Interleukin-15 mRNA is expressed by human keratinocytes Langerhans cells, and blood-derived dendritic cells and is downregulated by ultraviolet B radiation

Molecular, cellular, and functional characterization of chicken cytokines homologous to mammalian IL-15 and IL-2

DNA sequence analysis of a chicken interleukin (IL)-15 cDNA identified a 187 amino acid open reading frame encoding a protein with a predicted molecular weight of 21,964Da, two potential N-linked glycosylation sites, four highly conserved Cys residues, two out-of-frame AUG initiation codons in the 5' untranslated region, and an unusually long (66 amino acid) signal peptide such that the expected size of the mature protein is 14,462Da. Chicken IL-15 and IL-2 were compared with regard to their molecular, cellular, and functional characteristics. The predicted amino acid sequences of both chicken cytokines showed greater homologies with mammalian IL-15s compared with mammalian IL-2s. Northern hybridization and RT-PCR demonstrated chicken IL-15 gene transcripts in a wide variety of tissues and cell types while the chicken IL-2 gene was expressed only in concanavalin A (con A)-activated spleen cells. Both recombinant cytokines stimulated the growth of spleen T-cells and enhanced the activity of natural killer (NK) cells in vitro. Subcutaneous injection with an expression plasmid encoding IL-15 increased the percentage of CD3+ spleen T-lymphocytes whereas injection of an IL-2 cDNA augmented CD3+, CD4+, CD8+, T-cell receptor (TCR)1+, and TCR2+ T-cells. Collectively, these results indicate that chicken IL-15 and IL-2 are T-cell growth factors potentially capable of enhancing cell-mediated immunity in vivo.

Constitutive and interleukin-7- and interleukin-15-stimulated DNA binding of STAT and novel factors in cutaneous T cell lymphoma cells

On testing cutaneous T cell lymphoma cell lines and skin lesions, we found that the transcription factors STAT2, STAT3, STAT5, and STAT6 (STAT, signal transducer and activator of transcription) were present in the nuclei of these cells and that the binding to their specific DNA binding sites was stimulated by interleukin-7 and interleukin-15. DNA binding studies also revealed the presence of three additional DNA factors in cutaneous T cell lymphoma cells that bound to the same sequences and could also be stimulated by interleukin-7 and interleukin-15. One of these novel factors was also present in the adult T cell leukemia cell line Jurkat and malignant T cells from the blood of Sézary syndrome patients, but not in normal peripheral blood lymphocytes. It may therefore be a marker of T cell leukemia. It seems to interfere with the binding of STAT1 to the sis inducible element, suggesting that the DNA binding activity of STAT1 in cutaneous T cell lymphoma cells is disturbed.

Cytokine production by mouse myeloid dendritic cells in relation to differentiation and terminal maturation induced by lipopolysaccharide or CD40 ligation

Although it is known that dendritic cells (DCs) produce cytokines, there is little information about how cytokine synthesis is regulated during DC development. A range of cytokine mRNA/proteins was analyzed in immature (CD86-) or mature (CD86+) murine bone marrow (BM)- derived DCs. Highly purified, flow-sorted, immature DCs exhibited higher amounts of interleukin-1alpha (IL-1alpha), IL-1beta, tumor necrosis factor-alpha (TNF-alpha), transforming growth factor beta1 (TGF-beta1), and macrophage migration inhibitory factor (MIF) mRNA/protein than mature DCs. After differentiation, DC up-regulated the levels of IL-6 and IL-15 mRNA/protein and synthesized de novo mRNA/protein for IL-12p35, IL-12p40, and IL-18. Although immature BM-derived DCs did not stimulate naive allogeneic T cells, mature DCs elicited a mixed population of T helper (Th) 1 (mainly) and Th2 cells in 3d-mixed leukocyte reactions. CD86+ BM DCs switched to different cytokine patterns according to whether they were terminally differentiated by lipopolysaccharide (LPS) or CD40 ligation. Although both stimuli increased IL-6, IL-12p40, IL-15, and TNF-alpha mRNA/protein levels, only LPS up-regulated transcription of IL-1alpha, IL-1beta, IL-12p35, and MIF genes. Although LPS and CD40 cross-linking increased the T-cell allostimulatory function of BM DCs, only LPS stimulation shifted the balance of naive Th differentiation to Th1 cells, a mechanism dependent on the up-regulation of IL-12p35 and not of IL-23. These results demonstrate that, depending on the stimuli used to terminally mature BM DCs, DCs synthesize a different pattern of cytokines and exhibit distinct Th cell-driving potential.

Candidate microbicides block HIV-1 infection of human immature Langerhans cells within epithelial tissue explants

Initial biologic events that underlie sexual transmission of HIV-1 are poorly understood. To model these events, we exposed human immature Langerhans cells (LCs) within epithelial tissue explants to two primary and two laboratory-adapted HIV-1 isolates. We detected HIV-1(Ba-L) infection in single LCs that spontaneously emigrated from explants by flow cytometry (median of infected LCs = 0.52%, range = 0.08-4.77%). HIV-1-infected LCs downregulated surface CD4 and CD83, whereas MHC class II, CD80, and CD86 were unchanged. For all HIV-1 strains tested, emigrated LCs were critical in establishing high levels of infection (0.1-1 microg HIV-1 p24 per milliliter) in cocultured autologous or allogeneic T cells. HIV-1(Ba-L) (an R5 HIV-1 strain) more efficiently infected LC-T cell cocultures when compared with HIV-1(IIIB) (an X4 HIV-1 strain). Interestingly, pretreatment of explants with either aminooxypentane-RANTES (regulated upon activation, normal T cell expressed and secreted) or cellulose acetate phthalate (potential microbicides) blocked HIV-1 infection of LCs and subsequent T cell infection in a dose-dependent manner. In summary, we document HIV-1 infection in single LCs after exposure to virus within epithelial tissue, demonstrate that relatively low numbers of these cells are capable of inducing high levels of infection in cocultured T cells, and provide a useful explant model for testing of agents designed to block sexual transmission of HIV-1.

Triggering CD101 molecule on human cutaneous dendritic cells inhibits T cell proliferation via IL-10 production

Since the CD101 molecule is expressed on a major subpopulation of HLA-DR(+), CD1a(+), CD1c(+) cutaneous dendritic cells (DC), we studied the functional role of CD101 on cutaneous DC. Anti-CD101 monoclonal antibody (mAb) inhibited the proliferation of T cells induced by cutaneous DC. There was a synergistic inhibition between anti-CD101 mAb and anti-CD86/anti-CD80 mAb. Anti-CD101 mAb exerted its inhibitory effect when binding to the CD101 expressed on cutaneous DC. No positive role of CD101 putative ligand expressed by T cells in T cell proliferation was demonstrated, as T cells proliferated in response to soluble anti-CD3 mAb in the presence of CD86-transfected cells but not in the presence of CD101-transfected cells. Of major significance is the fact that IL-10 was produced by cutaneous DC after CD101 triggering with anti-CD101 mAb, while IL-10 secretion was up-regulated in mixed cutaneous DC-T cell cultures after CD101 triggering. Furthermore, IL-10-neutralizing mAb could reverse the inhibition induced by anti-CD101 mAb. Our results demonstrate that the CD101 triggering on cutaneous DC inhibits T cell proliferation via IL-10 production, suggesting an important regulatory role played by the CD101 molecule on DC during T cell activation.

IL-2-induced activation-induced cell death is inhibited in IL-15 transgenic mice

A transgenic (Tg) mouse expressing human IL-15 was generated to define the role of IL-15 in the normal immune response. Overexpression of IL-15 resulted in an increase of NK, CD44(hi)CD8 memory T cells, and gammadelta T cells. Additionally, we observed the emergence of a novel type of NK-T cells with CD8alphaalpha' expression. Due to the expansion and activation of NK cells, the IL-15Tg mouse showed enhanced innate immunity. In adaptive T cell immunity, the roles of IL-15 contrasted with those of IL-2. IL-15 inhibited IL-2-induced T cell death, which plays a role in the maintenance of peripheral self-tolerance. IL-15 thus seems to contribute to enhanced immune memory by selectively propagating memory T cells and by blocking T cell death mediated by IL-2.

Inhibition of keratinocyte apoptosis by IL-15: a new parameter in the pathogenesis of psoriasis?

Keratinocytes (KC) are important source of and targets for several cytokines. Although KC express IL-15 mRNA, the functional effects of IL-15 on these epithelial cells remain to be dissected. Investigating primary human foreskin KC and HaCaT cells, we show here by semiquantitative RT-PCR and flow cytometric analysis that both translate IL-15 and IL-15R mRNA and express IL-15 and IL-15Ralpha protein on the cell surface, suggesting that human KC can employ IL-15 for juxtacrine signaling. While IL-15 exerted no significant effect on KC proliferation and IL-6 or IL-8 secretion, IL-15 inhibited both anti-Fas and methylcellulose-induced KC apoptosis in vitro. This is in line with the recognized potent anti-apoptotic effects of IL-15. IL-2, whose receptor shares two components with the IL-15R, failed to inhibit KC apoptosis. Together with the role of IL-15 in sustaining chronic immune reactions, this invited the question of whether a reduction of KC apoptosis by IL-15 may be involved in the pathogenesis of psoriasis, a chronic hyperproliferative inflammatory skin disease characterized by abnormally low KC apoptosis in the epidermis. Remarkably, compared with nonlesional psoriatic skin and skin of healthy volunteers, lesional psoriatic epidermis showed high IL-15 protein expression in the epidermis and enhanced binding activity for IL-15. Therefore, antagonizing the inhibitory effects of IL-15 on KC apoptosis deserves exploration as a novel therapeutic strategy in psoriasis management.

HIV-infected human Langerhans cells transmit infection to human lymphoid tissue ex vivo

OBJECTIVES

To create a novel ex vivo model for early biologic events involved in sexual transmission of HIV and to demonstrate that Langerhans cells (LC), the purported initial mucosal target cells for HIV, play a critical role in this process.

METHODS

Epidermal cells containing LC were isolated from normal-appearing skin of healthy volunteers and exposed to a panel of primary and laboratory-adapted R5- and X4-HIV isolates, washed and applied to the surfaces of allogeneic tonsil tissue blocks. Viral replication was followed by measuring HIV p24 protein in culture supernatants by ELISA.

RESULTS

Both R5- and X4-HIV isolates could be transmitted by LC and established high levels of infection in lymphoid tissue (p24 > 10 ng/ml). Depletion of LC within epidermal cell suspensions abrogated the ability of HIV-exposed suspensions to transmit virus to tonsil histocultures.

CONCLUSIONS

Using a novel ex vivo model, human LC are shown for the first time to be the major epidermal cell type that is involved in transmission of HIV infection to human lymphoid tissue. Importantly, this system could prove useful in further understanding LC trafficking and other early biological events involved in primary HIV infection.

Cytokines and chemokines in the initiation and regulation of epidermal Langerhans cell mobilization

Langerhans cells (LC) are members of the wider family of dendritic cells. LC reside in the epidermis where they serve as sentinels of the immune system, their responsibilities being to sample the external environment for changes and challenges and to deliver information (antigen) to responsive T lymphocytes within skin draining lymph nodes. The ability of LC to migrate from the epidermis to regional lymph nodes is therefore of pivotal importance to the induction of cutaneous immune responses. The journey that LC have to make from the skin has a number of requirements. Initially it is necessary that LC disassociate themselves from surrounding keratinocytes and are liberated from other influences that encourage their retention in the epidermis. Subsequently, migrating LC must successfully traverse the basement membrane of the dermal-epidermal junction and make their way, via afferent lymphatics, to draining lymph nodes. Effective entry into lymph nodes is necessary, as is correct positioning of cells within the paracortex. There is increasing evidence that both cytokines and chemokines, and their interaction with appropriate receptors expressed by LC, orchestrate the mobilization and movement of these cells. We here consider the parts played by these molecules, and how collectively they induce and direct LC migration.

Epiregulin, a novel member of the epidermal growth factor family, is an autocrine growth factor in normal human keratinocytes

Epiregulin is a new member of the epidermal growth factor (EGF) family purified from conditioned medium of NIH-3T3 clone T7. Some EGF family growth factors play essential roles in human keratinocytes in an autocrine manner. We show here that epiregulin is another autocrine growth factor for human keratinocytes. Epiregulin stimulated human keratinocyte proliferation under both subconfluent and confluent culture conditions in the absence of exogenous EGF family growth factors. Immunoprecipitation of [(35)S]methionine-labeled conditioned medium revealed a 5-kDa band corresponding to epiregulin. Northern blot analysis detected a 4. 8-kilobase transcript of epiregulin, and the addition of epiregulin up-regulated epiregulin mRNA synthesis. Furthermore, an anti-epiregulin blocking antibody reduced DNA synthesis by 25%. Epiregulin up-regulated the mRNA levels of heparin-binding EGF-like growth factor (HB-EGF), amphiregulin, and TGF-alpha. In turn, the addition of EGF, HB-EGF, amphiregulin, and TGF-alpha increased epiregulin mRNA levels. These results demonstrate that epiregulin acts as an autocrine growth factor in human epidermal keratinocytes and is part of auto- and cross-induction mechanisms involving HB-EGF, amphiregulin, and TGF-alpha. The mRNA expression profile resulting from induction of differentiation with high calcium and fetal calf serum revealed the differential expression of epiregulin, HB-EGF, amphiregulin, and TGF-alpha in keratinocytes. This indicates that these four growth factors have distinct, non-redundant biological functions.

Accessory role of human peritoneal mesothelial cells in antigen presentation and T-cell growth

BACKGROUND

To assess the role of human peritoneal mesothelial cells (HPMCs) in the generation of an immune response during peritonitis, we tested their ability to activate T-cells by antigen presentation (AP) and by the secretion of interleukin-15 (IL-15). IL-15 is a potent leukocyte activator that stimulates the proliferation of CD4+, CD8+, and B and natural killer (NK) cells.

METHODS

HPMCs and mononuclear cells were derived from six volunteer patients who underwent elective abdominal surgery. Flow cytometry was used to analyze human lymphocyte antigen-DR (HLA-DR), intercellular adhesion molecule-1 (ICAM-1), and B7 molecules on HPMCs. Affinity-purified CD4 cells were used for AP assays. We used a specific enzyme-linked immunosorbent assay to detect interferon-gamma (IFN-gamma), IL-2, and IL-15 protein and reverse transcription-polymerase chain reaction for mRNA analysis.

RESULTS

HPMCs expressed HLA-DR molecules following IFN-gamma treatment. ICAM-1 molecules were expressed at high levels, and B7-1 and B7-2 molecules could not be detected. The accessory function of HPMCs was assayed by T-cell stimulation using anti-CD3 antibodies (OKT3). HPMCs were essential for a significant OKT3-induced T-cell proliferation. Anti-ICAM-1 antibodies blocked OKT3-induced proliferation. HPMCs served as effective antigen-presenting cells when Tetanus toxoid (TT) or Staphylococcus aureus-alpha-toxin were used as antigens. IFN-gamma, IL-2, and IL-15 accumulated during AP reactions. We found that IL-15 is produced by HPMCs, and IFN-gamma up-regulated its mRNA levels and protein secretion in a dose-dependent manner. We also detected IL-15 in the peritoneal effluent of patients undergoing continuous peritoneal dialysis treatment. In patients suffering from peritonitis, IL-15 levels were elevated (35.0 +/- 6.0 pg/mL, N = 10) as compared with noninfected patients (16.2 +/- 4.0 pg/mL, N = 7).

CONCLUSIONS

HPMCs participate in the peritoneal immune response against invading pathogens by AP. For this process, ICAM-1 is the major accessory molecule. In addition, HPMCs may contribute to T-cell activation by secretion of IL-15.

Interleukin-15 as an Activator of Natural Killer Cell-Mediated Antiviral Response

Natural killer (NK) cells are large granular lymphocytes capable of efficient killing of virus-infected and tumor cells in a major histocompatibility complex-independent manner. The cytotoxic killing potential of NK cells can be modulated by a variety of factors, including cytokines such as interleukin-12 (IL-12), IL-15, and interferon (IFN). IL-15 also plays an important role in NK cell development and survival. Killing of virally infected cells by NK cells is likely to represent an important antiviral defense mechanism, especially during the early phase of infection when antigen-specific immunity has yet to be generated. In the present work, we studied the potential of IL-15 to act as a modulator of NK cell-mediated antiviral defense. Our results clearly indicate that IL-15 can curtail infections by 3 human herpesviruses: Herpes simplex virus type 1, Epstein-Barr virus, and human herpesvirus 6. The antiviral activity of IL-15 is dose-, time-, and NK cell-dependent. IL-15–treated NK cells showed an increased killing potential against a variety of cells, including virus-infected target cells. Lastly, using highly purified cell population, we report that IL-15 triggers the synthesis of IFN-γ from both CD4+ and NK cells, which can act in both autocrine and paracrine fashion to modulate NK cells cytotoxic potential. In conclusion, IL-15 is a cytokine that can contribute to the establishment of an antiviral state in 2 ways: first by increasing the killing ability of NK cells and second by stimulating the synthesis and secretion of IFN.

Interleukin-15 as an Activator of Natural Killer Cell-Mediated Antiviral Response

Natural killer (NK) cells are large granular lymphocytes capable of efficient killing of virus-infected and tumor cells in a major histocompatibility complex-independent manner. The cytotoxic killing potential of NK cells can be modulated by a variety of factors, including cytokines such as interleukin-12 (IL-12), IL-15, and interferon (IFN). IL-15 also plays an important role in NK cell development and survival. Killing of virally infected cells by NK cells is likely to represent an important antiviral defense mechanism, especially during the early phase of infection when antigen-specific immunity has yet to be generated. In the present work, we studied the potential of IL-15 to act as a modulator of NK cell-mediated antiviral defense. Our results clearly indicate that IL-15 can curtail infections by 3 human herpesviruses: Herpes simplex virus type 1, Epstein-Barr virus, and human herpesvirus 6. The antiviral activity of IL-15 is dose-, time-, and NK cell-dependent. IL-15–treated NK cells showed an increased killing potential against a variety of cells, including virus-infected target cells. Lastly, using highly purified cell population, we report that IL-15 triggers the synthesis of IFN-γ from both CD4+ and NK cells, which can act in both autocrine and paracrine fashion to modulate NK cells cytotoxic potential. In conclusion, IL-15 is a cytokine that can contribute to the establishment of an antiviral state in 2 ways: first by increasing the killing ability of NK cells and second by stimulating the synthesis and secretion of IFN.

Expression and role of IL-15 in post-burn hypertrophic scars

Hypertrophic scarring is a skin disorder that occurs after wounding and thermal injury. There is accumulating evidence that immunologic processes such as infiltration of activated T lymphocytes and altered cytokine production may play a role in the formation of hypertrophic scars. Interleukin-15, a cytokine identified as a T cell growth factor, also acts as a chemoattractant for T cells and has pro-inflammatory properties. We investigated the expression and the role of this cytokine in hypertrophic scarring. IL-15 expression was compared in skin biopsies of hypertrophic scars (HS) both in active (AHS) and in remission (RHS) phases, in normotrophic scars (NTS) and in normal skin using reverse transcriptase-polymerase chain reaction and immunohistochemistry. IL-15 expression in HS was significantly higher than in NTS or normal skin. Furthermore, AHS expressed higher levels of IL-15 than RHS. Immunohistologic analysis of AHS samples showed strong IL-15 immunoreactivity in keratinocytes and Langerhans cells in the epidermis and in macrophages, fibroblasts, and dermal dendritic cells in the dermis. High levels of IL-15 expression in AHS correlated with abundant infiltration of activated CD3+ cells. Ex vivo experiments indicate that IL-15 can sustain the proliferative response of T cells derived from AHS but not from RHS and NTS. In addition, IL-15 prevents both cytokine deprivation and activation-induced apoptosis of T cells derived from AHS. Taken together, these results suggest that IL-15 can be involved in the recruitment, proliferation, and apoptosis inhibition of T cells in AHS. The findings that the evolution from an AHS to a RHS is associated with a decrease in IL15 expression, and with a loss of IL-15 responsiveness in ex vivo-cultured T cells, indicate that this cytokine plays an important role in the biology of pathologic scar formation.

The multifaceted regulation of interleukin-15 expression and the role of this cytokine in NK cell differentiation and host response to intracellular pathogens

Interleukin-15 (IL-15) is a 14- to 15-kDa member of the 4 alpha-helix bundle family of cytokines. IL-15 expression is controlled at the levels of transcription, translation, and intracellular trafficking. In particular, IL-15 protein is posttranscriptionally regulated by multiple controlling elements that impede translation, including 12 upstream AUGs of the 5' UTR, 2 unusual signal peptides, and the C-terminus of the mature protein. IL-15 uses two distinct receptor and signaling pathways. In T and NK cells the IL-15 receptor includes IL-2/15R beta and gamma c subunits, which are shared with IL-2, and an IL-15-specific receptor subunit, IL-15R alpha. Mast cells respond to IL-15 with a receptor system that does not share elements with the IL-2 receptor but uses a novel 60- to 65-kDa IL-15RX subunit. In mast cells IL-15 signaling involves Jak2/STAT5 activation rather than the Jak1/Jak3 and STAT5/STAT3 system used in activated T cells. In addition to its other functional activities in immune and nonimmune cells, IL-15 plays a pivotal role in the development, survival, and function of NK cells. Abnormalities of IL-15 expression have been described in patients with rheumatoid arthritis or inflammatory bowel disease and in diseases associated with the retroviruses HIV and HTLV-I. New approaches directed toward IL-15, its receptor, or its signaling pathway may be of value in the therapy of these disorders.

The effects of ultraviolet radiation on the human immune system

The adverse outcome of increased ultraviolet (UV) irradiation on human health is currently of concern. While many experiments have been carried out in rodent models, fewer have been designed to test the effects of UV exposure in human subjects. This review concentrates on the modulations induced in the human immune system by UV, and outlines changes in antigen presentation by Langerhans cells and macrophages, in the activities of natural killer cells and T cells, and in cytokine regulation. Precautionary measures which might be taken to help protect people against the immunosuppressive action of UV irradiation are considered.

Dendritic cell secretion of IL-15 is induced by recombinant huCD40LT and augments the stimulation of antigen-specific cytolytic T cells

Dendritic cells (DC) are professional antigen-presenting cells which stimulate strong proliferative and cytolytic T cell responses. Stimulation of CD40 on dendritic cells by its ligands and anti-CD40 antibodies induces maturation and enhances DC stimulatory ability. In order to understand the mechanism by which ligand:CD40 interactions augment DC function, we assessed the role of T cell stimulatory cytokines IL-12 and IL-15 in the function of DC stimulated with soluble trimeric CD40L, a recombinant fusion protein incorporating three covalently linked extracellular CD40L domains (huCD40LT). Peripheral blood derived DC treated with huCD40LT and/or IFN-gamma were used to stimulate T cell responses in vitro to specific antigens. DC treated with huCD40LT or IFN-gamma/huCD40LT stimulated enhanced T cell proliferation to CASTA, a soluble protein from C. albicans, induced T cells with augmented antigen-specific lysis, and increased the yield of antigen-specific IFN-gamma-producing T cells. IL-15 production by DC was enhanced in cultures treated with huCD40LT and correlated with expansion of antigen-specific cytolytic T cells. Addition of a neutralizing anti-IL-15 monoclonal antibody inhibited the expansion of viral and tumor antigen-specific T cells stimulated by IFN-gamma and huCD40LT-treated DC. In contrast, this enhanced stimulatory ability of DC did not appear to depend on synthesis of IL-12 since huCD40LT treatment stimulated the generation of antigen-specific cytokine producing and cytolytic T cells without increased IL-12 production. Addition of anti-IL-12 monoclonal antibody did not inhibit expansion of these cells. These data suggest that production of IL-15 but not IL-12 is an important factor in the enhanced immunostimulatory ability of huCD40LT-treated DC.

Constitutive and Interleukin-7/Interleukin-15 Stimulated DNA Binding of Myc, Jun, and Novel Myc-Like Proteins in Cutaneous T-Cell Lymphoma Cells

Members of the Myc and Jun/Fos gene families have been found to be expressed in late stages of cutaneous T-cell lymphoma (CTCL) and may be responsible for the transition from low-grade to high-grade tumors. The composition of these complexes is an important parameter, as the different homo- and heterodimeric jun and myc complexes can have gene transcription activating or suppressing activities. We determined the composition of the jun and myc DNA-binding complexes in three CTCL cell lines and malignant cells of seven Sézary patients by electrophoretic mobility shift assays (EMSAs) and “supershift” assays in which specific antibodies against the different members of the tested gene families were included in the binding reactions. Complexes containing JunD were found in three cell lines and two patients. The three cell lines and one patient contained also c-Myc/Max heterodimers. Because c-Myc/Max heterodimers are strong gene transcription activators and are necessary for cell-cycle progression, they may play a role in the progression of CTCL. JunD may also promote cell-cycle progression and influence the expression of cell death survival genes. Interleukin-7 (IL-7) and IL-15, which have been identified as growth factors for CTCL cells, stimulated the DNA binding of JunD and two novel c-Myc recognition site (E-box) binding proteins, but not the DNA binding of c-Myc/Max heterodimers.

Constitutive and Interleukin-7/Interleukin-15 Stimulated DNA Binding of Myc, Jun, and Novel Myc-Like Proteins in Cutaneous T-Cell Lymphoma Cells

Members of the Myc and Jun/Fos gene families have been found to be expressed in late stages of cutaneous T-cell lymphoma (CTCL) and may be responsible for the transition from low-grade to high-grade tumors. The composition of these complexes is an important parameter, as the different homo- and heterodimeric jun and myc complexes can have gene transcription activating or suppressing activities. We determined the composition of the jun and myc DNA-binding complexes in three CTCL cell lines and malignant cells of seven Sézary patients by electrophoretic mobility shift assays (EMSAs) and “supershift” assays in which specific antibodies against the different members of the tested gene families were included in the binding reactions. Complexes containing JunD were found in three cell lines and two patients. The three cell lines and one patient contained also c-Myc/Max heterodimers. Because c-Myc/Max heterodimers are strong gene transcription activators and are necessary for cell-cycle progression, they may play a role in the progression of CTCL. JunD may also promote cell-cycle progression and influence the expression of cell death survival genes. Interleukin-7 (IL-7) and IL-15, which have been identified as growth factors for CTCL cells, stimulated the DNA binding of JunD and two novel c-Myc recognition site (E-box) binding proteins, but not the DNA binding of c-Myc/Max heterodimers.

Cutting Edge: Cytokines Regulate Expression and Function of the HIV Coreceptor CXCR4 on Human Mature Dendritic Cells

HIV-infected dendritic cells (DC) efficiently transmit infection to CD4+ T cells during the process of T cell activation. To further understand interactions between DC and HIV, cytokine regulation of HIV coreceptors on cultured Langerhans cells (cLC, as prototypes of mature DC) was studied. Expression of cell surface CXCR4 on cLC was up-regulated by IL-4 and TGF-β1 and inhibited by IFN-α, IFN-β, and IFN-γ, whereas cytokines did not appreciably regulate CCR5. Changes in cell surface CXCR4 expression on cLC correlated with T cell-tropic (X4)-HIV envelope-mediated syncytium formation and X4-HIV infection levels. A relative increase in the ratio of type 2/type 1 cytokine production, which can occur in HIV disease, may up-regulate CXCR4 expression on mature DC and promote infection by X4 viruses. Importantly, these findings suggest that cytokine dysregulation may be linked to the emergence of X4-HIV strains as HIV-infected individuals progress to AIDS.

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.

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.

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.

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.

Productive infection of dendritic cells by HIV-1 and their ability to capture virus are mediated through separate pathways

There is substantial evidence that dendritic cells (DC) residing within epithelial surfaces (e.g., Langerhans cells) are the initial cells infected with HIV after mucosal exposure to virus. To study DC-HIV interactions in detail, we propagated Langerhans cell-like DC from cord blood CD34(+) cells and from adult blood plastic-adherent PBMC in the presence of cytokines (GM-CSF, IL-4, and/or TNF-alpha). DC pulsed overnight with HIVBaL or HIVIIIB were infected productively with both viral subtypes (as assessed by PCR, supernatant p24 protein levels, electron microscopy, and antibody staining). Productive infection could be blocked by anti-CD4 mAbs, RANTES (regulated upon activation, normal T cell expressed and secreted) (for HIVBaL), stromal cell-derived factor-1 (for HIVIIIB), or azidothymidine added during the HIV pulse, as well as by blocking DC proliferation. However, pulsing DC with HIV under these blocking conditions had no effect on the ability of DC to capture virus and transmit infection to cocultured antigen-stimulated CD4(+) T cells. Thus, we show by several criteria that (a) productive infection of DC and (b) the ability of DC to capture virus are mediated through separate pathways. We suggest that strategies designed to block mucosal transmission of HIV should consider interfering with both virus infection and virus capture by DC.

Photocarcinogenesis: an overview

Photocarcinogenesis represents the sum of a complex of simultaneous and sequential biochemical events that ultimately lead to the occurrence of skin cancer. These events, initiated by UV radiation of appropriate wavelength, include the formation of DNA photoproducts: DNA repair; mutation of proto-oncogenes and tumor suppressor genes; UV-production of radical species with subsequent effects on mutation and extra-nuclear function; and other epigenetic events that influence the course of carcinogenesis. The epigenetic influences may include immunological responses, antioxidant defenses, and dietary factors. This review represents an effort to provide current research results in the aforementioned areas and an attempt to meld these events into a comprehensive overview of photocarcinogenesis. If effective prevention and intervention strategies for skin cancer are to developed, a more thorough understanding of the disease process is imperative.

Pteridines in the control of pigmentation

The influence of UVB irradiation on the metabolic pathway for the production of L-tyrosine from L-phenylalanine in the human epidermis has been examined in 12 healthy volunteers with photo skin types I-VI (Fitzpatrick classification). This metabolic pathway involves the induction of GTP-cyclohydrolase 1 (GTP-CH-1), the rate-limiting enzyme for de novo synthesis of (6R)L-erythro-5,6,7,8-tetrahydrobiopterin (6-BH4). This essential cofactor controls the production of L-tyrosine from L-phenylalanine via phenylalanine hydroxylase (PAH). The de novo synthesis of 6-BH4 depends on the induction of GTP-CH-1, e.g., by tumor necrosis factor-alpha (TNF alpha). Epidermal suction blister tissues were taken before (0 h) and after (24 and 72 h) UVB exposure with a standardized dosage [1 minimal erythema dose (MED)]. In all cases, there was a significant increase in TNF alpha release, GTP-CH-1 activity, total 6-biopterin level, and PAH activity, indicative of enhanced L-tyrosine production. The response of this metabolic cascade over baseline activities was pronounced in fair photo skin types (I-III) compared to dark skin (IV-VI). Taken together, our results suggest that UVB can control the direct supply of L-tyrosine in the epidermis, and this process may represent an important factor in de novo melanogenesis.