Medical Microbiology and Immunology

Adverse immunological imprinting by cytomegalovirus sensitizing for allergic airway disease Abstract Cytomegalovirus (CMV) infection has a profound impact on the host's immune system. Immunological imprinting by CMV is not restricted to immunity against CMV itself, but can affect immunity against other viral or non-viral infectious agents and also immunopathological responses. One category is heterologous immunity based on molecular mimicry, where antigen recognition receptors specific for a CMV antigen with broad avidity distribution also bind with some avidity to unrelated antigens and exert effector functions against target structures other than those linked to CMV. Another category is induction of cytokines by CMV infection that inhibit or drive immune responses to bystander antigens unrelated to CMV, and a third category is the activation of antigen-presenting cells by CMV from which unrelated antigens profit as "stowaways". A striking example of the "stowaway" category, actually one that is of medical importance, has been published recently and will be discussed here for the more general reader. Specifically, in a murine model, CMV airway infection and inhaled environmental antigen of poor intrinsic allergenic potential were found to sensitize for allergic airway disease (AAD) only when combined. As to the mechanism, viral activation of CD11b+ conventional dendritic cells (CD11b+ cDC) that localize to airway mucosa facilitates uptake and processing of inhaled antigen. Thus, CMV serves as a "door opener" for otherwise harmless environmental antigens that have no intrinsic property to activate DC. Antigen-laden CD11b+ cDC migrate selectively to the airway draining lymph nodes, where they prime type-2 CD4+ T helper (Th-2) cells. Upon airway re-exposure to the inhaled antigen, Th-2 cells secrete interleukins (IL-4, IL-5, IL-9, and IL-25) known to induce goblet cell metaplasia, the lead histopathological manifestation of AAD that is characterized by thickening of airway epithelia and increased numbers of mucus-producing goblet cells, resulting in enhanced mucus secretion and airflow obstruction.

'Checks and balances' in cytomegalovirus-host cohabitation

Intertwined: SAMHD1 cellular functions, restriction, and viral evasion strategies Abstract SAMHD1 was initially described for its ability to efficiently restrict HIV-1 replication in myeloid cells and resting CD4+ T cells. However, a growing body of evidence suggests that SAMHD1-mediated restriction is by far not limited to lentiviruses, but seems to be a general concept that applies to most retroviruses and at least a number of DNA viruses. SAMHD1 anti-viral activity was long believed to be solely due to its ability to deplete cellular dNTPs by enzymatic degradation. However, since its discovery, several new functions have been attributed to SAMHD1. It has been demonstrated to bind nucleic acids, to modulate innate immunity, as well as to participate in the DNA damage response and resolution of stalled replication forks. Consequently, it is likely that SAMHD1-mediated anti-viral activity is not or not exclusively mediated through its dNTPase activity. Therefore, in this review, we summarize current knowledge on SAMHD1 cellular functions and systematically discuss how these functions could contribute to the restriction of a broad range of viruses besides retroviruses: herpesviruses, poxviruses and hepatitis B virus. Furthermore, we aim to highlight different ways how viruses counteract SAMHD1-mediated restriction to bypass the SAMHD1-mediated block to viral infection.

Role of antibodies in confining cytomegalovirus after reactivation from latency: three decades' résumé Abstract Cytomegaloviruses (CMVs) are highly prevalent herpesviruses, characterized by strict species specificity and the ability to establish non-productive latent infection from which reactivation can occur. Reactivation of latent human CMV (HCMV) represents one of the most important clinical challenges in transplant recipients secondary to the strong immunosuppression. In addition, HCMV is the major viral cause of congenital infection with severe sequelae including brain damage. The accumulated evidence clearly shows that cellular immunity plays a major role in the control of primary CMV infection as well as establishment and maintenance of latency. However, the efficiency of antiviral antibodies in virus control, particularly in prevention of congenital infection and virus reactivation from latency in immunosuppressed hosts, is much less understood. Because of a strict species specificity of HCMV, the role of antibodies in controlling CMV disease has been addressed using murine CMV (MCMV) as a model. Here, we review and discuss the role played by the antiviral antibody response during CMV infections with emphasis on latency and reactivation not only in the MCMV model, but also in relevant clinical settings. We provide evidence to conclude that antiviral antibodies do not prevent the initiating molecular event of virus reactivation from latency but operate by preventing intra-organ spread and inter-organ dissemination of recurrent virus.

Generation, maintenance and tissue distribution of T cell responses to human cytomegalovirus in lytic and latent infection Abstract Understanding how the T cell memory response directed towards human cytomegalovirus (HCMV) develops and changes over time while the virus persists is important. Whilst HCMV primary infection and periodic reactivation is well controlled by T cell responses in healthy people, when the immune system is compromised such as post-transplantation, during pregnancy, or underdeveloped such as in new-born infants and children, CMV disease can be a significant problem. In older people, HCMV infection is associated with increased risk of mortality and despite overt disease rarely being seen there are increases in HCMV-DNA in urine of older people suggesting that there is a change in the efficacy of the T cell response following lifelong infection. Therefore, understanding whether phenomenon such as "memory inflation" of the immune response is occurring in humans and if this is detrimental to the overall health of individuals would enable the development of appropriate treatment strategies for the future. In this review, we present the evidence available from human studies regarding the development and maintenance of memory CD8 + and CD4 + T cell responses to HCMV. We conclude that there is only limited evidence supportive of "memory inflation" occurring in humans and that future studies need to investigate immune cells from a broad range of human tissue sites to fully understand the nature of HCMV T cell memory responses to lytic and latent infection.

Impact of CMV upon immune aging: facts and fiction Abstract Aging is accompanied by significant defects in immunity and compromised responses to new, previously unencountered microbial pathogens. Most humans carry several persistent or latent viruses as they age, interacting with the host immune systems for years. In that context maybe the most studied persistent virus is Cytomegalovirus, infamous for its ability to recruit very large T cell responses which increase with age and to simultaneously evade elimination by the immune system. Here we will address how lifelong CMV infection and the immunological burden of its control might affect immune reactivity and health of the host over time.

'From immunosenescence to immune modulation': a re-appraisal of the role of cytomegalovirus as major regulator of human immune function Abstract In the year 2000, cytomegalovirus was identified as a risk factor for mortality in a seminal study of octogenarian residents in Sweden. This finding triggered a wave of additional epidemiological investigations, some of which supported this association whilst others observed no such effect. In addition, this increased risk of death in CMV-seropositive people was correlated with observed changes within the T-cell repertoire such that accelerated 'immunosenescence' became a de facto explanation, without strong evidence to this effect. Recent years have seen a re-appraisal of these findings. Interestingly, many studies show that cytomegalovirus acts to improve immune function, most clearly in younger donors. In addition, the excess mortality in older people that is observed in CMV-seropositive cohorts appears to be related primarily to an excess of vascular disease rather than impairment of immune function. CMV is an important member of the natural 'virome' of Homo sapiens and has an important, and generally positive, modulatory influence on human immune function throughout most of life. However, within certain populations, this influence can become negative and age, co-morbidity and environment all act as determinants of this effect. As such, it is important that new interventions are developed that can mitigate the damaging influence of CMV on human health in populations at risk.

Caspase-8 restricts natural killer cell accumulation during MCMV Infection Abstract Natural killer (NK) cells provide important host defense against herpesvirus infections and influence subsequent T cell control of replication and maintenance of latency. NK cells exhibit phases of expansion, contraction and memory formation in response to the natural mouse pathogen murine cytomegalovirus (MCMV). Innate and adaptive immune responses are tightly regulated in mammals to avoid excess tissue damage while preventing acute and chronic viral disease and assuring resistance to reinfection. Caspase (CASP)8 is an autoactivating aspartate-specific cysteine protease that initiates extrinsic apoptosis and prevents receptor interacting protein (RIP) kinase (RIPK)1–RIPK3-driven necroptosis. CASP8 also promotes death-independent signal transduction. All of these activities make contributions to inflammation. Here, we demonstrate that CASP8 restricts NK cell expansion during MCMV infection but does not influence NK memory. Casp8−/−Ripk3−/− mice mount higher NK response levels than Casp8+/−Ripk3−/− littermate controls or WT C57BL/6 J mice, indicating that RIPK3 deficiency alone does not contribute to NK response patterns. MCMV m157-responsive Ly49H+ NK cells support increased expansion of both Ly49H− NK cells and CD8 T cells in Casp8−/−Ripk3−/− mice. Surprisingly, hyperaccumulation of NK cells depends on the pronecrotic kinase RIPK1. Ripk1−/−Casp8−/−Ripk3−/− mice fail to show the enhanced expansion of lymphocytes observed in Casp8−/−Ripk3−/− mice even though development and homeostasis are preserved in uninfected Ripk1−/−Casp8−/−Ripk3−/− mice. Thus, CASP8 naturally regulates the magnitude of NK cell responses in response to infection where strong activation signals depend on another key regulator of death signaling, RIPK1. In addition, the strong NK cell response promotes survival of effector CD8 T cells during their expansion. Thus, hyperaccumulation of NK cells and crosstalk with T cells becomes amplified in the absence of extrinsic cell death machinery.

Persistent viral replication and the development of T-cell responses after intranasal infection by MCMV Abstract Natural transmission of cytomegalovirus (CMV) has been difficult to observe. However, recent work using the mouse model of murine (M)CMV demonstrated that MCMV initially infects the nasal mucosa after transmission from mothers to pups. We found that intranasal (i.n.) inoculation of C57BL/6J mice resulted in reliable recovery of replicating virus from the nasal mucosa as assessed by plaque assay. After i.n. inoculation, CD8+ T-cell priming occurred in the mandibular, deep-cervical, and mediastinal lymph nodes within 3 days of infection. Although i.n. infection induced "memory inflation" of T cells specific for the M38316–323 epitope, there were no detectable CD8+ T-cell responses against the late-appearing IE3416–423 epitope, which contrasts with intraperitoneal (i.p.) infection. MCMV-specific T cells migrated into the nasal mucosa where they developed a tissue-resident memory (TRM) phenotype and this could occur independently of local virus infection or antigen. Strikingly however, virus replication was poorly controlled in the nasal mucosa and MCMV was detectable by plaque assay for at least 4 months after primary infection, making the nasal mucosa a second site for MCMV persistence. Unlike in the salivary glands, the persistence of MCMV in the nasal mucosa was not modulated by IL-10. Taken together, our data characterize the development of local and systemic T-cell responses after intranasal infection by MCMV and define the nasal mucosa, a natural site of viral entry, as a novel site of viral persistence.

T-cell immunity against cytomegalovirus in HIV infection and aging: relationships with inflammation, immune activation, and frailty Abstract Both aging and treated human immunodeficiency virus (HIV) infection are characterized by low-level chronic inflammation and immune activation which contribute to the development of age-related diseases, frailty, and early mortality. Chronic cytomegalovirus (CMV) infection is highly prevalent in older adults and HIV-infected populations. A number of studies have shown that CMV induces broad and strong T-cell responses in CMV-seropositive older adults and HIV-infected individuals. CMV infection rarely develops into clinical disease in immunocompetent individuals. However, a large body of literature has shown adverse effects of chronic CMV infection on the health and longevity of these populations. It has been hypothesized that chronic CMV infection may be a driver of chronic inflammation and immune activation, and may further contribute to the development of frailty. Thus, there is a need to better understand the extent of the impact of chronic CMV infection on T-cell immunity and health in aging and HIV infection. In this review, we will address important considerations and challenges in the assessment of chronic CMV infection and CMV-specific T-cell responses. We will then review recent data on relationships between T-cell responses to CMV and levels of inflammatory markers and immune activation, as well as the onset of frailty.

The peculiar physiological responses of Rhizoctonia solani under the antagonistic interaction coupled by a novel antifungalmycin N2 from Streptomyces sp. N2 Abstract A novel antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) was previously discovered from Streptomyces sp. N2, which exerted a broad-spectrum antagonistic activity against phytopathogenic fungi. To provide comprehensive insights into the antagonistic mechanisms and biocontrol efficacy of antifungalmycin N2, the present work investigated the physiological responses of Rhizoctonia solani under interaction with antifungalmycin N2. First, the mycelial growth of R. solani was significantly inhibited by antifungalmycin N2 during liquid shake-flask culture. Morphological observations showed that the morphogenesis of R. solani was influenced by antifungalmycin N2, in which the hyphae became severely shriveled and flattened, irregularly folded and branched. Additionally, an obvious accumulation of reactive oxygen species (ROS) was detected in R. solani hyphae, indicating oxidative stress induced by antifungalmycin N2. Further results showed that chitinase activity and its hydrolytic N-acetylglucosamine were significantly accelerated by antifungalmycin N2, demonstrating the cell wall of R. solani was damaged. Interestingly, the enzymatic antioxidant activities of R. solani were significantly induced in response to a relatively low concentration of antifungalmycin N2 (1.44–5.77 µg/mL). However, all antioxidant enzymes became highly inactive when the antifungalmycin N2 was increased to 11.53 µg/mL, suggesting that the enzymatic antioxidant system in R. solani was probably collapsed by the oxidative stress beyond its acceptance scope. In conclusion, antifungalmycin N2 exerted its antagonistic activity by inducing both cell wall degradation and oxidative stress in R. solani, thus leading to fungal morphogenesis and autolysis. Meanwhile, R. solani could induce and activate its antioxidant enzymes as a defence response to the oxidative stress caused by antifungalmycin N2.

Actively detached Pseudomonas aeruginosa biofilm cell susceptibility to benzalkonium chloride and associated resistance mechanism Abstract The present work aimed at studying physiological properties of Pseudomonas aeruginosa cells actively detached from biofilm formed on stainless steel and comparing them with their planktonic counterparts as a function of growth temperature (20 °C and 37 °C). The susceptibility of P. aeruginosa cells to benzalkonium chloride (BAC) was studied. Furthermore, the effect of BAC on the cell membrane integrity and the role of the cell membrane fluidity in the cell-scale-resistance mechanism were investigated. Our results showed that actively detached biofilm cells were more susceptible to BAC treatment than planktonic ones. A greater leakage of intracellular potassium after BAC addition was observed in actively detached biofilm cells, which reflects their membrane vulnerability. The rise of the growth temperature from 20 to 37 °C increased the membrane rigidity of planktonic cells comparatively to their actively detached biofilm ones. Under experimental conditions developed in this work, our data highlighted that actively biofilm-detached and planktonic P. aeruginosa cells have distinguishable phenotypes.

Bacterial communities of the microbial mats of Chokrak sulfide springs Abstract This is the comparative investigation of the composition of phototrophic microbial mats developing in sulfide-rich saline Chokrak springs with outflow at the shore of the hypersaline lake Chokrak by means of next-generation sequencing. The springs are characterized by low temperature (~ 15 °C), near-neutral pH (6.7–8.5), and high-sulfide content. In the species composition the benthic microbial communities of Chokrak springs are similar to microbial mats of marine supralittoral and lagoons. Our results showed that salinity limitation had a significant effect on the species composition of benthic microbial communities developing at the outflow of the Chokrak springs. Predominant oxygenic phototrophs belonged to the genera Phormidium, Lyngbya, Leptolyngbya, Geitlerinema, and Arthrospira. Anoxygenic phototrophic bacteria were represented by halophilic green sulfur bacteria Prosthecochloris spp., halotolerant Chlorobaculum sp., as well as marine and extremely halophilic purple bacteria Roseospira, Rhodovibrio, and Halochromatium. Monoculture of a new species of halotolerant anoxygenic filamentous phototrophic bacteria was isolated.

Heavy metal spill influences bacterial communities in freshwater sediments Abstract Bacteria are highly abundant in freshwater sediments and play a crucial role in biogeochemical cycling. Bacterial assemblage is known to be sensitive to heavy metal pollution. However, the shift in freshwater sediment bacterial community after a sudden exposure to heavy metal spill remains unknown. The present study explored the impact of metal (metalloid) spill on sediment bacterial community in a freshwater reservoir. Although sediment bacterial abundance was relatively insensitive to metal (metalloid) spill, bacterial richness, diversity and community structure displayed considerable temporal variations. In addition, the proportions of Proteobacteria Chloroflexi, Nitrospirae, Acidobacteria and Bacteroidetes drastically declined, while a significant enrichment of Firmicutes was observed.

Antibacterial activity against porcine respiratory bacterial pathogens and in vitro biocompatibility of essential oils Abstract Bacterial respiratory infections affecting pigs such as pneumonia, pleuropneumonia, and pleurisy, are a major health concern in the swine industry and are associated with important economic losses. This study aimed to investigate the antibacterial activities of essential oils against major swine respiratory pathogens with a view to developing a potential alternative to antibiotics. Their synergistic interactions with the bacteriocin nisin was also examined. Lastly, we assessed the in vitro biocompatibility of the most efficient essential oils using a pig tracheal epithelial cell line. Of the nine essential oils tested, those from cinnamon, thyme, and winter savory were the most active against Streptococcus suis, Actinobacillus pleuropneumoniae, Actinobacillus suis, Bordetella bronchiseptica, Haemophilus parasuis, and Pasteurella multocida, with minimum inhibitory concentrations and minimum bactericidal concentrations ranging from 0.01 to 0.156% (v/v). The main component found in cinnamon, thyme, and winter savory oils were cinnamaldehyde, thymol, and carvacrol, respectively. Treating pre-formed S. suis and A. pleuropneumoniae biofilms with thyme or winter savory oils significantly decreased biofilm viability. We also observed a synergistic growth inhibition of S. suis with mixtures of nisin and essential oils from thyme and winter savory. Concentrations of nisin and cinnamon, thyme and winter savory essential oils that were effective against bacterial pathogens had no effect on the viability of pig tracheal epithelial cells. The present study brought evidence that essential oils are potential antimicrobial agents against bacteria associated with porcine respiratory infections.

Isolation, characterization, and structural elucidation of 4-methoxyacetanilide from marine actinobacteria Streptomyces sp. SCA29 and evaluation of its enzyme inhibitory, antibacterial, and cytotoxic potential Abstract Marine actinobacteria are less explored than their terrestrial counterparts as potential source of natural products. The present study was aimed to elucidate the bioactive potential of metabolites produced by marine-derived actinobacterial strain Streptomyces sp.SCA29 isolated from Havelock Island, Andaman and Nicobar Islands, India. The potential isolate SCA29 was identified as Streptomyces sp. by phenotypic, genotypic (16S-rRNA) and phylogenetic analyses. The crude bioactive compound was extracted using organic solvents. The compounds were subjected to separation and purification by column chromatography which yielded six fractions. Each fraction was assayed for inhibition of α-glucosidase and α-amylase enzymes, antagonistic activity against bacterial pathogens, and cytotoxic activity against various cell lines. The fraction F3c was considered to be highly active owing to its significant inhibition potential against α-glucosidase and α-amylase enzymes with IC50 values as 44.26 and 53.19 µg/mL, respectively. The active fraction showed antibacterial activity against test bacterial pathogens with the MIC value ranged from 3.90 to 31.25 µg/mL. The compound also exhibited concentration-dependent cytotoxicity on various cell lines without significant effect against human normal cells. The bioassay-guided fractionation of extract led to the identification of 4-methoxyacetanilide, an acetamide derivative. The structure of the bioactive compound was confirmed by HR-MS, NMR (1H and 13C) and FT-IR spectra, and by comparison with literature data.

Biodiversity and antifouling activity of fungi associated with two soft corals from the South China Sea Abstract Bacteria in corals have been studied in detail in the past decades. However, the biodiversity and bioactivity of fungi in corals are still poorly understood. This study investigated the biodiversity and antifouling activity of fungi in soft corals Cladiella krempfi and Sarcophyton tortuosum from the South China Sea. A high diverse and abundant fungal community was found in the two soft corals. Furthermore, five isolates shared 83–95% similarity with their closest relatives, indicating that they might be novel species in genera Phaeoshaeria and Mucor. In addition, approximately 50% of the representative isolates exhibited distinct antifouling activity. In particular, isolates Fungal sp. SCAU132 and Fungal sp. SCAU133 displayed very strong antifouling activity against Bugula neritina, suggesting they can provide a potential resource for further investigation on isolation of novel antifouling metabolites. To our knowledge, this study is the first report to investigate the biodiversity and antifouling activity of fungi in C. krempfi and S. tortuosum.

Synergistic deletion of RGS1 and COS1 may reduce the pathogenicity of Magnaporthe oryzae Abstract Rice blast, caused by Magnaporthe oryzae, is a serious threat to global rice production. In recent years, many pathogenicity genes of M. oryzae have been identified, although most of their functions remain unknown. In this study, we report the synergistic deletion of RGS1 and COS1 that may reduce the pathogenicity of M. oryzae. The investigation involved comparing ΔMorgs1, ΔMocos1, and ΔMorgs1/ΔMocos1 mutants. The ΔMorgs1/ΔMocos1 mutant showed a weak reduction in vegetative growth, and the colonies displayed fewer and smoother aerial hyphae. The ΔMorgs1/ΔMocos1 mutant exhibited delayed appressorium-like structure formation and 'low pathogenicity' on detached rice seedling leaves when compared with ΔMocos1. Moreover, the melanin content of the single and double mutants was remarkably lower than that of the WT type. Thus, our results indicate that the synergy between RGS1 and COS1may be crucial in the pathogenicity of M. oryzae.

Arbuscular mycorrhiza: a viable strategy for soil nutrient loss reduction Abstract Arbuscular mycorrhiza fungi's (AMF) role in plant nutrition and stress management is well known, but very few researches and studies have been conducted so far on the fungal ability to reduce different nutrient losses (runoff, leaching and volatilization) from the soil system. This important ecosystem service of AMF had been neglected largely. From the recent findings, it has been confirmed that mycorrhizal symbiosis has potential to check the losses of applied nutrients. The role of soil biota in nutrient cycling is indispensable and determines the nutrient availability to plants. Among these biota, AMF's association with plants is the most prevalent, but the exact mechanisms followed by AMF in nutrient cycling, transformation and reducing nutrient loss ability are still inconclusive. In this review, we will try to unlock this particular aspect of AMF which is important to achieve global food demand in a sustainable way.

The stimulatory effects of plant growth promoting rhizobacteria and plant growth regulators on wheat physiology grown in sandy soil Abstract The present study was aimed to investigate the effects of plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) on the physiology and yield of wheat grown in less fertile sandy soil. The isolated PGPR strains were identified by 16S-rRNA gene sequencing as Planomicrobium chinense (P1), Bacillus cereus (P2) and Pseudomonas fluorescens (P3). Wheat varieties (Galaxy-13 and Pak-2013) differing in sensitivity to drought were soaked in fresh cultures of bacterial isolates and the PGRs (salicylic acid and putrescine) were sprayed at 150 mg/L on seedlings at three leaf stage. PGPR and PGRs treated plants showed significant increase in the contents of chlorophyll, sugar and protein even under harsh environmental conditions. Drought stress enhanced the production of proline, antioxidant enzymes and lipid peroxidation but a decrease was noted in the biochemical content (i.e. chlorophyll, protein and sugar) of inoculated plants. PGPR inoculation also significantly enhanced the yield parameters (i.e. plant height, spike length, grain yield and weight) and improved the fertility status of sandy soil. The accumulation of macronutrient, total NO3-N and P concentration and soil moisture content of rhizosphere soil was also enhanced by PGPRs inoculation. It is concluded that the combined effects of PGPR and PGRs have profound effects on the biochemical responses and drought tolerance of wheat grown in sandy soils.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
Crete.Greece.72100
2841026182

6948891480

alsfakia@gmail.com