Interleukin 2 and its receptors: recent advances and new immunological functions

IL-2 responsiveness of CD4 and CD8 lymphocytes: further investigations with human IL-2Rbeta transgenic mice

Responsiveness to IL-2 varies from one lympho-mononuclear subset to another. NK lymphocytes and monocytes spontaneously respond to IL-2 whereas it is generally accepted that T and B lymphocytes need to be activated to fully acquire this competence. To further investigate this phenomenon, we studied human IL-2Rbeta (hIL-2Rbeta) transgenic mice constitutively expressing heterospecific, intermediate-affinity IL-2R (hIL-2Rbeta/mouse IL-2Rgamma(c)). We noted that the B lymphocytes and monocytes from spleens of these hIL-2Rbeta transgenic animals failed to grow when cultured in IL-2-containing medium. Under the same experimental conditions, CD4 lymphocytes survived, again without growth, whereas CD8 lymphocytes and NK cells were able to proliferate and develop potent LAK cytotoxicity. The properties of these CD4 and CD8 lymphocytes were then compared after purification. Both subsets expressed functional IL-2R able to induce global protein phosphorylation and, more precisely, signal transducer and activation of transcription 5 and Erk phosphorylation. Therefore, the differential growth potential of these CD4 and CD8 lymphocytes cannot be explained by the lack of IL-2R-dependent early signaling events. When the entrance of purified CD4 and CD8 lymphocytes into the cell cycle was analyzed, we found that the CD4 lymphocytes were unable to enter the G1 phase in the absence of anti-CD3 stimulation. This correlates with the effect of IL-2 on cyclin-dependent kinase inhibitor p27(kip1). In CD4 lymphocytes, IL-2 does not affect p27(kip1) expression. But in CD8 lymphocytes, IL-2 down-modulates p27(kip1). These results indicate that, aside from IL-2R expression and function, IL-2 responsiveness is also controlled by lineage-specific mechanisms.

Adoptive transfer of gene-engineered CD4+ helper T cells induces potent primary and secondary tumor rejection

Because CD4+ T cells play a key role in aiding cellular immune responses, we wanted to assess whether increasing numbers of gene-engineered antigen-restricted CD4+ T cells could enhance an antitumor response mediated by similarly gene-engineered CD8+ T cells. In this study, we have used retroviral transduction to generate erbB2-reactive mouse T-cell populations composed of various proportions of CD4+ and CD8+ cells and then determined the antitumor reactivity of these mixtures. Gene-modified CD4+ and CD8+ T cells were shown to specifically secrete Tc1 (T cytotoxic-1) or Tc2 cytokines, proliferate, and lyse erbB2+ tumor targets following antigen ligation in vitro. In adoptive transfer experiments using severe combined immunodeficient (scid) mice, we demonstrated that injection of equivalent numbers of antigen-specific engineered CD8+ and CD4+ T cells led to significant improvement in survival of mice bearing established lung metastases compared with transfer of unfractionated (largely CD8+) engineered T cells. Transferred CD4+ T cells had to be antigen-specific (not just activated) and secrete interferon gamma (IFN-gamma) to potentiate the antitumor effect. Importantly, antitumor responses in these mice correlated with localization and persistence of gene-engineered T cells at the tumor site. Strikingly, mice that survived primary tumor challenge could reject a subsequent rechallenge. Overall, this study has highlighted the therapeutic potential of using combined transfer of antigen-specific gene-modified CD8+ and CD4+ T cells to significantly enhance T-cell adoptive transfer strategies for cancer therapy.

The structure of interleukin-2 complexed with its alpha receptor

Interleukin-2 (IL-2) is an immunoregulatory cytokine that binds sequentially to the alpha (IL-2Ralpha), beta (IL-2Rbeta), and common gamma chain (gammac) receptor subunits. Here we present the 2.8 angstrom crystal structure of a complex between human IL-2 and IL-2Ralpha, which interact in a docking mode distinct from that of other cytokine receptor complexes. IL-2Ralpha is composed of strand-swapped "sushi-like" domains, unlike the classical cytokine receptor fold. As a result of this domain swap, IL-2Ralpha uses a composite surface to dock into a groove on IL-2 that also serves as a binding site for antagonist drugs. With this complex, we now have representative structures for each class of hematopoietic cytokine receptor-docking modules.

IL-2 induces expression and secretion of IFN-γ in murine peritoneal macrophages

We investigated the effect of interleukin (IL)-2, a T cell growth factor capable of activating certain macrophage functions, on interferon (IFN)-gamma expression in resting mouse peritoneal macrophages (PM). IL-2 addition to PM from different mouse strains up-modulated IFN-gamma mRNA and protein secretion. It is notable that endogenous type I and II IFNs did not play any role in the IL-2-mediated effect, as comparable levels of secreted IFN-gamma were observed upon IL-2 stimulation of PM from deficient mice. In contrast, endogenous IFN-gamma was requested for the IL-12-induced IFN-gamma production. It is interesting that blocking of each component of the IL-2 receptor (IL-2R) by neutralizing antibodies almost completely abolished IL-2-induced IFN-gamma production, suggesting that all IL-2R chains contribute to the PM biological response to IL-2. The simultaneous treatment of PM with IL-2 and IL-12 resulted in a higher IFN-gamma secretion with respect to that obtained upon treatment with IL-2 or IL-12 alone. It is notable that IFN-gamma protein was expressed intracellularly in the majority of cells exhibiting a macrophage phenotype (i.e., F4/80+) and was secreted upon IL-2 stimulation. Overall, these findings demonstrate that IL-2 regulates at different levels IFN-gamma expression in macrophages, highlighting the crucial role of these cells and their regulated responsiveness to key cytokines in the cross-talk between innate and adaptive immunity.

Reduced susceptibility to dextran sulphate sodium-induced colitis in the interleukin-2 heterozygous (IL-2) mouse

Summary Mice homozygous for an inactivation of the interleukin-2 (IL-2) gene develop a T-cell dependent colitis. Heterozygous (IL-2+/-) mice are clinically healthy but have been shown to express reduced levels of IL-2 in the colon. Splenocytes from the IL-2+/- mice had a poorer proliferative response to polyclonal T-cell activation and these mice have reduced numbers of intestinal regulatory T cells (CD4+ CD25+ cells) when compared to wild type mice. When exposed to dextran sulphate sodium (DSS) IL-2+/- mice showed a markedly reduced susceptibility to DSS-induced colitis. While DSS treatment caused a marked increase in both CD4+ and CD8+ colonic T cells expressing increased levels of IL-2, IL-4, and IL-10 in wild type mice none of these changes were seen in IL-2+/- mice. On the contrary, cytokine expression in intestinal T cells of IL-2+/- mice was actually reduced after DSS treatment. These results suggest that reduced levels of IL-2 leads to attenuated activation and function of intestinal T cells in IL-2+/- mice and a failure to react adequately to DSS exposure.

Ligation of RARgamma inhibits proliferation of phytohaemagglutinin-stimulated T-cells via down-regulating JAK3 protein levels

The mechanisms whereby Vitamin A regulates the immune system are poorly understood. We have shown previously that retinoic acids, the Vitamin A derivatives, promote both apoptosis of neglected thymocytes and the activation-induced cell death of peripheral T-cells via ligating the nuclear retinoid receptor (RAR) gamma. In the present study, we found that human peripheral T-cells express RARalpha and gamma, but not RARbeta. Increasing concentrations of 9-cis RA inhibited phytohaemagglutinin (PHA)-induced proliferation of T-cells, an effect that could be mimicked only by addition of RARgamma agonists and could be inhibited by an RARgamma antagonist. Interleukin-2 (IL-2) produced is known to mediate PHA-induced proliferation of T lymphocytes. Ligation of RARgamma did not affect the PHA-induced high affinity IL-2 receptor expression, slightly reduced the PHA-induced IL-2 production, but interfered with the IL-2-mediated signal transduction resulting in inhibition of PHA-induced phosphorylation of retinoblastoma protein and of up-regulation of Bcl-2. Janus kinases JAK1 and JAK3 play a determinant role in IL-2-dependent signal transduction. Ligation of RARgamma did not affect the levels of JAK1, but prevented IL-2-induced expression of JAK3 resulting in inhibition of PHA-induced phosphorylation of Stat5 molecules. Our data suggest that the previously observed toxic effect of high concentrations of retinoids on the immune system might be mediated via formation of 9-cis RA, which via ligation of RARgamma not only induces cell death in immature thymocytes, but inhibits proliferation of T-cells as well.

IFN-gamma decreases CTL generation by limiting IL-2 production: A feedback loop controlling effector cell production

IFN-gamma is produced by cytotoxic T lymphocytes (CTL) but can also decrease CTL generation. We used IFN-gamma-R1-deficient (GRKO) and IFN-gamma-deficient (GKO) mice to study the effects of IFN-gamma in MLC on the generation of CTL activity and CTL number, IL-2 production and cell proliferation. CTL activity was increased in MLC when GRKO responders or GKO stimulators and responders were used, compared to wild-type (WT) MLC. The number of cells displaying the CTL phenotype (CD3+, CD8+, CD25+) was also increased, accompanied by increased IL-2 production and proliferation. Combinations of WT or GRKO CD4+ T cells with WT or GRKO CD8+ T cells as responders showed that IFN-gamma mostly affects CD4+ T cells to limit CTL generation. Intracellular staining indicated that IL-2 production was largely by CD4+ T cells. Moreover, addition of IL-2 to WT responders mimicked GKO CTL generation and activity, whereas neutralizing IL-2 decreased CTL activity in GRKO and WT responders. Thus IFN-gamma reduces CTL generation in alloimmune responses largely by limiting proliferation of IL-2 producing CD4+ T cells. This creates a feedback loop in which effectors produce IFN-gamma that limits IL-2 production which in turn limits CTL generation.

Antibodies in the prevention of renal allograft rejection

The rejection of renal allografts is mediated largely by the intragraft accumulation of alloreactive T lymphocytes. Current immunosuppressive drugs impair lymphocyte function, but also have specific toxicities and lead to nonspecific impairment of immune responses, resulting in an increased risk of infections and malignancy. Initial studies examined the usefulness of antibodies that depleted lymphocytes in preventing rejection. More recently, antibodies that impair lymphocyte function by blocking the interleukin-2 receptor-alpha (IL-2Ralpha), thereby reducing IL-2-mediated activation of T cells, were shown to reduce the risk of rejection. As an additional strategy, antibodies that impair lymphocyte trafficking have been investigated for their effect on acute rejection. This review describes the results of clinical trials of depleting antilymphocyte antibodies, IL-2Ralpha blockers and antibodies to intercellular adhesion molecule-1, lymphocyte function-associated antigen-1, CD154 and CD52 in the prevention of allograft rejection. Particular emphasis has been placed on therapies for which there is evidence obtained from good, randomised, controlled trials or registry data.

Shared cytokine signaling receptors: structural insights from the gp130 system

The vast majority of cytokine signaling is mediated by "shared" receptors that form central signaling components of higher-order complexes incorporating ligand-specific receptors. These include the common gamma chain (gamma(c)), common beta chain (beta(c)), and gp130, as well as others. These receptors have the dual tasks of cross-reactive cytokine recognition, and formation of precisely oriented multimeric signaling assemblies. Currently, detailed structural information on a shared receptor complex exists only for gp130, which is a highly pleiotropic shared cytokine signaling receptor essential for mammalian cell growth and homeostasis. To date, more than 10 different four-helix bundle ligands have been identified that incorporate gp130, or one of its close relatives such as LIF receptor, into functional oligomeric signaling complexes. In this review we summarize our current knowledge of shared receptor recognition and activation, with a focus on gp130. We discuss recent structural and functional information to analyze overall architectural assemblies of gp130 cytokine complexes and probe the basis for the extreme cross-reactivity of gp130 for its multiple cytokine ligands.

Interleukin-2-induced survival of natural killer (NK) cells involving phosphatidylinositol-3 kinase-dependent reduction of ceramide through acid sphingomyelinase, sphingomyelin synthase, and glucosylceramide synthase

Interleukin 2 (IL-2) rescued human natural killer (NK) KHYG-1 cells from apoptosis along with a reduction of ceramide. Conversely, an increase of ceramide inhibited IL-2-rescued survival. IL-2 deprivation-induced activation of acid sphingomyelinase (SMase) and inhibition of glucosylceramide synthase (GCS) and sphingomyelin synthase (SMS) were normalized by IL-2 supplementation. A phosphatidyl inositol-3 (PI-3) kinase inhibitor, LY294002, inhibited IL-2-rescued survival, but a mitogen-activated protein kinase inhibitor, PD98059, and an inhibitor of Janus tyrosine kinase/signal transducer and activator of transcription pathway, AG490, did not. LY294002 inhibited IL-2-induced reduction of ceramide through activation of acid SMase and inhibition of GCS and SMS, suggesting the positive involvement of PI-3 kinase in ceramide reduction through enzymatic regulation. Indeed, a constitutively active PI-3 kinase enhanced growth rate and ceramide reduction through inhibition of acid SMase and activation of GCS and SMS. Further, LY294002 inhibited IL-2-induced changes of transcriptional level as well as mRNA and protein levels in acid SMase and GCS but did not affect the stability of the mRNAs. These results suggest that PI-3 kinase-dependent reduction of ceramide through regulation of acid SMase, GCS, and SMS plays a role in IL-2-rescued survival of NK cells. (Blood. 2004;104:3285-3293)

Immunity to chronic myelogenous leukemia

Given the high rate of cytogenetic responses to imatinib mesylate in chronic myelogenous leukemia (CML), logical future treatment strategies will include combinations of tyrosine kinase inhibitors and immunotherapies such as vaccines. Increased understanding of highly specific immune responses will lead to novel and improved immunotherapy strategies for CML patients. Such advances can be expected to revolutionize the field much in the same way that imatinib mesylate and other targeted small molecules have revolutionized our conception of traditional chemotherapy. This article begins with a brief discussion of why CML may represent a model disease for immunotherapy-based strategies. Laboratory evidence of the immunoresponsiveness of CML is discussed and used to highlight the principles for understanding tumor immunity. Finally,the authors discuss how advances in the understanding of the molecular and cellular nature of immunity are being translated into new therapeutic strategies for the treatment of CML.

NK cells and polymorphonuclear neutrophils are both critical for IL-2-induced pulmonary vascular leak syndrome

The mechanism of IL-2-induced vascular leak syndrome (VLS) is still poorly understood. Cells of both innate and adaptive immune systems have been implicated, but no definitive conclusions have been reached concerning their respective roles. In this study we report a new mouse model of IL-2-induced pulmonary VLS used to obtain a detailed analysis of the early events (sequestration of polymorphonuclear neutrophils and bronchoconstriction) and late events (modifications in the cell and protein content of bronchoalveolar lavages, followed by edema) that characterize this lung injury. This model and knockout animals are used to reconsider the importance of the different leukocyte lineages in early and late events. Recombinase-activating gene 2(-/-) mice are used to demonstrate that adaptive lymphocytes, including NK T cells, are not required for pulmonary VLS induction. By contrast, results obtained with newly described recombinase-activating gene 2(-/-)/IL-15(-/-) mice indicate that NK cells play a key role in both early and late events. In parallel, polymorphonuclear neutrophil depletion is used to evaluate the contributions made by these cells to the late alterations occurring in the lung. Furthermore, when used in combination with inhibition of NO synthase, granulocyte depletion was completely effective in protecting mice from the late events of IL-2-induced pulmonary VLS. Together our results indicate that both NK and PMN cells play a central role in the late events of IL-2-induced VLS.

Immunoregulatory role of nitric oxide in Kilham rat virus-induced autoimmune diabetes in DR-BB rats

Macrophages play a critical role in the pathogenesis of Kilham rat virus (KRV)-induced autoimmune diabetes in diabetes-resistant BioBreeding (DR-BB) rats. This investigation was initiated to determine the role of macrophage-derived soluble mediators, particularly NO, in the pathogenesis of KRV-induced diabetes in DR-BB rats. We found that the expression of inducible NO synthase (iNOS), an enzyme responsible for NO production, was significantly increased during the early phase of KRV infection. Inhibition of iNOS by aminoguanidine (AG) treatment resulted in the prevention of diabetes in KRV-infected animals. The expression of IL-1beta, TNF-alpha, and IL-12 was significantly decreased in the spleen of AG-treated, KRV-infected DR-BB rats compared with PBS-treated, KRV-infected control rats. Subsequent experiments revealed that AG treatment exerted its preventive effect in KRV-infected rats by maintaining the finely tuned immune balance normally disrupted by KRV, evidenced by a significant decrease in the expression of IFN-gamma, but not IL-4, and a decrease in Th1-type chemokine receptors CCR5, CXCR3, and CXCR4. We also found that iNOS inhibition by AG decreased the KRV-induced expression of MHC class II molecules and IL-2R alpha-chain, resulting in the suppression of T cell activation, evidenced by the decreased cytolytic activity of CD8(+) T cells. We conclude that NO plays a critical immunoregulatory role by up-regulating macrophage-derived proinflammatory cytokines, up-regulating the Th1 immune response, and activating T cells, leading to type 1 diabetes after KRV infection, whereas suppression of NO production by AG treatment prevents KRV-induced autoimmune diabetes in DR-BB rats.

Adenosine acts through A2 receptors to inhibit IL-2-induced tyrosine phosphorylation of STAT5 in T lymphocytes: role of cyclic adenosine 3',5'-monophosphate and phosphatases

Adenosine is a purine nucleoside with immunosuppressive activity that acts through cell surface receptors (A(1), A(2a), A(2b), A(3)) on responsive cells such as T lymphocytes. IL-2 is a major T cell growth and survival factor that is responsible for inducing Jak1, Jak3, and STAT5 phosphorylation, as well as causing STAT5 to translocate to the nucleus and bind regulatory elements in the genome. In this study, we show that adenosine suppressed IL-2-dependent proliferation of CTLL-2 T cells by inhibiting STAT5a/b tyrosine phosphorylation that is associated with IL-2R signaling without affecting IL-2-induced phosphorylation of Jak1 or Jak3. The inhibitory effect of adenosine on IL-2-induced STAT5a/b tyrosine phosphorylation was reversed by the protein tyrosine phosphatase inhibitors sodium orthovanadate and bpV(phen). Adenosine dramatically increased Src homology region 2 domain-containing phosphatase-2 (SHP-2) tyrosine phosphorylation and its association with STAT5 in IL-2-stimulated CTLL-2 T cells, implicating SHP-2 in adenosine-induced STAT5a/b dephosphorylation. The inhibitory effect of adenosine on IL-2-induced STAT5a/b tyrosine phosphorylation was reproduced by A(2) receptor agonists and was blocked by selective A(2a) and A(2b) receptor antagonists, indicating that adenosine was mediating its effect through A(2) receptors. Inhibition of STAT5a/b phosphorylation was reproduced with cell-permeable 8-bromo-cAMP or forskolin-induced activation of adenylyl cyclase, and blocked by the cAMP/protein kinase A inhibitor Rp-cAMP. Forskolin and 8-bromo-cAMP also induced SHP-2 tyrosine phosphorylation. Collectively, these findings suggest that adenosine acts through A(2) receptors and associated cAMP/protein kinase A-dependent signaling pathways to activate SHP-2 and cause STAT5 dephosphorylation that results in reduced IL-2R signaling in T cells.

Compensatory energetic mechanisms mediating the assembly of signaling complexes between interleukin-2 and its alpha, beta, and gamma(c) receptors

Interleukin-2 is a key immuno-regulatory cytokine whose actions are mediated by three different cell surface receptors: the alpha, beta and the "common gamma" (gamma(c)) chains. We have undertaken a complete thermodynamic characterization of the stepwise assembly cycle for multiple possible combinations of the receptor-ligand, and receptor-receptor interactions that are necessary for formation of the high-affinity IL-2/alphabetagamma(c) signaling complex. We find an entropically favorable high affinity interaction between IL-2 and its alpha receptor, a moderately entropically favorable low affinity interaction between IL-2 and its beta receptor, and no interaction between IL-2 and the shared receptor, gamma(c). Formation of the stable intermediate trimolecular complexes of IL-2 with alpha and beta receptors, as well as IL-2 with beta and gamma(c) receptors proceeds through enthalpy-entropy compensation mechanisms. Surprisingly, we see a moderate affinity interaction between the unliganded receptor alpha and beta chains, suggesting that a preformed alphabeta complex may serve as the initial interaction complex for IL-2. Reconstitution of the IL-2/Ralphabetagamma(c) high-affinity quaternary signaling complex shows it to be assembled through cooperative energetics to form a 1:1:1:1 assembly. Collectively, the favorable entropy of the bimolecular interactions appears to be offset by the loss in rigid body entropy of the receptor components in the higher-order complexes, but overcome by the formation of increasingly enthalpically favorable composite interfaces. This enthalpic mechanism utilized by gamma(c) contrasts with the favorable entropic mechanism utilized by gp130 for degenerate cytokine interaction. In conclusion, we find that several energetically redundant pathways exist for formation of IL-2 receptor signaling complexes, suggesting a more complex equilibrium on the cell surface than has been previously appreciated.

Familial clustering of autoimmune diseases in patients with dilated cardiomyopathy

In this study, we examined the hypothesis that dilated cardiomyopathy (DCM) shares genetic risk factors with other diseases of presumed autoimmune etiology, and, therefore, the same multiple genes in combination with environmental factors lead to numerous different autoimmune diseases. In accordance with this hypothesis, we showed an increased prevalence of autoimmune diseases in first-degree relatives of patients with DCM. Also, T-cell activation, as reflected in high levels of the soluble interleukin-2 receptor, appears to identify patients with DCM with a clustering of autoimmune diseases.

Activation marker expression and apoptotic susceptibility of T-cell clones derived from CD34(+), young and SENIEUR donors

T-cell clones (TCC) derived from human peripheral blood lymphocytes of a young control, a healthy elderly (SENIEUR) donor, or from CD34(+) hematopoietic progenitor cells were utilised in this study to examine how in vivo and in vitro ageing affects T-cell apoptotic capability. The role of CD25, CD28 and the intracellular proteins, FLICE-inhibitory protein (FLIP), receptor-interacting protein (RIP) and caspase 3 were investigated. We observed an age-related decline in the expression of the IL-2 receptor alpha chain CD25, and absence of the co-stimulatory receptor CD28 on three of the four TCC studied. In young donor- and CD34 cell-derived TCC, but not in SENIEUR donor-derived TCC, we observed an age-related increase in susceptibility of the cells to mFas-L-induced apoptosis, which correlated with the age-related decrease of CD25 expression. Expression levels of full-length RIP and FLIP did not show any correlation to apoptotic susceptibility. However, expression levels of the cleaved form of RIP were greatly reduced in the SENIEUR donor-derived TCC, which together with a trend towards increased caspase 3 activity, could indicate an age-related alteration in utilisation of different apoptotic signalling pathways.

Role of IFN-gamma and IL-2 in rat lung epithelial cell migration and apoptosis after oxidant injury

In the present study, IFN-gamma exposure to primary cultures of rat type II epithelial cells (TIIP) upregulated membrane expression of the common gamma-chain of the IL-2 receptor (approximately 2.5- to 4-fold increase) and redistributed receptor affinity in TIIP, as assessed by Western blot, cell, and tissue histochemistry and Scatchard analysis. As for restitution processes of the lung epithelium, functionality of IL-2R on TIIP was conditional to IFN-gamma exposure: 1) IFN-gamma priming promoted a fivefold increase of IL-2-driven TIIP locomotion (P < 0.05 vs. control at 100 U/ml) and 2) IFN-gamma coincubation with IL-2 reduced bleomycin-induced TIIP apoptosis in vitro by 25% (caspase-3 activity) and by approximately 70% (TdT-mediated dUTP nick end labeling/4',6'-diamidino-2-phenylindole assay) as well as in vivo by approximately 90% (caspase-3 activity; P < 0.05 vs. control). Sustained p42/44 extracellular signal-regulated kinase activity played a protective role in this process, whereas specific inhibition by PD-98059 (50 microM) significantly reversed bleomycin-induced TIIP apoptosis (P < 0.05 vs. control). From these in vitro and in vivo data, it is proposed that combinations of IFN-gamma and IL-2 can drive repair activity of TIIP by stimulating migration and preventing programmed cell death, both of which are speculated to be very fast restitution events after oxidant-induced acute lung injury.

Improved Effector Activity and Memory CD8 T Cell Development by IL-2 Expression during Experimental Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a major cause of lower respiratory infection in young children and the elderly. Studies of mice suggest that RSV suppresses the effector activity of CD8 T cells and the development of pulmonary CD8 T cell memory, in which the impaired effector activity could be recovered by in vitro IL-2 treatment. To investigate the effect of in vivo IL-2 expression on RSV immunity, mice were infected with RSV followed by administration of replication-defective adenovirus expressing IL-2. The effector activity of RSV M2-specific CD8 T cells and the development of CD8 T cell memory in the lung was significantly increased by IL-2 expression. Furthermore, the Ab responses against RSV were augmented by IL-2. Interestingly, weight loss and illness caused by RSV challenge were substantially reduced by IL-2 priming, suggesting that the pathogenesis of RSV-related disease could be prevented by IL-2-mediated enhancement of beneficial immune responses. Thus, our results show that IL-2 has potential to be used as a vaccine adjuvant against RSV infection.

Specific Signaling Pathways Triggered by IL-2 in Human Vγ9Vδ2 T Cells: An Amalgamation of NK and αβ T Cell Signaling

The global immune response can be simplified into two components: the innate and the acquired systems. The innate immune response comprises primarily macrophages and NK cells, while B and T cells orchestrate the acquired response. Human Vgamma9Vdelta2 T cells represent a minor T cell subpopulation in blood (1-5%) that is activated via the TCR by small nonpeptidic molecules. Their percentage dramatically increases during the early phase of infection by intracellular pathogens, and they display many characteristics of NK cells, which places them at a unique position within the immune system. Our aim was to explore the behavior of these cells when they are activated by a receptor that is common to NK and alphabeta T cells, and to determine signaling pathways and biological responses induced in these cells through this receptor. Thus, we investigated whether Vgamma9Vdelta2 T cells behave as NK cells or as alphabeta T cells. We demonstrated that IL-2 activates not only STAT3, STAT5, the phosphatidylinositol 3-kinase pathway, and extracellular signal-regulated kinase-2 pathway, but also STAT4 as in NK cells, and the p38 mitogen-activated protein kinase pathway as in alphabeta T cells. Moreover, IL-2 induces the production of IFN-gamma in Vgamma9Vdelta2 T cells as observed in NK cells. Due to their double profiles, Vgamma9Vdelta2 T cells are at the interface of the innate and the acquired immune response and may therefore not only modulate the activity of innate cells, but also influence Th1/Th2 differentiation.

Expression of an active p110 catalytic subunit of phosphatidylinositol 3-kinase alters the proliferative capacity of interleukin-2 receptor signals

Activation of phosphatidylinositol 3-kinase (PI3K) is an early and essential step in interleukin-2 receptor (IL-2R) signalling, and plays an important role in regulating both cell survival and cellular proliferation. In the present study, we utilized Baf-B03 cells expressing mutated IL-2R to examine the contribution of PI3K to proliferative capacity. In this model IL-2-mediated induction of the downstream PI3K-dependent signalling molecule p70 S6 kinase was detected, but there was no proliferative response. Increasing the level of PI3K activity by transfection of an active form of the catalytic subunit, p110*, enabled the proliferative capacity of the mutated receptor. Whereas, in cells without p110*, IL-2 lacked the capacity to induce c-myc and to overcome an S-phase checkpoint, S-phase transition was restored by transfection of p110*, and this was accompanied by an increase in the c-myc response. Despite the presence of p110*, activity cells still required IL-2R-derived signals for proliferation, and IL-2Rbeta truncated at amino acid 350 were sufficient to provide this signalling activity. The data support a model in which the level of available PI3K can determine the cellular response to IL-2.

Interleukin-15 production during liver allograft rejection in humans

BACKGROUND

The activity of interleukin (IL)-15, a cytokine produced by macrophages, is similar to that of IL-2. We investigated whether IL-15 plays a role in liver allograft rejection.

METHODS

We evaluated plasma levels and intrahepatic expression of IL-15 in 35 patients after liver transplantation, and then analyzed in vitro the influence of anticalcineurin drugs or steroids on IL-15 production and secretion. Finally, we examined the effects of IL-15 on lymphocyte proliferation in mixed lymphocyte culture in the presence or absence of anticalcineurin drugs or steroids.

RESULTS

Plasma levels and in situ expression of IL-15 were enhanced during liver allograft rejection, particularly during steroid-resistant acute rejection and during chronic rejection. In vitro, IL-15 production and secretion were inhibited by neither anticalcineurin drugs nor steroids. Exogenous IL-15 enhanced cell-mediated immune response, and this effect was not inhibited by immunosuppressive drugs.

CONCLUSIONS

IL-15 can play a role in the initiation and outcome of acute and chronic rejection. Anti-IL-15 therapy in combination with classic immunosuppression therapy might thus be beneficial in the prevention of acute, and especially chronic, allograft rejection.

Structural analysis and modeling of a synthetic interleukin-2 mimetic and its interleukin-2Rbeta2 receptor

Peptide p1-30, which is composed of the 30 amino-terminal residues (alpha-helix A) of human interleukin-2 (IL-2), binds as a tetramer to the dimeric IL-2Rbeta2 receptor, whereas the entire IL-2 recognizes the tricomponent receptor IL-2Ralphabetagamma. p1-30 is an IL-2 mimetic that activates CD8 low lymphocytes and natural killer cells, because these cells produce IL-2Rbeta constitutively. It also induces a strong lymphokine-activated killer cell response. A series of truncated peptides were analyzed by circular dichroism and analytical centrifugation to elucidate the role of p1-30 residues. We propose a model where residues 10-30 of the p1-30 peptide form an alpha-helix with eight hydrophobic side chains on the same surface buried in a hydrophobic core when four anti-parallel helices combine to form a bundle. IL-2Rbeta dimerization was further studied, and three-dimensional models of the free IL-2Rbeta2 receptor and the p1-304.IL-2Rbeta2 complex were built by comparative modeling based on the crystal structure of the erythropoietin receptor complex, because this belongs to the same hematopoietin family as IL-2. These models suggest that binding of the p1-30 tetramer rotates the COOH-terminal domains and brings both transmembrane regions 50 A closer together, driving the association of the two intracytoplasmic domains that would transduce the signal into the cytoplasm.

Prognostic significance of soluble interleukin-2 receptor levels in patients with dilated cardiomyopathy

BACKGROUND

Activation of T lymphocytes is thought to mediate myocardial dysfunction in dilated cardiomyopathy (CMP), probably through cytotoxic cytokines, but its value as a prognostic factor has not been evaluated.

METHODS

For 2 years we prospectively followed 76 patients (65 males, 11 females, age 49 +/- 7 years) with CMP and New York Heart Association(NYHA) Class II-III heart failure; left ventricular (LV) function was assessed echocardiographically. Thirty-three patients (28 males, five females, age 52 +/- 6 years) with ischaemic heart disease (IHD) and similar NYHA and LV function characteristics were used as controls. Serum sIL-2R levels, peripheral blood lymphocyte proliferation (basal, + concanavalin A) and HLA-DQB1 genotyping was carried out in all patients.

RESULTS

The CMP patients had increased sIL-2R levels (1259 +/- 130 pg mL-1) compared with the IHD patients (703 +/- 80 pg mL-1, P < 0.01, only 3 > 800 pg mL-1). In the CMP patients, there was a significant (r = +0.45, P= 0.04) correlation between sIL-2R and the LV end-diastolic diameter but not with the LV ejection fraction or NYHA Class. During the 24-month follow up, 17 of the CMP patients had an adverse clinical course (death, need for cardiac transplantation, or worsening heart failure). Of these, 14 (75%) had elevated (>or= 800 pg mL-1) sIL-2R levels (Group I) compared with only five (6%) with a stable clinical course (Group II). Neither [3H] thymidine incorporation into the peripheral blood lymphocytes nor the excess of HLA-DQB1-30 histidine homozygotes in the Group I patients (38% vs. 17%, P < 0.05) could predict the clinical outcome.

CONCLUSION

Increased sIL-2R levels in CMP patients are an independent predictor of a more aggressive clinical course.

Discordant effects of interleukin-2 on viral and immune parameters in human immunodeficiency virus-1-infected monocyte-derived mature dendritic cells

Use of interleukin-2 (IL-2) in the immunotherapy of human immunodeficiency virus (HIV) has frequently resulted in the restoration of CD4 lymphocyte counts but not of virus-specific responses. We reasoned that the absence of reconstituted functional immune parameters could be related to the inability of IL-2 to correct HIV-induced dysfunctions in antigen-presenting cells. In this study, we used in vitro-differentiated monocyte-derived macrophages (MDMs) and mature dendritic cells (MDDCs), acutely infected with primary HIV-1 isolates, to analyse the effects of IL-2 on virus replication, co-receptor expression, and cytokine or chemokine release. Stimulation of MDMs with IL-2 had no measurable effect on HIV-1 replication, on cytokine secretion, or on CD4 and CXCR4 gene expression. Moreover, although a significant down-regulation of CCR5 mRNA expression could be repeatedly detected in MDMs, this IL-2-mediated effect was not of substantial magnitude to affect virus replication. On the other hand, IL-2 stimulation of MDDCs dramatically increased HIV-1 replication and this effect was highly evident on low-replicating, CXCR4-dependent isolates. Nevertheless, the HIV-enhancing activity of IL-2 in MDDCs was not accompanied by any measurable change in cytokine or chemokine release, in virus receptor and co-receptor mRNA accumulation, or in the surface expression of a battery of receptors implicated in virus entry, cell activation or costimulatory function. Taken together, these findings point to a role for IL-2 in inducing virus purging from dendritic cell reservoirs but indicate no relevant potential of the cytokine in restoring defective elements of innate immunity in HIV infection.

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.

Human immunodeficiency virus-1 envelope glycoproteins and anti-CD4 antibodies inhibit interleukin-2-induced Jak/STAT signalling in human CD4 T lymphocytes

Human immunodeficiency virus (HIV) infection leads to a profound T cell dysfunction well before the clinical onset of acquired immunodeficiency syndrome (AIDS). We have been accumulating evidence that one of the mechanisms responsible for this T cell deficiency may be the dysregulation of signal transduction via the interleukin (IL)-2/IL-2 receptor (R) complex. In CD4 T cells, we have observed previously that viral envelope (env) glycoproteins induce IL-2 unresponsiveness and the down-regulation of the three chains making up the IL-2R (alpha, beta, gamma) in vitro. We have now established further that this disruption of the IL-2/IL-2R system manifests itself in defective signal propagation via the Janus kinase (Jak)/signal transducer and activator of transcription (STAT) pathway in response to IL-2. The treatment of CD4 T cells with HIV env or surface ligation of CD4 with anti-CD4 monoclonal antibodies inhibited the IL-2-induced activation of Jak-1 and Jak-3, as well as their targets, STAT5a and STAT5b. This Jak/STAT deficiency may contribute to the crippling of CD4 T cell responses to a cytokine central to the immune response by HIV.

Retinoic acid stimulates the cell cycle machinery in normal T cells: involvement of retinoic acid receptor-mediated IL-2 secretion

The mechanisms whereby vitamin A stimulates the immune system are poorly understood. In the current study, we attempted to elucidate the potential mechanisms of action of all-trans retinoic acid (atRA) on proliferation of human T lymphocytes. We found that physiological levels of atRA potently augmented T cell proliferation when added in combination with common T cell-stimulating agents. This was reflected in a time- and concentration-dependent stimulation of the cell cycle machinery. The presence of atRA led to elevated levels of cyclin D3, -E, and -A, decreased levels of p27(Kip1), increased activity of cyclin-dependent kinase 2, and enhanced phosphorylation of the retinoblastoma protein (pRB). The atRA-mediated changes in the cell cycle machinery were late events, appearing after 20 h of stimulation, indicating that the effects of atRA were indirect. atRA did not alter the expression of the high-affinity IL-2R. However, the level of IL-2 secreted by T cells was strongly enhanced by atRA. rIL-2 was able to substitute for the effects of atRA on the cell cycle machinery and on DNA synthesis, and blocking the IL-2R markedly inhibited atRA-induced cell proliferation and pRB phosphorylation. A retinoic acid receptor (RAR)-selective agonist and 9-cis-RA had the same potency as atRA on T cell proliferation and IL-2 secretion, whereas a retinoid X receptor-selective agonist had only marginal effects. Furthermore, a RAR-selective antagonist completely suppressed T cell proliferation and pRB phosphorylation induced by atRA. Taken together, these results suggest that atRA stimulates the cell cycle machinery and proliferation of normal human T cells by increasing IL-2 secretion through mechanisms involving RARs.

Lymphoadenopathy in IL-2-deficient mice: further characterization and overexpression of the antiapoptotic molecule cellular FLIP

IL-2 was originally identified as a potent T cell growth factor. It was subsequently demonstrated that IL-2 also exerts proapoptotic effects under certain conditions. Inactivation of IL-2 by gene targeting in mice showed that whereas IL-2 is not essential for the generation, clonal expansion, or differentiation of lymphocytes to effector cells, it has a unique role in preventing the accumulation of activated lymphocytes. IL-2(-/-) mice show lymphoadenopathy and autoimmune reactions, suggesting that the proapoptotic effects of IL-2 may predominate in vivo. In this study, we confirm that lymph nodes (LNs) are enlarged in IL-2(-/-) animals, but surprisingly, we found that their spleens are almost normal in size. Subsequent to this observation, we compare lymphocytes from LNs and spleens of IL-2(-/-) and IL-2(+/-) animals to analyze molecular and cellular correlates of the immunopathological disorders found in IL-2-deficient mice. LN lymphocytes from IL-2(-/-) are selectively activated and show an enhanced survival capacity and an increased ability to proliferate in vitro when compared with LN cells from IL-2(+/-) mice and splenocytes from IL-2(-/-) and IL-2(+/-) mice. Because the apoptosis inhibitor FLIP has been shown in vitro to participate in the IL-2 control of activation-induced cell death, we analyze its expression in IL-2(-/-) mice. FLIP was found to be selectively overexpressed in the LNs of IL-2(-/-) mice, but no overexpression was found in spleen cells or thymocytes. These results suggest that FLIP, in conjunction with other IL-2-regulated genes previously characterized in our laboratory, is involved in controlling lymphoadenopathy in IL-2(-/-) mice.

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.

Immunological weapons against acute myeloid leukaemia

A better understanding of the biology of malignant cells and of the host immune system together with dramatic advances in technology have led to the design of innovative immune-mediated approaches to control neoplastic clones, including various haematological malignancies. One of the major problems with conventional cancer therapies is their inability to eradicate residual cancer cells that are resistant to therapy, hence immune intervention might improve the clinical outcome of patients. This mini-review will focus mainly on immunological approaches to the therapy of acute myeloid leukaemia (AML), a subset of a much larger family of leukaemias. Immune-mediated approaches ranging from allogeneic lymphocyte transplants to cytokine therapy, immune-gene therapy and vaccination by dendritic-cell-based vaccines will be discussed.

IL-2-IgG2b fusion protein suppresses murine contact hypersensitivity in vivo

Interleukin-15 shares several functional properties with interleukin-2, and signals through the beta and gamma chain of the interleukin-2 receptor as well as through its own high affinity alpha chain. In agreement with the concept that interleukin-2 plays a key role in type IV immune responses, we have recently shown that an IL-2-IgG2b fusion protein potently suppresses Th1-type delayed type hypersensitivity reaction and Th2-type allergic sensitization in mice. We have now compared the in vivo effects of IL-2-IgG2b fusion protein with those of IL-15-IgG2b fusion protein in a murine model of Th1-type contact hypersensitivity reaction. Daily systemic injections of IL-2-IgG2b fusion protein during the sensitization phase or application of IL-2-IgG2b fusion protein just 2 h before and 10 h after antigen challenge significantly inhibited the contact hypersensitivity ear swelling response, and this without any overt signs of associated toxicity. Even local injection of IL-2-IgG2b fusion protein into the earlobe around the time of antigen challenge inhibited the ear swelling reaction significantly. In contrast, neither systemic nor local injection of the IL-15-IgG2b fusion protein modulated the contact hypersensitivity reaction significantly. IL-2-IgG2b but not IL-15-IgG2b fusion protein reduced migration of antigen-presenting cells from the skin to local lymph nodes, inhibited the expression of CD80 and CD86, and induced a significant higher number of CD4+CD25+ T cells. Therefore, the IL-2-IgGb fusion protein offers a powerful tool for suppressing and/or preventing T-cell-mediated hypersensitivity reaction in vivo.

Interleukin-2 directly induces activation and proliferation of chicken T cells in vivo

Cytokines, as immune activators, have been investigated in mammalian systems as natural adjuvants and therapeutics. In particular, interleukin-2 (IL-2) has been studied widely as a vaccine adjuvant and immuno-enhancer because of its role in activating T cell proliferation. We show here that the first nonmammalian IL-2 gene cloned, chicken IL-2 (ChIL-2), exhibits similar biologic activities to those of mammalian IL-2. To assess the activities of ChIL-2 in vivo, we injected birds with recombinant ChIL-2 (rChIL-2) protein. rChIL-2 treatment induced peripheral blood lymphocytes to express cell surface IL-2 receptors (IL-2R) within 48 h and resulted in an increase in the proportion of peripheral blood CD4+ and CD8+ T cells. Using bromodeoxyuridine (BrdU) incorporation as a measurement of cell proliferation, we showed the increase in T cell populations to be due to cell proliferation. The ability of ChIL-2 to cause both activation and proliferation of T cells in vivo indicates that it has the potential to be used as an immune activator.

Salp15, an ixodes scapularis salivary protein, inhibits CD4(+) T cell activation

Tick saliva has pleiotropic properties that facilitate persistence of the arthropod upon the host. We now describe a feeding-inducible protein in Ixodes scapularis saliva, Salp15, that inhibits CD4(+) T cell activation. The mechanism involves the repression of calcium fluxes triggered by TCR ligation and results in lower production of interleukin-2. Salp15 also inhibits the development of CD4(+) T cell-mediated immune responses in vivo, demonstrating the functional importance of this protein. Salp15 provides a molecular basis for understanding the immunosuppressive activity of I. scapularis saliva and vector-host interactions.

Inhibition of the IL-15 pathway in anti-CD25 mAb treated renal allograft recipients

Anti-CD25 mAb's are used for prophylaxis of rejection in allograft transplantation. These agents target the alpha-chain, part of the IL-2Ralphabetagamma complex. The beta- and gamma-chain are signaling components that are not specific for IL-2. The T-cell growth factors IL2, IL-7 and IL-15 utilize the gamma-chain and IL-2 and IL-15 share the beta-chain. We have studied the consequences of targeting the IL-2R alpha-chain with the anti-CD25 mAb basiliximab by measuring the IL-2R alphabetagamma expression levels and the IL-2, IL-7 and IL-15 driven proliferation. By flowcytometry and limiting dilution analysis, the IL-2R complex was analyzed in peripheral blood samples from renal allograft recipients (n = 29) who received basiliximab (20 mg IV bolus on day 0 and 4), cyclosporin and mycophenolate mofetil. In peripheral blood, after induction therapy with basiliximab, no CD25 positive T-cells were detectable for 61 days (median, range 25-93 days). When CD25 cells were covered with basiliximab, the percentage and the mean fluorescence intensity (MFI) of IL-2Rbeta positive T-cells significantly decreased, P = 0.02 and P = 0.013, respectively, whereas the expression level of the IL-2Rgamma was not affected. The inhibition of the expression of the IL-2R alpha- and beta-chain had significant consequences for the function of these cells. Both the IL-2- and the IL-15-dependent proliferation were inhibited, P = 0.007 and P = 0.01, respectively. The control, the IL-7 driven proliferation, was not influenced by basiliximab. In conclusion, therapy with anti-CD25 mAb's affect T-cell-dependent allogeneic immune responses, not only by blocking IL-2 signaling but also by impairing IL-15 signaling through downregulating the IL-2/IL-15 receptor beta-chain.

Involvement of Bcl-2 and IL-2R in HIV-positive patients whose CD4 cell counts fail to increase rapidly with highly active antiretroviral therapy

OBJECTIVE

Combination antiretroviral therapy in a subset of HIV-infected patients, here called CD4-low responders (CD4-LR), fails to produce a rapid rise in CD4 cell counts despite effective control of plasma viral load (< 50 copies/ml). The mechanism responsible for this failure was investigated.

DESIGN AND METHODS

CD4-LR patients (n = 13) included in the study had been receiving stable antiretroviral therapy for > 9 months, resulting in undetectable viral load, but nontheless showed a CD4 cell count of < 200 x 106 cells/l. Samples from these patients were analysed for intracellular expression of the anti-apoptotic molecule Bcl-2 and the in vitro apoptosis of their CD4 lymphocytes. Since interleukin-2 (IL-2) induces Bcl-2 and participates in the control of lymphocyte apoptosis, we also investigated the IL-2/IL-2 receptor (IL-2R) system in these CD4-LR patients. All these investigations were performed before and after the CD4-LR patients received IL-2 therapy.

RESULTS

CD4 T lymphocytes from these patients underexpressed the anti-apoptotic molecule Bcl-2 and were more susceptible to spontaneous apoptosis. Peripheral CD4 T lymphocytes from the CD4-LR patients showed a regulatory dysfunction in the IL-2R system that resulted in a lack of reactivity to IL-2. Overall, the results obtained with CD4-LR patients differed radically from those in patients undergoing successful antiretroviral therapy. Finally, an increase in Bcl-2 expression and IL-2 reactivity was observed in the CD4 T lymphocytes of CD4-LR patients receiving IL-2 immunotherapy. This correlated with a reduction in their apoptosis.

CONCLUSION

Our study characterizes the defective maintenance of peripheral CD4 T lymphocytes in CD4-LR patients, probably resulting from Bcl-2 underexpression and dysregulation of the IL-2R system.

Peripheral blood and granuloma CD4(+)CD28(-) T cells are a major source of interferon-gamma and tumor necrosis factor-alpha in Wegener's granulomatosis

To elucidate whether the fraction of CD28(-) T cells within the CD4(+) T-cell population is a major source of Th1-like and proinflammatory cytokine production driving Wegener's granulomatosis (WG) granuloma formation, we analyzed the phenotype and functional characteristics of peripheral blood CD4(+)CD28(-) T cells and of T cells in granulomatous lesions of 12 patients with active WG. Surface markers and intracytoplasmic cytokine and perforin expression were assessed by flow cytometry. Cytokine secretion was measured by enzyme-linked immunosorbent assay. Immunohistological studies demonstrated interferon-gamma and tumor necrosis factor-alpha cytokine positivity attributable to CD4(+)CD28(-) T cells in granulomatous lesions. Peripheral blood CD4(+)CD28(-) T cells expressed CD57, also found on natural killer cells, and intracytoplasmic perforin. They were generally CD25 (interleukin-2 receptor)-negative. CD18 (adhesion molecule beta(2)-integrin) was strongly up-regulated on CD4(+)CD28(-) T cells, whereas only a minority of CD4(+)CD28(+) T cells expressed CD18. CD4(+)CD28(-) T cells appeared as a major source of interferon-gamma and tumor necrosis factor-alpha. In contrast, CD4(+)CD28(+) T cells were able to produce and secrete a wider variety of cytokines including interleukin-2. One-quarter of CD4(+)CD28(+) T cells expressed the activation marker CD25, but they lacked perforin. Thus, CD4(+)CD28(-) T cells appeared more differentiated than CD4(+)CD28(+) T cells. They displayed Th1-like cytokine production and features suggestive of the capability of CD4(+) T-cell-mediated cytotoxicity. CD4(+)CD28(-) T cells may be recruited into granulomatous lesions from the blood via CD18 interaction, and may subsequently promote monocyte accumulation and granuloma formation through their cytokine secretion in WG.

Effect of HLA-DR matching on acute rejection after clinical heart transplantation might be influenced by an IL-2 gene polymorphism

BACKGROUND

To examine whether genetic factors are involved in the development of acute rejection (AR), we investigated a (CA)m(CT)n repeat in the 3'-flanking region of the interleukin (IL)-2 gene.

METHOD

We genotyped 290 heart transplant recipients with and without AR (International Society for Heart and Lung Transplantation criteria > or =3A) and 101 controls.

RESULTS

The frequency of allele 135 of the repeat and its genotype distribution (carriers/noncarriers) were significantly associated with freedom from AR (P=0.03 and P=0.02, respectively). We also found interaction between allele 135 and HLA-DR matching. More carriers of allele 135 with no or one mismatch remained free from AR compared to patients without the allele (P=0.01). This was not found in the HLA-DR group with two mismatches.

CONCLUSION

HLA-DR matching might only be effective in reducing AR after heart transplantation in recipients who carry allele 135 of the (CA)m(CT)n repeat in the 3'-flanking region of the IL-2 gene.

Activation-induced T cell death, and aberrant T cell activation via TNFR1 and CD95-CD95 ligand pathway in stable cardiac transplant recipients

Specific blockade by antibodies (Abs) utilized in induction therapy may cause activation-induced cell death (AICD) in lymphocytes of transplant recipients, preactivated via CD95 and tumour necrosis factor-alpha receptor type 1 (TNFR1), and reduce allograft rejection frequency. Amongst 618 heart transplant (HTX) patients receiving antithymocytes globulin (ATG) therapy, 14 recipients with IVUS-verified freedom of transplant vasculopathy were studied. The control group contained 14 patients awaiting transplantation, classified by the New York Hearth Association heart failure as class IV. From 618 HTX patients 89% were free of rejection grade ISHLT > or =2-3 within 3-month post transplantation and 86% after one year. The death inducing receptors (DIR) such as CD95, CD95L and soluble TNFR1 were significantly increased in HTX recipients versus controls, as demonstrated by FACS, immunoblotting or ELISA (P < 0.001). The presence of increased DIR and in vivo apoptosis in HTX recipients, indicated by annexin-V binding, was further confirmed by the presence of high concentration of histones in the sera of patients. ATG, anti-IL-2R and OKT-3 Abs inhibited cell proliferation in a dose-dependent manner. The induction of apoptosis and/or necrosis was demonstrated in cells cultured with these Abs by annexin-V and 7-aminoactinomycin staining, respectively. Our findings demonstrate that T cells from HTX recipients express high level of CD95, CD95L and soluble TNFR1, and undergo apoptosis and AICD. These cells recognizing donor alloantigens may be selectively eliminated in vivo, and should be responsible for the observed immunological unresponsiveness, indicated by low rejection rates in our patient cohort treated by conventional triple therapy.

Cell-surface expression of CD25, CD26, and CD30 by allergen-specific T cells is intrinsically different in cow's milk allergy

BACKGROUND

The release of T(H)2 cytokines by food-specific T cells is thought to be important in the etiology of food allergy. It has been suggested that the activation state of food-specific T cells also plays a significant role, but this has not yet been studied at the single-cell level.

OBJECTIVE

Differences in the expression of cell-surface markers by cow's milk protein (CMP)-specific T cells between infants with and without cow's milk allergy (CMA) were evaluated at the clonal level. In addition, expression after the spontaneous development of tolerance of cow's milk in infants with CMA was analyzed.

METHODS

We established CMP-specific T-cell clones (TCCs) from blood of infants with CMA and atopic dermatitis, from atopic controls with atopic dermatitis but without CMA, and from nonatopic controls. In addition, we established TCCs from infants with CMA after they had spontaneously developed tolerance to cow's milk. Expression levels of CD25, CD26, and CD30 by each TCC were analyzed by use of flow cytometry.

RESULTS

Cow's milk protein-specific T cells from infants with CMA expressed much higher levels of CD25 and CD30 than CMP-specific T cells from infants without CMA. Expression of CD26 was much lower than in normal controls. After development of tolerance for cow's milk, expression of CD25 and CD30 was decreased, whereas the expression of CD26 was increased to normal levels.

CONCLUSION

Antigen-specific T cells from patients with food allergy display an increased expression of cell-surface markers of activation compared with cells of patients without food allergy. This suggests an intrinsically stronger food-specific T-cell response in food-allergic patients, and points to the key role of food-specific T cells in the pathogenesis of food allergy.

Selective inhibitor of Janus tyrosine kinase 3, PNU156804, prolongs allograft survival and acts synergistically with cyclosporine but additively with rapamycin

Janus kinase 3 (Jak3) is a cytoplasmic tyrosine (Tyr) kinase associated with the interleukin-2 (IL-2) receptor common gamma chain (gamma(c)) that is activated by multiple T-cell growth factors (TCGFs) such as IL-2, -4, and -7. Using human T cells, it was found that a recently discovered variant of the undecylprodigiosin family of antibiotics, PNU156804, previously shown to inhibit IL-2-induced cell proliferation, also blocks IL-2-mediated Jak3 auto-tyrosine phosphorylation, activation of Jak3 substrates signal transducers and activators of transcription (Stat) 5a and Stat5b, and extracellular regulated kinase 1 (Erk1) and Erk2 (p44/p42). Although PNU156804 displayed similar efficacy in blocking Jak3-dependent T-cell proliferation by IL-2, -4, -7, or -15, it was more than 2-fold less effective in blocking Jak2-mediated cell growth, its most homologous Jak family member. A 14-day alternate-day oral gavage with 40 to 120 mg/kg PNU156804 extended the survival of heart allografts in a dose-dependent fashion. In vivo, PNU156804 acted synergistically with the signal 1 inhibitor cyclosporine A (CsA) and additively with the signal 3 inhibitor rapamycin to block allograft rejection. It is concluded that inhibition of signal 3 alone by targeting Jak3 in combination with a signal 1 inhibitor provides a unique strategy to achieve potent immunosuppression.

Immune reconstitution after autologous peripheral blood progenitor cell transplantation: effect of interleukin-15 on T-cell survival and effector functions

OBJECTIVE

The aim of this study was to evaluate the occurrence of T-cell spontaneous apoptosis (A(spont)) and its modulation in vitro by the interleukin-2 receptor (IL-2R) gamma-chain (gammac)-signaling cytokine IL-15 in patients transplanted with autologous peripheral blood progenitor cells (PBPC) for hematologic malignancies.

MATERIALS AND METHODS

Patients were examined on days 30-60, 60-90, and 90-120 after PBPC infusion. Dissipation of mitochondrial transmembrane potential, a hallmark of T-cell apoptosis, has been detected using the fluorescent probe 3,3'-dihexyloxacarbocyanine iodide, after short-term T-cell culture in the absence or presence of exogenous cytokines. Expression of Bcl-2 family members has been studied by flow cytometry and reverse transcriptase polymerase chain reaction. T-cell proliferative responses to recall antigens have been estimated in autologous mixed leukocyte cultures.

RESULTS

A(spont) was seen in 45% +/- 6% of CD4(+) and 55% +/- 6% of CD8(+) T cells cultured in the absence of cytokines. Of interest, IL-15 and, to a lesser extent, its structural cousin IL-2 counteracted T-cell A(spont) by inhibiting the processing of caspase-3 and up-regulating Bcl-2 mRNA and protein levels. Cell division tracking confirmed that IL-15 did not rescue T cells from A(spont) by promoting proliferation but rather acted as a genuine survival factor. Addition of a gammac-blocking antibody to cytokine-conditioned cultures abrogated both apoptosis inhibition and Bcl-2 induction by IL-15, suggesting involvement of the IL-2Rgammac signal transduction pathway. Whereas cytokine-unprimed posttransplant T cells mounted inadequate responses to recall antigens, T cells conditioned with IL-15 expanded vigorously, indicating restoration of antigen-specific proliferation.

CONCLUSIONS

T cells recovering after autologous PBPC transplantation are highly susceptible to spontaneous apoptosis in vitro. This phenomenon can be counteracted by the gammac-signaling cytokine IL-15. These findings suggest that IL-15 might be a promising immunomodulating agent to improve postgrafting T-cell function.

Transcription factors

The regulation of gene expression by transcription factors is fundamental to the phenotype of all cells. The activated phenotype of cells engaged in inflammatory processes is characterized by induced expression of a diverse set of genes, including cytokines, enzymes and cell adhesion molecules. A relatively small number of inducible transcription factors, particularly NF-kappaB, AP-1, NFATs and STATs, are responsible for the expression of a wide variety of inflammatory phenotypic characteristics and therefore play a central role in the pathogenesis of rheumatic diseases. Each of these transcription factors can be modified by existing anti-rheumatic and anti-inflammatory drugs, although adverse effects and limited efficacy remain problems. The future development of therapeutic agents with specificity for transcription factors, especially NF-kappaB, might lead to safer and more effective treatment.

Anti-HIV agent MAP30 modulates the expression profile of viral and cellular genes for proliferation and apoptosis in AIDS-related lymphoma cells infected with Kaposi's sarcoma-associated virus

The anti-HIV agent MAP30 (Momordica anti-HIV protein, 30 kDa) inhibits the proliferation of BC-2, an AIDS-related primary effusion lymphoma (PEL) cell line derived from an AIDS patient. BC-2 cells are latently infected with Kaposi's sarcoma-associated herpes virus (KSHV), also known as human herpes virus 8 (HHV8). We examined the effect of MAP30 on the expression of viral and cellular genes in BC-2 during latent and lytic states of the viral life cycle. By Northern analysis and RT-PCR, we found that MAP30 downregulates the expression of viral cyclin D (vCD), viral interleukin-6 (vIL-6), and viral FLIP (vFLIP), genes involved in cell cycle regulation, viral pathogenesis, and apoptosis. By pathway-specific cDNA microarray analysis, we found that BC-2 cells express high levels of egr-1, ATF-2, hsp27, hsp90, IkappaB, mdm2, skp1, and IL-2, cellular genes involved in mitogenesis, tumorigenesis, and inhibition of apoptosis in NFkappaB and p53 signaling pathways. These results define for the first time the specific cellular pathways involved in AIDS-related tumorigenesis and suggest specific novel targets for the treatment. Furthermore, we found that MAP30 downregulates the expression of egr-1, ATF-2, hsp27, hsp90, IkappaB, mdm2, and Skp1, while it upregulates the pro-apoptotic-related genes Bax, CRADD, and caspase-3. Thus, MAP30 modulates the expression of both viral and cellular genes involved in KS pathogenesis. These results provide valuable insight into the molecular mechanisms of MAP30 anti-KS action and suggest its utility as a therapeutic agent against AIDS-related tumors.

Polyunsaturated fatty acids and T-cell function: implications for the neonate

Infant survival depends on the ability to respond effectively and appropriately to environmental challenges. Infants are born with a degree of immunological immaturity that renders them susceptible to infection and abnormal dietary responses (allergies). T-lymphocyte function is poorly developed at birth. The reduced ability of infants to respond to mitogens may be the result of the low number of CD45RO+ (memory/antigen-primed) T cells in the infant or the limited ability to produce cytokines [particularly interferon-y, interleukin (IL)-4, and IL-10. There have been many important changes in optimizing breast milk substitutes for infants; however, few have been directed at replacing factors in breast milk that convey immune benefits. Recent research has been directed at the neurological, retinal, and membrane benefits of adding 20:4n-6 (arachidonic acid; AA) and 22:6n-3 (docosahexaenoic acid; DHA) to infant formula. In adults and animals, feeding DHA affects T-cell function. However, the effect of these lipids on the development and function of the infant's immune system is not known. We recently reported the effect of adding DHA + AA to a standard infant formula on several functional indices of immune development. Compared with standard formula, feeding a formula containing DHA + AA increased the proportion of antigen mature (CD45RO+) CD4+ cells, improved IL-10 production, and reduced IL-2 production to levels not different from those of human milk-fed infants. This review will briefly describe T-cell development and the potential immune effect of feeding long-chain polyunsaturated fatty acids to the neonate.

Subcutaneous administration of interleukin-2 triggers Fcgamma receptor I expression on human peripheral blood neutrophils in solid and hematologic malignancies

Freshly isolated human polymorphonuclear cells (PMNCs) constitutively express Fcgamma receptor (Fc-gammaR) II and FcgammaRIII on the cell surface but not FcgammaRI. Cytokines such as interferon-gamma (IFNgamma), granulocyte-macrophage colony-stimulating factor (CSF), and granulocyte-CSF trigger FcgammaRI expression on (PMNCs). Because PMNCs express interleukin (IL)-2 receptor, we investigated whether IL-2 can induce FcgammaRI expression on PMNCs isolated from IL-2-treated metastatic renal cell carcinoma (MRCC) and low-grade non-Hodgkin lymphoma (LGNHL) patients. Pretherapy flow cytometry analysis of Fcgamma receptors on PMNCs did not show FcgammaRI expression. Interestingly, 3 days after therapy, PMNCs displayed a detectable amount of FcgammaRI on the cell surface. Kinetic studies on the in vivo effects of IL-2 on MRCC patients showed that FcgammaRI was transiently expressed, starting within 3-6 days of therapy, remaining expressed for 10-15 days, and rapidly declining, whereas such expression remained stable for months in LGNHL patients. In contrast, Fc-gammaRII was not affected. In addition, FcgammaRI+ PMNCs coated in vitro with a bispecific antibody Fab anti-FcgammaRI x anti-HER-2/neu formed intercellular conjugates with a human HER-2/neu-transfected 3T3 cell line (HER-2/neu-3T3). Interleukin-2 treatment increased the number of FcgammaRIII low eosinophils, leading to a change in FcgammaRIII distribution among granulocyte cell subsets. In vitro IL-2 treatment of purified PMNCs failed to generate Fc-gammaRI expression, suggesting that IL-2 indirectly causes FcgammaRI expression. During the IL-2 administration, we did not observe significant changes in IFNgamma serum level. In conclusion, our observation may be used to potentiate the antitumor effects of IL-2 in novel immunotherapy regimens, perhaps by redirecting FcgammaRI+ PMNCs against cancer cells by heteroconjugate antibodies and monitoring the biologic activity of subcutaneous IL-2 in cancer patients.

Comparative toxicity of dithiocarbamates and butadiene metabolites in human lymphoid and bone marrow cells

Apparent differences in the pattern of leukemia risk have been observed between workers employed in 1,3-butadiene (BD) monomer production and those working in styrene-butadiene rubber production (SBR). There are a number of possible explanations for these discrepancies, including differences in disease classification and diagnosis as well as possible quantitative and qualitative differences in occupational exposure between these two industries. This led us to evaluate the possibility that the pattern of disease observed in SBR might be influenced by the presence of an important class of biologically reactive chemicals, dithiocarbamates (DTC), that were present in SBR but not BD monomer production. Therefore, we compared the immunotoxic and hematotoxic activities of DTC and BD metabolites in human immune and hematopoietic cells. Relative to the mouse, human CD34+ bone marrow cells are relatively resistant to the direct effects of BD metabolites, with only the bis-oxide producing any evidence of suppression of clonogenic response at concentrations between 1 and 10 microM. Similarly, treatment of human CD4+ lymphocytes with known (2,3-epoxybutene) and putative BD metabolites (D,L-butane-bis-oxide, (2S,3R)-3-epoxybutane-1,2-diol) does not result in appreciable T-cell toxicity at concentrations likely to be encountered in vivo. In contrast, treatment of human cells with DTC at concentrations as low as 100 nM results in significant suppression of hematopoietic clonogenic response and T-lymphocyte function. Additional studies in our laboratory and others suggest a role for copper in DTC toxicity in both human lymphocytes and bone marrow cells, although the pattern of altered transcriptional regulation observed is markedly different in these two cell populations. These results are consistent with the pattern of DTC toxicity previously observed in clinical and molecular studies.

Neonatal exposure to antigen induces a defective CD40 ligand expression that undermines both IL-12 production by APC and IL-2 receptor up-regulation on splenic T cells and perpetuates IFN-gamma-dependent T cell anergy

T cell deletion and/or inactivation were considered the leading mechanisms for neonatal tolerance. However, recent investigations have indicated that immunity develops at the neonatal stage but evolves to guide later T cell responses to display defective and/or biased effector functions. Although neonatal-induced T cell modulation provides a useful approach to suppress autoimmunity, the mechanism underlying the biased function of the T cells remains unclear. In prior studies, we found that exposure of newborn mice to Ig-PLP1, a chimera expressing the encephalitogenic proteolipid protein (PLP) sequence 139-151, induced deviated Th2 lymph node cells producing IL-4 instead of IL-2 and anergic splenic T cells that failed to proliferate or produce IFN-gamma yet secreted significant amounts of IL-2. However, if assisted with IFN-gamma or IL-12, these anergic splenic T cells regained full responsiveness. The consequence of such biased/defective T cells responses was protection of the mice against experimental allergic encephalomyelitis. In this study, investigations were performed to delineate the mechanism underlying the novel form of IFN-gamma-dependent splenic anergy. Our findings indicate that CD40 ligand expression on these splenic T cells is defective, leading to noneffective cooperation between T lymphocytes and APCs and a lack of IL-12 production. More striking, this cellular system revealed a requirement for IL-2R expression for CD40 ligand-initiated, IL-12-driven progression of T cells into IFN-gamma production.