Sarah L. Gaffen

IL-23 and IL-17 in the establishment of protective pulmonary CD4+ T cell responses after vaccination and during Mycobacterium tuberculosis challenge.

Interferon-γ is key in limiting Mycobacterium tuberculosis infection. Here we show that vaccination triggered an accelerated interferon-γ response by CD4+ T cells in the lung during subsequent M. tuberculosis infection. Interleukin 23 (IL-23) was essential for the accelerated response, for early cessation of bacterial growth and for establishment of an IL-17-producing CD4+ T cell population in the lung. The recall response of the IL-17-producing CD4+ T cell population occurred concurrently with expression of the chemokines CXCL9, CXCL10 and CXCL11. Depletion of IL-17 during challenge reduced the chemokine expression and accumulation of CD4+ T cells producing interferon-γ in the lung. We propose that vaccination induces IL-17-producing CD4+ T cells that populate the lung and, after challenge, trigger the production of chemokines that recruit CD4+ T cells producing interferon-γ, which ultimately restrict bacterial growth.

An Overview of IL-17 Function and Signaling

Since the discovery of interferons over 50 years ago, efforts to understand the biochemistry, molecular biology and biological activities of cytokines have been intense and rewarding. Although there are several hundred cytokines and receptors currently recognized, they in fact fall into a fairly limited set of subfamilies (reviewed in [Ozaki K, Leonard WJ. Cytokine and cytokine receptor pleiotropy and redundancy. J Biol Chem 2002;277:29355-58 [1]; Shen F, Gaffen SL. Structure-function relationships in the IL-17 receptor: implications for signal transduction and therapy. Cytokine 2008;41:92-104 [2]). Within these families (and in some cases even outside them), cytokines share many structural and functional features that have provided a framework for understanding their biological activities and signal transduction mechanisms. This review will focus on interleukin (IL)-17, the founding member of the newest subclass of cytokines, which has received considerable attention in the last several years due to its central role in the Th17 system.

Functional Cooperation between Interleukin-17 and Tumor Necrosis Factor-α Is Mediated by CCAAT/Enhancer-binding Protein Family Members

Interleukin (IL)-17 is a recently described cytokine involved in the amplification of inflammatory responses and pathologies. A hallmark feature of IL-17 is its ability to induce expression of other cytokines and chemokines. In addition, IL-17 potently synergizes with tumor necrosis factor-α (TNFα) to up-regulate expression of many target genes, particularly IL-6. Despite the many observations of IL-17 signaling synergy observed to date, little is known about the molecular mechanisms that underlie this phenomenon. In the osteoblastic cell line MC-3T3, we have found that IL-17 and TNFα exhibit potent synergy in mediating IL-6 secretion. Here, we show that at least part of the functional cooperation between IL-17 and TNFα occurs at the level of IL-6 gene transcription. Both the NF-κB and CCAAT/enhancer-binding protein (C/EBP; NF-IL6) sites in the IL-6 promoter are important for cooperative gene expression, but NF-κB does not appear to be the direct target of the combined signal. Microarray analysis using the Affymetrix mouse MG-U74v2 chip identified C/EBPδ as another gene target of combined IL-17- and TNFα-induced signaling. Because C/EBP family members are known to control IL-6, we examined whether enhanced C/EBPδ expression is involved in the cooperative up-regulation of IL-6 by IL-17 and TNFα. Accordingly, we show that C/EBPδ (or the related transcription factor C/EBPβ) is essential for expression of IL-6. Moreover, overexpression of C/EBPδ (and, to a lesser extent, C/EBPβ) could substitute for the IL-17 signal at the level of IL-6 transcription. Thus, C/EBP family members, particularly C/EBPδ, appear to be important for the functional cooperation between IL-17 and TNFα.

Cytokines link osteoblasts and inflammation: microarray analysis of interleukin-17- and TNF-α-induced genes in bone cells

The novel cytokine interleukin (IL)‐17 has been implicated in many infectious and autoimmune settings, especially rheumatoid arthritis. Consistent with its proinflammatory effects on bone, osteoblast cells are highly responsive to IL‐17, particularly in combination with other inflammatory cytokines. To better understand the spectrum of activities controlled by IL‐17, we globally profiled genes regulated by IL‐17 and tumor necrosis factor α (TNF‐α) in the preosteoblast cell line MC3T3‐E1. Using Affymetrix microarrays, 80–90 genes were up‐regulated, and 19–50 genes were down‐regulated with IL‐17 and TNF‐α as compared with TNF‐α alone. These included proinflammatory chemokines and cytokines, inflammatory genes, transcriptional regulators, bone‐remodeling genes, signal transducers, cytoskeletal genes, genes involved in apoptosis, and several unknown or unclassified genes. The CXC family chemokines were most dramatically induced by IL‐17 and TNF‐α, confirming the role of IL‐17 as a potent mediator of inflammation and neutrophil recruitment. Several transcription factor‐related genes involved in inflammatory gene expression were also enhanced, including molecule possessing ankyrin repeats induced by lipopolysaccharide/inhibitor of κBζ (MAIL/κBζ), CCAAT/enhancer‐binding protein δ (C/EBPδ), and C/EBPβ. We also identified the acute‐phase gene lipocalin‐2 (LCN2/24p3) as a novel IL‐17 target, which is regulated synergistically by TNF‐α and IL‐17 at the level of its promoter. A similar but not identical pattern of genes was induced by IL‐17 and TNF‐α in ST2 bone marrow stromal cells and murine embryonic fibroblasts. This study provides a profile of genes regulated by IL‐17 and TNF‐α in osteoblasts and suggests that in bone, the major function of IL‐17 is to cooperate and/or synergize with other cytokines to amplify inflammation.

CD3/CD28 Costimulation-Induced NF-κB Activation Is Mediated by Recruitment of Protein Kinase C-θ, Bcl10, and IκB Kinase β to the Immunological Synapse through CARMA1

ABSTRACT CARMA1 (also known as CARD11) is a scaffold molecule and contains a caspase-recruitment domain (CARD) and a membrane-associated guanylate kinase-like (MAGUK) domain. It plays an essential role in mediating CD3/CD28 costimulation-induced NF-κB activation. However, the molecular mechanism by which CARMA1 mediates costimulatory signals remains to be determined. Here, we show that CARMA1 is constitutively associated with the cytoplasmic membrane. This membrane association is essential for the function of CARMA1, since a mutant of CARMA1, CARMA1(L808P), that is defective in the membrane association cannot rescue CD3/CD28 costimulation-induced NF-κB activation in JPM50.6 CARMA1-deficient T cells. Although CD3/CD28 costimulation effectively induces the formation of the immunological synapse in CARMA1-deficient T cells, the recruitment of protein kinase C-θ (PKC-θ), Bcl10, and IκB kinase β (IKKβ) into lipid rafts of the immunological synapse is defective. Moreover, expression of wild-type CARMA1, but not CARMA1(L808P), restores the recruitment of PKC-θ, Bcl10, and IKKβ into lipid rafts in CARMA1-deficient T cells. Consistently, expression of a mutant CARMA1, CARMA1(ΔCD), that cannot associate with Bcl10 failed to restore CD3/CD28 costimulation-induced NF-κB activation in JPM50.6 cells, whereas expression of Bcl10-CARMA(ΔCD) fusion protein effectively restored this NF-κB activation. Together, these results indicate that CARMA1 mediates CD3/CD28 costimulation-induced NF-κB activation by recruiting downstream signaling components into the immunological synapse.

Interleukin-17 regulates expression of the CXC chemokine LIX/CXCL5 in osteoblasts: implications for inflammation and neutrophil recruitment

Interleukin (IL)‐17 is the founding member of an emerging family of inflammatory cytokines whose functions remain poorly defined. IL‐17 has been linked to the pathogenesis of rheumatoid arthritis, and numerous studies implicate this cytokine in inflammation‐induced bone loss. It is clear that a major function of IL‐17 is to amplify the immune response by triggering production of chemokines, cytokines, and cell‐surface markers, ultimately leading to neutrophil chemotaxis and inflammation. As an IL‐17 signaling deficiency in mice causes a dramatic reduction in neutrophil chemotaxis and a consequent increased susceptibility to bacterial infection, it is important to define gene targets involved in IL‐17‐mediated neutrophil trafficking. Here, we demonstrate that IL‐17 and tumor necrosis factor α (TNF‐α) cooperatively induce the lipopolysaccharide‐inducible CXC chemokine (LIX; a.k.a., CXC chemokine ligand 5, Scya5, or murine granulocyte chemotactic protein‐2) in the preosteoblast cell line MC3T3. LIX is induced rapidly at the mRNA and protein levels, likely through the activation of new gene transcription. Conditioned media from MC3T3 cells treated with IL‐17 and/or TNF‐α stimulates neutrophil mobility potently, and LIX is a significant contributing factor to this process. In addition, IL‐17 cooperates with bacterial components involved in periodontal disease to up‐regulate LIX expression. This study is the first demonstration of LIX expression in bone cells and has implications for inflammatory bone diseases such as arthritis and periodontal disease.

The Interleukin (IL)‐2 Family Cytokines: Survival and Proliferation Signaling Pathways in T Lymphocytes

Lymphocyte populations in the immune system are maintained by a well-organized balance between cellular proliferation, cellular survival and programmed cell death (apoptosis(. One of the primary functions of many cytokines is to coordinate these processes. In particular, the interleukin (IL(‐2 family of cytokines, which consists of six cytokines ‐IL‐2, IL‐4, IL‐7, IL‐9, IL‐15 and IL‐21) that all share a common receptor subunit (gc), plays a major role in promoting and maintaining T lymphocyte populations. The details of the molecular signaling pathways mediated by these cytokines have not been fully elucidated. However, the three major pathways clearly involved include the JAK/STAT, MAPK and phosphatidylinositol 3‐kinase ‐PI3K‐ pathways. The details of these pathways as they apply to the IL‐2 family of cytokines is discussed, with a focus on their roles in proliferation and survival signaling.

Biology of recently discovered cytokines: Interleukin-17 – a unique inflammatory cytokine with roles in bone biology and arthritis

IL-17 and its receptor are founding members of an emerging family of cytokines and receptors with many unique characteristics. IL-17 is produced primarily by T cells, particularly those of the memory compartment. In contrast, IL-17 receptor is ubiquitously expressed, making nearly all cells potential targets of IL-17. Although it has only limited homology to other cytokines, IL-17 exhibits proinflammatory properties similar to those of tumor necrosis factor-α, particularly with respect to induction of other inflammatory effectors. In addition, IL-17 synergizes potently with other cytokines, placing it in the center of the inflammatory network. Strikingly, IL-17 has been associated with several bone pathologies, most notably rheumatoid arthritis.

The IL-17 cytokine family.

IL-17A and its receptor are the founding members of a recently described cytokine family, with unique sequences and functions in the immune system and elsewhere. Consisting of six ligands (IL-17A-F) and five receptors (IL-17RA-IL-17RE) in mammals, these molecules have distinct primary amino acid structures with only minimal homology to other cytokine families. By far the best studied of these cytokines to date are IL-17A and its receptor, IL-17RA. IL-17A is produced primarily by T cells, and is the hallmark cytokine of a newly defined T helper cell subset that appears to be involved in generation of autoimmunity. Despite its production by the adaptive immune system, IL-17A exhibits proinflammatory activities similar to innate immune cytokines such as IL-1beta and TNF-alpha and appears to play important and nonredundant roles in regulating granulocytes in vivo. As a result, IL-17A also plays key roles in host defense. In contrast to the restricted expression of IL-17A, the IL-17RA receptor is ubiquitously expressed, and thus most cells are potential physiological targets of IL-17A. This chapter describes the major molecular properties, biological activities, and known signaling pathways of the IL-17 family, with an emphasis on IL-17A and IL-17RA.

Host responses to Candida albicans: Th17 cells and mucosal candidiasis

Candida albicans causes mucosal and disseminated candidiasis, which represent serious problems for the rapidly expanding immunocompromised population. Until recently, Th1-mediated immunity was thought to confer the primary protection, particularly for oral candidiasis. However, emerging data indicate that the newly-defined Th17 compartment appears to play the predominant role in mucosal candidiasis.