IL-12p40-dependent agonistic effects on the development of protective innate and adaptive immunity against Salmonella enteritidis

IL-12 induces a B cell-intrinsic IL-12/IFNγ feed-forward loop promoting extrafollicular B cell responses

While some infections elicit germinal centers, others produce only extrafollicular responses. The mechanisms controlling these dichotomous fates are poorly understood. We identify IL-12 as a cytokine switch, acting directly on B cells to promote extrafollicular and suppress germinal center responses. IL-12 initiates a B cell-intrinsic feed-forward loop between IL-12 and IFNγ, amplifying IFNγ production, which promotes proliferation and plasmablast differentiation from mouse and human B cells, in synergy with IL-12. IL-12 sustains the expression of a portion of IFNγ-inducible genes. Together, they also induce unique gene changes, reflecting both IFNγ amplification and cooperative effects between both cytokines. In vivo, cells lacking both IL-12 and IFNγ receptors are more impaired in plasmablast production than those lacking either receptor alone. Further, B cell-derived IL-12 enhances both plasmablast responses and T helper 1 cell commitment. Thus, B cell-derived IL-12, acting on T and B cells, determines the immune response mode, with implications for vaccines, pathogen protection and autoimmunity.

Transcriptomic signatures reveal a shift towards an anti-inflammatory gene expression profile but also the induction of type I and type II interferon signaling networks through aryl hydrocarbon receptor activation in murine macrophages

Introduction

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates a broad range of target genes involved in the xenobiotic response, cell cycle control and circadian rhythm. AhR is constitutively expressed in macrophages (Mϕ), acting as key regulator of cytokine production. While proinflammatory cytokines, i.e., IL-1β, IL-6, IL-12, are suppressed through AhR activation, anti-inflammatory IL-10 is induced. However, the underlying mechanisms of those effects and the importance of the specific ligand structure are not yet completely understood.

Methods

Therefore, we have compared the global gene expression pattern in activated murine bone marrow-derived macrophages (BMMs) subsequently to exposure with either benzo[a]pyrene (BaP) or indole-3-carbinol (I3C), representing high-affinity vs. low-affinity AhR ligands, respectively, by means of mRNA sequencing. AhR dependency of observed effects was proved using BMMs from AhR-knockout (Ahr^-/-) mice.

Results and discussion

In total, more than 1,000 differentially expressed genes (DEGs) could be mapped, covering a plethora of AhR-modulated effects on basal cellular processes, i.e., transcription and translation, but also immune functions, i.e., antigen presentation, cytokine production, and phagocytosis. Among DEGs were genes that are already known to be regulated by AhR, i.e., Irf1, Ido2, and Cd84. However, we identified DEGs not yet described to be AhR-regulated in Mϕ so far, i.e., Slpi, Il12rb1, and Il21r. All six genes likely contribute to shifting the Mϕ phenotype from proinflammatory to anti-inflammatory. The majority of DEGs induced through BaP were not affected through I3C exposure, probably due to higher AhR affinity of BaP in comparison to I3C. Mapping of known aryl hydrocarbon response element (AHRE) sequence motifs in identified DEGs revealed more than 200 genes not possessing any AHRE, and therefore being not eligible for canonical regulation. Bioinformatic approaches modeled a central role of type I and type II interferons in the regulation of those genes. Additionally, RT-qPCR and ELISA confirmed a AhR-dependent expressional induction and AhR-dependent secretion of IFN-γ in response to BaP exposure, suggesting an auto- or paracrine activation pathway of Mϕ.

Dendritic cells Trigger IFN-γ secretion by NK cells independent of IL-12 and IL-18

It is commonly believed that IL-12 produced by DCs in response to pathogens is the first signal that stimulates the production of IFN-γ by NK cells. However, IL-12 production by DCs in response to bacterial LPS depends on either engagement of CD40 by CD40L on activated T cells or IFN-γ from NK cells. This suggests that during the primary immune response, NK cells produce IFN-γ before IL-12 production by DCs. Here, using single-cell measurements, cell sorting and mouse lines deficient in IL-12, IL-23, type I IFN receptor and the IL-18 receptor, we show that a subset of BM-derived DCs characterized by low expression of MHC class II (MHCIIlow ) stimulates IFN-γ production by NK cells. The expression of Toll-like Receptor (TLR) 4 on DCs but not NK cells was required for such NK-derived IFN-γ. In addition, soluble factor(s) produced by LPS-activated MHCIIlow DCs were sufficient to induce IFN-γ production by NK cells independent of IL-12, IL-23, and IL-18. This response was enhanced in the presence of a low dose of IL-2. These results delineate a previously unknown pathway of DC-mediated IFN-γ production by NK cells, which is independent of commonly known cytokines.

Aryl Hydrocarbon Receptor Activation by Benzo[a]pyrene Prevents Development of Septic Shock and Fatal Outcome in a Mouse Model of Systemic Salmonella enterica Infection

This study focused on immunomodulatory effects of aryl hydrocarbon receptor (AhR) activation through benzo[a]pyrene (BaP) during systemic bacterial infection. Using a well-established mouse model of systemic Salmonella enterica (S.E.) infection, we studied the influence of BaP on the cellular and humoral immune response and the outcome of disease. BaP exposure significantly reduced mortality, which is mainly caused by septic shock. Surprisingly, the bacterial burden in BaP-exposed surviving mice was significantly higher compared to non-exposed mice. During the early phase of infection (days 1-3 post-infection (p.i.)), the transcription of proinflammatory factors (i.e., IL-12, IFN-γ, TNF-α, IL-1β, IL-6, IL-18) was induced faster under BaP exposure. Moreover, BaP supported the activity of antigen-presenting cells (i.e., CD64 (FcγRI), MHC II, NO radicals, phagocytosis) at the site of infection. However, early in infection, the anti-inflammatory cytokines IL-10 and IL-22 were also locally and systemically upregulated in BaP-exposed S.E.-infected mice. BaP-exposure resulted in long-term persistence of salmonellae up to day 90 p.i., which was accompanied by significantly elevated S.E.-specific antibody responses (i.e., IgG1, IgG2c). In summary, these data suggest that BaP-induced AhR activation is capable of preventing a fatal outcome of systemic S.E. infection, but may result in long-term bacterial persistence, which, in turn, may support the development of chronic inflammation.

Humoral Immunity vs. Salmonella

In primary infection with Salmonella, it has been reported—without consideration of Salmonella's functions—that humoral immunity plays no role in the clearance of bacteria. In fact, Salmonella targets and suppresses several aspects of humoral immunity, including B cell lymphopoiesis, B cell activation, and IgG production. In particular, the suppression of IgG-secreting plasma cell maintenance allows the persistence of Salmonella in tissues. Therefore, the critical role(s) of humoral immunity in the response to Salmonella infection, especially at the late phase, should be re-investigated. The suppression of IgG plasma cell memory strongly hinders vaccine development against non-typhoidal Salmonella (NTS) because Salmonella can also reduce humoral immune memory against other bacteria and viruses, obtained from previous vaccination or infection. We propose a new vaccine against Salmonella that would not impair humoral immunity, and which could also be used as a treatment for antibody-dependent autoimmune diseases to deplete pathogenic long-lived plasma cells, by utilizing the Salmonella's own suppression mechanism of humoral immunity.

The translation of non-canonical open reading frames controls mucosal immunity

The annotation of the mammalian protein-coding genome is incomplete. Arbitrary size restriction of open reading frames (ORFs) and the absolute requirement for a methionine codon as the sole initiator of translation have constrained the identification of potentially important transcripts with non-canonical protein-coding potential1,2. Here, using unbiased transcriptomic approaches in macrophages that respond to bacterial infection, we show that ribosomes associate with a large number of RNAs that were previously annotated as 'non-protein coding'. Although the idea that such non-canonical ORFs can encode functional proteins is controversial3,4, we identify a range of short and non-ATG-initiated ORFs that can generate stable and spatially distinct proteins. Notably, we show that the translation of a new ORF 'hidden' within the long non-coding RNA Aw112010 is essential for the orchestration of mucosal immunity during both bacterial infection and colitis. This work expands our interpretation of the protein-coding genome and demonstrates that proteinaceous products generated from non-canonical ORFs are crucial for the immune response in vivo. We therefore propose that the misannotation of non-canonical ORF-containing genes as non-coding RNAs may obscure the essential role of a multitude of previously undiscovered protein-coding genes in immunity and disease.

CNBP controls IL-12 gene transcription and Th1 immunity

These studies reveal a previously unrecognized role for Cnbp as a novel transcriptional regulator engaged downstream of innate immune receptors controlling the c-Rel–IL-12–Th1 axis, which has important implications for both host defense and inflammatory disease.

An inducible program of inflammatory gene expression is a hallmark of antimicrobial defenses. Recently, cellular nucleic acid–binding protein (CNBP) was identified as a regulator of nuclear factor-kappaB (NF-κB)–dependent proinflammatory cytokine gene expression. Here, we generated mice lacking CNBP and found that CNBP regulates a very restricted gene signature that includes IL-12β. CNBP resides in the cytosol of macrophages and translocates to the nucleus in response to diverse microbial pathogens and pathogen-derived products. Cnbp-deficient macrophages induced canonical NF-κB/Rel signaling normally but were impaired in their ability to control the activation of c-Rel, a key driver of IL-12β gene transcription. The nuclear translocation and DNA-binding activity of c-Rel required CNBP. Lastly, Cnbp-deficient mice were more susceptible to acute toxoplasmosis associated with reduced production of IL-12β, as well as a reduced T helper type 1 (Th1) cell IFN-γ response essential to controlling parasite replication. Collectively, these findings identify CNBP as important regulator of c-Rel–dependent IL-12β gene transcription and Th1 immunity.

Mouse Model of Cat Allergic Rhinitis and Intranasal Liposome-Adjuvanted Refined Fel d 1 Vaccine

Cats (Felis domesticus) are rich source of airborne allergens that prevailed in the environment and sensitized a number of people to allergy. In this study, a mouse model of allergic rhinitis caused by the cat allergens was developed for the first time and the model was used for testing therapeutic efficacy of a novel intranasal liposome-entrapped vaccines made of native Fel d 1 (major cat allergen) in comparison with the vaccine made of crude cat hair extract (cCE). BALB/c mice were sensitized with cCE mixed with alum intraperitoneally and intranasally. The allergic mice were treated with eight doses of either liposome (L)-entrapped native Fel d 1 (L-nFD1), L-cCE), or placebo on every alternate day. Vaccine efficacy evaluation was performed one day after provoking the treated mice with aerosolic cCE. All allergenized mice developed histological features of allergic rhinitis with rises of serum specific-IgE and Th2 cytokine gene expression. Serum IgE and intranasal mucus production of allergic mice reduced significantly after vaccination in comparison with the placebo mice. The vaccines also caused a shift of the Th2 response (reduction of Th2 cytokine expressions) towards the non-pathogenic responses: Th1 (down-regulation of the Th1 suppressive cytokine gene, IL-35) and Treg (up-regulation of IL-10 and TGF-β). In conclusions, a mouse model of allergic rhinitis to cat allergens was successfully developed. The intranasal, liposome-adjuvanted vaccines, especially the refined single allergen formulation, assuaged the allergic manifestations in the modeled mice. The prototype vaccine is worthwhile testing further for clinical use in the pet allergic patients.

Making many from few: IL-12p40 as a model for the combinatorial assembly of heterodimeric cytokines

How dendritic cells (DCs) gather information from the local milieu at a site of infection or injury and communicate this to influence adaptive immunity is not well understood. We and others have reported that soon after microbial encounter, DCs secrete the p40 subunit of IL-12, by itself, in a monomeric form. Based on recent data that this p40 monomer subsequently associates with p35 released from other cells to generate functional IL-12, we proposed that p40 can function as a DC-derived probe which samples the composition of the local milieu by looking for other binding partners. In this opinion, we discuss how such a sampling function might generate an elaborate combinatorial "code" of heterodimeric cytokines, capable of conveying location-specific information to cells downstream of DC activation, including NK and T cells.

Immunological study of an attenuated Salmonella Typhimurium expressing ApxIA, ApxIIA, ApxIIIA and OmpA of Actinobacillus pleuropneumoniae in a mouse model

Salmonella Typhimurium strain expressing the Actinobacillus pleuropneumoniae antigens, ApxIA, ApxIIA, ApxIIIA and OmpA, was previously constructed as a vaccine candidate for porcine pleuropneumonia. This strain was a live attenuated (∆lon∆cpxR∆asd)Salmonella as a delivery host and contained a vector containing asd. An immunological study of lymphocyte proliferation, T-lymphocyte subsets and cytokines in the splenocytes of a mouse model was carried out after stimulation with the candidate Salmonella Typhimurium by intranasal inoculation. The splenic lymphocyte proliferation and the levels of IL-4, IL-6 and IL-12 of the inoculated mice were significantly increased, and the T- and B-cell populations were also elevated. Collectively, the candidate may efficiently induce the Th1- and Th2-type immune responses.

Immunity to intestinal pathogens: lessons learned from Salmonella

Salmonella are a common source of food- or water-borne infection and cause a wide range of clinical disease in human and animal hosts. Salmonella are relatively easy to culture and manipulate in a laboratory setting, and the infection of laboratory animals induces robust innate and adaptive immune responses. Thus, immunologists have frequently turned to Salmonella infection models to expand understanding of host immunity to intestinal pathogens. In this review, I summarize current knowledge of innate and adaptive immunity to Salmonella and highlight features of this response that have emerged from recent studies. These include the heterogeneity of the antigen-specific T-cell response to intestinal infection, the prominence of microbial mechanisms to impede T- and B-cell responses, and the contribution of non-cognate pathways for elicitation of T-cell effector functions. Together, these different issues challenge an overly simplistic view of host-pathogen interaction during mucosal infection, but also allow deeper insight into the real-world dynamic of protective immunity to intestinal pathogens.

Crosstalks between cytokines and Sonic Hedgehog in Helicobacter pylori infection: a mathematical model

Helicobacter pylori infection of gastric tissue results in an immune response dominated by Th1 cytokines and has also been linked with dysregulation of Sonic Hedgehog (SHH) signaling pathway in gastric tissue. However, since interactions between the cytokines and SHH during H. pylori infection are not well understood, any mechanistic understanding achieved through interpretation of the statistical analysis of experimental results in the context of currently known circuit must be carefully scrutinized. Here, we use mathematical modeling aided by restraints of experimental data to evaluate the consistency between experimental results and temporal behavior of H. pylori activated cytokine circuit model. Statistical analysis of qPCR data from uninfected and H. pylori infected wild-type and parietal cell-specific SHH knockout (PC-SHH^KO) mice for day 7 and 180 indicate significant changes that suggest role of SHH in cytokine regulation. The experimentally observed changes are further investigated using a mathematical model that examines dynamic crosstalks among pro-inflammatory (IL1β, IL-12, IFNγ, MIP-2) cytokines, anti-inflammatory (IL-10) cytokines and SHH during H. pylori infection. Response analysis of the resulting model demonstrates that circuitry, as currently known, is inadequate for explaining of the experimental observations; suggesting the need for additional specific regulatory interactions. A key advantage of a computational model is the ability to propose putative circuit models for in-silico experimentation. We use this approach to propose a parsimonious model that incorporates crosstalks between NFĸB, SHH, IL-1β and IL-10, resulting in a feedback loop capable of exhibiting cyclic behavior. Separately, we show that analysis of an independent time-series GEO microarray data for IL-1β, IFNγ and IL-10 in mock and H. pylori infected mice further supports the proposed hypothesis that these cytokines may follow a cyclic trend. Predictions from the in-silico model provide useful insights for generating new hypothesis and design of subsequent experimental studies.

IL-23 p19 knockout mice exhibit minimal defects in responses to primary and secondary infection with Francisella tularensis LVS

Our laboratory’s investigations into mechanisms of protective immunity against Francisella tularensis Live Vaccine Strain (LVS) have uncovered mediators important in host defense against primary infection, as well as those correlated with successful vaccination. One such potential correlate was IL-12p40, a pleiotropic cytokine that promotes Th1 T cell function as part of IL-12p70. LVS-infected IL-12p40 deficient knockout (KO) mice maintain a chronic infection, but IL-12p35 KO mice clear LVS infection; thus the role that IL-12p40 plays in immunity to LVS is independent of the IL-12p70 heterodimer. IL-12p40 can also partner with IL-23p19 to create the heterodimeric cytokine IL-23. Here, we directly tested the role of IL-23 in LVS resistance, and found IL-23 to be largely dispensable for immunity to LVS following intradermal or intranasal infection. IL-23p19 KO splenocytes were fully competent in controlling intramacrophage LVS replication in an in vitro overlay assay. Further, antibody responses in IL-23p19 KO mice were similar to those of normal wild type mice after LVS infection. IL-23p19 KO mice or normal wild type mice that survived primary LVS infection survived maximal doses of LVS secondary challenge. Thus p40 has a novel role in clearance of LVS infection that is unrelated to either IL-12 or IL-23.

Insertion of a 59 amino acid peptide in Salmonella Typhimurium membrane results in loss of virulence in mice

We demonstrated previously that expression of a single trans-membrane region of the Δ(12) -desaturase gene of Synechocystis sp. PCC 6803 in Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) altered the membrane physical state of this pathogen, induced a significant change in the pattern of mRNA transcription of major heat shock genes, and inhibited pathogen growth inside murine macrophages. In this study, we demonstrate that injection of the modified Salmonella strain [Stm(pBAD200)] into C57Bl6j mice is safe. Survival of mice was associated with bacterial clearance, an increased number of splenic leukocytes, and high levels of interleukin-12, interferon γ and tumor necrosis factor α in spleens as well as in sera. Furthermore, Stm(pBAD200)-injected mice developed a Salmonella-specific antibody and Th1-like responses. Mice challenged with Stm(pBAD200) are protected from systemic infection with Salmonella wild-type. Similarly, mice infected with Stm(pBAD200) by the oral route survived when challenged with an oral lethal dose of Salmonella wild-type. The avirulent Stm(pBAD200) phenotype is associated with a remarkable change in the expression of the hilC, hilD, hilA, invF and phoP genes, among others, whose products are required for invasion and replication of Salmonella inside phagocytic cells. These data demonstrate the use of trans-membrane peptides to generate attenuated strains, providing a potential novel strategy to develop vaccines for both animal and human use.

The prognostic value of preoperative serum levels of IL-12p40 and IL-23 for survival of patients with colorectal cancer

Colorectal cancer (CRC) patients were previously shown to express a signature of cytokines that contribute to cancer pathogenesis and are detectable in serum. The aim of this study was to evaluate the potential clinical use of circulating cytokine measurements in CRC patients preoperatively as markers for disease outcome. The levels of cytokines IL-12p40 and IL-23 were assessed by ELISA in the sera of 91 patients with previously untreated CRC and then 5-year survival was determined using Kaplan-Meier analyses. The levels of circulating interleukin IL-12p40 significantly decreased with the progression of CRC, whereas the levels of IL-23 remained with no significant differences between disease stages. None of the cytokine levels were influenced by age, gender and colon vs rectum localization. We found that preoperative serum concentration of IL-12p40 cytokine is a good prognostic marker for survival; as for IL-23 levels, we found no outcome prognostic value. In addition, 5-year survival confirmed that tumor grade, bowel wall invasion, lymph node and metastatic status have an impact on overall survival. In conclusion, we believe that our findings show clinical significance of the preoperative serum concentration for IL-12p40 and provide an additional prognostic biomarker for CRC survival.

Enhanced IL-12p40 production in LPS-stimulated macrophages by inhibiting JNK activation by artemisinin

Artemisinin can be isolated from Artemisia annua L. In addition to its well-known anti-malarial activity, artemisinin has antitumor and anti-microbial effects. In this study, we investigated the effect of artemisinin on the production of IL-12p40, which is important in the generation of T helper 1 responses. Artemisinin significantly induced IL-12p40 production in LPS-stimulated RAW264.7 macrophage cells. To elucidate the signaling molecules regulated by artemisinin in induced IL-12p40 production, the DNA-binding activity of several transcription factors and activation of mitogen-activated protein kinase (MAPK)s were investigated. The band intensities of NF-κB, AP-1, and SP1, and the activation of p38 MAPK and ERK were not changed by artemisinin. However, the induced phosphorylation of JNK was significantly decreased by artemisinin, and inhibition of the JNK signaling pathway further increased IL-12p40 production in LPS-stimulated RAW264.7 macrophage cells. Taken together, these data suggest that artemisinin induces the production of IL-12p40 in LPS-stimulated macrophage cells by inhibiting JNK activity.

Homeostatic regulation of Salmonella-induced mucosal inflammation and injury by IL-23

IL-12 and IL-23 regulate innate and adaptive immunity to microbial pathogens through influencing the expression of IFN-γ, IL-17, and IL-22. Herein we define the roles of IL-12 and IL-23 in regulating host resistance and intestinal inflammation during acute Salmonella infection. We find that IL-23 alone is dispensable for protection against systemic spread of bacteria, but synergizes with IL-12 for optimal protection. IL-12 promotes the production of IFN-γ by NK cells, which is required for resistance against Salmonella and also for induction of intestinal inflammation and epithelial injury. In contrast, IL-23 controls the severity of inflammation by inhibiting IL-12A expression, reducing IFN-γ and preventing excessive mucosal injury. Our studies demonstrate that IL-23 is a homeostatic regulator of IL-12-dependent, IFN-γ-mediated intestinal inflammation.

Gastric Sonic Hedgehog acts as a macrophage chemoattractant during the immune response to Helicobacter pylori

BACKGROUND & AIMS

Macrophages mediate the epithelial response to Helicobacter pylori and are involved in the development of gastritis. Sonic Hedgehog (Shh) regulates gastric epithelial differentiation and function, but little is known about its immunoregulatory role in the stomach. We investigated whether gastric Shh acts as a macrophage chemoattractant during the innate immune response to H pylori infection.

METHODS

Mice with parietal cell-specific deletion of Shh (PC-Shh(KO)) and control mice were infected with H pylori. Levels of gastric Shh, cytokines, and chemokines were assayed by quantitative reverse-transcriptase polymerase chain reaction or by a Luminex-based multiplex assay 2, 7, or 180 days after infection. Circulating concentrations of Shh were measured by enzyme-linked immunosorbent assay. Bone marrow chimera experiments were performed with mice that have myeloid cell-specific deletion of the Hedgehog signal transduction protein Smoothened (LysMCre/Smo(KO)). Macrophage recruitment was measured in gastric tissue and peripheral blood by fluorescence-activated cell sorting analysis.

RESULTS

Control mice infected with H pylori for 6 months developed an inflammatory response characterized by infiltration of CD4(+) T cells and increased levels of interferon gamma and interleukin 1β in the stomach. PC-Shh(KO) mice did not develop gastritis, even after 6 months of infection with H pylori. Control mice had increased concentrations of Shh, accompanied by the recruitment of CD11b(+)F4/80(+)Ly6C(high) macrophages 2 days after infection. Control mice that received bone marrow transplants from control mice had an influx of macrophages to the gastric mucosa in response to H pylori infection; this was not observed in H pylori-infected control mice that received bone marrow transplants from LysMCre/Smo(KO) mice.

CONCLUSIONS

H pylori induces release of Shh from the stomach; Shh acts as a macrophage chemoattractant during initiation of gastritis.

Iatrogenic effects of biologics for psoriasis

Use of the biologic agents in moderate to severe chronic plaque psoriasis has provided novel and highly efficacious treatment options. Generally less systemically toxic than more traditional agents, the risks and benefits for these agents must also be considered. We present a review of the iatrogenic effects associated with use of the biologic agents in psoriasis. Focus is placed on antitumor necrosis factor agents, because they are the most studied and commonly used agents, as well as T-cell modulators and interleukin inhibitors.

Cholinergic stimulation of the immune system protects against lethal infection by Salmonella enterica serovar Typhimurium

SUMMARY

The cholinergic nervous system has been demonstrated to attenuate the inflammatory response during sepsis via the inhibitory action of acetylcholine (ACh) on macrophages. These findings were largely based on experimental sepsis models using endotoxin as the inducing agent. Herein, however, we report that the specific inhibition of acetylcholinesterase (AChE) renders animals more resistant to infection by a virulent strain of Salmonella enterica serovar Typhimurium, a Gram-negative enteric pathogen. Inhibition of AChE was induced by a subchronic exposure to paraoxon, a potent anti-cholinesterase metabolite of the organophosphorous compound parathion. Our findings indicate that inhibition of AChE enhanced survival of infected mice in a dose-dependent fashion and this correlated with efficient control of bacterial proliferation in target organs. Immunologically, inhibition of AChE enabled the animals to mount a more effective inflammatory anti-microbial response, and to secrete higher levels of interleukin-12, a key T helper type 1-promoting cytokine. The ACh-induced enhancement in resistance to infection was abrogated by co-administration of an oxime which can reactivate AChE. Hence, in a model of Gram-negative bacterial infection, cholinergic stimulation is shown to enhance the anti-microbial immune response leading to effective control of bacterial proliferation and enhanced animal survival.

IL-23 is required for protection against systemic infection with Listeria monocytogenes

Listeria monocytogenes (LM) is a Gram-positive, intracellular bacterium that can induce spontaneous abortion, septicemia, and meningitis. Although it is known that neutrophils are required for elimination of the bacteria and for survival of the host, the mechanisms governing the recruitment of neutrophils to LM-infected tissues are not fully understood. We demonstrate here that IL-23 and the IL-17 receptor A (IL-17RA), which mediates both IL-17A and IL-17F signaling, are necessary for resistance against systemic LM infection. LM-infected IL-23p19 knockout (KO) mice have decreased production of IL-17A and IL-17F, while IFN-gamma production is not altered by the lack of IL-23. LM induces the production of IL-17A from gammadelta T cells, but not CD4, CD8, or NK cells. Furthermore, a lack of efficient neutrophil recruitment to the liver is evident in both IL-23p19 KO and IL-17RA KO mice during LM infection. Immunocytochemical analysis of infected livers revealed that neutrophils were able to localize with LM in IL-23p19 KO and IL-17RA KO mice, indicating that IL-23 and IL-17RA do not regulate the precise localization of neutrophils with LM. The importance of IL-23-induced IL-17A was demonstrated by injecting IL-23p19 KO mice with recombinant IL-17A. These mice had reduced LM bacterial burdens compared with IL-23p19 KO mice that did not receive IL-17A. These results indicate that during LM infection, IL-23 regulates the production of IL-17A and IL-17F from gammadelta T cells, resulting in optimal liver neutrophil recruitment and enhanced bacterial clearance.

Both hemolytic anemia and malaria parasite-specific factors increase susceptibility to Nontyphoidal Salmonella enterica serovar typhimurium infection in mice

Severe pediatric malaria is an important risk factor for developing disseminated infections with nontyphoidal Salmonella serotypes (NTS). While recent animal studies on this subject are lacking, early work suggests that an increased risk for developing systemic NTS infection during malaria is caused by hemolytic anemia, which leads to reduced macrophage microbicidal activity. Here we established a model for oral Salmonella enterica serotype Typhimurium challenge in mice infected with Plasmodium yoelii nigeriensis. Initial characterization of this model showed that 5 days after coinoculation, P. yoelii nigeriensis infection increased the recovery of S. Typhimurium from liver and spleen by approximately 1,000-fold. The increased bacterial burden could be only partially recapitulated by antibody-mediated hemolysis, which increased the recovery of S. Typhimurium from liver and spleen by 10-fold. These data suggested that both hemolysis and P. yoelii nigeriensis-specific factors contributed to the increased susceptibility to S. Typhimurium. The mechanism by which hemolysis impaired resistance to S. Typhimurium was further investigated. In vitro, S. Typhimurium was recovered 24 h after infection of hemophagocytic macrophages in 2-fold-higher numbers than after infection of mock-treated macrophages, making it unlikely that reduced macrophage microbicidal activity was solely responsible for hemolysis-induced immunosuppression during malaria. Infection with P. yoelii nigeriensis, but not antibody-mediated hemolysis, reduced serum levels of interleukin-12p70 (IL-12p70) in response to S. Typhimurium challenge. Collectively, studies establishing a mouse model for this coinfection suggest that multiple distinct malaria-induced immune defects contribute to increased susceptibility to S. Typhimurium.

Administration of IL-23 engages innate and adaptive immune mechanisms during fungal infection

IL-23 is a key cytokine in promotion of chronic inflammation. Here, we address if its pro-inflammatory potential can be harnessed to protect against chronic cryptococcosis. Mice were infected with Cryptococcus neoformans and treated with recombinant IL-23. Administration of IL-23 led to prolonged survival and reduced fungal burden but was inferior to IL-12 treatment. Independent of endogenous IL-23/IL-12, IL-23 treatment induced an altered cytokine profile accompanied by marked changes in composition of the inflammatory infiltrate characterized by T cell and dendritic cell recruitment. Although IL-23 induced hallmarks of the T(h)17 pathway, also non-T cells produced IL-17A and IL-22. IL-23 treatment of T-cell-deficient mice resulted in increased IL-17A and IL-22 production and modulation of the cellular response at the site of infection with elevated expression of CD86 on macrophages. Our data show that IL-23 treatment induces innate and adaptive tissue inflammation with limited impact on resistance to chronic cryptococcosis.

Interleukin-23/Th17 pathways and inflammatory bowel disease

The IL-23/Th17 pathway has recently been identified to play a critical role in a number of chronic inflammatory diseases including inflammatory bowel disease (IBD). The identification in IBD patients of associations in IL23R and regions that include other genes in the IL-23/Th17 pathway has highlighted the importance of proper IL-23/Th17 pathway regulation in intestinal immune homeostasis. IL-23 plays a role in CD4+ Th17 lineage cells, characterized by IL-17 secretion and the expression of the transcription factor retinoic acid-related orphan receptor (ROR)gamma tau, and in other immune and nonimmune cells. The balance between effector T cell subsets, such as Th17 cells, and CD4+ T regulatory subsets is finely regulated; dysregulation of this balance can lead to inflammation and autoimmunity. As such, the IL-23/Th17 pathway contributes to immune responses that play a role in defenses to microbial infection, as well as in the intestinal inflammation observed in both animal models of colitis and human IBD.

Endotoxin augmented antigen-induced Th1 cell trafficking amplifies airway neutrophilic inflammation

CD4(+) Th1 cells play a critical role in orchestrating host defense against pathogens and in the pathogenesis of many immune-mediated diseases. The control of Th1 cell trafficking into sites of infection and inflammation is an important determinant of Th1 cell function. We have previously shown that trafficking of adoptively transferred Ag-specific Th1 cells into the lung following airway Ag challenge depends on CXCR3 expression on Th1 cells and STAT1-inducible CXCR3 ligands in the lung. In this study, we show that LPS alters the mechanisms of Th1 cell recruitment. After a single intranasal dose of LPS, trafficking of adoptively transferred Ag-specific Th1 cell into the lung in response to airway Ag challenges was no longer dependent on CXCR3 and its ligands and instead was mediated through additional Galphai-coupled chemoattractant receptor pathways, including CCR5. In addition, LPS markedly increased the magnitude of Ag-specific Th1 cell homing into the airways following airway Ag challenges. The increased trafficking of Ag-activated Th1 cells, in turn, dramatically amplified LPS-induced airway neutrophilic infiltration by maintaining high levels of the neutrophil active chemokines, KC and MIP-2, through an IFN-gamma dependent mechanism. Therefore, LPS increases Ag-specific Th1 cell trafficking into the airways and Ag-specific Th1 cells amplify the airway neutrophilic inflammatory response initiated by LPS. This reciprocal interaction between LPS and Ag-activated Th1 cells represents a collaborative connection between the innate and adaptive arms of the immune system.

Differential IL-23 requirement for IL-22 and IL-17A production during innate immunity against Salmonella enterica serovar Enteritidis

Early activation of the IL-12/IFN-gamma axis has been shown following Salmonella enterica serovar Enteritidis (S. Enteritidis) infection. We were interested to study whether IL-22 and IL-17A production is initiated early in response to S. Enteritidis. We demonstrate here that IL-22 was strongly elevated in the peritoneal lavage fluid and in serum already 1 day post-intraperitoneal infection (d.p.i.) of mice; not only IL-22 but also IL-17A was produced ex vivo by activated peritoneal exudate cells (PEC). Peritoneal gammadelta T cells were identified as cellular source of IL-17A. The early IL-22 production was completely IL-23-dependent. In contrast, IL-17A production was only partially IL-23-dependent. To investigate the local production of upstream cytokines important for induction of IL-22, IL-17A and IFN-gamma during salmonellosis, the production of IL-23 and IL-12 was studied. Elevated p19 and p40 mRNA levels were found in PEC at 1 d.p.i., whereas p35 mRNA levels were not changed. Besides, the T(h)17-promoting cytokines IL-6, IL-1beta and transforming growth factor-beta were produced in response to S. Enteritidis. However, IL-6 was not required for IL-22 or IL-17A production by PEC. By ex vivo analysis of PEC at 1 d.p.i., we show that the major producers of early IL-12/23p40 in the peritoneal cavity were dendritic cells (DC), whereas macrophages notably contributed to IL-6 production. Taken together, these data suggest that DC initiate early IL-22 production at the site of infection which may contribute to resistance against salmonellosis. Furthermore, we provide evidence that production of IL-22 and IL-17A is differentially regulated during infection.

Cytokines in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of autoantibodies that can form immune complexes and deposit in tissues, causing inflammation and organ damage. There is evidence that interferons and some interleukins can have an active role in the pathogenesis of SLE and can contribute significantly to the immune imbalance in the disease, whereas the role of some cytokines (such as TNF) is still debated. This review discusses the activity of several cytokines in SLE, their effects on the immune cells in relation to the disease pathogenesis, and the promise and limitations of cytokine-based therapies in clinical trials for lupus patients.

The roles of IL-17A in inflammatory immune responses and host defense against pathogens

T-helper 17 (Th17) cells are a newly discovered CD4(+) helper T-cell subset that produces interleukin-17A (IL-17A) and IL-17F. IL-17A plays important roles in allergic responses such as delayed-type hypersensitivity, contact hypersensitivity, and allergic airway inflammation. IL-17A promotes inflammation by inducing various proinflammatory cytokines and chemokines, recruiting neutrophils, enhancing antibody production, and activating T cells. IL-17A expression is also augmented in autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. Using mouse models of these diseases, we found that IL-17A plays a central role in their development. IL-6 is required for the development of Th17 cells and tumor necrosis factor functions downstream of IL-17A during the effector phase. IL-1 is important both for developing Th17 cells and eliciting inflammation. Th17 cells, like Th1 and Th2 cells, are involved in host defense against infections, but the contribution of these Th subsets to defense mechanisms differs among pathogens. The roles of IL-17F remain largely unknown. In this review, we introduce how IL-17A/IL-17F are involved in inflammatory immune responses and host defense mechanisms and discuss their relationship with other cytokines in the development of inflammatory and infectious diseases.

IL-23 modulates CD56+/CD3- NK cell and CD56+/CD3+ NK-like T cell function differentially from IL-12

NK and NK-like T cells play an essential role in linking innate and adaptive immunity through their ability to secrete IFN-gamma. The exact trigger initiating production of IFN-gamma is uncertain. Antigen-presenting cell (APC)-derived IL-12 is thought to be the classical IFN-gamma-inducing cytokine but requires an additional stimulus such as IFN-gamma itself. IL-23 and IL-18 are among the first cytokines secreted by APC in response to binding of pathogen-associated molecular patterns such as LPS. Thus, early APC-derived IL-23 may be an initial trigger of IFN-gamma production in NK and NK-like T cells. Herein, we characterized the effect of IL-23 on IFN-gamma secretion by NK and NK-like T cells. Our findings show that IL-23 and IL-18 synergistically elicit IFN-gamma production in NK-like T cells but not in NK cells. In contrast, IL-12 together with IL-18-induced secretion of IFN-gamma in both populations. The observed synergy between IL-23 and IL-18 in NK-like T cells coincided with IL-23-mediated up-regulation of IL-18Ralpha. Furthermore, IL-23 up-regulated CD56 expression in NK-like T cells and, together with IL-18, induced proliferation of NK and NK-like T cells. We postulate a role for APC-derived IL-23 in the activation of NK and NK-like T cells early in infection and in shaping T(h)1 differentiation, via induction of IFN-gamma, which provides the additional stimulus needed for APC to subsequently produce IL-12.

Protective immunity to systemic infection with attenuated Salmonella enterica serovar enteritidis in the absence of IL-12 is associated with IL-23-dependent IL-22, but not IL-17

IL-12 is essential for protective T cell-mediated immunity against Salmonella infection. To characterize the role of the related cytokine IL-23, wild-type (WT) C57BL/6 and p19(-/-) mice were infected systemically with an attenuated strain of Salmonella enterica serovar Enteritidis (S. Enteritidis). IL-23-deficient mice controlled infection with S. Enteritidis similarly as WT mice. Similar IFN-gamma production as compared with WT mice, but defective IL-17A and IL-22 production was found in the absence of IL-23. Nevertheless, although IL-23 is required for T cell-dependent cytokine responses, IL-23 is dispensable for protection against S. Enteritidis when IL-12 is present. To analyze the role of IL-23 in the absence of IL-12, low doses of S. Enteritidis were administered to p35(-/-) mice (lacking IL-12), p35/19(-/-) mice (lacking IL-12 and IL-23), p35/40(-/-) mice (lacking IL-12, IL-23, and homodimeric IL-12p40), or p35/IL-17A(-/-) mice (lacking IL-12 and IL-17A). We found survival of p35(-/-) and p35/IL-17A(-/-) mice, whereas p35/19(-/-) and p35/40(-/-) mice died within 3-6 wk and developed liver necrosis. This indicates that IL-23, but not homodimeric IL-12p40, is required for protection, which, surprisingly, is independent of IL-17A. Moreover, protection was associated with IL-22, but not IL-17F or IL-21 expression or with neutrophil recruitment. Finally, anti-IL-22 treatment of S. Enteritidis-infected p35(-/-) mice resulted in liver necrosis, indicating a central role of IL-22 in hepatocyte protection during salmonellosis. In conclusion, IL-23-dependent IL-22, but not IL-17 production is associated with protection against systemic infection with S. Enteritidis in the absence of IL-12.

The role of interleukin-12 in the heavy metal-elicited immunomodulation: relevance of various evaluation methods

Background

Increasing evidence exists that heavy metals modulate T helper cell (Th) responses and thereby elicit various pathological manifestation. Interleukin (IL)-12, a crucial innate cytokine, was found to be regulated by such xenobiotic agents. This study aimed at testing whether IL-12 profiles may be indicative of heavy metals-induced immunomodulation.

Methods

Human immunocompetent cells, activated either by monoclonal antibodies or heat-killed Salmonella enterica, were cultured in the absence or presence of cadmium (Cd) acetate or mercuric (Hg) chloride. In vivo experiments were set up where BALB/c mice were exposed to sub-lethal doses of Cd or Hg salts for 3 or 5 weeks. Cytotoxicity was assessed by MTT-reduction assay. Modulation of cytokine profiles was evaluated by enzyme-linked immunosorbent assay (ELISA), cytometric bead-based array (CBA) and real-time polymerase chain reaction (RT-PCR); the relevance of these methods of cytokine quantification was explored.

Results

Modulation of IL-12 profiles in Cd- or Hg-exposed human PBMC was dose-dependent and significantly related to IFN-γ levels as well as to the Th1- or Th2-polarized responses. Similarly, skewing the Th1/Th2 ratios in vivo correlated significantly with up- or down-regulation of IL-12 levels in both cases of investigated metals.

Conclusion

It can be inferred that: (i) IL-12 profiles alone may represent a relevant indicator of heavy metal-induced immune modulation; (ii) evaluating cytokine profiles by CBA is relevant and can adequately replace other methods such as ELISA and RT-PCR in basic research as well as in immune diagnostics; and (iii) targeting IL-12 in therapeutic approaches may be promising to modify Th1/Th2-associated immune disorders.

LPS and poly I:C induce chromatin modifications at a novel upstream region of the IL-23 p19 promoter

IL-23, a heterodimer of IL-12 p40 and IL-23 p19, is critical for an effective immune response to many infections and has been implicated in several autoimmune diseases, however, little is known about the regulation of IL-23 gene expression in monocytes. We found that poly I:C, LPS, flagellin, and zymogen activated significant IL-23 production in primary human monocytes. Using chromatin immunoprecipitation, we found that a distal upstream region of the IL-23 p19 promoter at -601 to -521 underwent extensive histone modifications in response to stimuli. This distal region of the promoter is not highly conserved between species and has not been previously implicated in the regulation of IL-23 expression. Knockdown of CBP markedly decreased IL-23 p19 responses to poly I:C but had a less dramatic effect on LPS responses, confirming different chromatin responses to these two stimuli. Our data suggest that one of the mechanisms regulating IL-23 expression is the regulation of histone modifications at this distal upstream region of the promoter.

Galectin-3 is a negative regulator of lipopolysaccharide-mediated inflammation

Galectin-3 is a beta-galactoside-binding lectin that plays an important role in inflammatory diseases. It also interacts with the surface carbohydrates of many pathogens, including LPS. However, its role in infection is not fully understood. Data presented herein demonstrate for the first time that galectin-3 is a negative regulator of LPS-induced inflammation. Galectin-3 is constitutively produced by macrophages and directly binds to LPS. Galectin-3-deficient macrophages had markedly elevated LPS-induced signaling and inflammatory cytokine production compared with wild-type cells, which was specifically inhibited by the addition of recombinant galectin-3 protein. In contrast, blocking galectin-3 binding sites by using a neutralizing Ab or its ligand, beta-lactose, enhanced LPS-induced inflammatory cytokine expression by wild-type macrophages. In vivo, mice lacking galectin-3 were more susceptible to LPS shock associated with excessive induction of inflammatory cytokines and NO production. However, these changes conferred greater resistance to Salmonella infection. Thus, galectin-3 is a previously unrecognized, naturally occurring, negative regulator of LPS function, which protects the host from endotoxin shock but, conversely, favors Salmonella survival.

IL-17A is produced by Th17, gammadelta T cells and other CD4- lymphocytes during infection with Salmonella enterica serovar Enteritidis and has a mild effect in bacterial clearance

T(h)17 cells represent a new pro-inflammatory T(h) cell lineage distinct from T(h)1 and T(h)2 cells. T(h)17 cells have been shown to be involved in extracellular bacterial infection but their role in intracellular infection remains unclear. We found antigen-specific IL-17A production during a systemic infection of mice with the facultative intracellular bacterium Salmonella enterica serovar Enteritidis (S. Enteritidis) and examined the function and cellular source of IL-17A during the adaptive immune response to S. Enteritidis. Infected IL-17A-/- mice survived completely after inoculation with the highest infection dose found to be sub-lethal for wild-type (WT) C57BL/6 mice. However, at 20 and 80 days post-infection (d.p.i.), we repeatedly found mildly elevated bacterial burden in spleen and liver of IL-17A-/- mice as compared with WT mice. Overall, IL-17A-/- mice showed reduced clearance of S. Enteritidis. S. Enteritidis-specific IL-17A production was induced in splenocytes and lymph node cells of infected WT mice at both time points, 20 and 80 d.p.i. Classical CD4+ T(h)17 cells developed upon infection with Salmonella. CD4- gammadelta TCR+ and CD4- gammadelta TCR- cells were found to be additional IL-17A-producing cell populations. In infected IL-17A-/- mice, a normal T(h)1 cytokine profile was observed consistent with the overall subtle phenotype. Nevertheless, in the absence of IL-17A, recruitment of neutrophils and delayed-type hypersensitivity (DTH) reactivity was significantly compromised. Our data indicate that IL-17A responses are induced by Salmonella and mildly contribute to protective immunity during S. Enteritidis infection. Thus, IL-17A complements the IL-12/IFN-gamma axis which is essential for protective immunity against salmonellosis in mice and men.

The capacity of Salmonella to survive inside dendritic cells and prevent antigen presentation to T cells is host specific

Infection with Salmonella enterica serovar Typhimurium (S. Typhimurium) causes a severe and lethal systemic disease in mice, characterized by poor activation of the adaptive immune response against Salmonella-derived antigens. Recently, we and others have reported that this feature relies on the ability of S. Typhimurium to survive within murine dendritic cells (DCs) and avoid the presentation of bacteria-derived antigens to T cells. In contrast, here we show that infection of murine DCs with either S. Typhi or S. Enteritidis, two serovars adapted to different hosts, leads to an efficient T-cell activation both in vitro and in vivo. Accordingly, S. Typhi and S. Enteritidis failed to replicate within murine DCs and were quickly degraded, allowing T-cell activation. In contrast, human DCs were found to be permissive for survival and proliferation of S. Typhi, but not for S. Typhimurium or S. Enteritidis. Our data suggest that Salmonella host restriction is characterized by the ability of these bacteria to survive within DCs and avoid activation of the adaptive immune response in their specific hosts.

Targets of anticytokine therapy and the risk of infections in humans and mice

PURPOSE OF REVIEW

To examine the type and risk of infections in humans and mice deficient in proinflammatory cytokines. Naturally occurring or manipulated genetic defects of tumor necrosis factor, interleukins-1, -6, -12, and -15, and interferon-gamma are examined for their increased susceptibility to, or protection from, infection.

RECENT FINDINGS

Interleukin-12p40 and interferon-gamma-blockers may lead to increased incidence of infections with intracellular bacteria, parasites, and fungi. In addition, we may see viral infections with interferon-gamma-blockers. Increased risk of infections is unlikely with either interleukin-1- or interleukin-15-blockers. Interleukin-6-blockers may lead to increased risk of infection with extracellular bacteria, viruses, parasites and fungi.

SUMMARY

In tumor necrosis factor knockout mice, increased susceptibility to pathogens are reported that are normally controlled by granuloma formation. In patients treated with tumor necrosis factor-blockers, a two-fold increase of granulomatous infections, predominantly reactivation of latent tuberculosis, is found. The infections detected in tumor necrosis factor knockout mice were accurate for predicting the infections observed when using tumor necrosis factor-blockers. If a similar correlation exists for other cytokines, the use of interferon-gamma and interleukin-12p40 blockers, and possibly interleukin-6 blockers, will lead to an increased risk for severe infections. Care should be taken when new cytokine blockers/antagonists are introduced.

Signal transducer and activator of transcription 4 (STAT4), but not IL-12 contributes to Pseudomonas aeruginosa-induced lung inflammation in mice

Pseudomonas aeruginosa is a major opportunistic pathogen in immune-compromised individuals and cystic fibrosis patients. This organism stimulates a complex inflammatory response in the lung, including production of various cytokines and chemokines. The specific contribution of these mediators in the host defense against this bacterium has yet to be fully characterized. Interleukin-12 (IL-12) is commonly known as a master regulator of innate and adaptive immunity. IL-12 induces its biological effects through its associated intracellular signaling molecule, the signal transducer and activator of transcription 4 (STAT4). To examine a specific role of IL-12 and STAT4 in P. aeruginosa lung infection in mice, STAT4-deficient (STAT4-/-) and IL-12 p40-deficient (IL-12 p40-/-) mice were infected with P. aeruginosa intranasally. Interestingly, STAT4-/- mice, but not IL-12 p40-/- mice after 24h infection showed impaired production of the pro-inflammatory cytokines tumor necrosis factor, interleukin-1beta, and macrophage-inflammatory protein-2. However, neither STAT4 nor IL-12 p40 deficiency significantly affected INFgamma production or bacterial clearance compared to wild-type mice. Similarly, neutrophil recruitment was not affected in the STAT4-/- and IL-12 p40-/- mice. These results suggest that STAT4 contributes to P. aeruginosa-induced inflammation, but it is not essential for bacterial clearance. Although IL-12 is essential for the host defense against various pathogens, this cytokine is likely not a major player in the host response to P. aeruginosa lung infection.

Gamma interferon-independent effects of interleukin-12 on immunity to Salmonella enterica serovar Typhimurium

Interleukin-12 (IL-12) and IL-18 are both central to the induction of gamma interferon (IFN-gamma), and various roles for IL-12 and IL-18 in control of intracellular microbial infections have been demonstrated. We used IL-12p40(-/-) and IL-18(-/-) mice to further investigate the role of IL-12 and IL-18 in control of Salmonella enterica serovar Typhimurium. While C57BL/6 and IL-18(-/-) mice were able to resolve attenuated S. enterica serovar Typhimurium infections, the IL-12p40(-/-) mice succumbed to a high bacterial burden after 60 days. Using ovalbumin (OVA)-specific T-cell receptor transgenic T cells (OT-II cells), we demonstrated that following oral infection with recombinant S. enterica serovar Typhimurium expressing OVA, the OT-II cells proliferated in the mesenteric lymph nodes of C57BL/6 and IL-18(-/-) mice but not in IL-12p40(-/-) mice. In addition, we demonstrated by flow cytometry that equivalent or increased numbers of T cells produced IFN-gamma in IL-12p40(-/-) mice compared with the numbers of T cells that produced IFN-gamma in C57BL/6 and IL-18(-/-) mice. Finally, we demonstrated that removal of macrophages from S. enterica serovar Typhimurium-infected C57BL/6 and IL-12p40(-/-) mice did not affect the bacterial load, suggesting that impaired control of S. enterica serovar Typhimurium infection in the absence of IL-12p40 is not due to reduced macrophage bactericidal activities, while IL-18(-/-) mice did rely on the presence of macrophages for control of the infection. Our results suggest that IL-12p40, but not IL-18, is critical to resolution of infections with attenuated S. enterica serovar Typhimurium and that especially the effects of IL-12p40 on proliferative responses of CD4+ T cells, but not the ability of these cells to produce IFN-gamma, are important in the resolution of infection by this intracellular bacterial pathogen.

Interleukin-12, interleukin-23, and psoriasis: Current prospects

The clinical phenotype of psoriasis results from infiltration of T cells in the skin and elaboration of inflammatory cytokines. Interleukin (IL)-12 and, more recently, IL-23 have been implicated in the pathogenesis of psoriatic lesions. New therapies, including a monoclonal antibody against a subunit shared by IL-12 and IL-23, have been developed to treat psoriasis. Our purpose was to review the literature on IL-12 and IL-23 as a basis for understanding the use of anti-IL-12/IL-23 therapy for psoriasis. A review of English-language articles was performed using PubMed to identify articles pertaining to IL-12, IL-23, and psoriasis. IL-12 and IL-23 share a common subunit (p40) and have a distinct subunit (p35 and p19, respectively). Transgenic mice that overexpress IL-12 p40 develop inflammatory skin lesions. Both IL-12 knockout mice, which are deficient in IL-12, and human beings with a genetic IL-12 deficiency show increased susceptibility to intracellular pathogens and defective delayed-type hypersensitivity responses. These genetic deficiency states suggest the potential for adverse side effects from clinical administration of anti IL-12 p40 therapy. IL-12 p40 antibody was well tolerated in a phase I clinical trial with few adverse events and substantial improvements in psoriasis in most individuals. There was dose-dependent efficacy and substantial improvement in a larger cohort of patients in a phase II clinical trial. Larger and longer trials of anti IL-12/IL-23 therapies are needed to assess their clinical use and potential for infection and other adverse events.

Production of IL-12, IL-23 and IL-27p28 by bone marrow-derived conventional dendritic cells rather than macrophages after LPS/TLR4-dependent induction by Salmonella Enteritidis

Induction of the interleukin-12 (IL-12) cytokine family comprising IL-12, IL-23, IL-27, and IL-12p40 by intracellular pathogens is required for orchestration of cell-mediated immune responses. Macrophages (MPhi) have been shown to be a source of IL-12 following TLR4-dependent activation by Salmonella (S.). In this study another antigen-presenting cell type, the conventional dendritic cell (cDC), was analyzed and its cytokine responses compared with those of MPhi. We generated bone marrow-derived conventional dendritic cells (BMDC) and macrophages (BMMPhi) by incubating murine bone marrow cells with supernatants containing granulocyte/macrophage colony-stimulating factor (GM-CSF) or macrophage colony-stimulating factor (M-CSF), respectively. Stimulation of BMDC and BMMPhi with S. enterica serovar Enteritidis (SE) or LPS resulted in the release of IL-12 and IL-23 by BMDC but not by BMMPhi. Furthermore, BMDC secreted approx. 20-fold more IL-12p40 and IL-27p28 than BMMPhi. However, BMDC and BMMPhi produced similar levels of IL-10. Using BMDC originating from wild-type (wt), TLR2(def) and TLR4(def) mice, we show that in BMDC the induction of IL-12, IL-23, and IL-27p28 by SE is dependent on TLR4, whereas low-level production of p40 is also mediated by pattern recognition receptors (PRR) other than TLR4. Interestingly, LPS- and SE-provoked responses of BMDC were remarkably similar indicating that LPS is the primary danger molecule of SE. Taken together, our results point to cDC rather than MPhi as the major producers of the IL-12 family members during in vitro infection with SE. The mechanisms of recognition of SE, however, appear to be the same for cDC and MPhi.

Monocyte and dendritic cell recruitment and activation during oral Salmonella infection

Immunity to bacterial infection involves the joint effort of the innate and adaptive immune systems. The innate immune response is triggered when the body senses bacterial components, such as lipopolysaccharide, that alarm the body of the invader. An array of cell types function in the innate response. These cells are rapidly recruited to the infection site and activated to optimally perform their functions. The adaptive immune response follows the innate response, and one cell type in particular, dendritic cells (DCs), are the critical link between the innate and adaptive responses. This review will summarize recent data concerning the events that occur early during oral infection with the intracellular pathogen Salmonella, with emphasis on the phagocytic cells involved in combating the infection in the gut-associated lymphoid tissues. In particular, recent findings concerning the recruitment and activation of mononuclear phagocyte populations and dendritic cell subsets will be presented after an overview of the Salmonella infection model.

Immunomodulatory Dendritic Cells Inhibit Th1 Responses and Arthritis via Different Mechanisms

Dendritic cells (DCs) are professional APCs which have the unique ability to present both foreign and self-Ags to T cells and steer the outcome of immune responses. Because of these characteristics, DCs are attractive vehicles for the delivery of therapeutic vaccines. Fully matured DCs are relatively well-defined and even used in clinical trials in cancer. DCs also have the potential to influence the outcome of autoimmunity by modulating the underlying autoimmune response. To gain a better appreciation of the abilities and mechanisms by which immunomodulatory DCs influence the outcome of T cell responses, we studied several immunomodulatory DCs (TNF-, IL-10-, or dexamethasone-stimulated bone marrow-derived DCs) side by side for their ability to modulate T cell responses and autoimmune diseases. Our data show that these differentially modulated DCs display a different composition of molecules involved in T cell activation. Although, all DC subsets analyzed were able to inhibit the induction of collagen-induced arthritis, the modulation of the underlying immune response was different. Vaccination with TNF- or IL-10-modulated DCs altered the Th1/Th2 balance as evidenced by the induction of IL-5- and IL-10-secreting T cells and the concomitant reduction of the IgG2a-IgG1 ratio against the immunizing Ag. In contrast, DCs modulated with dexamethasone did not affect the ratio of IL-5-producing vs IFN-gamma-producing T cells and tended to affect the Ab response in a nonspecific manner. These data indicate that distinct mechanisms can be used by distinct DC subsets to change the outcome of autoimmunity.

Chorionic gonadotropin can enhance innate immunity by stimulating macrophage function

Human chorionic gonadotropin (hCG) is a placental glycoprotein, mainly secreted by trophoblasts during pregnancy. Its function in endocrine regulation has been well documented, but its immunological role is still largely unclear. For a successful pregnancy, an effective innate immunity is needed to protect the mother and fetus against infection, while maintaining tolerance against the paternal antigens of the fetus. The aim of this study was to investigate the effect of hCG on the function of macrophages (Mvarphi), which are major players in the innate response. hCG treatment of IFN-gamma-primed Mvarphi resulted in increased production of NO, reactive oxygen species, IL-6 and IL-12p40, and enhanced phagocytosis of apoptotic cells. hCG treatment did not affect the induction of allogeneic T cell proliferation by IFN-gamma-primed Mvarphi. The observed effects were receptor-mediated and involved the protein kinase A signaling pathway, as indicated by blocking studies using specific inhibitors. In vivo thioglycollate-elicited Mvarphi also exhibited increased phagocytic ability upon IFN-gamma activation and hCG treatment. In conclusion, hCG enhances Mvarphi functions involved in innate immunity, while the capacity to stimulate allogeneic T cells remains unchanged.

Yersinia-triggered arthritis in IL-12p40-deficient mice: relevant antigens and local expression of Toll-like receptor mRNA

OBJECTIVES

To study the role of IL-12p40 at the onset of reactive arthritis (ReA) after Yersinia enterocolitica O:3 infection, and analyse relevant microbial antigens and articular expression of Toll-like receptor (TLR) mRNA.

METHODS

Wild-type C57BL/6 and IL-12p40-deficient (IL-12p40-/-) mice were orogastrically infected with Y. enterocolitica O:3. Early (day 3) and late (day 21) after infection, the number of bacteria were determined in Peyer's patches (PP), mesenteric lymph nodes (MLN), the spleen, and joints. Histological studies of joints were performed. Collagen-specific and anti-Yersinia antibodies were measured by enzyme-linked immunosorbent assay (ELISA). The presence of Yersinia antigens was studied by dot blot. Induction of articular mRNA of TLR2, TLR4, and tumour necrosis factor (TNF)-alpha was analysed by reverse transcription-polymerase chain reaction (RT-PCR). TNFalpha protein levels were measured by ELISA.

RESULTS

At day 3, bacterial recovery in PP, MLN, and spleen was significantly increased in IL-12p40-/- mice. Histopathological changes were observed in IL-12p40-/- mice at day 21 after infection, and correlated with higher antibody response against type II collagen. Although live bacteria could not be isolated at day 21 after infection, articular microbial components, especially from the outer membrane (OM), were detected. Moreover, intra-articular immunoglobulins to Yersinia antigens were significantly higher in IL-12p40-/- mice. Furthermore, mRNA levels for TLR2, TLR4 and TNFalpha, and TNFalpha protein were increased in joints from IL-12p40-/- mice.

CONCLUSIONS

We concluded that IL-12p40 influences the resistance against Yersinia-triggered ReA. Bacterial products such as Yersinia OM could contribute to the ReA by induction of articular TLR expression, which results in an inflammatory response in the joint.

Impact of Salmonella Typhimurium DT104 virulence factors invC and sseD on the onset, clinical course, colonization patterns and immune response of porcine salmonellosis

The present study was conducted to study the impact of the virulence factors invC and sseD of the two type III secretion systems of Salmonella enterica serovar Typhimurium (S. Typhimurium) on the pathogenesis of the porcine S. Typhimurium DT104 infection. For this purpose, two S. Typhimurium mutant strains with a disrupted invC gene of the Salmonella pathogenicity island 1 or with a disrupted sseD gene of the Salmonella pathogenicity island 2 have been studied in experimental infection of pigs. Twenty-two 7-week-old male hybrid pigs were either infected with one of the mutants or the wild-type S. Typhimurium DT104 strain. Each group was examined for clinical signs, Salmonella shedding rate and the specific antibody response. Survival and replication were evaluated by qualitative and quantitative determination of the colonization rate. The humoral and cellular immune responses were examined using isotype-specific ELISA and quantitative real-time PCR of IL-2, IL-4, IL-10, IL-12 and IFN-gamma. The results proved that both mutants had a lower virulence (with marked differences between both mutants) than the wild-type and that both virulence factors have importance in porcine salmonellosis. Only pigs infected with the wild-type S. Typhimurium DT104 exhibited typical clinical symptoms of salmonellosis like anorexia, vomiting, disturbed demeanour, fever and diarrhoea. Deletion of the invC gene resulted in a significantly reduced colonization rate. Interestingly, the mRNA expression of both type-1 and type-2 cytokines were significantly decreased in pigs infected with either the invC-mutant and the sseD-mutant strain.

Interleukin-23 (IL-23)-IL-17 cytokine axis in murine Pneumocystis carinii infection

Host defense mechanisms against Pneumocystis carinii are not fully understood. Previous work in the murine model has shown that host defense against infection is critically dependent upon host CD4(+) T cells. The recently described Th17 immune response is predominantly a function of effector CD4(+) T cells stimulated by interleukin-23 (IL-23), but whether these cells are required for defense against P. carinii infection is unknown. We tested the hypothesis that P. carinii stimulates the early release of IL-23, leading to increases in IL-17 production and lung effector CD4(+) T-cell population that mediate clearance of infection. In vitro, stimulation of alveolar macrophages with P. carinii induced IL-23, and IL-23p19 mRNA was expressed in lungs of mice infected with this pathogen. To address the role of IL-23 in resistance to P. carinii, IL-23p19-/- and wild-type control C57BL/6 mice were infected and their fungal burdens and cytokine/chemokine responses were compared. IL-23p19-/- mice displayed transient but impaired clearance of infection, which was most apparent 2 weeks after inoculation. In confirmatory studies, the administration of either anti-IL-23p19 or anti-IL-17 neutralizing antibody to wild-type mice infected with P. carinii also caused increases in fungal burdens. IL-17 and the lymphocyte chemokines IP-10, MIG, MIP-1alpha, MIP-1beta, and RANTES were decreased in the lungs of infected IL-23p19-/- mice in comparison to their levels in the lungs of wild-type mice. In IL-23p19-/- mice infected with P. carinii, there were fewer effector CD4(+) T cells in the lung tissue. Collectively, these studies indicate that the IL-23-IL-17 axis participates in host defense against P. carinii.

Salmonella, the host and disease: a brief review

Salmonella species cause substantial morbidity, mortality and burden of disease globally. Infections with Salmonella species cause multiple clinical syndromes. Central to the pathophysiology of all human salmonelloses is the induction of a strong host innate immune/inflammatory response. Whether this ultimately reflects an adaptive advantage to the host or pathogen is not clear. However, it is evident that both the host and pathogen have evolved mechanisms of triggering host responses that are detrimental to the other. In this review, we explore some of the host and pathogenic mechanisms mobilized in the two predominant clinical syndromes associated with infection with Salmonella enterica species: enterocolitis and typhoid.

IL-12p40: an inherently agonistic cytokine

IL-12p40 is known as a component of the bioactive cytokines interleukin (IL)-12 and IL-23 but it is not widely recognized as having intrinsic functional activity. Recent publications have altered this perception and support an independent role for IL-12p40. IL-12p40 is induced in excess over the other subunits of IL-12 and IL-23 and can exist in a monomeric or homodimeric form. Its most widely appreciated function is to provide a negative feedback loop by competitively binding to the IL-12 receptor. However, IL-12p40 acts as a chemoattractant for macrophages and promotes the migration of bacterially stimulated dendritic cells. It is associated with several pathogenic inflammatory responses such as silicosis, graft rejection and asthma but it is also protective in a mycobacterial model. An appreciation of the independent function of IL-12p40 is important for improving our understanding of both protective and pathogenic immune responses.