Compartment-specific and sequential role of MyD88 and CARD9 in chemokine induction and innate defense during respiratory fungal infection.

Aspergillus fumigatus forms ubiquitous airborne conidia that humans inhale on a daily basis. Although respiratory fungal infection activates the adaptor proteins CARD9 and MyD88 via C-type lectin, Toll-like, and interleukin-1 family receptor signals, defining the temporal and spatial pattern of MyD88- and CARD9-coupled signals in immune activation and fungal clearance has been difficult to achieve. Herein, we demonstrate that MyD88 and CARD9 act in two discrete phases and in two cellular compartments to direct chemokine- and neutrophil-dependent host defense. The first phase depends on MyD88 signaling because genetic deletion of MyD88 leads to delayed induction of the neutrophil chemokines CXCL1 and CXCL5, delayed neutrophil lung trafficking, and fatal pulmonary damage at the onset of respiratory fungal infection. MyD88 expression in lung epithelial cells restores rapid chemokine induction and neutrophil recruitment via interleukin-1 receptor signaling. Exogenous CXCL1 administration reverses murine mortality in MyD88-deficient mice. The second phase depends predominately on CARD9 signaling because genetic deletion of CARD9 in radiosensitive hematopoietic cells interrupts CXCL1 and CXCL2 production and lung neutrophil recruitment beyond the initial MyD88-dependent phase. Using a CXCL2 reporter mouse, we show that lung-infiltrating neutrophils represent the major cellular source of CXCL2 during CARD9-dependent recruitment. Although neutrophil-intrinsic MyD88 and CARD9 function are dispensable for neutrophil conidial uptake and killing in the lung, global deletion of both adaptor proteins triggers rapidly progressive invasive disease when mice are challenged with an inoculum that is sub-lethal for single adapter protein knockout mice. Our findings demonstrate that distinct signal transduction pathways in the respiratory epithelium and hematopoietic compartment partially overlap to ensure optimal chemokine induction, neutrophil recruitment, and fungal clearance within the respiratory tract.

Unexpected role for IL-17 in protective immunity against hypervirulent Mycobacterium tuberculosis HN878 infection.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), infects one third of the world's population. Among these infections, clinical isolates belonging to the W-Beijing appear to be emerging, representing about 50% of Mtb isolates in East Asia, and about 13% of all Mtb isolates worldwide. In animal models, infection with W-Beijing strain, Mtb HN878, is considered "hypervirulent" as it results in increased mortality and causes exacerbated immunopathology in infected animals. We had previously shown the Interleukin (IL) -17 pathway is dispensable for primary immunity against infection with the lab adapted Mtb H37Rv strain. However, it is not known whether IL-17 has any role to play in protective immunity against infection with clinical Mtb isolates. We report here that lab adapted Mtb strains, such as H37Rv, or less virulent Mtb clinical isolates, such as Mtb CDC1551, do not require IL-17 for protective immunity against infection while infection with Mtb HN878 requires IL-17 for early protective immunity. Unexpectedly, Mtb HN878 induces robust production of IL-1ß through a TLR-2-dependent mechanism, which supports potent IL-17 responses. We also show that the role for IL-17 in mediating protective immunity against Mtb HN878 is through IL-17 Receptor signaling in non-hematopoietic cells, mediating the induction of the chemokine, CXCL-13, which is required for localization of T cells within lung lymphoid follicles. Correct T cell localization within lymphoid follicles in the lung is required for maximal macrophage activation and Mtb control. Since IL-17 has a critical role in vaccine-induced immunity against TB, our results have far reaching implications for the design of vaccines and therapies to prevent and treat emerging Mtb strains. In addition, our data changes the existing paradigm that IL-17 is dispensable for primary immunity against Mtb infection, and instead suggests a differential role for IL-17 in early protective immunity against emerging Mtb strains.

Mucosal pre-exposure to Th17-inducing adjuvants exacerbates pathology after influenza infection.

Mucosal vaccines are thought to confer superior protection against mucosal infectious diseases. In addition, mucosal routes of vaccine delivery preferentially induce the generation of T helper 17 (Th17) cells, which produce the cytokine IL-17. Th17 cells are critical in mediating vaccine-induced immunity against several mucosal infectious diseases. However, IL-17 is also a potent proinflammatory cytokine, and we recently showed that IL-17 mediates immunopathology and lung injury after influenza infection in mice. In the present study, we tested the hypothesis that mucosal pre-exposure to Th17-inducing adjuvants can promote disease exacerbation upon subsequent infection with influenza virus. Mice mucosally pre-exposed to Th17-inducing adjuvants, such as type II heat-labile enterotoxin or cholera toxin, resulted in increased morbidity and exacerbated lung inflammation upon subsequent infection with influenza virus. Furthermore, the increased morbidity was accompanied by increased expression of inflammatory chemokines and increased accumulation of neutrophils. Importantly, blockade of the IL-17 pathway in mice pre-exposed to Th17-inducing adjuvants resulted in attenuation of the inflammatory phenotype seen in influenza-infected mice. Our findings indicate that, before mucosal Th17-inducing adjuvants can be used in vaccine strategies, the short- and long-term detrimental effects of such adjuvants on disease exacerbation and lung injury in response to infections, such as influenza, should be carefully studied.

Massive mobilization of dendritic cells during influenza A virus subtype H5N1 infection of nonhuman primates.

Highly pathogenic avian influenza virus infection is characterized by a marked inflammatory response, but the impact of infection on dendritic cells (DCs) is unknown. We show that influenza A virus subtype H5N1 infection rapidly and profoundly impacts DCs in cynomolgus macaques, increasing the number of blood myeloid and plasmacytoid DCs by 16- and 60-fold, respectively. Infection was associated with recruitment, activation, and apoptosis of DCs in lung-draining lymph nodes; granulocyte and macrophage infiltration in lungs was also detected, together with expression of CXCL10. This degree of DC mobilization is unprecedented in viral infection and suggests a potential role for DCs in the pathogenesis of highly pathogenic avian influenza virus.

S100A8/A9 proteins mediate neutrophilic inflammation and lung pathology during tuberculosis.

RATIONALE: A hallmark of pulmonary tuberculosis (TB) is the formation of granulomas. However, the immune factors that drive the formation of a protective granuloma during latent TB, and the factors that drive the formation of inflammatory granulomas during active TB, are not well defined. OBJECTIVES: The objective of this study was to identify the underlying immune mechanisms involved in formation of inflammatory granulomas seen during active TB. METHODS: The immune mediators involved in inflammatory granuloma formation during TB were assessed using human samples and experimental models of Mycobacterium tuberculosis infection, using molecular and immunologic techniques. MEASUREMENTS AND MAIN RESULTS: We demonstrate that in human patients with active TB and in nonhuman primate models of M. tuberculosis infection, neutrophils producing S100 proteins are dominant within the inflammatory lung granulomas seen during active TB. Using the mouse model of TB, we demonstrate that the exacerbated lung inflammation seen as a result of neutrophilic accumulation is dependent on S100A8/A9 proteins. S100A8/A9 proteins promote neutrophil accumulation by inducing production of proinflammatory chemokines and cytokines, and influencing leukocyte trafficking. Importantly, serum levels of S100A8/A9 proteins along with neutrophil-associated chemokines, such as keratinocyte chemoattractant, can be used as potential surrogate biomarkers to assess lung inflammation and disease severity in human TB. CONCLUSIONS: Our results thus show a major pathologic role for S100A8/A9 proteins in mediating neutrophil accumulation and inflammation associated with TB. Thus, targeting specific molecules, such as S100A8/A9 proteins, has the potential to decrease lung tissue damage without impacting protective immunity against TB.

TNF-alpha from inflammatory dendritic cells (DCs) regulates lung IL-17A/IL-5 levels and neutrophilia versus eosinophilia during persistent fungal infection.

Aspergillus fumigatus is commonly associated with allergic bronchopulmonary aspergillosis in patients with severe asthma in which chronic airway neutrophilia predicts a poor outcome. We were able to recapitulate fungus-induced neutrophilic airway inflammation in a mouse model in our efforts to understand the underlying mechanisms. However, neutrophilia occurred in a mouse strain-selective fashion, providing us with an opportunity to perform a comparative study to elucidate the mechanisms involved. Here we show that TNF-α, largely produced by Ly6c(+)CD11b(+) dendritic cells (DCs), plays a central role in promoting IL-17A from CD4(+) T cells and collaborating with it to induce airway neutrophilia. Compared with C57BL/6 mice, BALB/c mice displayed significantly more TNF-α-producing DCs and macrophages in the lung. Lung TNF-α levels were drastically reduced in CD11c-DTR BALB/c mice depleted of CD11c+ cells, and TNF-α-producing Ly6c(+)CD11b(+) cells were abolished in Dectin-1(-/-) and MyD88(-/-) BALB/c mice. TNF-α deficiency itself blunted accumulation of inflammatory Ly6c(+)CD11b(+) DCs. Also, lack of TNF-α decreased IL-17A but promoted IL-5 levels, switching inflammation from a neutrophil to eosinophil bias resembling that in C57BL/6 mice. The TNF-α(low) DCs in C57BL/6 mice contained more NF-κB p50 homodimers, which are strong repressors of TNF-α transcription. Functionally, collaboration between TNF-α and IL-17A triggered significantly higher levels of the neutrophil chemoattractants keratinocyte cytokine and macrophage inflammatory protein 2 in BALB/c mice. Our study identifies TNF-α as a molecular switch that orchestrates a sequence of events in DCs and CD4 T cells that promote neutrophilic airway inflammation.

Functional characterization of ferret CCL20 and CCR6 and identification of chemotactic inhibitors.

CCL20 is currently the only known chemokine ligand for the receptor CCR6, and is a mucosal chemokine involved in normal and pathological immune responses. Although nucleotide sequence data are available for ccl20 and ccr6 sequences from multiple species, the ferret ccl20 and ccr6 sequences have not been determined. To increase our understanding of immune function in ferret models of infection and vaccination, we have used RT-PCR to obtain the ferret ccl20 and ccr6 cDNA sequences and functionally characterize the encoded proteins. The open reading frames of both genes were highly conserved across species and mostly closely related to canine sequences. For functional analyses, single cell clones expressing ferret CCR6 were generated, a ferret CCL20/mouse IgG(2a) fusion protein (fCCL20-mIgG(2a)) was produced, and fCCL20 was chemically synthesized. Cell clones expressing ferret CCR6 responded chemotactically to fCCL20-mIgG2a fusion protein and synthetic ferret CCL20. Chemotaxis inhibition studies identified the polyphenol epigallocatechin-3-gallate and the murine γ-herpesvirus 68 M3 protein as inhibitors of fCCL20. Surface plasmon resonance studies revealed that EGCG bound directly to fCCL20. These results provide molecular characterization of previously unreported ferret immune gene sequences and for the first time identify a broad-spectrum small molecule inhibitor of CCL20 and reveal CCL20 as a target for the herpesviral M3 protein.

Epigallocatechin-3-gallate reduces airway inflammation in mice through binding to proinflammatory chemokines and inhibiting inflammatory cell recruitment.

One major activity of chemokines is the recruitment of immune cells to sites of infection and inflammation. CD4(+) Th1 cells play critical roles in host defense against pathogens and in the pathogenesis of many immune-mediated diseases. It was reported that epigallocatechin-3-gallate (EGCG) exhibits anti-inflammatory properties, but the mechanisms have not been completely defined. In this study, we found that EGCG markedly decreased recruitment of murine OVA-specific Th1 cells and other inflammatory cells into the airways in a Th1 adoptive-transfer mouse model. In vitro analysis revealed that EGCG inhibited CXCR3 ligand-driven chemotaxis of murine and human cells. Surface plasmon resonance studies revealed that EGCG bound directly to chemokines CXCL9, CXCL10, and CXCL11. These results indicated that one anti-inflammatory mechanism of EGCG is binding of proinflammatory chemokines and limiting their biological activities. These findings support further development of EGCG as a potent therapeutic for inflammatory diseases.

IL-23 is required for long-term control of Mycobacterium tuberculosis and B cell follicle formation in the infected lung.

IL-23 is required for the IL-17 response to infection with Mycobacterium tuberculosis, but is not required for the early control of bacterial growth. However, mice deficient for the p19 component of IL-23 (Il23a(-/-)) exhibit increased bacterial growth late in infection that is temporally associated with smaller B cell follicles in the lungs. Cxcl13 is required for B cell follicle formation and immunity during tuberculosis. The absence of IL-23 results in decreased expression of Cxcl13 within M. tuberculosis-induced lymphocyte follicles in the lungs, and this deficiency was associated with increased cuffing of T cells around the vessels in the lungs of these mice. Il23a(-/-) mice also poorly expressed IL-17A and IL-22 mRNA. These cytokines were able to induce Cxcl13 in mouse primary lung fibroblasts, suggesting that these cytokines are likely involved in B cell follicle formation. Indeed, IL-17RA-deficient mice generated smaller B cell follicles early in the response, whereas IL-22-deficient mice had smaller B cell follicles at an intermediate time postinfection; however, only Il23a(-/-) mice had a sustained deficiency in B cell follicle formation and reduced immunity. We propose that in the absence of IL-23, expression of long-term immunity to tuberculosis is compromised due to reduced expression of Cxcl13 in B cell follicles and reduced ability of T cells to migrate from the vessels and into the lesion. Further, although IL-17 and IL-22 can both contribute to Cxcl13 production and B cell follicle formation, it is IL-23 that is critical in this regard.

PGE(2) transiently enhances DC expression of CCR7 but inhibits the ability of DCs to produce CCL19 and attract naive T cells.

Prostaglandin E(2) (PGE(2)) is an inflammatory mediator often used to increase CCR7 expression in the dendritic cells (DCs) used as cancer vaccines and to enhance their responsiveness to lymph node-associated chemokines. Here, we show that high surface expression of CCR7 on PGE(2)-matured DCs is associated with their suppressed production of the endogenous CCR7 ligand, CCL19, and is reversible by exogenous CCL19. In contrast to the PGE(2)-matured DCs, DCs matured in the presence of toll-like receptor (TLR) ligands and interferons produce high levels of both CCL19 and CCR7 mRNA/protein, but show selectively reduced expression of surface CCR7, which is compensated after DC removal from the CCL19-rich maturation environment. In accordance with these findings, PGE(2)-matured DCs show significantly higher in vitro migratory responsiveness to lymph node-associated chemokines directly after DC generation, but not after additional short-term culture in vitro, nor in vivo in patients injected with (111)indium-labeled DCs. The differences in CCL19-producing ability imprinted during DC maturation result in their different abilities to attract CCR7(+) naive T cells. Our data help to explain the impact of PGE(2) on CCR7 expression in maturing DCs and demonstrate a novel mechanism of regulatory activity of PGE(2), mediated by the inhibition of DCs ability to attract naive T cells.