Serum biomarkers differentiating Kawasaki disease from febrile infections: A pilot case-control study

Although some serum biomarkers are elevated in both Kawasaki disease (KD) and infections, these conditions have not been compared by individual or combined biomarkers. The aim of this study, undertaken between January 2016 and May 2018 in a large teaching hospital, was to compare the serum concentration of cytokines, metalloproteinases (MMP) and heat shock protein (HSP) between cases defined as children with Kawasaki disease (KD) and those with febrile infections (controls). Serum concentrations of tumour necrosis factor-alpha (TNF-alpha), interleukins (IL 1beta, 6, and 8), heat shock proteins (HSP 60 and 70) and matrix metalloproteinase (MMP 9) were measured on admission in 17 children under six years of age with a temperature >38.5 °C for ≥five days, and compared between the two groups. The median age was 25 months and the median duration of fever eight days. Seven children were diagnosed with KD and ten had a febrile infection. Only the serum concentrations of IL-6 and TNF-alpha were significantly higher in the former than in the latter group (P = 0.01 and 0.04 respectively). To differentiate between the two groups with the best sensitivity and specificity, the optimal cut-off value for IL-6 was 12.6 pg/mL, and for TNF-alpha 47.9 pg/mL. Their combined increase, however, outperformed their individual concentrations. The characteristic diagnostic “signature” of the combined elevation of IL-6 and TNF-alpha serum levels has the potential, in febrile children, to differentiate early KD from febrile infections, allowing the institution of appropriate therapy.

Neuroprotection by Neurotropin through Crosstalk of Neurotrophic and Innate Immune Receptors in PC12 Cells

Infected or damaged tissues release multiple “alert” molecules such as alarmins and damage-associated molecular patterns (DAMPs) that are recognized by innate immune receptors, and induce tissue inflammation, regeneration, and repair. Recently, an extract from inflamed rabbit skin inoculated with vaccinia virus (Neurotropin^®, NTP) was found to induce infarct tolerance in mice receiving permanent ischemic attack to the middle cerebral artery. Likewise, we report herein that NTP prevented the neurite retraction in PC12 cells by nerve growth factor (NGF) deprivation. This effect was accompanied by interaction of Fyn with high-affinity NGF receptor TrkA. Sucrose density gradient subcellular fractionation of NTP-treated cells showed heretofore unidentified membrane fractions with a high-buoyant density containing Trk, B subunit of cholera toxin-bound ganglioside, flotillin-1 and Fyn. Additionally, these new membrane fractions also contained Toll-like receptor 4 (TLR4). Inhibition of TLR4 function by TAK-242 prevented the formation of these unidentified membrane fractions and suppressed neuroprotection by NTP. These observations indicate that NTP controls TrkA-mediated signaling through the formation of clusters of new membrane microdomains, thus providing a platform for crosstalk between neurotrophic and innate immune receptors. Neuroprotective mechanisms through the interaction with innate immune systems may provide novel mechanism for neuroprotection.

Host membrane glycosphingolipids and lipid microdomains facilitate Histoplasma capsulatum internalisation by macrophages

Recognition and internalisation of intracellular pathogens by host cells is a multifactorial process, involving both stable and transient interactions. The plasticity of the host cell plasma membrane is fundamental in this infectious process. Here, the participation of macrophage lipid microdomains during adhesion and internalisation of the fungal pathogen Histoplasma capsulatum (Hc) was investigated. An increase in membrane lateral organisation, which is a characteristic of lipid microdomains, was observed during the first steps of Hc-macrophage interaction. Cholesterol enrichment in macrophage membranes around Hc contact regions and reduced levels of Hc-macrophage association after cholesterol removal also suggested the participation of lipid microdomains during Hc-macrophage interaction. Using optical tweezers to study cell-to-cell interactions, we showed that cholesterol depletion increased the time required for Hc adhesion. Additionally, fungal internalisation was significantly reduced under these conditions. Moreover, macrophages treated with the ceramide-glucosyltransferase inhibitor (P4r) and macrophages with altered ganglioside synthesis (from B4galnt1^-/- mice) showed a deficient ability to interact with Hc. Coincubation of oligo-GM1 and treatment with Cholera toxin Subunit B, which recognises the ganglioside GM1, also reduced Hc association. Although purified GM1 did not alter Hc binding, treatment with P4 significantly increased the time required for Hc binding to macrophages. The content of CD18 was displaced from lipid microdomains in B4galnt1^-/- macrophages. In addition, macrophages with reduced CD18 expression (CD18^low ) were associated with Hc at levels similar to wild-type cells. Finally, CD11b and CD18 colocalised with GM1 during Hc-macrophage interaction. Our results indicate that lipid rafts and particularly complex gangliosides that reside in lipid rafts stabilise Hc-macrophage adhesion and mediate efficient internalisation during histoplasmosis.

Analyses of lipid rafts, Toll-like receptors 2 and 4, and cytokines in foals vaccinated with Virulence Associated Protein A/CpG oligonucleotide vaccine against Rhodococcus equi

Rhodococcus equi establishes long-term pulmonary infection, survives in phagolysosomes of alveolar macrophages and causes pneumonia in foals. The failure of the foal to clear R. equi bacteria is believed to be due to its inability to produce IFN-γ and defects in Toll-like receptor(TLR) signaling. Lipid rafts sequester immune receptors such as TLRs and facilitate efficient cell signaling and therefore, a deficiency in accumulation of receptors in lipid rafts may result in failure to activate. We tested whether a Virulence Associated Protein A (VapA)/CpG vaccine against R. equi would impact the production of IL-10, IFN-γ and TNF-α in lung tissue and fluid samples, alter expression of TLR2 and TLR4 and alter their association with the lipid rafts in broncho-alveolar lavage (BAL) cells. Eight foals, 1–6 days of age, were vaccinated against R. equi followed by a booster at day 14 and challenged with R. equi (5 x 10(6) CFU/ml;10 ml) on day 28. This group was termed "vaccinated pre-challenge" before the infection and "vaccinated post-challenge" after the infection. A second group of foals (n = 7) was not vaccinated but challenged with R. equi on day 28 of the study. This group was termed "non-vaccinated pre-challenge" and after infection with R. equi was named "non-vaccinated post-challenged. We report adaptation of previous protocols to isolate plasma membrane fractions from BAL cells and identification of lipid raft fractions based on the presence of flotillin-1 and GM-1 and absence of transferrin receptor. TLR2 and TLR4 were restricted to plasma membrane fractions 7–9 of alveolar cells collected from vaccinated foals before and after the challenge. Western blots showed that vaccinated post-challenge foals had higher expression of TLR2 in their lung tissues compared to non-vaccinated pre-challenge foals. TNF- concentration was higher in BAL fluid collected from the vaccinated compared to the non-vaccinated foals on day 28. Lung tissue extracts collected on day 49 from the non-vaccinated R. equi challenged foals showed higher expression of IL-10 compared to the vaccinated-challenged foals. However, there were no differences among the groups with respect to the concentration of IFN-γ in BAL fluid or lung tissue extracts. Taken together, we modified previous protocols to isolate plasma membrane fractions from BAL cells of foals and report that the vaccination with a VapA/CPG vaccine increases association of TLR2 and TLR4 with lipid raft fractions and alters expression of TNF-α and IL-10. The data point to a subtle effect of vaccination on the association of TLR2 and TLR4 with lipid rafts in BAL cells.

Signaling of high mobility group box 1 (HMGB1) through toll-like receptor 4 in macrophages requires CD14

High mobility group box 1 (HMGB1) is a DNA-binding protein that possesses cytokinelike, proinflammatory properties when released extracellularly in the C23-C45 disulfide form. HMGB1 also plays a key role as a mediator of acute and chronic inflammation in models of sterile injury. Although HMGB1 interacts with multiple pattern recognition receptors (PRRs), many of its effects in injury models occur through an interaction with toll-like receptor 4 (TLR4). HMGB1 interacts directly with the TLR4/myeloid differentiation protein 2 (MD2) complex, although the nature of this interaction remains unclear. We demonstrate that optimal HMGB1-dependent TLR4 activation in vitro requires the coreceptor CD14. TLR4 and MD2 are recruited into CD14-containing lipid rafts of RAW264.7 macrophages after stimulation with HMGB1, and TLR4 interacts closely with the lipid raft protein GM1. Furthermore, we show that HMGB1 stimulates tumor necrosis factor (TNF)-α release in WT but not in TLR4(-/-), CD14(-/-), TIR domain-containing adapter-inducing interferon-β (TRIF)(-/-) or myeloid differentiation primary response protein 88 (MyD88)(-/-) macrophages. HMGB1 induces the release of monocyte chemotactic protein 1 (MCP-1), interferon gamma-induced protein 10 (IP-10) and macrophage inflammatory protein 1α (MIP-1α) in a TLR4- and CD14-dependent manner. Thus, efficient recognition of HMGB1 by the TLR4/MD2 complex requires CD14.

Membrane partitioning: is location everything when it comes to endotoxin recognition?

Lipid rafts are envisaged as islands of highly ordered saturated lipids and cholesterol that are laterally mobile in the plane of the plasma membrane. Lipid rafts are thought to provide a means to explain the spatial segregation of certain signalling pathways emanating from the cell surface. They seem to provide the necessary microenvironment in order for certain specialised signalling events to take place- such as the innate immune recognition. The innate immune system seems to employ germ-lined encoded receptors, called pattern recognition receptors (PRRs) in order to "sense" pathogens. One family of such receptors are the Toll like receptors (TLRs), which are the central "sensing" apparatus of the innate immune system. In recent years, it has become apparent that TLRs are recruited into membrane microdomains in response to ligands and these constitute signalling platforms, which transducer singals that lead to innate immune activation. In this chapter will review all past and current literature concerning recruitment of TLRs into lipid rafts and how this membrane compartmentalization is crucial for innate immune responses.

Sperm-zona pellucida interaction: molecular mechanisms and the potential for contraceptive intervention

At the moment of insemination, millions of mammalian sperm cells are released into the female reproductive tract with the single goal of finding the oocyte. The spermatozoa subsequently ignore the thousands of cells they make contact with during their journey to the site of fertilization, until they reach the surface of the oocyte. At this point, they bind tenaciously to the acellular coat, known as the zona pellucida, which surrounds the oocyte and orchestrate a cascade of cellular interactions that culminate in fertilization. These exquisitely cell- and species- specific recognition events are among the most strategically important cellular interactions in biology. Understanding the cellular and molecular mechanisms that underpin them has implications for the etiology of human infertility and the development of novel targets for fertility regulation. Herein we describe our current understanding of the molecular basis of successful sperm-zona pellucida binding.

Membrane sorting of toll-like receptor (TLR)-2/6 and TLR2/1 heterodimers at the cell surface determines heterotypic associations with CD36 and intracellular targeting

Toll-like receptors (TLRs) are receptors of the innate immune system responsible for recognizing pathogen-associated molecular patterns. TLR2 seems to be the most promiscuous TLR receptor able to recognize the most diverse set of pathogen-associated patterns. Its promiscuity has been attributed to its unique ability to heterodimerize with TLRs 1 and 6 and, most recently, to its association with CD36 in response to diacylated lipoproteins. Thus, it seems that TLR2 forms receptor clusters in response to different microbial ligands. In this study we investigated TLR2 cell surface heterotypic interactions in response to different ligands as well as internalization and intracellular trafficking. Our data show that TLR2 forms heterodimers with TLR1 and TLR6 and that these heterodimer pre-exist and are not induced by the ligand. Upon stimulation by the specific ligand, these heterodimers are recruited within lipid rafts. In contrast, heterotypic associations of TLR2/6 with CD36 are not preformed and are ligand-induced. All TLR2 receptor clusters accumulate in lipid rafts and are targeted to the Golgi apparatus. This localization and targeting is ligand-specific. Activation occurs at the cell surface, and the observed trafficking is independent of signaling.

Tissue-factor-bearing microvesicles arise from lipid rafts and fuse with activated platelets to initiate coagulation

Tissue factor (TF) circulates in plasma, largely on monocyte/macrophage-derived microvesicles that can bind activated platelets through a mechanism involving P-selectin glycoprotein ligand-1 (PSGL-1) on the microvesicles and P-selectin on the platelets. We found these microvesicles to be selectively enriched in both TF and PSGL-1, and deficient in CD45, suggesting that they arise from distinct membrane microdomains. We investigated the possibility that microvesicles arise from cholesterol-rich lipid rafts and found that both TF and PSGL-1, but not CD45, localize to lipid rafts in blood monocytes and in the monocytic cell line THP-1. Consistent with a raft origin of TF-bearing microvesicles, their shedding was significantly reduced with depletion of membrane cholesterol. We also evaluated the interaction between TF-bearing microvesicles and platelets. Microvesicles bound only activated platelets, and required PSGL-1 to do so. The microvesicles not only bound the activated platelets, they fused with them, transferring both proteins and lipid to the platelet membrane. Fusion was blocked by either annexin V or an antibody to PSGL-1 and had an important functional consequence: increasing the proteolytic activity of the TF-VIIa complex. These findings suggest a mechanism by which all of the membrane-bound reactions of the coagulation system can be localized to the surface of activated platelets.

Linking the "two-hit" response following injury to enhanced TLR4 reactivity

Severe injury can initiate an exaggerated systemic inflammatory response and multiple organ failure (MOF) if a subsequent immune stimulus, "second hit", occurs. Using a mouse thermal injury model, we tested whether changes in innate immune cell reactivity following injury can contribute to the development of heightened inflammation and MOF. Using high-purity Escherichia coli lipopolysaccharide (LPS) to selectively stimulate Toll-like receptor 4 (TLR4), we demonstrate augmented interleukin (IL)-1beta, tumor necrosis factor alpha (TNF-alpha), and IL-6 production by 1 day but particularly, at 7 days after injury. The in vivo significance of enhanced TLR4 responsiveness was explored by challenging sham or burn mice with LPS at 1 or 7 days after injury and determining mortality along with in vivo cytokine and chemokine levels. Mortality was high (75%) in LPS-challenged burn but not sham mice at 7 days, although not at 1 day, after injury. Death was associated with leukocyte sequestration in the lungs and livers along with increased proinflammatory cytokine and chemokine levels in these organs. Blocking TNF-alpha activity prevented this mortality, suggesting that excessive TNF-alpha production contributes to this lethal response. These findings demonstrate the potential lethality of excessive TLR4 reactivity after injury and provide an explanation for the exaggerated inflammatory response to a second hit, which can occur following severe injury.