Current status of immune mechanisms of killing of intracellular microorganisms

Regulation of Type I Interferon and Autophagy in Immunity against Mycobacterium Tuberculosis: Role of CGAS and STING1

Mycobacterium tuberculosis (M. tb) is a significant intracellular pathogen responsible for numerous infectious disease-related deaths worldwide. It uses ESX-1 T7SS to damage phagosomes and to enter the cytosol of host cells after phagocytosis. During infection, M. tb and host mitochondria release dsDNA, which activates the CGAS-STING1 pathway. This pathway leads to the production of type I interferons and proinflammatory cytokines and activates autophagy, which targets and degrades bacteria within autophagosomes. However, the role of type I IFNs in immunity against M. tb is controversial. While previous research has suggested a protective role, recent findings from cgas-sting1 knockout mouse studies have contradicted this. Additionally, a study using knockout mice and non-human primate models uncovered a new mechanism by which neutrophils recruited to lung infections form neutrophil extracellular traps. Activating plasmacytoid dendritic cells causes them to produce type I IFNs, which interfere with the function of interstitial macrophages and increase the likelihood of tuberculosis. Notably, M. tb uses its virulence proteins to disrupt the CGAS-STING1 signaling pathway leading to enhanced pathogenesis. Investigating the CGAS-STING1 pathway can help develop new ways to fight tuberculosis.

Proteome Analysis for Inflammation Related to Acute and Convalescent Infection

Infectious diseases are a significant burden in global healthcare. Pathogens engage with different host defense mechanisms. However, it is currently unknown if there are disease-specific immune signatures and/or if different pathogens elicit common immune-associated molecular entities to common therapeutic interventions. We studied patients enrolled through the Human Immunology Project Consortium (HIPC), which focuses on immune responses to various infections. Blood samples were collected and analyzed from patients during infection and follow-up time points at the convalescent stage. The study included samples from patients with Lyme disease (LD), tuberculosis (TB), malaria (MLA), dengue virus (DENV), and West Nile virus (WNV), as well as kidney transplant patients with cytomegalovirus (CMV) and polyomavirus (BKV) infections. Using an antibody-based assay, we quantified ~ 350 cell surface markers, cytokines, and chemokines involved in inflammation and immunity. Unique protein signatures were identified specific to the acute phase of infection irrespective of the pathogen type, with significant changes during convalescence. In addition, tumor necrosis factor receptor superfamily member 6 (TNR6), C-C Motif Chemokine Receptor 7 (CCR7), and C-C motif chemokine ligand-1 (CCL1) were increased in the acute and convalescent phases across all viral, bacterial, and protozoan compared to blood from healthy donors. Furthermore, despite the differences between pathogens, proteins were enriched in common biological pathways such as cell surface receptor signaling pathway and response to external stimulus. In conclusion, we demonstrated that irrespective of the pathogen type, there are common immunoregulatory and proinflammatory signals.

Salmonella delivers H9N2 influenza virus antigens via a prokaryotic and eukaryotic dual-expression vector and elicits bivalent protection against avian influenza and fowl typhoid

The H9N2 avian influenza virus significantly affects the health of poultry and humans. We identified a prokaryotic and eukaryotic dual-expression vector system, pJHL270, that can provide simultaneous MHC class I and II stimulation of the host immune system, and we designed vaccine antigens by selecting the consensus HA1 sequence and M2e antigens from H9N2 virus circulating in South Korea from 2000 to 2021. The genes were cloned into the pJHL270 vector, and the cloned plasmid was delivered by a live-attenuated Salmonella Gallinarum (SG) strain. The immunity and protective efficacy of the SG-based H9N2 vaccine construct, JOL2922, against avian influenza and fowl typhoid (FT) were evaluated. The Ptrc and CMV promoters conferred antigen expression in prokaryotic and eukaryotic cells to induce balanced Th-1/Th-2 immunity. Chickens immunized with JOL2922 yielded high antigen-specific humoral and mucosal immune responses. qRT-PCR revealed that the strain generated polyfunctional IFN-γ and IL-4 secretion in immunized chickens. Furthermore, a FACS analysis showed increased CD3CD4+ and CD3CD8+ T-cell subpopulations following immunization. Peripheral Blood Mononuclear Cells (PBMCs) harvested from the immunized chickens significantly increased MHC class I and II expression, 3.5-fold and 2.5-fold increases, respectively. Serum collected from the immunized groups had an evident hemagglutinin inhibition titer of ≥6 log2. Immunization reduced the lung viral titer by 3.8-fold within 5 days post-infection. The strain also generated SG-specific humoral and cellular immune responses. The immunized birds all survived a virulent SG wild-type challenge. In addition, the bacterial burden was reduced by 2.7-fold and 2.1-fold in spleen and liver tissue, respectively, collected from immunized chickens. Our data indicate that an attenuated SG strain successfully delivered the dual-expression vector system and co-stimulated MHC class I and II antigen presentation pathways via exogenous and endogenous antigen presentation, thereby triggering a balanced Th-1/Th-2-based immune response and conferring effective protection against avian influenza and FT.

State of the art in epitope mapping and opportunities in COVID-19

The understanding of any disease calls for studying specific biological structures called epitopes. One important tool recently drawing attention and proving efficiency in both diagnosis and vaccine development is epitope mapping. Several techniques have been developed with the urge to provide precise epitope mapping for use in designing sensitive diagnostic tools and developing rpitope-based vaccines (EBVs) as well as therapeutics. In this review, we will discuss the state of the art in epitope mapping with a special emphasis on accomplishments and opportunities in combating COVID-19. These comprise SARS-CoV-2 variant analysis versus the currently available immune-based diagnostic tools and vaccines, immunological profile-based patient stratification, and finally, exploring novel epitope targets for potential prophylactic, therapeutic or diagnostic agents for COVID-19.

Nanoparticle delivery through the BBB in central nervous system tuberculosis

Recent advances in Nanotechnology have revolutionized the production of materials for biomedical applications. Nowadays, there is a plethora of nanomaterials with potential for use towards improvement of human health. On the other hand, very little is known about how these materials interact with biological systems, especially at the nanoscale level, mainly because of the lack of specific methods to probe these interactions. In this review, we will analytically describe the journey of nanoparticles (NPs) through the brain, starting from the very first moment upon injection. We will preliminarily provide a brief overlook of the physicochemical properties of NPs. Then, we will discuss how these NPs interact with the body compartments and biological barriers, before reaching the blood-brain barrier (BBB), the last gate guarding the brain. Particular attention will be paid to the interaction with the biomolecular, the bio-mesoscopic, the (blood) cellular, and the tissue barriers, with a focus on the BBB. This will be framed in the context of brain infections, especially considering central nervous system tuberculosis (CNS-TB), which is one of the most devastating forms of human mycobacterial infections. The final aim of this review is not a collection, nor a list, of current literature data, as it provides the readers with the analytical tools and guidelines for the design of effective and rational NPs for delivery in the infected brain.

Responses of Humoral and Cellular Immune Mediators in BALB/c Mice to LipX (PE11) as Seed Tuberculosis Vaccine Candidates

A member of the pe/ppe gene family, lipX (pe11), is capable of directing persistent Mycobacterium tuberculosis and avoiding host immune responses. Some studies have indicated that LipX (PE11) can detect humoral antibodies in tuberculosis patients. Hence, information on immune mediators’ responses to this protein is essential to understand its protective efficacy against M. tuberculosis infections. This study aimed to examine the response of immune mediators to pCDNA3.1-lipX expression in vivo. In the experiment, pCDNA3.1-lipX was injected into BALB/c strain male mice aged between 6 and 8 weeks, and they were compared to groups injected with pCDNA3.1 and without injection. The injection was carried out three times intramuscularly every two weeks. Blood was taken retro-orbitally and used for humoral response analysis by Western blotting against LipX-His protein. Simultaneously, the splenocytes were cultured and induced with LipX-His protein for cellular immunity analyses. Our study showed that the recombinant DNA of pCDNA3.1-lipX induced a humoral and cellular immune response, especially in IL-4, IL-12, and IFN-γ, which are the primary cellular responses to M. tuberculosis infections. However, additional studies, such as a challenge study, are needed to strengthen the argument that this plasmid construction is feasible as a tuberculosis seed vaccine candidate.

Evaluation of Immune Responses and Protective Efficacy of a Novel Live Attenuated Salmonella Enteritidis Vaccine Candidate in Chickens

An ideal vaccine for controlling Salmonella infection in chicken flocks should be safe, inducing both humoral and cellular immunity. Live attenuated vaccines against Salmonella Enteritidis (S. Enteritidis) have been used as a potential control method of Salmonella infection in the poultry industry. However, live attenuated vaccines can persistently infect poultry for long periods and can become virulent revertant strains. In this study, we assessed the immune responses and protective efficacy of a temperature-sensitive attenuated S. Enteritidis mutant as a potential vaccine candidate. In addition, we evaluated the combined vaccine administration methods to maximize both humoral and cellular immune responses in chickens induced by the vaccine candidate. Immune responses and protective efficacy were compared between the Oral/IM group, vaccinated using one oral dose at four weeks old and a booster intramuscular dose at seven weeks old, and the IM/Oral group, vaccinated using one intramuscular dose at four weeks old and a booster oral dose at seven weeks old. The Oral/IM group showed stronger immune responses than those of the IM/Oral group. Spleens from the Oral/IM group showed a promising tendency of reduction of challenged Salmonella compared with those of other groups. Overall, the results indicated that the S. Enteritidis mutant strain is a promising live attenuated vaccine candidate with good efficacy.

Cytokine responses of immunosuppressed and immunocompetent patients with Neoehrlichia mikurensis infection

Purpose

The tick-borne bacterium Neoehrlichia mikurensis causes the infectious disease neoehrlichiosis in humans. Vascular endothelium is one of the target cells of the infection. Neoehrlichiosis patients with compromised B cell immunity present with more severe inflammation than immunocompetent patients. The aim of this study was to compare the cytokine profiles of immunocompetent and immunosuppressed patients with neoehrlichiosis.

Methods

Blood samples from Swedish and Norwegian immunosuppressed (N = 30) and immunocompetent (N = 16) patients with neoehrlichiosis were analyzed for the levels of 30 cytokines, using a multiplex cytokine assay and ELISA. A gender-matched healthy control group (N = 14) was analyzed in parallel. Data were analyzed using the multivariate method OPLS-DA.

Results

The multiplex cytokine analyses generated more cytokine results than did the uniplex ELISA analyses. Multivariate analysis of the multiplex cytokine results established that increased levels of FGF2, GM-CSF, CXCL10, and IFN-γ were associated with immunosuppressed patients, whereas increased levels of IL-15 and VEGF were associated with immunocompetent neoehrlichiosis patients. When multivariate analysis findings were confirmed with uniplex ELISA, it was found that both groups of patients had similarly elevated levels of VEGF, FGF2 and IFN-γ. In contrast, the immunosuppressed patients had clearly elevated levels of CXCL10, CXCL13 and BAFF, whereas the immunocompetent patients had the same levels as healthy controls.

Conclusion

Pro-angiogenic and type 1 cytokines were produced as part of the host response of neoehrlichiosis independent of immune status, whereas immunosuppressed neoehrlichiosis patients produced cytokines required for B cell-mediated defense.

Partial human Janus kinase 1 deficiency predominantly impairs responses to interferon gamma and intracellular control of mycobacteria

Purpose

Janus kinase-1 (JAK1) tyrosine kinase mediates signaling from multiple cytokine receptors, including interferon alpha/beta and gamma (IFN-α/β and IFN-γ), which are important for viral and mycobacterial protection respectively. We previously reported autosomal recessive (AR) hypomorphic JAK1 mutations in a patient with recurrent atypical mycobacterial infections and relatively minor viral infections. This study tests the impact of partial JAK1 deficiency on cellular responses to IFNs and pathogen control.

Methods

We investigated the role of partial JAK1 deficiency using patient cells and cell models generated with lentiviral vectors expressing shRNA.

Results

Partial JAK1 deficiency impairs IFN-γ-dependent responses in multiple cell types including THP-1 macrophages, Epstein-Barr Virus (EBV)-transformed B cells and primary dermal fibroblasts. In THP-1 myeloid cells, partial JAK1 deficiency reduced phagosome acidification and apoptosis and resulted in defective control of mycobacterial infection with enhanced intracellular survival. Although both EBV-B cells and primary dermal fibroblasts with partial JAK1 deficiency demonstrate reduced IFN-α responses, control of viral infection was impaired only in patient EBV-B cells and surprisingly intact in patient primary dermal fibroblasts.

Conclusion

Our data suggests that partial JAK1 deficiency predominantly affects susceptibility to mycobacterial infection through impact on the IFN-γ responsive pathway in myeloid cells. Susceptibility to viral infections as a result of reduced IFN-α responses is variable depending on cell type. Description of additional patients with inherited JAK1 deficiency will further clarify the spectrum of bacterial and viral susceptibility in this condition. Our results have broader relevance for anticipating infectious complications from the increasing use of selective JAK1 inhibitors.

Evaluation of Actin-1 Expression in Wild Caught Wuchereria bancrofti-Infected Mosquito Vectors

Background

Wuchereria bancrofti is the major cause of lymphatic filariasis transmitted by mosquito vectors. In the vector-parasite interaction and among other proteins, actin-1 has been implicated for successful transmission of the pathogen in laboratory-controlled experiments. However, validation of this finding from the pathogen's natural environment is required.

Objective

This study is aimed at evaluating actin-1 expression upon Wuchereria bancrofti infection in mosquito vectors collected during an epidemiology study in Tsafe Local Government Area of Zamfara State, Nigeria.

Methods

Mosquitoes were collected and identified using morphological keys, which include length of maxillary palps, pale spots on the wings, and scale patterns on the abdomen. This was followed by detection of the 188 bp SspI marker of Wuchereria bancrofti infection using polymerase chain reaction (PCR). The mRNA levels of the actin-1 gene were evaluated in the infected Anopheles gambiae sl and Culex quinquefasciatus and their controls, which were adult reared from the larvae in the study area.

Results

The mosquitoes were identified to be Anopheles gambiae sl and Culex quinquefasciatus, while infection by Wuchereria bancrofti was confirmed by amplification of the 188 bp SspI marker. A 4.85 and 4.09 relative fold increase in actin-1 gene expression in Wuchereria bancrofti-infected Anopheles gambiae sl and Culex quinquefasciatus was observed. Thus, for the first time we reported that the actin-1 gene in wild caught mosquito vectors (Anopheles gambiae sl and Culex quinquefasciatus) infected with Wuchereria bancrofti is upregulated.

Conclusion

The actin-1 gene is upregulated and similarly expressed during W. bancrofti infection in mosquito vectors in the study area and this may likely serve as a biomarker and viable strategy for the control of parasite transmission in endemic areas.

Differential expression of cytokine genes in THP-1-derived macrophages infected with mild and virulence strains of Shigella flexneri 2a

Shigella is an intracellular bacterial pathogen that causes bacterial dysentery called shigellosis. The assessment of pro- and anti-inflammatory mediators produced by immune cells against this bacteria are vital in identifying the effectiveness of the immune reaction in protecting the host. In Malaysia, Shigella is ranked as the third most common bacteria causing diarrheal disease among children below 5 years old. In the present study, we aim to examine the differential cytokine gene expressions of macrophages in response to two types of clinical strains of Shigella flexneri 2a (S. flexneri 2a) isolated from patients admitted in Hospital Universiti Sains Malaysia, Kelantan, Malaysia. THP-1-derived macrophages, as the model of human macrophages, were infected separately with S. flexneri 2a mild (SH062) and virulence (SH057) strains for 6, 12, and 24 h, respectively. The gene expression level of inflammatory mediators was identified using real-time quantitative polymerase chain reaction (RT-qPCR). The production of nitric oxide (NO) by the macrophages was measured by using a commercialized NO assay kit. The ability of macrophages to kill the intracellular bacteria was assessed by intracellular killing assay. Induction of tumor necrosis factor-alpha (TNFα), interleukin (IL)-1β, IL-6, IL-12, inducible NO synthase (iNOS), and NO, confirmed the pro-inflammatory reaction of the THP-1-derived macrophages in response to S. flexneri 2a, especially against the SH507 strain. The SH057 also induced a marked increase in the expression levels of the anti-inflammatory cytokine mRNAs at 12 h and 24 h post-infection. In the intracellular killing assay, both strains showed less viable, indicating the generation of pro-inflammatory cytokines in the presence of iNOS and NO was crucial in the stimulation of macrophages for the host defense against shigellosis. Transcription analysis of THP-1-derived macrophages in this study identifies differentially expressed cytokine genes that correlated with the virulence factor of S. flexneri 2a.

Interleukin 34 Serves as a Novel Molecular Adjuvant against Nocardia Seriolae Infection in Largemouth Bass (Micropterus Salmoides)

DNA vaccines have been widely employed in controlling viral and bacterial infections in mammals and teleost fish. Co-injection of molecular adjuvants, including chemokines, cytokines, and immune co-stimulatory molecules, is one of the potential strategies used to improve DNA vaccine efficacy. In mammals and teleost fish, interleukin-34 (IL-34) had been described as a multifunctional cytokine and its immunological role had been confirmed; however, the adjuvant capacity of IL-34 remains to be elucidated. In this study, IL-34 was identified in largemouth bass. A recombinant plasmid of IL-34 (pcIL-34) was constructed and co-administered with a DNA vaccine encoding hypoxic response protein 1 (Hrp1; pcHrp1) to evaluate the adjuvant capacity of pcIL-34 against Nocardia seriolae infection. Our results indicated that pcIL-34 co-injected with pcHrp1 not only triggered innate immunity and a specific antibody response, but also enhanced the mRNA expression level of immune-related genes encoding for cytokines, chemokines, and humoral and cell-mediated immunity. Moreover, pcIL-34 enhanced the protection of pcHrp1 against N. seriolae challenge and conferred the relative percent survival of 82.14%. Collectively, IL-34 is a promising adjuvant in a DNA vaccine against nocardiosis in fish.

Effects of skin abrasion in immersion challenge with Vibrio harveyi in Asian seabass Lates calcarifer fingerlings

Skin abrasions often occur in farmed fish following handling by labourers, injury by farm facilities, cannibalism and ectoparasites. Vibrio spp. are opportunistic pathogens that can invade host fish through damaged tissues and cause outbreaks of vibriosis. This study describes the effect of skin abrasions on the infectivity of V. harveyi using Asian seabass Lates calcarifer (Bloch, 1790) fingerlings as a case example and compares bacterial load and fish survival following immersion challenge with different doses. In total, 315 fish (6.67 ± 1.8 g) were divided into 3 treatments: skin abrasion followed by immersion infection, immersion infection only and an uninfected, uninjured control. Fish in the infection treatments were divided into 3 subgroups and exposed in triplicate to a 7 d immersion challenge with 106, 107 and 108 CFU ml-1 of live V. harveyi. No mortalities were observed in the control and immersion infection groups. However, fish in the skin abrasion treatment group that were infected with 108 CFU ml-1 of live V. harveyi showed signs of progressing disease throughout the experiment, which resulted in mortalities. Significantly higher bacterial loads (p < 0.05) were recorded in the intestine, liver and gills of the fish in this group. Fish in the skin abrasion treatment that were exposed to 107 and 108 CFU ml-1 of V. harveyi showed 100% mortality by Days 5 and 4, respectively. These findings confirm that skin injuries increase the susceptibility of seabass fingerlings to V. harveyi infection.

Polydopamine -aminoglycoside nanoconjugates: Synthesis, characterization, antimicrobial evaluation and cytocompatibility

Development of nanoparticle- and self-assembled nanomaterial-based therapeutics has become a rapidly growing area in the field of nanotechnology. One of the natural compounds, dopamine, presents as a neurotransmitter in the human brain serving as a messenger and deals with the behavioural responses, has provided an ideal platform through self-polymerization under aerobic conditions leading to the formation of a beneficial organic biopolymer, polydopamine (PDA). This polymer provides sufficient reactive functionalities, which can further be use to attach amine- or thiol-containing ligands to obtain conjugates. In the present study, self-polymerized polydopamine nanoparticles have been synthesized and tethered to aminoglycosides (AGs: Gentamicin, Kanamycin and Neomycin) through amino moieties to obtain PDA-AG nanoconjugates. These nanoconjugates are characterized by physicochemical techniques and evaluated for their antimicrobial potency against various bacterial strains including resistant ones. Simultaneously, cytocompatibility was also assessed for PDA-AG nanoconjugates. Of these three nanoconjugates (PDA-Gentamicin, PDA-Kanamycin and PDA-Neomycin), PDA-Kanamycin (PDA-K) nanoconjugate exhibited the highest activity against potent pathogens, least toxicity in human embryonic kidney (HEK 293) cells and intense toxic effects on human glioblastoma (U87) cells. Together, these results advocate the promising potential of these nanoconjugates to be used as potent antimicrobials in future applications.

Assessment of the immunogenicity and protective efficiency of a novel dual-promoter DNA vaccine, harboring SAG1 and GRA7 genes, from RH strain of Toxoplasma gondii in BALB/c mice

BACKGROUND

Toxoplasmosis, a protozoan parasitic disease caused by Toxoplasma gondii, has been a serious human and veterinary medicine problem with global distribution. In the current study, we assessed immunogenicity and protective efficiency of a novel dual-promoter DNA vaccine, harboring SAG1 and GRA7 genes, from RH strain of Toxoplasma gondii (T. gondii) with or without CpG-ODN as adjuvant in a murine model.

METHODS

BALB/c mice were immunized intramuscularly with pVitro-SAG1-GRA7 alone and pVitro-SAG1-GRA7 with CpG-ODN three times at three-week intervals. Enzyme-linked immunosorbent assay (ELISA) was used to assess total IgG, IgG1 and IgG2a antibodies and gamma interferon (IFN-γ) and interleukin-10 (IL-10) cytokines in mice sera. Four weeks post final vaccination, MTT assay and lethal challenge-infection with 1×103 tachyzoites of T. gondii RH strain were carried out to assess stimulation index (SI) and mice survival time, respectively.

RESULTS

The IgG levels in mice immunized with multicomponent vaccines, including pVitro-SAG1-GRA7 alone and pVitro-SAG1-GRA7 with CpG-ODN, were significantly higher than those in control mice or single-gene DNA-vaccinated ones (P<0.05). Furthermore, level of IgG2a in mice receiving pVitro-SAG1-GRA7 with CpG-ODN was significantly higher than that in mice receiving pVitro-SAG1-GRA7 alone (P<0.05). The Toxoplasma lysate antigen (TLA)-stimulated lymphocytes from pVitro-SAG1-GRA7 with CpG-ODN group responded more dramatically than those from control groups or single-gene DNA-vaccinated groups (P<0.001). The pVitro-SAG1-GRA7 with CpG-ODN-vaccinated mice developed high levels of IgG2a and IFN-γ (P<0.001) and low levels of IgG1 and IL-10, compared to control groups, suggesting a modulated immune response type Th1. In addition, survival time of the mice immunized with pVitro-SAG1-GRA7 with CpG-ODN was significantly extended, compared to controls (P<0.05); however, all mice died.

CONCLUSION

The multivalent pVitro-SAG1-GRA7 DNA vaccine with CpG-ODN adjuvant is a promising vaccine candidate against toxoplasmosis.

New insights into the molecular physiology of sulfoxide reduction in bacteria

Sulfoxides occur in biology as products of the S-oxygenation of small molecules as well as in peptides and proteins and their formation is often associated with oxidative stress and can affect biological function. In bacteria, sulfoxide damage can be reversed by different types of enzymes. Thioredoxin-dependent peptide methionine sulfoxide reductases (MSR proteins) repair oxidized methionine residues and are found in all Domains of life. In bacteria MSR proteins are often found in the cytoplasm but in some bacteria, including pathogenic Neisseria, Streptococci, and Haemophilus they are extracytoplasmic. Mutants lacking MSR proteins are often sensitive to oxidative stress and in pathogens exhibit decreased virulence as indicated by reduced survival in host cell or animal model systems. Molybdenum enzymes are also known to reduce S-oxides and traditionally their physiological role was considered to be in anaerobic respiration using dimethylsulfoxide (DMSO) as an electron acceptor. However, it now appears that some enzymes (MtsZ) of the DMSO reductase family of Mo enzymes use methionine sulfoxide as preferred physiological substrate and thus may be involved in scavenging/recycling of this amino acid. Similarly, an enzyme (MsrP/YedY) of the sulfite oxidase family of Mo enzymes has been shown to be involved in repair of methionine sulfoxides in periplasmic proteins. Again, some mutants deficient in Mo-dependent sulfoxide reductases exhibit reduced virulence, and there is evidence that these Mo enzymes and some MSR systems are induced by hypochlorite produced by the innate immune system. This review describes recent advances in the understanding of the molecular microbiology of MSR systems and the broadening of the role of Mo-dependent sulfoxide reductase to encompass functions beyond anaerobic respiration.

Interleukin 1 alpha (IL-1α) restricts Brucella abortus 544 survival through promoting lysosomal-mediated killing and NO production in macrophages

The interleukin-1 (IL-1) family of cytokines, particularly IL-1α and IL-1β, are potent regulators of innate immunity that play key roles in host defense against infection, hence we evaluated the role of these cytokines in the control of brucellosis within RAW 264.7 cells. Marked expression and secretion of IL-1α and IL-1β were observed during Brucella infection in macrophages. Blocking of IL-1α and IL-1β reduced induction of IL-10, IL-1β and TNF, and IL-6 and TNF, respectively. However, interference of IL-1α and not IL-1β signaling notably augmented susceptibility of macrophages to Brucella infection which indicates that IL-1α is required for a downstream signaling cascade of innate immunity for efficient clearance of Brucella. This protection requires binding to interleukin-1 receptor (IL-1R) mediated by myeloid differentiation factor 88 (MyD88) signaling and associated with increased lysosomal-mediated killing and nitric oxide (NO) production. Expression of pro-inflammatory cytokines was observed to be mediated via NF-κB-p50, HIF-1α and CEBPA, but negatively controlled by CEBPB while transcription of some important phagolysosomal genes was regulated via CEBPA and c-Jun which indicates the important role of these transcription factors in the control of Brucella infection in macrophages via IL-1α signaling pathway.

NK-4 exerts selective regulatory effects on the activation and function of allergy-related Th2 cells

NK-4 is the main component of the antiallergic drug Lumin, which has been in popular usage since the early 1950s. In this study, we examined whether NK-4 exerts a regulatory effect on the activation and effector function of Th2 cells. NK-4 inhibited IL-4 production by anti-CD3ε mAb-stimulated BALB/c mouse spleen cells, whereas NK-4 had little effect on IFN-γ production. IL-4 and IL-5 secretion by anti-CD3ε mAb- or antigen-stimulated Th2 cells (D10.G4.1) was abrogated by NK-4 without affecting cell numbers, whereas IFN-γ secretion by activated Th1 cells was unchanged. Mechanistic analysis revealed that NK-4 inhibited mRNA expression of the Th2-associated transcription factors GATA-3 and NFATc1 in anti-CD3ε mAb-stimulated D10.G4.1 cells. Regarding the regulation of Th2 cell effector functions, NK-4 inhibited the secretion of eotaxin and thymus and activation-regulated chemokine (TARC) by normal human dermal fibroblasts in response to IL-4 and/or TNF-α. NK-4 achieved TARC attenuation comparable to what is observed with suplatast tosilate, an antiallergic drug that selectively inhibits Th2 cytokine production, at 14-fold lower concentrations of suplatast tosilate. Dexamethasone increased TARC production by 2.2- to 2.6-fold of control cultures. NK-4 successfully inhibited the STAT6 signaling pathway, suggesting a potential mechanism for down-regulating chemokines expression. In addition, NK-4 abrogated IL-4-driven modulation of cytokine production profile in human monocytic THP-1 cells from proinflammatory to anti-inflammatory response, as seen in the inverted ratio of TNF-α to IL-10 produced in response to LPS. These results suggest that NK-4 could prevent IL-4-driven polarization to alternatively activated macrophages, which are proposed to have pathogenic roles in allergic asthma. The importance of Th2 cytokines and chemokines in the development and progression of type 2 inflammatory disorders has been highlighted by recent advance in our understanding the immunological mechanism underlying allergic disease. Our results support the use of NK-4 as a reasonable therapeutic option to alleviate Th2-mediated allergic inflammation.

Effects of priming with cytokines on intracellular survival and replication of Rhodococcus equi in equine macrophages

Rhodococcus equi is a common cause of pneumonia in foals and an opportunistic pathogen in immunosuppressed people. The ability of R. equi to survive and replicate in macrophages is the basis of its pathogenicity. Limited knowledge about the role of cytokines in host defense against R. equi comes from studies in mice and the role of cytokines in intracellular survival of R. equi in equine macrophages is unknown. The objectives of this study were to determine the effect of priming with interferon (IFN)-γ, interleukin (IL)-1β, IL-4, IL-6, IL-10, or tumor necrosis factor (TNF)-α at various concentrations on intracellular survival of virulent R. equi in equine monocyte-derived macrophages (MDM), and to determine the effects of various combinations of the same cytokines on intracellular survival of R. equi. MDM from 10 adult horses were primed with recombinant equine cytokines at doubling concentrations ranging from 25 to 200 ng/mL prior to infection with virulent R. equi. Priming with IFN-γ, TNF-α, or IL-6 significantly decreased intracellular replication of R. equi compared to unprimed monolayers. In contrast, priming with IL-10 or IL-1β significantly increased intracellular replication of R. equi. Pairwise combinations of the cytokines listed above did not results in synergism or antagonism. This study demonstrated that IFN-γ, TNF-α, or IL-6 improved equine MDM function against R. equi whereas IL-1β or IL-10 were detrimental.

Nitric oxide enhanced the growth of an obligated intracellular bacterium Orientia tsutsugamushi in murine macrophages

Orientia tsutsugamushi is the causative agent of scrub typhus. It is an obligate intracellular bacterium that grows only in eukaryotic cells. Macrophages play an important role in innate immunity by surveilling the human body for pathogens. In present study, it was demonstrated that O. tsutsugamushi propagated well in LPS-activated RAW 264.7 macrophages, but not in non-activated macrophages. In LPS-activated macrophages, the expression of Nos2, which encodes the inducible nitric oxide (NO) synthase (iNOS), was highly upregulated compared to those in non-activated macrophages. Parallel to this upregulation, high NO production was observed in LPS-activated macrophages. Transmissible electron microscopy showed that O. tsutsugamushi replicated in the cytosol of macrophages. Thus, O. tsutsugamushi was thought to escape the phagosomes at an early stage of phagosome maturation to avoid the bactericidal effect of NO. Furthermore, O. tsutsugamushi growth was enhanced in NO donor-supplied RAW 264.7 macrophages, as well as in LPS-activated, but not in non-activated macrophages. Consequently, these results suggested that NO was rather essential for enhancing the replication of O. tsutsugamushi in RAW 264.7 macrophages, despite the typically detrimental effects of NO against intracellular pathogens. In the present study, NO was suggested to activate specific pathways to enhance the growth of O. tsutsugamushi.

Persisting Rickettsia typhi Causes Fatal Central Nervous System Inflammation

Rickettsioses are emerging febrile diseases caused by obligate intracellular bacteria belonging to the family Rickettsiaceae. Rickettsia typhi belongs to the typhus group (TG) of this family and is the causative agent of endemic typhus, a disease that can be fatal. In the present study, we analyzed the course of R. typhi infection in C57BL/6 RAG1(-/-) mice. Although these mice lack adaptive immunity, they developed only mild and temporary symptoms of disease and survived R. typhi infection for a long period of time. To our surprise, 3 to 4 months after infection, C57BL/6 RAG1(-/-) mice suddenly developed lethal neurological disorders. Analysis of these mice at the time of death revealed high bacterial loads, predominantly in the brain. This was accompanied by a massive expansion of microglia and by neuronal cell death. Furthermore, high numbers of infiltrating CD11b(+) macrophages were detectable in the brain. In contrast to the microglia, these cells harbored R. typhi and showed an inflammatory phenotype, as indicated by inducible nitric oxide synthase (iNOS) expression, which was not observed in the periphery. Having shown that R. typhi persists in immunocompromised mice, we finally asked whether the bacteria are also able to persist in resistant C57BL/6 and BALB/c wild-type mice. Indeed, R. typhi could be recultivated from lung, spleen, and brain tissues from both strains even up to 1 year after infection. This is the first report demonstrating persistence and reappearance of R. typhi, mainly restricted to the central nervous system in immunocompromised mice.

Interferon-γ Is a Crucial Activator of Early Host Immune Defense against Mycobacterium ulcerans Infection in Mice

Buruli ulcer (BU), caused by infection with Mycobacterium ulcerans, is a chronic necrotizing human skin disease associated with the production of the cytotoxic macrolide exotoxin mycolactone. Despite extensive research, the type of immune responses elicited against this pathogen and the effector functions conferring protection against BU are not yet fully understood. While histopathological analyses of advanced BU lesions have demonstrated a mainly extracellular localization of the toxin producing acid fast bacilli, there is growing evidence for an early intra-macrophage growth phase of M. ulcerans. This has led us to investigate whether interferon-γ might play an important role in containing M. ulcerans infections. In an experimental Buruli ulcer mouse model we found that interferon-γ is indeed a critical regulator of early host immune defense against M. ulcerans infections. Interferon-γ knockout mice displayed a faster progression of the infection compared to wild-type mice. This accelerated progression was reflected in faster and more extensive tissue necrosis and oedema formation, as well as in a significantly higher bacterial burden after five weeks of infection, indicating that mice lacking interferon-γ have a reduced capacity to kill intracellular bacilli during the early intra-macrophage growth phase of M. ulcerans. This data demonstrates a prominent role of interferon-γ in early defense against M. ulcerans infection and supports the view that concepts for vaccine development against tuberculosis may also be valid for BU.

Mycobacterium ulcerans is the causative agent of Buruli ulcer (BU), a slow progressing ulcerative skin disease. The mode of transmission of M. ulcerans remains unknown and only little is known about the early stages of the disease and the nature of protective immune responses against this pathogen. Given the increasing evidence for an early intracellular growth phase of M. ulcerans, we aimed at evaluating the impact of cell-mediated immunity for immunological defense against M. ulcerans infections. By comparing wild-type and interferon-γ-deficient mice in a BU mouse model, we could demonstrate that interferon-γ is a critical regulator of early host immune defense against M. ulcerans infections, indicative for an important role of early intracellular multiplication of the pathogen. In mice lacking interferon-γ the bacterial burden increased faster, resulting in accelerated pathogenesis. The observed differences between the two mouse strains were most likely due to differences in the capacity of macrophages to kill intracellular bacilli during the early stages of infection.

The Rising Dominance of Shigella sonnei: An Intercontinental Shift in the Etiology of Bacillary Dysentery

Shigellosis is the major global cause of dysentery. Shigella sonnei, which has historically been more commonly isolated in developed countries, is undergoing an unprecedented expansion across industrializing regions in Asia, Latin America, and the Middle East. The precise reasons underpinning the epidemiological distribution of the various Shigella species and this global surge in S. sonnei are unclear but may be due to three major environmental pressures. First, natural passive immunization with the bacterium Plesiomonas shigelloides is hypothesized to protect populations with poor water supplies against S. sonnei. Improving the quality of drinking water supplies would, therefore, result in a reduction in P. shigelloides exposure and a subsequent reduction in environmental immunization against S. sonnei. Secondly, the ubiquitous amoeba species Acanthamoeba castellanii has been shown to phagocytize S. sonnei efficiently and symbiotically, thus allowing the bacteria access to a protected niche in which to withstand chlorination and other harsh environmental conditions in temperate countries. Finally, S. sonnei has emerged from Europe and begun to spread globally only relatively recently. A strong selective pressure from localized antimicrobial use additionally appears to have had a dramatic impact on the evolution of the S. sonnei population. We hypothesize that S. sonnei, which exhibits an exceptional ability to acquire antimicrobial resistance genes from commensal and pathogenic bacteria, has a competitive advantage over S. flexneri, particularly in areas with poorly regulated antimicrobial use. Continuing improvement in the quality of global drinking water supplies alongside the rapid development of antimicrobial resistance predicts the burden and international distribution of S. sonnei will only continue to grow. An effective vaccine against S. sonnei is overdue and may become one of our only weapons against this increasingly dominant and problematic gastrointestinal pathogen.

Type I interferon contributes to noncanonical inflammasome activation, mediates immunopathology, and impairs protective immunity during fatal infection with lipopolysaccharide-negative ehrlichiae

Ehrlichia species are intracellular bacteria that cause fatal ehrlichiosis, mimicking toxic shock syndrome in humans and mice. Virulent ehrlichiae induce inflammasome activation leading to caspase-1 cleavage and IL-18 secretion, which contribute to development of fatal ehrlichiosis. We show that fatal infection triggers expression of inflammasome components, activates caspase-1 and caspase-11, and induces host-cell death and secretion of IL-1β, IL-1α, and type I interferon (IFN-I). Wild-type and Casp1(-/-) mice were highly susceptible to fatal ehrlichiosis, had overwhelming infection, and developed extensive tissue injury. Nlrp3(-/-) mice effectively cleared ehrlichiae, but displayed acute mortality and developed liver injury similar to wild-type mice. By contrast, Ifnar1(-/-) mice were highly resistant to fatal disease and had lower bacterial burden, attenuated pathology, and prolonged survival. Ifnar1(-/-) mice also had improved protective immune responses mediated by IFN-γ and CD4(+) Th1 and natural killer T cells, with lower IL-10 secretion by T cells. Importantly, heightened resistance of Ifnar1(-/-) mice correlated with improved autophagosome processing, and attenuated noncanonical inflammasome activation indicated by decreased activation of caspase-11 and decreased IL-1β, compared with other groups. Our findings demonstrate that IFN-I signaling promotes host susceptibility to fatal ehrlichiosis, because it mediates ehrlichia-induced immunopathology and supports bacterial replication, perhaps via activation of noncanonical inflammasomes, reduced autophagy, and suppression of protective CD4(+) T cells and natural killer T-cell responses against ehrlichiae.

Host immune responses after hypoxic reactivation of IFN-γ induced persistent Chlamydia trachomatis infection

Genital tract infections with Chlamydia trachomatis (C. trachomatis) are the most frequent sexually transmitted disease worldwide. Severe clinical sequelae such as pelvic inflammatory disease (PID), tubal occlusion, and tubal infertility are linked to inflammatory processes of chronically infected tissues. The oxygen concentrations in the female urogenital tract are physiologically low and further diminished (0.5–5% O₂, hypoxia) during an ongoing inflammation. However, little is known about the effect of a low oxygen environment on genital C. trachomatis infections. In this study, we investigated the host immune responses during reactivation of IFN-γ induced persistent C. trachomatis infection under hypoxia. For this purpose, the activation of the MAP-kinases p44/42 and p38 as well as the induction of the pro-inflammatory cytokines IL-1β, IL-6, IL-8, and MCP-1 were analyzed. Upon hypoxic reactivation of IFN-γ induced persistent C. trachomatis infection, the phosphorylation of the p44/42 but not of the p38 MAP-kinase was significantly diminished compared to IFN-γ induced chlamydial persistence under normoxic condition. In addition, significantly reduced IL-6 and IL-8 mRNA expression levels were observed for reactivated Chlamydiae under hypoxia compared to a persistent chlamydial infection under normoxia. Our findings indicate that hypoxia not only reactivates IFN-γ induced persistent C. trachomatis infections resulting in increased bacterial growth and progeny but also dampens inflammatory host immune signaling responses that are normally observed in a normoxic environment.

Infection of human monocytes by Chlamydia pneumoniae and Chlamydia trachomatis: an in vitro comparative study

Background

An increasing number of studies suggest that chlamydiae can infect immune cells. The altered immune cell function could contribute to the progression of several chronic inflammatory diseases.

The aim of this study was to comparatively evaluate Chlamydia pneumoniae (CP) and Chlamydia trachomatis (CT) interactions with in vitro infected human blood monocytes.

Results

Fresh isolated monocytes were infected with viable CP and CT elementary bodies and infectivity was evaluated by recultivating disrupted monocytes in permissive epithelial cells.

The production of reactive oxygen and nitrogen species was studied in the presence of specific fluorescent probes. Moreover, TNF-α, INF-α, INF-β and INF-γ gene expression was determined.

CT clearance from monocytes was complete at any time points after infection, while CP was able to survive up to 48 hours after infection. When NADPH oxydase or nitric oxide synthase inhibitors were used, CT infectivity in monocytes was restored, even if at low level, and CT recovery’s rate was comparable to CP one.

CT-infected monocytes produced significantly higher levels of reactive species compared with CP-infected monocytes, at very early time points after infection. In the same meanwhile, TNF-α and INF-γ gene expression was significantly increased in CT-infected monocytes.

Conclusions

Our data confirm that CP, but not CT, is able to survive in infected monocytes up to 48 hours post-infection. The delay in reactive species and cytokines production by CP-infected monocytes seems to be crucial for CP survival.

Intracellular infections in Drosophila melanogaster: host defense and mechanisms of pathogenesis

The fruit-fly Drosophila melanogaster has emerged as a powerful model to study innate immunity against intracellular pathogens. To combat infection, the fly relies on multiple lines of defense, many of which are shared with mammals and arthropod vectors of human diseases. In addition to conserved immune pathways, the ease of performing sophisticated genetic screens has allowed the identification of novel host immune factors and novel pathogen virulence factors. Recently, some groups have exploited this to simultaneously analyze the host and pathogen genetics of intracellular infection. This review aims to unravel the Drosophila immune response against intracellular pathogens, highlighting recent discoveries.

Toxoplasma gondii: immune response and protective efficacy induced by ROP16/GRA7 multicomponent DNA vaccine with a genetic adjuvant B7-2

Toxoplasma gondii infection occurs commonly in humans and other warm-blooded animals. Its serious impact on public health and livestock sectors makes the development of an effective vaccine particularly important. In the current study, we constructed a multiantigenic DNA vaccine expressing ROP16 and GRA7 of T. gondii and evaluated the protective efficacy of these two fragments with or without a plasmid encoding murine costimulatory molecule B7-2. These recombinant eukaryotic expression plasmids were termed pROP16, pGRA7, pROP16-GRA7 and pB7-2, respectively. After intramuscular immunization in Kunming mice, we assessed the immune response using cytokine and antibody determinations, T lymphocyte subsets analysis, and the survival times of mice post acute T. gondii challenge. The results showed that mice immunized with the multiantigenic DNA vaccine pROP16-GRA7 gained higher levels of IgG titers and IgG2a subclass titers, production of IFN-γ, percentage of CD8+ T cells and median survival times against the acute infection of T. gondii compared with those of mice administered with pROP16 or pGRA7 and those in control groups. Moreover, the adjuvant pB7-2 formulated with DNA vaccine boosted these humoral and cellular (Th1, CD8+ T cell) immune responses. Therefore, it might be a promising genetic adjuvant to DNA vaccine against T. gondii for further investigation.

Characterizing virulence-specific perturbations in the mitochondrial function of macrophages infected with Mycobacterium tuberculosis

To probe how the pathogen Mycobacterium tuberculosis controls host cellular death pathways, we compared mitochondrial responses in human macrophages infected either with the avirulent mycobacterial strain H37Ra, or its virulent counterpart H37Rv. Following H37Ra infection, induction of the apoptotic response was foreshadowed by the early suppression of stress-induced mitochondrial activity. In contrast, mitochondria in H37Rv-infected cells displayed robust activity with increased membrane potential and ATP synthesis. An examination of the mitochondrial proteome revealed that attenuation of mitochondrial function was also coupled with the vigorous activation of bactericidal mechanisms in H37Ra-infected cells. In contrast, augmentation of mitochondrial activity by H37Rv enabled manipulation of host cellular mechanisms to inhibit apoptosis on the one hand, while ensuring fortification against anti-microbial pathways on the other. These results thus provide novel insights into the molecular interplay that facilitates adaptation of virulent mycobacteria within the hostile intracellular milieu of the host macrophage.

BAY 41-2272, a soluble guanylate cyclase agonist, activates human mononuclear phagocytes

BACKGROUND AND PURPOSE

Phagocyte function is critical for host defense against infections. Defects in phagocytic function lead to several primary immunodeficiencies characterized by early onset of recurrent and severe infections. In this work, we further investigated the effects of BAY 41-2272, a soluble guanylate cyclase (sGC) agonist, on the activation of human peripheral blood monocytes (PBM) and THP-1 cells.

EXPERIMENTAL APPROACH

THP-1 cells and PBM viability was evaluated by methylthiazoletetrazolium assay; reactive oxygen species production by lucigenin chemiluminescence; gene and protein expression of NAPDH oxidase components by qRT-PCR and Western blot analysis, respectively; phagocytosis and microbicidal activity by co-incubation, respectively, with zymosan and Escherichia coli; and cytokine release by elisa.

KEY RESULTS

BAY 41-2272, compared with the untreated group, increased spreading of monocytes by at least 35%, superoxide production by at least 50%, and gp91(PHOX) and p67(PHOX) gene expression 20 to 40 times, in both PBM and THP-1 cells. BAY 41-2272 also augmented phagocytosis of zymosan particles threefold compared with control, doubled microbicidal activity against E. coli and enhanced the release of TNF-α and IL-12p70 by both PBM and THP-1 cells. Finally, by inhibiting sGC with ODQ, we showed that BAY 41-2272-induced superoxide production and phagocytosis is not dependent exclusively on sGC activation.

CONCLUSIONS AND IMPLICATIONS

In addition to its ability to induce vasorelaxation and its potential application for therapy of vascular diseases, BAY 41-2272 was shown to activate human mononuclear phagocytes. Hence, it is a novel pro-inflammatory drug that may be useful for controlling infections in the immunocompromised host.

Coxiella burnetii induces apoptosis during early stage infection via a caspase-independent pathway in human monocytic THP-1 cells

The ability of Coxiella burnetii to modulate host cell death may be a critical factor in disease development. In this study, human monocytic THP-1 cells were used to examine the ability of C. burnetii Nine Mile phase II (NMII) to modulate apoptotic signaling. Typical apoptotic cell morphological changes and DNA fragmentation were detected in NMII infected cells at an early stage of infection. FACS analysis using Annexin-V-PI double staining showed the induction of a significant number of apoptotic cells at an early stage of NMII infection. Double staining of apoptotic cell DNA and intracellular C. burnetii indicates that NMII infected cells undergoing apoptosis. Interestingly, caspase-3 was not cleaved in NMII infected cells and the caspase-inhibitor Z-VAD-fmk did not prevent NMII induced apoptosis. Surprisingly, the caspase-3 downstream substrate PARP was cleaved in NMII infected cells. These results suggest that NMII induces apoptosis during an early stage of infection through a caspase-independent pathway in THP-1 cells. In addition, NMII-infected monocytes were unable to prevent exogenous staurosporine-induced apoptotic death. Western blot analysis indicated that NMII infection induced the translocation of AIF from mitochondria into the nucleus. Cytochrome c release and cytosol-to-mitochondrial translocation of the pore-forming protein Bax in NMII infected cells occurred at 24 h post infection. These data suggest that NMII infection induced caspase-independent apoptosis through a mechanism involving cytochrome c release, cytosol-to-mitochondrial translocation of Bax and nuclear translocation of AIF in THP-1 monocytes. Furthermore, NMII infection increased TNF-α production and neutralization of TNF-α in NMII infected cells partially blocked PARP cleavage, suggesting TNF-α may play a role in the upstream signaling involved in NMII induced apoptosis. Antibiotic inhibition of C. burnetii RNA synthesis blocked NMII infection-induced PARP activation. These results suggest that both intracellular C. burnetii replication and secreted TNF-α contribute to NMII infection-triggered apoptosis during an early stage of infection.

Role of Mycobacterium tuberculosis pknD in the pathogenesis of central nervous system tuberculosis

BACKGROUND

Central nervous system disease is the most serious form of tuberculosis, and is associated with high mortality and severe neurological sequelae. Though recent clinical reports suggest an association of distinct Mycobacterium tuberculosis strains with central nervous system disease, the microbial virulence factors required have not been described previously.

RESULTS

We screened 398 unique M. tuberculosis mutants in guinea pigs to identify genes required for central nervous system tuberculosis. We found M. tuberculosis pknD (Rv0931c) to be required for central nervous system disease. These findings were central nervous system tissue-specific and were not observed in lung tissues. We demonstrated that pknD is required for invasion of brain endothelia (primary components of the blood-brain barrier protecting the central nervous system), but not macrophages, lung epithelia, or other endothelia. M. tuberculosis pknD encodes a "eukaryotic-like" serine-threonine protein kinase, with a predicted intracellular kinase and an extracellular (sensor) domain. Using confocal microscopy and flow cytometry we demonstrated that the M. tuberculosis PknD sensor is sufficient to trigger invasion of brain endothelia, a process which was neutralized by specific antiserum.

CONCLUSIONS

Our findings demonstrate a novel in vivo role for M. tuberculosis pknD and represent an important mechanism for bacterial invasion and virulence in central nervous system tuberculosis, a devastating and understudied disease primarily affecting young children.

Inflammatory monocytes and neutrophils are licensed to kill during memory responses in vivo

Immunological memory is a hallmark of B and T lymphocytes that have undergone a previous encounter with a given antigen. It is assumed that memory cells mediate better protection of the host upon re-infection because of improved effector functions such as antibody production, cytotoxic activity and cytokine secretion. In contrast to cells of the adaptive immune system, innate immune cells are believed to exhibit a comparable functional effector response each time the same pathogen is encountered. Here, using mice infected by the intracellular bacterium Listeria monocytogenes, we show that during a recall bacterial infection, the chemokine CCL3 secreted by memory CD8⁺ T cells drives drastic modifications of the functional properties of several populations of phagocytes. We found that inflammatory ly6C⁺ monocytes and neutrophils largely mediated memory CD8⁺ T cell bacteriocidal activity by producing increased levels of reactive oxygen species (ROS), augmenting the pH of their phagosomes and inducing antimicrobial autophagy. These events allowed an extremely rapid control of bacterial growth in vivo and accounted for protective immunity. Therefore, our results provide evidence that cytotoxic memory CD8⁺ T cells can license distinct antimicrobial effector mechanisms of innate cells to efficiently clear pathogens.

The immune system comprises white blood cells that belong to the innate or the adaptive immune arms. Adaptive immune cells such as T and B lymphocytes can give rise to memory cells which mediate long-lived immunity against pathogens. During a recall infection, innate immune phagocytic cells such as monocytes and neutrophils can be critical to kill microbial pathogens inside infected tissues. Whether and how such antimicrobial features of phagocytic cells of the innate immune system are modulated during a memory response in a vaccinated host is not known. The present report shows that cytolytic memory T lymphocytes, an important subpopulation of effector T cells, can drastically enhance the functional killing capacities of monocytes and neutrophils for optimized pathogen clearance from infected hosts. These phagocytes exhibit enhanced generation of oxidative burst, increased phagosomal pH and autophagy, three mechanisms that lead to intracellular pathogen death. This result is important since it suggests that modulating innate immune cells effector activities could be an interesting strategy to enhance vaccine efficacy.

The biological basis of severe outcomes in Anaplasma phagocytophilum infection

Anaplasma phagocytophilum causes granulocytic anaplasmosis, an acute disease in humans that is also often subclinical. However, 36% are hospitalized, 7% need intensive care, and the case fatality rate is 0.6%. The biological basis for severe disease is not understood. Despite A. phagocytophilum's mechanisms to subvert neutrophil antimicrobial responses, whether these mechanisms lead to disease is unclear. In animals, inflammatory lesions track with IFNγ and IL-10 expression and infection of Ifng(-/-) mice leads to increased pathogen load but inhibition of inflammation. Suppression of STAT signaling in horses impacts IL-10 and IFN-γ expression, and also suppresses disease severity. Similar inhibition of inflammation with infection of NKT-deficient mice suggests that innate immune responses are key for disease. With severe disease, tissues can demonstrate hemophagocytosis, and measures of macrophage activation/hemophagocytic syndromes (MAS/HPS) support the concept of human granulocytic anaplasmosis as an immunopathologic disease. MAS/HPS are related to defective cytotoxic lymphocytes that ordinarily diminish inflammation. Pilot studies in mice show cytotoxic lymphocyte activation with A. phagocytophilum infection, yet suppression of cytotoxic responses from both NKT and CD8 cells, consistent with the development of MAS/HPS. Whether severity relates to microbial factors or genetically determined diversity in human immune and inflammatory response needs more investigation.

OsmC proteins of Mycobacterium tuberculosis and Mycobacterium smegmatis protect against organic hydroperoxide stress

Bacterial antioxidants play a critical role in the detoxification of endogenously and host derived oxidative radicals during host-pathogen interactions. Recently, the osmotically induced bacterial protein C (OsmC) is included in the antioxidant category of enzymes as it shows structural and functional relationships with organic hydroperoxide reductase (Ohr) enzyme. A copy of the gene encoding OsmC is conserved across mycobacterial species, including Mycobacterium tuberculosis (Rv2923c) and Mycobacterium smegmatis (MSMEG2421), but its role in protecting these species against oxidative stress is unknown. To determine the role of OsmC in mycobacterial oxidative stress, we overexpressed and purified OsmCs of M. tuberculosis and M. smegmatis and assessed their ability to reduce peroxide substrates like hydrogen peroxide (H(2)O(2)), cumene hydroperoxide (CHP) and t-butyl hydroperoxide (t-BHP) in Ferrous Ion Oxidation in Xylenol (FOX) assay. This revealed that OsmCs from both species were capable of reducing both inorganic (H(2)O(2)) and organic (CHP and t-BHP) peroxides. Further, an M. smegmatis mutant (MS∆osmC) deficient in OsmC exhibited reduced reduction of CHP and t-BHP than the parental wild type strain, indicating that OsmC protein contributes significantly for the total peroxide reductase activity of mycobacteria. The MS∆osmC strain was also sensitive to organic hydroperoxides, which could be reversed by complementing with a plasmid borne osmC. Plasmid borne osmC also increased the resistance of M. smegmatis wild type strain to isoniazid (INH) but at a relatively lower level than ahpC, an organic hydroperoxide reductase. These results suggest that OsmC plays an important role in peroxide metabolism and protecting mycobacteria against oxidative stress.

Interferon gamma activated macrophages kill mycobacteria by nitric oxide induced apoptosis

Mycobacterium tuberculosis is an intracellular pathogen of macrophages and escapes the macrophages' bactericidal effectors by interfering with phagosome-lysosome fusion. IFN-γ activation renders the macrophages capable of killing intracellular mycobacteria by overcoming the phagosome maturation block, nutrient deprivation and exposure to microbicidal effectors including nitric oxide (NO). While the importance about NO for the control of mycobacterial infection in murine macrophages is well documented, the underlying mechanism has not been revealed yet. In this study we show that IFN-γ induced apoptosis in mycobacteria-infected macrophages, which was strictly dependent on NO. Subsequently, NO-mediated apoptosis resulted in the killing of intracellular mycobacteria independent of autophagy. In fact, killing of mycobacteria was susceptible to the autophagy inhibitor 3-methyladenine (3-MA). However, 3-MA also suppressed NO production, which is an important off-target effect to be considered in autophagy studies using 3-MA. Inhibition of caspase 3/7 activation, as well as NO production, abolished apoptosis and elimination of mycobacteria by IFN-γ activated macrophages. In line with the finding that drug-induced apoptosis kills intracellular mycobacteria in the absence of NO, we identified NO-mediated apoptosis as a new defense mechanism of activated macrophages against M. tuberculosis.

The KdpD/KdpE two-component system of Photorhabdus asymbiotica promotes bacterial survival within M. sexta hemocytes

Many bacteria persist within phagocytes, deploying complex sets of tightly regulated virulence factors to manipulate and survive within host cells. So far, no single factor has been identified that is sufficient to allow intracellular persistence of an otherwise non-pathogenic bacterium. Here we report that the two-component KdpD/KdpE sensor kinase/response regulator of the insect and human pathogen Photorhabdus asymbiotica (Pa) is sufficient to allow a harmless laboratory strain of E. coli to resist phagocytic killing and persist within insect hemocytes, ultimately killing the insect. Screening of a cosmid library of Pa in E. coli by injection into the moth Manduca sexta, previously identified three overlapping clones which caused the insect to cease feeding and subsequently die. Transposon mutagenesis revealed a cosmid encoded kdp high affinity potassium pump regulon was responsible for this phenotype. Gentamycin protection assays and confocal microscopy revealed the cosmid clones were persisting inside insect hemocytes far longer than control bacteria. Cloning and expression of PakdpD/kdpE alone into E. coli recapitulated the phenotype. Bioassay results and transcriptional analysis of various E. coli kdp mutants harboring the Pa kdp genes confirmed that Pa KdpD/KdpE was able to induce the E. coli kdp pump structural genes in response to exposure to insect hemocytes but not blood plasma alone. The finding that Pa KdpD/KdpE can facilitate resistance of E. coli to phagocytic killing suggests a central role for potassium in this process, supporting previous work implicating potassium sensing in virulence of other bacteria and also in the normal process of protease killing of engulfed bacteria by neutrophils.

Acanthamoeba castellanii an environmental host for Shigella dysenteriae and Shigella sonnei

The interaction between Shigella dysenteriae or Shigella sonnei and Acanthamoeba castellanii was studied by viable counts, gentamicin assay and electron microscopy. The result showed that Shigella dysenteriae or Shigella sonnei grew and survived in the presence of amoebae for more than 3 weeks. Gentamicin assay showed that the Shigella were viable inside the Acanthamoeba castellanii which was confirmed by electron microscopy that showed the Shigella localized in the cytoplasm of the Acanthamoeba castellanii. In conclusion, the relationship between Shigella dysenteriae and Shigella sonnei with Acanthamoeba castellanii is symbiotic, and accordingly free-living amoebae may serve as a transmission reservoir for Shigella in water.

Methionine sulfoxide reductases and virulence of bacterial pathogens

Oxidation of methionine (Met) residues in proteins by reactive oxygen species and reactive nitrogen intermediates results in altered protein structures, which subsequently affect their functions. Oxidized Met (Met-O) residues are reduced to Met by the methionine sulfoxide reductase (Msr) system, which includes mainly MsrA and MsrB. MsrA and MsrB show no sequence and structural identity with each other but both reduce methionine sulfoxides. MsrA is specific to the reduction of methionine-S-sulfoxide, whereas MsrB is specific to the reduction of methionine-R-sulfoxide. Genes encoding the enzymes MsrA and MsrB exist in most living organisms including bacteria. In recent times, absence of these enzymes has been implicated in the virulence of bacterial pathogens. In particular, pathogens deficient in Msr have been reported to have reduced ability to adhere with eukaryotic cells, to survive inside hosts and to resist in vitro oxidative stress. Bacterial proteins that are susceptible to Met oxidation, in the absence of Msr, have also been identified. This review discusses the current knowledge on the role of Msr in bacterial virulence.

Differential interaction of dendritic cells with Rickettsia conorii: impact on host susceptibility to murine spotted fever rickettsiosis

Spotted fever group rickettsioses are emerging and reemerging infectious diseases, some of which are life-threatening. In order to understand how dendritic cells (DCs) contribute to the host resistance or susceptibility to rickettsial diseases, we first characterized the in vitro interaction of rickettsiae with bone marrow-derived DCs (BMDCs) from resistant C57BL/6 (B6) and susceptible C3H/HeN (C3H) mice. In contrast to the exclusively cytosolic localization within endothelial cells, rickettsiae efficiently entered and localized in both phagosomes and cytosol of BMDCs from both mouse strains. Rickettsia conorii-infected BMDCs from resistant mice harbored higher bacterial loads compared to C3H mice. R. conorii infection induced maturation of BMDCs from both mouse strains as judged by upregulated expression of classical major histocompatibility complex (MHC) and costimulatory molecules. Compared to C3H counterparts, B6 BMDCs exhibited higher expression levels of MHC class II and higher interleukin-12 (IL-12) p40 production upon rickettsial infection and were more potent in priming naïve CD4(+) T cells to produce gamma interferon. In vitro DC infection and T-cell priming studies suggested a delayed CD4(+) T-cell activation and suppressed Th1/Th2 cell development in C3H mice. The suppressive CD4(+) T-cell responses seen in C3H mice were associated with a high frequency of Foxp3(+) T regulatory cells promoted by syngeneic R. conorii-infected BMDCs in the presence of IL-2. These data suggest that rickettsiae can target DCs to stimulate a protective type 1 response in resistant hosts but suppressive adaptive immunity in susceptible hosts.

Infection in a dish: high-throughput analyses of bacterial pathogenesis

Diverse aspects of host-pathogen interactions have been studied using non-mammalian hosts such as Dictyostelium discoideum, Caenorhabditis elegans, Drosophila melanogaster and Danio rerio for more than 20 years. Over the past two years, the use of these model hosts to dissect bacterial virulence mechanisms has been expanded to include the important human pathogens Vibrio cholerae and Yersinia pestis. Innovative approaches using these alternative hosts have also been developed, enabling the isolation of new antimicrobials through screening large libraries of compounds in a C. elegans Enterococcus faecalis infection model. Host proteins required by Mycobacterium and Listeria during their invasion and intracellular growth have been uncovered using high-throughput dsRNA screens in a Drosophila cell culture system, and immune evasion mechanisms deployed by Pseudomonas aeruginosa during its infection of flies have been identified. Together, these reports further illustrate the potential and relevance of these non-mammalian hosts for modelling many facets of bacterial infection in mammals.

Lymph node hemophagocytosis in rickettsial diseases: a pathogenetic role for CD8 T lymphocytes in human monocytic ehrlichiosis (HME)?

BACKGROUND

Human monocytic ehrlichiosis (HME) and Rocky Mountain spotted fever (RMSF) are caused by Ehrlichia chaffeensis and Rickettsia rickettsii, respectively. The pathogenesis of RMSF relates to rickettsia-mediated vascular injury, but it is unclear in HME.

METHODS

To study histopathologic responses in the lymphatic system for correlates of immune injury, lymph nodes from patients with HME (n = 6) and RMSF (n = 5) were examined. H&E-stained lymph node tissues were examined for five histopathologic features, including hemophagocytosis, cellularity, necrosis, and vascular congestion and edema. The relative proportions of CD68 macrophages, CD8 and CD4 T lymphocytes, and CD20 B lymphocytes were evaluated by immunohistochemical staining.

RESULTS

Hemophagocytosis was similar in HME and RMSF, and was greater than in control cases (p = .015). Cellularity in HME was not different from controls, whereas RMSF lymph nodes were markedly less cellular (p < 0.002). E. chaffeensis-infected mononuclear phagocytes were infrequent compared to R. rickettsii-infected endothelial cells. More CD8 cells in lymph nodes were observed with HME (p < .001), but no quantitative differences in CD4 lymphocytes, macrophages, or B lymphocytes were identified.

CONCLUSION

Hemophagocytosis, CD8 T cell expansion, and the paucity of infected cells in HME, suggest that E. chaffeensis infection leads to macrophage activation and immune-mediated injury.

Phagocytosis and production of H2O2 by human peripheral blood mononuclear cells from patients with obstructive jaundice

BACKGROUND

The immune function is altered in jaundiced patients; here, the ability of their peripheral blood mononuclear cells to perform phagocytosis and to release H2O2 was analyzed.

METHODS

Cells from 53 patients before surgery for relief of cholestasis, from 38 patients 1 week and from 15 patients 2 weeks after surgery were separated and cultured for 1 h in the presence of phorbol myristate acetate. H2O2 release was evaluated colorimetrically and phagocytosis by the ingestion of Escherichia coli in vitro.

RESULTS

Before surgery for relief of cholestasis, the cells of the patients were unable to release H2O2, but, after surgery, an increasing percentage of patients had cells that were able to produce H2O2 (13% after 1 week; 33% after 2 weeks). This recovery did not correlate with bilirubinemia. When cultured for 1 week in the presence of normal or jaundiced plasma, regardless of collection time, cells of 12/12 patients released H2O2, but in lower levels if in the presence of jaundiced plasma. In contrast, H2O2 release by normal donor cells was enhanced in the presence of jaundiced plasma. Phagocytosis by cells of the patients was lower, but when present was associated with a significantly higher bactericidal activity.

CONCLUSION

These significant, but reversible alterations of monocyte function in jaundiced patients might contribute to their enhanced susceptibility to surgical complications.

RNA interference reveals a role for TLR2 and TLR3 in the recognition ofLeishmania donovani promastigotes by interferon–γ-primed macrophages

Leishmania donovani promastigotes evade the induction of a proinflammatory response during their invasion of naive macrophages. However, their entry into IFN-gamma-primed macrophages is accompanied by the secretion of nitric oxide (NO) and proinflammatory cytokines. In the present study, we addressed the hypothesis that priming with IFN-gamma induces the expression of a receptor that enables mouse macrophages to recognize L. donovani promastigotes. We observed that in IFN-gamma-primed macrophages, L. donovani promastigotes stimulated Interleukin-1 receptor-associated kinase-1 (IRAK-1) activity. We next showed that Toll-like receptor (TLR)3 is barely detectable in naive macrophages but is expressed in IFN-gamma-treated macrophages. Silencing of TLR3, TLR2, IRAK-1 and myeloid differentiation factor 88 (MyD88) expression by RNA interference revealed that both TLR are involved in the secretion of NO and TNF-alpha induced by L. donovani promastigotes. Using L. donovani mutants, we showed that TLR2-mediated responses are dependent on Galbeta1,4Manalpha-PO(4)-containing phosphoglycans, whereas TLR3-mediated responses are independent of these glycoconjugates. Furthermore, our data indicate a participation of TLR2 and TLR3 in the phagocytosis of L. donovani promastigotes and a role for TLR3 in the leishmanicidal activity of the IFN-gamma-primed macrophages. Collectively, our data are consistent with a model where recognition of L. donovani promastigotes depends on the macrophage activation status and requires the expression of TLR3.

Zinc and infection: a review

Dietary zinc deficiency is widespread in developing countries and is often aggravated by intercurrent acute and chronic infections. Recent studies have demonstrated that zinc supplementation can significantly reduce the morbidity and mortality of apparently well-nourished children and shorten the time to recovery from acute infectious diseases. This review summarises current knowledge of the role of zinc in childhood diarrhoea, acute respiratory infections and malaria, and its potential role in diseases associated with impaired cellular immunity, namely tuberculosis, lepromatous leprosy and leishmaniasis, and explores avenues for future research.

Molecular basis for the potency of IL-10-deficient dendritic cells as a highly efficient APC system for activating Th1 response

Identification and targeting of novel immunobiological factors that regulate the induction of Th1 cells are crucial for designing effective vaccines against certain intracellular pathogens, including Chlamydia. IL-10-deficient dendritic cells (DC) are potent APCs and effective cellular vaccines that activate a high frequency of specific Th1 cells. To elucidate the molecular basis for the potency of the IL-10-deficient APC system, we tested the hypothesis that Chlamydia Ag-primed IL-10 knockout (IL-10KO) DC are quantitatively and qualitatively distinct in their metabolic characteristics relating to T cell activation. Using a combination of RT-PCR, two-dimensional gel electrophoresis, and MALDI-TOF-based proteomics analyses, the transcriptional and translational activities of Chlamydia-pulsed DC from wild-type and IL-10KO mice were assessed. IL-10 deficiency caused early maturation and activation of pulsed DC (i.e., high CD11c, CD40, CD80, CD83, CD86, IL-1, IL-12, and the T cell-attracting chemokine CCL27/CTACK) and consequently an enhanced ability to process and present Ags for a rapid and robust T cell activation. Supporting comparative proteomics revealed further that IL-10 deficient DC possess specific immunobiological properties, e.g., the T cell-attracting chemokine CCL27/CTACK, calcium-dependent protein kinase, and the IL-1/IL-12 inducer, NKR-P1A (CD161), which differentiated them immunologically from wild-type DC that express molecules relating to anti-inflammatory, differentiative, and metabolic processes, e.g., the anti-IL-12 molecule peroxisome proliferator-activated receptor-alpha and thymidine kinase. Collectively, these results provide a molecular basis for the high Th1-activating capacity of IL-10KO APC and may provide unique immunomodulation targets when designing vaccines against pathogens controlled by T cell immunity.

Bacillus cereus Fur regulates iron metabolism and is required for full virulence

A homologue of the Bacillus subtilis fur gene was identified in Bacillus cereus and characterized. The predicted amino acid sequence of the cloned gene was found to be highly similar to other members of the Fur family of transcriptional regulators. The B. cereus fur gene was shown to partially complement an Escherichia coli fur mutant. Purified B. cereus Fur bound specifically to a 19 bp DNA sequence homologous to the B. subtilis Fur box in a metal-dependent manner. Analysis of the available B. cereus genome data identified a number of genes which contain predicted Fur box sequences in the promoter region. Many of these genes are predicted to play a role in bacterial iron uptake and metabolism, but several have also been implicated as having a role in virulence. Fur and iron regulation of a siderophore biosynthesis operon was confirmed in a beta-galactosidase assay. A B. cereus fur null strain was constructed by allelic replacement of the chromosomal gene with a copy disrupted with a kanamycin resistance cassette. The Deltafur mutant was found to constitutively express siderophores, to accumulate iron intracellularly to a level approximately threefold greater than the wild-type, and to be hypersensitive to hydrogen peroxide. In an insect infection model, the virulence of the fur null strain was found to be significantly attenuated, highlighting the essential role played by Fur in the virulence of this pathogen.