Low-luminosity active galactic nuclei (LLAGN) are special among their kind due to the profound structural changes that the central engine experiences at low accretion rates (≲ 10
−3
in Eddington ...units). The disappearance of the accretion disc – the blue bump – leaves behind a faint optical nuclear continuum whose nature has been largely debated. This is mainly due to serious limitations on the observational side imposed by the starlight contamination from the host galaxy and the absorption by hydrogen, preventing the detection of these weak nuclei in the infrared (IR) to ultraviolet (UV) range. We addressed these challenges by combining multi-wavelength sub-arcsecond resolution observations – able to isolate the genuine nuclear continuum – with nebular lines in the mid-IR, which allowed us to indirectly probe the shape of the extreme UV continuum. We found that eight of the nearest prototype LLAGN are compatible with pure compact jet emission over more than ten orders of magnitude in frequency. This consists of self-absorbed synchrotron emission from radio to the UV plus the associated synchrotron self-Compton component dominating the emission in the UV to X-ray range. Additionally, the LLAGN continua show two particular characteristics when compared with the typical jet spectrum seen in radio galaxies: (i) a very steep spectral slope in the IR-to-optical/UV range (−3.7 <
α
0
< −1.3;
F
ν
∝
ν
α
0
); and (ii) a very high turnover frequency (0.2–30 THz; 1.3 mm–10 μm) that separates the optically thick radio emission from the optically thin continuum in the IR-to-optical/UV range. These attributes can be explained if the synchrotron continuum is mainly dominated by thermalised particles at the jet base or the corona with considerably high temperatures, whereas only a small fraction of the energy (∼20%) would be distributed along the high-energy power-law tail of accelerated particles. On the other hand, the nebular gas excitation in LLAGN is in agreement with photo-ionisation from inverse Compton radiation (
α
x
∼ −0.7), which would dominate the nuclear continuum shortwards of ∼3000 Å, albeit a possible contribution from low-velocity shocks (< 500 km s
−1
) to the line excitation cannot be discarded. No sign of a standard hot accretion disc is seen in our sample of LLAGN, nevertheless, a weak cold disc (< 3000 K) is detected at the nucleus of the Sombrero galaxy, though its contribution to the nebular gas excitation is negligible. Our results suggest that the continuum emission in LLAGN is dominated at all wavelengths by undeveloped jets, powered by a thermalised particle distribution with high energies, on average. This is in agreement with their compact morphology and their high turnover frequencies. This behaviour is similar to that observed in peaked-spectrum radio sources and also compact jets in quiescent black hole X-ray binaries. Nevertheless, the presence of extended jet emission at kiloparsec scales for some of the objects in the sample is indicative of past jet activity, suggesting that these nuclei may undergo a rejuvenation event after a more active phase that produced their extended jets. These results imply that the dominant channel for energy release in LLAGN is mainly kinetic via the jet, rather than the radiative one. This has important implications in the context of galaxy evolution, since LLAGN probably represent a major but underestimated source of kinetic feedback in galaxies.
The coexistence of numerous tree species in tropical forests is commonly explained by negative dependence of recruitment on the conspecific seed and tree density due to specialist natural enemies ...that attack seeds and seedlings (‘Janzen–Connell’ effects). Less known is whether guilds of shared seed predators can induce a negative dependence of recruitment on the density of different species of the same plant functional group. We studied 54 plots in tropical forest on Barro Colorado Island, Panama, with contrasting mature tree densities of three coexisting large seeded tree species with shared seed predators. Levels of seed predation were far better explained by incorporating seed densities of all three focal species than by conspecific seed density alone. Both positive and negative density dependencies were observed for different species combinations. Thus, indirect interactions via shared seed predators can either promote or reduce the coexistence of different plant functional groups in tropical forest.
Aim
Biodiversity monitoring at global scales has been identified as one of the priorities to halt biodiversity loss. In this context, Latin America and the Caribbean (LAC), home to 60% of the global ...biodiversity, play an important role in the development of an integrative biodiversity monitoring platform. In this review, we explore to what extent LAC has advanced in the adoption of remote sensing for biodiversity monitoring and what are the gaps and opportunities to integrate local monitoring into global efforts to halt biodiversity loss.
Location
Latin America and the Caribbean.
Time period
1995 to 2022.
Taxa studied
Terrestrial organisms.
Methods
We reviewed the application of remote sensing for biodiversity monitoring in LAC aiming to identify gaps and opportunities across countries, ecosystem types and research networks.
Results
Our analysis illustrates how the use of remote sensing in LAC is disproportionately low in relation to the biodiversity it supports.
Main conclusions
Build upon this analysis, we present, discuss and offer perspectives regarding four gaps identified in the application of remote sensing for biodiversity monitoring in Latin America and the Caribbean, namely (1) alignment between remote sensing data resolution and ecosystem structure; (2) investment in research, institutions and capacity building within researchers and stakeholders; (3) decolonized practices that promote access to publishing outlets and pluralistic participation among countries that facilitate exchange of experiences and capacity building; and (4) development of networks within and across regions to advance in ground surveys, ensure access and to foster the use of remote sensing data.
Microsatellite instability (MSI) accounts for 15% of all colorectal tumours. Several specific clinicopathologicals (e.g., preference for the proximal colon over the distal colon, improved prognosis ...and altered response to chemotherapeutics) are described for this subset of tumours. This study aimed to analyse morphological, inflammatory and angiogenic features of MSI vs microsatellite stable (MSS) tumours.
Twenty-seven MSS and 29 MSI, TNM stage matched, colorectal tumours were selected from the archive of the Department of Pathology, UZ Leuven. Morphology was analysed on haematoxylin-eosin sections. Immunohistochemistry for CD3, CD4, CD8, CD20 and CD68 was used to map tumour infiltration in both a digital and traditional microscope-based manner for all distinct morphological components of the tumour. CD31 immunostains were performed to assess angiogenesis.
Morphological tumour heterogeneity was a marked feature of MSI tumours, occurring in 53% of the cases as compared with 11% of the MSS tumours (P<0.001). Digital immune quantification showed an increased number of tumour-infiltrating cytotoxic T-lymphocytes (CD8+) in MSI compared with MSS tumours for both the tumour (P=0.02) and peritumoural area (P=0.03). Traditional microscope-based quantification confirmed these results (P<0.001 for both) and, in addition, revealed large numbers of CD68+ macrophages in the peritumoural area of MSI cancers (P=0.001). Moreover, traditional microscope-based analysis was able to distinguish between lymphocytes directly infiltrating the tumoural glands (intra-epithelial) and those infiltrating only the neoplastic stroma around the glands (intratumoural). Quantification showed high numbers of intra-epithelial CD3+, CD4+, CD8+, CD20+ and CD68+ cells in MSI compared with MSS cancers (P<0.001, P=0.01, P<0.001, P<0.001 and P=0.006, respectively). Higher microvessel density (MVD) was observed in MSI tumours compared with their MSS counterpart.
Mixed morphology, reflecting tumour heterogeneity, is an important feature of MSI tumours and may have both diagnostic and therapeutic impact. The inflammatory reaction also presented with significant differences in MSI vs MSS colorectal tumours. MSI cancers showed mainly infiltration by cytotoxic T-cells in both the tumour and the close border around the tumour, as well as increased intra-epithelial infiltration in contrast to MSS tumours. The type of immune cell and the compartment it resides in (intratumoural or intra-epithelial) depend both on MSI status and morphology. Finally, MSI tumours showed a higher angiogenic capacity represented by an increased MVD, hinting for possible therapeutic consequences.
QUESTIONS: Niche differentiation is a central explanation for the co‐existence and distribution patterns of numerous tree species in tropical forests, but functional equivalence leading to neutral ...dynamics has been proposed as an alternative explanation. This niche vs neutral debate is fuelled by the highly variable results yielded by studies of the association between tree species distributions and environmental factors, where some studies find strong associations but others do not. Here, we ask how differences in sampling scale between studies contribute to this variation. LOCATION: Barro Colorado Island, Panama. METHODS: Using distribution maps of canopy‐statured individuals, we evaluated patterns of habitat association in five tropical tree species on Barro Colorado Island across a wide range of sampling scales (from 50 to 1600 ha). We investigated the scale‐dependency of species clumping patterns (Ripley's K) and the association of species distributions with important environmental variables (forest age, topography and geological formation) using point pattern analyses. RESULTS: Clump size and clump density had high variances within and among spatial scales. Significant habitat associations were found in all five species, with the number of habitat associations generally increasing with the sampling scale. Ignoring dispersal constraints inflated the number of significant habitat associations. CONCLUSIONS: We found that patterns of habitat association (and hence conclusions on the importance of niche vs neutral processes) are strongly affected by the choice of sampling scale and location. Explicit inclusion of the effect of spatial scale is critical for studies of habitat association and the main processes that structure communities of tropical trees.
Aims/hypothesis
Endoplasmic reticulum (ER) stress may play a role in cytokine-mediated beta cell death in type 1 diabetes, but it remains controversial whether ER stress markers are present in islets ...from type 1 diabetic individuals. Therefore, we evaluated by immunostaining the expression of markers of the three main branches of the ER stress response in islets from 13 individuals with and 15 controls without type 1 diabetes (eight adults and seven children).
Methods
Antibodies against the ER stress markers C/EBP homologous protein (CHOP), immunoglobulin heavy chain (BIP) and X-box binding protein 1 (XBP-1) were validated using HeLa cells treated with the ER stressor thapsigargin. These antibodies were then used to stain serial sections of paraffin-embedded pancreas from type 1 diabetic and non-diabetic individuals; samples were also immunostained for CD45, insulin and glucagon. Immunostaining intensities of the ER stress markers were quantified using a software-based, unbiased quantitative approach.
Results
Islets from individuals with type 1 diabetes showed increased levels of CHOP and, at least for insulitis-positive and beta cell-containing islets, BIP. XBP-1 expression was not, however, increased.
Conclusions/interpretation
Islet cells from individuals with type 1 diabetes display a partial ER stress response, with evidence of the induction of some, but not all, components of the unfolded protein response.
Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan-catabolising enzyme that induces immune tolerance by modulating T-cell responses. Carcinomas may create an immunosuppressive state via IDO1 ...expression. Here we examined a possible contribution of IDO1 on this phenomenon and investigated whether IDO1 has prognostic value in colorectal cancer (CRC).
IDO1 expression was investigated by quantitative PCR and western blotting in three colon cancer cell lines, in basal state and after interferon (IFN)-γ stimulation. Semi-quantitative immunohistochemistry was used to evaluate IDO1 expression in 265 pT1-4N0-2Mx-staged CRCs. Results were related to clinical variables and correlated with amounts of CD3(+) and CD8(+) T lymphocytes, which were quantitatively evaluated using image analysis.
In vitro expression of IDO1 depended on IFN-γ stimulation. Higher IDO1 expression at the tumour invasion front was an independent adverse prognostic factor in pT1-4N1Mx-staged CRC. It was associated with overall survival (P=0.001) and with metachronous metastases (P=0.018). IDO1 expression was not associated with the presence of CD3(+) or CD8(+) T lymphocytes.
Higher IDO1 expression at the tumour invasion front is involved in CRC progression and correlates with impaired clinical outcome, suggesting that IDO1 is an independent prognostic indicator for CRC.
Absorption spectra of very small metal clusters exhibit individual peaks that reflect the discreteness of their localized electronic states. With increasing size, these states develop into bands and ...the discrete absorption peaks give way to smooth spectra with, at most, a broad localized surface-plasmon resonance band. The widely accepted view over the last decades has been that clusters of more than a few dozen atoms are large enough to have necessarily smooth spectra. Here we show through theory and experiment that for the ubiquitous thiolate cluster compound Au144(SR)60 this view has to be revised: clearly visible individual peaks pervade the full near-IR, VIS and near-UV ranges of low-temperature spectra, conveying information on quantum states in the cluster. The peaks develop well reproducibly with decreasing temperature, thereby highlighting the importance of temperature effects. Calculations using time-dependent density-functional theory indicate the contributions of different parts of the cluster-ligand compound to the spectra.
The possibility for an Al-superoxide complex to reduce Fe(III) to Fe(II), promoting oxidative damage through the Fenton reaction, is investigated using highly accurate ab initio methods and density ...functional theory in conjunction with solvation continuum methods to simulate bulk solvent effects. It is found that the redox reaction between Al-superoxide and Fe(III) to produce Fe(II) is exothermic. Moreover, the loss of an electron from the superoxide radical ion in the Al-superoxide complex leads to a spontaneous dissociation of molecular oxygen from aluminum, recovering therefore an Al3+ hexahydrated complex. As demonstrated in previous studies, this complex is again prone to stabilize another superoxide molecule, suggesting a catalytic cycle that augments the concentration of Fe(II) in the presence of Al(III). Similar results are found for Al(OH)2+ and Al(OH)2+ hydrolytic species. Our work reinforces the idea that the presence of aluminum in biological systems could lead to an important pro-oxidant activity through a superoxide formation mechanism.
A theoretical study of the favorable redox reaction between Al-superoxide complex and Fe(III) is presented. The results may help in the explanation of the experimentally observed pro-oxidant activity of aluminum and the enhanced redox activity of iron in the presence of aluminum. Display omitted
► Theoretical study of the redox reaction between Al-superoxide and Fe(III). ► We found favorable redox reactions which suggest a Fenton cycle catalized by Al. ► Presented data may help in the explanation of observed pro-oxidant activity of Al. ► Contribution of ab initio calculations to the knowledge of toxicity of Al.
Imaging techniques have shown the association between left atrial adipose tissue (LAAT) volume and atrial fibrillation (AF) risk.
To analyze 1) adipokines in peripheral and atrial plasma from ...patients undergoing AF ablation; 2) its association with LAAT volume measured by multislice CT and 3) its predictive value for AF recurrence.
Seventy consecutive patients undergoing AF catheter ablation were screened. Blood samples were extracted from the left atrium and peripheral vein before catheter ablation. Multiplex fluorimetric immunoassay, enzyme-linked immunoassay and Western blot techniques were used for analyzing some adipokines, fatty acid binding protein 4 (FABP4), and leptin and perilipin analysis, respectively. Patients were followed up with clinical visits until one year after ablation. Generalized additive regression (GAM) was used for determining the best indicator of LAAT volume. Logistic regression analysis determined the best predictor of AF recurrence after persistent AF catheter ablation.
Our results showed 1) differences in the levels of FABP4 between peripheral and left atrial blood samples. 2) persistent AF patients had higher LAAT volume than those with paroxysmal AF (5.12 ± 2.76 vs. 3.82 ± 1.81 mL; p < 0.036). FABP4 was the best adipokine associated with LAAT in persistent AF (p < 0.01) 3) and predictive value for AF recurrence after catheter ablation (AUC-ROC 0.883 with 95% CI 0.739–1.028).
Plasma FABP4 levels, which were associated with LAAT volume in persistent AF, can be predictors of recurrence after catheter ablation. Whether persistent AF patients require more intensive management and monitoring according to FABP4 deserves further investigation.
•Differential FABP4 levels between atrial and peripheral plasma•FABP4 was associated with left atrial fat volume in persistent atrial fibrillation.•FABP4 predicts recurrence after persistent atrial fibrillation catheter ablation.
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