Prophylactic treatment with Toll-like receptor ligands enhances host immunity to avian influenza virus in chickens

Avian influenza viruses (AIV) pose a threat towards the health of both poultry and humans. To interrupt the transmission of the virus, novel prophylactic strategies must be considered which may reduce the shedding of AIV. One potential is the prophylactic use of Toll-like receptor (TLR) ligands. Many cells of the immune system express TLRs, and cellular responses to TLR stimulation include activation and the production of cytokines. TLR ligands have been employed as prophylactic treatments to enhance host resistance to pathogens both in mammals and chickens. Therefore, the present study was conducted to determine whether TLR ligands may be used prophylactically in chickens to enhance host immunity to AIV. Chickens received intramuscular injections of either low or high doses of the TLR ligands poly I:C, lipopolysaccharide (LPS) and CpG ODN. Twenty-four hours post-treatment, chickens were infected with the low pathogenic avian influenza virus H4N6, and both oropharyngeal and cloacal virus shedding were assessed on days 4 and 7 post-infection. To identify potential correlates of immunity, spleen and lungs were collected on days 2, 4 and 7 post-infection for RNA extraction. The results suggested that all of the TLR ligand treatments induced a significant reduction in virus shedding, with the TLR3 ligand poly I:C conferring the greatest AIV immunity compared to control birds, followed by CpG ODN and LPS. Furthermore, transcriptional analysis of gene expression in the spleen and lungs suggest IFN-α and IL-8 as correlates of immunity conferred by poly I:C, and IFN-γ for CpG ODN and LPS. In conclusion, TLR ligands, have the ability to enhance host immunity against AIV, and future studies should consider exploring the combinatory effects of poly I:C and CpG ODN prophylaxis in conjunction with AIV vaccination.

PTEN directly activates the actin depolymerization factor cofilin-1 during PGE2-mediated inhibition of phagocytosis of fungi

Macrophage ingestion of the yeast Candida albicans requires its recognition by multiple receptors and the activation of diverse signaling programs. Synthesis of the lipid mediator prostaglandin E(2) (PGE(2)) and generation of cyclic adenosine monophosphate (cAMP) also accompany this process. Here, we characterized the mechanisms underlying PGE(2)-mediated inhibition of phagocytosis and filamentous actin (F-actin) polymerization in response to ingestion of C. albicans by alveolar macrophages. PGE(2) suppressed phagocytosis and F-actin formation through the PGE(2) receptors EP2 and EP4, cAMP, and activation of types I and II protein kinase A. Dephosphorylation and activation of the actin depolymerizing factor cofilin-1 were necessary for these inhibitory effects of PGE(2). PGE(2)-dependent activation of cofilin-1 was mediated by the protein phosphatase activity of PTEN (phosphatase and tensin homolog deleted on chromosome 10), with which it directly associated. Because enhanced production of PGE(2) accompanies many immunosuppressed states, the PTEN-dependent pathway described here may contribute to impaired antifungal defenses.

Leukotriene B(4) receptors BLT1 and BLT2 are involved in interleukin-8 production in human neutrophils induced by Trichomonas vaginalis-derived secretory products

OBJECTIVE AND METHOD

Trichomonas vaginalis is a flagellated protozoan parasite that causes human trichomoniasis. Although T. vaginalis itself can secrete lipid mediator leukotriene (LT) B(4) leading to neutrophil activation, information regarding the signaling mechanism involved in neutrophil activation induced by T. vaginalis-secreted LTB(4) is limited. We investigated whether LTB(4) contained in the T. vaginalis-derived secretory products (TvSP) is closely involved in interleukin (IL)-8 production in human neutrophils via LTB(4) receptors BLT1 or BLT2.

RESULTS

T. vaginalis produced more than 714 pg/ml of LTB(4) per 1 × 10(7) trichomonads. The ability of trichomonads to secrete LTB(4) was inhibited by treatment of trichomonads with the 5-lipo-oxygenease inhibitor AA861, but not the cyclo-oxygenease I inhibitor FR122047. When neutrophils were incubated with TvSP obtained from 1 × 10(7) trichomonads, IL-8 protein secretion was significantly increased compared to results for cells incubated with medium alone. The stimulatory effect of TvSP on IL-8 production was strongly inhibited by pretreatment of TvSP with lipase, although pretreatment with heat or proteinase K showed little inhibitory effect. Moreover, TvSP-induced IL-8 production was efficiently inhibited when trichomonads were pretreated with AA861 or when neutrophils were pretreated with antagonists for BLT1 or BLT2.

CONCLUSION

Our results suggest that LTB(4) receptors BLT1 and BLT2 are involved in IL-8 production in neutrophils induced by T. vaginalis.

LL37 and cationic peptides enhance TLR3 signaling by viral double-stranded RNAs

Background

Toll-like Receptor 3 (TLR3) detects viral dsRNA during viral infection. However, most natural viral dsRNAs are poor activators of TLR3 in cell-based systems, leading us to hypothesize that TLR3 needs additional factors to be activated by viral dsRNAs. The anti-microbial peptide LL37 is the only known human member of the cathelicidin family of anti-microbial peptides. LL37 complexes with bacterial lipopolysaccharide (LPS) to prevent activation of TLR4, binds to ssDNA to modulate TLR9 and ssRNA to modulate TLR7 and 8. It synergizes with TLR2/1, TLR3 and TLR5 agonists to increase IL8 and IL6 production. This work seeks to determine whether LL37 enhances viral dsRNA recognition by TLR3.

Methodology/Principal Findings

Using a human bronchial epithelial cell line (BEAS2B) and human embryonic kidney cells (HEK 293T) transiently transfected with TLR3, we found that LL37 enhanced poly(I:C)-induced TLR3 signaling and enabled the recognition of viral dsRNAs by TLR3. The presence of LL37 also increased the cytokine response to rhinovirus infection in BEAS2B cells and in activated human peripheral blood mononuclear cells. Confocal microscopy determined that LL37 could co-localize with TLR3. Electron microscopy showed that LL37 and poly(I:C) individually formed globular structures, but a complex of the two formed filamentous structures. To separate the effects of LL37 on TLR3 and TLR4, other peptides that bind RNA and transport the complex into cells were tested and found to activate TLR3 signaling in response to dsRNAs, but had no effect on TLR4 signaling. This is the first demonstration that LL37 and other RNA-binding peptides with cell penetrating motifs can activate TLR3 signaling and facilitate the recognition of viral ligands.

Conclusions/Significance

LL37 and several cell-penetrating peptides can enhance signaling by TLR3 and enable TLR3 to respond to viral dsRNA.

LTB4 increases nasal neutrophil activity and conditions neutrophils to exert antiviral effects

BACKGROUND

Leukotriene B4 (LTB4) recruits and activates neutrophils. Accordingly, this leukotriene is involved in innate defense actions.

OBJECTIVE

To examine if nasal LTB4 can produce neutrophil activity and to explore whether or not LTB4 can condition neutrophils to exert virucidal effects in vitro and in vivo.

METHODS

1. Twenty-three healthy subjects received nasal LTB4 in a randomized and sham-controlled design. Symptoms were scored and nasal lavages carried out. Myeloperoxidase (MPO) and α-defensins were monitored as indices of neutrophil activity. IL-8, eosinophil cationic protein (ECP) and α(2)-macroglobulin were measured as indices of pro-inflammatory cytokine production, eosinophil activity, and plasma exudation. 2. Supernatants from neutrophils activated by LTB4 in vitro were assayed for virucidal activity against respiratory viruses. 3. In 38 healthy individuals, nasal inoculation with human rhinovirus-16 (HRV-16) was performed. In a preliminary study, intervention with LTB4 was given in a randomized and controlled design. Symptoms, virus replication, and antibody-titres were monitored.

RESULTS

1. LTB4 produced statistically significant increases in MPO and α-defensins, whereas IL-8, ECP, and α(2)-macroglobulin were unaffected. 2. The supernatants efficiently killed human coronavirus, respiratory syncytial virus, and influenza B virus. 3. HRV-16 replication was lower in subjects receiving LTB4, but this difference failed to reach statistical significance. Common cold symptoms and incidence of seroconversion were unaffected.

CONCLUSION

Nasal LTB4 induces a selective recruitment/activation of neutrophils. LTB4 can condition neutrophils to exert virucidal effects in vitro and may reduce virus replication in vivo. We suggest that the condition induced by LTB4 reflects an enhanced state of innate defense.

Kallikrein-related peptidases: bridges between immune functions and extracellular matrix degradation

Kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases encoded by the largest uninterrupted cluster of protease-encoding genes within the human genome. Recent studies, mostly relying on in vitro proteolysis of recombinant proteins, have suggested that KLK activities are regulated by proteolytic activation cascades that can operate in a tissue-specific manner, such as the semen liquefaction and skin desquamation cascades. The validity of KLK activation cascades in vivo largely remains to be demonstrated. Here, we focus on recent investigations showing that KLKs represent interesting players in the broader field of immunology based on their ability to bridge their inherent ability to degrade the extracellular matrix with major functions of the immune system. More specifically, KLKs assist in the infiltration of immune cells through the skin and the blood brain barrier, whereas they catalyze the generation of antimicrobial peptides by proteolytic activation and further processing of protein precursors. In an attempt to integrate current knowledge, we propose KLK-mediated pathways that are putatively involved in inflammation associated with skin wounding and central nervous system disorders, including multiple sclerosis. Finally, we present evidence of KLK participation in autoimmune diseases and allergies.

Review: Defensins and cathelicidins in lung immunity

Defensins were first identified in 1985 and are now recognized as part of a large family of antimicrobial peptides, divided into three categories: alpha-, beta-, and -defensins. These defensin classes differ in structure, sites of expression and biological activities. Human alpha-defensins include peptides that are expressed primarily in neutrophils, whereas human beta-defensins are widely expressed in epithelial cells, including those lining the respiratory tract. Defensins were first studied for their broad spectrum activity against bacteria, fungi and viruses; however, it is now clear that they also recruit inflammatory cells and promote innate and adaptive immune responses. Recent evidence shows that defensins have anti-inflammatory effects as well. Hence, defensins can participate in all phases of an immune response in the lung, including initial killing of pathogens and mounting - and resolution -- of an immune or inflammatory response. The cathelicidin, LL-37, is an antimicrobial peptide produced by neutrophils and respiratory epithelial cells that has similar roles in lung immunity as the defensins. A major challenge for the coming years will be to sort out the relative contributions of defensins and LL-37 to overall immune responses in the lung and to determine which of their many in vitro activities are most important for lung immunity.

Human defensins and LL-37 in mucosal immunity

Defensins are widespread in nature and have activity against a broad range of pathogens. Defensins have direct antimicrobial effects and also modulate innate and adaptive immune responses. We consider the role of human defensins and the cathelicidin LL-37 in defense of respiratory, gastrointestinal, and genitourinary tracts and the oral cavity, skin, and eye. Human beta-defensins (hBDs) and human defensins 5 and 6 (HD5 and -6) are involved most obviously in mucosal responses, as they are produced principally by epithelial cells. Human alpha-defensins 1-4 (or HNPs 1-4) are produced principally by neutrophils recruited to the mucosa. Understanding the biology of defensins and LL-37 is the beginning to clarify the pathophysiology of mucosal inflammatory and infectious diseases (e.g., Crohn's disease, atopic dermatitis, lung or urinary infections). Challenges for these studies are the redundancy of innate defense mechanisms and the presence and interactions of many innate defense proteins in mucosal secretions.

Leukotriene B4 potentiates CpG signaling for enhanced cytokine secretion by human leukocytes

TLRs are known to be important in innate host defense against a variety of microbial infections. In particular, TLR9 has been associated with immune defense against different foreign organisms by recognition of unmethylated DNA sequences. In this report, we provide evidence that leukotriene B(4) (LTB(4)) has the capacity to modulate TLR9 expression on human neutrophils. The effect of LTB(4) was found to be specific, because related leukotrienes such as LTC(4) and LTD(4) or neutrophil agonists IL-8 and C5a failed to modulate TLR9 expression in neutrophils. Using fluorochrome-tagged CpG DNA, we observed that LTB(4) treatment also increased TLR9 ligand binding in neutrophils. Moreover, LTB(4) stimulation potentiates CpG-mediated signaling via an endosome-independent mechanism in human neutrophils, leading to enhanced secretion of proinflammatory cytokines. The increase in cytokine secretion by LTB(4) following CpG stimulation of neutrophils was associated with the activation of TGF-beta-activated kinase (TAK-1) as well as p38 and c-Jun (JNK) kinases. In contrast, in PBMC LTB(4) leads to an increase in cytokine secretion following CpG stimulation but via a MyD88- and endosome-dependent mechanism. As observed in neutrophils, PBMC stimulation with LTB(4) in the presence of CpG also results in enhanced TAK-1, p38, and JNK phosphorylation/activation. These data provide new evidence underlying the immunomodulatory properties of LTB(4) leading to antimicrobial defense.

The roles of cathelicidin LL-37 in immune defences and novel clinical applications

PURPOSE OF REVIEW

LL-37 is the only member of the cathelicidin family of host defence peptides expressed in humans. It is primarily produced by phagocytic leucocytes and epithelial cells, and mediates a wide range of biological responses: direct killing of microorganisms, chemotaxis and chemokine induction, regulation of inflammatory responses, as well as adjuvant, angiogenic and wound healing effects. In this review we will cover the recent advances in the understanding of LL-37 biology: its activities, the mechanisms of its induction and roles in immune defence.

RECENT FINDINGS

Recent studies advanced our understanding of the mechanisms controlling LL-37 expression, demonstrating the key involvement of the vitamin D3 and the hypoxia response pathways, and the impacts of commensal and pathogenic microorganisms on its production. The synergistic and antagonistic interactions between LL-37 and other immune mediators have been further elucidated. Furthermore, studies in animal models and human patients further characterized the roles of cathelicidins in immunity, with roles in infectious and inflammatory conditions. The underlying properties of LL-37 have been exploited to create innate defence regulator peptides that represent a novel immunomodulatory approach to treating infections.

SUMMARY

The understanding of the biological properties and functions of LL-37 and other host defence peptides advances our knowledge of innate immunity, the interactions of the host with pathogens and the microflora, as well as the pathology of infectious and inflammatory diseases, creating many strategies and opportunities for therapeutic intervention.

Inhibition of leukotriene B4 production in murine macrophages by lactic acid bacteria

Leukotriene B(4) (LTB(4)) is a lipid mediator associated with innate immune function. LTB(4) is produced mainly by polymorphonuclear leukocytes and macrophages and plays important roles in host defense. However, LTB(4) is also associated with inflammation, and excessive production of LTB(4) can result in inflammation, allergic reactions, and carcinogenesis. Regulation of excessive LTB(4) production may therefore assist in controlling these conditions. In this study, we investigated the capacity of 7 strains of lactic acid bacteria to inhibit LTB(4) production by the murine macrophage cell line J774.1. All strains tested inhibited calcium ionophore (A23187)-stimulated LTB(4) production in macrophages, but to varying extents. Lactobacillus helveticus Bc-10 exhibited the highest level of inhibitory activity. The inhibitory activity of strain Bc-10 was sustained after heat-killing and was observed in the intracellular cell-free extract prepared from this strain. This is the first report that intact lactic acid bacteria and their isolated cellular components can directly inhibit LTB(4) production by macrophages, and provides a useful method to screen the inhibitory activity of lactic acid bacteria. This study also highlights the potential of the strain Bc-10 as a treatment option for the regulation of LTB(4) production in vivo.