Host Immune System Research Articles

Eugenol targeting CrtM inhibits the biosynthesis of staphyloxanthin in Staphylococcus aureus

Staphylococcus aureus is a serious foodborne pathogen threatening food safety and public health. Especially the emergence of methicillin-resistant Staphylococcus aureus (MRSA) increased the difficulty of S. aureus treatment. Staphyloxanthin is a crucial virulence factor of S. aureus. Blocking staphyloxanthin production could help the host immune system counteract the invading S. aureus cells. In this study, we first screened for staphyloxanthin inhibitors using a virtual screening method. The outcome of the virtual screening method resulted in the identification of eugenol (300 μg/mL), which significantly inhibits the staphyloxanthin production in S. aureus ATCC 29213, S. aureus Newman, MRSA ATCC 43300 and MRSA ATCC BAA1717 by 84.2 %, 63.5 %, 68.1 %, and 79.5 %, respectively. The outcome of the growth curve assay, field-emission scanning electron, and confocal laser scanning microscopy analyses confirmed that eugenol at the test concentration did not affect the morphology and growth of S. aureus. Moreover, the survival rate of S. aureus ATCC 29213 and MRSA ATCC 43300 under H2O2 pressure decreased to 51.9 % and 45.5 % in the presence of eugenol, respectively. The quantitative RT-PCR and molecular simulation studies revealed that eugenol targets staphyloxanthin biosynthesis by downregulating the transcription of the crtM gene and inhibiting the activity of the CrtM enzyme. Taken together, we first determined that eugenol was a prominent compound for staphyloxanthin inhibitor to combat S. aureus especially MRSA infections.

Computational Screening for the Identification of Potential Phytochemical Inhibitors of Leishmania infantum Trypanothione Reductase

AbstractLeishmaniasis is a vector‐borne parasitic disease that possesses high morbidity and a variety of clinical manifestations. Of all the clinical manifestations, visceral leishmaniasis (VL) is the deadliest and its etiological organisms are mainly Leishmania infantum (L. infantum) and Leishmania donovani (L. donovani). In the tropical and subtropical regions, L. infantum is the main causative agent of VL, and it creates a favorable biological milieu in the host through the multifaceted action of its trypanothione reductase (TryR), which mediates the reduction of oxidized trypanothione to its reduced form, leading to the replenishment of the antioxidant capacity of the parasite and detoxifying the reactive oxygen and nitrogen species imposed by the host's immune system. The distinct structural and functional differences of this enzyme compared to its human homologs and its pivotal role in the survival of the parasite have rendered it an attractive target for drug discovery odysseys. Consequently, this study aims to identify potential inhibitors of TryR of L. infantum from Allium sativum (A. sativum) using molecular modeling techniques. The identified compounds were first screened using molecular docking, after which the pharmacokinetics properties of the top‐scoring compounds were further evaluated. Further evaluation of the stability of the complexes of the lead compounds with TryR revealed their relative stability over 100 ns simulation period. Ultimately, the lead compounds namely beta‐sitosterol, (E)‐alpha‐bisabolene, and agapanthagenin were found to possess suitable properties based on the results of this study and can serve as inhibitors of TryR of L. infantum upon further in vitro and in vivo study.

Role of auto-antibodies in the mechanisms of dengue pathogenesis and its progression: a comprehensive review.

A complex interaction among virulence factors, host-genes and host immune system is considered to be responsible for dengue virus (DENV) infection and disease progression. Generation of auto-antibodies during DENV infection is a major phenomenon that plays a role in the pathophysiology of dengue hemorrhagic fever and dengue shock syndrome. Hemostasis, thrombocytopenia, hepatic endothelial dysfunction, and autoimmune blistering skin disease (pemphigus) are different clinical manifestations of dengue pathogenesis; produced due to the molecular mimicry of DENV proteins with self-antigens like coagulation factors, platelets and endothelial cell proteins. This review elaborately describes the current advancements in auto-antibody-mediated immunopathogenesis which inhibits coagulation cascade and promotes hyperfibrinolysis. Auto-antibodies like anti-endothelial cell antibodies-mediated hepatic inflammation during severe DENV infection have also been discussed. Overall, this comprehensive review provides insight to target auto-antibodies that may act as potential biomarkers for disease severity, and a ground for the development of therapeutic strategy against DENV.

Review of Virulence Factors in Candida

Candida albicans is a prevalent commensal fungus that inhabits various anatomical regions, including the oropharyngeal cavity, gastrointestinal and vaginal tract, as well as the skin of persons in good condition. C. albicans is present in the normal flora of the microbiota in around 50% of the population. The clinical presentations of Candida species encompass a spectrum of symptoms, spanning from localized. The spectrum of mucocutaneous issues ranges from superficial to invasive disorders that impact many organ systems and present a substantial threat to human life. Disruptions in the normal homeostasis of Candida can be attributed to a range of reasons, encompassing systemic and local factors as well as genetic and environmental influences.
 These disruptions ultimately lead to a shift from a state of normal flora to the development of Infections caused by pathogens and opportunistic agents. The initiation and advancement of infection are regulated by the virulence characteristics of Candida, which play a role in the emergence of candidiasis. Oral candidiasis presents with a wide range of symptoms, which can be classified into major and minor types. The gastrointestinal tract is the main reservoir for Candida albicans in the human body. Infection occurs due to an imbalance in the local microbiota, impaired immune function, and damage to the intestinal mucosal barrier. Candidaemia, a term used to describe invasive infections caused by candida, is associated with the presence of Candida albicans in the bloodstream. The mutual relationship remains intact by maintaining a balance between the host immune system and C. albicans virulence factors. This study investigates the virulence traits exhibited by Candida albicans. These components have a significant impact on the development of disorders.

Additive and Dose-Dependent Effect of Rituximab on ‎Pediatric ‎Patients’ Outcomes Concurrently Receiving Immunosuppressive ‎Chemotherapy, A Prospective Cohort Study

Background: Rituximab (RTX) is approved for treating CD20-positive B-cell malignancies, including non-Hodgkin lymphoma, when used alongside chemotherapy. It has the potential to interact with and alter the host immune system, putting patients at a heightened risk of infection. Therefore, the use of RTX necessitates a meticulous assessment of infectious risks based on the latest evidence. Objectives: We conducted a prospective investigation into infectious complications and mortality among children undergoing RTX treatment over the observation period of the study. Methods: In this observational cohort study, we included 61 pediatric patients treated with RTX for malignancy and immune thrombocytopenic purpura (ITP), as well as 122 cancer patients who had never received RTX (the unexposed group). These patients were prospectively monitored for febrile neutropenia (FN), bloodstream infection (BSI), invasive fungal infection (IFI), and mortality. All infectious complications were documented starting from the initial dose of RTX and continuing for at least six months following the last dose. Logistic regression and Cox regression analyses, with consideration for the proportional hazards assumption, were utilized to evaluate the impact of covariates on mortality and infection-related outcomes. Results: Infectious complications were observed in 52.5% of children treated with RTX. These complications were notably more prevalent in children with malignancy compared to those with chronic ITP (89.5% versus 10.5%, respectively). RTX was found to be associated with an increased likelihood of mortality in children with malignancy (OR [95% CI]: 1.54 [0.41, 5.69]). According to Cox regression analysis, RTX was linked to a higher risk of IFIs, death, FN events, and BSIs over a 36-month observation period (4.33 [1.21, 15.52], 3.26 [1.008, 10.59], 1.68 [0.83, 3.41], and 1.59 [0.27, 9.17], respectively). The total dose of RTX administered was also associated with adverse patient outcomes, with the odds of infectious events and death increasing in the second, third, and fourth quartiles of the total RTX dose administered. Furthermore, the estimated one-year and two-year survival rates for cancer patients treated with RTX were 77% and 58%, respectively. Conclusions: RTX treatment, when used concurrently with immunosuppressive chemotherapy for hematologic malignancies in children, showed additive and dose-dependent effects on clinical outcomes.

A natural inhibitor of diapophytoene desaturase attenuates methicillin-resistant Staphylococcus aureus (MRSA) pathogenicity and overcomes drug-resistance.

At present, the inhibition of staphyloxanthin biosynthesis has emerged as a prominent strategy in combating methicillin-resistant Staphylococcus aureus (MRSA) infection. Nonetheless, there remains a limited understanding regarding the bio-structural characteristics of staphyloxanthin biosynthetic enzymes, as well as the molecular mechanisms underlying the interaction between inhibitors and proteins. Furthermore, the functional scope of these inhibitors is relatively narrow. In this study, we address these limitations by harnessing the power of deep learning techniques to construct the 3D structure of diapophytoene desaturase (CrtN). We perform efficient virtual screening and unveil alnustone as a potent inhibitor of CrtN. Further investigations employing molecular modelling, site-directed mutagenesis and biolayer interferometry (BLI) confirmed that alnustone binds to the catalytic active site of CrtN. Transcriptomic analysis reveals that alnustone significantly down-regulates genes associated with staphyloxanthin, histidine and peptidoglycan biosynthesis. Under the effects of alnustone, MRSA strains exhibit enhanced sensitivity to various antibiotics and the host immune system, accompanied by increased cell membrane permeability. In a mouse model of systemic MRSA infection, the combination of alnustone and antibiotics exhibited a significant therapeutic effect, leading to reduced bacterial colony counts and attenuated pathological damage. Alnustone, as a natural inhibitor targeting CrtN, exhibits outstanding antibacterial properties that are single-targeted yet multifunctional. This finding provides a novel strategy and theoretical basis for the development of drugs targeting staphyloxanthin producing bacteria.

Unveiling Cryptosporidium parvum sporozoite-derived extracellular vesicles: profiling, origin, and protein composition

Cryptosporidium parvum is a common cause of a zoonotic disease and a main cause of diarrhea in newborns. Effective drugs or vaccines are still lacking. Oocyst is the infective form of the parasite; after its ingestion, the oocyst excysts and releases four sporozoites into the host intestine that rapidly attack the enterocytes. The membrane protein CpRom1 is a large rhomboid protease that is expressed by sporozoites and recognized as antigen by the host immune system. In this study, we observed the release of CpRom1 with extracellular vesicles (EVs) that was not previously described. To investigate this phenomenon, we isolated and resolved EVs from the excystation medium by differential ultracentrifugation. Fluorescence flow cytometry and transmission electron microscopy (TEM) experiments identified two types of sporozoite-derived vesicles: large extracellular vesicles (LEVs) and small extracellular vesicles (SEVs). Nanoparticle tracking analysis (NTA) revealed mode diameter of 181 nm for LEVs and 105 nm for SEVs, respectively. Immunodetection experiments proved the presence of CpRom1 and the Golgi protein CpGRASP in LEVs, while immune-electron microscopy trials demonstrated the localization of CpRom1 on the LEVs surface. TEM and scanning electron microscopy (SEM) showed that LEVs were generated by means of the budding of the outer membrane of sporozoites; conversely, the origin of SEVs remained uncertain. Distinct protein compositions were observed between LEVs and SEVs as evidenced by their corresponding electrophoretic profiles. Indeed, a dedicated proteomic analysis identified 5 and 16 proteins unique for LEVs and SEVs, respectively. Overall, 60 proteins were identified in the proteome of both types of vesicles and most of these proteins (48 in number) were already identified in the molecular cargo of extracellular vesicles from other organisms. Noteworthy, we identified 12 proteins unique to Cryptosporidium spp. and this last group included the immunodominant parasite antigen glycoprotein GP60, which is one of the most abundant proteins in both LEVs and SEVs.

Identification of Critical Amino Acid Residues of a Two-Component Sensor Protein for Signal Sensing in Porphyromonas gingivalis Fimbriation via Random Mutant Library Construction

Porphyromonas gingivalis (Pg) utilizes FimA fimbriae to colonize the gingival sulcus and evade the host immune system. The biogenesis of all FimA-related components is positively regulated by the FimS–FimR two-component system, making the FimS sensory protein an attractive target for preventing Pg infection. However, the specific environmental signal received by FimS remains unknown. We constructed random Pg mutant libraries to identify critical amino acid residues for signal sensing by FimS. Optimized error-prone polymerase chain reaction (PCR) was used to introduce a limited number of random mutations in the periplasmic-domain-coding sequence of fimS, and expression vectors carrying various mutants were generated by inverse PCR. More than 500 transformants were obtained from the fimS-knockout Pg strain using the Escherichia coli–Pg conjugal transfer system, whereas only ~100 transformants were obtained using electroporation. Four and six transformant strains showed increased and decreased fimA expression, respectively. Six strains had single amino acid substitutions in the periplasmic domain, indicating critical residues for signal sensing by FimS. This newly developed strategy should be generally applicable and contribute to molecular genetics studies of Pg, including the elucidation of structure–function relationships of proteins of interest.

Melanin depletion affects Aspergillus flavus conidial surface proteins, architecture, and virulence.

Melanin is an Aspergillus flavus cell wall component that provides chemical and physical protection to the organism. However, the molecular and biological mechanisms modulating melanin-mediated host-pathogen interaction in A. flavus keratitis are not well understood. This work aimed to compare the morphology, surface proteome profile, and virulence of melanized conidia (MC) and non-melanized conidia (NMC) of A. flavus. Kojic acid treatment inhibited melanin synthesis in A. flavus, and the conidial surface protein profile was significantly different in kojic acid-treated non-melanized conidia. Several cell wall-associated proteins and proteins responsible for oxidative stress, carbohydrate, and chitin metabolic pathways were found only in the formic acid extracts of NMC. Scanning electron microscopy (SEM) analysis showed the conidial surface morphology difference between the NMC and MC, indicating the role of melanin in the structural integrity of the conidial cell wall. The levels of calcofluor white staining efficiency were different, but there was no microscopic morphology difference in lactophenol cotton blue staining between MC and NMC. Evaluation of the virulence of MC and NMC in the Galleria mellonella model showed NMC was less virulent compared to MC. Our findings showed that the integrity of the conidial surface is controlled by the melanin layer. The alteration in the surface protein profile indicated that many surface proteins are masked by the melanin layer, and hence, melanin can modulate the host response by preventing the exposure of fungal proteins to the host immune defense system. The G. mellonella virulence assay also confirmed that the NMC were susceptible to host defense as in other Aspergillus pathogens. KEY POINTS: • l-DOPA melanin production was inhibited in A. flavus isolates by kojic acid, and for the first time, scanning electron microscopy (SEM) analysis revealed morphological differences between MC and NMC of A. flavus strains • Proteome profile of non-melanized conidia showed more conidial surface proteins and these proteins were mainly involved in the virulence, oxidative stress, and metabolism pathways • Non-melanized conidia of A. flavus strains were shown to be less virulent than melanised conidia in an in vivo virulence experiment with the G. melonella model.

Protecting Orthopaedic Implants from Infection: Antimicrobial Peptide Mel4 Is Non-Toxic to Bone Cells and Reduces Bacterial Colonisation When Bound to Plasma Ion-Implanted 3D-Printed PAEK Polymers

Even with the best infection control protocols in place, the risk of a hospital-acquired infection of the surface of an implanted device remains significant. A bacterial biofilm can form and has the potential to escape the host immune system and develop resistance to conventional antibiotics, ultimately causing the implant to fail, seriously impacting patient well-being. Here, we demonstrate a 4 log reduction in the infection rate by the common pathogen S. aureus of 3D-printed polyaryl ether ketone (PAEK) polymeric surfaces by covalently binding the antimicrobial peptide Mel4 to the surface using plasma immersion ion implantation (PIII) treatment. The surfaces with added texture created by 3D-printed processes such as fused deposition-modelled polyether ether ketone (PEEK) and selective laser-sintered polyether ketone (PEK) can be equally well protected as conventionally manufactured materials. Unbound Mel4 in solution at relevant concentrations is non-cytotoxic to osteoblastic cell line Saos-2. Mel4 in combination with PIII aids Saos-2 cells to attach to the surface, increasing the adhesion by 88% compared to untreated materials without Mel4. A reduction in mineralisation on the Mel4-containing surfaces relative to surfaces without peptide was found, attributed to the acellular portion of mineral deposition.

Borrelia burgdorferi and autoimmune mechanisms: implications for mimicry, misdiagnosis, and mismanagement in Lyme disease and autoimmune disorders.

The genus Borrelia encompasses a diverse group of spirochetes transmitted primarily by ticks, with Borrelia burgdorferi causing Lyme disease, which is prevalent in North America and Europe. Borrelia's structural adaptations and ability to persist in diverse host tissues underscore its pathogenic potential. Beyond traditional infectious responses, Borrelia engages in complex interactions with the host immune system, contributing to autoimmune mechanisms such as molecular mimicry and persistent infections. This intricate interplay manifests in symptoms resembling various autoimmune diseases, including systemic lupus erythematosus, dermatomyositis, local scleroderma, and systemic sclerosis. However, these associations lack a precise explanation, emphasizing the need for further investigation. The cases of misdiagnosis between Lyme borreliosis and autoimmune diseases highlight the critical importance of accurate diagnostics and adherence to guidelines. Understanding Borrelia's impact on immune responses is pivotal for advancing diagnostics and targeted therapeutic interventions in Lyme borreliosis and its potential autoimmune implications.

Abstract CT035: Proof-of-concept and preliminary efficacy of triple IAP blockade to maximize immunogenic cell death and induce efficient adaptive immune response: First report on the ASTEROID phase 1 trial

Abstract Background: Dying cells play an important role in CD8+ T cell-mediated immunity. While apoptosis is mainly immunologically silent, necroptosis is immunogenic and can more efficiently initiate an adaptive immune response that could be augmented by immune checkpoint inhibition (ICI). Inhibitor of Apoptosis (IAP) proteins are key gatekeepers of how a cell dies, and frequently overexpressed in cancer. ASTX660 (tolinapant) is a triple blocker of cIAP1/2 and XIAP, sensitizing cancer cells to death ligands through ripoptosome formation, activating ‘danger’ co-stimulatory signals and dendritic cell (DC) maturation required to prime a potent antitumor response. Methods: We assessed the safety, pharmacodynamic (PD), and clinical activity of 7 days of oral ASTX660 given prior to pembrolizumab 200 mg (Q3W), in patients (pts) refractory to standard therapy. TITE-CRM was used to explore ASTX660 doses 90-180 mg. Serial paired blood and tumor samples were analyzed to interrogate the effect of ASTX660 on cell death, tumor microenvironment and host immune system. Results: 22 pts have been enrolled; median age 55 years (range 38-81); male:female 5:17; all ECOG PS ≤1; median 4.5 prior therapies. Tumor types included breast, head and neck (HN), hepatocellular, cervical, pancreatic and cholangiocarcinoma. Combination ASTX660-pembrolizumab is currently recruiting at highest dose 180 mg without any dose limiting toxicities (DLT) seen within the 6-week DLT observation period. Most common adverse events (AE) were G1-2 rash, nausea, and asymptomatic increases in amylase, lipase and transaminases; all reversible and easily manageable. Four iRECIST confirmed partial responses were seen in 10 efficacy evaluable pts treated at biologically active dose levels 120 and 150 mg (Overall response rate 40%), including 2 pts with ER+ HER2- breast cancer, 1 cervical adenocarcinoma pt (exceptional response following initial pseudoprogression) and a HN cancer pt refractory to ICI monotherapy. 3/4 responders are ongoing. Efficacy data from pts treated at highest dose level 180 mg is pending. FACS of paired blood samples from responders shows a significant rise in %CD57+/CD3+ cytotoxic effector T cells [mean 11.90% (pre-) vs 14.25% (post-ASTX660); p=.0176]. These changes were not seen in the non-responders group. Full PD from paired blood and tumour sampling will be shared at the meeting. Conclusion: ASTX660-pembrolizumab is is well-tolerated with durable antitumor responses in pts with immunologically cold tumors, providing the first clinical proof-of-concept of immunogenic cell death induction leading to effective adaptive immune response when combined with ICI. Recommended Phase 2 dose optimization and expansion cohorts in immunologically cold cancers are ongoing. Citation Format: Crescens Tiu, Wing Yau, Victoria Sanchez-Perez, Giovanni Codacci-Pisanelli, Ching Leung, Eden S. Andrews, Bristi Basu, Anna Zachariou, Toby Prout, Mona Parmar, Alison Turner, Xiaoran Lai, Zhulin Yin, Karen E. Swales, Syed Haider, Thomas Lund, Diego C. Dos Reis, Tatiany L. Silveira, Alan S. Dunlop, Ann-Marie Baker, Bora Gurel, Ana Ferreira, Claudia Bertan, Nina Tunariu, Edward W. Johnston, Alistair Ring, Tencho Tenev, Tomoko Smyth, Simone Jueliger, Udai Banerji, Johann S. de Bono, Alec Paschalis, Adam Sharp, Anna Minchom, Christina Yap, Pascal Meier, Juanita S. Lopez. Proof-of-concept and preliminary efficacy of triple IAP blockade to maximize immunogenic cell death and induce efficient adaptive immune response: First report on the ASTEROID phase 1 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT035.

Abstract LB075: Small molecule procaspase activating compound 1 (PAC-1) enhances CAR-T immunotherapy for solid tumors in syngeneic murine models

Abstract Chimeric antigen receptor (CAR)-T cell therapy has been shown to effectively treat solid tumors in syngeneic murine models, but antigen loss and T cell trafficking into the tumors pose major obstacles to its long-term efficacy. Here we explored a combination therapy against advanced stages of colorectal and ovarian syngeneic murine tumor models using a tumor-specific small molecule (PAC-1) that triggers the engagement of the host immune system and synergizes with a Tn-specific adoptively transferred 237 CAR-T immunotherapy. PAC-1 has been shown to induce apoptosis in tumor cells with high expression of procaspase 3, via chelation of inhibitory zinc and release of active executioner caspase 3. PAC-1 also recently completed a phase I trial (NCT02355535) and was shown to be well-tolerated in late-stage cancer patients. RNA sequencing of CT26 colorectal cells stimulated with PAC-1 for 24 hours revealed that PAC-1 induced global changes at the transcriptome level, up-regulating genes involved in immune activation and apoptosis, and down-regulating genes involved in DNA repair, cell cycle regulation, and myc-driven proliferation. Validation of RNAseq data was performed using a combination of RT-qPCR, Western blot, flow cytometry, and co-culture studies. A combination of transcriptome and exome sequencing analyses in murine colorectal cell line CT26 revealed that the PAC-1-mediated down-regulation of DNA repair machinery led to somatic alterations in the genome and a higher mutational load in tumor cells, subsequently presented as neo-antigens by antigen-presenting cells. As a result, host CD8+ cytotoxic T cells were able to infiltrate tumors and reduce the tumor burden. Tn-dependent CARs have been used recently to demonstrate the proof of concept in the targeting of cancer-specific Tn-antigens such as the Tn-MUC1 antigen in humans, and an analogous Tn-OTS8 target in mice. In our murine ID8 ovarian tumor model, untreated mice with disseminated tumors have a median survival of 71 days. As a single agent administered intraperitoneally, PAC-1 extended the median survival to 90 days (p<0.0001), while 237 CAR-T treated mice have a median survival of 103 days (p<0.0001). A combination of the two treatment modalities (PAC-1 administered before 237 CAR-T) further extended the median survival to 145 days (p=0.048). Administering PAC-1 after 237 CAR-T also modestly extended the median survival to 132 days (p=0.06). Taken altogether, our results demonstrate that PAC-1 engages the immune system to treat cancer by inducing expression of pro-inflammatory cytokines in tumor cells allowing the recruitment of CD8+ effector T cells to the tumor microenvironment. Combination strategies that boost T cell trafficking shows great promise to enhance the anti-tumor efficacy and feasibility of adoptive CAR-T therapy against solid tumors. Citation Format: Diana R. Ranoa, Yifei Kang, Jenny Drnevich, Gloria Rendon, Christopher J. Fields, Keith Bailey, Edward J. Roy, Timothy M. Fan, David M. Kranz, Paul J. Hergenrother. Small molecule procaspase activating compound 1 (PAC-1) enhances CAR-T immunotherapy for solid tumors in syngeneic murine models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB075.

A genome-centric view of the role of the Acropora kenti microbiome in coral health and resilience

Microbial diversity has been extensively explored in reef-building corals. However, the functional roles of coral-associated microorganisms remain poorly elucidated. Here, we recover 191 bacterial and 10 archaeal metagenome-assembled genomes (MAGs) from the coral Acropora kenti (formerly A. tenuis) and adjacent seawater, to identify microbial functions and metabolic interactions within the holobiont. We show that 82 MAGs were specific to the A. kenti holobiont, including members of the Pseudomonadota, Bacteroidota, and Desulfobacterota. A. kenti-specific MAGs displayed significant differences in their genomic features and functional potential relative to seawater-specific MAGs, with a higher prevalence of genes involved in host immune system evasion, nitrogen and carbon fixation, and synthesis of five essential B-vitamins. We find a diversity of A. kenti-specific MAGs encode the biosynthesis of essential amino acids, such as tryptophan, histidine, and lysine, which cannot be de novo synthesised by the host or Symbiodiniaceae. Across a water quality gradient spanning 2° of latitude, A. kenti microbial community composition is correlated to increased temperature and dissolved inorganic nitrogen, with corresponding enrichment in molecular chaperones, nitrate reductases, and a heat-shock protein. We reveal mechanisms of A. kenti-microbiome-symbiosis on the Great Barrier Reef, highlighting the interactions underpinning the health of this keystone holobiont.

A commensal protozoan attenuates Clostridioides difficile pathogenesis in mice via arginine-ornithine metabolism and host intestinal immune response

Antibiotic-induced dysbiosis is a major risk factor for Clostridioides difficile infection (CDI), and fecal microbiota transplantation (FMT) is recommended for treating CDI. However, the underlying mechanisms remain unclear. Here, we show that Tritrichomonas musculis (T.mu), an integral member of the mouse gut commensal microbiota, reduces CDI-induced intestinal damage by inhibiting neutrophil recruitment and IL-1β secretion, while promoting Th1 cell differentiation and IFN-γ secretion, which in turn enhances goblet cell production and mucin secretion to protect the intestinal mucosa. T.mu can actively metabolize arginine, not only influencing the host’s arginine-ornithine metabolic pathway, but also shaping the metabolic environment for the microbial community in the host’s intestinal lumen. This leads to a relatively low ornithine state in the intestinal lumen in C. difficile-infected mice. These changes modulate C. difficile’s virulence and the host intestinal immune response, and thus collectively alleviating CDI. These findings strongly suggest interactions between an intestinal commensal eukaryote, a pathogenic bacterium, and the host immune system via inter-related arginine-ornithine metabolism in the regulation of pathogenesis and provide further insights for treating CDI.

Nor climate nor human impact factors: Chytrid infection shapes the skin bacterial communities of an endemic amphibian in a biodiversity hotspot.

The bacterial communities of the amphibian skin (i.e., the bacteriome) are critical to the host's innate immune system. However, it is unclear how different drivers can alter this function by modulating the bacteriome's structure. Our aim was to assess the extent to which different host attributes and extrinsic factors influence the structure of the bacterial communities of the skin. Skin bacterial diversity was examined in 148 individuals of the four-eyed frog (Pleurodema thaul) from 16 localities spanning almost 1800 km in latitude. The richness and beta diversity of bacterial families and the richness and abundance of Bd-inhibitory bacterial genera were used to describe their structure. Predictors associated with the host (developmental stage, genetic lineage, individual Batrachochytrium dendrobatidis [Bd] infection status) and the landscape (current climate, degree of anthropogenic disturbance) were used in the statistical modeling in an information theoretical approach. Bd infection and host developmental stage were the only predictors affecting bacteriome richness, with Bd+ individuals and postmetamorphic stages (adults and juveniles) having higher richness than Bd- ones and tadpoles. High diversity in Bd+ individuals is not driven by bacterial genera with known anti-Bd properties. Beta diversity was not affected by Bd infection and was mainly a consequence of bacterial family turnover rather than nestedness. Finally, for those bacterial genera known to have inhibitory effects on chytrid, Bd+ individuals had a slightly higher diversity than Bd- ones. Our study confirms an association between Bd infection and the host developmental stage with the bacterial communities of the skin of P. thaul. Unexpectedly, macroclimate and human impact factors do not seem to play a role in shaping the amphibian skin microbiome. Our study exemplifies that focusing on a single host-parasite system over a large geographic scale can provide essential insights into the factors driving host-parasite-bacteriome interactions.

A pan-cancer analysis of the microbiome in metastatic cancer.

Microbial communities are resident to multiple niches of the human body and are important modulators of the host immune system and responses to anticancer therapies. Recent studies have shown that complex microbial communities are present within primary tumors. To investigate the presence and relevance of the microbiome in metastases, we integrated mapping and assembly-based metagenomics, genomics, transcriptomics, and clinical data of 4,160 metastatic tumor biopsies. We identified organ-specific tropisms of microbes, enrichments of anaerobic bacteria in hypoxic tumors, associations between microbial diversity and tumor-infiltrating neutrophils, and the association of Fusobacterium with resistance to immune checkpoint blockade (ICB) in lung cancer. Furthermore, longitudinal tumor sampling revealed temporal evolution of the microbial communities and identified bacteria depleted upon ICB. Together, we generated a pan-cancer resource of the metastatic tumor microbiome that may contribute to advancing treatment strategies.

Association mechanism between Arabidopsis immune coreceptor BAK1 and Pseudomonas syringae effector HopF2

Brassinosteroid activated kinase 1 (BAK1) is a cell-surface coreceptor which plays multiple roles in innate immunity of plants. HopF2 is an effector secreted by the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 into Arabidopsis and suppresses host immune system through interaction with BAK1 as well as its downstream kinase MKK5. The association mechanism of HopF2 to BAK1 remains unclear, which prohibits our understanding and subsequent interfering of their interaction for pathogen management. Herein, we found the kinase domain of BAK1 (BAK1-KD) is sufficient for HopF2 association. With a combination of hydrogen/deuterium exchange mass spectrometry and mutational assays, we found a region of BAK1-KD N-lobe and a region of HopF2 head subdomain are critical for intermolecular interaction, which is also supported by unbiased protein-protein docking with ClusPro and kinase activity assay. Collectively, this research presents the interaction mechanism between Arabidopsis BAK1 and P. syringae HopF2, which could pave the way for bactericide development that blocking the functioning of HopF2 toward BAK1.

Association between cytomegalovirus infection and neurological disorders: A systematic review.

Cytomegalovirus (CMV) belongs to the Herpesviridae family and is also known as human herpesvirus type 5. It is a common virus that usually doesn't cause any symptoms in healthy individuals. However, once infected, the virus remains in the host's body for life and can reactivate when the host's immune system weakens. This virus has been linked to several neurological disorders, including Alzheimer's disease, Parkinson's disease, Autism spectrum disorder, Huntington's disease (HD), ataxia, Bell's palsy (BP), and brain tumours, which can cause a wide range of symptoms and challenges for those affected. CMV may influence inflammation, contribute to brain tissue damage, and elevate the risk of moderate-to-severe dementia. Multiple studies suggest a potential association between CMV and ataxia in various conditions, including Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, acute cerebellitis, etc. On the other hand, the evidence regarding CMV involvement in BP is conflicting, and also early indications of a link between CMV and HD were challenged by subsequent research disproving CMV's presence. This systematic review aims to comprehensively investigate any link between the pathogenesis of CMV and its potential role in neurological disorders and follows the preferred reporting items for systematic review and meta-analysis checklist. Despite significant research into the potential links between CMV infection and various neurological disorders, the direct cause-effect relationship is not fully understood and several gaps in knowledge persist. Therefore, continued research is necessary to gain a better understanding of the role of CMV in neurological disorders and potential treatment avenues.

Chronic viral infection impairs immune memory to a different pathogen.

Chronic viral infections cause T cell dysfunction in both animal models and human clinical settings, thereby affecting the ability of the host immune system to clear viral pathogens and develop proper virus-specific immune memory. However, the impact of chronic viral infections on the host's immune memory to other pathogens has not been well described. In this study, we immunized mice with recombinant Listeria monocytogenes expressing OVA (Lm-OVA) to generate immunity to Lm and allow analysis of OVA-specific memory T (Tm) cells. We then infected these mice with lymphocytic choriomeningitis virus (LCMV) strain Cl-13 which establishes a chronic infection. We found that chronically infected mice were unable to protect against Listeria re-challenge. OVA-specific Tm cells showed a progressive loss in total numbers and in their ability to produce effector cytokines in the context of chronic LCMV infection. Unlike virus-specific T cells, OVA-specific Tm cells from chronically infected mice did not up-regulate the expression of inhibitory receptors, a hallmark feature of exhaustion in virus-specific T cells. Finally, OVA-specific Tm cells failed to mount a robust recall response after bacteria re-challenge both in the chronically infected and adoptively transferred naïve hosts. These results show that previously established bacteria-specific Tm cells become functionally impaired in the setting of an unrelated bystander chronic viral infection, which may contribute to poor immunity against other pathogens in the host with chronic viral infection.