B and T lymphocyte attenuator tempers early infection immunity.

Coinhibitory pathways are thought to act in later stages of an adaptive immune response, but whether coinhibition contributes to early innate immunity is unclear. We show that engagement of the newly discovered coinhibitory receptor B and T lymphocyte attenuator (BTLA) by herpesvirus entry mediator (HVEM) is critical for negatively regulating early host immunity against intracellular bacteria. Both HVEM(-/-) and BTLA(-/-), but not LIGHT(-/-), mice are more resistant to listeriosis compared with wild-type mice, and blockade of the BTLA pathway promotes, while engagement inhibits, early bacterial clearance. Differences in bacterial clearance were seen as early as 1 day postinfection, implicating the initial innate response. Therefore, innate cell function in BTLA(-/-) mice was studied. We show that innate cells from BTLA(-/-) mice secrete significantly more proinflammatory cytokines upon stimulation with heat-killed Listeria. These results provide the first evidence that a coinhibitory pathway plays a critical role in regulating early host innate immunity against infection.

T cell-derived lymphotoxin regulates liver regeneration.

BACKGROUND & AIMS: The ability of the liver to regenerate hepatic mass is essential to withstanding liver injury. The process of liver regeneration is tightly regulated by distinct signaling cascades involving components of the innate immune system, cytokines, and growth factors. However, the role of the adaptive immune system in regulation of liver regeneration is not well-defined. The role of adaptive immune system in liver regeneration was investigated in lymphocyte-deficient mice and in conditional lymphotoxin-deficient mice. METHODS: A model of liver regeneration after 70% partial hepatectomy was used, followed by examination of liver pathology, survival, DNA synthesis, and cytokine expression. RESULTS: We found that mice deficient in T cells show a reduced capacity for liver regeneration following partial hepatectomy. Furthermore, surface lymphotoxin, provided by T cells, is critical for liver regeneration. Mice specifically deficient in T-cell lymphotoxin had increased liver damage and a reduced capacity to initiate DNA synthesis after partial hepatectomy. Transfer of splenocytes from wild-type but not lymphotoxin-deficient mice improved liver regeneration in T cell-deficient mice. We found that an agonistic antibody against the lymphotoxin beta receptor was able to facilitate liver regeneration by reducing liver injury, increasing interleukin-6 production, hepatocyte DNA synthesis, and survival of lymphocyte-deficient (Rag) mice after partial hepatectomy. CONCLUSIONS: The adaptive immune system directly regulates liver regeneration via a T cell-derived lymphotoxin axis, and pharmacological stimulation of lymphotoxin beta receptor might represent a novel therapeutic approach to improve liver regeneration.

The interleukin-17 receptor plays a gender-dependent role in host protection against Porphyromonas gingivalis-induced periodontal bone loss.

Interleukin-17 (IL-17) is a proinflammatory cytokine secreted by the newly described CD4(+) Th17 subset, which is distinct from classic Th1 and Th2 lineages. IL-17 contributes to bone destruction in rheumatoid arthritis but is essential in host defense against pathogens that are susceptible to neutrophils. Periodontal disease (PD) is a chronic inflammatory condition initiated by anaerobic oral pathogens such as Porphyromonas gingivalis, and it is characterized by host-mediated alveolar bone destruction due primarily to the immune response. The role of IL-17 in PD is controversial. Whereas elevated IL-17 levels have been found in humans with severe PD, we recently reported that female C57BL/6J mice lacking the IL-17 receptor (IL-17RA(KO)) are significantly more susceptible to PD bone loss due to defects in the chemokine-neutrophil axis (J. J. Yu, M. J. Ruddy, G. C. Wong, C. Sfintescu, P. J. Baker, J. B. Smith, R. T. Evans, and S. L. Gaffen, Blood 109:3794-3802, 2007). Since different mouse strains exhibit differences in susceptibility to PD as well as Th1/Th2 cell skewing, we crossed the IL-17RA gene knockout onto the BALB/c background and observed a similar enhancement in alveolar bone loss following P. gingivalis infection. Unexpectedly, in both strains IL-17RA(KO) female mice were much more susceptible to PD bone loss than males. Moreover, female BALB/c-IL-17RA(KO) mice were defective in producing anti-P. gingivalis immunoglobulin G and the chemokines KC/Groalpha and MIP-2. In contrast, male mice produced normal levels of chemokines and anti-P. gingivalis antibodies, but they were defective in granulocyte colony-stimulating factor upregulation. This study demonstrates a gender-dependent effect of IL-17 signaling and indicates that gender differences should be taken into account in the preclinical and clinical safety testing of anti-IL-17 biologic therapies.

Cytokines link osteoblasts and inflammation: microarray analysis of interleukin-17- and TNF-alpha-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 alpha (TNF-alpha) 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-alpha as compared with TNF-alpha 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-alpha, 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 kappaBzeta (MAIL/kappaBzeta), CCAAT/enhancer-binding protein delta (C/EBPdelta), and C/EBPbeta. We also identified the acute-phase gene lipocalin-2 (LCN2/24p3) as a novel IL-17 target, which is regulated synergistically by TNF-alpha and IL-17 at the level of its promoter. A similar but not identical pattern of genes was induced by IL-17 and TNF-alpha in ST2 bone marrow stromal cells and murine embryonic fibroblasts. This study provides a profile of genes regulated by IL-17 and TNF-alpha 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.

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 alpha (TNF-alpha) 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-alpha 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.

An essential role for IL-17 in preventing pathogen-initiated bone destruction: recruitment of neutrophils to inflamed bone requires IL-17 receptor-dependent signals.

IL-17 and its receptor are founding members of a novel family of inflammatory cytokines. IL-17 plays a pathogenic role in rheumatoid arthritis (RA)-associated bone destruction. However, IL-17 is also an important regulator of host defense through granulopoiesis and neutrophil trafficking. Therefore, the role of IL-17 in pathogen-initiated bone loss was not obvious. The most common form of infection-induced bone destruction occurs in periodontal disease (PD). In addition to causing significant morbidity, PD is a risk factor for atherosclerotic heart disease and chronic obstructive pulmonary disease (COPD). Similar to RA, bone destruction in PD is caused by the immune response. However, neutrophils provide critical antimicrobial defense against periodontal organisms. Since IL-17 is bone destructive in RA but a key regulator of neutrophils, we examined its role in inflammatory bone loss induced by the oral pathogen Porphyromonas gingivalis in IL-17RA-deficient mice. These mice showed enhanced periodontal bone destruction, suggesting a bone-protective role for IL-17, reminiscent of a neutrophil deficiency. Although IL-17RA-deficient neutrophils functioned normally ex vivo, IL-17RA knock-out (IL-17RA(KO)) mice exhibited reduced serum chemokine levels and concomitantly reduced neutrophil migration to bone. Consistently, CXCR2(KO) mice were highly susceptible to alveolar bone loss; interestingly, these mice also suggested a role for chemokines in maintaining normal bone homeostasis. These results indicate a nonredundant role for IL-17 in mediating host defense via neutrophil mobilization.

Functional cooperation between interleukin-17 and tumor necrosis factor-alpha 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-alpha (TNFalpha) 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 TNFalpha exhibit potent synergy in mediating IL-6 secretion. Here, we show that at least part of the functional cooperation between IL-17 and TNFalpha occurs at the level of IL-6 gene transcription. Both the NF-kappaB and CCAAT/enhancer-binding protein (C/EBP; NF-IL6) sites in the IL-6 promoter are important for cooperative gene expression, but NF-kappaB does not appear to be the direct target of the combined signal. Microarray analysis using the Affymetrix mouse MG-U74v2 chip identified C/EBPdelta as another gene target of combined IL-17- and TNFalpha-induced signaling. Because C/EBP family members are known to control IL-6, we examined whether enhanced C/EBPdelta expression is involved in the cooperative up-regulation of IL-6 by IL-17 and TNFalpha. Accordingly, we show that C/EBPdelta (or the related transcription factor C/EBPbeta) is essential for expression of IL-6. Moreover, overexpression of C/EBPdelta (and, to a lesser extent, C/EBPbeta) could substitute for the IL-17 signal at the level of IL-6 transcription. Thus, C/EBP family members, particularly C/EBPdelta, appear to be important for the functional cooperation between IL-17 and TNFalpha.