PLoS Pathogens最新文献

Protein-energy malnutrition (PEM) is a risk factor for developing visceral leishmaniasis (VL). While nutrient deficiency can impair immunity, its mechanistic impact on protective adaptive immune responses following Leishmania infection remains unknown. To determine the potential negative impacts of malnutrition on anti-parasitic responses in chronic VL, we provided mice with a polynutrient-deficient diet (deficient protein, energy, zinc, and iron) that mimics moderate human malnutrition. The polynutrient-deficient diet resulted in growth stunting and reduced mass of visceral organs and following infection with Leishmania infantum, malnourished-mice harbored more parasites in the spleen and liver. Malnourished and infected mice also had fewer T lymphocytes, with reduced T cell production of IFN-γ required for parasite clearance and enhanced production of the immunosuppressive cytokine, IL-10. To determine if IL-10 was causative in disease progression in the malnourished mice, we treated infected mice with monoclonal antibody α-IL-10R. α-IL-10R treatment reduced the parasite number in malnourished mice, restored the number of T cells producing IFN-γ, and enhanced hepatic granuloma formation. Our results indicate that malnutrition increases VL susceptibility due to defective IFN-γ-mediated immunity attributable to increased IL-10 production.

Microsporidia MB is a promising candidate for developing a symbiont-based strategy for malaria control because it disrupts the capacity of An. arabiensis to transmit the Plasmodium parasite. The symbiont is predominantly localized in the reproductive organs and is transmitted vertically from mother to offspring and horizontally (sexually) during mating. Due to the contribution of both transmission routes, Microsporidia MB has the potential to spread through target vector populations and become established at high prevalence. Stable and efficient vertical transmission of Microsporidia MB is important for its sustainable use for malaria control, however, the vertical transmission efficiency of Microsporidia MB can vary. In this study, we investigate the mechanistic basis of Microsporidia MB vertical transmission in An. arabiensis. We show that vertical transmission occurs through the acquisition of Microsporidia MB by Anopheles cystocyte progenitors following the division of germline stem cells. We also show that Microsporidia MB replicates to increase infection intensity in the oocyte of developing eggs when mosquitoes take a blood meal suggesting that symbiont proliferation in the ovary is coordinated with egg development. The rate of Microsporidia MB transmission to developing eggs is on average higher than the recorded (mother to adult offspring) vertical transmission rate. This likely indicates that a significant proportion of An. arabiensis offspring lose their Microsporidia MB symbionts during development. The stability of germline stem cell infections, coordination of symbiont proliferation, and very high rate of transmission from germline stem cells to developing eggs indicate that Microsporidia MB has a highly specialized vertical transmission strategy in An. arabiensis, which may explain host specificity.

The common rust disease of maize is caused by the obligate biotrophic fungus Puccinia sorghi. The maize Rp1-D allele imparts resistance against the P. sorghi IN2 isolate by initiating a defense response that includes a rapid localized programmed cell death process, the hypersensitive response (HR). In this study, to identify AvrRp1-D from P. sorghi IN2, we employed the isolation of haustoria, facilitated by a biotin-streptavidin interaction, as a powerful approach. This method proves particularly advantageous in cases where the genome information for the fungal pathogen is unavailable, enhancing our ability to explore and understand the molecular interactions between maize and P. sorghi. The haustorial transcriptome generated through this technique, in combination with bioinformatic analyses such as SignalP and TMHMM, enabled the identification of 251 candidate effectors. We ultimately identified two closely related genes, AvrRp1-D.1 and AvrRp1-D.2, which triggered an Rp1-D-dependent defense response in Nicotiana benthamiana. AvrRp1-D-induced Rp1-D-dependent HR was further confirmed in maize protoplasts. We demonstrated that AvrRp1-D.1 interacts directly and specifically with the leucine-rich repeat (LRR) domain of Rp1-D through yeast two-hybrid assay. We also provide evidence that, in the absence of Rp1-D, AvrRp1-D.1 plays a role in suppressing the plant immune response. Our research provides valuable insights into the molecular interactions driving resistance against common rust in maize.

Middle East respiratory syndrome coronavirus (MERS-CoV) and the pangolin MERS-like coronavirus MjHKU4r-CoV-1 employ dipeptidyl peptidase 4 (DPP4) as an entry receptor. MjHKU4r-CoV-1 could infect transgenic mice expressing human DPP4. To understand the mechanism of MjHKU4r-CoV-1 entry into cells, we determined the crystal structures of the receptor binding domain (RBD) of MjHKU4r-CoV-1 spike protein bound to human DPP4 (hDPP4) and Malayan pangolin DPP4 (MjDPP4), respectively. The overall hDPP4-binding mode of MjHKU4r-CoV-1 RBD is similar to that of MERS-CoV RBD. MjHKU4r-CoV-1 RBD shows higher binding affinity to hDPP4 compared to the bat MERS-like coronavirus Ty-BatCoV-HKU4. Via swapping residues between MjHKU4r-CoV-1 RBD and Ty-BatCoV-HKU4 RBD, we identified critical determinants on MjHKU4r-CoV-1 that are responsible for virus usage of hDPP4. Our study suggests that MjHKU4r-CoV-1 is more adapted to the human receptor compared to the bat HKU4 coronavirus and highlights the potential of virus emergence into the human population.

In sheep infected with bovine leukemia virus (BLV), transcription of structural, enzymatic, and accessory genes is silenced. However, the BLV provirus transcribes a series of non-coding RNAs that remain undetected by the host immune response. Specifically, three RNAs (AS1-L, AS1-S, and AS2) are consistently expressed from the antisense strand, originating from transcriptional initiation at the 3'-Long Terminal Repeat (LTR). To investigate the role of these non-coding RNAs in viral replication and pathogenesis, a reverse genetics approach was devised, capitalizing on a mechanistic disparity in transcription initiation between the 5' and 3' promoters. A two-nucleotide mutation (GG>TA) in the TFIIB-recognition element (BRE) impaired antisense transcription originating from the 3'-LTR. In the context of the provirus, this 2bp mutation significantly diminished the expression of antisense RNAs, while not notably affecting sense transcription. When inoculated to sheep, the mutated provirus was infectious but exhibited reduced replication levels, shedding light on the role of antisense transcription in vivo. In comparison to lymphoid organs in sheep infected with a wild-type (WT) provirus, the mutant demonstrated alterations in both the spatial distribution and rates of cell proliferation in the lymph nodes and the spleen. Analysis through RNA sequencing and RT-qPCR unveiled an upregulation of the Hmcn1/hemicentin-1 gene in B-lymphocytes from sheep infected with the mutated provirus. Further examination via confocal microscopy and immunohistochemistry revealed an increase in the amount of hemicentin-1 protein encoded by Hmcn1 in peripheral blood mononuclear cells (PBMCs) and lymphoid organs of sheep infected with the mutant. RNA interference targeting Hmcn1 expression impacted the migration of ovine kidney (OVK) cells in vitro. In contrast to the WT, the mutated provirus showed reduced oncogenicity when inoculated into sheep. Collectively, this study underscores the essential role of antisense transcription in BLV replication and pathogenicity. These findings may offer valuable insights into understanding the relevance of antisense transcription in the context of human T-cell leukemia virus (HTLV-1).

Both Metarhizium robertsii ARSEF 2575 (Mr2575) and Metarhizium anisopliae ARSEF 549 (Ma549) infect a range of insects whilst also interacting with plants; however, little is known about the traits that affect the competitive ability of different strains. We examined the interactions between Mr2575 and Ma549 in culture and during co-infection of plants (Arabidopsis thaliana) and insects. Mr2575 outcompetes Ma549 under nutrient-limiting conditions, including root exudates, giving it a priority advantage on Arabidopsis roots. However, during co-infection of Manduca sexta or Drosophila melanogaster, Ma549's higher blastospore production enhanced its competitive ability within the host. In large M. sexta (fifth instar), blastospores facilitate dispersal, suppress host melanization and prevent Mr2575 from spreading from infection sites, reducing conidia production. However, colonization of smaller hosts such as first instar M. sexta and D. melanogaster did not provide Ma549 with a competitive advantage, as conidial production was dependent on retaining control of the cuticle through which conidiating hyphae emerge. Unexpectedly, Ma549 and Mr2575 segregate within hosts, suggesting resource partitioning with Mr2575 predominating in the thoraxes of Drosophila, especially in females, and Ma549 in the abdomen. In fifth instar M. sexta, Mr2575 was most prevalent around spiracles and the front end of segments, despite Ma549 and Mr2575 having similar susceptibility to hypoxia. Dispersing conidia homogeneously into the hemocoel of fifth instar M. sexta eliminated the blastospore production advantage, making Ma549 and Mr2575 equally competitive, with strict partitioning of Mr2575 at the anterior and Ma549 at the posterior ends of segments. As Metarhizium species have multiple roles in natural ecosystems and agroecosystems these discoveries are relevant to understanding their impact on maintaining biodiversity and for exploiting them to enhance food security.

The interactions among viruses and host plants are complex and fascinating because these organisms interact with and adapt to each other continuously. Many plant transcription factors play important roles in plant growth and development and in the resistance to viral infection. To facilitate the infection of plants, some viral proteins typically target and inhibit the function of plant transcription factors. In this study, we found an interesting phenomenon wherein the p3a protein of barley yellow dwarf virus (BYDV) can interact with the zinc finger domain of the TaDOF transcription factor in wheat; the zinc finger domain of TaDOF can interact with the promoter of TaHSP70 and inhibit the transcription of the TaHSP70 gene; and p3a interacts with the TaDOF zinc finger domain through competitive binding, alleviating TaDOF zinc finger domain-mediated inhibition of the TaHSP70 promoter, thereby promoting TaHSP70 expression and promoting infection by BYDV. This study demonstrates that BYDV p3a is an immunosuppressive factor and enriches our understanding of the pathogenesis of BYDV.

Cyst nematodes use a stylet to secrete CLE-like peptide effector mimics into selected root cells of their host plants to hijack endogenous plant CLE signaling pathways for feeding site (syncytium) formation. Here, we identified ATHB8, encoding a HD-ZIP III family transcription factor, as a downstream component of the CLE signaling pathway in syncytium formation. ATHB8 is expressed in the early stages of syncytium initiation, and then transitions to neighboring cells of the syncytium as it expands; an expression pattern coincident with auxin response at the infection site. Conversely, MIR165a, which expresses in endodermal cells and moves into the vasculature to suppress HD-ZIP III TFs, is down-regulated near the infection site. Knocking down HD-ZIP III TFs by inducible over-expression of MIR165a in Arabidopsis dramatically reduced female development of the sugar beet cyst nematode (Heterodera schachtii). HD-ZIP III TFs are known to function downstream of auxin to promote cellular quiescence and define stem cell organizer cells in vascular patterning. Taken together, our results suggest that HD-ZIP III TFs function together with a CLE and auxin signaling network to promote syncytium formation, possibly by inducing root cells into a quiescent status and priming them for initial syncytial cell establishment and/or subsequent cellular incorporation.

Mycoplasma pneumoniae is a common cause of community-acquired pneumonia in which neutrophils play a critical role. Immune-responsive gene 1 (IRG1), responsible for itaconate production, has emerged as an important regulator of inflammation and infection, but its role during M. pneumoniae infection remains unknown. Here, we reveal that itaconate is an endogenous pro-inflammatory metabolite during M. pneumoniae infection. Irg1 knockout (KO) mice had lower levels of bacterial burden, lactate dehydrogenase (LDH), and pro-inflammatory cytokines compared with wild-type (WT) controls after M. pneumoniae infection. Neutrophils were the major cells producing itaconate during M. pneumoniae infection in mice. Neutrophil counts were positively correlated with itaconate concentrations in bronchoalveolar lavage fluid (BALF) of patients with severe M. pneumoniae pneumonia. Adoptive transfer of Irg1 KO neutrophils, or administration of β-glucan (an inhibitor of Irg1 expression), significantly attenuated M. pneumoniae pneumonia in mice. Mechanistically, itaconate impaired neutrophil bacterial killing and suppressed neutrophil apoptosis via inhibiting mitochondrial ROS. Moreover, M. pneumoniae induced Irg1 expression by activating NF-κB and STAT1 pathways involving TLR2. Our data thus identify Irg1/itaconate pathway as a potential therapeutic target for the treatment of M. pneumoniae pneumonia.