Cloning of a T cell growth factor that interacts with the beta chain of the interleukin-2 receptor

Quiescence-Inducing and Antiapoptotic Activities of IL-15 Enhance Secondary CD4+ T Cell Responsiveness to Antigen

IL-15 shows functional redundancy with IL-2 due to its usage of the β and γc subunit of the IL-2R. Yet, the requirement of IL-15 for an IL-15Rα chain for high affinity interaction and the separate cellular sources of IL-2 and IL-15 suggest divergent activities for both cytokines. We compared the growth-inducing and proapoptotic or antiapoptotic activities of IL-15 and IL-2 on mature CD4+ T lymphocytes in the presence or absence of TCR occupancy. We found that the nature of IL-15 activity was critically dependent on the activation status of the T cells. In the absence of TCR triggering, IL-15 did not exert the growth factor activity of IL-2, but induced a quiescent phenotype, characterized by maintenance of the cells in the G0/G1 phase of the cell cycle and down-regulation of CD25, CD71, and CD95 expression. In the presence of appropriate TCR engagement, the IL-15-induced quiescent T cells were resistant against TCR-induced cell death and proliferated strongly. IL-2-treated cells, on the contrary, were sensitized to cell death, resulting in a negative feedback on cellular expansion and weak proliferative responsiveness. Consecutive action of IL-15 during the distinct phases of an in vitro immune response markedly increased the cell output of a second antigenic stimulation, as compared with IL-2. These results imply that during immune reactivity in vivo, IL-15 may take over from the transiently available IL-2 the role of survival factor but not of growth factor, hence promoting the long term maintenance of resting, Ag-experienced CD4+ T cells.

Effect of interleukin (IL)-12 and IL-15 on activated natural killer (ANK) and antibody-dependent cellular cytotoxicity (ADCC) in HIV infection

The ability of IL-12 and IL-15 to enhance natural killer (NK) activity and antibody-dependent cellular cytotoxicity (ADCC) of mononuclear cells (MNCs) from HIV+ children and their mothers was investigated. MNCs from HIV+ patients were deficient in NK and ADCC activity compared to control MNCs against several target cells. Overnight incubation with IL-15 or IL-12 augmented NK activity of MNCs from both patients and controls, and the combination of IL-12 and IL-15 resulted in the greatest enhancement. ADCC in HIV+ patients against gp120-coated CEM.NKR cells or chicken erythrocytes could also be enhanced by IL-2 or IL-15 in overnight cultures. Culturing MNCs with either IL-2 or IL-15 for 1 week increased the NK activity in patients to levels of controls treated with these cytokines. However, the response to the combination of IL-12 and IL-15 was less than that to IL-15 alone in 1-week cultures. Culturing MNCs with IL-2 and IL-15 for 1 week also increased the percentage of CD16+/CD56+ cells in both patients and controls. Thus, IL-15 can restore the deficient NK activity in patients and may be a candidate for immunomodulative therapy in HIV+ patients.

The Role of Apoptosis in the Resolution of T Cell-Mediated Cutaneous Inflammation

We have investigated cutaneous purified protein derivative-induced delayed-type hypersensitivity (DTH) responses in healthy volunteers to determine features associated with both the generation and resolution of the reaction. The clinical peak of the response occurred at day 3; however, T cell numbers were maximal on day 7. There was a preferential increase of CD4+CD45RO+ T cells on day 7, which was largely due to proliferation, since a mean of 19% was in cycle. The proliferation of this subset was associated with the presence of IL-15, which was expressed as early as 12 h, and IL-2, which showed peak expression at 7 days. By day 14, there was a significant decrease in both the mean T cell number/unit area and IL-2 and IL-15 expression in perivascular infiltrates. Maximal CD95 (Fas/Apo-1) ligand and TNF-α expression were observed at 7 days and were associated with the presence of 1.83% (range 0.81–2.48%) apoptotic T cells. At 14 days, CD95 ligand and TNF-α expression were reduced significantly, and the presence of 2.5% (range 1.5–3.75%) of apoptotic T cells at this time was probably due to cytokine deprivation, associated with decreased Bcl-2 relative to Bax expression. The induction and resolution of the Mantoux reaction may depend on the expression of cytokines, such as IL-2 and IL-15, which regulate both proliferation and apoptosis in T cells. Failure to control either of these phases of the Mantoux reaction may contribute to the chronicity of inflammatory responses in certain cutaneous diseases.

Characterization of a novel subset of CD8(+) T cells that expands in patients receiving interleukin-12

IL-12 has significant antitumor activity in mice that may be mediated by CD8(+) T cells. We show in this report that repeated subcutaneous injections of IL-12 in patients with cancer resulted in the selective expansion of a subset of peripheral blood CD8(+) T cells. This T cell subset expressed high levels of CD18 and upregulated IL-12 receptor expression after IL-12 treatment in vivo. In normal subjects, these CD3(+)CD8(+)CD18(bright) T cells expressed IL-12 and IL-2 receptors and adhesion/costimulatory molecules to a greater degree than other CD8(+) and CD4(+) T cells. They appeared morphologically as large granular lymphocytes, although they did not express NK cell markers such as CD56. In addition, CD8(+)CD18(bright) T cells were almost exclusively T cell receptor (TCR) alphabeta+, and exhibited a TCR Vbeta repertoire that was strikingly oligoclonal, whereas the Vbeta repertoire of CD18(dim) T cells was polyclonal. Although CD8+CD18(bright) T cells demonstrated little functional responsiveness to IL-12 or IL-2 alone in vitro, they responded to the combination of IL-12+IL-2 with strong IFN-gamma production and proliferation and enhanced non-MHC-restricted cytolytic activity. In contrast, CD18(dim) T cells were not activated by IL-12 or IL-2, alone or in combination. These findings demonstrate that CD8+CD18(bright) T cells are a unique population of peripheral blood lymphocytes with features of both memory and effector cells that are capable of TCR-independent activation through combined stimulation with IL-12+IL-2. As this activation results in IFN-gamma production and enhanced cytolytic activity, these T cells may play a role in innate as well as acquired immunity to tumors and infectious pathogens. Additional studies will be necessary to determine whether CD8+CD18(bright) T cells mediate the antitumor effect of IL-12 or IL-2 administered to cancer patients, and if so, whether maximal activation of these T cells with the combination of IL-12+IL-2 in vivo can augment the clinical effectiveness of these cytokines.

Dysregulation of lymphokine production in the neonate and its impact on neonatal cell mediated immunity

Haematopoiesis and immune functions in cord blood (CB) are developmentally immature when compared with adult peripheral blood (APB). The defects in CB immune function and cytokine production may both contribute to the immaturity of CB immunity. We have studied the mechanisms associated with the dysregulation of myeloid lineage cytokines, GM-CSF and M-CSF, and lymphokines, IL-12, and IL-15 in activated CB when compared with APB MNC. Furthermore, we have studied the effects of IL-12 and IL-15 on induction of IFN-gamma and TNF-alpha production, NK, and LAK activities in CB and APB. GM-CSF, M-CSF, IL-12 and IL-15 protein and mRNA are decreased in activated CB MNC. These discrepancies are secondary, at least in part, to the altered post-transcriptional regulation. The impaired ability of CB to produce IL-12 and IL-15 in response to stimulation may contribute to the decrease in IFN-gamma, TNF-alpha production, NK and LAK activities. Furthermore, combination of low dose IL-12 and IL-15 may augment cytotoxic activities and minimize toxicity. These findings suggest that reduced cytokine expression from activated CB may contribute to the impaired CB cellular immunity and exogenous lymphokines may compensate for the immaturity in CB.

Growth and survival of B-chronic lymphocytic leukaemia cells

Although chronic lymphocytic leukaemia of B cell type (B-CLL) is the most common form of leukaemia in the Western world, several questions about the biology of B-CLL remain to be clarified. To obtain a conceptual model for B-CLL, defined as a relentless accumulation of resting B-CLL cells, it is particularly relevant to ask which cell type is the normal counterpart of B-CLL; what is the site of proliferation; which signals are involved in the recruitment and induction of proliferation and which signals contribute to the survival of the B-CLL cells? The significance of the studies on B-CLL cells in vitro for the interpretation of the in vivo situation may be questioned since they oversimplify the multiple and complex cellular interactions that occur in vivo. However, the in vitro studies have been instrumental in elucidating signals that may regulate growth, differentiation and survival of B-CLL cells. This knowledge, herein reviewed, can be used to put forward a hypothesis on B-CLL cell regulation in vivo.

Interleukin-15 Is an Autocrine/Paracrine Viability Factor for Cutaneous T-Cell Lymphoma Cells

In this study we investigated the role of interleukin-15 (IL-15) in the immunobiology of cutaneous T-cell lymphoma (CTCL) cells. Using cell culture techniques, reverse transcriptase-polymerase chain reaction (RT-PCR), and immunhistochemistry we found that IL-15, like IL-7, is a growth factor for the Sézary cell line SeAx and that both cytokines prolonged the survival of malignant T cells directly isolated from Sézary syndrome (SS) patients. Both IL-15 and IL-7 were more potent than IL-2. IL-4 and IL-9, whose receptors share the same gamma chain with the receptors of IL-2, IL-7, and IL-15, did not sustain the growth of CTCL cells, indicating that signaling through the common gamma chain (γc) is not sufficient for continuous growth. IL-13 and tumor necrosis factor-α (TNF-α) had no effect. IL-7 and IL-15 also supported the growth of SeAx cells in the presence of the apoptosis inducing agents dexamethasone and retinoic acid. The analysis of patient Sézary cells and three CTCL cell lines by RT-PCR showed that all these cells expressed IL-15 mRNA, but only a few (25%) produced IL-7 mRNA. Immunohistological analyses of skin biopsy samples of SS and Mycosis fungoides patients showed immunoreactivity for IL-15 in basal cell layer keratinocytes and in the infiltrating lymphocytes. We conclude that IL-15 is a growth or viability factor for CTCL-derived cell lines or shortly cultivated Sézary cells. The findings that IL-15 mRNA can be detected in Sézary syndrome peripheral blood mononuclear cells and that the IL-15 protein is detected in skin sections from CTCL patients suggest that IL-15 plays an important role in the biology of CTCL.

Protective roles of gamma delta T cells and interleukin-15 in Escherichia coli infection in mice

The number of gamma delta T cells in the peritoneal cavity was increased after an intraperitoneal (i.p.) infection with Escherichia coli in lipopolysaccharide (LPS)-responsive C3H/HeN mice but not in LPS-hyporesponsive C3H/HeJ mice. The gamma delta T cells preferentially expressed invariant Vgamma6 and Vdelta1 chains and proliferated to produce a large amount of gamma interferon in the presence of LPS. Mice depleted of gamma delta T cells by T-cell receptor delta gene mutation showed impaired resistance against E. coli as assessed by bacterial growth. Macrophages from C3H/HeN mice infected with E. coli expressed higher levels of interleukin-15 (IL-15) mRNA than those from the infected C3H/HeJ mice. Administration of anti-IL-15 monoclonal antibody inhibited, albeit partially, the appearance of gamma delta T cells in C3H/HeN mice after E. coli infection and diminished the host defense against the infection. These results suggest that LPS-stimulated gamma delta T cells play an important role in the host defense against E. coli infection and that IL-15 may be partly involved in the protection via an increase in the gamma delta T cells.

Induction of IL-15 mRNA and protein in A549 cells by pro-inflammatory cytokines

Interleukin-15 is a recently discovered cytokine which is functionally similar to IL-2. In order to learn more about possible targets for modulation of the expression of IL-15 we investigated the expression of IL-15 mRNA and protein in the A549 (human lung carcinoma) cell line. Constitutive expression of IL-15 mRNA was detected in A549 cells. Treatment with TNF-alpha or IL-1 beta (10 ng/ml each) induced an about 2-fold increase of IL-15 mRNA; IFN-gamma induced significant effects only at 100 ng/ml. Stimulation with a combination of TNF-alpha and IFN-gamma was not superior to stimulation with TNF-alpha alone. EGF, KGF and the combination thereof were without effects. IL-15 protein was detected in cellular lysates of unstimulated cells and was increased by stimulation with TNF-alpha or IL-1 beta. No significant amounts of IL-15 protein were detected in cellular supernatants.

Targeting the IL-15 Receptor with an Antagonist IL-15 Mutant/Fcγ2a Protein Blocks Delayed-Type Hypersensitivity

Owing to shared receptor components, the biologic activities of IL-15 are similar to those of IL-2. However, the patterns of tissue expression of IL-2/IL-2Rα and IL-15/IL-15Rα differ. The development of agents targeting the receptor and signaling elements of IL-15 may provide a new perspective for treatment of diseases associated with expression of IL-15/IL-15R. We designed, genetically constructed, and expressed a receptor site-specific IL-15 antagonist by mutating glutamine residues within the C terminus of IL-15 to aspartic acid and genetically linked this mutant IL-15 to murine Fcγ2a. These mutant IL-15 proteins specifically bind to the IL-15R, competitively inhibit IL-15-triggered cell proliferation, and do not activate the STAT-signaling pathway. Because the receptor site-specific antagonist IL-15 mutant/Fcγ2a fusion proteins had a prolonged t1/2 in vivo and the potential for destruction of IL-15R+ leukocytes, we examined the immunosuppressive activity of this agent. An IL-15 mutant/Fcγ2a fusion protein markedly attenuated Ag-specific delayed-type hypersensitivity responses and decreased leukocyte infiltration within the delayed-type hypersensitivity sites. These findings suggest that 1) IL-15/IL-15R+ cells are crucial to these T cell-dependent immune responses, and 2) treatment with IL-15 mutant/Fcγ2a protein may ameliorate T cell-dependent immune/inflammatory diseases.

Soluble IL-15 Receptor α-Chain Administration Prevents Murine Collagen-Induced Arthritis: A Role for IL-15 in Development of Antigen-Induced Immunopathology

IL-15 has recently been detected in the synovium of patients with rheumatoid arthritis. IL-15-activated T cells induce significant TNF-α synthesis by macrophages via a cell contact-dependent mechanism, suggesting a key regulatory role for IL-15. Here, we report that the administration of a soluble fragment of IL-15Rα into DBA/1 mice, profoundly suppressed the development of collagen-induced arthritis. This was accompanied in vitro by marked reductions in Ag-specific proliferation and IFN-γ synthesis by spleen cells from treated mice compared with control mice and in vivo by a significant reduction in serum anti-collagen Ab levels. These data directly demonstrate a pivotal role for IL-15 in the development of inflammatory arthritis and also suggest that antagonists to IL-15 may have therapeutic potential in rheumatic diseases.

Interleukin-15 (IL-15) Can Replace the IL-2 Signal in IL-2–Dependent Adult T-Cell Leukemia (ATL) Cell Lines: Expression of IL-15 Receptor α on ATL Cells

Interleukin-15 receptor (IL-15R) and IL-2R have the same β and γ chains, but IL-15R has a specific α chain distinct from that of IL-2Rα, which is indispensable for the high affinity binding of IL-15. In the present study, we examined four IL-2-dependent adult T-cell leukemia (ATL) cell lines for their IL-15R expression. All cell lines bound IL-15, which was not inhibited by a 100-fold excess amount of IL-2, proliferated in response to IL-15 to the same degree as to the stimulation with IL-2, and were maintained without IL-2. The responses to 1L-15 were inhibited by the antibodies against IL-2R β or γ chains but was not by the IL-2R α chain antibody. [125I]–IL-15 exhibited a single high-affinity binding with an apparent kd of 0.17 nmol/L. Reverse transcription–coupled polymerase chain reaction (RT-PCR) showed that the cell lines had the mRNA of IL-15R α. The cell lines also had IL-15 mRNA. Despite the presence of IL-15 mRNA, the cell lines did not secrete IL-15, and the culture supernatants of fresh ATL cells and plasma from the patients did not contain a detectable amount of IL-15 with a few exceptional cases, although fresh ATL cells also responded to IL-15. These results suggest that ATL cells have the complete form of IL-15R and respond to IL-15. Such an IL-15–dependent cell proliferation mechanism might be used in the development of ATL and for the invasion and proliferation of ATL cells in the visceral organs.

T-cell dysfunction in hairy cell leukemia: an updated review

Hairy cell leukemia (HCL) is clinically associated with severe T-cell dysfunction. Several new observations have given more insight into the abnormal T-cell responses seen in this disease. T-lymphocytes in the spleen of patients with HCL seem to be abnormally activated. On the other hand, they are non-responsive, possibly as a result of monocytopenia which may lead to inadequate antigen presentation. This, together with the lack of CD28 on T-cells, may cause T-cell dysfunction. Furthermore, there is a very restricted repertoire of the T-cell receptor-beta family, which may also result in non-responsiveness. Otherwise, T-cell clonal excess may be indicative for activated, possibly autoreactive T-cells.

Interleukin-15 (IL-15) Can Replace the IL-2 Signal in IL-2–Dependent Adult T-Cell Leukemia (ATL) Cell Lines: Expression of IL-15 Receptor α on ATL Cells

Interleukin-15 receptor (IL-15R) and IL-2R have the same β and γ chains, but IL-15R has a specific α chain distinct from that of IL-2Rα, which is indispensable for the high affinity binding of IL-15. In the present study, we examined four IL-2-dependent adult T-cell leukemia (ATL) cell lines for their IL-15R expression. All cell lines bound IL-15, which was not inhibited by a 100-fold excess amount of IL-2, proliferated in response to IL-15 to the same degree as to the stimulation with IL-2, and were maintained without IL-2. The responses to 1L-15 were inhibited by the antibodies against IL-2R β or γ chains but was not by the IL-2R α chain antibody. [125I]–IL-15 exhibited a single high-affinity binding with an apparent kd of 0.17 nmol/L. Reverse transcription–coupled polymerase chain reaction (RT-PCR) showed that the cell lines had the mRNA of IL-15R α. The cell lines also had IL-15 mRNA. Despite the presence of IL-15 mRNA, the cell lines did not secrete IL-15, and the culture supernatants of fresh ATL cells and plasma from the patients did not contain a detectable amount of IL-15 with a few exceptional cases, although fresh ATL cells also responded to IL-15. These results suggest that ATL cells have the complete form of IL-15R and respond to IL-15. Such an IL-15–dependent cell proliferation mechanism might be used in the development of ATL and for the invasion and proliferation of ATL cells in the visceral organs.

Interleukin 15 activity in the rectal mucosa of inflammatory bowel disease

BACKGROUND & AIMS

Interleukin (IL)-15 has been found to share many immunoregulatory activities in lymphocytes with IL-2. The aim of this study was to investigate IL-15 activity in organ cultures, localization of IL-15 messenger RNA (mRNA), and proliferation of lamina propria mononuclear cells (LPMCs) in response to recombinant IL-15 using the mucosal tissues obtained from patients with inflammatory bowel disease (IBD).

METHODS

The contents of IL-15, tumor necrosis factor alpha, and IL-2 in the culture supernatant of the rectal mucosal tissues were determined by an enzyme-linked immunosorbent assay. Expression of IL-15 mRNA was analyzed by in situ hybridization, and proliferative response of LPMCs to recombinant IL-15 was determined by [3H]thymidine incorporation into DNA.

RESULTS

Significantly greater IL-15 activity was detected in active IBD, and this elevation was also observed in inactive ulcerative colitis. In contrast, greater tumor necrosis factor alpha activity was observed only in active IBD, and IL-2 was not detected in organ cultures. In situ hybridization showed IL-15 mRNA in macrophages and epithelial cells in active IBD specimens, and recombinant IL-15 induced a dose-dependent proliferative response in LPMCs.

CONCLUSIONS

Mucosal IL-15 may be involved in the pathogenesis of IBD as one of the important mediators in activation of mucosal immune cells.

Requirement of the IL-2 receptor beta chain for the development of Vgamma3 dendritic epidermal T cells

Vgamma3 TCR cells develop in the fetal thymus and migrate to the skin as dendritic epidermal T cells (DETC). Fetal Vgamma3 thymocytes differentiate from immature heat stable antigen (HSA)high cells to mature HSAlow cells and the latter subset predominantly expresses IL-2 receptor beta chain (IL-2Rbeta). In this study, the role of IL-2Rbeta in the development of Vgamma3 cells was determined in IL-2Rbeta-deficient mice. There was a moderate reduction of mature HSAlow Vgamma3 thymocytes in IL-2Rbeta-deficient mice. Small numbers of Vgamma3 DETC were detected in the fetal skin of IL-2Rbeta-deficient mice, but they were absent in newborn and adult mice. These results suggest that IL-2Rbeta may transduce the crucial signal for survival and/or expansion of Vgama3 cells in the fetal thymus and in the fetal skin. In normal mice, IL-15 but not IL-2 mRNA was expressed in the fetal epidermis and exogenous addition of low concentration of IL-15 to fetal skin organ culture induced proliferation of Vgamma3 DETC. The dependence of fetal Vgamma3 DETC on the expression of IL-2Rbeta and the presence of IL-15 mRNA in the fetal epidermis imply an essential role of IL-15 signaling through IL-2Rbeta in the selective localization of this gammadelta T cell subpopulation in the skin.

Interleukin-15 activates proinflammatory and antimicrobial functions in polymorphonuclear cells

Interleukin-15 (IL-15) is a recently discovered cytokine produced by a wide range of different cell types including fibroblasts, keratinocytes, endothelial cells, and macrophages in response to lipopolysaccharide or microbial infection. This suggests that IL-15 may play a crucial role in the activation of phagocytic cells against pathogens. We studied polymorphonuclear leukocyte (PMN) activation by IL-15, evaluated as enhancement of PMN anti-Candida activity as well as IL-8 production, following stimulation with the cytokine. The PMN response to IL-15 depends on binding to the IL-15 receptor. Our experiments show that binding of a biotinylated human IL-15-immunoglobulin G2b IgG2b fusion protein was competed by the addition of human recombinant IL-15 (rIL-15) or of human rIL-2, suggesting that IL-15 binding to PMN might involve the IL-2Rbeta and IL-2Rgamma chains, which have been shown to be constitutively expressed by PMN. In addition, we show by reverse transcription-PCR and by flow cytometry with a specific anti-IL-15Ralpha chain monoclonal antibody that PMN express the IL-15Ralpha chain at the mRNA and protein levels. Incubation with IL-15 activated PMN to secrete the chemotactic factor IL-8, and the amount secreted was increased by costimulation with heat-inactivated Candida albicans. In addition, IL-15 primed the metabolic burst of PMN in response to formyl-methionyl-leucyl-phenylalanine but was not sufficient to trigger the respiratory burst or to increase the production of superoxide in PMN exposed to C. albicans. IL-15 also increased the ability of PMN to phagocytose heat-killed C. albicans organisms in a dose-dependent manner, without opsonization by antibodies or complement-derived products. In the same concentration range, IL-15 was as effective as gamma interferon (IFN-gamma) and IL-2 in increasing the C. albicans growth-inhibitory activity of PMN. Taken together, these results suggest that IL-15 is a potent stimulant of both proinflammatory and antifungal activities of PMN, activating several antimicrobial functions of PMN involved in the cellular response against C. albicans.

Sepsis induces increased apoptosis in lamina propria mononuclear cells which is associated with altered cytokine gene expression

Studies indicate that lymphoid tissue (e.g., thymus, bone marrow, and Peyer's patches) shows evidence of increase apoptosis (Ao, a form of nonnecrotic cell death) during sepsis. However, it is not known if mucosal lymphoid tissue, such as lamina propria (LP), also shows evidence of increased Ao and if so, is this associated with functional changes, i.e., cytokine gene expression in the LP. To examine this, male C3H/HeN mice were subjected to cecal ligation and puncture (CLP) and lamina propria mononuclear cells (LPMC) were harvested at 4 h (early sepsis) or 24 h (late sepsis). Alterations in the cell phenotype as well as Ao (Tunel assay) were determined by three-color flow cytometry. Cytokine gene expression was assessed by multiprobe RNase protection assay. Sham LPMC preparations were found to be 34.4 +/- 2.4% B220(+) (B-cells), while 12.4 +/- 2.1% were CD8(+) (cytotoxic T-cells), 22.0 +/- 0.8% were CD4(+) (helper T-cells), and 6.4 +/- 0.7% were F4/80(+) (macrophages). The frequency of B220(+) (9%* upward arrow) and CD8 (6%* upward arrow) populations increased markedly at 4 h after CLP; however, this increase was not seen at 24 h. The percentage of Ao+ in CD8(+), B220(+), and F4/80(+) cells increased markedly at both 4 and 24 h. CD4(+) cells showed a marked increase in Ao only at 24 h after CLP. When LPMC mRNA expression was examined, a significant increase in IL-2, -10, and -15 gene expression was observed only at 24 h but not 4 h after CLP. Thus, the early phenotypic changes associated with increased Ao may be a reflection of localized immune cell activation in early sepsis contributing to the increased cytokine gene expression seen in late sepsis. This localized activation may contribute to gastrointestinal inflammation and/or immune dysfunction in sepsis.

Interleukin (IL)-15 enhances antibody-dependent cellular cytotoxicity and natural killer activity in neonatal cells

Interleukin (IL)-15 is a novel cytokine that is very similar to IL-2 in receptor specificity and biological activities. We compared the ability of IL-15 and IL-12 to enhance the cytotoxicity of neonatal (cord blood) and adult mononuclear cells (MNC) in both natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) assays. Incubation with IL-15 (10 ng/ml) or IL-12 (1 ng/ml) for 18 h enhanced the NK activity (using K562 target cells) of both cord and adult MNC, increasing cord cell cytotoxicity threefold. Similar enhancement was seen in ADCC assays using erythrocyte targets and NK-resistant CEM cells coated with HIV gp-120 antigen. Incubation of cord cells with IL-15 or IL-12 for 1 week increased both NK and ADCC, although the combination produced less of an effect than either cytokine alone. IL-15 also increased the percentage of CD16+/CD56+ cells after 1 week incubation. This enhancement of NK and ADCC activities and the number of NK cells by IL-15 suggests it may be clinically useful in treating immunodeficient patients.

IL-15 Enhances the Response of Human γδ T Cells to Nonpetide Microbial Antigens

Human γδ T cells have the ability to rapidly expand and produce IFN-γ in response to nonpeptide Ags of microbial pathogens, in particular a class of compounds known as the prenyl phosphates. We investigated the ability of IL-15, a T cell growth factor, to modulate prenyl phosphate-induced γδ T cell proliferation and cytokine production. IL-15 significantly enhanced the expansion of γδ T cells in the peripheral blood after stimulation in vitro with isopentenyl pyrophosphate. Moreover, using γδ T cell clones, we determined that IL-15-induced T cell proliferation was dependent on the IL-2Rβ chain but not the IL-2Rα chain. We therefore studied the IL-15Rα chain expression in human γδ T cells in the presence or absence of nonpeptide Ags. We found IL-15Rα mRNA expression in IL-15-stimulated and Ag-stimulated human γδ T cells but not in resting γδ T cells. Although IL-15 itself had little effect on the production of IFN-γ, IL-15 plus IL-12 acted synergistically to augment IFN-γ production by γδ T cells. Moreover, we showed that this increase in IFN-γ could be explained by the dual activation of STAT1 and STAT4 by IL-15 and IL-12, respectively. Taken together, these results suggest that IL-15 may contribute to activation of human γδ T cells in the immune response to microbial pathogens.

The 5′ Untranslated Region, Signal Peptide, and the Coding Sequence of the Carboxyl Terminus of IL-15 Participate in Its Multifaceted Translational Control

We previously reported that the AUG-burdened 5′ untranslated region (UTR) of IL-15 mRNA impedes its translation. Here we demonstrate that the nucleotide or protein sequences of the IL-15 signal peptide and carboxyl terminus also contribute to the poor translation of IL-15 transcripts. In particular, the exchange of the IL-15 signal peptide coding sequence with that of IL-2 increased cellular and secreted levels of IL-15 protein 15- to 20-fold in COS cells, while IL-2 transcripts with the IL-15 signal peptide generated 30- to 50-fold less IL-2 protein than wild-type IL-2. Furthermore, the addition of an artificial epitope tag to the 3′ coding sequence of IL-15 increased its protein production 5- to 10-fold. Combining these two IL-15 message modifications, in addition to removing the 5′ UTR, increased IL-15 synthesis 250-fold compared with a wild-type construct with an intact 5′ UTR. These data suggest that IL-15 mRNA, unlike IL-2 mRNA, may exist in translationally inactive pools. By storing translationally quiescent IL-15 mRNA, cells might respond to intracellular infections or other stimuli by rapidly transforming IL-15 message into one that can be efficiently translated.

Potent and selective stimulation of memory-phenotype CD8+ T cells in vivo by IL-15

Proliferation of memory-phenotype (CD44hi) CD8+ cells induced by infectious agents can be mimicked by injection of type I interferon (IFN I) and by IFN I-inducing agents such as lipopolysaccharide and Poly I:C; such proliferation does not affect naive T cells and appears to be TCR independent. Since IFN I inhibits proliferation in vitro, IFN I-induced proliferation of CD8+ cells in vivo presumably occurs indirectly through production of secondary cytokines, e.g., interleukin-2 (IL-2) or IL-15. We show here that, unlike IL-2, IL-15 closely mimics the effects of IFN I in causing strong and selective stimulation of memory-phenotype CD44hi CD8+ (but not CD4+) cells in vivo; similar specificity applies to purified T cells in vitro and correlates with much higher expression of IL-2Rbeta on CD8+ cells than on CD4+ cells.

The regulation and biological activity of interleukin 12

Interleukin 12 (IL-12) is a pleiotropic cytokine and mediates several biological activities on human T and natural killer (NK) cells, including induction of IFN-gamma production, enhancement of cell-mediated cytotoxicity and comitogenic effects on resting T-cells. The major cellular sources producing IL-12 are antigen-stimulated monocytes, macrophages, and B-cells isolated from peripheral blood mononuclear cells (PBMC). Our laboratory has investigated the regulation of IL-12 gene expression in both cord blood and adult PBMC, and the effects of IL-12 on induction of IFN-gamma production, NK, and lymphokine-activated killer (LAK) cytotoxicity. IL-12 mRNA expression and protein production in LPS-stimulated cord blood MNC were 3-4 fold decreased when compared with adult PBMC. There were no differences between cord blood and adult PBMC in both basal levels of transcription or the degree of transcriptional activation of the IL-12 gene. Additionally, the half-life of IL-12 p40 mRNA was 3-fold lower in activated cord blood compared to adult PBMC. Exogenous IL-12 induced a significant increase of IFN-gamma from both cord and adult PBMC. Cord MNC has significantly reduced levels of NK activity, and IL-12 significantly enhanced cord blood NK cytotoxicity up to similar levels in adult PBMC. IL-12 also significantly enhanced cord blood NK and LAK activities against a broad range of neuroblastoma, leukemia, and lymphoma cell lines. Lower doses of IL-12 and IL-15 concomitantly generated either synergistic or additive effects on cord blood NK and LAK cytotoxicities. In light of the important biological functions of IL-12, reduced expression and production of IL-12 from activated cord blood may contribute to the immaturity of cord blood cellular immunity and contribute, in part, to decreased severe graft vs. host disease following unrelated cord blood stem cell transplantation. IL-12 enhancement of IFN-gamma, NK, and LAK activity in activated cord blood MNC up to comparable levels in adult PBMC suggests that exogenous IL-12 stimulation can compensate for the immaturity in cord blood cellular immunity. These characteristics of IL-12 biological activity strongly suggest its potential usefulness in future cancer immunotherapy.

CD28 co-stimulation is intact and contributes to prolonged ex vivo survival of hyporesponsive synovial fluid T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), T cells in the inflamed joint are considered to play a crucial role in the pathogenesis. However, despite the fact that synovial T cells have an activated memory phenotype, they are functionally suppressed upon combined CD3 and CD28 stimulation. Here, we analyzed the contribution of both CD3 and CD28 to the hyporesponsiveness of synovial T cells in RA. In contrast to the low CD3 responsiveness of synovial fluid (SF) T cells compared to peripheral blood (PB) T cells, the CD28 co-stimulatory response was observed to be unaffected. Hyporesponsiveness of SF T cells has previously been associated with decreased levels of intracellular glutathione (GSH), an antioxidant and regulator of the intracellular redox state. Treatment of SF T cells with N-acetylcysteine, an antioxidant and replenisher of GSH, selectively improved CD3-induced responses, while leaving CD28 responsiveness unaffected. These data show that the CD3 pathway is highly sensitive to intracellular GSH alterations, whereas CD28 responsiveness is relatively refractory. Furthermore, in support for a functional role of CD28 co-stimulation, it was demonstrated that CD28 ligation acted in synergy with the IL-2 receptor gamma chain signaling cytokine IL-15 in the enhancement of the ex vivo survival of SF T cells. These data indicate that CD28 co-stimulatory capacity of SF T cells, in contrast to CD3 stimulation, remains intact despite an altered intracellular redox state. Thereby, CD28 stimulation may contribute to the persistence of T cells at the site of inflammation, which might be of relevance in the pathogenesis of RA.

Heteromerization of the gammac chain with the interleukin-9 receptor alpha subunit leads to STAT activation and prevention of apoptosis

Interleukin-9 (IL-9) is a cytokine with pleiotropic effects on mast cell and T cell lines. It exerts its effects through the IL-9R complex consisting of IL-9Ralpha and the common gammac subunit. Here we report functional evidence for receptor heteromerization for efficient signal transduction, and we define minimal requirements in the two receptor subunits for IL-9R function. Tyrosine 336 of the IL-9Ralpha and the membrane-proximal segment of gammac are both crucial for signaling. The activated IL-9R complex employs the Janus kinases JAK1 and JAK3 for subsequent activation of the signal transducer and activator transcription (STAT) factors STAT-1, STAT-3, and STAT-5. This process is independent of Tyk2. We demonstrate further that the activated STAT complexes consist of STAT-1 and STAT-5 homodimers and STAT-1-STAT-3 heterodimers. Finally, we show that IL-9R signaling in a T cell line does not result in detectable mitogen-activated protein kinase activation and leads to unsustained proliferation. Nonetheless, these T cells are efficiently protected from dexamethasone-induced apoptosis. These results further define the molecular architecture of the IL-9R and its specific connections to various biologic responses.

Mouse NK1.1+ cytotoxic T cells can be generated by IL-2 exposure from lymphocytes which express an intermediate level of T cell receptor

NK-like T cells which express the NK1.1 molecule and CD3 (or TCR) of intermediate level (CD3int or TCRint cells) were recently demonstrated to be present in various immune organs, and to have NK-like cytotoxic activity against NK target cells. In this study, we investigated whether NK1.1- T cells could express NK1.1. We found that NK1.1+ TCRint cells were much more abundant in the liver (20%) than in the spleen (2%). When hepatic and splenic mononuclear cells (MNCs) were cultured either in the absence of IL-2 or in the presence of CD3/TCR cross-linking, the original NK1.1+ TCRint cells disappeared. However, when they were cultured in the presence of a high dose of IL-2 for 4 days, a new type of NK1.1+ T cell was formed to the extent of approximately 15-20%, and the liver and spleen contained similar percentages of this new type of NK1.1+ T cells. The phenotypes of the original and the new type of NK1.1+ T cells were clearly distinct. The freshly obtained NK1.1+ TCRint cells consisted of double-negative (DN) CD4-CD8- cells and single-positive (SP) CD4+ cells, whereas the new type of NK1.1+ T cells predominantly consisted of DN CD4-CD8- cells and SP CD8+ cells and expressed a high level of CD3 (CD3high or TCRhigh cells). When NK1.1- cells or IL-2 receptor beta-chain (IL-2Rbeta)- cells were isolated from the liver and spleen, and cultured in the presence of IL-2 for 4 days, NK1.1+ T cells were generated from NK1.1- cells, but not from IL-2Rbeta- cells. Our results suggested that the NK1.1- cells, but not IL-2Rbeta- cells, contained the precursor of IL-2-stimulated NK1.1+ TCRhigh cells. When purified NK1.1- IL-2Rbeta+ TCRint cells were cultured in the presence of IL-2 for 4 days, approximately 10% of the cells became NK1.1+ TCRhigh cells. Approximately 60% of the purified NK1.1+ TCRint cells lost NK1.1 expression. The IL-2-stimulated NK1.1+ TCRhigh cells that had arisen from NK1.1- TCRint cells exerted an NK cell-like cytotoxic activity similar to that of the original NK1.1+ T cells. Thus, NK1.1- TCRint cells could express NK1.1 and exert NK-like cytotoxic activity regardless of their origin. It appears that NK1.1+ TCRhigh cells can only be induced through an IL-2-stimulation pathway but not via CD3/TCR cross-linking.

Natural Killer and B-Lymphoid Potential in CD34+ Cells Derived From Embryonic Stem Cells Differentiated in the Presence of Vascular Endothelial Growth Factor

Differentiation of totipotent mouse embryonic stem (ES) cells to various lymphohematopoietic cells is an in vitro model of the hematopoietic cell development during embryogenesis. To understand this process at cellular levels, differentiation intermediates were investigated. ES cells generated progeny expressing CD34, which was significantly enhanced by vascular endothelial growth factor (VEGF). The isolated CD34+ cells were enriched for myeloid colony-forming cells but not significantly for erythroid colony-forming cells. When cultured on OP9 stroma cells in the presence of interleukin-2 and interleukin-7, the CD34+ cells developed two types of B220+ CD34−lymphocytes: CD3− cytotoxic lymphocytes and CD19+ pre-B cells, and such lymphoid potential was highly enriched in the CD34+ population. Interestingly, the cytotoxic cells expressed the natural killer (NK) cell markers, such as NKR-P1, perforin, and granzymes, classified into two types, one of which showed target specificity of NK cells. Thus, ES cells have potential to generate NK-type cytotoxic lymphocytes in vitro in addition to erythro-myeloid cells and pre-B cells, and both myeloid and lymphoid cells seem to be derived from the CD34+intermediate, on which VEGF may play an important role.

Natural Killer and B-Lymphoid Potential in CD34+ Cells Derived From Embryonic Stem Cells Differentiated in the Presence of Vascular Endothelial Growth Factor

Differentiation of totipotent mouse embryonic stem (ES) cells to various lymphohematopoietic cells is an in vitro model of the hematopoietic cell development during embryogenesis. To understand this process at cellular levels, differentiation intermediates were investigated. ES cells generated progeny expressing CD34, which was significantly enhanced by vascular endothelial growth factor (VEGF). The isolated CD34+ cells were enriched for myeloid colony-forming cells but not significantly for erythroid colony-forming cells. When cultured on OP9 stroma cells in the presence of interleukin-2 and interleukin-7, the CD34+ cells developed two types of B220+ CD34−lymphocytes: CD3− cytotoxic lymphocytes and CD19+ pre-B cells, and such lymphoid potential was highly enriched in the CD34+ population. Interestingly, the cytotoxic cells expressed the natural killer (NK) cell markers, such as NKR-P1, perforin, and granzymes, classified into two types, one of which showed target specificity of NK cells. Thus, ES cells have potential to generate NK-type cytotoxic lymphocytes in vitro in addition to erythro-myeloid cells and pre-B cells, and both myeloid and lymphoid cells seem to be derived from the CD34+intermediate, on which VEGF may play an important role.

Cytokine-induced survival of activated T cells in vitro and in vivo

Many antigen-specific T cells die after exposure to antigen in animals. These cells also die if they are isolated from animals shortly after activation and cultured. Various cytokines were tested for their ability to interfere with this in vitro death. Surprisingly, tumor necrosis factor alpha and other inflammatory cytokines did not prevent the in vitro death of activated T cells, even though these cytokines do prevent activated T cell death in animals. Therefore, the inflammatory cytokines probably act on T cells in vivo via an intermediary factor. Four cytokines, interleukin (IL)-2, IL-4, IL-7, and IL-15, did prevent activated T cell death in vitro, with IL-4 and IL-15 more effective than IL-2 or IL-7. These cytokines share a component of their receptors, the common gamma chain, gammac. Therefore, their collective ability to protect activated T cells from death may be mediated by signals involving gammac. To assess their activity in vivo, two of the cytokines, IL-2 and IL-4, were expressed in animals at local sites of superantigen responses. Both cytokines increased the numbers of T cells found at the local sites 14 days later. Interleukin 4 was more effective than IL-2, even though IL-2 stimulates T cell proliferation better than IL-4. This result suggested that IL-4 and related cytokines can promote T cell survival in vivo as well as in vitro. The ability of these cytokines to prevent the death of activated T cells may be important at certain stages of immune responses in animals.

Interleukin-2, interleukin-15, and their receptors

Both IL-15 and IL-2 are 14-15 kDa members of the four alpha-helical bundle family of cytokines that have T cell growth factor activity. In contrast to the pattern manifested by IL-2, IL-15 mRNA is produced by a wide variety of tissues other than T cells. We have demonstrated that IL-15 expression is posttranscriptionally regulated by multiple elements, including the ten upstream AUGs of the 5' UTR, a 48aa signal peptide and the carboxy-terminus of the mature protein. IL-15 utilizes two distinct receptor signaling pathways. In T cells the IL-15 receptor includes IL-2R beta and gamma c subunits shared with IL-2 as well as an IL-15 specific receptor, IL-15R alpha. However, mast cells respond to IL-15 using a receptor system that does not share elements with the IL-2R system but involves a novel 60-65 kDa IL-15RX subunit. In mast cells, IL-15 signaling involves JAK-2 and STAT-5 activation rather than the JAK-1 and JAK-3 as well as the STAT-3 and STAT-5 used by both IL-2 and IL-15 in activated T cells.

Interleukin 15 is produced by endothelial cells and increases the transendothelial migration of T cells In vitro and in the SCID mouse-human rheumatoid arthritis model In vivo

The capacity of endothelial cells (EC) to produce IL-15 and the capacity of IL-15 to influence transendothelial migration of T cells was examined. Human umbilical vein endothelial cells expressed both IL-15 mRNA and protein. Moreover, endothelial-derived IL-15 enhanced transendothelial migration of T cells as evidenced by the inhibition of this process by blocking monoclonal antibodies to IL-15. IL-15 enhanced transendothelial migration of T cells by activating the binding capacity of the integrin adhesion molecule LFA-1 (CD11a/CD18) and also increased T cell motility. In addition, IL-15 induced expression of the early activation molecule CD69. The importance of IL-15 in regulating migration of T cells in vivo was documented by its capacity to enhance accumulation of adoptively transferred human T cells in rheumatoid arthritis synovial tissue engrafted into immune deficient SCID mice. These results demonstrate that EC produce IL-15 and imply that endothelial IL-15 plays a critical role in stimulation of T cells to extravasate into inflammatory tissue.

Detection of an interleukin-1 intracellular receptor antagonist mRNA variant

At least two versions of interleukin-1 receptor antagonist generated by alternative splicing are found intracellularly, but their functions remain poorly characterized. During studies aimed at characterizing the expression of these transcripts in human articular cartilage, we detected a variant cDNA species that contained an additional 171 nucleotides within the type I interleukin-1 intracellular receptor antagonist cDNA which interrupted the coding region. This mRNA variant was also found to be expressed in keratinocytes. Translation likely initiates at an alternate methionine codon than that utilized for the previously reported interleukin-1 intracellular receptor antagonist isoforms, suggesting that this mRNA variant encodes a novel polypeptide that may play a role in interleukin-1 signaling.

Interleukin-15, a T-cell growth factor, is expressed in human neural cell lines and tissues

Interleukin-15 (IL-15) is a novel cytokine which shares activities and receptor components with IL-2. To investigate the biological roles of IL-15 in the human nervous system, we examined the expression of mRNAs for IL-15 and the IL-15 receptor three subunits (IL-15alpha, IL-2Rbeta and IL-2Rgamma) in human neural cell lines and tissues using reverse transcription-polymerase chain reaction and Southern blot analysis. The constitutive expression of high levels of IL-15 mRNA was observed in all the cell lines examined, including Y79 retinoblastoma, IMR-32 neuroblastoma, SK-N-SH neuroblastoma, U-373MG glioma, KG-1-C glioma, NTera2 teratocarcinoma and neurons derived from NTera2 cells following treatment with retinoic acid (RA). Among these cell lines, IL-15 protein was detectable at high levels in culture supernatants of SK-N-SH cells and NTera2-derived neurons. The expression of an alternatively-spliced transcript of the IL-15 gene was up-regulated in NTera2 cells during RA-induced neuronal differentiation, suggesting the existence of differentiation-dependent transcriptional regulation. The expression of IL-15 mRNA was also identified in the human cerebral and cerebellar tissues, peripheral nerve and skeletal muscle, while the mRNAs for the complete set of IL-15R components were detectable only in U-373MG cells, cerebral and cerebellar tissues at significant levels. These results indicate that the expression of IL-15 but not of IL-15R mRNA is universal in human neural cell lines and tissues and raise the possibility that IL-15 acts as a neuroimmune regulatory factor in the human central nervous system.

Human T cell lymphotropic virus type I Tax protein trans-activates interleukin 15 gene transcription through an NF-kappaB site

Interleukin 15 (IL-15) mRNA is expressed in a wide variety of tissue types. However, with the exception of some T cell lines, IL-15 transcript expression has not been described in T cells. Herein we demonstrate that IL-15 mRNA can be detected in freshly isolated normal T cells and T cell lines. Furthermore, its expression is 3- to 4-fold higher in human T cell lymphotropic virus type I (HTLV-I)-infected T cells. By using reporter constructs bearing the 5' regulatory region of the IL-15 gene, we observed a positive correlation between HTLV-I Tax protein expression and IL-15 promoter activity in HTLV-I-infected T cells. Additionally, by using a Jurkat T cell transfectant that expresses Tax under an inducible promoter, we demonstrated that the expression of IL-15 mRNA increased 3-fold as Tax was expressed, suggesting that the Tax protein activates IL-15 transcription. An NF-kappaB consensus sequence is located at the -75 and -65 region of the IL-15 5' regulatory region. Mutations in the NF-kappaB motif or deletion of this sequence abrogated the promoter activity in both HTLV-I-positive and Jurkat Tax-transfectant cells. These data represent evidence for trans-activation of the IL-15 gene by the HTLV-I Tax protein through an NF-kappaB motif and suggest a potential role for IL-15 in HTLV-I-associated diseases such as adult T cell leukemia and HTLV-I-associated myopathy/tropical spastic paraparesis.

Modulation of amplitude and direction of in vivo immune responses by co-administration of cytokine gene expression cassettes with DNA immunogens

Immunization with nucleic acids has been shown to induce both antigen-specific cellular and humoral immune responses in vivo. We hypothesize that immunization with DNA could be enhanced by directing specific immune responses induced by the vaccine based on the differential correlates of protection known for a particular pathogen. Recently we and others reported that specific immune responses generated by DNA vaccine could be modulated by co-delivery of gene expression cassettes encoding for IL-12, granulocyte-macrophage colony-stimulating factor and the co-stimulatory molecule CD86. To further engineer the immune response in vivo, we investigated the induction and regulation of immune responses following the co-delivery of pro-inflammatory cytokine (IL-1 alpha, TNF-alpha, and TNF-beta), Th1 cytokine (IL-2, IL-12, IL-15, and IL-18), and Th2 cytokine (IL-4, IL-5 and IL-10) genes. We observed enhancement of antigen-specific humoral response with the co-delivery of Th2 cytokine genes IL-4, IL-5, and IL-10 as well as those of IL-2 and IL-18. A dramatic increase in antigen-specific T helper cell proliferation was seen with IL-2 and TNF-alpha gene co-injections. In addition, we observed a significant enhancement of the cytotoxic response with the co-administration of TNF-alpha and IL-15 genes with HIV-1 DNA immunogens. These increases in CTL response were both MHC class I restricted and CD8+ T cell dependent. Together with earlier reports on the utility of co-immunizing using immunologically important molecules together with DNA immunogens, we demonstrate the potential of this strategy as an important tool for the development of more rationally designed vaccines.

Modulation of amplitude and direction of in vivo immune responses by co-administration of cytokine gene expression cassettes with DNA immunogens

Immunization with nucleic acids has been shown to induce both antigen-specific cellular and humoral immune responses in vivo. We hypothesize that immunization with DNA could be enhanced by directing specific immune responses induced by the vaccine based on the differential correlates of protection known for a particular pathogen. Recently we and others reported that specific immune responses generated by DNA vaccine could be modulated by co-delivery of gene expression cassettes encoding for IL-12, granulocyte-macrophage colony-stimulating factor and the co-stimulatory molecule CD86. To further engineer the immune response in vivo, we investigated the induction and regulation of immune responses following the co-delivery of pro-inflammatory cytokine (IL-1 alpha, TNF-alpha, and TNF-beta), Th1 cytokine (IL-2, IL-12, IL-15, and IL-18), and Th2 cytokine (IL-4, IL-5 and IL-10) genes. We observed enhancement of antigen-specific humoral response with the co-delivery of Th2 cytokine genes IL-4, IL-5, and IL-10 as well as those of IL-2 and IL-18. A dramatic increase in antigen-specific T helper cell proliferation was seen with IL-2 and TNF-alpha gene co-injections. In addition, we observed a significant enhancement of the cytotoxic response with the co-administration of TNF-alpha and IL-15 genes with HIV-1 DNA immunogens. These increases in CTL response were both MHC class I restricted and CD8+ T cell dependent. Together with earlier reports on the utility of co-immunizing using immunologically important molecules together with DNA immunogens, we demonstrate the potential of this strategy as an important tool for the development of more rationally designed vaccines.

Induction of HIV-1 replication by type 1-like cytokines, interleukin (IL)-12 and IL-15: effect on viral transcriptional activation, cellular proliferation, and endogenous cytokine production

Cytokine dysregulation is evident in HIV-1 infection and it may play an important role in HIV-1 pathogenesis. Administration of T helper cytokines potentially may restore the functional abnormalities to the HIV-1 immune response. Type 1-like cytokines, IL-2, IL-12, and IL-15, are candidates for immune-based therapy for HIV. Given their potential therapeutic use, we determined the effects of IL-2, IL-12, and IL-15 on HIV-1 replication in both primary blood mononuclear cells (PBMC) and the T-cell line, Kit 225-K6. We demonstrate that both IL-2 and IL-12 induce a similar level of HIV-1 replication (9- and 11-fold, respectively) in mitogen-stimulated PBMC. The effect of IL-2 plateaued by day 6, while that of IL-12 continued to increase HIV-1 expression. IL-15 induced a 2.5-fold increase in HIV-1 expression that remained at the same level through day 6. In Kit 225-K6, an IL-2-dependent T cell line, IL-12 and IL-15 enhanced HIV-1 replication by 5- and 3.5-fold over IL-2-treated cultures, respectively. IL-2-, IL-12-, and IL-15-mediated induction of HIV was independent of direct HIV-1 LTR activation, since none of the cytokines induced LTR activity from transfected reporter gene constructs. The cytokine-mediated induction of HIV-1 expression was also independent of cellular proliferation. In PBMC, the IL-12-mediated effect was partially mediated by endogenous cytokine production of IL-1beta and IL-7, whereas in Kit 225-K6, TNFalpha, INFgamma, IL-1beta, and IL-7 did not contribute significantly to the IL-12-mediated effect. IL-15 effect on HIV-1 in PBMC was independent of endogenous cytokine production. However, in Kit 225-K6, neutralizing antibodies to IL-7 had a significant effect on HIV-1 expression. These data suggest that IL-2, IL-12, and IL-15 increase HIV-1 replication predominantly through a posttranscriptional mechanism that may be enhanced by endogenous cytokine production.

Alteration of gene expression by intestinal epithelial cells precedes colitis in interleukin-2-deficient mice

Intestinal epithelial cells may be actively involved in the immunoregulatory pathways leading to intestinal inflammation. The aim of this study was to assess expression by intestinal epithelial cells of cytokines with potential involvement in the development of intestinal inflammation in interleukin (IL)-2-deficient [(-/-)] mice. Wild-type mice, mice heterozygous for the disrupted IL-2 gene, and IL-2(-/-) mice were studied at 6, 16, and 24 wk of age. The mRNA levels of transforming growth factor-beta 1 (TGF-beta 1), tumor necrosis factor-alpha (TNF-alpha), IL-1 beta, IL-6, IL-15, KC, JE, and CD14 in colonic and small intestinal epithelial cells were assessed by Northern blot analysis. CD14 was also measured by Western blotting and reverse transcriptase polymerase chain reaction (RT-PCR). TGF-beta 1 mRNA was constitutively expressed in both colonic and small intestinal epithelial cells with increased expression in the colonic epithelium of colitic mice. CD14 was detected only in colonic epithelial cells, and mRNA levels increased severalfold in IL-2(-/-) mice with colitis. Northern analysis demonstrated increased levels of TGF-beta 1 and CD14 mRNA in colonic epithelial cells of IL-2(-/-) mice before the development of signs of colitis. CD14 mRNA and protein expression in the epithelial cells of colitic mice were confirmed by RT-PCR and Western blot analysis of isolated cells. In addition, IL-2(-/-) mice also expressed increased levels of IL-15 mRNA in small intestinal and colonic epithelial cells compared with heterozygous control mice. TNF-alpha, IL-1 beta, IL-6, KC, and JE mRNAs were only detectable in colonic epithelial cells of mice after the onset of colitis. Enhanced expression of TGF-beta 1, IL-15, and CD14 by colonic epithelial cells may play a role in the subsequent development of colitis in IL-2(-/-) mice.

Mechanism of gamma sigma T-cell-mediated inhibition of stem cell differentiation in vitro: possible relevance for myelosuppression in HIV-infected individuals

We investigated whether gamma delta T cells contribute to the suppression of myelopoiesis in HIV infection. Freshly isolated gamma delta T cells from HIV seropositive patients suppressed CFU-GM growth in vitro. Preactivation of gamma delta T cells with IL-2 and/or IL-15 further reduced the number of CFU-GM. Natural killer cells and to a lower extent CD4+ and CD8+ cells also inhibited CFU-GM growth. In contrast to gamma delta T cells, this effect was not dependent on IL-15 or IL-2 preactivation. Moreover, no enhanced inhibitory effect of CD56+ and CD4+ cells was observed in HIV+ subjects compared to HIV- donors. The myelosuppressive effect of supernatants of gamma delta T cells could be inhibited by antibodies against IFN-gamma or TNF-alpha. Accordingly, we found increased numbers of TNF-alpha or IFN-gamma-secreting CD8+ gamma delta T cells in HIV+ patients. We conclude that the increased fraction of activated gamma delta T cells producing myelosuppressive cytokines might contribute to the dyshematopoiesis frequently observed in HIV-infected individuals.

Interleukin-7 (IL-7) Enhances Class Switching to IgE and IgG4 in the Presence of T Cells Via IL-9 and sCD23

Interleukin-7 (IL-7) is a B-cell growth factor produced by both bone marrow stroma cells and follicular dendritic cells (FDCs) located in primary lymphoid follicles and germinal centers. In this study, we have evaluated the role of IL-7 on human Ig class switching. IL-7 was added to peripheral blood mononuclear cells (PBMCs) or tonsillar B cells in the absence or presence of IL-4 and/or anti-CD40 monoclonal antibody (MoAb). Alone, IL-7 did not affect Ig production by PBMCs or by anti-CD40 MoAb-stimulated B cells. Rather, IL-7 potentiated IL-4–induced IgE and IgG4 production by PBMCs. In parallel, IgG3 production was also enhanced but to a lesser extent, whereas the production of the other isotypes was unaltered. The activity of IL-2, IL-9, or IL-15, which share usage of the common γ chain for signaling, was also assessed. IL-9, like IL-7, potentiated mainly IgE and IgG4 production by IL-4–stimulated PBMCs. IL-15, in contrast, was ineffective, whereas IL-2 enhanced the production of all isotypes. More precisely, IL-7 potentiation of IgE and IgG4 production required the presence of T cells and was accompanied by an increase of the expression of two soluble molecules favoring preferentially IgE and IgG4 synthesis: CD23 (sCD23) and IL-9. Moreover, neutralizing anti-CD23 and anti–IL-9 antibodies partly inhibited the increase of IgE synthesis induced by IL-7. Thus, IL-7 produced locally in the germinal centers by FDCs may interact with T cells and potentiate human IgE and IgG4 switching by favoring IL-9 and sCD23 production.

The Cytokine Profile Expressed by Human Dendritic Cells Is Dependent on Cell Subtype and Mode of Activation

In the present study, we have analyzed the pattern of cytokines expressed by two independent dendritic cell (DC) subpopulations generated in vitro from human cord blood CD34+ progenitors cultured with granulocyte-macrophage CSF and TNF-α. Molecularly, we confirmed the phenotypic differences discriminating the two subsets: E-cadherin mRNA was only detected in CD1a+-derived DC, whereas CD68 and factor XIIIa mRNAs were observed exclusively in CD14+-derived DC. Semiquantitative reverse-transcriptase PCR analysis revealed that both DC subpopulations spontaneously expressed IL-1α, IL-1β, IL-6, IL-7, IL-12 (p35 and p40), IL-15, IL-18, TNF-α, TGF-β, macrophage CSF, and granulocyte-macrophage CSF, but not IL-2, IL-3, IL-4, IL-5, IL-9, and IFN-γ transcripts. Both subpopulations were shown to secrete IL-12 after CD40 triggering. Interestingly, only the CD14+-derived DC secreted IL-10 after CD40 activation, strengthening the notion that the two DC subpopulations indeed represent two independent pathways of DC development. Furthermore, both DC subpopulations expressed IL-13 mRNA and protein following activation with PMA-ionomycin, but not with CD40 ligand, in contrast to IL-12 and IL-10, revealing the existence of different pathways for DC activation. Finally, we confirmed the expression of IL-7, IL-10, and IL-13 mRNA by CD4+CD11c+CD3− DC isolated ex vivo from tonsillar germinal centers. Thus, CD14+-derived DC expressing IL-10 and factor XIIIa seemed more closely related to germinal center dendritic cellsGCDC than to Langerhans cells.

Requirement for IRF-1 in the microenvironment supporting development of natural killer cells

Natural killer (NK) cells are critical for both innate and adaptive immunity. The development of NK cells requires interactions between their progenitors and the bone-marrow microenvironment; however, little is known about the molecular nature of such interactions. Mice that do not express the transcription factor interferon-regulatory factor-1 (IRF-1; such mice are IRF-1(-/-) mice) have been shown to exhibit a severe NK-cell deficiency. Here we demonstrate that the lack of IRF-1 affects the radiation-resistant cells that constitute the microenvironment required for NK-cell development, but not the NK-cell progenitors themselves. We also show that IRF-1(-/-) bone-marrow cells can generate functional NK cells when cultured with the cytokine interleukin-15 and that the interleukin-15 gene is transcriptionally regulated by IRF-1. These results reveal, for the first time, a molecular mechanism by which the bone-marrow microenvironment supports NK-cell development.

HLA class I-specific inhibitory receptors in human T lymphocytes: interleukin 15-induced expression of CD94/NKG2A in superantigen- or alloantigen-activated CD8+ T cells

A fraction of human T lymphocytes, predominantly CD8+, express receptors for HLA class I molecules typical of natural killer cells (natural killer receptors or NKRs) that inhibit T cell receptor-mediated functions. Herein, we analyzed possible mechanism(s) leading to the expression of NKRs by T cells responding to superantigens or allogeneic cells in vitro. We show that, in the presence of interleukin 15 (IL-15), T cells (depleted of NKR+ cells) responding to toxic shock syndrome toxin 1 de novo express CD94, a molecule that is part of a heterodimeric NKR with a broad specificity for different HLA class I alleles. Maximal CD94 expression occurred when IL-15 was added shortly after the cells were placed into culture, and CD94 expression started 4-6 days after addition of IL-15. Although both CD4+ and CD8+ cells expressed CD94, the simultaneous expression of NKG2A (i.e., the other component of the CD94/NKG2A inhibitory NKR) was confined to CD8+ cells. Similar data were obtained in T cell populations activated in mixed lymphocyte cultures in the presence of IL-15. The expression of CD94/NKG2A led to an impairment of allo-specific cytolytic activity by mixed lymphocyte culture-derived T cell populations or clones. Remarkably, cytolysis could be restored by the addition of anti-CD94 mAb, i.e., by masking the inhibitory NKRs.

Cytokines in exertion-induced skeletal muscle injury

Cytokines are a diverse family of intercellular signaling proteins that influence the movement, proliferation, differentiation, metabolism and membrane processes of target cells. Synthesis and release of cytokines from leukocytes in response to microbial stimuli are well known. This review, however, will present evidence that non-infectious stimuli can induce cytokine secretion from leukocytes and other cells (including muscle cells) following myocellular injury. The biological actions and potential adaptive values of these cytokines through the course of muscle necrosis and regeneration will be described.

Suppression of proliferation and phosphorylation of Jak3 and STAT5 in malignant T-cell lymphoma cells by derivatives of octylamino-undecyl-dimethylxanthine

IL-2R signal transduction involves tyrosine phosphorylation of several proteins including Jak3 and STAT5. In the present study we examined the effect of two octylamino-undecyl-dimethylxanthine (OUDMX) derivatives, designated CT2576 and CT5589, on proliferation and protein tyrosine phosphorylation in human malignant T-cell lymphoma lines. These T-cell lines (PB-1, 2A, and 2B), obtained from a progressive T-cell lymphoma involving skin, are IL-2 independent but have constitutively activated IL-2R-associated signal transduction pathway common to IL-2 and several other cytokines: IL-4, IL-7, IL-9, and IL-15. CT2576, characterized previously on the functional level as an inhibitor of IL-2 signaling and, on the biochemical level, as an inhibitor of phosphatidic acid biosynthesis, suppressed completely growth of the malignant T cell lymphoma lines. CT5589 which is a novel analog of the CT2576, displayed a similar, although weaker, effect. Furthermore, both CT compounds inhibited constitutive tyrosine phosphorylation of two proteins: Jak3 and STAT5 which are key downstream elements in the signal transduction pathway activated by IL-2 and the other cytokines. The CT compounds inhibited also Jak3 phosphorylation induced by IL-2 in the IL-2 dependent SZ-4 cells. Inhibition of phosphorylation by CT2576 and CT5589 was only partially selective since phosphorylation of several other proteins was also affected. Phosphorylation of many others was, however, unaffected. These findings demonstrate that the OUDMX derivatives suppress proliferation of malignant T lymphocytes. Furthermore, they suggest that this suppression may be mediated by inhibition of the IL-2R-associated Jak/STAT signaling pathway. A potential role for OUDMX derivatives in therapy of human T-cell lymphoma should be further explored.

Translational Efficiency Is Up-Regulated by Alternative Exon in Murine IL-15 mRNA

IL-15 promotes the growth of T cells and shares properties of IL-2. IL-2 is produced exclusively by T cells, while IL-15 message is expressed by a variety of tissues. However, it has been difficult to demonstrate IL-15 in the supernatants of many cells that express message for this cytokine. This suggests that IL-15 production is regulated by post-transcriptional controls. In this study, we cloned three types of murine IL-15 cDNA isoforms generated by alternative splicing and compared the translational efficiency among these isoforms. The translational efficiency of isoforms with alternative exon 5 containing another 3′ splice site was significantly higher than that of IL-15 cDNA with originally described exon 5, which is generated by internal splicing of alternative exon 5. The translation product of the isoform containing alternative exon 5 has a shorter open reading frame due to stop codons in additional sequence, followed by a new AUG codon, and displays a shorter leader sequence. The shorter isoform of the IL-15 was detected in peritoneal macrophages stimulated with IFN-γ and LPS, which expressed an abundant level of alternative exon 5. These results suggest that normal IL-15 production in stimulated macrophages is regulated by splicing of alternative exon 5.

IL-15 mRNA expression is up-regulated in blood and cerebrospinal fluid mononuclear cells in multiple sclerosis (MS)

IL-15, produced by monocytes and epithelial cells, is a novel cytokine with actions similar to IL-2. IL-15 induces T cell proliferation, B cell maturation and natural killer (NK) cell cytotoxicity, and is a chemoattractant for T cells. We investigated the expression of IL-15 mRNA in blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) in MS, an inflammatory disease of the central nervous system where cytokines are involved. MS patients had higher numbers of IL-15 mRNA-expressing blood MNC than patients with aseptic meningo-encephalitis (AM) and healthy controls. In CSF, MS patients had even higher numbers of IL-15 mRNA-expressing cells than in blood. This discrepancy between IL-15 mRNA expression between blood and CSF MNC was not seen in AM patients. Patients examined during the secondary chronic-progressive phase of MS had higher numbers of IL-15 mRNA-expressing blood MNC compared with patients examined during the relapsing-remitting phase. Levels of IL-15 mRNA-positive blood MNC were similar in patients with AM, myasthenia gravis, non-inflammatory neurological diseases and healthy controls. Taken together these data indicate that IL-15 mRNA expression is up-regulated in MS, further suggesting a role for proinflammatory cytokines in the pathogenesis of MS.