Infection and Immunity最新文献

In polymicrobial infections, how the host recognizes and responds to pathogens influences which species will persist to cause chronic infections. The human respiratory tract is a common anatomical site for viral-bacterial co-infections, where primary viral infections predispose to secondary bacterial infections, leading to increased morbidity and mortality. Additionally, co-infections are disproportionately prevalent in people with chronic lung diseases, such as chronic obstructive pulmonary disease and cystic fibrosis. We previously reported that primary viral infections and antiviral interferon (IFN) signaling stimulate Pseudomonas aeruginosa biofilm formation on airway epithelial cells (AECs). IFN signaling induces aerobic glycolysis in AECs and generates lactate as a cellular byproduct. Given that innate immune systems play an integral role in co-infection dynamics, we investigated the role of host-secreted metabolites (i.e., lactate) on innate immune cell activity during respiratory co-infections. We found that exposure to the apical secretions from IFNβ-treated AECs significantly compromised macrophage antibacterial activity, with the soluble metabolite lactate playing an important role. Macrophages used monocarboxylate transporters (MCTs) and G-protein receptors to transport and/or sense lactate, respectively, and this exposure to lactate diminished their bacterial-killing activity in a time exposure-dependent manner. Lactate exposure particularly reprogrammed macrophage cellular metabolism toward a metabolically uncoupled state by increasing oxidative phosphorylation, fatty acid oxidation, and downregulating the proinflammatory antimicrobial functions. Collectively, these findings provide insights into metabolites as complex regulators of trans-kingdom interactions and epithelial-macrophage crosstalk during respiratory co-infections.

Mycoplasma gallisepticum (MG) causes chronic respiratory disease, which is thought to be contributed to by its capacity to evade the immune response of infected birds. It possesses multiple copies of the genes encoding the mycoplasma immunoglobulin binding-protease (MIB-MIP) system, which binds and cleaves avian immunoglobulins (Igs), but also encodes homologs of the Ig-binding Protein-M of M. genitalium and M. pneumoniae and the Ig-cleaving CysP of M. synoviae. However, the interactions between these homologs, their host-specificity, and their interplay with the MIB-MIP system have not been defined. Here, the putative Protein-M and CysP in MG were expressed as recombinant glutathione-S-transferase (GST)-fusion proteins, functionally characterized, and their interactions with different MIB-MIP system components, as well as their impact on antibody-dependent complement-mediated killing of MG, examined. GST-Protein-M bound avian and mammalian immunoglobulins, but did not interact with the MIP proteases. GST-CysP selectively cleaved free chicken IgY and IgY complexed with GST-MIB or GST-Protein-M. GST-Protein-M, GST-CysP, and GST-MIB-MIP proteins all bound ATP, but only GST-CysP had ATPase activity. Sera from MG-infected chickens contained antibodies against a subset of MIP proteins, but not antibodies against Protein-M or CysP. The capacity of rabbit anti-MG antibodies to enhance complement-mediated killing of MG was inhibited by GST-MIB-MIP and GST-Protein-M. GST-CysP could not cleave rabbit IgG and had no detectable effect in the antibody-dependent complement-mediated killing assays. Collectively, these findings establish that Protein-M and CysP function as additional Ig-targeting systems in M. gallisepticum alongside the MIB-MIP system through distinct but complementary mechanisms, enhancing immune evasion and persistence of this important pathogen.

Staphylococcus aureus deploys an arsenal of secreted proteases to remodel the host environment during infection. While traditional substrate-by-substrate characterization has revealed critical host proteins under protease modulation, these conventional strategies cannot reveal the full scope of proteolytic activity occurring at the host-pathogen interface. Degradomic and N-terminomic technologies have begun to bridge this gap by enabling an unbiased, global mapping of protease-generated neo-N-termini across complex host tissues and cell proteomes. Recent work applying these tools to define discrete S. aureus protease pathodegradomes has propelled the field toward a system-level understanding of proteolytic activity. In this minireview, we highlight how terminal amine isotopic labeling of substrates and a newer methodology, terminal amine guanidination of substrates-charge reversal, have captured a deeper understanding of the V8 protease and how this enzyme can dismantle host immune defenses and engender disease. These techniques offer a powerful framework for the future in characterizing the substrate repertoires of other S. aureus secreted proteases, such as aureolysin, staphopain A and B, and the Spls. Furthermore, these advances demonstrate the applicability of degradomic profiling to diverse infection niches, revealing previously unrecognized roles for proteolytic activity in varying host contexts. Finally, we consider how this comprehensive understanding of S. aureus protease activity can inform clinical applications such as protease inhibitor design, host-directed therapies, and pathodegradome-based diagnostics.

Amino acids are the fundamental building blocks of proteins. Dietary proteins and endogenous protein turnover are the main sources of amino acids in the body. Over the past decade, our understanding of the role of the gut microbiota in amino acid metabolism has expanded considerably. The gut microbiota metabolizes dietary amino acids, regulates intestinal amino acid bioavailability, and maintains host nutrient homeostasis. Besides nutrient regulation, emerging evidence has revealed that amino acid availability in the gut also plays a crucial role in modulating enteric infections. Amino acids can influence infection outcomes both directly, by affecting the virulence of enteric pathogens, and indirectly, by shaping host immune responses. While most studies have focused on bacterial metabolism of amino acids, recent findings highlight important contributions from non-bacterial members of the gut microbiota, including fungi and protists. Both fungi and protists can shape amino acid availability in the gut and, consequently, infection outcomes. In this review, we integrate current knowledge on how diet and amino acid metabolism, mediated by both bacterial and non-bacterial communities, collectively influence enteric infection dynamics.

Self-destructing attenuated adjuvant Salmonella (SDAAS) strains are next-generation attenuated S. Typhimurium strains designed to be used as live adjuvants. They possess diverse means to prevent persistence in vivo, survival if excreted, and to enhance the induction of innate immunity. In this study, we investigated whether SDAAS strains can be safely delivered to chicken embryos by in ovo inoculation without compromising hatchability or hatchling health. We then evaluated their growth in different media, sensitivity to complement-mediated killing, motility, serum agglutination, flagellar and LPS profiling, their ability to attach to and invade Int-407 cells, and the activation of different pattern recognition receptors displayed by HEK-Blue cells. We also determined whether these strains could induce protective immune responses in chicks following homologous challenge at day of hatch with a virulent S. Typhimurium strain by reducing intestinal colonization and organ invasion. Our findings demonstrate that SDAAS strains can be safely administered in ovo in a dose-dependent manner. Family A strains exhibit strict requirements for 2,6-diaminopimelic acid and D-alanine, while Family B strains demonstrate absolute dependence on L-arabinose for growth in liquid and solid media. Adjuvant strains demonstrate increased activation of murine receptors NOD1, NOD2, TLR4, TLR5, TLR8, and TLR9 in HEK-Blue cells compared to the parent strain χ3761, despite having lower rates of cell adhesion to and invasion of Int-407 cells. Lastly, we observed that in ovo administration of SDAAS strains reduced titers of S. Typhimurium recovered from birds as they became older, suggesting a time-dependent enhancement of protective immunity induced by SDAAS strains.

Mycoplasma gallisepticum (MG) is an avian respiratory pathogen responsible for global economic loss to the poultry industry. We previously developed an efficacious subunit vaccine to address the drawbacks of current bacterin and live-attenuated vaccine designs. To improve our understanding of how the subunit vaccine works, we sought to understand if the vaccine influences the biology of the pathogen, whether the subunit vaccine has correlates of protection when analyzing antibody responses or tracheal-associated cells, and whether each component of the subunit vaccine contributes to protection. We performed five experiments to answer these questions. In the first experiment, we found that the subunit vaccine induces changes in the in vivo vlhA expression patterns of the infecting MG. We also found that on day 1 post-challenge, anti-VlhA 3.06 systemic IgY correlated negatively with the thickest tracheal mucosal section. In the second experiment, we found that on day 1 post-challenge, anti-MG lysate systemic IgY, anti-VlhA 3.03 systemic IgY, and anti-VlhA 5.05 systemic IgY negatively correlated with bacterial recovery. We also found that when looking at tracheal-associated cell frequencies, γδ T cells, with specific regard to CD8^- γδ T cells, and monocytes/macrophages, with specific regard to the monocyte/macrophage:granulocyte ratio, were negatively correlated with bacterial recovery, average tracheal mucosal thickness, or thickest tracheal mucosal section. In experiments three through five, we found that VlhAs 3.03, 3.06, and 5.05 contributed to reducing bacterial recovery, whereas VlhA 4.07 was dispensable, and we found that GapA and CrmA contributed to reducing bacterial recovery and average tracheal mucosal thickness.

The development of predictive understanding of bacterial resistance to antibiotics is one of the greatest challenges of modern medicine. Genome-scale metabolic models (GEMs) are mathematical representations of the metabolic network of a given organism assembled from genomic data that predict cellular activity across many environmental and genetic contexts. Because a single model can be solved under thousands of conditions, GEMs generate data at scales that support downstream analysis with artificial intelligence tools, helping to elucidate how pathogens adapt to host environments, evade immune responses, and acquire resistance. Here, we review how GEMs of ESKAPE pathogens are built, what data they require, and what they can and cannot do. We describe the reconstruction workflow from automated draft network through manual curation, gap filling, and experimental validation and the public and experimental data sources each stage depends on. We then describe how accessory genes and transcriptomic measurements are incorporated to yield strain- and condition-specific models and where machine learning contributes both in expanding functional annotation and in consuming model-generated flux distributions. Applications are illustrated with ESKAPE examples throughout, including conserved metabolic vulnerabilities identified across strain collections and flux rewiring observed under antibiotic exposure. Despite this progress, high-quality GEMs exist for only a fraction of ESKAPE species; many are constrained by incomplete annotation or limited experimental validation, and non-metabolic resistance mechanisms are captured only insofar as they impose a metabolic cost. Providing reliable tools to build new models from trustworthy templates, therefore, remains a priority for narrowing the gap between genotype and phenotype.

Histoplasma capsulatum is a fungal pathogen that thrives in macrophages until activated by interferon-gamma (IFN-γ). Tumor necrosis factor-α (TNF-α) is required for control of infection during adaptive immunity but does not directly activate macrophages to eliminate fungal elements. Collapse of immunity associated with TNF-α blockade is not accompanied by depression of IFN-γ. To determine if TNF-α antagonism impairs fungal clearance prior to adaptive immunity, we infected mice given anti-TNF-α and quantified lung H. capsulatum up to day 3 of infection. Anti-TNF-α elevated the number of organisms in the lungs by day 3. Neutralization of IFN-γ manifested a similar effect. Since neutralization of both cytokines impaired innate immunity, we hypothesized that the action of IFN-γ required TNF-α. IFN-γ-stimulated macrophages expressed fungicidal activity in vitro, and TNF-α neutralization or its congenital deficiency in macrophages reversed this effect. Blockade of TNF-α slightly dampened M1 response but did not promote M2. TNF-α was not required for IFN-γ to shift the metabolic capacity of macrophages. We investigated the production of nitric oxide, which is a mediator of anti-H. capsulatum activity by macrophages. In the absence of TNF-α, there was no difference when compared to IFN-γ stimulation alone. Lung macrophages harbored the highest infection burden in anti-TNF-α recipients. Though IFN-γ receptor 1 was modestly downregulated by anti-TNF-α blockade, this treatment downregulated pSTAT1 at day 2 of infection. TNF-α is required for optimal IFN-γ signaling and effector function of cytokine-stimulated macrophages. When TNF-α is absent, macrophages are insufficiently activated and fail to halt intracellular growth of yeast cells.

A consequence of the Borrelia (Borreliella) burgdorferi lifecycle is that a "standard" host-pathogen interaction involving the spirochete is challenging to define. The bacteria continuously cycle between vertebrate and invertebrate hosts, each inflicting substantially different selective pressures on the spirochete. Focusing solely on vertebrate infections, the spirochete can be found in numerous hosts in nature, including deermice, shrews, birds, and lizards. The immune pressures that the bacteria face in each of these hosts are variable and are thought to drive broad intraspecific variation across B. burgdorferi strains-with different strains appearing to be avian adapted, mammalian adapted, or generalist. In addition to its natural zoonotic hosts, B. burgdorferi can infect humans and cause Lyme disease. Here, natural human genetic variation can drive dramatically different disease outcomes, as some individuals seem capable of killing the bacteria before it can successfully colonize, while others are predisposed to continue reacting to the pathogen even long after it is killed by antibiotics. In this review, we describe studies investigating how host and bacterial diversity affect B. burgdorferi infection outcomes, with an emphasis on how this variability impacts the bacteria's spread in nature and Lyme disease severity during human infection.