Subversion of Phagocytosis for Pathogen Survival

Understanding bacterial pathogenicity: a closer look at the journey of harmful microbes

Bacteria are the most prevalent form of microorganisms and are classified into two categories based on their mode of existence: intracellular and extracellular. While most bacteria are beneficial to human health, others are pathogenic and can cause mild to severe infections. These bacteria use various mechanisms to evade host immunity and cause diseases in humans. The susceptibility of a host to bacterial infection depends on the effectiveness of the immune system, overall health, and genetic factors. Malnutrition, chronic illnesses, and age-related vulnerabilities are the additional confounders to disease severity phenotypes. The impact of bacterial pathogens on public health includes the transmission of these pathogens from healthcare facilities, which contributes to increased morbidity and mortality. To identify the most significant threats to public health, it is crucial to understand the global burden of common bacterial pathogens and their pathogenicity. This knowledge is required to improve immunization rates, improve the effectiveness of vaccines, and consider the impact of antimicrobial resistance when assessing the situation. Many bacteria have developed antimicrobial resistance, which has significant implications for infectious diseases and favors the survival of resilient microorganisms. This review emphasizes the significance of understanding the bacterial pathogens that cause this health threat on a global scale.

Impact of MgtC on the Fitness of Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is an extracellular foodborne pathogen and usually causes self-limiting diarrhea in healthy humans. MgtC is known as a key subversion factor that contributes to intramacrophage adaptation and intracellular survival in certain important pathogens. Whether MgtC influences the fitness of Y. pseudotuberculosis is unclear. According to in silico analysis, MgtC in Y. pseudotuberculosis might share similar functions with other bacterial pathogens, such as Salmonella. Studies indicated that MgtC was clearly required for Y. pseudotuberculosis growth in vitro and bacterial survival in macrophages under Mg2+ starvation. Transcriptome analysis by RNA-seq indicated that 127 differentially expressed genes (DEGs) (fold change > 2 and p < 0.001) were discovered between wild-type PB1+ and mgtC mutant inside macrophages. However, a lack of MgtC only moderately, albeit significantly, reduced the virulence of Y. pseudotuberculosis in mice. Overall, this study provides additional insights for the role of MgtC in Y. pseudotuberculosis.

Genomic analysis and assessment of pathogenic (toxicogenic) potential of Staphylococcus haemolyticus and Bacillus paranthracis consortia isolated from bovine mastitis in Russia

Three stable microbial consortia, each composed of Bacillus paranthracis and Staphylococcus haemolyticus strains, were isolated from milk of cows diagnosed with mastitis in three geographically remote regions of Russia. The composition of these consortia remained stable following multiple passages on culture media. Apparently, this stability is due to the structure of the microbial biofilms formed by the communities. The virulence of the consortia depended on the B. paranthracis strains. It seems plausible that the ability of the consortia to cause mastitis in cattle was affected by mutations of the cytK gene of B. paranthracis.

Mycobacterium tuberculosis: Pathogenesis and therapeutic targets

Tuberculosis (TB) remains a significant public health concern in the 21st century, especially due to drug resistance, coinfection with diseases like immunodeficiency syndrome (AIDS) and coronavirus disease 2019, and the lengthy and costly treatment protocols. In this review, we summarize the pathogenesis of TB infection, therapeutic targets, and corresponding modulators, including first-line medications, current clinical trial drugs and molecules in preclinical assessment. Understanding the mechanisms of Mycobacterium tuberculosis (Mtb) infection and important biological targets can lead to innovative treatments. While most antitubercular agents target pathogen-related processes, host-directed therapy (HDT) modalities addressing immune defense, survival mechanisms, and immunopathology also hold promise. Mtb's adaptation to the human host involves manipulating host cellular mechanisms, and HDT aims to disrupt this manipulation to enhance treatment effectiveness. Our review provides valuable insights for future anti-TB drug development efforts.

Aggregatibacter actinomycetemcomitans cytolethal distending toxin modulates host phagocytic function

Cytolethal distending toxins (Cdt) are a family of toxins produced by several human pathogens which infect mucocutaneous tissue and induce inflammatory disease. Human macrophages exposed to Aggregatibacter actinomycetemcomitans (Aa) Cdt respond through canonical and non-canonical inflammasome activation to stimulate cytokine release. The inflammatory response is dependent on PI3K signaling blockade via the toxin's phosphatidylinositol-3,4,5-triphosphate (PIP3) phosphatase activity; converting PIP3 to phosphatidylinsoitol-3,4-diphosphate (PI3,4P2) thereby depleting PIP3 pools. Phosphoinositides, also play a critical role in phagosome trafficking, serving as binding domains for effector proteins during phagosome maturation and subsequent fusion with lysosomes. We now demonstrate that AaCdt manipulates the phosphoinositide (PI) pools of phagosome membranes and alters Rab5 association. Exposure of macrophages to AaCdt slowed phagosome maturation and decreased phago-lysosome formation, thereby compromising macrophage phagocytic function. Moreover, macrophages exposed to Cdt showed decreased bactericidal capacity leading to increase in Aggregatibacter actinomycetemcomitans survival. Thus, Cdt may contribute to increased susceptibility to bacterial infection. These studies uncover an underexplored aspect of Cdt function and provide new insight into the virulence potential of Cdt in mediating the pathogenesis of disease caused by Cdt-producing organisms such as Aa.

Biofilm formation on human immune cells is a multicellular predation strategy of Vibrio cholerae

Biofilm formation is generally recognized as a bacterial defense mechanism against environmental threats, including antibiotics, bacteriophages, and leukocytes of the human immune system. Here, we show that for the human pathogen Vibrio cholerae, biofilm formation is not only a protective trait but also an aggressive trait to collectively predate different immune cells. We find that V. cholerae forms biofilms on the eukaryotic cell surface using an extracellular matrix comprising primarily mannose-sensitive hemagglutinin pili, toxin-coregulated pili, and the secreted colonization factor TcpF, which differs from the matrix composition of biofilms on other surfaces. These biofilms encase immune cells and establish a high local concentration of a secreted hemolysin to kill the immune cells before the biofilms disperse in a c-di-GMP-dependent manner. Together, these results uncover how bacteria employ biofilm formation as a multicellular strategy to invert the typical relationship between human immune cells as the hunters and bacteria as the hunted.

Adh Promotes Actinobacillus pleuropneumoniae Survival in Porcine Alveolar Macrophages by Inhibiting CHAC2-Mediated Respiratory Burst and Inflammatory Cytokine Expression

Actinobacillus pleuropneumoniae (A. pleuropneumoniae) causes porcine pleuropneumonia that seriously endangers pig's health. Adh, located in the head region of trimeric autotransporter adhesion of A. pleuropneumoniae, affects bacterial adhesion and pathogenicity. However, how Adh mediates A. pleuropneumoniae immune invasion is still unclear. Here, we established the A. pleuropneumoniae strain L20 or L20 ΔAdh-infected porcine alveolar macrophages (PAM) model, and applied protein overexpression, RNA interference, qRT-PCR, Western blot and immunoflourescence techniques to dissect the effects of Adh on PAM during A. pleuropneumoniae infection. We found that Adh could increase the A. pleuropneumoniae adhesion and intracellular survival in PAM. Gene chip analysis of piglet lungs further showed that Adh significantly induced cation transport regulatory-like protein 2 (CHAC2) expression, whose overexpression suppressed the phagocytic capacity of PAM. Furthermore, CHAC2 overexpression dramatically increased glutathione (GSH) expression, decreased reactive oxygen species (ROS), and promoted A. pleuropneumoniae survival in PAM, while the knockdown of CHAC2 reversed these phenomena. Meanwhile, CHAC2 silence activated the NOD1/NF-κB pathway, resulting in an increase in IL-1β, IL-6, and TNF-α expression, whereas this effect was weakened by CHAC2 overexpression and addition of NOD1/NF-κB inhibitor ML130. Moreover, Adh enhanced the secretion of LPS of A. pleuropneumoniae, which regulated the expression of CHAC2 via TLR4. In conclusion, through a LPS-TLR4-CHAC2 pathway, Adh inhibits respiratory burst and inflammatory cytokines expression to promote A. pleuropneumoniae survival in PAM. This finding may provide a novel target for the prevention and treatment of A. pleuropneumoniae.

Interactions between host epithelial cells and Acinetobacter baumannii promote the emergence of highly antibiotic resistant and highly mucoid strains

Acinetobacter baumannii is an important nosocomial pathogen. Upon colonizing a host, A. baumannii are subjected to selective pressure by immune defenses as they adapt to the host environment. However, the mechanism of this pathoadaptation is unknown. Here, we established an in vitro system to evolve A. baumannii driven by the continuous selective pressure exerted by epithelial cells, and we used a combination of experimental evolution, phenotypic characterization and multi-omics analysis to address the underlying mechanism. When continuously exposed to selective pressure by pulmonary epithelial cells, A. baumannii showed ptk mutation-mediated mucoid conversion (reduced adhesion and increased anti-phagocytic ability) by enhancement of capsular exopolysaccharide chain length; rsmG mutation-mediated deficiency of 7-methylguanosine modification in the 524th nucleotide of 16S rRNA, which increased ribosome translation efficiency; and rnaseI mutation-mediated changes in outer membrane permeability and efflux pump expression. Together, these mutations altered susceptibility to a variety of antimicrobial agents, including the novel antibiotic cefiderocol, by regulating siderophore and siderophore-receptor biosynthesis. In conclusion, pulmonary epithelial cells modulate A. baumannii pathoadaptation, implicating the host–microbe interaction in the survival and persistence of A. baumannii.

Differential immune response to two Staphylococcus aureus strains with distinct adaptation genotypes after experimental intramammary infection of dairy cows

The aim of this study was to evaluate and compare the ability of two S. aureus strains with different adaptation genotypes (low and high) to the bovine mammary gland (MG) to establish an intramammary infection (IMI) and induce an immune response after an experimental challenge in lactating cows. Two isolates (designated 806 and 5011) from bovine IMI with different genotypic profiles, harboring genes involved in adherence and biofilm production, belonging to different capsular polysaccharide (CP) type, accessory gene regulator (agr) group, pulsotype (PT) and sequence type/clonal complex (ST/CC) were selected. Strains 806 and 5011 were associated with low (nonpersistent-NP) and high (persistent-P) adaptation to the MG, respectively. Strain 806 (NP) was characterized as agr group II, cap5 positive and ST350; strain 5011 (P) agr group I, cap8 positive and CC188. Three groups of clinically healthy cows, 4 cows/treatment group, were inoculated by the intramammary route with strain 806 (NP), strain 5011 (P) and pyrogen-free saline solution. All mammary quarters challenged with strain 806 (NP) developed mild clinical mastitis between 1 and 7 d post inoculation (pi). Quarters challenged with strain 5011 (P) developed a persistent IMI; bacteria were recovered from milk from d 7 pi and up to d 56 pi. In quarters inoculated with strain 806 (NP) the inflammatory response induced was greater and earlier than the one induced by strain 5011 (P), since a somatic cell count (SCC) peak was observed at d 2 pi, while in quarters inoculated with strain 5011 (P) no variations in SCC were observed until d 4 pi reaching the maximum values at d 14 pi; indicating a lower and delayed initial inflammatory response. The highest levels of nitric oxide (NO) and lactoferrin (Lf) detected in milk from quarters inoculated with both S. aureus strains coincided with the highest SCC at the same time periods, indicating an association with the magnitude of inflammation. The high levels of IL-1β induced by strain 806 (NP) were associated with the highest SCC detected (d 2 pi); while quarters inoculated with strain 5011 (P) showed similar IL-1β levels to those found in control quarters. In quarters inoculated with strain 806 (NP) two peaks of IL-6 levels on d 2 and 14 pi were observed; while in quarters inoculated with strain 5011 (P) IL-6 levels were similar to those found in control quarters. The strain 806 (NP) induced a higher total IgG and IgG₁ response; while strain 5011 (P) generated a higher IgG₂ response (even against the heterologous strain). The present study demonstrated that S. aureus strains with different genotype and adaptability to bovine MG influence the local host immune response and the course and severity of the infectious process.

A Porcine Model for the Development and Testing of Preoperative Skin Preparations

Clinical preoperative skin preparations (PSPs) do not eradicate skin flora dwelling in the deepest dermal regions. Survivors constitute a persistent infection risk. In search of solutions, we created a porcine model intended for PSP developmental testing. This model employed microbiological techniques sensitive to the deep-dwelling microbial flora as these microorganisms are frequently overlooked when using institutionally-entrenched testing methodologies. Clinical gold-standard PSPs were assessed. Ten Yorkshire pigs were divided into two groups: prepared with either povidone iodine (PVP-I) or chlorhexidine gluconate (CHG) PSP. Bioburdens were calculated on square, 4 cm by 4 cm, full-thickness skin samples homogenized in neutralizing media. Endogenous bioburden of porcine skin (3.3 log10 CFU/cm2) was consistent with natural flora numbers in dry human skin. On-label PSP scrub kits with PVP-I (n = 39) or CHG (n = 40) failed the 2-3 log10-reduction criteria established for PSPs by the Food and Drug Administration (FDA), resulting in a 1.46 log10 and 0.58 log10 reduction, respectively. Porcine dermal microbiota mirrored that of humans, displaying abundant staphylococcal species. Likewise, histological sections showed similarity in hair follicle depths and sebaceous glands (3.2 ± 0.7 mm). These shared characteristics and the considerable fraction of bacteria which survived clinical PSPs make this model useful for developmental work.

Interactions Between Streptococcus gordonii and Fusobacterium nucleatum Altered Bacterial Transcriptional Profiling and Attenuated the Immune Responses of Macrophages

Interspecies coaggregation promotes transcriptional changes in oral bacteria, affecting bacterial pathogenicity. Streptococcus gordonii (S. gordonii) and Fusobacterium nucleatum (F. nucleatum) are common oral inhabitants. The present study investigated the transcriptional profiling of S. gordonii and F. nucleatum subsp. polymorphum in response to the dual-species coaggregation using RNA-seq. Macrophages were infected with both species to explore the influence of bacterial coaggregation on both species' abilities to survive within macrophages and induce inflammatory responses. Results indicated that, after the 30-min dual-species coaggregation, 116 genes were significantly up-regulated, and 151 genes were significantly down-regulated in S. gordonii; 97 genes were significantly down-regulated, and 114 genes were significantly up-regulated in F. nucleatum subsp. polymorphum. Multiple S. gordonii genes were involved in the biosynthesis and export of cell-wall proteins and carbohydrate metabolism. F. nucleatum subsp. polymorphum genes were mostly associated with translation and protein export. The coaggregation led to decreased expression levels of genes associated with lipopolysaccharide and peptidoglycan biosynthesis. Coaggregation between S. gordonii and F. nucleatum subsp. polymorphum significantly promoted both species' intracellular survival within macrophages and attenuated the production of pro-inflammatory cytokines IL-6 and IL-1β. Physical interactions between these two species promoted a symbiotic lifestyle and repressed macrophage's killing and pro-inflammatory responses.

Bioinspired macrophage-targeted anti-inflammatory nanomedicine: A therapeutic option for the treatment of myocarditis

Myocarditis is a disease characterized by inflammation of the heart muscle, which increases the risk of dilated cardiomyopathy and heart failure. Macrophage migration is a major histopathological hallmark of myocarditis, making macrophages a potential therapeutic target for the management of this disease. In the present study, we synthesized a bioinspired anti-inflammatory nanomedicine conjugated with protein G (PSL-G) that could target macrophages and induce macrophage polarization from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. Notably, PSL-G exhibited a higher affinity for macrophages than non-macrophage cells. The addition of PSL-G decreased the levels of pro-inflammatory cytokines (e.g., IL-1α, IL-6, and TNF-α), but increased the level of the anti-inflammatory cytokine IL-10 in macrophages treated with lipopolysaccharide and/or interferon-γ. Furthermore, the lifetime of PSL-G in murine blood circulation was found to be significantly higher than that of PSL. Systemic injection of PSL-G into a mouse model of experimental autoimmune myocarditis remarkably reduced macrophage migration in the myocardium (16-fold compared with the positive control group) and myocardial fibrosis (8-fold). Based on these results and the fact that macrophages play a critical role in the pathogenesis of various diseases, we believe that bioinspired macrophage-targeted anti-inflammatory nanomedicines may be effective therapeutic options for the treatment of autoimmune and autoinflammatory diseases, especially myocarditis.

Cholesterol and sphingomyelin are critical for Fcγ receptor-mediated phagocytosis of Cryptococcus neoformans by macrophages

Cryptococcus neoformans is a fungal pathogen that causes life-threatening meningoencephalitis in lymphopenic patients. Pulmonary macrophages comprise the first line of host defense upon inhalation of fungal spores by aiding in clearance but can also potentially serve as a niche for their dissemination. Given that macrophages play a key role in the outcome of a cryptococcal infection, it is crucial to understand factors that mediate phagocytosis of C. neoformans. Since lipid rafts (high-order plasma membrane domains enriched in cholesterol and sphingomyelin [SM]) have been implicated in facilitating phagocytosis, we evaluated whether these ordered domains govern macrophages' ability to phagocytose C. neoformans. We found that cholesterol or SM depletion resulted in significantly deficient immunoglobulin G (IgG)-mediated phagocytosis of fungus. Moreover, repletion of macrophage cells with a raft-promoting sterol (7-dehydrocholesterol) rescued this phagocytic deficiency, whereas a raft-inhibiting sterol (coprostanol) significantly decreased IgG-mediated phagocytosis of C. neoformans. Using a photoswitchable SM (AzoSM), we observed that the raft-promoting conformation (trans-AzoSM) resulted in efficient phagocytosis, whereas the raft-inhibiting conformation (cis-AzoSM) significantly but reversibly blunted phagocytosis. We observed that the effect on phagocytosis may be facilitated by Fcγ receptor (FcγR) function, whereby IgG immune complexes crosslink to FcγRIII, resulting in tyrosine phosphorylation of FcR γ-subunit (FcRγ), an important accessory protein in the FcγR signaling cascade. Correspondingly, cholesterol or SM depletion resulted in decreased FcRγ phosphorylation. Repletion with 7-dehydrocholesterol restored phosphorylation, whereas repletion with coprostanol showed FcRγ phosphorylation comparable to unstimulated cells. Together, these data suggest that lipid rafts are critical for facilitating FcγRIII-mediated phagocytosis of C. neoformans.

Macrophages in Microbial Pathogenesis: Commonalities of Defense Evasion Mechanisms

Macrophages are key arsenals of the immune system against invaders. After compartmental isolation of a pathogen in phagosomes, the host immune response attempts to neutralize the pathogen. However, pathogens possess the ability to subvert these assaults and can also convert macrophages into their replicative niche. The multiple host defense evasion mechanisms employed by these pathogens like phagosome maturation arrest, molecular mimicry through secretory antigens, interference with host signaling, active radical neutralization, inhibition of phagosome acidification, alteration of programmed cell death and many other mechanisms. Macrophage biology as a part of the host-pathogen interaction has expanded rapidly in the past decade. The present review aims to shed some light upon the macrophage defense evasion strategies employed by infecting pathogens. We have also incorporated recent knowledge in the field of macrophage dynamics during infection and evolutionary perspectives of macrophage dynamics.

The multifaceted nature of antimicrobial peptides: current synthetic chemistry approaches and future directions

Bacterial infections caused by 'superbugs' are increasing globally, and conventional antibiotics are becoming less effective against these bacteria, such that we risk entering a post-antibiotic era. In recent years, antimicrobial peptides (AMPs) have gained significant attention for their clinical potential as a new class of antibiotics to combat antimicrobial resistance. In this review, we discuss several facets of AMPs including their diversity, physicochemical properties, mechanisms of action, and effects of environmental factors on these features. This review outlines various chemical synthetic strategies that have been applied to develop novel AMPs, including chemical modifications of existing peptides, semi-synthesis, and computer-aided design. We will also highlight novel AMP structures, including hybrids, antimicrobial dendrimers and polypeptides, peptidomimetics, and AMP-drug conjugates and consider recent developments in their chemical synthesis.

Promoters and Antagonists of Phagocytosis: A Plastic and Tunable Response

Recent observations indicate that, rather than being an all-or-none response, phagocytosis is finely tuned by a host of developmental and environmental factors. The expression of key phagocytic determinants is regulated via transcriptional and epigenetic means that confer memory on the process. Membrane traffic, the cytoskeleton, and inside-out signaling control the activation of phagocytic receptors and their ability to access their targets. An exquisite extra layer of complexity is introduced by the coexistence of distinct "eat-me" and "don't-eat-me" signals on targets and of corresponding "eat" and "don't-eat" receptors on the phagocyte surface. Moreover, assorted physical barriers constitute "don't-come-close-to-me" hurdles that obstruct the engagement of ligands by receptors. The expression, mobility, and accessibility of all these determinants can be modulated, conferring extreme plasticity on phagocytosis and providing attractive targets for therapeutic intervention in cancer, atherosclerosis, and dementia. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Host immune response against leishmaniasis and parasite persistence strategies: A review and assessment of recent research

Leishmaniasis, a neglected parasitic disease caused by a unicellular protozoan of the genus Leishmania, is transmitted through the bite of a female sandfly. The disease remains a major public health problem and is linked to tropical and subtropical regions, with an endemic picture in several regions, including East Africa, the Mediterranean basin and South America. The different causative species display a diversity of clinical presentations; therefore, the immunological data on leishmaniasis are both scarce and controversial for the different forms and infecting species of the parasite. The present review highlights the main immune parameters associated with leishmaniasis that might contribute to a better understanding of the pathogenicity of the parasite and the clinical outcomes of the disease. Our aim was to provide a concise overview of the immunobiology of the disease and the factors that influence it, as this knowledge may be helpful in developing novel chemotherapeutic and vaccine strategies.

Histone deacetylase SIR2 in Toxoplasma gondii modulates functions of murine macrophages in vitro and protects mice against acute toxoplasmosis in vivo

Silent information regulator 2 (SIR2) in histone deacetylase (HDAC) is particularly conserved and widely expressed in all eukaryotic cells. HDAC is a crucial post-translational modification protein regulating gene expression. In the present study, a Toxoplasma gondii (T. gondii) silent information regulator 2 (TgSIR2) gene in HDAC was cloned and the modulation effects of recombinant TgSIR2 (rTgSIR2) on murine Ana-1 macrophages were characterized in vitro. The results indicated that rTgSIR2 had a good capacity to eliminate T. gondii by promoting proliferation, apoptosis, and phagocytosis, and modulating the secretion of nitric oxide (NO), pro-inflammatory cytokines, and anti-inflammatory cytokines. In in vivo experiments, animals were immunized with recombinant TgSIR2, followed by a lethal dose of T. gondii RH strain challenge 14 days after the second immunization. As compared to the blank and control group, the animals immunized with rTgSIR2 could generate specific humoral responses, as demonstrated by the significantly high titers of total IgG and subclasses IgG1 and IgG2a. Significant increases of IFN-γ, IL-4, and IL-10 were seen, while no significant changes were detected in IL-17. The percentage of CD4⁺ and CD8⁺ T lymphocytes in animals immunized with rTgSIR2 significantly increased. A significantly long survival time was also observed in animals vaccinated with rTgSIR2 14 days after the last immunization. All these results clearly indicate that rTgSIR2 played an essential role in modulating host macrophages and offered the potential to develop a therapeutic strategy against T. gondii.

Effect of Surface Modifications on Cellular Uptake of Gold Nanorods in Human Primary Cells and Established Cell Lines

Endocytosis is a cellular process in which substances are engulfed by the cellular membrane and budded off inside the cells to form vesicles. It plays key roles in controlling nutritional component uptake, immune responses, and other biological functions. A comprehensive understanding of endocytosis gives insights into such physiological functions and informs the design of medical nanodevices that need to enter cells. So far, endocytosis has been studied mostly using established cell lines. However, the established cell lines generally originate from cancer cells or are transformed from normal cells into immortalized cells. Therefore, primary cells may give us more reliable information about the endocytosis process of nanoparticles into cells. In this research, we studied the uptake of gold nanorods (AuNRs) with four different surface modifications (anionic/cationic polymers and anionic/cationic silica) by two kinds of primary cells (human monocyte-derived macrophages and human umbilical vein endothelial cells) and two kinds of established cell lines (HeLa cells and RAW 264.7 cells). We found that the surface properties of AuNRs affected their cellular uptake, and the cationic surface tended was advantageous for uptake, but it depended on the cell types. Control experiments using inhibitors of representative endocytosis pathways (macropinocytosis, clathrin-mediated endocytosis, and caveolae-mediated endocytosis) indicated that primary cells had a dominant uptake pathway for internalization of the AuNRs, whereas the established cell lines had multiple pathways. Our results provide us with novel insights into cellular uptake of AuNRs in that they depend not only on surface characters of the nanoparticles but also cell types, such as primary cells and established cell lines.

Pathogenic effects of inhibition of mTORC1/STAT3 axis facilitates Staphylococcus aureus-induced pyroptosis in human macrophages

BACKGROUND

Pyroptosis is a recently identified pathway of caspase-mediated cell death in response to microbes, lipopolysaccharide, or chemotherapy in certain types of cells. However, the mechanism of how pyroptosis is regulated is not well-established.

METHODS

Herein, the intracellular bacteria were detected by staining and laser confocal microscopy and TEM. Live/dead cell imaging assay was used to examine macrophage death. Western blot and immunohistochemical staining were used to examine the protein changes. IFA was used to identify typical budding vesicles of pyroptosis and the STAT3 nuclear localization. SEM was used to observe the morphological characteristics of pyroptosis. ELISA was used to detect the level of inflammatory cytokines. Pyroptosis was filmed in macrophages by LSCM.

RESULTS

S. aureus was internalized by human macrophages. Intracellular S. aureus induced macrophage death. S. aureus invasion increased the expression of NLRP3, Caspase1 (Casp-1 p20) and the accumulation of GSDMD-NT, GSDMD-NT pore structures, and the release of IL-1β and IL-18 in macrophages. Macrophages pyroptosis induced by S. aureus can be abrogated by blockage of S. aureus phagocytosis. The pyroptosic effect by S. aureus infection was promoted by either rapamycin or Stattic, a specific inhibitor for mTORC1 or STAT3. Inhibition of mTORC1 or STAT3 induced pyroptosis. mTORC1 regulated the pyroptosic gene expression through governing the nuclear localization of STAT3. mTORC1/STAT3 axis may play a regulatory role in pyroptosis within macrophages.

CONCLUSIONS

S. aureus infection induces human macrophage pyroptosis, inhibition of mTORC1/STAT3 axis facilitates S. aureus-induced pyroptosis. mTORC1 and STAT3 are associated with pyroptosis. Our findings demonstrate a regulatory function of the mTORC1/STAT3 axis in macrophage pyroptosis, constituting a novel mechanism by which pyroptosis is regulated in macrophages. Video Abstract Macrophages were infected with S. aureus for 3 h (MOI 25:1), and pyroptosis was filmed in macrophages by laser confocal microscopy. A representative field was recorded. Arrow indicates lysing dead cell.

Bacteria Modify Candida albicans Hypha Formation, Microcolony Properties, and Survival within Macrophages

Candida albicans is the predominant fungus colonizing the oral cavity that can have both synergistic and antagonistic interactions with other bacteria. Interkingdom polymicrobial associations modify fungal pathogenicity and are believed to increase microbial resistance to innate immunity. However, it is not known how these interactions alter fungal survival during phagocytic killing. We demonstrated that secreted molecules of S. gordonii and P. aeruginosa alter C. albicans survival within the phagosome of macrophages and alter fungal pathogenic phenotypes, including filamentation and microcolony formation. Moreover, we provide evidence for a dual interaction between S. gordonii and C. albicans such that S. gordonii signaling peptides can promote C. albicans commensalism by decreasing microcolony attachment while increasing invasion in epithelial cells. Our results identify bacterial diffusible factors as an attractive target to modify virulence of C. albicans in polymicrobial infections.

Phagocytic cells are crucial components of the innate immune system preventing Candida albicans mucosal infections. Streptococcus gordonii and Pseudomonas aeruginosa often colonize mucosal sites, along with C. albicans, and yet interkingdom interactions that might alter the survival and escape of fungi from macrophages are not understood. Murine macrophages were coinfected with S. gordonii or P. aeruginosa, along with C. albicans to evaluate changes in fungal survival. S. gordonii increased C. albicans survival and filamentation within macrophage phagosomes, while P. aeruginosa reduced fungal survival and filamentation. Coinfection with S. gordonii resulted in greater escape of C. albicans from macrophages and increased size of fungal microcolonies formed on macrophage monolayers, while coinfection with P. aeruginosa reduced macrophage escape and produced smaller microcolonies. Microcolonies formed in the presence of P. aeruginosa cells outside macrophages also had significantly reduced size that was not found with P. aeruginosa phenazine deletion mutants. S. gordonii cells, as well as S. gordonii heat-fixed culture supernatants, increased C. albicans microcolony biomass but also resulted in microcolony detachment. A heat-resistant, trypsin-sensitive pheromone processed by S. gordonii Eep was needed for these effects. The majority of fungal microcolonies formed on human epithelial monolayers with S. gordonii supernatants developed as large floating structures with no detectable invasion of epithelium, along with reduced gene expression of C. albicansHYR1, EAP1, and HWP2 adhesins. However, a subset of C. albicans microcolonies was smaller and had greater epithelial invasiveness compared to microcolonies grown without S. gordonii. Thus, bacteria can alter the killing and escape of C. albicans from macrophages and contribute to changes in C. albicans pathogenicity.

IMPORTANCECandida albicans is the predominant fungus colonizing the oral cavity that can have both synergistic and antagonistic interactions with other bacteria. Interkingdom polymicrobial associations modify fungal pathogenicity and are believed to increase microbial resistance to innate immunity. However, it is not known how these interactions alter fungal survival during phagocytic killing. We demonstrated that secreted molecules of S. gordonii and P. aeruginosa alter C. albicans survival within the phagosome of macrophages and alter fungal pathogenic phenotypes, including filamentation and microcolony formation. Moreover, we provide evidence for a dual interaction between S. gordonii and C. albicans such that S. gordonii signaling peptides can promote C. albicans commensalism by decreasing microcolony attachment while increasing invasion in epithelial cells. Our results identify bacterial diffusible factors as an attractive target to modify virulence of C. albicans in polymicrobial infections.

CD89/CD35 Expression Ratio in Salivary Neutrophil as an Early Detection Marker for Severe Early Childhood Caries

Objectives  To analyze CD35/CD89 expression ratio on the surface of neutrophils as an early detection marker for S-ECC.

Materials and Methods  Saliva was collected from 4- to 6-year-old kindergarten students. Salivary neutrophils were obtained by instructing the subjects to rinse their mouth with 1 mL of sterile 1.5% NaCl for 30 seconds before expectorating it into a sterile glass. The expression of CFSE ⁺ CD35 ⁺ and CFSE ⁺ CD89 ⁺ was measured and analyzed using flow cytometry.

Results The expression of CFSE ⁺ CD89 ⁺ in the caries-free group (2.46 ± 0.39) was significantly lower than that in the S-ECC group (3.41 ± 1.11), with a p -value of 0.0001, while the expression of CFSE ⁺ CD35 ⁺ in the caries-free group was (2.35 ± 0.56) compared with (1.54 ± 0.35) ( p = 0.0001) in the S-ECC group.

Conclusions  The expression ratio of CFSE ⁺ CD89 ⁺ and CFSE ⁺ CD35 ⁺ constitutes a marker for S-ECC.

Identification of single-nucleotide variants associated with susceptibility to Salmonella in pigs using a genome-wide association approach

BACKGROUND

Salmonella enterica serovars are a major cause of foodborne illness and have a substantial impact on global human health. In Canada, Salmonella is commonly found on swine farms and the increasing concern about drug use and antimicrobial resistance associated with Salmonella has promoted research into alternative control methods, including selecting for pig genotypes associated with resistance to Salmonella. The objective of this study was to identify single-nucleotide variants in the pig genome associated with Salmonella susceptibility using a genome-wide association approach. Repeated blood and fecal samples were collected from 809 pigs in 14 groups on farms and tonsils and lymph nodes were collected at slaughter. Sera were analyzed for Salmonella IgG antibodies by ELISA and feces and tissues were cultured for Salmonella. Pig DNA was genotyped using a custom 54 K single-nucleotide variant oligo array and logistic mixed-models used to identify SNVs associated with IgG seropositivity, shedding, and tissue colonization.

RESULTS

Variants in/near PTPRJ (p = 0.0000066), ST6GALNAC3 (p = 0.0000099), and DCDC2C (n = 3, p < 0.0000086) were associated with susceptibility to Salmonella, while variants near AKAP12 (n = 3, p < 0.0000358) and in RALGAPA2 (p = 0.0000760) may be associated with susceptibility.

CONCLUSIONS

Further study of the variants and genes identified may improve our understanding of neutrophil recruitment, intracellular killing of bacteria, and/or susceptibility to Salmonella and may help future efforts to reduce Salmonella on-farm through genetic approaches.

Macrophage Cell-Cell Interactions Promoting HIV-1 Infection

Many pathogens infect macrophages as part of their intracellular life cycle. This is particularly true for viruses, of which HIV-1 is one of the best studied. HIV-1 infection of macrophages has important consequences for viral persistence and pathogenesis, but the mechanisms of macrophage infection remain to be fully elucidated. Despite expressing viral entry receptors, macrophages are inefficiently infected by cell-free HIV-1 virions, whereas direct cell-cell spread is more efficient. Different modes of cell-cell spread have been described, including the uptake by macrophages of infected T cells and the fusion of infected T cells with macrophages, both leading to macrophage infection. Cell-cell spread can also transmit HIV-1 between macrophages and from macrophages to T cells. Here, we describe the current state of the field concerning the cell-cell spread of HIV-1 to and from macrophages, discuss mechanisms, and highlight potential in vivo relevance.

Capacity of two Staphylococcus aureus strains with different adaptation genotypes to persist and induce damage in bovine mammary epithelial cells and to activate macrophages

The aim of this study was to evaluate and compare the ability to adhere/internalize, persist, and induce damage in mammary epithelial cells (MAC-T) of two Staphylococcus aureus strains with different adaptation genotypes (low and high) to the bovine mammary gland (MG). Also, the phagocytic and bactericidal capacity induced after the interaction between macrophages, isolated from mammary secretion, of both S. aureus strains was evaluated. Two isolates (designated 806 and 5011) from bovine intramammary infection (IMI) harboring genes involved in adherence and biofilm production, belonging to different capsular polysaccharide (CP) type, accessory gene regulator (agr) group, pulsotype (PT) and sequence type/clonal complex (ST/CC). Strains 806 and 5011 were associated with low (nonpersistent-NP) and high (persistent-P) adaptation to the MG, respectively. Strain 5011 (P), agr group I, cap8 positive and strong biofilm producer showed higher capacity to adhere/internalize in MAC-T compared with strain 806 (NP), characterized as agr group II, cap5 positive and weak biofilm producer. Strain 5011(P) could be recovered from MAC-T lysates up to 72 h pi; while strain 806 (NP) could be recovered only at 4 h pi. Strain 5011 (P) showed greater capacity to induce apoptosis compared with strain 806 (NP) at 4, 24 and 48 h pi. Macrophages infected with strain 5011 (P) showed a greater phagocytic capacity and higher percentage of intracellular reactive oxygen species (ROS) production than strain 806 (NP). No viable bacteria were isolated from macrophages lysates stimulated with any of the S. aureus strains at 2, 4, 8 and 24 h pi. The knowledge of the molecular profile of the S. aureus strains causing bovine mastitis in a herd could become a tool to expose the most prevalent virulence gene patterns and advance in the elucidation of the pathogenesis of chronic mastitis.

Using Imaging Flow Cytometry to Quantify Neutrophil Phagocytosis

Neutrophils are professional phagocytes that are important for innate host defenses against pathogens and resolution of inflammation. Traditionally, the phagocytic capacity of neutrophils was quantified by enumeration of cells containing either internalized or bound bacteria or other cargo from a series of microscopic images. Here we describe an imaging flow cytometry-based protocol and analysis method for quantifying the binding and uptake of Neisseria gonorrhoeae by primary adherent human neutrophils. Imaging flow cytometry combines the capacity for quantitative, high-throughput analysis of tens of thousands of cells per condition, with the imaging power of fluorescence microscopy. Here, all bacteria are labeled with Tag-it Violet™ and bound bacteria are differentially stained with a DyLight™ 650-conjugated antibody. Images are analyzed using spot count and other algorithms. Outputs include the percent of neutrophils associated with bacteria, the percent of neutrophils with internalized bacteria, and the percent of internalized bacteria. This basic protocol can be adapted to a variety of particle types and can be used for multiplex analysis in combination with staining for different neutrophil surface and intracellular markers.

Understanding the pathogenesis of Flavobacterium psychrophilum using the rainbow trout monocyte/macrophage-like cell line, RTS11, as an infection model

The life cycle of Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome (RTFS), appears to involve interactions with spleen and head kidney macrophages. To develop an in vitro model for studying this, F. psychrophilum was incubated with a rainbow trout splenic monocyte/macrophage-like cell line (RTS11) and fundamental macrophage functions evaluated. The animal cell basal medium, L15, supplemented with bovine serum (FBS) supports RTS11 maintenance, and surprisingly, L15 with 2% FBS (L15/FBS) also supported F. psychrophilum growth. L15/FBS in which the bacteria had been grown is referred to as F. psychrophilum conditioned medium (FpCM). Adding FpCM to RTS11 cultures caused a small, yet significant, percentage of cells to die, many cells to become more diffuse, and phagocytosis to be temporarily reduced. FpCM also significantly stimulated transcript expression for pro-inflammatory cytokines (IL-1β, TNFα and IL-6) and the anti-inflammatory cytokine (IL-10) after one day of exposure but this upregulation rapidly declined over time. Adding live F. psychrophilum to RTS11 cultures also altered the cellular morphology and stimulated cytokine expression more profoundly than FpCM. Additionally, the phagocytic activity of RTS11 was also significantly impaired by live F. psychrophilum, but not to the same extent as when exposed to FpCM. Adding heat-killed bacteria to RTS11 cultures elicited few changes. These bacteria/RTS11 co-cultures should be useful for gaining a deeper understanding of the pathogenesis of F. psychrophilum and may aid in the development of effective measures to prevent infection and spread of this troublesome disease.

Thioredoxin-Interacting Protein Promotes Phagosomal Acidification Upon Exposure to Escherichia coli Through Inflammasome-Mediated Caspase-1 Activation in Macrophages

In host defense, it is crucial to maintain the acidity of the macrophage phagosome for effective bacterial clearance. However, the mechanisms governing phagosomal acidification upon exposure to gram-negative bacteria have not been fully elucidated. In this study, we demonstrate that in macrophages exposed to Escherichia coli, the thioredoxin-interacting protein (TXNIP)-associated inflammasome plays a role in pH modulation through the activated caspase-1-mediated inhibition of NADPH oxidase. While there was no difference in early-phase bacterial engulfment between Txnip knockout (KO) macrophages and wild-type (WT) macrophages, Txnip KO macrophages were less efficient at destroying intracellular bacteria in the late phase, and their phagosomes failed to undergo appropriate acidification. These phenomena were associated with reactive oxygen species production and were reversed by treatment with an NADPH oxidase inhibitor or a caspase inhibitor. In line with these results, Txnip KO mice were more susceptible to both intraperitoneally administered E. coli and sepsis induced by cecum ligation and puncture than WT mice. Taken together, this study suggests that the TXNIP-associated inflammasome-caspase-1 axis regulates NADPH oxidase to modulate the pH of the phagosome, controlling bacterial clearance by macrophages.

Complement Receptor 1 (CR1)/ CD35+ Expression Analysis of Salivary Neutrophils on Streptococcus mutans Phagocytosis

BACKGROUND

Severe early childhood caries (S-ECC) is a form of dental caries which is very destructive in early childhood since involving several teeth, include the maxillary anterior teeth. Streptococcus mutans (S. mutans) play an etiological integral role of ECC so that S. mutans are considered as the predictor of dental caries. The neutrophil is a key component of the rst line of defense against microbial invasion. The essential function of neutrophil is to kill pathogenic microbes through a phagocytosis process which is mediated by Complement Receptor 1 (CR1)/ (CD35+).

AIMS AND OBJECTIVES

To analyze the phagocytosis process of the salivary neutrophil which is mediated by innate immunity component, i.e., Complement Receptor 1/CR1 (CD35) on S-ECC.

MATERIALS AND METHODS

his study was an observational analysis with cross-sectional approach using t-test analysis. This study employed the isolation steps of neutrophils saliva of caries-free children and the S-ECC and then conducted phagocytosis of salivary neutrophils test on S. mutans mediated by CD35 using ow cytometry.

RESULTS

Phagocytosis of salivary neutrophils on S. mutans mediated by CD35 on caries-free (2.35 ± 0.56) is higher than that on the S-ECC (1.54 ± 0.35).

CONCLUSIONS

It is concluded that there is a decrease of phagocytic on S. mutans mediated by Complement Receptor 1/CR1 (CD35+) on S-ECC.

Bordetella Adenylate Cyclase Toxin Inhibits Monocyte-to-Macrophage Transition and Dedifferentiates Human Alveolar Macrophages into Monocyte-like Cells

Monocytes arriving at the site of infection differentiate into functional effector macrophages to replenish the resident sentinel cells. Bordetella pertussis, the pertussis agent, secretes an adenylate cyclase toxin-hemolysin (CyaA) that binds myeloid phagocytes through complement receptor 3 (CD11b/CD18) and swiftly delivers its adenylyl cyclase enzyme domain into phagocytes. This ablates the bactericidal capacities of phagocytes through massive and unregulated conversion of cytosolic ATP into the key signaling molecule cAMP. We show that exposure of primary human monocytes to as low a concentration as 22.5 pM CyaA, or a low (2:1) multiplicity of infection by CyaA-producing B. pertussis bacteria, blocks macrophage colony-stimulating factor (M-CSF)-driven differentiation of monocytes. CyaA-induced cAMP signaling mediated through the activity of protein kinase A (PKA) efficiently blocked expression of macrophage markers, and the monocytes exposed to 22.5 pM CyaA failed to acquire the characteristic intracellular complexity of mature macrophage cells. Neither M-CSF-induced endoplasmic reticulum (ER) expansion nor accumulation of Golgi bodies, mitochondria, or lysosomes was observed in toxin-exposed monocytes, which remained small and poorly phagocytic and lacked pseudopodia. Exposure to 22.5 pM CyaA toxin provoked loss of macrophage marker expression on in vitro differentiated macrophages, as well as on primary human alveolar macrophages, which appeared to dedifferentiate into monocyte-like cells with upregulated CD14 levels. This is the first report that terminally differentiated tissue-resident macrophage cells can be dedifferentiated in vitro The results suggest that blocking of monocyte-to-macrophage transition and/or dedifferentiation of the sentinel cells of innate immunity through cAMP-elevating toxin action may represent a novel immune evasion strategy of bacterial pathogens.IMPORTANCE Macrophages are key sentinel cells of the immune system, and, as such, they are targeted by the toxins produced by the pertussis agent Bordetella pertussis The adenylate cyclase toxin (CyaA) mediates immune evasion of B. pertussis by suspending the bactericidal activities of myeloid phagocytes. We reveal a novel mechanism of potential subversion of host immunity, where CyaA at very low (22 pM) concentrations could inhibit maturation of human monocyte precursors into the more phagocytic macrophage cells. Furthermore, exposure to low CyaA amounts has been shown to trigger dedifferentiation of mature primary human alveolar macrophages back into monocyte-like cells. This unprecedented capacity is likely to promote survival of the pathogen in the airways, both by preventing maturation of monocytes attracted to the site of infection into phagocytic macrophages and by dedifferentiation of the already airway-resident sentinel cells.

In Vivo Effects of A Pro-PO System Inhibitor on the Phagocytosis of Xenorhabdus Nematophila in Galleria Mellonella Larvae

Xenorhabdus nematophila is a Gram-negative bacterium symbiont of the entomopathogen nematode Steinernema carpocapsae whose immunosuppressive properties over host's immune response have been thoroughly investigated. In particular, live X. nematophila actively impairs phagocytosis in host's hemocytes through the secretion of inhibitors of eicosanoids synthesis. In this article we have investigated the cell surface structural features of X. nematophila responsible for the elusion from phagocytosis. To this end we have studied the uptake of heat-killed (hk), fluorescein isothiocyanate (FITC)-labeled X. nematophila by phagocytes from both a host insect and a mammalian species. In vitro dead X. nematophila passively resists engulfment by insect hemocytes without impairing the phagocytosis machinery whereas, unexpectedly, in vivo a significant phagocytosis of dead X. nematophila was observed. X. nematophila in vivo phagocytosis was increased by the co-injection of the specific inhibitor of pro-phenoloxidase (PO) system phenylthiourea (PTU), even if these effects were not observed in in vitro tests. Furthermore, biochemical modifications of X. nematophila cell wall implement in vivo phagocytosis, suggesting that this bacterium avoid phagocytosis because the ligand of phagocytic receptors is somehow buried or disguised in the cell wall. Finally, dead X. nematophila escapes engulfment even by human phagocytes suggesting that X. nematophila could be a useful model to investigate escape from phagocytosis by mammalian macrophages.

Differential Immune Activation in Fetal Macrophage Populations

Distinct macrophage subsets populate the developing embryo and fetus in distinct waves. However little is known about the functional differences between in utero macrophage populations or how they might contribute to fetal and neonatal immunity. Here we tested the innate immune response of mouse macrophages derived from the embryonic yolk sac and from fetal liver. When isolated from liver or lung, CD11bHI fetal liver derived macrophages responded to the TLR4 agonist LPS by expressing and releasing inflammatory cytokines. However F4/80HI macrophages from the yolk sac did not respond to LPS treatment. While differences in TLR4 expression did not appear to explain these data, F4/80HI macrophages had much lower NLRP3 inflammasome expression compared to CD11bHI macrophages. Gene expression profiling also demonstrated LPS-induced expression of inflammatory genes in CD11bHI macrophages, but not in F4/80HI cells. Genes expressed in LPS-treated CD11bHI macrophages were more likely to contain predicted NF-κB binding sites in their promoter regions. Our data show that CD11bHI macrophages derived from fetal liver are the major pro-inflammatory cells in the developing fetus. These findings could have important implications in better understanding the fetal inflammatory response and the unique features of neonatal immunity.

A Pathogen and a Non-pathogen Spotted Fever Group Rickettsia Trigger Differential Proteome Signatures in Macrophages

We have previously reported that Rickettsia conorii and Rickettsia montanensis have distinct intracellular fates within THP-1 macrophages, suggesting that the ability to proliferate within macrophages may be a distinguishable factor between pathogenic and non-pathogenic Spotted fever group (SFG) members. To start unraveling the molecular mechanisms underlying the capacity (or not) of SFG Rickettsia to establish their replicative niche in macrophages, we have herein used quantitative proteomics by SWATH-MS to profile the alterations resulted by the challenge of THP-1 macrophages with R. conorii and R. montanensis. We show that the pathogenic, R. conorii, and the non-pathogenic, R. montanensis, member of SFG Rickettsia trigger differential proteomic signatures in macrophage-like cells upon infection. R. conorii specifically induced the accumulation of several enzymes of the tricarboxylic acid cycle, oxidative phosphorylation, fatty acid β-oxidation, and glutaminolysis, as well as of several inner and outer membrane mitochondrial transporters. These results suggest a profound metabolic rewriting of macrophages by R. conorii toward a metabolic signature of an M2-like, anti-inflammatory activation program. Moreover, several subunits forming the proteasome and immunoproteasome are found in lower abundance upon infection with both rickettsial species, which may help bacteria to escape immune surveillance. R. conorii-infection specifically induced the accumulation of several host proteins implicated in protein processing and quality control in ER, suggesting that this pathogenic Rickettsia may be able to increase the ER protein folding capacity. This work reveals novel aspects of macrophage-Rickettsia interactions, expanding our knowledge of how pathogenic rickettsiae explore host cells to their advantage.

Expression profile of microRNAs in porcine alveolar macrophages after Toxoplasma gondii infection

BACKGROUND

Toxoplasma gondii is an apicomplexan protozoan parasite that can cause serious clinical illnesses in both humans and animals. microRNAs (miRNAs) are non-protein-coding RNAs that can regulate the expression of target genes. A previous study found that many miRNAs were differentially expressed after T. gondii infection and exert significant effects and revealed that both host survival and the virulence of different strains can be regulated by different miRNAs. Macrophages play an important role in T. gondii infection, but few studies have investigated the relationship between miRNAs and porcine alveolar macrophages infected with T. gondii.

METHODS

Porcine alveolar macrophages (3D4-21) were infected with the RH (Type I) and Me49 (Type II) strains of T. gondii for 12 h and 24 h and then harvested. miRNA libraries were generated using the NEBNext® Multiplex Small RNA Library Prep Set for Illumina® (NEB, USA), and the miRNA expression levels were estimated based on transcripts per million reads (TPM).

RESULTS

Our study generated six miRNA expression profiles from macrophages infected with RH and Me49 compared with the control groups. The comparison of the T. gondii-infected and uninfected samples identified 81 differentially expressed miRNAs, including 36 novel miRNAs and 45 mature miRNAs. The target genes of these differentially expressed miRNAs were predicted using miRanda software, and ssc-miR-127 and ssc-miR-143-3p were predicted to regulate nitric oxide synthase 1 (NOS1) and nitric oxide synthase 3 (NOS3), respectively, which play essential roles in synthesizing nitric oxide (NO) by oxidizing L-arginine. These genes were differentially expressed in both the RH- and Me49-infected groups. A KEGG enrichment analysis indicated that the predicted target genes were involved in multiple signaling pathways, including FcγR-mediated phagocytosis, the AMPK signaling pathway, the mTOR signaling pathway, and the FcγRI signaling pathway, all of which are indispensable for the normal functioning of porcine alveolar macrophages.

CONCLUSIONS

Our results provide data on the miRNA profile of porcine alveolar macrophages infected with T. gondii. To our knowledge, this study provides the first demonstration of the relationship between miRNA and macrophages of swine origin. Understanding the functions of these regulated miRNAs will aid the investigation of T. gondii infectious diseases, and the differentially expressed miRNAs might be candidate drug targets for T. gondii infection in pigs.

Monocyte phagocytosis of malaria β-haematin in the presence of artemisinin, amodiaquine, chloroquine, doxycycline, primaquine, pyrimethamine and quinine

The intraerythrocytic malaria parasite digests haemoglobin to provide amino acids for metabolism and releases toxic haem that is sequestered into haemozoin, a non-toxic, insoluble, crystalline pigment. Following erythrocyte rupture, haemozoin is released into circulation and phagocytosed by monocytes. Phagocytosed haemozoin and antimalarial drugs have both been reported to modulate monocyte functions. This study determined the effects of therapeutic concentrations of seven antimalarial drugs; amodiaquine, artemisinin, chloroquine, doxycycline, primaquine, pyrimethamine and quinine, on the phagocytosis of β-haematin (synthetic haemozoin) by two monocytic cell lines, J774A.1 and U937, and human peripheral blood mononuclear cells. A novel spectrophotometric method based on the absorbance (O.D 400 nm) of alkali/SDS treated monocytes containing β-haematin was developed to complement counting phagocytosis with microscopy. The method has potential use for the large scale screening of monocyte phagocytic activity. Artemisinin, quinine, primaquine and pyrimethamine activated β-haematin phagocytosis by 12% or more, whereas amodiaquine, chloroquine and doxycyline inhibited β-haematin phagocytosis. In contrast, antimalarial drugs had minimal inhibitory effects on the phagocytosis of latex beads with only quinine resulting in more than 20% inhibition. Antimalarial drugs appear to alter monocyte phagocytic activity which has implications for the treatment, pathogenicity and adjunct therapies for malaria.

A Fluorescence Based-Proliferation Assay for the Identification of Replicating Bacteria Within Host Cells

Understanding host pathogen interactions is paramount to the development of novel antimicrobials. An important facet of this pursuit is the accurate characterization of pathogen replication within infected host cells. Here we describe the use of a fluorescence-based proliferation assay to identify intracellular populations of replicating bacteria at the subcellular level. Using Staphylococcus aureus as a model Gram-positive bacterial pathogen and macrophages as a model host phagocyte, we demonstrate this assay can be used to reliably identify individual phagocytes that contain replicating bacteria. Furthermore, we demonstrate this assay is compatible with additional cellular probes that enable characterization of cellular compartments in which replicating bacteria reside. Finally, we demonstrate that this assay facilitates the investigation of both Gram-negative and Gram-positive bacteria within host cells.

Clever Cooperation: Interactions Between EspF and Host Proteins

EspF is a central effector protein of enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli (EPEC), and Citrobacter rodentium (CR) that is secreted through the type III secretion system to host cells. The interaction between EspF and host proteins plays an important role in bacterial pathogenesis. EspF protein binds to host SNX9 and N-WASP proteins to promote the colonization of pathogenic bacteria in intestinal epithelial cells; combines with cytokeratin 18, actin, 14-3-3ζ, Arp2/3, profilin, and ZO-1 proteins to intervene in the redistribution of intermediate filaments, the rearrangement of actin, and the disruption of tight junctions; acts together with Abcf2 to boost host cell intrinsic apoptosis; and collaborates with Anxa6 protein to inhibit phagocytosis. The interaction between EspF and host proteins is key to the pathogenic mechanism of EHEC and EPEC. Here, we review how EspF protein functions through interactions with these 10 host proteins and contributes to the pathogenicity of EHEC/EPEC.

Pseudomonas syringae evades phagocytosis by animal cells via type III effector-mediated regulation of actin filament plasticity

Certain animal and plant pathogenic bacteria have developed virulence factors including effector proteins that enable them to overcome host immunity. A plant pathogen, Pseudomonas syringae pv. tomato (Pto) secretes a large repertoire of effectors via a type III secretory apparatus, thereby suppressing plant immunity. Here, we show that Pto causes sepsis in mice. Surprisingly, the effector HopQ1 disrupted animal phagocytosis by inhibiting actin rearrangement via direct interaction with the LIM domain of the animal target protein LIM kinase, a key regulator of actin polymerization. The results provide novel insight into animal host-plant pathogen interactions. In addition, the current study firstly demonstrates that certain plant pathogenic bacteria such as Pto evade phagocytosis by animal cells due to cross-kingdom suppression of host immunity.

Macrophage-microbe interaction: lessons learned from the pathogen Mycobacterium tuberculosis

Macrophages, being the cornerstone of the immune system, have adapted the ancient nutrient acquisition mechanism of phagocytosis to engulf various infectious organisms thereby helping to orchestrate an appropriate host response. Phagocytosis refers to the process of internalization and degradation of particulate material, damaged and senescent cells and microorganisms by specialized cells, after which the vesicle containing the ingested particle, the phagosome, matures into acidic phagolysosomes upon fusion with hydrolytic enzyme-containing lysosomes. The destructive power of the macrophage is further exacerbated through the induction of macrophage activation upon a variety of inflammatory stimuli. Despite being the end-point for many phagocytosed microbes, the macrophage can also serve as an intracellular survival niche for a number of intracellular microorganisms. One microbe that is particularly successful at surviving within macrophages is the pathogen Mycobacterium tuberculosis, which can efficiently manipulate the macrophage at several levels, including modulation of the phagocytic pathway as well as interfering with a number of immune activation pathways that normally would lead to eradication of the internalized bacilli. M. tuberculosis excels at circumventing destruction within macrophages, thus establishing itself successfully for prolonged times within the macrophage. In this contribution, we describe a number of general features of macrophages in the context of their function to clear an infection, and highlight the strategies employed by M. tuberculosis to counter macrophage attack. Interestingly, research on the evasion tactics employed by M. tuberculosis within macrophages not only helps to design strategies to curb tuberculosis, but also allows a better understanding of host cell biology.

Platelets Enhance Dendritic Cell Responses against Staphylococcus aureus through CD40-CD40L

Staphylococcus aureus is a major human pathogen that can cause mild to severe life-threatening infections in many tissues and organs. Platelets are known to participate in protection against S. aureus by direct killing and by enhancing the activities of neutrophils and macrophages in clearing S. aureus infection. Platelets have also been shown to induce monocyte differentiation into dendritic cells and to enhance activation of dendritic cells. Therefore, in the present study, we explored the role of platelets in enhancing bone marrow-derived dendritic cell (BMDC) function against S. aureus We observed a significant increase in dendritic cell phagocytosis and intracellular killing of a methicillin-resistant Staphylococcus aureus (MRSA) strain (USA300) by thrombin-activated platelets or their releasates. Enhancement of bacterial uptake and killing by DCs is mediated by platelet-derived CD40L. Coculture of USA300 and BMDCs in the presence of thrombin-activated platelet releasates invokes upregulation of the maturation marker CD80 on DCs and enhanced production of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin 12 (IL-12), and IL-6. Overall, these observations support our hypothesis that platelets play a critical role in the host defense against S. aureus infection. Platelets stimulate DCs, leading to direct killing of S. aureus and enhanced DC maturation, potentially leading to adaptive immune responses against S. aureus.

From Phagocytes to Immune Defense: Roles for Coronin Proteins in Dictyostelium and Mammalian Immunity

Microbes have interacted with eukaryotic cells for as long as they have been co-existing. While many of these interactions are beneficial for both the microbe as well as the eukaryotic cell, several microbes have evolved into pathogenic species. For some of these pathogens, host cell invasion results in irreparable damage and thus host cell destruction, whereas others use the host to avoid immune detection and elimination. One of the latter pathogens is Mycobacterium tuberculosis, arguably one of the most notorious pathogens on earth. In mammalian macrophages, M. tuberculosis manages to survive within infected macrophages by avoiding intracellular degradation in lysosomes using a number of different strategies. One of these is based on the recruitment and phagosomal retention of the host protein coronin 1, that is a member of the coronin protein family and a mammalian homolog of coronin A, a protein identified in Dictyostelium. Besides mediating mycobacterial survival in macrophages, coronin 1 is also an important regulator of naïve T cell homeostasis. How, exactly, coronin 1 mediates its activity in immune cells remains unclear. While in lower eukaryotes coronins are involved in cytoskeletal regulation, the functions of the seven coronin members in mammals are less clear. Dictyostelium coronins may have maintained multiple functions, whereas the mammalian coronins may have evolved from regulators of the cytoskeleton to modulators of signal transduction. In this minireview, we will discuss the different studies that have contributed to understand the molecular and cellular functions of coronin proteins in mammals and Dictyostelium.

The Multirole of Liposomes in Therapy and Prevention of Infectious Diseases

Liposomes are closed bilayer structures spontaneously formed by hydrated phospholipids that are widely used as efficient delivery systems for drugs or antigens, due to their capability to encapsulate bioactive hydrophilic, amphipathic, and lipophilic molecules into inner water phase or within lipid leaflets. The efficacy of liposomes as drug or antigen carriers has been improved in the last years to ameliorate pharmacokinetics and capacity to release their cargo in selected target organs or cells. Moreover, different formulations and variations in liposome composition have been often proposed to include immunostimulatory molecules, ligands for specific receptors, or stimuli responsive compounds. Intriguingly, independent research has unveiled the capacity of several phospholipids to play critical roles as intracellular messengers in modulating both innate and adaptive immune responses through various mechanisms, including (i) activation of different antimicrobial enzymatic pathways, (ii) driving the fusion–fission events between endosomes with direct consequences to phagosome maturation and/or to antigen presentation pathway, and (iii) modulation of the inflammatory response. These features can be exploited by including selected bioactive phospholipids in the bilayer scaffold of liposomes. This would represent an important step forward since drug or antigen carrying liposomes could be engineered to simultaneously activate different signal transduction pathways and target specific cells or tissues to induce antigen-specific T and/or B cell response. This lipid-based host-directed strategy can provide a focused antimicrobial innate and adaptive immune response against specific pathogens and offer a novel prophylactic or therapeutic option against chronic, recurrent, or drug-resistant infections.

Bcl10 synergistically links CEACAM3 and TLR-dependent inflammatory signalling

The neutrophil-specific innate immune receptor CEACAM3 functions as a decoy to capture Gram-negative pathogens, such as Neisseria gonorrhoeae, that exploit CEACAM family members to adhere to the epithelium. Bacterial binding to CEACAM3 results in their efficient engulfment and triggers activation of an nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-dependent inflammatory response by human neutrophils. Herein, we report that CEACAM3 cross-linking is not sufficient for induction of cytokine production and show that the inflammatory response induced by Neisseria gonorrhoeae infection is elicited by an integration of signals from CEACAM3 and toll-like receptors. Using neutrophils from a human CEACAM-expressing mouse line (CEABAC), we use a genetic approach to reveal a molecular bifurcation of the CEACAM3-mediated antimicrobial and inflammatory responses. Ex vivo experiments with CEABAC-Rac2-/- , CEABAC-Bcl10-/- , and CEABAC-Malt1-/- neutrophils indicate that these effectors are not necessary for gonococcal engulfment, yet all 3 effectors contribute to CEACAM3-mediated cytokine production. Interestingly, although Bcl10 and Malt1 are often inextricably linked, Bcl10 enabled synergy between toll-like receptor 4 and CEACAM3, whereas Malt1 did not. Together, these findings reveal an integration of the specific innate immune receptor CEACAM3 into the network of more conventional pattern recognition receptors, providing a mechanism by which the innate immune system can unleash its response to a relentless pathogen.

The Potential of Phage Therapy in Sepsis

Sepsis remains a difficult clinical challenge, since our understanding of its immunopathology is incomplete and no efficacious treatment currently exists. Its earlier stage results from an uncontrolled inflammatory response to bacteria while in the later stage disturbed immune response with immunodeficiency syndrome develops. More than a hundred of clinical trials have not provided an efficient therapy which could ascertain an improvement or cure. Recent advancements in immunobiology of bacterial viruses (phages) indicate that in addition to their well-known antibacterial action phages have potent immunomodulating properties. Those data along with preliminary observations in experimental animals and the clinic strongly suggest that clinical trials on the efficacy of phages in sepsis are urgently needed.

Group A Streptococcus encounters with host macrophages

Group A Streptococcus (GAS) is a leading human bacterial pathogen with diverse clinical manifestations. Macrophages constitute a critical first line of host defense against GAS infection, using numerous surface and intracellular receptors such as Toll-like receptors and inflammasomes for pathogen recognition and activation of inflammatory signaling pathways. Depending on the intensity of the GAS infection, activation of these signaling cascades may provide a beneficial early alarm for effective immune clearance, or conversely, may cause hyperinflammation and tissue injury during severe invasive infection. Although traditionally considered an extracellular pathogen, GAS can invade and replicate within macrophages using specific molecular mechanisms to resist phagolysosomal and xenophagic killing. Unraveling GAS-macrophage encounters may reveal new treatment options for this leading agent of infection-associated mortality. [Formula: see text].

Metabolic adaptation of intracellular bacteria and fungi to macrophages

The mature phagosome of macrophages is a hostile environment for the vast majority of phagocytosed microbes. In addition to active destruction of the engulfed microbes by antimicrobial compounds, restriction of essential nutrients in the phagosomal compartment contributes to microbial growth inhibition and killing. However, some pathogenic microorganisms have not only developed various strategies to efficiently withstand or counteract antimicrobial activities, but also to acquire nutrients within macrophages for intracellular replication. Successful intracellular pathogens are able to utilize host-derived amino acids, carbohydrates and lipids as well as trace metals and vitamins during intracellular growth. This requires sophisticated strategies such as phagosome modification or escape, efficient nutrient transporters and metabolic adaptation. In this review, we discuss the metabolic adaptation of facultative intracellular bacteria and fungi to the intracellular lifestyle inside macrophages.

Monocyte dysregulation and systemic inflammation during pediatric falciparum malaria

BACKGROUND

Inflammation and monocytes are thought to be important to human malaria pathogenesis. However, the relationship of inflammation and various monocyte functions to acute malaria, recovery from acute malaria, and asymptomatic parasitemia in endemic populations is poorly understood.

METHODS

We evaluated plasma cytokine levels, monocyte subsets, monocyte functional responses, and monocyte inflammatory transcriptional profiles of 1- to 10-year-old Kenyan children at the time of presentation with acute uncomplicated malaria and at recovery 6 weeks later; these results were compared with analogous data from asymptomatic children and adults in the same community.

RESULTS

Acute malaria was marked by elevated levels of proinflammatory and regulatory cytokines and expansion of the inflammatory "intermediate" monocyte subset that returned to levels of healthy asymptomatic children 6 weeks later. Monocytes displayed activated phenotypes during acute malaria, with changes in surface expression of markers important to innate and adaptive immunity. Functionally, acute malaria monocytes and monocytes from asymptomatic infected children had impaired phagocytosis of P. falciparum-infected erythrocytes relative to asymptomatic children with no blood-stage infection. Monocytes from both acute malaria and recovery time points displayed strong and equivalent cytokine responsiveness to innate immune agonists that were independent of infection status. Monocyte transcriptional profiles revealed regulated and balanced proinflammatory and antiinflammatory and altered phagocytosis gene expression patterns distinct from malaria-naive monocytes.

CONCLUSION

These observations provide insights into monocyte functions and the innate immune response during uncomplicated malaria and suggest that asymptomatic parasitemia in children is not clinically benign.

FUNDING

Support for this work was provided by NIH/National Institute of Allergy and Infectious Diseases (R01AI095192-05), the Burroughs Wellcome Fund/American Society of Tropical Medicine and Hygiene, and the Rainbow Babies & Children's Foundation.