells in old mice causes an immune activation which results in tumor rejection and induction of specific immune memory as occurs in young animals. Young and old mice were inoculated with syngeneic parental mammary adenocarcinoma cells (TS/A p.c.) or with TS/A cells engineered to release IL-2 (TS/A-IL2). Three clones of TS/A-IL-2 cells were used producing low (30 U, B1.30), intermediate (3600 U, B6.3600), or high (6000 U, B4.6000) IL-2. While the B1.30 clone grew in 100% of mice, the B6.3600 and B4.6000 clones were promptly rejected in both young and old animals. In young mice, rejection was associated with a large neutrophil and macrophage infiltration, with a minor number of CD4+ and CD8+ lymphocytes. In old mice, neutrophils and macrophages were the main cells involved in tumor rejection whereas both CD4+ and CD8+ lymphocytes were scarcely present in tumoral infiltrate. A lower number of apoptotic tumor cells was found in TS/A-IL2-challenged old mice in comparison with young animals. To test whether the injection of TS/A-IL2 cells induced a specific immune memory, mice with no tumors after the challenge with B6.3600 and B4.6000 clones received a lethal challenge of TS/A p.c. 90% and 30% of young mice previously injected with B4.6000 or B6.3600 clones, respectively, rejected TS/A p.c. In old mice, B4.6000 cells did not confer protection, whereas only 10% of mice which received B6.3600 cells were able to reject TS/A p.c. Neither the graft of a young thymus or the adoptive transfer of young T lymphocytes to old mice induced specific immune memory for TS/A p.c. in old animals. These data suggest the necessity to refine antitumor vaccination procedures in aging.

Neutrophils augment the release of TNFalpha from LPS-stimulated macrophages via hydrogen peroxide

We examined the effect of polymorphonuclear cells on the release of tumor necrosis factor (TNFalpha) in endotoxin-treated macrophages. Human peripheral blood neutrophils were co-cultured with mouse peritoneal macrophages stimulated with lipopolysaccharide (LPS). In a dose-dependent manner, FMLP (n-formyl-methionyl-leucyl-phenylalanine) augmented the release of TNFalpha by LPS-stimulated macrophages in the presence, but not in the absence, of neutrophils. The stimulating effect of neutrophils on macrophages was reversed by catalase, suggesting that the release of hydrogen peroxide from neutrophils was responsible for augmenting macrophage TNFalpha. Moreover, the direct addition of hydrogen peroxide to macrophages resulted in an increased secretion of TNFalpha. In addition, insertion of a porous membrane between the neutrophils and macrophages cancelled the effect, indicating that adherence of neutrophils may be necessary for augmentation of TNFalpha release. In summary, the data suggest that hydrogen peroxide released from stimulated neutrophils may act as an activator of macrophage function by increasing their release of TNFalpha.

Enhanced B7-2 Gene Expression by Interferon-γ in Human Monocytic Cells Is Controlled Through Transcriptional and Posttranscriptional Mechanisms

B7-2 is a costimulatory molecule expressed on professional antigen-presenting cells that provides T cells with a critical signal resulting in T-cell activation. Interferon-γ (IFN-γ) enhances B7-2 protein expression in monocytic cells. However, the molecular mechanisms controlling the enhanced expression of B7-2 are poorly understood. Northern blot and flow cytometry analysis revealed that human monocytes and the human monocytic cell line MonoMac6 (MM6) constitutively expressed B7-2 mRNA and protein and IFN-γ treatment further enhanced the expression of both molecules. The ability of IFN-γ to enhance B7-2 mRNA was evident at the dose of 31 U/mL and reached plateau levels at 500 U/mL. The effects of IFN-γ on B7-2 mRNA expression were time dependent and occurred within 3 hours of treatment and increased through 24 hours. In vitro transcription assays and mRNA stability experiments showed that IFN-γ increases both transcriptional activity and the stability of B7-2 mRNA. Treatment of MM6 cells with cycloheximide showed that de novo protein synthesis was not required for the IFN-γ–enhanced expression of B7-2 mRNA. Overall, these studies show for the first time that IFN-γ–enhanced expression of B7-2 protein in human monocytic cells is controlled at the gene level through a dual mechanism involving transcriptional and posttranscriptional mechanisms.

Enhanced B7-2 Gene Expression by Interferon-γ in Human Monocytic Cells Is Controlled Through Transcriptional and Posttranscriptional Mechanisms

B7-2 is a costimulatory molecule expressed on professional antigen-presenting cells that provides T cells with a critical signal resulting in T-cell activation. Interferon-γ (IFN-γ) enhances B7-2 protein expression in monocytic cells. However, the molecular mechanisms controlling the enhanced expression of B7-2 are poorly understood. Northern blot and flow cytometry analysis revealed that human monocytes and the human monocytic cell line MonoMac6 (MM6) constitutively expressed B7-2 mRNA and protein and IFN-γ treatment further enhanced the expression of both molecules. The ability of IFN-γ to enhance B7-2 mRNA was evident at the dose of 31 U/mL and reached plateau levels at 500 U/mL. The effects of IFN-γ on B7-2 mRNA expression were time dependent and occurred within 3 hours of treatment and increased through 24 hours. In vitro transcription assays and mRNA stability experiments showed that IFN-γ increases both transcriptional activity and the stability of B7-2 mRNA. Treatment of MM6 cells with cycloheximide showed that de novo protein synthesis was not required for the IFN-γ–enhanced expression of B7-2 mRNA. Overall, these studies show for the first time that IFN-γ–enhanced expression of B7-2 protein in human monocytic cells is controlled at the gene level through a dual mechanism involving transcriptional and posttranscriptional mechanisms.

Human Monocytes Constitutively Express Membrane-Bound, Biologically Active, and Interferon-γ–Upregulated Interleukin-15

Interleukin-15 (IL-15) is a potent regulator of T-, B-, and natural killer cell proliferation and displays unusually tight controls of secretion. Even though IL-15 mRNA is constitutively expressed in monocytes/macrophages and is upregulated by a variety of stimuli, evidence for IL-15 cytokine secretion is only found exceptionally, eg, conditions of pathological, chronic inflammation. This raises the possibility that monocytes express membrane-bound IL-15 rather than secrete it. The current study explores this hypothesis. We demonstrate here that biologically active IL-15 is indeed detectable in a constitutively expressed, membrane-bound form on normal human monocytes, as well as on monocytic cell lines (MONO-MAC-6, THP-1, and U937), but not on human T or B cells (MT4, M9, C5966, JURKAT, DAUDI, RAJI, and Epstein-Barr virus-immortalized B-cell clones). Furthermore, cell surface-bound IL-15 is upregulated upon interferon-γ stimulation. Interestingly, monocyte/macrophage inhibitory cytokines such as IL-4 and IL-13 fail to downregulate both constitutive and induced cell-surface expression of IL-15. Membrane-bound IL-15 does not elute with acetate buffer or trypsin treatment, suggesting that it is an integral membrane protein and that it is not associated with the IL-15 receptor complex. Finally, membrane-bound IL-15 stimulates T lymphocytes to proliferate in vitro, indicating that it is biologically active. These findings enlist IL-15 in the fairly small family of cytokines for which the presence of a biologically active membrane-bound form has been demonstrated (eg, IL-1, tumor necrosis factor-, and IL-10) and invites the speculation that most of the biological effects of IL-15 under physiological conditions are exerted by the cell surface-bound form.

Inhibitory effects of the Trypanosoma cruzi membrane glycoprotein AGC10 on the expression of IL-2 receptor chains and secretion of cytokines by subpopulations of activated human T lymphocytes

The Trypanosoma cruzi membrane glycoprotein AGC10 has been shown to alter some human macrophage functions (De Diego, J. L. et al., J. Immunol. 1997. 159: 4983-4989). We show here that, in the presence of AGC10, [3H]thymidine incorporation by normal human lymphocytes stimulated with anti-CD3 or phytohemagglutinin (PHA) is severely curtailed. This effect was found to involve down-regulation of the expression of both CD25 (IL-2R alpha) and CD122 (IL-2R beta) on the lymphocyte membrane and a marked decrease in the level of up-regulation of the expression of surface CD132 (IL-2R gamma or gamma(c)). These alterations occurred in fairly large proportions of CD4+ and CD8+ lymphocytes. AGC10 also inhibited proliferation and expression of IL-2 receptor chains by activated T lymphocytes virtually depleted of monocytes/macrophages, indicating that these effects do not necessarily require prior modification of monocyte/macrophage function by AGC10. Human lymphocytes stimulated with anti-CD3 or PHA also displayed a markedly decreased capacity to secrete IL-2 and IFN-gamma, suggesting that AGC10 affected at least Th1 cell functions. Cell viability in cultures containing or lacking AGC10 was comparable over a 72-h period, and neither CD25 expression by, nor the viability of, PHA-stimulated Jurkat cells was altered by AGC10, ruling out that the effects of AGC10 are due to cell killing. These results highlight down-regulatory effects on activated T lymphocytes exerted by a membrane molecule from a parasite causing a disease whose acute phase is accompanied by immunosuppression.

Activation of NF-kappaB in Mycobacterium tuberculosis- induced interleukin-2 receptor expression in mononuclear phagocytes

Soluble interleukin-2 receptor-alpha (IL-2Ralpha) has been reported to be increased in the sera of patients with advanced tuberculosis, and levels decline after therapy in accordance with improvement of radiologic findings. We investigated expression of the IL-2Ralpha in bronchoalveolar lavage (BAL) cells in active pulmonary tuberculosis, and evaluated the mechanism Mycobacterium tuberculosis induces in the IL-2Ralpha using the THP-1 mononuclear phagocyte cell line. We found IL-2Ralpha expression to be increased in BAL cells from involved sites of active pulmonary tuberculosis. Expression of the alpha-chain of IL-2Ralpha on peripheral blood monocytes (PBM) was induced by M. tuberculosis by flow cytometry evaluation. Northern analysis demonstrated increased IL-2Ralpha gene expression after stimulation with M. tuberculosis which was further induced by interferon-gamma (IFN-gamma). The IL-2Ralpha promoter containing the nuclear factor kappa B (NF-kappaB) site was transcriptionally induced by M. tuberculosis and this NF-kappaB site could confer inducibility to a heterologous herpes thymidine kinase (TK) promoter by M. tuberculosis. Electrophoretic mobility shift assays (EMSAs) revealed specific binding of nuclear protein to the NF-kappaB site upon induction with M. tuberculosis. Using antibodies against the p50 and p65 subunits of NF-kappaB in EMSAs, the involvement of both p50 and p65 proteins was further demonstrated. Functional expression of the IL-2Ralpha on mononuclear phagocytes in M. tuberculosis infection may play an important immunomodulatory role in the host response.

IL-2Rα on One Cell Can Present IL-2 to IL-2Rβ/γc on Another Cell to Augment IL-2 Signaling

IL-2Rα augments IL-2 signaling. Although this is generally believed to occur only when the three known components of IL-2R are associated within a single cell membrane, we demonstrate here an intercellular interaction. Cocultivation of cells individually expressing chimerae incorporating the extracellular domain of IL-2Rα alone with cells expressing chimerae of IL-2Rβ alone permitted IL-2 dose-dependent oligomerization of the chimerae. Likewise, native IL-2Rα-bearing cells augmented the IL-2 proliferative response of ex vivo large granular lymphocytic leukemia cells expressing IL-2Rβ/γc but lacking IL-2Rα. In both cases, the response was inhibitable by an Ab to IL-2Rα. Intercellular augmentation of cytokine effects, acting in trans, has important implications for biology and medicine.

Biology of the interleukin-2 receptor

Studies of the biology of the IL-2 receptor have played a major part in establishing several of the fundamental principles that govern our current understanding of immunology. Chief among these is the contribution made by lymphokines to regulation of the interactions among vast numbers of lymphocytes, comprising a number of functionally distinct lineages. These soluble mediators likely act locally, within the context of the microanatomic organization of the primary and secondary lymphoid organs, where, in combination with signals generated by direct membrane-membrane interactions, a wide spectrum of cell fate decisions is influenced. The properties of IL-2 as a T-cell growth factor spawned the view that IL-2 worked in vivo to promote clonal T-cell expansion during immune responses. Over time, this singular view has suffered from increasing appreciation that the biologic effects of IL-2R signals are much more complex than simply mediating T-cell growth: depending on the set of conditions, IL-2R signals may also promote cell survival, effector function, and apoptosis. These sometimes contradictory effects underscore the fact that a diversity of intracellular signaling pathways are potentially activated by IL-2R. Furthermore, cell fate decisions are based on the integration of multiple signals received by a lymphocyte from the environment; IL-2R signals can thus be regarded as one input to this integration process. In part because IL-2 was first identified as a T-cell growth factor, the major focus of investigation in IL-R2 signaling has been on the mechanism of mitogenic effects in cultured cell lines. Three critical events have been identified in the generation of the IL-2R signal for cell cycle progression, including heterodimerization of the cytoplasmic domains of the IL-2R beta and gamma(c) chains, activation of the tyrosine kinase Jak3, and phosphorylation of tyrosine residues on the IL-2R beta chain. These proximal events led to the creation of an activated receptor complex, to which various cytoplasmic signaling molecules are recruited and become substrates for regulatory enzymes (especially tyrosine kinases) that are associated with the receptor. One intriguing outcome of the IL-2R signaling studies performed in cell lines is the apparent functional redundancy of the A and H regions of IL-2R beta, and their corresponding downstream pathways, with respect to the proliferative response. Why should the receptor complex induce cell proliferation through more than one mechanism or pathway? One possibility is that this redundancy is an unusual property of cultured cell lines and that primary lymphocytes require signals from both the A and the H regions of IL-2R beta for optimal proliferative responses in vivo. An alternative possibility is that the A and H regions of IL-2R beta are only redundant with respect to proliferation and that each region plays a unique and essential role in regulating other aspects of lymphocyte physiology. As examples, the A or H region could prove to be important for regulating the sensitivity of lymphocytes to AICD or for promoting the development of NK cells. These issues may be resolved by reconstituting IL-2R beta-/-mice with A-and H-deleted forms of the receptor chain and analyzing the effect on lymphocyte development and function in vivo. In addition to the redundant nature of the A and H regions, there remains a large number of biochemical activities mediated by the IL-2R for which no clear physiological role has been identified. Therefore, the circumstances are ripe for discovering new connections between molecular signaling events activated by the IL-2R and the regulation of immune physiology. Translating biochemical studies of Il-2R function into an understanding of how these signals regulate the immune system has been facilitated by the identification of natural mutations in IL-2R components in humans with immunodeficiency and by the generation of mice with targeted mutations in these gen

Interleukin-2 inhibits HIV-1 replication in human macrophages by modulating expression of CD4 and CC-chemokine receptor-5

OBJECTIVE

To determine the effect of recombinant human interleukin (IL)-2 on HIV-1 replication and macrophage colony stimulating factor (M-CSF) production by HIV-1-infected monocyte-derived macrophages (MDM).

DESIGN

Therapeutic use of IL-2 increases the number and function of CD4+ T cells. IL-2 also increases M-CSF production and M-CSF receptor expression by human monocytes, but the subsequent effects on HIV-1 replication in MDM have yet to be determined. MDM from HIV-1-seronegative donors were cultured in the presence and absence of IL-2 and infected with HIV-1. Harvested supernatants were monitored for reverse transcriptase activity and M-CSF production.

RESULTS

Reverse transcriptase activity was significantly lower when MDM cultures were treated with IL-2 for 10 days prior to infection with HIV-1. IL-2 did not stimulate production of inhibitory chemokines or cytokines, but FACS analysis revealed that expression of CD4, the primary HIV-1 receptor, and CC-chemokine receptor-5, a coreceptor used by macrophage-tropic viruses, are down modulated after treatment with IL-2.

CONCLUSION

IL-2 may not only be of benefit in restoring immune function in AIDS patients, but may also help to prevent the infection of healthy macrophages by decreasing their expression of HIV-1 receptors.

Inhibition by sphingosine of leukemic cell killing by human monocytes activated with interleukin-2: a possible role of protein kinase C

Sphingosine and its analogs, which inhibit protein kinase C (PKC), are known to be potent inducers of apoptosis in tumor cells. However, we were concerned that sphingosine might also interfere with anti-tumor cells of the immune system. Therefore, we evaluated the effect of sphingosine on activation of human monocytes by interleukin-2 (IL-2) for killing of leukemic cells. Monocytes, purified by elutriation and adherence, were activated with IL-2 or interferon-gamma (IFN-gamma) in the presence or absence of sphingosine or another inhibitor for 18 h. Then the monocytes were washed and the culture medium was replaced with fresh medium to remove the sphingosine. HL- 60 and K562 leukemic cells were added to the monocyte cultures. Over the next 48 h, the cytotoxic activity of the monocytes towards the leukemic cells was assessed by means of an 111-indium-releasing assay. IL-2-activated monocytes lysed 48 +/- 3% of HL-60 cells and 44 +/- 3% of K562 cells. Sphingosine, dihydrosphingosine, N,N-dimethylsphingosine, and the PKC inhibitor H7 inhibited the activation of monocytes by IL-2, blocking cytotoxic activity against the leukemic cells by approximately 75%. These inhibitors were not toxic to monocytes at the concentrations used. In a PKC assay, sphingosine and H7 inhibited PKC activity in IL-2-treated monocytes. Thus, sphingosines, by inhibiting PKC activity, inhibited activation of monocytes by IL-2, which inhibited the killing of leukemic cells.

Abnormal Myelocytic Cell Development in Interleukin-2 (IL-2)–Deficient Mice: Evidence for the Involvement of IL-2 in Myelopoiesis

Mice lacking interleukin-2 (IL-2) developed a severe hematopoietic disorder characterized by the abnormal development of myeloid cells and neutropenia. Analysis of the bone marrow of IL-2–deficient (IL-2−/−) mice showed that the number of mature polymorphonuclear cells was decreased by 65% to 75%, and granulocyte/macrophage precursor cells were reduced by 50%. Bone marrow cells from IL-2−/− mice were unable to sustain myelopoiesis in lethally irradiated mice and in long-term bone marrow cultures (LTBMC). The addition of exogenous IL-2 to LTBMC of IL-2−/− cells partially restored hematopoietic progenitor activity. In the bone marrow of wild-type mice, immature (Mac-1lo) myeloid cells, including myeloblasts and promyelocytes, constitutively expressed the β-chain of the IL-2R, and the number of Mac-1loIL-2Rβ+ cells was increased by twofold to threefold in IL-2−/− mice. During culture in the presence of IL-2 and the absence of stromal cells, Mac-1loIL-2Rβ+ immature myeloid cells proliferated and gave rise to mature granulocytes and macrophages. Collectively, these observations indicate that defective myelopoiesis in IL-2−/− mice is at least in part a consequence of their direct dependency on IL-2, and by regulating the growth of immature myeloid cells, IL-2 plays an important role in the homeostatic regulation of myelocytic cell generation.

Acute myeloid leukaemia expressing the leucocyte integrin CD11b-a new leukaemic syndrome with poor prognosis: result of an ECOG database analysis. Eastern Cooperative Oncology Group

While assessing the prognostic implications of immunophenotyping in 382 patients enrolled in treatment protocols of the Eastern Cooperative Oncology Group (ECOG) for de novo adult acute myeloid leukaemia, we identified 95 patients with a unique antigen profile characterized by high expression of the leucocyte integrin CD11b (CD11b+ AML). High expression of CD11b was defined as > or = 32% positive blasts based on the retrospectively established prognostic cut-off point for this antigen. Although CD11b is normally expressed by mature monocytes, natural killer cells and granulocytes, leukaemic blasts in CD11b+ AML lacked other immunologic monocytic features (e.g. CD14 and CD122, the interleukin-2 receptor beta chain) and demonstrated a high degree of immaturity, as reflected by a high incidence of blasts expressing the stem cell factor receptor, CD117, and few blasts positive for the myeloid differentiation antigen CD15. Furthermore, by FAB criteria, only 41% of CD11b+ AML cases were classified as M4/M5. Patients with CD11b+ AML had a low response rate (54%) when compared with acute monocytic leukaemia (AMOL; 82%, P = 0.006) or AML overall (68%, P = 0.031), independent of age, cytogenetic abnormalities and P-glycoprotein expression. Because of its poor prognosis, recognition of CD11b+ AML is clinically warranted and, given its morphologic and cytogenetic ambiguity, must be based on the unique antigen profile.

Further Analysis of Interleukin-2 Receptor Subunit Expression on the Different Human Peripheral Blood Mononuclear Cell Subsets

We have investigated the expression of the three components of the interleukin-2 receptor (IL-2Rα, IL-2Rβ, and IL-2Rγ) on the surface of the various peripheral blood mononuclear cell (PBMC) subsets by flow cytometry analysis. The PBMC were immediately isolated (ficoll) from blood collected on heparin as anticoagulant. The three IL-2R components are absent or only marginally detectable on CD4 T lymphocytes. No expression of the IL-2R chains is found for the B lymphocytes. In most donors, the three chains are not detectable on CD8 T lymphocytes, but for a few of them, IL-2Rβ or IL-2Rγ are clearly expressed. CD56 high (IL-2Rα+) and CD56 low (IL-2Rα−) natural killer (NK) cells express IL-2Rβ, but not IL-2Rγ. IL-2Rγ is expressed by monocytes of all donors although with variable intensity. When blood is collected on other anticoagulants or when cells are isolated 1 day after collection, IL-2Rα, IL-2Rβ, and IL-2Rγ are largely expressed on the surface of most PBMC. This observation provides a possible explanation for divergent data previously reported on IL-2R expression. Finally, we show that IL-2Rγ, which is not detectable on the cell surface of lymphocytes, is nevertheless expressed and stored as an intracellular component. This result is in agreement with the constitutive expression of the IL-2Rγ gene and suggests a specific regulatory mechanism for IL-2Rγ membrane translocation.

Further Analysis of Interleukin-2 Receptor Subunit Expression on the Different Human Peripheral Blood Mononuclear Cell Subsets

We have investigated the expression of the three components of the interleukin-2 receptor (IL-2Rα, IL-2Rβ, and IL-2Rγ) on the surface of the various peripheral blood mononuclear cell (PBMC) subsets by flow cytometry analysis. The PBMC were immediately isolated (ficoll) from blood collected on heparin as anticoagulant. The three IL-2R components are absent or only marginally detectable on CD4 T lymphocytes. No expression of the IL-2R chains is found for the B lymphocytes. In most donors, the three chains are not detectable on CD8 T lymphocytes, but for a few of them, IL-2Rβ or IL-2Rγ are clearly expressed. CD56 high (IL-2Rα+) and CD56 low (IL-2Rα−) natural killer (NK) cells express IL-2Rβ, but not IL-2Rγ. IL-2Rγ is expressed by monocytes of all donors although with variable intensity. When blood is collected on other anticoagulants or when cells are isolated 1 day after collection, IL-2Rα, IL-2Rβ, and IL-2Rγ are largely expressed on the surface of most PBMC. This observation provides a possible explanation for divergent data previously reported on IL-2R expression. Finally, we show that IL-2Rγ, which is not detectable on the cell surface of lymphocytes, is nevertheless expressed and stored as an intracellular component. This result is in agreement with the constitutive expression of the IL-2Rγ gene and suggests a specific regulatory mechanism for IL-2Rγ membrane translocation.

Signaling from the IL-2 receptor to the nucleus

Interleukin-2 has pleiotropic actions on the immune system and plays a vital role in the modulation of immune responses. Our current understanding of IL-2 signaling has resulted from in vitro studies that have identified the signaling pathways activated by IL-2, including the Jak-STAT pathways, and from in vivo studies that have analyzed mice in which IL-2, each chain of the receptor, as well a number of signaling molecules have been individually targeted by homologous recombination. Moreover, mutations in IL-2Ralpha, gamma(c) and Jak3 have been found in patients with severe combined immunodeficiency. In addition, with the discovery that two components of the receptor, IL-2Rbeta and gamma(c), are shared by other cytokine receptors, we have an enhanced appreciation of the contributions of these molecules towards cytokine specificity, pleiotropy and redundancy.

The immediate-early gene product Egr-1 regulates the human interleukin-2 receptor beta-chain promoter through noncanonical Egr and Sp1 binding sites

The interleukin-2 IL-2 receptor beta-chain (IL-2Rbeta) is an essential component of the receptors for IL-2 and IL-15. Although IL-2Rbeta is constitutively expressed by lymphocytes, its expression can be further induced by a number of stimuli, including phorbol 12-myristate 13-acetate (PMA). We have now characterized factors that bind to an enhancer region located between nucleotides -170 and -139 of the human IL-2Rbeta promoter. Both Sp1 and Sp3 bound to the 5' portion of this region, whereas a PMA-inducible factor (PIF) mainly bound to its 3' portion and bound to the Sp binding motifs as well. In Jurkat T cells, induction of PIF DNA binding activity was rapidly induced, required de novo protein synthesis, and was sustained at a high level for at least 23 h. Interestingly, PIF was constitutively activated in human T-cell leukemia virus type 1-transformed MT-2 cells. In this paper, we demonstrate that PIF is Egr-1 based on its recognition by anti-Egr-1 antisera in gel mobility shift assays, even though the IL-2Rbeta DNA binding motif differed substantially from the canonical Egr-1 binding site. In addition, Egr-1 bound to the Sp binding site. In Jurkat cells, both sites were required for maximal IL-2Rbeta promoter activity, and in HeLaS3 cells, transfection of Egr-1 could drive activity of a reporter construct containing both sites. Moreover, Sp1 and Egr-1 could form a complex with kinetics that correlated with the production of Egr-1 in Jurkat cells upon PMA stimulation. Thus, Sp1 and Egr-1 physically and functionally cooperate to mediate maximal IL-2Rbeta promoter activity.

The Antineoplastic Agent Bryostatin-1 Induces Proinflammatory Cytokine Production in Human Monocytes: Synergy With Interleukin-2 and Modulation of Interleukin-2Rγ Chain Expression

The antineoplastic agent bryostatin-1 (bryo-1) possesses powerful immunomodulatory properties and can function as a biological response modifier in vivo. However, there is currently little information regarding the effects of bryo-1 on cells of the monocytic lineage. In this study, we demonstrate that bryo-1 can potently induce the production of proinflammatory cytokines from human peripheral blood monocytes. Stimulation of monocytes with subnanomolar concentrations of bryo-1 significantly upregulated the constitutive levels of interleukin-8 (IL-8) mRNA and induced the expression of IL-1β, tumor necrosis factor-α (TNF-α), and IL-6 mRNA in a time and dose-dependent manner. Accordingly, secretion of all four proinflammatory cytokines was induced after monocyte exposure to bryo-1. Furthermore, we showed that bryo-1 selectively synergized with IL-2 in triggering monocyte activation, and this effect seemed to be dependent, at least in part, on the ability of bryo-1 to upregulate IL-2Rγ chain expression. Finally, we demonstrated that the responses of monocytes to bryo-1 could be blocked by the protein kinase C (PKC) inhibitors staurosporine and UCN-01, indicating a role for PKC in monocyte activation by bryo-1. These results show for the first time that bryo-1 is a powerful activator of human monocytes and suggest that stimulation of monokine secretion by bryo-1 may represent at least one of the mechanisms responsible for the in vivo antitumor activity of this drug.

The immunomodulator AS-101 inhibits IL-10 release and augments TNF alpha and IL-1 alpha release by mouse and human mononuclear phagocytes

AS-101 is a tellurium-based compound with known immunomodulating properties. The ability of AS-101 to potentiate the effects of chemotherapeutic drugs and augment cytokine production in vivo has led to clinical trials on AS-101 which are currently being carried out in cancer patients. In the present study we show that AS-101 selectively augments the release of TNF alpha and IL-1 alpha and inhibits the release of IL-10 by lipopolysaccharide (LPS)-stimulated mouse peritoneal macrophages and human monocytes. It does not significantly affect the release of IL-6 or leukemia inhibitory factor (LIF). By itself AS-101 does not induce the release of any of these cytokines. Analysis of IL-10 and TNF alpha RNA levels using semiquantitative PCR reveals that AS-101 blocks the transcription of IL-10 mRNA, but does not significantly affect TNF alpha mRNA. Although both AS-101 and interferon (IFN)-gamma inhibit IL-10, AS-101, unlike IFN-gamma, does not prime macrophages for LPS-induced nitric oxide release and does not appear to significantly affect monocyte HLA-DR expression. Our data suggest that AS-101 is a partial IFN-gamma agonist and may explain the shift toward the release of Th-1 type cytokines observed in AS-101-treated patients.

Abnormal development of intestinal intraepithelial lymphocytes and peripheral natural killer cells in mice lacking the IL-2 receptor beta chain

The interleukin-2 receptor beta chain (IL-2R beta) is expressed on a variety of hematopoietic cell types, including natural killer (NK) cells and nonconventional T lymphocyte subsets such as intestinal intraepithelial lymphocytes (IEL). However, the importance of IL-2R beta-mediated signaling in the growth and development of these cells has yet to be clearly established. We have investigated IEL and NK cells in mice deficient for IL-2R beta and describe here striking defects in the development of these cells. IL-2R beta-/- mice exhibited an abnormal IEL cell population, characterized by a dramatic reduction in T cell receptor alpha beta CD8 alpha alpha and T cell receptor gamma delta lymphocytes. This selective decrease indicates that IEL can be classified into those whose development and/or differentiation is dependent on IL-2R beta function and those for which IL-2R beta-mediated signaling is not essential. NK cell development was also found to be disrupted in IL-2R beta-deficient mice, characterized by a reduction in NK1.1+CD3- cells in the peripheral circulation and an absence of NK cytotoxic activity in vitro. The dependence of NK cells and certain subclasses of IEL cells on IL-2R beta expression points to an essential role for signaling through this receptor, presumably by IL-2 and/or IL-15, in the development of lymphocyte-subsets of extrathymic origin.

Effects of nitric oxide (NO) synthesis inhibition on antitumor responses during interleukin-2 (IL-2) treatment of mice

OBJECTIVES

To evaluate if L-arginine: NO pathway is activated in tumor tissues during IL-2 therapy and to evaluate whether IL-2 induced NO synthesis represents an antitumor effector mechanism or an inhibitory factor against therapeutic effects of IL-2.

METHODS

Four groups [untreated control, NG-monomethyl-L-arginine (MLA) therapy only, IL-2 therapy only, IL-2/MLA therapy groups] of BALB/c mice were injected intraperitoneally with 2 x 10(8) Meth A tumor cells on day 0. MLA was administered subcutaneously with Alzet continuous infusion pumps on day 2. IL-2 therapy (180,000 IU s.c. every 12h for 5 days) was started on day 3. NO production within ascites tumors was assessed by measuring nitrite concentrations in cultures of ascites cells harvested on day 8. Survival and the rate of body weight increment of the mice were measured to evaluate therapeutic responses. Daily urinary nitrate excretion was monitored to demonstrate the effectiveness of MLA in inhibiting NO synthesis.

RESULTS

Nitrite production in supernatants of Meth A ascites cell cultures was 63 +/- 14 microM in IL-2 treated mice and 3.2 +/- 1.5 microM in untreated controls (p < 0.001). MLA prevented the IL-2 therapy induced increase in nitrite production. IL-2 therapy did not decrease the rate of body weight increment and marginally prolonged mean survival to 18.2 days, compared to 16.6 days in control mice (p = 0.255). MLA administration decreased the rate of body weight increment and prolonged mean survival of IL-2 treated mice (21.8 days, p = 0.001 versus IL-2 alone). Interestingly, the MLA treatment increased the rate of body weight increment and diminished the survival of control mice to 11.6 days (p = 0.003). MLA administration via Alzet continuous infusion pumps achieved approximately 60% suppression of urinary nitrate excretion by control mice. Subcutaneous IL-2 treatment strongly induced nitric oxide synthesis (up to 3.5 mumoles of urinary nitrate/ mouse/day). MLA also effectively suppressed IL-2 induced NO production.

CONCLUSION

L-arginine: NO pathway can be activated in malignant ascites by IL-2 therapy and NO synthesis functions as an inhibitory mechanism against IL-2 induced anti-tumor effects.

Myositis associated with interleukin-2 therapy in a patient with metastatic renal cell carcinoma

BACKGROUND

Interleukin-2 (IL-2) has been used successfully in the treatment of some patients with metastatic renal cell carcinoma and melanoma, with a partial response rate of 15%-20%. It produces a well documented spectrum of side effects. Autoimmune diseases have been associated with IL-2 immunotherapy and the development of autoimmune thyroiditis may correlate with antitumor clinical response.

METHODS

A patient with metastatic renal cell carcinoma is described who developed a polymyositis-like myopathy after an autologous tumor vaccine and IL-2 therapy.

RESULTS

The patient had a delayed response for 15 months after developing this previously unreported toxicity.

CONCLUSIONS

To the authors' knowledge, this represents the first reported case of necrotizing myositis in association with IL-2 therapy. Subsequent continuous partial response of the advanced malignancy was observed for 15 months. In this case, IL-2 may have broken tolerance to both normal muscle cells and tumor cells.

Deregulated T cell activation and autoimmunity in mice lacking interleukin-2 receptor beta

In mice lacking the interleukin-2 receptor beta chain (IL-2R beta), T cells were shown to be spontaneously activated, resulting in exhaustive differentiation of B cells into plasma cells and the appearance of high serum concentrations of immunoglobulins G1 and E as well as autoantibodies that cause hemolytic anemia. Marked infiltrative granulocytopoiesis was also apparent, and the animals died after about 12 weeks. Depletion of CD4+ T cells in mutant mice rescued B cells without reversion of granulocyte abnormalities. T cells did not proliferate in response to polyclonal activators, nor could antigen-specific immune responses be elicited. Thus, IL-2R beta is required to keep the activation programs of T cells under control, to maintain homeostasis, and to prevent autoimmunity.

Expression of interleukin-2 receptor gamma on human monocytes: characterization of lineage specific post-translational modifications

Functional interleukin-2 receptors (IL-2R) on lymphocytes contain both IL-2R beta and gamma chains. Whereas constitutive expression of IL-2R beta has been found on monocytes, the expression of IL-2R gamma on these phagocytes has not been examined. We performed reverse-transcription-polymerase chain reaction with Southern blot analysis on RNA derived from purified human monocytes and discovered that they constitutively produce IL-2R gamma mRNA. Western immunoblotting revealed 58- and 64-kDa forms of IL-2R gamma on YT-1 and human monocytes, whereas 58-, 64-, and 69-kDa bands were detected using peripheral blood mononuclear cells and non-adherent lymphocytes. These different forms resulted from variable N-linked glycosylation since culture of the cells in tunicamycin resulted in detection of a single 39-kDa band which corresponds to the molecular weight predicted from the deduced amino acid sequence. By co-immunoprecipitation, the IL-2R beta subunit associates with only the 64-kDa IL-2R gamma protein band in monocytes.

Interleukin 2 receptor gamma chain expression on resting and activated lymphoid cells

The interleukin 2 receptor (IL-2R) is known to be comprised of at least three genetically distinct subunits termed alpha, beta, and gamma. These chains can be expressed individually or in various combinations resulting in distinct receptors with different affinities for IL-2. In contrast to alpha and beta, the cell surface expression of the gamma chain protein previously has not been well-characterized. To examine cell surface expression of IL-2R gamma on hematopoietic cells, we developed two new monoclonal antibodies (mAbs) specific for this protein. Both 1A11 (immunoglobulin [IgG1]) and 3G11 (IgM) specifically reacted with murine cells transfected with IL-2R gamma cDNA, and immunoprecipitation studies indicated that both antibodies precipitated a protein of approximately 62-65 kD. Scatchard analysis of IL-2 binding to murine cells transfected with cDNA-encoding combinations of IL-2R components demonstrated that neither beta nor gamma chain bind IL-2 with measurable affinity, but coexpression of both beta and gamma is sufficient to form an intermediate affinity receptor. In the absence of gamma chain, beta chain interacts with alpha chain to form a "pseudo-high" affinity receptor. In contrast, gamma chain does not appear capable of interacting with alpha in the absence of beta chain. Thus, gamma chain appears to interact only with beta, but beta chain is capable of interacting with both alpha and gamma. Using the newly developed mAbs to examine cell surface expression by immunofluorescence, resting T cells were found to express low levels of gamma chain without detectable alpha or beta. Early after mitogen stimulation, T cells expressed higher levels of alpha, beta, and gamma. However, at later time points, T cells expressed alpha and gamma in marked excess over beta. Thus, formation of high affinity IL-2R on activated T cells was primarily limited by beta chain expression. In contrast, resting natural killer (NK) cells constitutively expressed IL-2R beta without detectable alpha or gamma. After activation with either IL-2 or IL-12, expression of both alpha and gamma transiently increased and then returned to very low levels. Expression of functional IL-2R on resting and activated NK cells, therefore, appeared to be primarily limited by the expression of gamma chain. IL-2 binding studies with resting NK cells confirmed the results of immunofluorescence studies indicating the presence of very low numbers of intermediate affinity (beta gamma) receptors for IL-2 on these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

The interleukin (IL) 2 receptor beta chain is shared by IL-2 and a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells

Late-phase human T-cell lymphotropic virus I-associated adult T-cell leukemia cells express IL-2 receptors (IL-2R) but no longer produce IL-2. We have reported that the IL-2-independent adult T-cell leukemia line HuT-102 secretes a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and lymphokine-activated killer cell activity. Stimulation of proliferation of the cytokine-dependent human T-cell line Kit-225 mediated by HuT-102-conditioned medium or by 3200-fold-purified IL-T was not blocked by the addition of antibodies against IL-2 or IL-2R alpha subunit. However, IL-T-mediated stimulation of this human T-cell line was inhibited by addition of Mik-beta 1, an antibody that binds specifically to IL-2R beta subunit. In addition, the activation of large granular lymphocytes to lymphokine-activated killer cells mediated by IL-T-containing conditioned medium was not blocked by antibodies directed toward IL-2 or IL-2 alpha but was inhibited by an antibody to IL-2R beta, suggesting the requirement of this receptor subunit for IL-T action. This conclusion was confirmed using an IL-3-dependent murine myeloid precursor cell line, 32D, that expresses IL-2R alpha and IL-2R gamma, but not IL-2R beta. Neither IL-2 nor IL-T stimulated 32D cell proliferation. However, after transfection with the gene encoding human IL-2R beta, 32D beta cells proliferated on addition of either cytokine. The IL-T-mediated stimulation of 32D beta proliferation was inhibited by an anti-IL-2R beta antibody but not by an anti-IL-2 antibody. Thus, the IL-T-mediated stimulation of T-cell and lymphokine-activated killer cell activation requires the expression of the IL-2R beta subunit.

Induction of soluble IL-2 receptor in patients with myelodysplastic syndromes undergoing high-dose interleukin-3 treatment

Sera of ten healthy controls and of 15 patients with myelodysplastic syndromes (MDS) were investigated for soluble interleukin-2 receptor (sIL-2R) with a cell-free enzyme-linked immunosorbent assay (ELISA). The patients with MDS underwent treatment with IL-3: eight patients at dose levels of 250 and 500 micrograms/m2 s.c. daily for 15 days, and seven patients at the dose levels of 60 and 125 micrograms/m2 s.c. three times per week for 12 weeks. None of the patients had reported infectious episodes or been under treatment with cytotoxic drugs and/or cytokines within the preceding 2 months. sIL-2R levels were elevated in MDS patients compared with healthy controls (p < 0.001). sIL-2R increased in the high-dose treatment group from 504 +/- 68 U/ml to 731 +/- 199 U/ml (p < 0.025). The increased sIL-2R expression in MDS could be a primary event due to involvement of lymphocytes in the malignant clone or due to a secondary alteration of the cytokine network caused by chronic neutropenia. A down-regulation of the immune response caused by neutralization of free IL-2 by sIL-2R during IL-3 therapy seems possible.

Role of LFA-1/ICAM-1 in interleukin-2-stimulated lymphocyte proliferation

Major adhesion routes between lymphoid cells involve the receptor/ligand pairs LFA-1/ICAM-1 and CD2/LFA-3, in addition to VLA or CD44 molecules. In this study we evaluated the role of these adhesion receptors in the proliferative response of lymphoid cells to interleukin-2 (IL-2). Blocking studies were performed with a panel of monoclonal antibodies (mAb) directed against these adhesion molecules. Selective inhibition of recombinant (r)IL-2-induced cell proliferation was observed with mAb directed against the alpha or beta subunit of LFA-1 or to its ligand ICAM-1. Interestingly, rIL-2-induced proliferation was also inhibited by NKI-L16, and anti-1 alpha antibody known to enhance cell-cell interaction. Resting lymphocytes were preferentially susceptible to the inhibition, particularly in an early phase of culture and when stimulated with a relatively low dose of rIL-2. By using mAb that specifically could block distinct rIL-2 activation pathways, LFA-1/ICAM-1 interaction was found to be required for p55 IL-2 receptor (IL-2R)-mediated interaction of rIL-2 with its high-affinity receptor, but not for p75 IL-2R-mediated responses. Furthermore, it was shown that the rIL-2 response of T lymphocytes, but not of natural killer cells, was dependent on LFA-1/ICAM-1 interaction. This suggests that LFA-1/ICAM-1 interaction is required for an optimal rIL-2 response of cells capable of IL-2 secretion. Our data provide evidence for the hypothesis that adhesion receptor-directed release of IL-2 may result in a locally high concentration of IL-2 that triggers high-affinity IL-2R signaling and up-regulates p55 IL-2R to enhance cytokine responsiveness.

Restricted cytokine expression in rheumatoid arthritis

OBJECTIVE

To determine the cytokine profile of the phenotypically activated T cell in rheumatoid arthritis (RA) synovium.

METHODS

Interleukin-2 (IL-2), IL-2 receptor (IL-2R), IL-6, IL-4, and interferon-gamma (IFN gamma) gene expression was examined in T cells from freshly isolated synovial fluids (SF) and synovial tissues (ST) from patients with RA. Estimates of baseline expression were determined using unstimulated peripheral blood (PB) T cells from healthy individuals. The corresponding positive controls were phytohemagglutinin-activated tonsil T cells.

RESULTS

In studies of paired PB and SF T cell samples from 17 RA patients, IL-2 messenger RNA (mRNA) levels in only 1 PB and 3 SF samples were more than 2 standard deviations above the mean of levels in unstimulated PB from healthy donors. Similarly, only 5 PB and 7 SF samples exhibited elevated IL-2R mRNA levels. IFN gamma gene expression was not detected in any of the paired RA PB or SF samples. Fractionated T cells from 12 RA ST were screened with similar results: Only 1 of 12 samples exhibited IL-2 mRNA levels more than 2 standard deviations above levels in baseline controls. IL-2R mRNA levels were low or not detected, and IFN gamma mRNA was absent. Subsequent studies showed that IL-4 and IL-6 gene expression levels were also low in RA tissues compared with tonsil T cell-positive controls.

CONCLUSION

These data provide evidence for restricted cytokine expression in the T cell population in RA tissues.

Temporal sequence and cellular origin of interleukin-2 stimulated cytokine gene expression

A study of activation of the cytokine network by interleukin 2, IL-2, may provide a rationale for devising cytokine combination and cytokine antagonist treatments with increased anti-tumour efficacy and decreased toxicity. We have investigated the expression of mRNA for 13 cytokines and three transcription factors during in vitro culture of peripheral blood mononuclear cells, PBMC, with IL-2. A consistent pattern of induction was seen in nine individuals, with early (2-24 h) induction of IL-1 beta, IL-6, tumour necrosis factor, TNF, lymphotoxin, LT, and gro. TNF and LT mRNA was expressed continually throughout culture, but levels of mRNA for IL-1 beta, IL-6, and gro declined by 24-48 h. After 48 h, PBMC began to express mRNA for IFN-gamma, IL-5, GM-CSF, and M-CSF. At 15 min to 1 h post IL-2 mRNA for c-fos, c-jun, and c-myc, and TNF was induced in three individuals studied. IL-4, IFN-alpha, and IL-1 alpha mRNA was not detected. Only a minority of cells expressed mRNA for TNF, IL-1 beta, IL-6 and IFN-gamma, and monocytes were the main source. Levels of cytokine protein in culture supernatants mirrored the pattern of mRNA induction. This in vitro model shows clear parallels with the reported in vivo production of cytokines during IL-2 therapy, and may prove useful in designing new therapeutic strategies.