Heike Weighardt

Ultraviolet-radiation-induced inflammation promotes angiotropism and metastasis in melanoma

Intermittent intense ultraviolet (UV) exposure represents an important aetiological factor in the development of malignant melanoma. The ability of UV radiation to cause tumour-initiating DNA mutations in melanocytes is now firmly established, but how the microenvironmental effects of UV radiation influence melanoma pathogenesis is not fully understood. Here we report that repetitive UV exposure of primary cutaneous melanomas in a genetically engineered mouse model promotes metastatic progression, independent of its tumour-initiating effects. UV irradiation enhanced the expansion of tumour cells along abluminal blood vessel surfaces and increased the number of lung metastases. This effect depended on the recruitment and activation of neutrophils, initiated by the release of high mobility group box 1 (HMGB1) from UV-damaged epidermal keratinocytes and driven by Toll-like receptor 4 (TLR4). The UV-induced neutrophilic inflammatory response stimulated angiogenesis and promoted the ability of melanoma cells to migrate towards endothelial cells and use selective motility cues on their surfaces. Our results not only reveal how UV irradiation of epidermal keratinocytes is sensed by the innate immune system, but also show that the resulting inflammatory response catalyses reciprocal melanoma–endothelial cell interactions leading to perivascular invasion, a phenomenon originally described as angiotropism in human melanomas by histopathologists. Angiotropism represents a hitherto underappreciated mechanism of metastasis that also increases the likelihood of intravasation and haematogenous dissemination. Consistent with our findings, ulcerated primary human melanomas with abundant neutrophils and reactive angiogenesis frequently show angiotropism and a high risk for metastases. Our work indicates that targeting the inflammation-induced phenotypic plasticity of melanoma cells and their association with endothelial cells represent rational strategies to specifically interfere with metastatic progression.

Cutting Edge: Myeloid Differentiation Factor 88 Deficiency Improves Resistance Against Sepsis Caused by Polymicrobial Infection

Toll-like receptors (TLRs) are important for the activation of innate immune cells upon encounter of microbial pathogens. The present study investigated the potential roles of TLR2, TLR4, and the signaling protein myeloid differentiation factor 88 (MyD88) in polymicrobial septic peritonitis. Whereas both TLR2 and TLR4 were dispensable for host defense against septic peritonitis, MyD88-deficient mice were protected in this infection model. Recruitment of neutrophils to the septic focus and bacterial clearance were normal in MyD88-deficient mice. In contrast, the systemic inflammatory response was strongly attenuated in the absence of MyD88. Surprisingly, MyD88 deficiency did not alter cytokine and chemokine production in spleen, but markedly reduced the inflammatory response in liver and lung. Production of monocyte chemoattractant protein-1 and macrophage-inflammatory protein-1α was entirely independent of MyD88. These results imply a central role of MyD88 for the systemic immune pathology of polymicrobial sepsis and show that cytokine production in spleen and induction of certain chemokines are MyD88 independent.

Signaling of Apoptosis through TLRs Critically Involves Toll/IL-1 Receptor Domain-Containing Adapter Inducing IFN-β, but Not MyD88, in Bacteria-Infected Murine Macrophages

TLRs are important sensors of the innate immune system that serve to identify conserved microbial components to mount a protective immune response. They furthermore control the survival of the challenged cell by governing the induction of pro- and antiapoptotic signaling pathways. Pathogenic Yersinia spp. uncouple the balance of life and death signals in infected macrophages, which compels the macrophage to undergo apoptosis. The initiation of apoptosis by Yersinia infection specifically involves TLR4 signaling, although Yersinia can activate TLR2 and TLR4. In this study we characterized the roles of downstream TLR adapter proteins in the induction of TLR-responsive apoptosis. Experiments using murine macrophages defective for MyD88 or Toll/IL-1R domain-containing adapter inducing IFN-β (TRIF) revealed that deficiency of TRIF, but not of MyD88, provides protection against Yersinia-mediated cell death. Similarly, apoptosis provoked by treatment of macrophages with the TLR4 agonist LPS in the presence of a proteasome inhibitor was inhibited in TRIF-defective, but not in MyD88-negative, cells. The transfection of macrophages with TRIF furthermore potently promoted macrophage apoptosis, a process that involved activation of a Fas-associated death domain- and caspase-8-dependent apoptotic pathway. These data indicate a crucial function of TRIF as proapoptotic signal transducer in bacteria-infected murine macrophages, an activity that is not prominent for MyD88. The ability to elicit TRIF-dependent apoptosis was not restricted to TLR4 activation, but was also demonstrated for TLR3 agonists. Together, these results argue for a specific proapoptotic activity of TRIF as part of the host innate immune response to bacterial or viral infection.

Increased Resistance Against Acute Polymicrobial Sepsis in Mice Challenged with Immunostimulatory CpG Oligodeoxynucleotides Is Related to an Enhanced Innate Effector Cell Response

Recent reports support the concept that the major defect in polymicrobial sepsis is an impaired immunologic response to infection. Oligodeoxynucleotides containing CpG sequence motifs (CpG-ODN) were previously shown to induce immune protection in models of chronic infection with intracellular bacteria, parasites, and viruses due to their ability to augment IFN-γ-dependent Th1 responses. Here, we demonstrate that challenging mice with CpG-ODN substantially increases the resistance against acute polymicrobial sepsis. Systemic levels of IL-12, IL-18, and IL-10 were not altered in CpG-ODN-treated mice as compared with controls. In contrast, administration of CpG-ODN resulted in a strongly enhanced accumulation of neutrophils at the primary site of infection. Neutrophils of CpG-ODN-treated mice exhibited an up-regulation of phagocytic receptors, an increased phagocytic activity, and an elevated production of reactive oxygen metabolites. These results suggest that the protective effects of CpG-ODNs in acute polymicrobial sepsis are related to an enhanced effector cell response of innate immunity. CpG-ODN may therefore represent potent agents for the treatment of sepsis-associated immunoparalysis.

Identification of a TLR4- and TRIF-dependent activation program of dendritic cells.

Dendritic cell activation by Toll‐like receptors (TLR) is crucial for the generation of protective immune responses. In addition to the common myeloid differentiation factor 88 (MyD88)‐dependent signaling pathway, TLR4 engages the adaptor protein Toll/IL‐1 receptor (TIR)‐domain‐containing adaptor inducing IFN‐β (TRIF), leading to interferon regulatory factor 3 (IRF‐3) activation and type I interferon production. Using microarray expression profiling we now identify TRIF as a major regulator of the TLR4‐triggered activation program of dendritic cells. We show that the expressionof 47% of the genes that are responsive to TLR4 stimulation in wild‐type dendritic cells is significantly altered in cells carrying a loss‐of‐function mutation of TRIF. Specifically, expression of IL‐12, IL‐18, and IL‐23 was impaired in the absence of functional TRIF, suggesting that TLR4‐promoted Th1 responses are TRIF‐dependent. Furthermore, we provide evidence that TRIF regulates TLR4‐mediated gene expression both by type I IFN‐dependent and ‐independent mechanisms. Whereas dendritic cell production of CXCL10 and CCL12 was dependent on both TRIF and the type I interferon receptor, expression of IL‐6 required TRIF but not type I interferon activity. Functional TRIF was also required for the normal induction of numerous genes considered important for host defense against diverse pathogens.Together, these data therefore identify TRIF as a crucial regulator of TLR4‐dependent dendritic cell responses.

Effects of functional Toll-like receptor-4 mutations on the immune response to human and experimental sepsis

Genetically determined responsiveness to microbial stimuli such as lipopolysaccharide (LPS) may affect the pathophysiology of human sepsis. The D299G mutation in human Toll‐like receptor‐4 (TLR4) impairs LPS signalling in homozygous and heterozygous individuals. To investigate whether the presence of the TLR4(D299G) mutation may correlate with the development or outcome of sepsis following major visceral surgery the presence of TLR4(D299G) mutation was analysed in 307 Caucasian patients (154 without and 153 with sepsis). Sepsis was caused in 84% of patients by polymicrobial infection. The presence of the mutant TLR4 did not significantly correlate with development or outcome of sepsis. Serum levels of tumour necrosis factor, interleukin (IL)‐10, and IL‐6 at sepsis onset did not significantly differ between patients carrying wild‐type and mutant TLR4. Moreover, studies in a murine model of polymicrobial septic peritonitis demonstrated that TLR4‐deficiency did neither influence the systemic cytokine response nor the development of organ injury. The results suggest that the signalling capacity of TLR4 as affected by loss‐of‐function mutations does not influence human or experimental sepsis caused by polymicrobial infection. Thus, in polymicrobial infection, other innate immune receptors may compensate for TLR4 defects.

Langerinneg conventional dendritic cells produce IL-23 to drive psoriatic plaque formation in mice

Psoriasis is an autoinflammatory skin disease of unknown etiology. Topical application of Aldara cream containing the Toll-like receptor (TLR)7 agonist Imiquimod (IMQ) onto patients induces flares of psoriasis. Likewise, in mice IMQ triggers pathological changes closely resembling psoriatic plaque formation. Key cytokines like IL-23 and type-I IFN (IFN-I), both being produced mainly by dendritic cells (DCs), have been implicated in psoriasis. Although plasmacytoid DCs (pDCs) are the main source of IFNα and thought to initiate disease, conventional DCs (cDCs) appear to maintain the psoriatic lesions. Any role of cDCs during lesion formation remains elusive. Here, we report that selective activation of TLR7 signaling specifically in CD11c+ DCs was sufficient to induce psoriasiform skin disease in mice. Intriguingly, both pDCs and the IFN-I pathway were dispensable for the development of local skin inflammation. Selective TLR7 triggering of Langerin+ DCs resulted in attenuated disease, whereas their depletion did not alter the severity of skin lesions. Moreover, after IMQ-painting, IL-23 was exclusively produced by Langerinneg DCs in vivo. In conclusion, TLR7-activated Langerinneg cDCs trigger psoriatic plaque formation via IL-23–mediated activation of innate IL-17/IL-22–producing lymphocytes, independently of pDCs or IFN-I. These results suggest therapeutic targeting of IL-23 production by cDCs to refine current treatment strategies for psoriasis.

Critical Role of Kupffer Cell-Derived IL-10 for Host Defense in Septic Peritonitis

Intra-abdominal infection in patients following major visceral surgery is associated with high mortality. Using a macrophage depletion technique, we demonstrate that in murine septic peritonitis, Kupffer cells are a major source of systemic IL-10 levels. Kupffer cell-depleted mice were highly susceptible to the lethal effects of septic peritonitis and exhibited an increased bacterial load. Kupffer cell-depleted mice were protected by the administration of an IL-10-Fc fusion protein. Loss of Kupffer cell-derived IL-10 was associated with a weak increase in serum IL-12 levels, whereas TNF, IL-1α, and IL-18 levels were not significantly elevated, suggesting that the loss of Kupffer cell-derived IL-10 did not result in a toxic cytokine release syndrome. Instead, loss of Kupffer cell-derived IL-10 was associated with a reduced splenocyte production of IFN-γ that is required for immune protection in murine septic peritonitis. Therefore, the results suggest that the protective function of IL-10 in septic peritonitis may not be restricted to the anti-inflammatory activities of IL-10.

Zinc Oxide Nanoparticles Induce Necrosis and Apoptosis in Macrophages in a p47phox- and Nrf2-Independent Manner

In view of the steadily increasing use of zinc oxide nanoparticles in various industrial and consumer applications, toxicological investigations to evaluate their safety are highly justified. We have investigated mechanisms of ZnO nanoparticle-induced apoptosis and necrosis in macrophages in relation to their important role in the clearance of inhaled particulates and the regulation of immune responses during inflammation. In the murine macrophage RAW 264.7 cell line, ZnO treatment caused a rapid induction of nuclear condensation, DNA fragmentation, and the formation of hypodiploid DNA nuclei and apoptotic bodies. The involvement of the essential effector caspase-3 in ZnO-mediated apoptosis could be demonstrated by immunocytochemical detection of activated caspase-3 in RAW 264.7 cells. ZnO specifically triggered the intrinsic apoptotic pathway, because Jurkat T lymphocytes deficient in the key mediator caspase-9 were protected against ZnO-mediated toxicity whereas reconstituted cells were not. ZnO also caused DNA strand breakage and oxidative DNA damage in the RAW 264.7 cells as well as p47phox NADPH oxidase-dependent superoxide generation in bone marrow-derived macrophages. However, ZnO-induced cell death was not affected in bone marrow-derived macrophages of mice deficient in p47phox or the oxidant responsive transcription factor Nrf2. Taken together, our data demonstrate that ZnO nanoparticles trigger p47phox NADPH oxidase-mediated ROS formation in macrophages, but that this is dispensable for caspase-9/3-mediated apoptosis. Execution of apoptotic cell death by ZnO nanoparticles appears to be NADPH oxidase and Nrf2-independent but rather triggered by alternative routes.

Differential regulation of systemic IL-18 and IL-12 release during postoperative sepsis: high serum IL-18 as an early predictive indicator of lethal outcome.

Systemic levels of the key immune regulatory cytokines IL-12 and IL-18 were measured over time in 66 patients with postoperative sepsis (38 survivors and 28 nonsurvivors). Sepsis mortality was not significantly associated with any of the clinical parameters examined, including age, gender, underlying disease, and surgical procedure. Analysis of cytokine levels showed that during the entire observation period, IL-12 was significantly reduced in sepsis patients compared with control surgical patients without sepsis. IL-12 serum levels did not significantly differ between sepsis survivors and nonsurvivors. In contrast to IL-12, IL-18 serum levels were significantly higher in both surviving and nonsurviving sepsis patients than in controls. Importantly, we also observed that IL-18 levels were significantly increased in patients with lethal sepsis compared with sepsis survivors at all time points studied, including day 1 after sepsis diagnosis. IL-18 levels were significantly increased during the course of lethal sepsis, but remained at a comparable level in sepsis survivors. Logistic regression analysis of IL-18 values measured on days 1 or 2 of sepsis revealed that high serum IL-18 represents an early predictive factor for the lethal outcome of postoperative sepsis. Consistent with previous work in mouse models, our results suggest that IL-12 may contribute to protective immune reactions against a septic challenge, whereas IL-18 may preferentially promote organ injury and lethal shock.