Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Multifunctional double-negative T cells in sooty mangabeys mediate T-helper functions irrespective of SIV infection.

Studying SIV infection of natural host monkey species, such as sooty mangabeys, has provided insights into the immune changes associated with these nonprogressive infections. Mangabeys maintain immune health despite high viremia or the dramatic CD4 T cell depletion that can occur following multitropic SIV infection. Here we evaluate double-negative (DN)(CD3+CD4-CD8-) T cells that are resistant to SIV infection due to a lack of CD4 surface expression, for their potential to fulfill a role as helper T cells. We first determined that DN T cells are polyclonal and predominantly exhibit an effector memory phenotype (CD95+CD62L-). Microarray analysis of TCR (anti-CD3/CD28) stimulated DN T cells indicated that these cells are multifunctional and upregulate genes with marked similarity to CD4 T cells, such as immune genes associated with Th1 (IFNγ), Th2 (IL4, IL5, IL13, CD40L), Th17 (IL17, IL22) and TFH (IL21, ICOS, IL6) function, chemokines such as CXCL9 and CXCL10 and transcription factors known to be actively regulated in CD4 T cells. Multifunctional T-helper cell responses were maintained in DN T cells from uninfected and SIV infected mangabeys and persisted in mangabeys exhibiting SIV mediated CD4 loss. Interestingly, TCR stimulation of DN T cells from SIV infected mangabeys results in a decreased upregulation of IFNγ and increased IL5 and IL13 expression compared to uninfected mangabeys. Evaluation of proliferative capacity of DN T cells in vivo (BrDU labeling) indicated that these cells maintain their ability to proliferate despite SIV infection, and express the homeostatic cytokine receptors CD25 (IL2 receptor) and CD127 (IL7 receptor). This study identifies the potential for a CD4-negative T cell subset that is refractory to SIV infection to perform T-helper functions in mangabeys and suggests that immune therapeutics designed to increase DN T cell function during HIV infection may have beneficial effects for the host immune system

Nonpathogenic SIV and Pathogenic HIV Infections Associate with Disparate Innate Cytokine Signatures in Response to <i>Mycobacterium bovis</i> BCG

<div><p>Infections with mycobacteria, including <i>Mycobacterium tuberculosis</i> (Mtb) and <i>Mycobacterium bovis (M</i>. <i>bovis)</i> BCG, are a leading cause of morbidity and mortality for HIV-infected persons. In contrast to HIV, nonpathogenic SIV infections of sooty mangabeys are characterized by a lack of clinical disease including an absence of opportunistic infections. The goal of this study was to identify innate immune responses to <i>M</i>. <i>bovis</i> BCG maintained during nonpathogenic lentiviral infections through a comparison of functional responses during pathogenic HIV or nonpathogenic SIV infections. Monocytes were evaluated for their ability to express key anti-mycobacterial cytokines TNF-α and IL-12 following a six-hour <i>ex vivo</i> BCG exposure. While HIV-infection was associated with a decreased percentage of IL-12-producing monocytes, nonpathogenic SIV-infection was associated with an increased percentage of monocytes producing both cytokines. Gene expression analysis of PBMC following <i>ex vivo</i> BCG exposure identified differential expression of NK cell-related genes and several cytokines, including IFN-γ and IL-23, between HIV-infected and control subjects. In contrast, SIV-infected and uninfected-control mangabeys exhibited no significant differences in gene expression after BCG exposure. Finally, differential gene expression patterns were identified between species, with mangabeys exhibiting lower IL-6 and higher IL-17 in response to BCG when compared to humans. Overall, this comparison of immune responses to <i>M</i>. <i>bovis</i> BCG identified unique immune signatures (involving cytokines IL-12, TNF-α, IL-23, IL-17, and IL-6) that are altered during HIV, but maintained or increased during nonpathogenic SIV infections. These unique cytokine and transcriptome signatures provide insight into the differential immune responses to Mycobacteria during pathogenic HIV-infection that may be associated with an increased incidence of mycobacterial co-infections.</p></div

Gene expression analysis of SIVneg and SIV+ mangabey PBMC following 4 hour BCG exposure.

<p>Semi-supervised hierarchical clustering via Principal Component Analysis (PCA) of 199 immunological gene targets (chosen <i>a priori</i>) was performed on RNA from whole PBMC following 4h BCG exposure and controls (without BCG), in SIV+ or SIVneg mangabeys via PCA (A). PC-1 (x-axis) represents the component responsible for the largest variation in the data set and explains 30% of the variation, while PC-2 (y-axis) represents the component contributing the second highest degree of variability in the dataset of 23%. Fold change in expression of these genes in SIVneg (x-axis) or SIV+ (y-axis) subjects after BCG exposure is depicted via scatterplot (B). No genes were found to diverge significantly from the trendline. A black outline denotes the genes that displayed statistically significant differences between HIVneg and HIV+ donors, for comparison.</p

Genes associated with HIV-status-specific effects following BCG exposure ex vivo.

<p>Genes associated with HIV-status-specific effects following BCG exposure ex vivo.</p

Whole PBMC cytokine gene regulation in HIVneg or HIV+ donors following BCG exposure. Plots demonstrate regulation of key proinflammatory.

<p>(A), Th1 (B), Th17 (C) and immunoregulatory genes (D) following 4h BCG exposure. Log2 copy number of RNA in an unstimulated control (U) or matched BCG-stimulated (B) samples in either humans (circles) or mangabeys (squares). The lower bound of the gray shaded portion of the graph represents the mean of the negative controls, and the upper bound represents two standard deviations above the mean, which ultimately determined the cutoff for expression. The most highly up- and down-regulated genes in humans or mangabeys are displayed via a heat map (E). FC: fold change; BD: below detection.</p

Whole blood monocyte proinflammatory cytokine production in HIVneg and HIV+ donors or SIVneg and SIV+ mangabeys following exposure to <i>M</i>. <i>bovis</i> BCG.

<p>(A) Representative flow cytometry plots and gating strategy of cytokine-producing monocytes, which were first defined as being live and CD3 negative (not shown), CD14+, and producing TNF-α, IL-12, or both following 6h exposure to BCG. (B-G) Percentage of TNF-α+ (B, E), IL-12+ (C, F), or double-positive (TNF-α+ and IL-12+) monocytes (D, G) in HIVneg (unfilled circles) and ART-naive HIV+ (filled circles) humans or SIVneg (unfilled squares) and SIV+ (filled squares) mangabeys following ex vivo BCG exposure. Lines represent the medians for each group (*p<0.05, Mann-Whitney).</p

Model of differential cellular responses during the innate immune response to BCG during pathogenic HIV or non-pathogenic SIV infection.

<p>Cytokines that are differentially expressed between HIVneg and HIV+ humans (A) or SIVneg and SIV+ mangabeys (B) are presented without boxes and are in bold type font. Arrow(s) represent the up or down modulation of these immune modulators in response to BCG, and fold change (FC) is presented as numeric values. Cytokines expressed differently between human subjects and mangabeys are boxed (B).</p

HIV infection is associated with a deficiency in IFNg mRNA and protein upregulation in response to M. bovis BCG.

<p>mRNA expression of IFN-γ in response to 4h of BCG exposure from HIVneg or ART-naïve HIV+ PBMC was measured via Nanostring analysis (left panel; HIVneg p<0.0001, HIV+ p = 0.02). IFN-γ protein was measured in supernatants from matched PBMC stimulations at an 18h time point (right panel; HIVneg-unstim vs HIVneg BCG p = 0.0001; HIV+ unstim vs HIV+ BCG p = 0.004; HIVneg-BCG vs HIV+ BCG p<0.0001; HIVneg unstim vs. HIV+ BCG n.s.). Statistical evaluation was performed via a two-tailed t-test on log-transformed data.</p

Selected genes that demonstrate HIV status-specific effects of BCG exposure.

<p>Fold change in the expression of 199 immunologic genes in response to 4h BCG exposure of PBMC from HIVneg (circles) or ART-naïve HIV+ (squares) was assessed via Nanostring gene expression analysis. Twelve genes remained significant following correction for multiple comparisons at an FDR threshold <10% (listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158149#pone.0158149.t001" target="_blank">Table 1</a>). Following the identification of these genes, further validation of the differences in response between HIVneg and HIV+ subjects was identified via a paired t-test: PRF1 (HIVneg p = 0.0045, HIV+ p = n.s), and NKp46 (HIVneg p = 0.0008, HIV+ p = n.s) perform cellular effector functions, and CCR5 (HIVneg p = 0.0029, HIV+ p = n.s) is an HIV coreceptor.</p