Reduced binding of apoE4 to complement factor H promotes amyloid-ß oligomerization and neuroinflammation.

The APOE4 variant of apolipoprotein E (apoE) is the most prevalent genetic risk allele associated with late-onset Alzheimer's disease (AD). ApoE interacts with complement regulator factor H (FH), but the role of this interaction in AD pathogenesis is unknown. Here we elucidate the mechanism by which isoform-specific binding of apoE to FH alters Aß1-42-mediated neurotoxicity and clearance. Flow cytometry and transcriptomic analysis reveal that apoE and FH reduce binding of Aß1-42 to complement receptor 3 (CR3) and subsequent phagocytosis by microglia which alters expression of genes involved in AD. Moreover, FH forms complement-resistant oligomers with apoE/Aß1-42 complexes and the formation of these complexes is isoform specific with apoE2 and apoE3 showing higher affinity to FH than apoE4. These FH/apoE complexes reduce Aß1-42 oligomerization and toxicity, and colocalize with complement activator C1q deposited on Aß plaques in the brain. These findings provide an important mechanistic insight into AD pathogenesis and explain how the strongest genetic risk factor for AD predisposes for neuroinflammation in the early stages of the disease pathology.

Regulation of the complement system and immunological tolerance in pregnancy.

Preeclampsia is a serious vascular complication of the human pregnancy, whose etiology is still poorly understood. In preeclampsia, exacerbated apoptosis and fragmentation of the placental tissue occurs due to developmental qualities of the placental trophoblast cells and/or mechanical and oxidative distress to the syncytiotrophoblast, which lines the placental villi. Dysregulation of the complement system is recognized as one of the mechanisms of the disease pathology. Complement has the ability to promote inflammation and facilitate phagocytosis of placenta-derived particles and apoptotic cells by macrophages. In preeclampsia, an overload of placental cell damage or dysregulated complement system may lead to insufficient clearance of apoptotic particles and placenta-derived debris. Excess placental damage may lead to sequestration of microparticles, such as placental vesicles, to capillaries in the glomeruli of the kidney and other vulnerable tissues. This phenomenon could contribute to the manifestations of typical diagnostic symptoms of preeclampsia: proteinuria and new-onset hypertension. In this review we propose that the complement system may serve as a regulator of the complex tolerance and clearance processes that are fundamental in healthy pregnancy. It is therefore recommended that further research be conducted to elucidate the interactions between components of the complement system and immune responses in the context of complicated and healthy pregnancy.

Proteomic changes of alveolar lining fluid in illnesses associated with exposure to inhaled non-infectious microbial particles.

BACKGROUND: Hyperresponsiveness to inhaled non-infectious microbial particles (NIMPs) has been associated with illnesses in the airways. Hypersensitivity pneumonitis (HP) is considered to be the prototype for these NIMPs-related diseases; however, there is no consensus on the definitions or diagnostic criteria for HP and the spectrum of related illnesses. METHODS AND FINDINGS: In order to identify the possible diagnostic markers for illnesses associated with NIMPs in alveolar lining fluid, we performed a proteomic analysis using a two-dimensional difference gel electrophoresis on bronchoalveolar lavage (BAL) fluid from patients with exposure to NIMPs in the context of damp building-related illness (DBRI) or conditions on the borderline to acute HP, designated here as agricultural type of microbial exposure (AME). Samples from patients with HP and sarcoidosis (SARC) were included for reference. Results were compared to results of healthy subjects (CTR). Western blot was used for validation of potential marker proteins from BAL fluid and plasma. Protein expression patterns suggest a close similarity between AME and HP, while DBRI was similar to CTR. However, in DBRI the levels of the inflammation associated molecules galectin-3 and alpha-1-antitrypsin were increased. A novel finding emerging from this study was the increases of semenogelin levels in BAL fluid from patients with AME, HP and SARC. Histone 4 levels were increased in AME, HP and SARC. Elevated plasma levels of histone 2B were detected in HP and SARC, suggesting it to be a potential blood indicator for inflammatory diseases of the lungs. CONCLUSIONS: In this study, the proteomic changes in bronchoalveolar lavage of DBRI patients were distinct from other NIMP exposure associated lung diseases, while changes in AME overlapped those observed for HP patient samples. Some of the proteins identified in this study, semenogelin and histone 4, could function as diagnostic markers for differential diagnosis between DBRI and HP-like conditions.

Dectin-1 pathway activates robust autophagy-dependent unconventional protein secretion in human macrophages.

Dectin-1 is a membrane-bound pattern recognition receptor for ß-glucans, which are the main constituents of fungal cell walls. Detection of ß-glucans by dectin-1 triggers an effective innate immune response. In this study, we have used a systems biology approach to provide the first comprehensive characterization of the secretome and associated intracellular signaling pathways involved in activation of dectin-1/Syk in human macrophages. Transcriptome and secretome analysis revealed that the dectin-1 pathway induced significant gene expression changes and robust protein secretion in macrophages. The enhanced protein secretion correlated only partly with increased gene expression. Bioinformatics combined with functional studies revealed that the dectin-1/Syk pathway activates both conventional and unconventional, vesicle-mediated, protein secretion. The unconventional protein secretion triggered by the dectin-1 pathway is dependent on inflammasome activity and an active autophagic process. In conclusion, our results reveal that unconventional protein secretion has an important role in the innate immune response against fungal infections.

Serum amyloid A activates the NLRP3 inflammasome via P2X7 receptor and a cathepsin B-sensitive pathway.

Serum amyloid A (SAA) is an acute-phase protein, the serum levels of which can increase up to 1000-fold during inflammation. SAA has a pathogenic role in amyloid A-type amyloidosis, and increased serum levels of SAA correlate with the risk for cardiovascular diseases. IL-1ß is a key proinflammatory cytokine, and its secretion is strictly controlled by the inflammasomes. We studied the role of SAA in the regulation of IL-1ß production and activation of the inflammasome cascade in human and mouse macrophages, as well as in THP-1 cells. SAA could provide a signal for the induction of pro-IL-1ß expression and for inflammasome activation, resulting in secretion of mature IL-1ß. Blocking TLR2 and TLR4 attenuated SAA-induced expression of IL1B, whereas inhibition of caspase-1 and the ATP receptor P2X(7) abrogated the release of mature IL-1ß. NLRP3 inflammasome consists of the NLRP3 receptor and the adaptor protein apoptosis-associated speck-like protein containing CARD (a caspase-recruitment domain) (ASC). SAA-mediated IL-1ß secretion was markedly reduced in ASC(-/-) macrophages, and silencing NLRP3 decreased IL-1ß secretion, confirming NLRP3 as the SAA-responsive inflammasome. Inflammasome activation was dependent on cathepsin B activity, but it was not associated with lysosomal destabilization. SAA also induced secretion of cathepsin B and ASC. In conclusion, SAA can induce the expression of pro-IL-1ß and activation of the NLRP3 inflammasome via P2X(7) receptor and a cathepsin B-sensitive pathway. Thus, during systemic inflammation, SAA may promote the production of IL-1ß in tissues. Furthermore, the SAA-induced secretion of active cathepsin B may lead to extracellular processing of SAA and, thus, potentially to the development of amyloid A amyloidosis.

(1,3)-beta-glucans activate both dectin-1 and NLRP3 inflammasome in human macrophages.

beta-Glucans are naturally occurring polysaccharides that are the major cell wall components of fungi. Recognition of beta-glucans is mediated through a membrane-bound pattern recognition receptor called dectin-1, and gene knock-out studies have shown that dectin-1 plays an important role in antifungal immune response in vivo. In this report, we have studied the effect of large particulate (1,3)-beta-glucans, including curdlan, glucan from baker's yeast, paramylon, and zymosan, on inflammatory response in human macrophages. We show that beta-glucans activate the transcription of the proinflammatory cytokine IL-1beta through a dectin-1-dependent pathway in human macrophages. Moreover, dectin-1 receptor associated Syk tyrosine kinase was essential for beta-glucan induced IL-1beta mRNA expression. In contrast to LPS, beta-glucans also strongly activated the secretion of IL-1beta. This beta-glucan triggered IL-1beta release was abolished by cytochalasin D, an inhibitor of phagocytosis, demonstrating that cytosolic recognition of beta-glucans is required for IL-1beta response in human macrophages. RNA interference-mediated gene knockdown experiments demonstrated that cytoplasmic NLRP3 inflammasome is essential for beta-glucan-induced IL-1beta secretion. Moreover, our results suggest that beta-glucan-induced NLRP3 inflammasome activation is dependent on the dectin-1/Syk signaling pathway. Furthermore, our results suggest that the lysosomal cathepsin B protease, the formation of reactive oxygen species, and the efflux of potassium are needed for beta-glucan-induced NLRP3 inflammasome activation. In conclusion, our results show that beta-glucans are recognized by membrane-associated dectin-1 and cytoplasmic NLRP3 inflammasome resulting in IL-1beta gene transcription and IL-1beta secretion in human macrophages, respectively.

An outbreak of pneumonia associated with S. pneumoniae at a military training facility in Finland in 2006.

Streptococcus pneumoniae is a well-known cause of community-acquired bacterial pneumonia. The purpose of this study was to assess the cause and extent of the outbreak of pneumonia which occurred among military recruits following a 1-week hard encampment in Finland. We also assessed the carriage rate and molecular characteristics of the S. pneumoniae isolates. All pneumococcal isolates were studied for antibiotic susceptibility, serotyped, genotyped by multilocus sequence typing (MLST), and the presence of pneumococcal rlrA pilus islet was detected. The genotype results defined by MLST corresponded with the serotype results. S. pneumoniae serotype 7F, ST2331, seemed to be associated with an outbreak of pneumonia and nasopharyngeal carriage among 43 military recruits. Of the 43 military recruits, five (12%) were hospitalized with pneumonia and two (40%) of them were positive for S. pneumoniae serotype 7F, ST2331 by blood culture. Eighteen (42%) of the 43 men were found to be positive for S. pneumoniae by nasopharyngeal culture, and nine (50%) of them carried pneumococcal serotype 7F, ST2331. The outbreak strain covered 55% of all the pneumococcal findings. Outbreaks of invasive pneumococcal disease seem to occur in a crowded environment such as a military training facility even among previously healthy young men.