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Preeclampsia is a hypertensive and inflammatory pregnancy disorder associated with cholesterol accumulation and inflammation at the maternal-fetal interface. Preeclampsia can be complicated with fetal growth restriction (FGR) and shares risk factors and pathophysiological mechanisms with cardiovascular disease. Cholesterol crystal mediated NLRP3 inflammasome activation is central to cardiovascular disease and the pathway has been implicated in placental inflammation in preeclampsia. Direct maternal-fetal interaction occurs both in the uterine wall decidua and at the placental surface and these aligned sites constitute the maternal-fetal interface. This study aimed to investigate cholesterol crystal accumulation and NLRP3 inflammasome expression by maternal and fetal cells in the uterine wall decidua of normal and preeclamptic pregnancies. Pregnant women with normal ( n = 43) and preeclamptic pregnancies with ( n = 28) and without ( n = 19) FGR were included at delivery. Cholesterol crystals were imaged in decidual tissue by both second harmonic generation microscopy and polarization filter reflected light microscopy. Quantitative expression analysis of NLRP3, IL-1β and cell markers was performed by immunohistochemistry and automated image processing. Functional NLRP3 activation was assessed in cultured decidual explants. Cholesterol crystals were identified in decidual tissue, both in the tissue stroma and near uterine vessels. The cholesterol crystals in decidua varied between pregnancies in distribution and cluster size. Decidual expression of the inflammasome components NLRP3 and IL-1β was located to fetal trophoblasts and maternal leukocytes and was strongest in areas of proximity between these cell types. Pathway functionality was confirmed by cholesterol crystal activation of IL-1β in cultured decidual explants. Preeclampsia without FGR was associated with increased trophoblast dependent NLRP3 and IL-1β expression, particularly in the decidual areas of trophoblast and leukocyte proximity. Our findings suggest that decidual accumulation of cholesterol crystals may activate the NLRP3 inflammasome and contribute to decidual inflammation and that this pathway is strengthened in areas with close maternal-fetal interaction in preeclampsia without FGR., (Copyright © 2020 Silva, Gierman, Rakner, Stødle, Mundal, Thaning, Sporsheim, Elschot, Collett, Bjørge, Aune, Thomsen and Iversen.)

Pre-eclampsia is associated with increased levels of cholesterol and uric acid and an inflamed placenta expressing danger-sensing pattern recognition receptors (PRRs). Crystalline cholesterol and uric acid activate the PRR Nod-like receptor protein (NLRP)3 inflammasome to release interleukin (IL)-1β and result in vigorous inflammation. We aimed to characterize crystal-induced NLRP3 activation in placental inflammation and examine its role in pre-eclampsia. We confirmed that serum total cholesterol and uric acid were elevated in pre-eclamptic compared to healthy pregnancies and correlated positively to high sensitivity C-reactive protein (hsCRP) and the pre-eclampsia marker soluble fms-like tyrosine kinase-1 (sFlt-1). The NLRP3 inflammasome pathway components (NLRP3, caspase-1, IL-1β) and priming factors [complement component 5a (C5a) and terminal complement complex (TCC)] were co-expressed by the syncytiotrophoblast layer which covers the placental surface and interacts with maternal blood. The expression of IL-1β and TCC was increased significantly and C5a-positive regions in the syncytiotrophoblast layer appeared more frequent in pre-eclamptic compared to normal pregnancies. In-vitro activation of placental explants and trophoblasts confirmed NLRP3 inflammasome pathway functionality by complement-primed crystal-induced release of IL-1β. This study confirms crystal-induced NLRP3 inflammasome activation located at the syncytiotrophoblast layer as a mechanism of placental inflammation and suggests contribution of enhanced NLRP3 activation to the harmful placental inflammation in pre-eclampsia., (© 2018 British Society for Immunology.)

Cholesterol crystals (CC) are abundant in atherosclerotic plaques and promote inflammatory responses via the complement system and inflammasome activation. Cyclic oligosaccharide 2-hydroxypropyl-β-cyclodextrin (BCD) is a compound that solubilizes lipophilic substances. Recently we have shown that BCD has an anti-inflammatory effect on CC via suppression of the inflammasome and liver X receptor activation. The putative effects of BCD on CC-induced complement activation remain unknown. In this study, we found that BCD bound to CC and reduced deposition of Igs, pattern recognition molecules, and complement factors on CC in human plasma. Furthermore, BCD decreased complement activation as measured by terminal complement complex and lowered the expression of complement receptors on monocytes in whole blood in response to CC exposure. In line with this, BCD also reduced reactive oxygen species formation caused by CC in whole blood. Furthermore, BCD attenuated the CC-induced proinflammatory cytokine responses (e.g., IL-1α, MIP-1α, TNF, IL-6, and IL-8) as well as regulated a range of CC-induced genes in human PBMC. BCD also regulated complement-related genes in human carotid plaques treated ex vivo. Formation of terminal complement complex on other complement-activating structures such as monosodium urate crystals and zymosan was not affected by BCD. These data demonstrate that BCD inhibits CC-induced inflammatory responses, which may be explained by BCD-mediated attenuation of complement activation. Thus, these findings support the potential for using BCD in treatment of atherosclerosis., (Copyright © 2017 by The American Association of Immunologists, Inc.)

Staphylococcus aureus may cause serious infections and is one of the most lethal and common causes of sepsis. TLR2 has been described as the main pattern recognition receptor that senses S. aureus and elicits production of proinflammatory cytokines via MyD88 -: NF-κB signaling. S. aureus can also induce the production of IFN-β, a cytokine that requires IFN regulatory factors (IRFs) for its transcription, but the signaling mechanism for IFN-β induction by S. aureus are unclear. Surprisingly, we demonstrate that activation of TLR2 by lipoproteins does not contribute to IFN-β production but instead can suppress the induction of IFN-β in human primary monocytes and monocyte-derived macrophages. The production of IFN-β was induced by TLR8-mediated sensing of S. aureus RNA, which triggered IRF5 nuclear accumulation, and this could be antagonized by concomitant TLR2 signaling. The TLR8-mediated activation of IRF5 was dependent on TAK1 and IκB kinase (IKK)β, which thus reveals a physiological role of the recently described IRF5-activating function of IKKβ. TLR8 -: IRF5 signaling was necessary for induction of IFN-β and IL-12 by S. aureus, and it also contributed to the induction of TNF. In conclusion, our study demonstrates a physiological role of TLR8 in the sensing of entire S. aureus in human primary phagocytes, including the induction of IFN-β and IL-12 production via a TAK1 -: IKKβ -: IRF5 pathway that can be inhibited by TLR2 signaling., (Copyright © 2015 by The American Association of Immunologists, Inc.)

Chronic inflammation of the arterial wall is a key element in the development of atherosclerosis, and cholesterol crystals (CC) that accumulate in plaques are associated with initiation and progression of the disease. We recently revealed a link between the complement system and CC-induced inflammasome caspase-1 activation, showing that the complement system is a key trigger in CC-induced inflammation. HDL exhibits cardioprotective and anti-inflammatory properties thought to explain its inverse correlation to cardiovascular risk. In this study, we sought to determine the effect of reconstituted HDL (rHDL) on CC-induced inflammation in a human whole blood model. rHDL bound to CC and inhibited the CC-induced complement activation as measured by soluble terminal C5b-9 formation and C3c deposition on the CC surface. rHDL attenuated the amount of CC-induced complement receptor 3 (CD11b/CD18) expression on monocytes and granulocytes, as well as reactive oxygen species generation. Moreover, addition of CC to whole blood resulted in release of proinflammatory cytokines that were inhibited by rHDL. Our results support and extend the notion that CC are potent triggers of inflammation, and that rHDL may have a beneficial role in controlling the CC-induced inflammatory responses by inhibiting complement deposition on the crystals., (Copyright © 2015 by The American Association of Immunologists, Inc.)

Inflammation is associated with development of atherosclerosis, and cholesterol crystals (CC) have long been recognized as a hallmark of atherosclerotic lesions. CC appear early in the atheroma development and trigger inflammation by NLRP3 inflammasome activation. In this study we hypothesized whether CC employ the complement system to activate inflammasome/caspase-1, leading to release of mature IL-1β, and whether complement activation regulates CC-induced cytokine production. In this study we describe that CC activated both the classical and alternative complement pathways, and C1q was found to be crucial for the activation. CC employed C5a in the release of a number of cytokines in whole blood, including IL-1β and TNF. CC induced minimal amounts of cytokines in C5-deficient whole blood, until reconstituted with C5. Furthermore, C5a and TNF in combination acted as a potent primer for CC-induced IL-1β release by increasing IL-1β transcripts. CC-induced complement activation resulted in upregulation of complement receptor 3 (CD11b/CD18), leading to phagocytosis of CC. Also, CC mounted a complement-dependent production of reactive oxygen species and active caspase-1. We conclude that CC employ the complement system to induce cytokines and activate the inflammasome/caspase-1 by regulating several cellular responses in human monocytes. In light of this, complement inhibition might be an interesting therapeutic approach for treatment of atherosclerosis.

Yersinia pestis, the causative agent of plague, is able to suppress production of inflammatory cytokines IL-18 and IL-1β, which are generated through caspase-1-activating nucleotide-binding domain and leucine-rich repeat (NLR)-containing inflammasomes. Here, we sought to elucidate the role of NLRs and IL-18 during plague. Lack of IL-18 signaling led to increased susceptibility to Y. pestis, producing tetra-acylated lipid A, and an attenuated strain producing a Y. pseudotuberculosis-like hexa-acylated lipid A. We found that the NLRP12 inflammasome was an important regulator controlling IL-18 and IL-1β production after Y. pestis infection, and NLRP12-deficient mice were more susceptible to bacterial challenge. NLRP12 also directed interferon-γ production via induction of IL-18, but had minimal effect on signaling to the transcription factor NF-κB. These studies reveal a role for NLRP12 in host resistance against pathogens. Minimizing NLRP12 inflammasome activation may have been a central factor in evolution of the high virulence of Y. pestis., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Toll-like receptor 4 (TLR4) is indispensable for recognition of Gram-negative bacteria. We described a trafficking pathway for TLR4 from the endocytic recycling compartment (ERC) to E. coli phagosomes. We found a prominent colocalization between TLR4 and the small GTPase Rab11a in the ERC, and Rab11a was involved in the recruitment of TLR4 to phagosomes in a process requiring TLR4 signaling. Also, Toll-receptor-associated molecule (TRAM) and interferon regulatory factor-3 (IRF3) localized to E. coli phagosomes and internalization of E. coli was required for a robust interferon-β induction. Suppression of Rab11a reduced TLR4 in the ERC and on phagosomes leading to inhibition of the IRF3 signaling pathway induced by E. coli, whereas activation of the transcription factor NF-κB was unaffected. Moreover, Rab11a silencing reduced the amount of TRAM on phagosomes. Thus, Rab11a is an important regulator of TLR4 and TRAM transport to E. coli phagosomes thereby controlling IRF3 activation from this compartment., (Copyright © 2010 Elsevier Inc. All rights reserved.)