Interleukin 1 participates in the development of anti-Listeria responses in normal and SCID mice

Nitric oxide inhibits interleukin-1-mediated protection against Escherichia coli K1-induced sepsis and meningitis in a neonatal murine model

Neonatal meningitis-associated Escherichia coli (NMEC) is a leading cause of sepsis and meningitis in newborn infants. Neonates are known to have impaired inflammasome activation and interleukin (IL)-1 production. However, it is unknown what role this plays in the context of NMEC infection. Here we investigated the role of IL-1 signaling in the pathogenesis of NMEC infection. We found both IL-1β and IL-1α were secreted from macrophages and microglial cells in response to NMEC in a Toll-like receptor 4- and NLR family pyrin domain containing 3 (NPLR3)-dependent manner. Intracerebral infection of adult mice indicated a protective role of IL-1 signaling during NMEC infection. However, IL-1 receptor blockade in wild-type neonatal mice did not significantly alter bacterial loads in the blood or brain, and we, therefore, investigated whether protection conferred by IL-1 was age dependent. Neonates are known to have increased nitric oxide (NO) levels compared with adults, and we found NO inhibited the secretion of IL-1 by macrophages in response to NMEC. In contrast to our results in wild-type neonates, blockade of IL-1 receptor in neonates lacking inducible nitric oxide synthase (iNOS) led to significantly increased bacterial loads in the blood and brain. These data indicate IL-1 signaling is protective during NMEC infection in neonates only when iNOS is absent. Collectively, our findings suggest that increased NO production by neonates inhibits IL-1 production, and that this suppresses the protective role of IL-1 signaling in response to NMEC infection. This may indicate a general mechanism for increased susceptibility of neonates to infection and could lead to new therapeutic strategies in the future.

Innate and Adaptive Immune Responses during Listeria monocytogenes Infection

It could be argued that we understand the immune response to infection with Listeria monocytogenes better than the immunity elicited by any other bacteria. L. monocytogenes are Gram-positive bacteria that are genetically tractable and easy to cultivate in vitro, and the mouse model of intravenous (i.v.) inoculation is highly reproducible. For these reasons, immunologists frequently use the mouse model of systemic listeriosis to dissect the mechanisms used by mammalian hosts to recognize and respond to infection. This article provides an overview of what we have learned over the past few decades and is divided into three sections: "Innate Immunity" describes how the host initially detects the presence of L. monocytogenes and characterizes the soluble and cellular responses that occur during the first few days postinfection; "Adaptive Immunity" discusses the exquisitely specific T cell response that mediates complete clearance of infection and immunological memory; "Use of Attenuated Listeria as a Vaccine Vector" highlights the ways that investigators have exploited our extensive knowledge of anti-Listeria immunity to develop cancer therapeutics.

Transition from metal-DTH resistance to susceptibility is facilitated by NLRP3 inflammasome signaling induced Th17 reactivity: Implications for orthopedic implants

Metal hypersensitivity has been recognized as an adverse biologic reaction that can compromise total joint arthroplasty (TJA) performance. However, the etiology of metal hypersensitivity responses in TJAs remains unclear. Metal implant debris is known to act as a danger signal that drives NLRP3 inflammasome activation. It remains unknown if implant debris induced inflammasome activation regulates T cell lineage in TJA metal hypersensitivity responses. In this study, we show both in vivo and in vitro that the pathogenesis of metal hypersensitivity responses to implant debris are largely dependent on activation of the inflammasome/caspase-1 pathway and subsequent production of IL-17A/F by CD4+ T cells. Inhibiting either the inflammasome pathway or IL-17A bioactivity in vivo and in vitro (in vivo using NLRP3 and Caspase-1 deficient mice or in vitro using blocking agents such as Capase-1 inhibitor, IL-1Ra and anti-IL-17A), significantly (p<0.05) mitigated metal-DTH paw inflammation as well as lymphocyte cytokine (IFN-γ and IL-17) and proliferation responses in metal-sensitized mice and primary human PBMCs. This study provides mechanistic insight into how in vivo exposure to orthopedic implant debris, and metals in general, elicits NLRP3 inflammasome activation that mediates the generation of IL-17A/F producing CD4+ T cells, leading to metal-delayed type hypersensitivity reactions.

MARCH3 attenuates IL-1β-triggered inflammation by mediating K48-linked polyubiquitination and degradation of IL-1RI

The proinflammatory cytokine IL-1β plays critical roles in inflammatory and autoimmune diseases. IL-1β signaling is tightly regulated to avoid excessive inflammatory response. In this study, we identified the E3 ubiquitin ligase membrane-associated RING-CH-type finger 3 (MARCH3) as a critical negative regulator of IL-1β-triggered signaling. Overexpression of MARCH3 inhibited IL-1β-triggered activation of NF-κB as well as expression of inflammatory genes, whereas MARCH3 deficiency had the opposite effects. MARCH3-deficient mice produced higher levels of serum inflammatory cytokines and were more sensitive to inflammatory death upon IL-1β injection or Listeria monocytogenes infection. Mechanistically, MARCH3 was associated with IL-1 receptor I (IL-1RI) and mediated its K48-linked polyubiquitination at K409 and lysosomal-dependent degradation. Furthermore, IL-1β stimulation triggered dephosphorylation of MARCH3 by CDC25A and activation of its E3 ligase activity. Our findings suggest that MARCH3-mediated IL-1RI degradation is an important mechanism for attenuating IL-1β-triggered inflammatory response.

Macrophage-derived IL-1α promotes sterile inflammation in a mouse model of acetaminophen hepatotoxicity

The metabolic intermediate of acetaminophen (APAP) can cause severe hepatocyte necrosis, which triggers aberrant immune activation of liver non-parenchymal cells (NPC). Overzealous hepatic inflammation determines the morbidity and mortality of APAP-induced liver injury (AILI). Interleukin-1 receptor (IL-1R) signaling has been shown to play a critical role in various inflammatory conditions, but its precise role and underlying mechanism in AILI remain debatable. Herein, we show that NLRP3 inflammasome activation of IL-1β is dispensable to AILI, whereas IL-1α, the other ligand of IL-1R1, accounts for hepatic injury by a lethal dose of APAP. Furthermore, Kupffer cells function as a major source of activated IL-1α in the liver, which is activated by damaged hepatocytes through TLR4/MyD88 signaling. Finally, IL-1α is able to chemoattract and activate CD11b⁺Gr-1⁺ myeloid cells, mostly neutrophils and inflammatory monocytes, to amplify deteriorated inflammation in the lesion. Therefore, this work identifies that MyD88-dependent activation of IL-1α in Kupffer cells plays a central role in the immunopathogenesis of AILI and implicates that IL-1α is a promising therapeutic target for AILI treatment.

Clash of the Cytokine Titans: counter-regulation of interleukin-1 and type I interferon-mediated inflammatory responses

Over the past decades the notion of 'inflammation' has been extended beyond the original hallmarks of rubor (redness), calor (heat), tumor (swelling) and dolor (pain) described by Celsus. We have gained a more detailed understanding of the cellular players and molecular mediators of inflammation which is now being applied and extended to areas of biomedical research such as cancer, obesity, heart disease, metabolism, auto-inflammatory disorders, autoimmunity and infectious diseases. Innate cytokines are often central components of inflammatory responses. Here, we discuss how the type I interferon and interleukin-1 cytokine pathways represent distinct and specialized categories of inflammatory responses and how these key mediators of inflammation counter-regulate each other.

Obesity-associated NLRC4 inflammasome activation drives breast cancer progression

Obesity is associated with an increased risk of developing breast cancer and is also associated with worse clinical prognosis. The mechanistic link between obesity and breast cancer progression remains unclear, and there has been no development of specific treatments to improve the outcome of obese cancer patients. Here we show that obesity-associated NLRC4 inflammasome activation/ interleukin (IL)-1 signalling promotes breast cancer progression. The tumour microenvironment in the context of obesity induces an increase in tumour-infiltrating myeloid cells with an activated NLRC4 inflammasome that in turn activates IL-1β, which drives disease progression through adipocyte-mediated vascular endothelial growth factor A (VEGFA) expression and angiogenesis. Further studies show that treatment of mice with metformin inhibits obesity-associated tumour progression associated with a marked decrease in angiogenesis. This report provides a causal mechanism by which obesity promotes breast cancer progression and lays out a foundation to block NLRC4 inflammasome activation or IL-1β signalling transduction that may be useful for the treatment of obese cancer patients.

Distinct contributions of interleukin-1α (IL-1α) and IL-1β to innate immune recognition of Pseudomonas aeruginosa in the lung

The bacterial pathogen Pseudomonas aeruginosa causes acute infections associated with significant morbidity and mortality. P. aeruginosa elicits strong innate immune responses in immunocompetent hosts, and the resulting recruitment of neutrophils to the site of infection is necessary for bacterial clearance. P. aeruginosa lipopolysaccharide and flagellin are recognized by extracellular Toll-like receptors, but the most rapid responses to infection occur when cytosolic receptors sense flagellin or type 3 secretion system (T3SS) structural proteins. The subsequent activation of the NLRC4 inflammasome and caspase-1 generates an interleukin-1β (IL-1β) signal that is required for the rapid neutrophilic response. A T3SS effector, exotoxin U (ExoU), can inhibit activation of the NLRC4 inflammasome and caspase-1. Thus, our observation that IL-1 receptor (IL-1R)-mediated signals were still required to initiate a response to ExoU-producing bacteria was unexpected. As both IL-1α and IL-1β signal via the IL-1R, we examined immune responses in mice lacking either of these cytokines. IL-1β-deficient mice responded to ExoU-producing P. aeruginosa bacteria similarly to wild-type animals; however, IL-1α-deficient mice had an attenuated immune response. The situation was reversed following infections by ExoU-negative bacteria: here, IL-1α was dispensable for neutrophil recruitment, while IL-1β was required. IL-1α secretion by macrophages infected with ExoU-producing P. aeruginosa isolates was independent of both caspase-1 and caspase-11. This study documents distinct roles for IL-1α and IL-1β in the response to P. aeruginosa infection as a function of the T3SS effectors produced by the infecting strain. The redundancy of these two cytokines nonetheless allows the infected host to mount a response to ExoU-positive and -negative bacterial isolates.

Deficits in serum amyloid A contribute to increased neonatal mortality during murine listeriosis

BACKGROUND

To understand the increased susceptibility of preterm neonates to infection.

METHODS

A murine listeriosis model using immunohistochemistry, microarray technology, and real-time polymerase chain reaction (PCR).

RESULTS

We report that recombinant serum amyloid A (SAA) administered prophylactically 18 h before intraperitoneal (i.p.) inoculation with Listeria monocytogenes conferred a dramatic survival benefit compared with administration of only vehicle in neonatal mice. Neonates that received the recombinant SAA protein had significantly fewer Listeria colony counts on plating of infected liver and showed significantly more activated macrophages, but SAA did not affect postnatal growth. Real-time PCR was used to confirm the microarray findings that gene expression levels for the SAA proteins 1 (Saa1) and 2 (Saa2), in addition to that for orosomucoid-2 (Orm2), were strikingly elevated in the adult compared with those in the neonate. Real-time PCR analysis showed that of the acute phase cytokines, tumor necrosis factor (TNF) gene expression increased exponentially with time in the infected adult, whereas neonates did not show similar increases.

CONCLUSION

The increased susceptibility of neonatal mice to listeriosis is in part mediated by a deficiency in the acute phase response, specifically expression of SAA, and that prophylactic SAA protein before neonatal murine listeriosis results in more macrophage activation, lower Listeria counts, and greater survival.

Identifying the initiating events of anti-Listeria responses using mice with conditional loss of IFN-γ receptor subunit 1 (IFNGR1)

Although IFN-γ is required for resolution of Listeria monocytogenes infection, the identities of the IFN-γ-responsive cells that initiate the process remain unclear. We addressed this question using novel mice with conditional loss of IFN-γR (IFNGR1). Itgax-cre(+)Ifngr1(f/f) mice with selective IFN-γ unresponsiveness in CD8α(+) dendritic cells displayed increased susceptibility to infection. This phenotype was due to the inability of IFN-γ-unresponsive CD8α(+) dendritic cells to produce the initial burst of IL-12 induced by IFN-γ from TNF-α-activated NK/NKT cells. The defect in early IL-12 production resulted in increased IL-4 production that established a myeloid cell environment favoring Listeria growth. Neutralization of IL-4 restored Listeria resistance in Itgax-cre(+)Ifngr1(f/f) mice. We also found that Itgax-cre(+)Ifngr1(f/f) mice survived infection with low-dose Listeria as the result of a second wave of IL-12 produced by Ly6C(hi) monocytes. Thus, an IFN-γ-driven cascade involving CD8α(+) dendritic cells and NK/NKT cells induces the rapid production of IL-12 that initiates the anti-Listeria response.

IL-1α signaling initiates the inflammatory response to virulent Legionella pneumophila in vivo

Legionella pneumophila is an intracellular bacterial pathogen that is the cause of a severe pneumonia in humans called Legionnaires' disease. A key feature of L. pneumophila pathogenesis is the rapid influx of neutrophils into the lungs, which occurs in response to signaling via the IL-1R. Two distinct cytokines, IL-1α and IL-1β, can stimulate the type I IL-1R. IL-1β is produced upon activation of cytosolic sensors called inflammasomes that detect L. pneumophila in vitro and in vivo. Surprisingly, we find no essential role for IL-1β in neutrophil recruitment to the lungs in response to L. pneumophila. Instead, we show that IL-1α is a critical initiator of neutrophil recruitment to the lungs of L. pneumophila-infected mice. We find that neutrophil recruitment in response to virulent L. pneumophila requires the production of IL-1α specifically by hematopoietic cells. In contrast to IL-1β, the innate signaling pathways that lead to the production of IL-1α in response to L. pneumophila remain poorly defined. In particular, although we confirm a role for inflammasomes for initiation of IL-1β signaling in vivo, we find no essential role for inflammasomes in production of IL-1α. Instead, we propose that a novel host pathway, perhaps involving inhibition of host protein synthesis, is responsible for IL-1α production in response to virulent L. pneumophila. Our results establish IL-1α as a critical initiator of the inflammatory response to L. pneumophila in vivo and point to an important role for IL-1α in providing an alternative to inflammasome-mediated immune responses in vivo.

T lymphocytes and muscle condition act like seeds and soil in a murine polymyositis model

OBJECTIVE

It has been reported that polymyositis (PM) is driven by CD8+ cytotoxic T lymphocytes. The C protein-induced myositis (CIM) model we have established is similar to PM in pathology except that it undergoes spontaneous remission. We undertook the present study to delineate the roles of innate and acquired immunity in myositis.

METHODS

C57BL/6 mice were immunized with recombinant C protein fragments together with Freund's complete adjuvant (CFA) and Toll-like receptor (TLR) ligands at hind leg footpads and tail bases. CIM mediated by adoptive transfer of T cells to naive mice was treated with cytokine antagonists.

RESULTS

Second immunization with C protein fragments revealed no induction of tolerance. Injection of CFA and TLR ligands at the hind leg footpads reinduced myositis in the same legs. Interestingly, initial myositis was observed only in the CFA-treated forelegs. Transfer of C protein fragment-specific T cells from mice with CIM induced myositis in CFA- and TLR ligand-treated legs of recipient mice. CFA treatment resulted in the recruitment of macrophages producing inflammatory cytokines. Induction of myositis was inhibited by blocking interleukin-1 receptor or tumor necrosis factor α.

CONCLUSION

Myositis development requires activation of autoaggressive T cells and conditioning of muscle tissue. CIM regression is due to attenuation of local CFA-induced immune activation. These results are in accordance with a "seed and soil" model of disease development and might offer clues to decipher clinical aspects of PM.

The IL-1-dependent sterile inflammatory response has a substantial caspase-1-independent component that requires cathepsin C

The sterile inflammatory response to cell death and irritant crystals is medically important because it causes disease. Although these stimuli are structurally distinct, they cause inflammation through a common pathway that requires the cytokine IL-1. In vitro, the inflammasome, and in particular its generation of active caspase-1, is absolutely required to produce bioactive IL-1β. However, in this study, we report that caspase-1 is not required in vivo for much of the IL-1β-dependent sterile inflammatory response. Furthermore, we find that cathepsin C, which controls the activity of a number of leukocyte serine proteases capable of processing IL-1β, plays a major role in this caspase-1-independent pathway. Mice that are deficient in cathepsin C have reduced inflammatory responses to dying cells and silica crystals. In the absence of cathepsin C, caspase-1 becomes rate limiting such that mice doubly deficient in both of these proteases make little IL-1β in vivo and have markedly attenuated inflammatory responses to the sterile stimuli. In contrast, these mutant mice generate normal inflammation in response to exogenous IL-1β, indicating that cathepsin C and caspase-1 function upstream of IL-1β, and, in their absence, all components of the pathway downstream of mature IL-1β are intact.

p47(phox) directs murine macrophage cell fate decisions

Macrophage differentiation and function are pivotal for cell survival from infection and involve the processing of microenvironmental signals that determine macrophage cell fate decisions to establish appropriate inflammatory balance. NADPH oxidase 2 (Nox2)-deficient chronic granulomatous disease (CGD) mice that lack the gp91(phox) (gp91(phox-/-)) catalytic subunit show high mortality rates compared with wild-type mice when challenged by infection with Listeria monocytogenes (Lm), whereas p47(phox)-deficient (p47(phox-/-)) CGD mice show survival rates that are similar to those of wild-type mice. We demonstrate that such survival results from a skewed macrophage differentiation program in p47(phox-/-) mice that favors the production of higher levels of alternatively activated macrophages (AAMacs) compared with levels of either wild-type or gp91(phox-/-) mice. Furthermore, the adoptive transfer of AAMacs from p47(phox-/-) mice can rescue gp91(phox-/-) mice during primary Lm infection. Key features of the protective function provided by p47(phox-/-) AAMacs against Lm infection are enhanced production of IL-1α and killing of Lm. Molecular analysis of this process indicates that p47(phox-/-) macrophages are hyperresponsive to IL-4 and show higher Stat6 phosphorylation levels and signaling coupled to downstream activation of AAMac transcripts in response to IL-4 stimulation. Notably, restoring p47(phox) protein expression levels reverts the p47(phox)-dependent AAMac phenotype. Our results indicate that p47(phox) is a previously unrecognized regulator for IL-4 signaling pathways that are important for macrophage cell fate choice.

Regulation and function of TPL-2, an IκB kinase-regulated MAP kinase kinase kinase

The IκB kinase (IKK) complex plays a well-documented role in innate and adaptive immunity. This function has been widely attributed to its role as the central activator of the NF-κB family of transcription factors. However, another important consequence of IKK activation is the regulation of TPL-2, a MEK kinase that is required for activation of ERK-1/2 MAP kinases in myeloid cells following Toll-like receptor and TNF receptor stimulation. In unstimulated cells, TPL-2 is stoichiometrically complexed with the NF-κB inhibitory protein NF-κB1 p105, which blocks TPL-2 access to its substrate MEK, and the ubiquitin-binding protein ABIN-2 (A20-binding inhibitor of NF-κB 2), both of which are required to maintain TPL-2 protein stability. Following agonist stimulation, the IKK complex phosphorylates p105, triggering its K48-linked ubiquitination and degradation by the proteasome. This releases TPL-2 from p105-mediated inhibition, facilitating activation of MEK, in addition to modulating NF-κB activation by liberating associated Rel subunits for translocation into the nucleus. IKK-induced proteolysis of p105, therefore, can directly regulate both NF-κB and ERK MAP kinase activation via NF-κB1 p105. TPL-2 is critical for production of the proinflammatory cytokine TNF during inflammatory responses. Consequently, there has been considerable interest in the pharmaceutical industry to develop selective TPL-2 inhibitors as drugs for the treatment of TNF-dependent inflammatory diseases, such as rheumatoid arthritis and inflammatory bowel disease. This review summarizes our current understanding of the regulation of TPL-2 signaling function, and also the complex positive and negative roles of TPL-2 in immune and inflammatory responses.

Identification of the cellular sensor that stimulates the inflammatory response to sterile cell death

Cell death provokes a robust inflammatory response. We have previously shown that this response is dependent on IL-1alpha. In this study, we investigate the cellular mechanism used by a host to sense cell death, produce IL-1alpha and also the role of IL-1beta in this response. In almost all cases examined, the IL-1 that stimulated the death-induced inflammatory response came from the host rather than the cell that was dying. In these situations, host bone marrow-derived cells were the key source of the IL-1alpha that was required for the inflammatory response. Conditional cellular depletion and reconstitution in CD11b promoter-driven diphtheria toxin receptor transgenic mice revealed that host macrophages played an essential role in the generation of the inflammatory response and were the source of the required IL-1alpha. In addition, we found a role for IL-1beta in the death-induced inflammatory response and that this cytokine was generated by both bone marrow-derived and radioresistant host cells. The one exception to these findings was that when dendritic cells were injected into mice, they provided a portion of the IL-1 that stimulated inflammation, and this was observed whether the dendritic cells were live or necrotic. Together, these findings demonstrate that macrophages play a key role as the primary sentinels that are required to sense and report cell death in ways that initiate the inflammatory response. One key way they accomplish this important task is by producing IL-1alpha that is needed to initiate the inflammatory response.

Listeriolysin O-dependent bacterial entry into the cytoplasm is required for calpain activation and interleukin-1 alpha secretion in macrophages infected with Listeria monocytogenes

Listeriolysin O (LLO), an hly-encoded cytolysin of Listeria monocytogenes, plays an essential role in the entry of L. monocytogenes into the host cell cytoplasm. L. monocytogenes-infected macrophages produce various proinflammatory cytokines, including interleukin-1 alpha (IL-1 alpha), that contribute to the host immune response. In this study, we have examined IL-1 alpha production in macrophages infected with wild-type L. monocytogenes or a nonescaping mutant strain deficient for LLO (Delta hly). Expression of IL-1 alpha mRNA and accumulation of pro-IL-1 alpha in the cytoplasm were induced by both strains. In contrast, the secretion of the mature form of IL-1 alpha from infected macrophages was observed in infection with wild-type L. monocytogenes but not with the Delta hly mutant. A recovery of the ability to induce IL-1 alpha secretion was shown in a mutant strain complemented with the hly gene. The Toll-like receptor (TLR)/MyD88 signaling pathway was exclusively required for the expression of pro-IL-1 alpha, independently of LLO-mediated cytoplasmic entry of L. monocytogenes. The LLO-dependent secretion of mature IL-1 alpha was abolished by addition of calcium chelators, and only LLO-producing L. monocytogenes strains were able to induce elevation of the intracellular calcium level in infected macrophages. A calcium-dependent protease, calpain, was implicated in the maturation and secretion of IL-1 alpha induced by LLO-producing L. monocytogenes strains based on the effect of calpain inhibitor. Functional activation of calpain was detected in macrophages infected with LLO-producing L. monocytogenes strains but not with a mutant strain lacking LLO. These results clearly indicated that LLO-mediated cytoplasmic entry of bacteria could induce the activation of intracellular calcium signaling, which is essential for maturation and secretion of IL-1 alpha in macrophages during L. monocytogenes infection through activation of a calcium-dependent calpain protease. In addition, recombinant LLO, when added to macrophages infected with the Delta hly strain, could induce calcium influx and IL-1 alpha secretion at doses exhibiting cytolytic activity, suggesting that LLO produced by intracellular L. monocytogenes may be implicated in induction of calcium influx through pore formation.

Precarious balance: Th17 cells in host defense

Lineage-specific responses from the effector T-cell repertoire form a critical component of adaptive immunity. The recent identification of Th17 cells-a third, distinct lineage of helper T cells-collapses the long-accepted paradigm in which Th1 and Th2 cells distinctly mediate cellular and humoral immunity, respectively. In this minireview, we discuss the involvement of the Th17 lineage during infection by extracellular bacteria, intracellular bacteria, and fungi. Emerging trends suggest that the Th17 population bridges innate and adaptive immunity to produce a robust antimicrobial inflammatory response. However, because Th17 cells mediate both host defense and pathological inflammation, elucidation of mechanisms that attenuate but do not completely abolish the Th17 response may have powerful implications for therapy.

Convergence of IL-1beta and VDR activation pathways in human TLR2/1-induced antimicrobial responses

Antimicrobial effector mechanisms are central to the function of the innate immune response in host defense against microbial pathogens. In humans, activation of Toll-like receptor 2/1 (TLR2/1) on monocytes induces a vitamin D dependent antimicrobial activity against intracellular mycobacteria. Here, we report that TLR activation of monocytes triggers induction of the defensin beta 4 gene (DEFB4), requiring convergence of the IL-1β and vitamin D receptor (VDR) pathways. TLR2/1 activation triggered IL-1β activity, involving the upregulation of both IL-1β and IL-1 receptor, and downregulation of the IL-1 receptor antagonist. TLR2/1L induction of IL-1β was required for upregulation of DEFB4, but not cathelicidin, whereas VDR activation was required for expression of both antimicrobial genes. The differential requirements for induction of DEFB4 and cathelicidin were reflected by differences in their respective promoter regions; the DEFB4 promoter had one vitamin D response element (VDRE) and two NF-κB sites, whereas the cathelicidin promoter had three VDREs and no NF-κB sites. Transfection of NF-κB into primary monocytes synergized with 1,25D3 in the induction of DEFB4 expression. Knockdown of either DEFB4 or cathelicidin in primary monocytes resulted in the loss of TLR2/1-mediated antimicrobial activity against intracellular mycobacteria. Therefore, these data identify a novel mechanism of host defense requiring the induction of IL-1β in synergy with vitamin D activation, for the TLR-induced antimicrobial pathway against an intracellular pathogen.

Innate immunity prevents tissue invasion by Entamoeba histolytica

Although innate and adaptive immunity both play a role in amoebiasis, the mechanisms involved in the elimination of Entamoeba histolytica are poorly understood. To provide more information about the innate immune mechanisms that may confer protection against invasive amoebiasis, we administered inflammatory substances (bacillus Calmette-Guérin, lipopolysaccharide, complete Freund's adjuvant, or mineral oil) into the peritoneum of hamsters. The animals were then challenged with pathogenic trophozoites of E. histolytica and, after 7 days, the protective host response was analysed. We found that the nonspecific inflammatory response induced in the peritoneum was sufficient to prevent liver invasion by E. histolytica. In vitro experiments showed that the killing of trophozoites was mediated by peritoneal macrophages and a protein of 68 kDa with peroxidase activity.

Cytokine response in Balb/c mice infected with Francisella tularensis LVS and the Pohang isolate

We investigated the immune response induced by the Francisella (F.) tularensis live vaccine strain (LVS) and the Pohang isolate. After the Balb/c mice were infected intradermally (i.d) with 2 x 10(4) cfu of F. tularensis LVS and Pohang, respectively, their blood and organs were collected at different times; 0, 3, 6, 24, 72, 96, 120 and 168 h after infection. Using these samples, RT-PCR and ELISA analysis were carried out for the comparative study of the cytokines, including TNF-alpha, INF-gamma, IL-2, IL-4, IL-10 and IL-12. In the Pohang-infected mice at 120 h, the liver showed a 53 times higher level of TNF-alpha and a 42 times higher level of IFN-gamma than the respective levels at the early time points after infection. The levels of TNF-alpha and IFN-gamma induced by LVS were 5 times lower than those induced by the Pohang isolate. Also, the organs from the Pohang-infected mice showed higher levels of TNF-alpha, IFN-gamma, IL-10 and IL-12 than the levels in the LVS-infected mice. The blood from the Pohang-infected mice at 120 h revealed about a 40 times increased level of IFN-gamma, and IL-10 was also increased by 4 times at 96 h compared to an early infection time point, while IL-4 was not induced during the whole infection period. These results suggest that F. tularensis may induce a Th1-mediated immune response to in vivo infection and the Pohang isolate has a higher capacity than the LVS to induce an acute immune response in Blab/c mice.

Neuritogenic effects of T cell-derived IL-3 on mouse splenic sympathetic neurons in vivo

To determine the role played by lymphocytes and cytokines in the growth of sympathetic neurons in vivo, the innervation and cytokine levels were examined in the spleens of SCID mice that lack T and B cells. Splenic noradrenaline, nerve growth factor (NGF), and IL-1beta levels were elevated in SCID mice. Immunohistochemical examination revealed that the density of tyrosine hydroxylase-positive (TH(+)) fibers of splenic central arteries in SCID mice was increased compared with wild-type C.B-17 mice, while SCID mice had significantly fewer TH(+) fibers in their periarteriolar lymphatic sheaths (PALS). Two weeks after SCID mice were injected with C.B-17 splenic T cells, their TH(+) fiber staining increased in the PALS. IL-3 levels increased significantly in SCID mice following T cell reconstitution, and the administration of anti-IL-3 Ab blocked the above T cell-induced increase in innervation in the PALS. Anti-IL-3 treatment also inhibited the regeneration of splenic sympathetic neurons in C.B-17 mice after they were chemically sympathetomized with 6-hydroxydopamine. Depletion of NK cells by anti-asialo GM1 promoted the splenic innervation in SCID mice, while there were no significant changes in the innervation between CD8(+) T cell-deficient beta(2)-microglobulin knockout mice and their wild type. Our results suggest that T cells (probably CD4(+) Th cells but not CD8(+) CTLs) play a role in regulating the sympathetic innervation of the spleen; this effect appeared to be mediated, at least in part, by IL-3. On the contrary, NK cells may exert an inhibitory effect on the sympathetic innervation.

Blocking monoclonal antibodies specific for mouse IFN-alpha/beta receptor subunit 1 (IFNAR-1) from mice immunized by in vivo hydrodynamic transfection

Herein we report the generation of mouse monoclonal antibodies (mAbs) specific for the IFNAR-1 subunit of the mouse interferon-alpha/beta (IFN-alpha/beta) receptor (MAR1 mAbs) that block type I IFN receptor signaling and biologic response induction in vitro and in vivo. These mAbs were generated from Ifnar1 (/) mice immunized by in vivo hydrodynamic transfection with a plasmid encoding the extracellular domain (ECD) of murine IFNAR-1. All MAR1 mAbs bound native receptor expressed on cell surfaces and immunoprecipitated IFNAR-1 from solubilized cells, and two mAbs also detected IFNAR-1 by Western blot analysis. in vitro, the mAbs prevented ligand-induced intracellular signaling and induction of a variety of type I IFN-induced biologic responses but had no effect on IFN-gamma-induced responses. The most effective in vitro blocker, MAR1-5A3, also blocked type I IFN-induced antiviral, antimicrobial, and antitumor responses in vivo. We also explored whether murine IFNAR-1 surface expression required the presence of Tyk2. In contrast to Tyk2-deficient human cell lines, comparable IFNAR-1 expression was found on primary cells derived either from wild-type or Tyk2 (/) mice. These mAbs represent much needed tools to more clearly elucidate the biochemistry, cell biology, and physiologic function of the type I IFNs and their receptor in mediating host-protective immunity and immunopathology.

Lymphocytes are detrimental during the early innate immune response against Listeria monocytogenes

Mice deficient in lymphocytes are more resistant than normal mice to Listeria monocytogenes infection during the early innate immune response. This paradox remains unresolved: lymphocytes are required for sterilizing immunity, but their presence during the early stage of the infection is not an asset and may even be detrimental. We found that lymphocyte-deficient mice, which showed limited apoptosis in infected organs, were resistant during the first four days of infection but became susceptible when engrafted with lymphocytes. Engraftment with lymphocytes from type I interferon receptor–deficient (IFN-αβR^−/−) mice, which had reduced apoptosis, did not confer increased susceptibility to infection, even when the phagocytes were IFN-αβR^+/+. The attenuation of innate immunity was due, in part, to the production of the antiinflammatory cytokine interleukin 10 by phagocytic cells after the apoptotic phase of the infection. Thus, immunodeficient mice were more resistant relative to normal mice because the latter went through a stage of lymphocyte apoptosis that was detrimental to the innate immune response. This is an example of a bacterial pathogen creating a cascade of events that leads to a permissive infective niche early during infection.

Interleukin-1 is responsible for acute lung immunopathology but increases survival of respiratory influenza virus infection

Interleukin-1alpha (IL-1alpha) and IL-1beta are proinflammatory cytokines, which induce a plethora of genes and activities by binding to the type 1 IL-1 receptor (IL-1R1). We have investigated the role of IL-1 during pulmonary antiviral immune responses in IL-1R1(-/-) mice infected with influenza virus. IL-1R1(-/-) mice showed markedly reduced inflammatory pathology in the lung, primarily due to impaired neutrophil recruitment. Activation of CD4(+) T cells in secondary lymphoid organs and subsequent migration to the lung were impaired in the absence of IL-1R1. In contrast, activation of virus-specific cytotoxic T lymphocytes and killing of virus-infected cells in the lung were intact. Influenza virus-specific immunoglobulin G (IgG) and IgA antibody responses were intact, while the IgM response was markedly reduced in both serum and mucosal sites in IL-1R1(-/-) mice. We found significantly increased mortality in the absence of IL-1R1; however, lung viral titers were only moderately increased. Our results demonstrate that IL-1alpha/beta mediate acute pulmonary inflammatory pathology while enhancing survival during influenza virus infection. IL-1alpha/beta appear not to influence killing of virus-infected cells but to enhance IgM antibody responses and recruitment of CD4(+) T cells to the site of infection.

Toll-like receptor 2 is required for optimal control of Listeria monocytogenes infection

The control of Listeria monocytogenes infection depends on the rapid activation of the innate immune system, likely through Toll-like receptors (TLR), since mice deficient for the common adapter protein of TLR signaling, myeloid differentiation factor 88 (MyD88), succumb to Listeria infection. In order to test whether TLR2 is involved in the control of infections, we compared the host response in TLR2-deficient mice with that in wild-type mice. Here we show that TLR2-deficient mice are more susceptible to systemic infection by Listeria than are wild-type mice, with a reduced survival rate, increased bacterial burden in the liver, and abundant and larger hepatic microabscesses containing increased numbers of neutrophils. The production of tumor necrosis factor, interleukin-12, and nitric oxide and the expression of the costimulatory molecules CD40 and CD86, which are necessary for the control of infection, were reduced in TLR2-deficient macrophages and dendritic cells stimulated by Listeria and were almost abolished in the absence of MyD88, coincident with the high susceptibility of MyD88-deficient mice to in vivo infection. Therefore, the present data demonstrate a role for TLR2 in the control of Listeria infection, but other MyD88-dependent signals may contribute to host resistance.

Identification of potent human anti‐IL‐1RI antagonist antibodies

Interleukin-1 (IL-1) blockade by IL-1 receptor antagonist benefits some arthritis patients by reducing joint damage. This fact inspired us to develop antagonist human therapeutic antibodies against IL-1R(I) using phage libraries that display single-chain variable fragment (scFv) antibody fragments. Panning libraries against human IL-1R(I) generated 39 unique scFv-phage whose binding to IL-1R(I) was competed by IL-1 ligands. Fifteen of these scFv-phage, identified using IL-1R(I)-binding assays and dissociation rate ranking, were reformatted as scFv-Fc and IgG(4) molecules. The ease of producing antibodies in the scFv-Fc format permitted rapid identification of four lead clones (C10, C13, C14, C15) that inhibit NF-kappaB nuclear translocation induced by IL-1. Reformatting these clones as IgG(4) molecules increased their inhibition potency by </=24-fold. C10 IgG(4) is the most potent antagonist of IL-1alpha (26 nM IC(50)) and IL-1beta (18 nM IC(50)) in the NF-kappaB bioassay, although less potent than IL-1ra ( approximately 0.4 nM IC(50)). C10 is the highest affinity clone for human IL-1R(I) (K(D) approximately 60 nM). Flow cytometry indicates that several lead clones bind cell-surface cynomolgus or murine IL-1R(I), characteristics advantageous for preclinical toxicology and efficacy studies. This study demonstrates the utility of scFv-Fc fusion proteins for rapid screening of clones derived from phage libraries to identify antibody leads with therapeutic potential.

Regulation of interleukin-1alpha expression by integrins and epidermal growth factor receptor in keratinocytes from a mouse model of inflammatory skin disease

Transgenic mice expressing beta1 integrins in the suprabasal epidermal layers have sporadic skin hyperproliferation and inflammation correlated with activation of extracellular signal-regulated kinase (Erk) mitogen-activated protein kinase and increased interleukin (IL)-1alpha production. We investigated the link between aberrant integrin expression, Erk activation, and expression of IL-1alpha. Transgenic keratinocytes had higher basal Erk activity and IL-1alpha levels than nontransgenic controls and were more sensitive to stimulation of Erk activity and IL-1alpha production by IL-1alpha, 12-O-tetradecanoylphorbol-13-acetate (TPA), epidermal growth factor (EGF), and serum. Inhibition of Erk in transgenic keratinocytes reduced basal IL-1alpha levels and the stimulation of IL-1alpha production by serum or phorbol ester, demonstrating that Erk could regulate IL-1alpha expression. TPA or IL-1alpha treatment resulted in rapid down-regulation of the EGF receptor in transgenic cells, indicative of transactivation. Inhibition of transactivation blocked basal and TPA or IL-1alpha induced Erk activation, but not IkappaBalpha degradation, and abolished increased IL-1alpha production in transgenic cells. In transgene-negative cells, constitutive activation of IL-1-dependent signaling by wild type or kinase-dead IRAK1 stimulated IL-1alpha production independent of Erk. We conclude that suprabasal integrin expression leads to Erk activation and increased IL-1alpha expression by potentiating activation of the EGF receptor. These results provide a mechanism by which aberrant integrin expression triggers epidermal hyperproliferation and inflammation.

MyD88-dependent but Toll-like receptor 2-independent innate immunity to Listeria: no role for either in macrophage listericidal activity

We have assessed the requirements for Toll-like receptor (TLR) signaling in vivo during early infection with Listeria monocytogenes. Mice deficient for TLR2, a receptor required for the recognition of Gram-positive peptidoglycan, showed equivalent Listeria resistance to wild-type mice. However, mice deficient for MyD88, an adaptor molecule used by all TLRs, showed profound susceptibility with 3-4 logs greater Listeria burden and severe spleen and liver pathology at day 3 postinfection. Listeria-infected MyD88-deficient mice also showed markedly diminished IFN-gamma, TNF-alpha, and NO responses, despite evidence of macrophage activation and up-regulation of MHC class II molecules. We demonstrate that although minor MyD88-independent responses to live Listeria do occur, these are insufficient for normal host defense. Lastly, we performed experiments in vitro in which macrophages deficient in TLR2 or MyD88 were directly infected with Listeria: Although TLR signaling was required for macrophage NO and cytokine production in response to Listeria, handling and direct killing of Listeria by activated macrophages occurred by TLR2- and MyD88-independent mechanisms.

Role of interleukin (IL)-1 type 1 receptor in mycobacterial infection

It is important to gain a better understanding of IL-1-mediated signaling events in mycobacterial infection. In order to clarify the role of IL-1 receptor type 1 (IL-1 R1) in IL-1 R1, knockout (KO) mice were infected with either Mycobacterium tuberculosis H37Rv or Kurono strain by the respiratory route, and their ability to control mycobacterial growth, pulmonary granuloma formation, and cytokine mRNA expression was investigated. IL-1 R1 KO mice developed significantly larger (P< 0.01) granulomatous lesions with neutrophil infiltration in their lungs than wild-type mice did after infection with the M. tuberculosis Kurono strain. The number of mycobacterial colonies in lungs and spleen increased from five weeks post-infection. Interferon-y production by spleen cells was low in IL-1 R1 KO mice. It is concluded that the IL-1 R1 is essential for IL-1-mediated signaling events in mycobacterial infection.

Administration of two macrophage-derived interferon-gamma-inducing factors (IL-12 and IL-15) induces a lethal systemic inflammatory response in mice that is dependent on natural killer cells but does not require interferon-gamma

Activation of macrophages by microbes results in the rapid production of monokines (e.g., interleukin-12 (IL-12), IL-15, and IL-18), which induce production of interferon-gamma (IFN-gamma) by natural killer (NK) cells. We examined the effects of administering IL-15 in combination with IL-12 in a murine toxicity model to determine how these two cytokines might contribute to the inflammatory state that accompanies infectious processes. The daily, simultaneous administration of IL-15 (3 x 10(5)U) and IL-12 (1 microg) to normal mice resulted in shock and 100% mortality within 3-7 days, whereas minimal toxicity was observed following the administration of IL-15 or IL-12 alone. Mice treated with IL-15 plus IL-12 exhibited lesions of the gastrointestinal tract, elevated serum levels of acute phase reactants and pro-inflammatory cytokines, and NK cell apoptosis. Neutralization of IFN-gamma, TNF-alpha, and IL-1beta was not protective in cytokine-treated mice, however, toxicity and death could be completely abrogated by depletion of NK cells. Mice deficient in the STAT4 transcription factor also exhibited complete protection while mice deficient in IFN-gamma or its downstream mediator, STAT1, did not. These findings suggest that cytokine- stimulated NK cells are able to promote systemic inflammation via the induction of STAT4-responsive genes other than IFN-gamma or TNF-alpha.

The role of IL-1beta in the regulation of IL-8 and IL-6 in human corneal epithelial cells during Pseudomonas aeruginosa colonization

PURPOSE

Recent studies have shown that the levels of interleukin (IL)-1beta, IL-6 and IL-8 are associated with the severity of infectious diseases. The purpose of this study was to investigate whether IL-1beta regulates the expression of IL-6 and IL-8 in human corneal epithelial cells during Pseudomonas aeruginosa colonization.

METHODS

Confluent immortalized human corneal epithelial cells were challenged with P. aeruginosa 6294 in the presence of anti-human IL-1beta antibody or matched control antibody. The cells were also challenged with recombinant IL-1beta protein without bacterial colonization. Expression of IL-1beta, IL-6 and IL-8 mRNA and protein was detected by reverse transcription (RT)-PCR and by enzyme-linked immunosorbent assay (ELISA), respectively. IL-1beta localization was determined by immunohistochemistry.

RESULTS

Human corneal epithelial cells expressed low levels of IL-1beta and high levels of IL-6 and IL-8 during P. aeruginosa colonization. Addition of IL-1beta Ab resulted in a significant decrease (P < 0.05) in IL-8 protein expression at 4 h, 8 h and 12 h. Addition of IL-1beta Ab reduced IL-6 protein expression at 8 h and increased IL-6 protein expression at 12 h. Addition of recombinant IL-1beta protein alone strongly stimulated the expression of IL-8 and IL-6. Immunohistochemical staining showed that IL-1beta protein was present both intracellularly and extracellularly in P. aeruginosa colonized cells.

CONCLUSIONS

IL-1beta is able to modulate expression of both IL-6 and IL-8 at transcriptional and post-transcriptional levels in human corneal epithelial cells.

Endogenous interleukin-10 is required for prevention of a hyperinflammatory intracerebral immune response in Listeria monocytogenes meningoencephalitis

To analyze the role of interleukin-10 (IL-10) in bacterial cerebral infections, we studied cerebral listeriosis in IL-10-deficient (IL-10(-/-)) and wild-type (WT) mice, the latter of which express high levels of IL-10 in both primary and secondary cerebral listeriosis. IL-10(-/-) mice succumbed to primary as well as secondary listeriosis, whereas WT mice were significantly protected from secondary listeriosis by prior intraperitoneal immunization with Listeria monocytogenes. Meningoencephalitis developed in both strains; however, in IL-10(-/-) mice the inflammation was more severe and associated with increased brain edema and multiple intracerebral hemorrhages. IL-10(-/-) mice recruited significantly increased numbers of leukocytes, in particular granulocytes, to the brain, and the intracerebral cytokine (tumor necrosis factor, IL-1, IL-12, gamma interferon, and inducible nitric oxide synthase) and chemokine (crg2/IP-10, RANTES, MuMig, macrophage inflammatory protein 1alpha [MIP-1alpha], and MIP-1beta) transcription was enhanced compared to that in WT mice. Despite this prominent hyperinflammation, the frequencies of intracerebral L. monocytogenes-specific CD8(+) T cells were reduced and the intracerebral bacterial load was not reduced in IL-10(-/-) mice compared to WT mice. Following intraperitoneal infection, IL-10(-/-) mice exhibited hepatic hyperinflammation without better bacterial clearance; however, in contrast to the mice with cerebral listeriosis, they did not succumb, illustrating that intrinsic factors of the target organ have a strong impact on the course and outcome of the infection.

Susceptibility to secondary Francisella tularensis live vaccine strain infection in B-cell-deficient mice is associated with neutrophilia but not with defects in specific T-cell-mediated immunity

Previous studies have demonstrated a role for B cells, not associated with antibody production, in protection against lethal secondary infection of mice with Francisella tularensis live vaccine strain (LVS). However, the mechanism by which B cells contribute to this protection is not known. To study the specific role of B cells during secondary LVS infection, we developed an in vitro culture system that mimics many of the same characteristics of in vivo infection. Using this culture system, we showed that B cells do not directly control LVS infection but that control of LVS growth is mediated primarily by LVS-primed T cells. Importantly, B cells were not required for the generation of effective memory T cells since LVS-primed, B-cell-deficient (BKO) mice generated CD4(+) and CD8(+) T cells that controlled LVS infection similarly to LVS-primed CD4(+) and CD8(+) T cells from wild-type mice. The control of LVS growth appeared to depend primarily on gamma interferon and nitric oxide and was similar in wild-type and BKO mice. Rather, the inability of BKO mice to survive secondary LVS infection was associated with marked neutrophil influx into the spleen very early after challenge. The neutrophilia was directly associated with B cells, since BKO mice reconstituted with naive B cells prior to a secondary challenge with LVS had decreased bacterial loads and neutrophils in the spleen and survived.

Impaired Cytokine Signaling in Mice Lacking the IL-1 Receptor-Associated Kinase

Stimulation of the type 1 IL-1R (IL-1R1) and the IL-18R by their cognate ligands induces recruitment of the IL-1R-associated kinase (IRAK). Activation of IRAK leads in turn to nuclear translocation of NF-κB, which directs expression of innate and adaptive immune response genes. To study IRAK function in cytokine signaling, we generated cells and mice lacking the IRAK protein. IRAK-deficient fibroblasts show diminished activation of NF-κB when stimulated with IL-1. Immune effector cells without IRAK exhibit a defective IFN-γ response to costimulation with IL-18. Furthermore, mice lacking the Irak gene demonstrate an attenuated response to injected IL-1. Deletion of Irak, however, does not affect the ability of mice to develop delayed-type hypersensitivity or clear infection with the intracellular parasite, Listeria monocytogenes. These results demonstrate that although IRAK participates in IL-1 and IL-18 signal transduction, residual cytokine responsiveness operates through an IRAK-independent pathway.

Effects of interleukin-1 receptor antagonist overexpression on infection by Listeria monocytogenes

Interleukin-1 receptor antagonist (IL-1ra) is a naturally occurring cytokine whose only known function is the inhibition of interleukin-1 (IL-1). Using a reverse genetic approach in mice, we previously showed that increasing IL-1ra gene dosage leads to reduced survival of a primary listerial infection. In this study, we characterize further the role of endogenously produced IL-1ra and, by inference, IL-1 in murine listeriosis. IL-1ra overexpression inhibits, but does not eliminate, primary immune responses, reducing survival and increasing bacterial loads in the target organs. We demonstrate that IL-1ra functions in the innate immune response to regulate the peak leukocyte levels in the blood, the accumulation of leukocytes at sites of infection, and the activation of macrophages during a primary infection. Reduced macrophage class II major histocompatibility complex expression was observed despite increased gamma interferon (IFN-gamma) levels, suggesting that IL-1 activity is essential along with IFN-gamma for macrophage activation in vivo. We also show that IL-1ra plays a more limited role during secondary listeriosis, blunting the strength of the delayed-type hypersensitivity response to listerial antigen while not significantly altering cellular immunity to a second infectious challenge. When these results are compared to those for other mutant mice, IL-1ra appears to be unique among the cytokines studied to date in its regulation of leukocyte migration during primary listeriosis.

Hemolytically active (acylated) alpha-hemolysin elicits interleukin-1beta (IL-1beta) but augments the lethality of Escherichia coli by an IL-1- and tumor necrosis factor-independent mechanism

Many pathogenic Escherichia coli produce the toxin alpha-hemolysin (Hly), and lipopolysaccharide (LPS), interleukin-1 (IL-1), and tumor necrosis factor (TNF) have all been recognized as important effector molecules during infections by gram-negative organisms. Despite the characterization of many in vitro effects of hemolysin, no direct relationship has been established between hemolysin, LPS, proinflammatory cytokine production, and E. coli-induced mortality. Previously, we have shown in vivo that hemolysin elicits a distinct IL-1alpha spike by 4 h into a lethal hemolytic E. coli infection. Using three transformed E. coli strains, WAF108, WAF270, and WAH540 (which produce no Hly [Hlynull], acylated Hly [Hlyactive], or nonacylated Hly [Hlyinactive], respectively), we sought to determine the specific roles of hemolysin acylation, LPS, IL-1, and TNF in mediating the lethality of E. coli infection in mice. WAF270 was 100% lethal in BALB/c, C3H/HeJ, and C57BL/6 mice; in mice pretreated with antibody to the type 1 IL-1 receptor; in type 1 IL-1 receptor-deficient mice; and in dual (type 1 IL-1 receptor-type 1 TNF receptor)-deficient mice at doses which were nonlethal (0%) with both WAF108 and WAH540. At lethal doses, WAF270 killed by 6 +/- 2.3 h while WAF108 and WAH540 killed at 36 +/- 9.4 and 36 +/- 13.8 h, respectively. These differences in mortality were not due to IL-1 or TNF release, and the enhanced expression of LPS, which corresponded to Hly expression, was not likely the primary factor causing mortality. We demonstrate that bacterial fatty acid acylation of hemolysin is required in order for it to elicit IL-1 release by monocytes and to confer its virulence on E. coli.

Targeted disruption of the interferon-gamma receptor 2 gene results in severe immune defects in mice

To study the role of the interferon- (IFN) gammaR2 chain in IFN-gamma signaling and immune function, IFN-gammaR2-deficient mice have been generated and characterized. Cells derived from IFN-gammaR2 -/- mice are unable to activate either JAK/STAT signaling proteins or gene transcription in response to IFN-gamma. The lack of IFN-gamma responsiveness alters IFN-gamma-induced Ig class switching by B cells from these mice. In vitro cultures of T cells demonstrate that the T cells from the IFN-gammaR2 -/- mice have a defect in Th1 cell differentiation. The IFN-gammaR2 (-/-) mice also produce lower amounts of IFN-gamma in response to antigenic challenge. In addition, IFN-gammaR2 -/- mice are defective in contact hypersensitivity and are highly susceptible to infection by Listeria monocytogenes. These results demonstrate that the IFN-gammaR2 is essential for IFN-gamma-mediated immune responses in vivo.

Demonstration of an interferon gamma-dependent tumor surveillance system in immunocompetent mice

This study demonstrates that endogenously produced interferon gamma (IFN-gamma) forms the basis of a tumor surveillance system that controls development of both chemically induced and spontaneously arising tumors in mice. Compared with wild-type mice, mice lacking sensitivity to either IFN-gamma (i.e., IFN-gamma receptor-deficient mice) or all IFN family members (i.e., Stat1-deficient mice) developed tumors more rapidly and with greater frequency when challenged with different doses of the chemical carcinogen methylcholanthrene. In addition, IFN-gamma-insensitive mice developed tumors more rapidly than wild-type mice when bred onto a background deficient in the p53 tumor-suppressor gene. IFN-gamma-insensitive p53(-/-) mice also developed a broader spectrum of tumors compared with mice lacking p53 alone. Using tumor cells derived from methylcholanthrene-treated IFN-gamma-insensitive mice, we found IFN-gamma's actions to be mediated at least partly through its direct effects on the tumor cell leading to enhanced tumor cell immunogenicity. The importance and generality of this system is evidenced by the finding that certain types of human tumors become selectively unresponsive to IFN-gamma. Thus, IFN-gamma forms the basis of an extrinsic tumor-suppressor mechanism in immunocompetent hosts.

Determinant capture by MHC class II DR3 during processing of mycobacteria leprae 65kD heat shock protein by human B cells

Using T cell immunoblotting we have characterised the immunogenic fragments derived from the Mycobacteria Leprae 65kD heat shock protein that become associated with MHC class II DR3 during processing by a human B cell line. After 5 h incubation with antigen, a peptide of approximately 12kD (approximately 110 amino acids) was the only major fragment found associated with the class II MHC. The association of this oligopeptide was abolished if an excess of a synthetic peptide representing the minimal epitope was included in the culture or when cells were incubated at 4 degrees C. This suggests that the generation of this moiety is dependent on cell metabolism and that its binding to MHC is specific. This large fragment may represent an intermediate in the processing pathway, directly demonstrating the role of MHC in determinant capture during antigen degradation.

Regulation of E-Cadherin-Mediated Adhesion in Langerhans Cell-Like Dendritic Cells by Inflammatory Mediators That Mobilize Langerhans Cells In Vivo

Adhesion of Langerhans cells (LC) to keratinocytes is mediated by E-cadherin. IL-1, TNF-α, and LPS mobilize LC from epidermis and presumably attenuate LC-keratinocyte adhesion. To determine whether these mediators modulated LC E-cadherin-dependent adhesion directly, we characterized their effects on LC-like dendritic cells expanded from murine fetal skin (FSDDC). FSDDC were propagated from day 16 C57BL/6 fetal skin and isolated as aggregates (FSDDC-A) in which homophilic adhesion was mediated by E-cadherin. IL-1, TNF-α, and LPS induced dissociation of FSDDC-A that began within 4 to 8 h and was complete within 20 h. Anti-IL-1RI mAb inhibited disaggregation caused by IL-1α and IL-1β, but not that induced by TNF-α or LPS. Anti-TNF-α mAb inhibited the effect of TNF-α and LPS, but not that caused by IL-1α or IL-1β. Flow cytometry of FSDDC-A revealed that IL-1, TNF-α, and LPS induced increased expression of MHC class II, CD40, and CD86 and decreased E-cadherin expression that was temporally related to dissociation of aggregates. IL-1 and TNF-α caused a rapid reduction in FSDDC E-cadherin mRNA levels that preceded the decrease in E-cadherin surface expression. These results demonstrate that cytokines that induce LC emigration in vivo act directly on LC-like cells in vitro, reduce E-cadherin mRNA levels, down-regulate E-cadherin surface expression, and induce a loss of E-cadherin-mediated adhesion.

IL-1α and TNF-α Are Required for IL-12-Induced Development of Th1 Cells Producing High Levels of IFN-γ in BALB/c But Not C57BL/6 Mice

The development of Th1- or Th2-type responses determines the type of immune response that is elicited in response to Ag. Responsiveness to IL-12 is critical for the development of Th1-type CD4+ T cells required for cell-mediated immune responses. Addition of IL-12 to primary cultures of CD4+ T cells stimulated with OVA and splenocytes or dendritic cells resulted in the development of a Th1 phenotype with the capacity to secrete high levels of IFN-γ upon restimulation with splenic APC. The present study shows that using dendritic cells to present Ag upon restimulation reveals a requirement for additional cofactors, including IL-1α and TNF-α, which were provided by spleen cells but not dendritic cells. Furthermore, these cofactors are required for optimal IL-12-induced Th1 development in BALB/c but not C57BL/6 mice. This differential requirement for such cofactors in IL-12-driven Th1 development may play a role in genetic predisposition to Th1 or Th2 responses to infectious agents.

Neuropeptides in the livers of mice during bacterial infections

Neuropeptides such as substance P (SP) and vasoactive intestinal peptide (VIP) are known to act as immunomodulators. We investigated the induction of SP and VIP in the livers of mice infected with Listeria monocytogenes or injected with Tsukamurella paurometabolum. VIP was detected in the livers of mice after L. monocytogenes infection by an immunohistochemical technique and preproVIP mRNA, which was detected by reverse transcription-polymerase chain reaction (PCR), was induced post infection. However, no SP was detected. In contrast, SP, but not VIP was detected within granulomas in the livers of T. paurometabolum-injected mice, suggesting VIP and SP might be selectively induced in the liver by different bacterial infections.

Chronic Listeria Infection in SCID Mice: Requirements for the Carrier State and the Dual Role of T Cells in Transferring Protection or Suppression

Listeriosis in mice with the SCID mutation results in a chronic infection. The chronic infection is characterized by abundant granulomas and neutrophil infiltrates. Both lesions were particularly noticeable in the liver. In the liver, about 95% are granulomas with 5% microabscesses involving intrahepatic infection. The majority of Listeria resided in membrane-bound vacuolar structures of the macrophages and not in the cytosol. Three manipulations resulted in alterations in the equilibrium between granulomas and liver microabscesses, with massive transfer of the infection to the hepatocyte and dissolution of the granulomas: depletion of neutrophils and neutralization of IFN-γ and TNF-α. We did not find a role for IL-12, IL-10, or nitric oxide. Adoptive transfer studies showed a decisive role for both CD4+ and CD8+ T cells for an effective immune response, i.e., clearance of bacteria, granuloma formation with lymphocytes, and disappearance of microabscess. Clearance of Listeria was induced by transfer of CD8+ T cells from mice with targeted disruption of the IFN-γ structural gene (IfgTM1KO), even in the presence of neutralizing mAb to IFN-γ. In marked contrast, transfer of CD4+ T cells from IfgTM1KO mice exacerbated the infection in the chronically infected SCID mice, resulting in increased mortality with dissolution of the granulomas and severe hepatic infection with neutrophil infiltration. Thus, these data indicate that both IFN-γ-dependent and -independent mechanisms are operative in the context of a chronic listerial infection.

Evidence for the presence of type I IL-1 receptors on beta-cells of islets of Langerhans

The cytokine interleukin-1beta (IL-1beta) has been shown to inhibit insulin secretion and destroy pancreatic islets by a mechanism that involves the expression of inducible nitric oxide synthase (iNOS), and the production of nitric oxide (NO). Insulin containing beta-cells, selectively destroyed during the development of autoimmune diabetes, appear to be the islet cellular source of iNOS following treatment with IL-1beta. In this study we have evaluated the presence of type I IL-1 signaling receptors on purified pancreatic beta-cells. We show that the interleukin-1 receptor antagonist protein (IRAP) prevents IL-1beta-induced nitrite formation and IL-1beta-induced inhibition of insulin secretion by isolated islets and primary beta-cells purified by fluorescence-activated cell sorting (FACS). The protective effects of IRAP correlate with an inhibition of IL-1beta-induced iNOS expression by islets and FACS purified beta-cells. To provide direct evidence to support beta-cell expression of IL-1 type I signaling receptors, we show that antiserum specific for the type I IL-1 receptor neutralizes IL-1beta-induced nitrite formation by RINm5F cells, and that RINm5F cells express the type I IL-1 receptor at the protein level. Using reverse transcriptase-polymerase chain reaction (RT-PCR), the expression of type I IL-1 signaling receptors by FACS purified beta-cells and not alpha-cells is demonstrated. These results provide direct support for the expression of type I IL-1 receptors by primary pancreatic beta-cells, the cell type selectively destroyed during the development of autoimmune diabetes.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.

Lymphocyte apoptosis during early phase of Listeria infection in mice

During the acute phase of growth of Listeria monocytogenes in spleen and lymph nodes, the infective foci consist of macrophages and neutrophils accompanied by extensive death of lymphocytes. Many of the lymphocytes die by apoptosis. The lesions are found by 48 hours after infection and can regress with time. Depending on the dose, the infected foci can be restricted to the thymus-dependent areas or can occupy the entire lymphoid tissue. The Listeria in the lesions are primarily found inside macrophages, but a few are extracellular amid cellular debris. Lymphocyte death appears to be an obligatory step in primary Listeria infection, the extent of which is controlled by the early restriction of Listeria growth by the innate cellular system.