Il-17 mobilizes peripheral blood stem cells with short- and long-term repopulating ability in mice

Endosome Traffic Modulates Pro-Inflammatory Signal Transduction in CD4+ T Cells-Implications for the Pathogenesis of Systemic Lupus Erythematosus

Endocytic recycling regulates the cell surface receptor composition of the plasma membrane. The surface expression levels of the T cell receptor (TCR), in concert with signal transducing co-receptors, regulate T cell responses, such as proliferation, differentiation, and cytokine production. Altered TCR expression contributes to pro-inflammatory skewing, which is a hallmark of autoimmune diseases, such as systemic lupus erythematosus (SLE), defined by a reduced function of regulatory T cells (Tregs) and the expansion of CD4⁺ helper T (Th) cells. The ensuing secretion of inflammatory cytokines, such as interferon-γ and interleukin (IL)-4, IL-17, IL-21, and IL-23, trigger autoantibody production and tissue infiltration by cells of the adaptive and innate immune system that induce organ damage. Endocytic recycling influences immunological synapse formation by CD4⁺ T lymphocytes, signal transduction from crosslinked surface receptors through recruitment of adaptor molecules, intracellular traffic of organelles, and the generation of metabolites to support growth, cytokine production, and epigenetic control of DNA replication and gene expression in the cell nucleus. This review will delineate checkpoints of endosome traffic that can be targeted for therapeutic interventions in autoimmune and other disease conditions.

A Review of Advances in Hematopoietic Stem Cell Mobilization and the Potential Role of Notch2 Blockade

Hematopoietic stem cell (HSC) transplantation can be a potential cure for hematological malignancies and some nonhematologic diseases. Hematopoietic stem and progenitor cells (HSPCs) collected from peripheral blood after mobilization are the primary source to provide HSC transplantation. In most of the cases, mobilization by the cytokine granulocyte colony-stimulating factor with chemotherapy, and in some settings, with the CXC chemokine receptor type 4 antagonist plerixafor, can achieve high yield of hematopoietic progenitor cells (HPCs). However, adequate mobilization is not always successful in a significant portion of donors. Research is going on to find new agents or strategies to increase HSC mobilization. Here, we briefly review the history of HSC transplantation, current mobilization regimens, some of the novel agents that are under investigation for clinical practice, and our recent findings from animal studies regarding Notch and ligand interaction as potential targets for HSPC mobilization.

Mobilized peripheral blood: an updated perspective

Enforced egress of hematopoietic stem cells (HSCs) out of the bone marrow (BM) into the peripheral circulation, termed mobilization, has come a long way since its discovery over four decades ago. Mobilization research continues to be driven by the need to optimize the regimen currently available in the clinic with regard to pharmacokinetic and pharmacodynamic profile, costs, and donor convenience. In this review, we describe the most recent findings in the field and how we anticipate them to affect the development of mobilization strategies in the future. Furthermore, the significance of mobilization beyond HSC collection, i.e. for chemosensitization, conditioning, and gene therapy as well as a means to study the interactions between HSCs and their BM microenvironment, is reviewed. Open questions, controversies, and the potential impact of recent technical progress on mobilization research are also highlighted.

Hematopoietic stem and multipotent progenitor cells produce IL-17, IL-21 and other cytokines in response to TLR signals associated with late apoptotic products and augment memory Th17 and Tc17 cells in the bone marrow of normal and lupus mice

We studied effects of early and late apoptotic (necroptotic) cell products, related damage associated alarmins and TLR agonists, on hematopoietic stem and progenitor cells (HSPC). Surprisingly, normal HSPC themselves produced IL-17 and IL-21 after 1½days of stimulation, and the best stimulators were TLR 7/8 agonist; HMGB1-DNA; TLR 9 agonist, and necroptotic B cells. The stimulated HSPC expressed additional cytokines/mediators, directly causing rapid expansion of IL-17(+) memory CD4 T (Th17), and CD8 T (Tc17) cells, and antigen-experienced IL-17(+) T cells with "naïve" phenotype. In lupus marrow, HSPC were spontaneously pre-stimulated by endogenous signals to produce IL-17 and IL-21. In contrast to HSPC, megakaryocyte progenitors (MKP) did not produce IL-17, and unlike HSPC, they could process and present particulate apoptotic autoantigens to augment autoimmune memory Th17 response. Thus abnormally stimulated primitive hematopoietic progenitors augment expansion of IL-17 producing immune and autoimmune memory T cells in the bone marrow, which may affect central tolerance.

Interleukin-17 and its implication in the regulation of differentiation and function of hematopoietic and mesenchymal stem cells

Adult stem cells have a great potential applicability in regenerative medicine and cell-based therapies. However, there are still many unresolved issues concerning their biology, and the influence of the local microenvironment on properties of stem cells has been increasingly recognized. Interleukin (IL-) 17, as a cytokine implicated in many physiological and pathological processes, should be taken into consideration as a part of a regulatory network governing tissue-associated stem cells' fate. This review is focusing on the published data on the effects of IL-17 on the properties and function of hematopoietic and mesenchymal stem cells and trying to discuss that IL-17 achieves many of its roles by acting on adult stem cells.

Requirement of TPO/c-mpl for IL-17A-induced granulopoiesis and megakaryopoiesis

IL-17A is a critical, proinflammatory cytokine essential to host defense and is induced in response to microbial invasion. It stimulates granulopoiesis, leading to neutrophilia, neutrophil activation, and mobilization. TPO synergizes with other cytokines in stimulating and expanding hematopoietic progenitors, also leading to granulopoiesis and megakaryopoiesis, and is required for thrombocytopoiesis. We investigated the effects of in vivo expression of IL-17A on granulopoiesis and megakaryopoiesis in TPO receptor c-mpl-/- mice. IL-17A expression expanded megakaryocytes by 2.5-fold in normal mice but had no such effect in c-mpl-/- mice. The megakaryocyte expansion did not result in increased peripheral platelet counts. IL-17A expression did not impact bone marrow precursors in c-mpl-/- mice; however, it expanded splenic precursors, although to a lesser extent compared with normal controls (CFU-HPP). No peripheral neutrophil expansion was observed in c-mpl-/- mice. Moreover, in c-mpl-/- mice, release of IL-17A downstream cytokines was reduced significantly (KC, MIP-2, GM-CSF). The data suggest that IL-17A requires the presence of functional TPO/c-mpl to exert its effects on granulopoiesis and megakaryopoiesis. Furthermore, IL-17A and its downstream cytokines are important regulators and synergistic factors for the physiologic function of TPO/c-mpl on hematopoiesis.

The nucleotide sugar UDP-glucose mobilizes long-term repopulating primitive hematopoietic cells

Hematopoietic stem progenitor cells (HSPCs) are present in very small numbers in the circulating blood in steady-state conditions. In response to stress or injury, HSPCs are primed to migrate out of their niche to peripheral blood. Mobilized HSPCs are now commonly used as stem cell sources due to faster engraftment and reduced risk of posttransplant infection. In this study, we demonstrated that a nucleotide sugar, UDP-glucose, which is released into extracellular fluids in response to stress, mediates HSPC mobilization. UDP-glucose-mobilized cells possessed the capacity to achieve long-term repopulation in lethally irradiated animals and the ability to differentiate into multi-lineage blood cells. Compared with G-CSF-mobilized cells, UDP-glucose-mobilized cells preferentially supported long-term repopulation and exhibited lymphoid-biased differentiation, suggesting that UDP-glucose triggers the mobilization of functionally distinct subsets of HSPCs. Furthermore, co-administration of UDP-glucose and G-CSF led to greater HSPC mobilization than G-CSF alone. Administration of the antioxidant agent NAC significantly reduced UDP-glucose-induced mobilization, coinciding with a reduction in RANKL and osteoclastogenesis. These findings provide direct evidence demonstrating a potential role for UDP-glucose in HSPC mobilization and may provide an attractive strategy to improve the yield of stem cells in poor-mobilizing allogeneic or autologous donors.

Abrogated RANKL expression in properdin-deficient mice is associated with better outcome from collagen-antibody-induced arthritis

Introduction

Properdin amplifies the alternative pathway of complement activation. In the present study, we evaluated its role in the development of collagen antibody-induced arthritis (CAIA).

Methods

Arthritis was induced by intraperitoneal injection of a collagen antibody cocktail into properdin-deficient (KO) and wild-type (WT) C57BL/6 mice. Symptoms of disease were evaluated daily. The degree of joint damage was assessed histologically and with immunostaining for bone-resorption markers. Phenotypes of cell populations, their receptor expression, and intracellular cytokine production were determined with flow cytometry. Osteoclast differentiation of bone marrow (BM) precursors was evaluated by staining for tartrate-resistant acid phosphatase (TRAP).

Results

Properdin-deficient mice developed less severe CAIA than did WT mice. They showed significantly improved clinical scores and downregulated expression of bone-resorption markers in the joints at day 10 of disease. The frequencies of Ly6G⁺CD11b⁺ cells were fewer in BM, blood, and synovial fluid (SF) of KO than of WT CAIA mice. The receptor activator of nuclear factor κB ligand (RANKL) was downregulated on arthritic KO neutrophils from BM and the periphery. Decreased C5a amounts in KO SF contributed to lower frequencies of CD5aR⁺-bearing neutrophils. In blood, surface C5aR was detected on KO Ly6G⁺ cells as a result of low receptor engagement. Circulating CD4⁺ T cells had an altered ability to produce interleukin (IL)-17 and interferon (IFN)-γ and to express RANKL. In KO CAIA mice, decreased frequencies of CD4⁺ T cells in the spleen were related to low CD86 expression on Ly6G^highCD11b⁺ cells. Arthritic KO T cells spontaneously secreted IFN-γ but not IL-17 and IL-6, and responded to restimulation with less-vigorous cytokine production in comparison to WT cells. Fewer TRAP-positive mature osteoclasts were found in KO BM cell cultures.

Conclusions

Our data show that the active involvement of properdin in arthritis is related to an increased proinflammatory cytokine production and RANKL expression on immune cells and to a stimulation of the RANKL-dependent osteoclast differentiation.

The dysregulation of cytokine networks in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease associated with chronic immune activation and tissue damage. Organ damage in SLE results from the deposition of immune complexes and the infiltration of activated T cells into susceptible organs. Cytokines are intimately involved in every step of the SLE pathogenesis. Defective immune regulation and uncontrolled lymphocyte activation, as well as increased antigen presenting cell maturation are all influenced by cytokines. Moreover, expansion of local immune responses as well as tissue infiltration by pathogenic cells is instigated by cytokines. In this review, we describe the main cytokine abnormalities reported in SLE and discuss the mechanisms that drive their aberrant production as well as the pathogenic pathways that their presence promotes.

Combined effect of IL-17 and blockade of nitric oxide biosynthesis on haematopoiesis in mice

AIM

The study was undertaken to extend our investigation concerning both the in vivo activity of interleukin (IL)-17 and the specific role of nitric oxide (NO) in IL-17-induced effects in the process of haematopoiesis.

METHODS

CBA mice were simultaneously treated with IL-17 and/or nitric oxide synthase (NOS) inhibitor, l-NAME, for 5 days and changes within various haematopoietic cell lineages in bone marrow, spleen and peripheral blood were analysed.

RESULTS

Findings showed that administration of both IL-17 and l-NAME stimulated increase in net haematopoiesis in normal mice. IL-17-enhanced myelopoiesis was characterized by stimulation of both femoral and splenic haematopoietic progenitor cells and morphologically recognizable granulocytes. Additionally, IL-17 induced alterations in the frequency of erythroid progenitor cells in both bone marrow and spleen, accompanied with their mobilization to the peripheral blood. As a consequence of these changes in the erythroid cell compartments, significant reticulocytosis was observed, which evidenced that in IL-17-treated mice effective erythropoiesis occurred. Exposure of mice to NOS inhibitor also increased the number of both granulocyte-macrophage and erythroid progenitors in bone marrow and spleens, and these alterations were followed by the mobilization of erythroid progenitors and elevated content of reticulocytes in peripheral blood. The specific role of NO in IL-17-induced haematopoiesis was demonstrated only in the IL-17-reducing effect on bone marrow late stage erythroid progenitors, CFU-E.

CONCLUSION

The results demonstrated the involvement of both IL-17 and NO in the regulation of haematopoietic cell activity in various haematopoietic compartments. They further suggest that IL-17 effects are differentially mediated depending on the haematopoietic microenvironments.

IL-17A controls IL-17F production and maintains blood neutrophil counts in mice

G-CSF, its receptor, and IL-17 receptor A (IL-17RA) are all required to maintain baseline neutrophil counts in mice. In this study, we tested whether IL-17F could compensate and maintain baseline neutrophil counts in the absence of IL-17A. Unlike the reduced neutrophil counts found in IL-17RA-deficient mice, neutrophil counts were mildly increased in IL-17A-deficient (Il17a(-/-)) animals. There was no evidence for infection or altered neutrophil function. Plasma G-CSF and IL-17F levels were elevated in Il17a(-/-) compared with wild-type mice. IL-17F was mainly produced in the spleen and mesenteric lymph nodes, but IL-23 was unaltered in Il17a(-/-) mice. Instead, Il17a(-/-) splenocytes differentiated with IL-6, TGF-beta, and IL-23 ex vivo produced significantly more IL-17F in response to IL-23 than wild-type cells. Adding rIL-17A to Il17a(-/-) splenocyte cultures reduced IL-17F mRNA and protein secretion. These effects were also observed in wild-type but not IL-17RA-deficient cells. We conclude that IL-17A mediated suppression of IL-17F production and secretion requires IL-17RA and is relevant to maintain the normal set point of blood neutrophil counts in vivo.

p38 MAPK signaling mediates IL-17-induced nitric oxide synthase expression in bone marrow cells

The effects of interleukin (IL)-17 on nitric oxide (NO) synthase (NOS) expression, as well as the participation of mitogen-activated protein kinases (MAPKs) in IL-17-mediated effects were examined in murine bone marrow cells. The results demonstrated the ability of IL-17 to upregulate the expression of mRNA for both inducible NOS and constitutive, endothelial NOS isoforms, as well as to enhance the phosphorylation of p38 MAPK. Moreover, both the NOS-inducing effect of IL-17 and the in vitro IL-17-mediated inhibition colony forming unit-erythroid (CFU-E) growth were dependent on p38 MAPK activity. The data demonstrating that the in vivo reducing effect of IL-17 on bone marrow CFU-E was prevented by co-treatment with the NOS inhibitor Nw-nitro-l-arginine methyl ester hydrochloride (L-NAME), implied that this effect is mediated through NOS activation. Besides revealing a link between the IL-17, NO, and haematopoiesis, data presented gave an insight into the mechanisms by which IL-17 exerts its modulatory effects on bone marrow cells.

Maitake beta-glucan enhances umbilical cord blood stem cell transplantation in the NOD/SCID mouse

Beta glucans are cell wall constituents of yeast, fungi and bacteria, as well as mushrooms and barley. Glucans are not expressed on mammalian cells and are recognized as pathogen-associated molecular patterns (PAMPS) by pattern recognition receptors (PRR). Beta glucans have potential activity as biological response modifiers for hematopoiesis and enhancement of bone marrow recovery after injury. We have reported that Maitake beta glucan (MBG) enhanced mouse bone marrow (BMC) and human umbilical cord blood (CB) cell granulocyte-monocyte colony forming unit (GM-CFU) activity in vitro and protected GM-CFU forming stem cells from doxorubicin (DOX) toxicity. The objective of this study was to determine the effects of MBG on expansion of phenotypically distinct subpopulations of progenitor and stem cells in CB from full-term infants cultured ex vivo and on homing and engraftment in vivo in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse. MBG promoted a greater expansion of CD34+CD33+CD38- human committed hematopoietic progenitor (HPC) cells compared to the conventional stem cell culture medium (P = 0.002 by ANOVA). CD34+CXCR4+CD38- early, uncommitted human hematopoietic stem cell (HSC) numbers showed a trend towards increase in response to MBG. The fate of CD34+ enriched CB cells after injection into the sublethally irradiated NOS/SCID mouse was evaluated after retrieval of xenografted human CB from marrow and spleen by flow cytometric analysis. Oral administration of MBG to recipient NOS/SCID mice led to enhanced homing at 3 days and engraftment at 6 days in mouse bone marrow (P = 0.002 and P = 0.0005, respectively) compared to control mice. More CD34+ human CB cells were also retrieved from mouse spleen in MBG treated mice at 6 days after transplantation. The studies suggest that MBG promotes hematopoiesis through effects on CD34+ progenitor cell expansion ex vivo and when given to the transplant recipient could enhance CD34+ precursor cell homing and support engraftment.

IL-17F/IL-17R interaction stimulates granulopoiesis in mice

OBJECTIVE

IL-17F, a member of the interleukin (IL)-17 cytokine family, most closely resembles IL-17A structurally. IL-17A is a potent stimulator of granulopoiesis; its expression is induced in response to microbial challenge. Although IL-17F is considered to be a weak IL-17A analog that is also mediating its effect via IL-17R, its exact role and in vivo functions are unknown. Our goal was to determine the in vivo activity of IL-17F on granulopoiesis as well as on release of granulopoiesis-stimulating downstream cytokines in mice and directly compare its effect to IL-17A.

MATERIALS AND METHODS

Murine IL-17A (mIL-17A) or IL-17F (mIL-17F) was expressed in vivo in C57BL6 mice using adenoviral gene transfer technology. Peripheral cell counts were assessed as well as hematopoietic precursors using colony-forming assays at set time points. Downstream cytokines were measured using enzyme-linked immunosorbent assay and reverse transcriptase polymerase chain reaction.

RESULTS

We found mIL-17F to have similar expression kinetics as mIL-17A in splenocytes in vitro and in vivo, following challenge with microbial agents. Overexpression of mIL-17F in vivo resulted in similar neutrophilia and only in slightly reduced myeloid progenitor expansion when compared to mIL-17A. In vivo, there was no difference in releases for granulocyte-macrophage colony-stimulating factor; regulated on activation, normal T expressed and secreted; interferon-inducible protein-10; IL-6; and monocyte chemotactic protein-1 between either cytokine. IL-1A, macrophage inflammatory protein -2 (MIP), KC, and granulocyte colony-stimulating factor expression was approximately half of that seen with mIL-17A.

CONCLUSION

Both IL-17A and IL-17F are induced by similar stimuli, have similar expression kinetics and despite only minimal in vitro activity for IL-17F, surprisingly they exert similar in vivo bioactivity. IL-17F bioactivity appears to be augmented in vivo through mechanisms that require further investigation.

Mobilization of hematopoietic stem and progenitor cells in mice

Animal models have added significantly to our understanding of the mechanism(s) of hematopoietic stem and progenitor cell (HSPC) mobilization. Such models suggest that changes in the interaction between the HSPC and the hematopoietic microenvironmental 'niche' (cellular and extracellular components) are critical to the process. The increasing availability of recombinant proteins (growth factors, cytokines, chemokines), antibodies, drugs (agonists and antagonists), and mutant and genetically modified animal models [gene knock-in (KI) and knock-out (KO)] continue to add to the tools available to better understand and manipulate mobilization processes.

Interleukin-17 augments tumor necrosis factor-alpha-induced granulocyte and granulocyte/macrophage colony-stimulating factor release from human colonic myofibroblasts

BACKGROUND

Interleukin (IL)-17 is a newly identified T-cell-specific cytokine. In this study, we investigated the effects of IL-17 on colony-stimulating factor (CSF) release in human colonic subepithelial myofibroblasts (SEMFs).

METHODS

CSF release and mRNA expression were determined by enzyme-linked immunosorbent assay (ELISA) and Northern blotting, respectively. Nuclear factor (NF)-kappaB- and activating protein (AP-1)-DNA binding activities were evaluated by electrophoretic gel mobility shift assays (EMSAs).

RESULTS

Unstimulated cells secreted a small amount of granulocyte G- and granulocyte/macrophage (GM)-CSF, and a considerable amount of M-CSF. IL-17 weakly enhanced G-CSF release, but did not affect GM- and M-CSF release. IL-17 selectively enhanced tumor necrosis factor (TNF)-alpha-induced G- and GM-CSF release. The combination of IL-17 plus TNF-alpha induced a marked increase in NF-kappaB- and AP-1-DNA binding activities. The adenovirus-mediated transfer of a stable form of IkappaBalpha and/or a dominant negative mutant of c-Jun markedly inhibited the IL-17 plus TNF-alpha-induced G- and GM-CSF mRNA expression. Furthermore, a stability study showed that IL-17 plus TNF-alpha markedly enhanced the stability of G- and GM-CSF mRNA.

CONCLUSIONS

IL-17 augments TNF-alpha-induced G- and GM-CSF release via transcriptional and posttranscriptional mechanisms.

The biology of hematopoietic stem cells

Rarely has so much interest from the lay public, government, biotechnology industry, and special interest groups been focused on the biology and clinical applications of a single type of human cell as is today on stem cells, the founder cells that sustain many, if not all, tissues and organs in the body. Granting organizations have increasingly targeted stem cells as high priority for funding, and it appears clear that the evolving field of tissue engineering and regenerative medicine will require as its underpinning a thorough understanding of the molecular regulation of stem cell proliferation, differentiation, self-renewal, and aging. Despite evidence suggesting that embryonic stem (ES) cells might represent a more potent regenerative reservoir than stem cells collected from adult tissues, ethical considerations have redirected attention upon primitive cells residing in the bone marrow, blood, brain, liver, muscle, and skin, from where they can be harvested with relative sociological impunity. Among these, it is arguably the stem and progenitor cells of the mammalian hematopoietic system that we know most about today, and their intense study in rodents and humans over the past 50 years has culminated in the identification of phenotypic and molecular genetic markers of lineage commitment and the development of functional assays that facilitate their quantitation and prospective isolation. This review focuses exclusively on the biology of hematopoietic stem cells (HSCs) and their immediate progeny. Nevertheless, many of the concepts established from their study can be considered fundamental tenets of an evolving stem cell paradigm applicable to many regenerating cellular systems.

Neutrophil-derived MMP-9 mediates synergistic mobilization of hematopoietic stem and progenitor cells by the combination of G-CSF and the chemokines GRObeta/CXCL2 and GRObetaT/CXCL2delta4

Mobilized peripheral blood stem cells (PBSCs) are widely used for transplantation, but mechanisms mediating their release from marrow are poorly understood. We previously demonstrated that the chemokines GRObeta/CXCL2 and GRObetaT/CXCL2Delta4 rapidly mobilize PBSC equivalent to granulocyte colony-stimulating factor (G-CSF) and are synergistic with G-CSF. We now show that mobilization by GRObeta/GRObetaT and G-CSF, alone or in combination, requires polymorphonuclear neutrophil (PMN)-derived proteases. Mobilization induced by GRObeta/GRObetaT is associated with elevated levels of plasma and marrow matrix metalloproteinase 9 (MMP-9) and mobilization and MMP-9 are absent in neutrophil-depleted mice. G-CSF mobilization correlates with elevated neutrophil elastase (NE), cathepsin G (CG), and MMP-9 levels within marrow and is partially blocked by either anti-MMP-9 or the NE inhibitor MeOSuc-Ala-Ala-Pro-Val-CMK. Mobilization and protease accumulation are absent in neutrophil-depleted mice. Synergistic PBSC mobilization observed when G-CSF and GRObeta/GRObetaT are combined correlates with a synergistic rise in the level of plasma MMP-9, reduction in marrow NE, CG, and MMP-9 levels, and a coincident increase in peripheral blood PMNs but decrease in marrow PMNs compared to G-CSF. Synergistic mobilization is completely blocked by anti-MMP-9 but not MeOSuc-Ala-Ala-Pro-Val-CMK and absent in MMP-9-deficient or PMN-depleted mice. Our results indicate that PMNs are a common target for G-CSF and GRObeta/GRObetaT-mediated PBSC mobilization and, importantly, that synergistic mobilization by G-CSF plus GRObeta/GRObetaT is mediated by PMN-derived plasma MMP-9.

Interleukin 17: an example for gene therapy as a tool to study cytokine mediated regulation of hematopoiesis

Interleukin 17 (IL-17) is an essential proinflammatory T-cell derived cytokine with various biological actions. IL-17 was found to have a pivotal role in microbial host defense by interconnecting lymphoid and myeloid host defense. It also acts as a stimulatory hematopoietic cytokine by expanding myeloid progenitors and initiating proliferation of mature neutrophils. This article summarizes results to date on IL-17 research and discusses gene therapy based strategies that were employed to determine its biological functions and significance. A comprehensive working model for IL-17 is introduced.

Interleukin 17 modulates the immune response to vaccinia virus infection

Interleukin 17 (IL-17) is a newly identified cytokine that has a homolog in herpesvirus saimiri. We inserted murine IL-17 into vaccinia virus to study the role of IL-17 in viral infection. Vaccinia virus expressing IL-17 (vv-IL17) and its parental control virus (vv-pRB) grew to similar titers in vitro; however, vv-IL17 was more virulent in mice with a threefold lower LD(50) than for vv-pRB, and mean time to death of 2.8 days versus 4.5 days. Mice infected with vv-IL17 had higher titers of virus in the ovaries (P < 0.02) and showed a decrease in NK cell cytotoxicity (P < 0.02) on day 3 after infection. No significant difference was found in CTL activity. In addition, a significant decrease in IgG2a (P < 0.01) and increases in IgG1, IgG3, and IgA (P < 0.03) vaccinia virus-specific antibody titers were observed in mice infected with vv-IL17 versus vv-pRB, suggesting a Th-2-like response to infection. These data indicate that IL-17 modulates the immune response during virus infection.

Cutting edge: IL-17D, a novel member of the IL-17 family, stimulates cytokine production and inhibits hemopoiesis

A novel cytokine termed IL-17D was cloned using nested RACE PCR. It is a secreted cytokine with homology to the IL-17 family of proteins. IL-17D is preferentially expressed in skeletal muscle, brain, adipose tissue, heart, lung, and pancreas. Treatment of endothelial cells with purified rIL-17D protein stimulated the production of IL-6, IL-8, and GM-CSF. The increased expression of IL-8 was found to be NF-kappa B-dependent. rIL-17D also demonstrated an inhibitory effect on hemopoiesis of myeloid progenitor cells in colony formation assays.