The natural resistance-associated macrophage protein and susceptibility to intracellular pathogens

Epigenetic paradigms/exemplars of the macrophage: inflammasome axis in Leishmaniasis

The infectious paradigms have recently led to the recognition interplay of complex phenomenon underpinning disease diagnosis and prognosis. Evidently, parasitic infection studies are depicting converging trends of the epigenetic, environmental, and microbiome contributions, assisting pathogen-directed modulations of host biological system. The molecular details of epigenetic variations and memory, along with the multi-omics data at the interface of the host-pathogen level becomes strong indicator of immune cell plasticity, differentiation, and pathogen survival. Despite being one of the most important aspects of the disease's etiopathology, the epigenetic regulation of host-pathogen interactions and evolutionary epigenetics have received little attention thus far. Recent evidence has focused on the growing need to link epigenetic and microbiome modulations on parasite phenotypic plasticity and pathogen-induced host phenotypic plasticity for designing futuristic therapeutic regimes. Leishmaniasis is a neglected tropical illness with varying degrees of disease severity that is linked to a trans-species and epigenetic heredity process, including the pathogen-induced host and strain-specific modulations. The review configures research findings aligning to the epigenetic epidemiology niche, involving co-evolutionary epigenetic inheritance and plasticity disease models. The epigenetic exemplars focus on the host-pathogen interactome expanse at the macrophage-inflammasome axis.

Iron in immune cell function and host defense

The control over iron availability is crucial under homeostatic conditions and even more in the case of an infection. This results from diverse properties of iron: first, iron is an important trace element for the host as well as for the pathogen for various cellular and metabolic processes, second, free iron catalyzes Fenton reaction and is therefore producing reactive oxygen species as a part of the host defense machinery, third, iron exhibits important effects on immune cell function and differentiation and fourth almost every immune activation in turn impacts on iron metabolism and spatio-temporal iron distribution. The central importance of iron in the host and microbe interplay and thus for the course of infections led to diverse strategies to restrict iron for invading pathogens. In this review, we focus on how iron restriction to the pathogen is a powerful innate immune defense mechanism of the host called "nutritional immunity". Important proteins in the iron-host-pathogen interplay will be discussed as well as the influence of iron on the efficacy of innate and adaptive immunity. Recently described processes like ferritinophagy and ferroptosis are further covered in respect to their impact on inflammation and infection control and how they impact on our understanding of the interaction of host and pathogen.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Triad3a induces the degradation of early necrosome to limit RipK1-dependent cytokine production and necroptosis

Understanding the molecular signaling in programmed cell death is vital to a practical understanding of inflammation and immune cell function. Here we identify a previously unrecognized mechanism that functions to downregulate the necrosome, a central signaling complex involved in inflammation and necroptosis. We show that RipK1 associates with RipK3 in an early necrosome, independent of RipK3 phosphorylation and MLKL-induced necroptotic death. We find that formation of the early necrosome activates K48-ubiquitin-dependent proteasomal degradation of RipK1, Caspase-8, and other necrosomal proteins. Our results reveal that the E3-ubiquitin ligase Triad3a promotes this negative feedback loop independently of typical RipK1 ubiquitin editing enzymes, cIAPs, A20, or CYLD. Finally, we show that Triad3a-dependent necrosomal degradation limits necroptosis and production of inflammatory cytokines. These results reveal a new mechanism of shutting off necrosome signaling and may pave the way to new strategies for therapeutic manipulation of inflammatory responses.

Susceptibility to Mycobacterium ulcerans Disease (Buruli ulcer) Is Associated with IFNG and iNOS Gene Polymorphisms

Buruli ulcer (BU) is a chronic necrotizing disease of the skin and subcutaneous fat tissue. The causative agent, Mycobacterium ulcerans, produces mycolactone, a macrolide toxin, which causes apoptosis of mammalian cells. Only a small proportion of individuals exposed to M. ulcerans develop clinical disease, as surrounding macrophages may control the infection by bacterial killing at an early stage, while mycolactone concentration is still low. Otherwise, bacterial multiplication leads to in higher concentrations of mycolactone, with formation of necrotizing lesions that are no more accessible to immune cells. By typing a cohort of 96 Ghanaian BU patients and 384 endemic controls without BU, we show an association between BU and single nucleotide polymorphisms (SNPs) in iNOS (rs9282799) and IFNG (rs2069705). Both polymorphisms influence promoter activity in vitro. A previously reported SNP in SLC11A1 (NRAMP, rs17235409) tended to be associated with BU. Altogether, these data reflect the importance of IFNG signaling in early defense against M. ulcerans infection.

Drug targeting of heme proteins in Mycobacterium tuberculosis

TB, caused by the human pathogen Mycobacterium tuberculosis (Mtb), causes more deaths than any other infectious disease. Iron is crucial for Mtb to infect the host and to sustain infection, with Mtb encoding large numbers of iron-binding proteins. Many of these are hemoproteins with key roles, including defense against oxidative stress, cellular signaling and regulation, host cholesterol metabolism, and respiratory processes. Various heme enzymes in Mtb are validated drug targets and/or products of genes essential for bacterial viability or survival in the host. Here, we review the structure, function, and druggability of key Mtb heme enzymes and strategies used for their inhibition.

NRAMP1 Polymorphisms like Susceptibility Marker in Mexican Focus of Cutaneous Leishmaniasis

Cutaneous leishmaniasis (CL) is endemic in Campeche state, Mexico. Host and parasite factors are involved in the establishment and development of CL. Host factors include immune response and genetic background. NRAMP1 (Natural Resistance Associated Macrophage Protein 1) is important in innate immunity. Polymorphisms in NRAMP1 have been associated with susceptibility or resistance to infectious and autoimmune diseases. To study the association of NRAMP1 mutations with CL in patients from Calakmul, Campeche, samples from 115 CL patients and 69 samples of healthy people from the same area were evaluated. Five regions in NRAMP1 were amplified and digested, looking for mutations in the promoter region (−524G/C), exon 3 (274C/T), exon 8 (823 C7T), and exon 15 (G/A) and deletion of 4 bp in the 3′UTR region. We found a statistical association between polymorphisms in 3′UTR region and exon 8 and CL [χ² = 13.26; p < 0.05; OR = 17.00; IC of 95% (2.24–128.99)]. Some patients who needed more than 40 doses of Glucantime® to heal injuries presented mutations in exons 3, 8, and 15. Multiple or ear lesions were not associated with NRAMP1 polymorphism.

Competition for Manganese at the Host-Pathogen Interface

Transition metals such as manganese are essential nutrients for both pathogen and host. Vertebrates exploit this necessity to combat invading microbes by restricting access to these critical nutrients, a defense known as nutritional immunity. During infection, the host uses several mechanisms to impose manganese limitation. These include removal of manganese from the phagolysosome, sequestration of extracellular manganese, and utilization of other metals to prevent bacterial acquisition of manganese. In order to cause disease, pathogens employ a variety of mechanisms that enable them to adapt to and counter nutritional immunity. These adaptations include, but are likely not limited to, manganese-sensing regulators and high-affinity manganese transporters. Even though successful pathogens can overcome host-imposed manganese starvation, this defense inhibits manganese-dependent processes, reducing the ability of these microbes to cause disease. While the full impact of host-imposed manganese starvation on bacteria is unknown, critical bacterial virulence factors such as superoxide dismutases are inhibited. This chapter will review the factors involved in the competition for manganese at the host-pathogen interface and discuss the impact that limiting the availability of this metal has on invading bacteria.

Separable roles for Mycobacterium tuberculosis ESX-3 effectors in iron acquisition and virulence

Mycobacterium tuberculosis (Mtb) encodes five type VII secretion systems (T7SS), designated ESX-1-ESX-5, that are critical for growth and pathogenesis. The best characterized is ESX-1, which profoundly impacts host cell interactions. In contrast, the ESX-3 T7SS is implicated in metal homeostasis, but efforts to define its function have been limited by an inability to recover deletion mutants. We overcame this impediment using medium supplemented with various iron complexes to recover mutants with deletions encompassing select genes within esx-3 or the entire operon. The esx-3 mutants were defective in uptake of siderophore-bound iron and dramatically accumulated cell-associated mycobactin siderophores. Proteomic analyses of culture filtrate revealed that secretion of EsxG and EsxH was codependent and that EsxG-EsxH also facilitated secretion of several members of the proline-glutamic acid (PE) and proline-proline-glutamic acid (PPE) protein families (named for conserved PE and PPE N-terminal motifs). Substrates that depended on EsxG-EsxH for secretion included PE5, encoded within the esx-3 locus, and the evolutionarily related PE15-PPE20 encoded outside the esx-3 locus. In vivo characterization of the mutants unexpectedly showed that the ESX-3 secretion system plays both iron-dependent and -independent roles in Mtb pathogenesis. PE5-PPE4 was found to be critical for the siderophore-mediated iron-acquisition functions of ESX-3. The importance of this iron-acquisition function was dependent upon host genotype, suggesting a role for ESX-3 secretion in counteracting host defense mechanisms that restrict iron availability. Further, we demonstrate that the ESX-3 T7SS secretes certain effectors that are important for iron uptake while additional secreted effectors modulate virulence in an iron-independent fashion.

Macrophage defense mechanisms against intracellular bacteria

Macrophages and neutrophils play a decisive role in host responses to intracellular bacteria including the agent of tuberculosis (TB), Mycobacterium tuberculosis as they represent the forefront of innate immune defense against bacterial invaders. At the same time, these phagocytes are also primary targets of intracellular bacteria to be abused as host cells. Their efficacy to contain and eliminate intracellular M. tuberculosis decides whether a patient initially becomes infected or not. However, when the infection becomes chronic or even latent (as in the case of TB) despite development of specific immune activation, phagocytes have also important effector functions. Macrophages have evolved a myriad of defense strategies to combat infection with intracellular bacteria such as M. tuberculosis. These include induction of toxic anti-microbial effectors such as nitric oxide and reactive oxygen intermediates, the stimulation of microbe intoxication mechanisms via acidification or metal accumulation in the phagolysosome, the restriction of the microbe's access to essential nutrients such as iron, fatty acids, or amino acids, the production of anti-microbial peptides and cytokines, along with induction of autophagy and efferocytosis to eliminate the pathogen. On the other hand, M. tuberculosis, as a prime example of a well-adapted facultative intracellular bacterium, has learned during evolution to counter-balance the host's immune defense strategies to secure survival or multiplication within this otherwise hostile environment. This review provides an overview of innate immune defense of macrophages directed against intracellular bacteria with a focus on M. tuberculosis. Gaining more insights and knowledge into this complex network of host-pathogen interaction will identify novel target sites of intervention to successfully clear infection at a time of rapidly emerging multi-resistance of M. tuberculosis against conventional antibiotics.

Parallel exploitation of diverse host nutrients enhances Salmonella virulence

Pathogen access to host nutrients in infected tissues is fundamental for pathogen growth and virulence, disease progression, and infection control. However, our understanding of this crucial process is still rather limited because of experimental and conceptual challenges. Here, we used proteomics, microbial genetics, competitive infections, and computational approaches to obtain a comprehensive overview of Salmonella nutrition and growth in a mouse typhoid fever model. The data revealed that Salmonella accessed an unexpectedly diverse set of at least 31 different host nutrients in infected tissues but the individual nutrients were available in only scarce amounts. Salmonella adapted to this situation by expressing versatile catabolic pathways to simultaneously exploit multiple host nutrients. A genome-scale computational model of Salmonella in vivo metabolism based on these data was fully consistent with independent large-scale experimental data on Salmonella enzyme quantities, and correctly predicted 92% of 738 reported experimental mutant virulence phenotypes, suggesting that our analysis provided a comprehensive overview of host nutrient supply, Salmonella metabolism, and Salmonella growth during infection. Comparison of metabolic networks of other pathogens suggested that complex host/pathogen nutritional interfaces are a common feature underlying many infectious diseases.

The streptomycin mouse model for Salmonella diarrhea: functional analysis of the microbiota, the pathogen's virulence factors, and the host's mucosal immune response

The mammalian intestine is colonized by a dense microbial community, the microbiota. Homeostatic and symbiotic interactions facilitate the peaceful co-existence between the microbiota and the host, and inhibit colonization by most incoming pathogens ('colonization resistance'). However, if pathogenic intruders overcome colonization resistance, a fierce, innate inflammatory defense can be mounted within hours, the adaptive arm of the immune system is initiated, and the pathogen is fought back. The molecular nature of the homeostatic interactions, the pathogen's ability to overcome colonization resistance, and the triggering of native and adaptive mucosal immune responses are still poorly understood. To study these mechanisms, the streptomycin mouse model for Salmonella diarrhea is of great value. Here, we review how S. Typhimurium triggers mucosal immune responses by active (virulence factor elicited) and passive (MyD88-dependent) mechanisms and introduce the S. Typhimurium mutants available for focusing on either response. Interestingly, mucosal defense turns out to be a double-edged sword, limiting pathogen burdens in the gut tissue but enhancing pathogen growth in the gut lumen. This model allows not only studying the molecular pathogenesis of Salmonella diarrhea but also is ideally suited for analyzing innate defenses, microbe handling by mucosal phagocytes, adaptive secretory immunoglobulin A responses, probing microbiota function, and homeostatic microbiota-host interactions. Finally, we discuss the general need for defined assay conditions when using animal models for enteric infections and the central importance of littermate controls.

Micronutrient (Zn, Cu, Fe)-gene interactions in ageing and inflammatory age-related diseases: implications for treatments

In ageing, alterations in inflammatory/immune response and antioxidant capacity lead to increased susceptibility to diseases and loss of mobility and agility. Various essential micronutrients in the diet are involved in age-altered biological functions. Micronutrients (zinc, copper, iron) play a pivotal role either in maintaining and reinforcing the immune and antioxidant performances or in affecting the complex network of genes (nutrigenomic approach) involved in encoding proteins for a correct inflammatory/immune response. By the other side, the genetic inter-individual variability may affect the absorption and uptake of the micronutrients (nutrigenetic approach) with subsequent altered effects on inflammatory/immune response and antioxidant activity. Therefore, the individual micronutrient-gene interactions are fundamental to achieve healthy ageing. In this review, we report and discuss the role of micronutrients (Zn, Cu, Fe)-gene interactions in relation to the inflammatory status and the possibility of a supplement in the event of a micronutrient deficiency or chelation in presence of micronutrient overload in relation to specific polymorphisms of inflammatory proteins or proteins related of the delivery of the micronutriemts to various organs and tissues. In this last context, we report the protein-metal speciation analysis in order to have, coupled with micronutrient-gene interactions, a more complete picture of the individual need in micronutrient supplementation or chelation to achieve healthy ageing and longevity.

Leprosy susceptibility: genetic variations regulate innate and adaptive immunity, and disease outcome

The past few years have been very productive concerning the identification of genes associated with leprosy. Candidate gene strategies using both case-control and family-based designs, as well as large-scale approaches such as linkage and gene-expression genomic scans and, more recently, genome-wide association studies, have refined and enriched the list of genes highlighting the most important innate and adaptive immune pathways associated with leprosy susceptibility or resistance. During the early events of host-pathogen interaction identified genes are involved in pattern recognition receptors, and mycobacterial uptake (TLRs, NOD2 and MRC1), which modulate autophagy. Another gene, LTA4H, which regulates the levels of lipoxin A4 and possibly interacts with lipid droplet-related events, also plays a role in the early immune responses to Mycobacterium leprae. Together, the activation of these pathways regulates cellular metabolism upon infection, activating cytokine production through NF-κB and vitamin D-vitamin D receptor pathways, while PARK2 and LRRK2 participate in the regulation of host-cell apoptosis. Concomitantly, genes triggered to form and maintain granulomas (TNF, LTA and IFNG) and genes involved in activating and differentiating T-helper cells (HLA, IL10, as well as the TNF/LTA axis and the IFNG/IL12 axis) bridge immunological regulation towards adaptive immunity. Subtle variations in these genes, mostly single nucleotide polymorphisms, alter the risk of developing the disease or the severity of leprosy. Knowing these genes and their role will ultimately lead to better strategies for leprosy prevention, treatment and early diagnosis. Finally, the same genes associated with leprosy were also associated with autoimmune (Crohn's disease, rheumathoid arthritis, psoriasis) or neurodegenerative diseases (Parkinson's and Alzheimer's). Thus, information retrieved using leprosy as a model could be valuable to understanding the pathogenesis of other complex diseases.

H-2 alleles contribute to antigen 85-specific interferon-gamma responses during Mycobacterium tuberculosis infection

The in vitro immune responses to mycobacterial antigens have been linked to the H-2 loci in mice. We evaluated in vitro and in vivo immune responses during early Mycobacterium tuberculosis (M.tb) pulmonary infection of C57BL/6 (H-2(b)), C57BL/6 (H-2(k)), CBA/J (H-2(k)), and C3H/HeJ (H-2(k)) mice to determine H-2(k)-dependent and -independent effects. H-2(k)-dependent effects included delayed and diminished Ag85-specific Th1 cell priming, a reduced frequency of Ag85-specific IFN-γ producing cells, reduced IFN-γ protein in vivo, and increased M.tb lung burden as demonstrated by C57BL/6 H-2(k) mice vs. C57BL/6 mice. H-2(k)-independent factors controlled the amount of Ag85-specific IFN-γ produced by each cell, T cell numbers, granuloma size, and lymphocytic infiltrates in the lungs. Overall, these results suggest that an H-2(k)-dependent suboptimal generation of Ag85-specific cells impairs control of early M.tb growth in the lungs. H-2(k)-independent factors influence the potency of IFN-γ producing cells and immune cell trafficking during pulmonary M.tb infection.

Gene expression profiles induced by Salmonella infection in resistant and susceptible mice

Mouse models have been extensively used to investigate the mechanisms of salmonellosis. However, the role of the hosts' local intestinal responses during early stages of infection remain unclear. In this study, transcript array analysis was employed to investigate regulation of gene expression in the murine intestine following oral challenge with Salmonella enterica serovar Enteritidis. Salmonella resistant C3H/HeN mice elicited only weak transcription responses in the ileum even in the presence of bacterial replication and systemic infection. This poor response was surprising given previously published results using in vitro models. Susceptible TLR4-deficient C3H/HeJ mice displayed a stronger response, suggesting a role for TLR4 in dampening the response to Salmonella. Responses of susceptible BALB/c mice were also unremarkable. In contrast, in vitro infection of murine rectal epithelial cells induced a strong transcription response consistent with previous in vitro studies. Although the pattern of genes expressed by the ileal tissue upon in vivo infection were similar in all three mouse lines, the genes up-regulated during in vitro infection were different, indicating that the responses seen in vitro do not mimic those seen in vivo. Taken together these data indicate that in vivo responses to Salmonella, at the level of the intestine, are tightly regulated by the host.

Ulcerative colitis and Crohn's disease: is Mycobacterium avium subspecies paratuberculosis the common villain?

Mycobacterium avium, subspecies paratuberculosis (MAP) causes a chronic disease of the intestines in dairy cows and a wide range of other animals, including nonhuman primates, called Johne's ("Yo-knee's") disease. MAP has been consistently identified by a variety of techniques in humans with Crohn's disease. The research investigating the presence of MAP in patients with Crohn's disease has often identified MAP in the "negative" ulcerative colitis controls as well, suggesting that ulcerative colitis is also caused by MAP. Like other infectious diseases, dose, route of infection, age, sex and genes influence whether an individual infected with MAP develops ulcerative colitis or Crohn's disease. The apparently opposite role of smoking, increasing the risk of Crohn's disease while decreasing the risk of ulcerative colitis, is explained by a more careful review of the literature that reveals smoking causes an increase in both diseases but switches the phenotype from ulcerative colitis to Crohn's disease. MAP as the sole etiologic agent of both ulcerative colitis and Crohn's disease explains their common epidemiology, geographic distribution and familial and sporadic clusters, providing a unified hypothesis for the prevention and cure of the no longer "idiopathic" inflammatory bowel diseases.

CD36 deficiency attenuates experimental mycobacterial infection

Background

Members of the CD36 scavenger receptor family have been implicated as sensors of microbial products that mediate phagocytosis and inflammation in response to a broad range of pathogens. We investigated the role of CD36 in host response to mycobacterial infection.

Methods

Experimental Mycobacterium bovis Bacillus Calmette-Guérin (BCG) infection in Cd36^+/+ and Cd36^-/- mice, and in vitro co-cultivation of M. tuberculosis, BCG and M. marinum with Cd36^+/+ and Cd36^-/-murine macrophages.

Results

Using an in vivo model of BCG infection in Cd36^+/+ and Cd36^-/- mice, we found that mycobacterial burden in liver and spleen is reduced (83% lower peak splenic colony forming units, p < 0.001), as well as the density of granulomas, and circulating tumor necrosis factor (TNF) levels in Cd36^-/- animals. Intracellular growth of all three mycobacterial species was reduced in Cd36^-/- relative to wild type Cd36^+/+ macrophages in vitro. This difference was not attributable to alterations in mycobacterial uptake, macrophage viability, rate of macrophage apoptosis, production of reactive oxygen and/or nitrogen species, TNF or interleukin-10. Using an in vitro model designed to recapitulate cellular events implicated in mycobacterial infection and dissemination in vivo (i.e., phagocytosis of apoptotic macrophages containing mycobacteria), we demonstrated reduced recovery of viable mycobacteria within Cd36^-/- macrophages.

Conclusions

Together, these data indicate that CD36 deficiency confers resistance to mycobacterial infection. This observation is best explained by reduced intracellular survival of mycobacteria in the Cd36^-/- macrophage and a role for CD36 in the cellular events involved in granuloma formation that promote early bacterial expansion and dissemination.

Investigation of the association of the SLC11A1 gene with resistance/sensitivity of goats (Capra hircus) to paratuberculosis

SLC11A1 (solute carrier family 11 member A1) protein is located on the phagolysosome membrane of macrophages and participates in bacterial killing. Here we have extended our previous work on the investigation of the potential association of polymorphisms of the 3'untranslated region (UTR) of SLC11A1 gene with test-positivity of goats to Mycobacterium avium subsp. paratuberculosis (MAP). Blood, serum and faeces were collected from 223 adult goats, from nine goat farms from Greece with a long-term record of paratuberculosis but no vaccination or tuberculin testing. The samples were subjected to sequence and structure analysis of the SLC11A1 gene and were evaluated by ELISA, culture and real time polymerase chain reaction. The 3'UTR region of the targeted gene revealed 2 microsatellites consisting of a variable number of guanine-thymine repeats named regions A and B. Statistically significant association was recorded between genotypes of region B and ELISA results, whereas the presence of B(7) allele was found to contribute to ELISA negativity. The comparison of the SLC11A1 mRNA level pre- and post-exposure to MAP shows elevated gene expression especially at the 3-h time point, in all macrophages tested regardless of their genotype. Unfortunately the latter could not be linked at a statistically significant level with any of the targeted genetic polymorphisms separately. In conclusion it can be stated that the evidence reported here provide the first indications on the association of B genotypes of the SLC11A1 gene and the detection of MAP-specific antibody by ELISA in goats.

Efficacy and immunogenicity of Mycobacterium bovis DeltaRD1 against aerosol M. bovis infection in neonatal calves

An attenuated Mycobacterium bovisRD1 deletion (DeltaRD1) mutant of the Ravenel strain was constructed, characterized, and sequenced. This M. bovis DeltaRD1 vaccine strain administered to calves at 2 weeks of age provided similar efficacy as M. bovis bacillus Calmette Guerin (BCG) against low dose, aerosol challenge with virulent M. bovis at 3.5 months of age. Approximately 4.5 months after challenge, both DeltaRD1- and BCG-vaccinates had reduced tuberculosis (TB)-associated pathology in lungs and lung-associated lymph nodes and M. bovis colonization of tracheobronchial lymph nodes as compared to non-vaccinates. Mean central memory responses elicited by either DeltaRD1 or BCG prior to challenge correlated with reduced pathology and bacterial colonization. Neither DeltaRD1 or BCG elicited IFN-gamma responses to rESAT-6:CFP-10 prior to challenge, an emerging tool for modern TB surveillance programs. The DeltaRD1 strain may prove useful for bovine TB vaccine programs, particularly if additional mutations are included to improve safety and immunogenicity.

Crohn's disease and SLC11A1 promoter polymorphism

Crohn's disease (CD) is a chronic multifactorial inflammatory disease. The prevalence of CD in Ashkenazi Jews is higher than in Sephardic Jews. SLC11A1, also known as Nramp1, is a divalent cation antiporter essential for the elimination of intraphagosomal pathogens. SLC11A1 has seven alleles in the promoter region and previous studies have suggested an association between CD and SLC11A1. The aim of this study was to check for a possible association between SLC11A1 promoter alleles and CD in Ashkenazi Jewish patients. DNA samples from healthy Ashkenazi donors and Ashkenazi CD patients were obtained and analyzed for SLC11A1 promoter polymorphism by PCR and DNA sequencing. One hundred thirty-one samples from healthy donors and 131 samples from CD patients were analyzed. Four alleles were identified: approximately 70% of the samples carried allele 3; approximately 30%, allele 2; approximately 1%, allele 1; and <1%, allele 5. There was no difference in allele frequencies between healthy donors and CD patients. No correlation was found between mutations in NOD2/CARD15 and the phenotype of CD. We conclude that the difference in SLC11A1 promoter polymorphism plays no role in CD in Ashkenazi Jews.

Mycobacterium paratuberculosisand the bovine immune system

Mycobacterium aviumsubspeciesparatuberculosis(M. paratuberculosis) is the causative agent of Johne’s disease, a deadly intestinal ailment of ruminants. Johne’s disease is of tremendous economic importance to the worldwide dairy industry, causing major losses due to reduced production and early culling of animals. A highly controversial but developing link between exposure toM. paratuberculosisand human Crohn’s disease in some individuals has led to the suggestion thatM. paratuberculosisis also a potential food safety concern. As with many other mycobacteria,M. paratuberculosisis exquisitely adapted to survival in the host, despite aggressive immune reactions to these organisms. One hallmark of mycobacteria, includingM. paratuberculosis, is their propensity to infect macrophages. Inside the macrophage,M. paratuberculosisinterferes with the maturation of the phagosome by an unknown mechanism, thereby evading the host’s normal first line of defense against bacterial pathogens. The host immune system begins a series of attacks againstM. paratuberculosis-infected macrophages, including the rapid deployment of activated γδ T cells, CD4+T cells and cytolytic CD8+T cells. These cells interact with the persistently infected macrophage and with each other through a complex network of cytokines and receptors. Despite these aggressive efforts to clear the infection,M. paratuberculosispersists and the constant struggle of the immune system leads to pronounced damage to the intestinal epithelial cells. Enhancing our ability to control this important and tenacious pathogen will require a deeper understanding of howM. paratuberculosisinterferes with macrophage action, the cell types involved in the immune response, the cytokines these cells use to communicate, and the host genetic factors that control the response to infection.

The phagosome: compartment with a license to kill

Phagosomes are fascinating subcellular structures. After all, there are only a few compartments that are born before our very eyes and whose development we can follow in a light microscope until their contents disintegrate and are completely absorbed. Yet, some phagosomes are taken advantage of by pathogenic microorganisms, which change their fate. Research into phagosome biogenesis has flourished in recent years - the purpose of this review is to give a glimpse of where this research stands, with emphasis on the cell biology of macrophage phagosomes, on new model organisms for the study of phagosome biogenesis and on intracellular pathogens and their interference with normal phagosome function.

Immunocontraception of mammalian wildlife: ecological and immunogenetic issues

Immunocontraception involves stimulating immune responses against gametes or reproductive hormones thus preventing conception. The method is being developed for the humane control of pest and overabundant populations of mammalian wildlife. This paper examines three fundamental issues associated with its use: (1) the difficulties of obtaining responses to self-antigens, (2) the likely evolution of genetically based non-response to immunocontraceptive agents, and (3) the possible changes in the array of pathogens possessed by the target species after generations of immunocontraception. Our review of the literature demonstrates that the barriers to an effective immunocontraceptive are at present very basic. Should they be overcome, the effects of immunocontraception on the immunogenetic constitution of wildlife populations through the selection for non-responders must be examined. We suggest that the attempt to use the animal’s own immune system to modulate reproduction may be incompatible with the basic biological function of protection against infectious disease. Research programs on mammalian immunocontraception should involve measurement of the heritability of non-response and an assessment of the likely change in the response of the contracepted population to possible pathogens.

Chronic Salmonella enterica serovar Typhimurium-induced colitis and cholangitis in streptomycin-pretreated Nramp1+/+ mice

Salmonella enterica subspecies 1 serovar Typhimurium is an enteric bacterial pathogen infecting a broad range of hosts. In susceptible Nramp1(-/-) (Slc11alpha1(-/-)) mice, serovar Typhimurium cannot efficiently colonize the intestine but causes a systemic typhoid-like infection. However, after pretreatment with streptomycin, these susceptible (C57BL/6 and BALB/c) mice develop acute serovar Typhimurium-induced colitis (M. Barthel et al., Infect. Immun. 71:2839-2858, 2003). It was not clear whether resistant Nramp1(+/+) (Slc11alpha1(+/+)) mouse strains would similarly develop colitis. Here we compared serovar Typhimurium infection in streptomycin-pretreated susceptible (C57BL/6) and resistant (DBA/2 and 129Sv/Ev) mouse strains: We found that acute colitis (days 1 and 3 postinfection) is strikingly similar in susceptible and resistant mice. In 129Sv/Ev mice we followed the serovar Typhimurium infection for as long as 6 weeks. After the initial phase of acute colitis, these animals developed chronic crypt-destructive colitis, including ulceration, crypt abscesses, pronounced mucosal and submucosal infiltrates, overshooting regeneration of the epithelium, and crypt branching. Moreover, we observed inflammation of the gall duct epithelium (cholangitis) in the 129Sv/Ev mice between days 14 and 43 of infection. Cholangitis was not attributable to side effects of the streptomycin treatment. Furthermore, chronic infection of 129Sv/Ev mice in a typhoid fever model did not lead to cholangitis. We propose that streptomycin-pretreated 129Sv/Ev mice provide a robust murine model for chronic enteric salmonellosis including complications such as cholangitis.

HIV-AIDS in Minorities

HIV-AIDS has disproportionately affected minority populations in the United States. Significant disparities in case rates and mortality have been noted. This article reviews the magnitude of the problem and the many factors involved in the development and perpetuation of these disparities. Possible measures to help correct the problem are also reviewed.

Role and regulation of the Shigella flexneri sit and MntH systems

Shigella flexneri possesses at least two putative high-affinity manganese acquisition systems, SitABCD and MntH. Mutations in the genes encoding the components of both of these systems were constructed in S. flexneri. The sitA mntH mutant showed reduced growth, relative to the wild type, in Luria broth (L broth) containing the divalent metal chelator ethylene diamino-o-dihydroxyphenyl acetic acid, and the addition of either iron or manganese restored growth to the level of the wild-type strain. Although the sitA mntH mutant was not defective in surviving exposure to superoxide generators, it was defective in surviving exposure to hydrogen peroxide. The sitA mntH mutant formed wild-type plaques on Henle cell monolayers but had a reduced ability to survive in activated macrophage lines. Expression of the S. flexneri sit and mntH promoters was higher when Shigella was in Henle cells than when it was in L broth. Expression of both the sit and mntH promoters was repressed by either iron or manganese, and this repression was partially dependent upon Fur and MntR, respectively. The mntH promoter, but not the sit promoter, exhibited OxyR-dependent induction in the presence of hydrogen peroxide.

Role of SLC11A1 (formerly NRAMP1) in regulation of signal transduction induced by Toll-like receptor 7 ligands

Modulation of immune responses using Toll-like receptor (TLR) ligands is fast becoming one of the main new approaches for the treatment of infectious and allergic diseases. Characterizing the role of genetic factors in modulating responses to these ligands will be crucial in determining the efficacy of a particular treatment. Our previous findings have shown that treatment of Mycobacterium bovis BCG infection with a synthetic TLR7 ligand resulted in a reduction of the splenic bacterial load only in mice carrying a wild-type allele of Nramp1. To understand further how natural resistance-associated macrophage protein 1 (NRAMP1) modulates responses to TLR7 ligands, we have analysed various important TLR7 signal transduction events in macrophage cell lines derived from B10.ANramp1r and B10.ANramp1-/- mice. The Nramp1 genotype did not affect TLR7 receptor expression, ligand uptake or intracellular processing. Following TLR7 ligand stimulation, p38 mitogen-activated protein kinase (MAPK) activation was significantly reduced in B10A.Nramp1-/- macrophages compared with B10A.Nramp1r cells. Interestingly, levels of protein kinase C zeta (PKCzeta) activation were also found to be lower in B10A.Nramp1-/- macrophages and inhibition of this kinase in B10A.Nramp1r cells led to a reduction in cytokine production. Taken together, the data demonstrate a role for NRAMP1 in modulating p38 MAPK and PKCzeta activity, which leads to reduced cytokine induction by TLR7 ligands.

Susceptibility and resistance to monocytic ehrlichiosis in the mouse

To address the role of cellular immunity during ehrlichia infection, we have utilized a model of monocytic ehrlichiosis that results from infection of mice by Ixodes ovatus ehrlichia (IOE). Although ehrlichiosis in humans is largely a disease of immunocompromised individuals, the use of the IOE model has allowed us to identify factors required for host defense in normal mice. Using a low-dose infection C57BL/6 mouse model, we have demonstrated that host defense requires immune mechanisms involving CD4 T cell-mediated, TNF-alpha-, IL-12-, and IFN-gamma-dependent, macrophage activation. We have also provided formal evidence that IFN-gamma produced by CD4 Th1 cells is sufficient for protective immunity. Our recent studies have demonstrated, in addition, an essential role for IL-10, which is probably important in inhibiting immunopathological responses, and for inducible nitric oxide synthase. The latter observation establishes an important role for reactive nitrogen intermediates in bacterial elimination in vivo. In contrast, evaluation of mice carrying wild-type and mutant alleles of Nramp1 revealed at most a modest role for this gene in resistance to fatal IOE infection. Other studies in low-dose infected mice have indicated that the generation of immunological memory may be impaired during low-dose IOE infection, possibly due to bacterial immune subversion. These studies highlight the utility of the IOE mouse model in identifying important parameters of the immune response during ehrlichiosis.

Iron and infection: effects of host iron status and the iron-regulatory genes haptoglobin and NRAMP1 (SLC11A1) on host-pathogen interactions in tuberculosis and HIV

There are many lines of evidence illustrating that iron plays a pivotal role in modulating the battle for survival between mammalian hosts and their pathogens. Each displays considerable genetic investment in a wide range of mechanisms for acquiring and maintaining iron. These competitive mechanisms are highly complex, existing within an interacting matrix of absorption, transport, storage and detoxification systems, each of which are iron-responsive and thus able to adapt to the different phases of infection. Considerable genetic polymorphism in some of these systems, with signals of geographic selection in the hosts, and niche selection in the pathogens, indicates that they are critical for species survival. In this review we briefly summarize the role of iron in host immune function before reviewing the available evidence that iron modulates susceptibility and disease outcomes in HIV and TB (tuberculosis). We then examine the putative role of iron-related host genes by focussing on two candidate genes, haptoglobin and NRAMP1, for which there are common polymorphic variants in humans with strong evidence of functionally distinct biochemical phenotypes that would be predicted to influence the course of HIV and TB infections. Finally, we examine the limited evidence so far available that nutrient-gene interactions are likely to influence the way in which gene variants can protect against infection. We conclude that there is a wealth of evidence associating alterations in iron balance and in iron-regulatory systems with disease progression, but that many issues related to the direction of causality, mechanisms of action and sensitivity to pharmacological intervention remain to be elucidated. Since iron is probably the most widely prescribed compound throughout the world, used in both preventative and treatment regimens, a deeper understanding of the host-pathogen interactions relating to iron constitutes an important area for both basic and clinical research.

Association of NRAMP 1 gene polymorphism with susceptibility to tuberculosis in Taiwanese aboriginals

BACKGROUND/PURPOSE

The human homologue of mice natural-resistance-associated macrophage protein 1 (Nramp 1) gene, NRAMP 1, has been reported to play a role in susceptibility to tuberculosis in humans. The aboriginal population in Taiwan has a five-fold higher prevalence of tuberculosis than people of Han ethnicity. Whether genetic factors such as NRAMP 1 polymorphism play a role in the prevalence of tuberculosis in Taiwanese aboriginals should be clarified.

METHODS

NRAMP 1 polymorphism was studied using a case-control design of patients with tuberculosis, including subjects of Han (Hans) and aboriginal ethnicity in Hualien, eastern Taiwan. The polymorphisms of NRAMP 1 at loci INT4, D543N, 77-385C/T, 3-UTR (CAAA) deletion and 5-(CA)n microsatellite markers were assessed by polymerase chain reaction on tissue DNA isolated from 105 aborigines and 110 Hans with tuberculosis. Comparable numbers of ethnically-matched controls were studied simultaneously.

RESULTS

Two NRAMP 1 polymorphisms, INT4 and 5-(CA)n, were significantly associated with susceptibility to tuberculosis in aboriginals (p = 0.0070 and p = 0.0031, respectively). However, no association was detected at the five loci of NRAMP 1 polymorphisms among Hans (p > 0.08).

CONCLUSION

Genetic variation in NRAMP 1 may affect susceptibility to and increase risk for tuberculosis in Taiwanese aboriginals. Although environmental factors play an important role in tuberculosis infection, genetic factors such as NRAMP 1 polymorphism may also contribute to the high prevalence of tuberculosis in Taiwanese aboriginals.

Role for inducible costimulator in control of Salmonella enterica serovar Typhimurium infection in mice

Inducible costimulator (ICOS) is expressed on activated T cells and plays a key role in sustaining and enhancing the effector function of CD4 T cells. Given the function of this molecule in sustaining T-cell responses, we reasoned that ICOS might play an important role in a prolonged infection model, such as Salmonella infection of mice. To test this hypothesis, wild-type (WT) and ICOS-deficient (ICOS-/-) mice were infected systemically with a Salmonella enterica serovar Typhimurium strain expressing the chicken ovalbumin gene (Salmonella-OVA). ICOS-/- mice exhibited greater splenomegaly than WT mice and showed delayed bacterial clearance. The acquired immune response in this model was slow to develop. Maximal T-cell responses to Salmonella-OVA were detected at 3 weeks postinfection in both WT and ICOS-/- mice. CD4 T-cell-dependent gamma interferon production and a class switch to immunoglobulin G2a were severely reduced in ICOS-/- mice. ICOS-/- mice also exhibited a substantial defect in antigen-specific CD8 T-cell responses. In vitro, the effect of anti-ICOS on CD8 T-cell division was greater when CD8 T cells rather than CD4 T cells expressed ICOS, suggesting that the in vivo effects of ICOS on CD8 T cells could be direct. Taken together, these studies show that ICOS plays a critical role in control of Salmonella infection in mice, with effects on antibody, Th1, and CD8 T-cell responses.

CD154 Is Essential for Protective Immunity in ExperimentalSalmonellaInfection: Evidence for a Dual Role in Innate and Adaptive Immune Responses

CD40-CD154 interactions are of central importance in the induction of humoral and cellular immune responses. In the present study, CD154-deficient (CD154-/-) mice were used to assess the role of CD40-CD154 interactions in regulating the immune response to a systemic Salmonella infection. Compared with C57BL/6 (CD154+/+) controls, CD154-/- mice were hypersusceptible to infection by an attenuated strain of Salmonella enterica serovar Typhimurium (S. typhimurium), as evidenced by decreased survival rate and mean time to death, which correlated with increased bacterial burden and persistence in target organs. CD154-/- mice exhibited a defect both in the production of IL-12, IFN-gamma, and NO during the acute phase of the disease and in the generation of Salmonella-specific Ab responses and Ig isotype switching. Furthermore, when CD154-/- animals were administered a sublethal dose of attenuated S. typhimurium and subsequently challenged with a virulent homologous strain, all mice succumbed to an overwhelming infection. Similar treatment of CD154+/+ mice consistently resulted in > or =90% protection. The lack of protective immunity in CD154-/- mice correlated with a decreased T cell recall response to Salmonella Ags. Significant protection against virulent challenge was conferred to presensitized CD154-/- mice by transfer of serum or T cells from immunized CD154+/+ mice. For best protection, however, a combination of immune serum and T cells was required. We conclude that intercellular communications via the CD40-CD154 pathway play a critical role in the induction of type 1 cytokine responses, memory T cell generation, Ab formation, and protection against primary as well as secondary Salmonella infections.

Lack of association of brucellosis resistance with (GT)13 microsatellite allele at 3′UTR of NRAMP1 gene in Indian zebu (Bos indicus) and crossbred (Bos indicus×Bos taurus) cattle

Natural resistance associated macrophage protein 1 (NRAMP1), an integral transmembrane protein, is reported to influence the intraphagosomal microbial replication and thereby confer resistance to several intracellular pathogens in mice. In bovine, a significant association of (GT)(13) allelic variant of polymorphic microsatellite at 3' untranslated region (UTR) of NRAMP1 gene with natural resistance to brucellosis has been established. The present study was aimed to detect polymorphism at 3'UTR of NRAMP1 gene in Hariana breed of Bos indicus cattle and Holstein Friesian crossbred (B. indicusxBos taurus) cattle, and to determine the association of this polymorphism with resistance/susceptibility to brucellosis. The (GT)(n) polymorphism at 3'UTR in terms of variation in fragment length was determined using denaturing polyacrylamide gel analysis of radioisotope incorporated amplicon of 174 bp. Screening of a total of 100 samples (comprising 50 random samples of each breed) revealed that animals were of same genotype, i.e., homozygous (GT)(13)/(GT)(13). Sequencing of amplicons from representative animals confirmed the presence of (GT)(13) repeat. For association study, the animals that were positive in all three serological tests (viz., RBPT, STAT and ELISA) and had history of abortion were grouped as "affected"; whereas the animals that were negative in all these tests and completed third lactation without any history of abortion were grouped as "non-affected". Since, all animals belonging to either group were homozygous (GT)(13), association could not be established. However, the present study demonstrated that the presence of (GT)(13) allele even in homozygous condition could not provide enough resistance to brucellosis in a naturally infected herd.

NRAMP1 is not associated with asthma, atopy, and serum immunoglobulin E levels in the French Canadian population

Reduced infection by mycobacteria, including Mycobacterium tuberculosis, may be partly responsible for increased prevalence of allergic and autoimmune diseases in developed countries. In a murine model of innate resistance to mycobacteria, the Nramp1 gene has been shown to affect asthma susceptibility. From this observation, it was proposed that human NRAMP1 may be a modulator of asthma risk in human populations. To experimentally test the candidacy of NRAMP1 in asthma susceptibility, we characterized five genetic variants of NRAMP1 (5'CAn, 274C>T, 469+14G>C, D543N, and 1729+del4) in an asthma family-based cohort from northeastern Quebec. We did not observe any significant association between NRAMP1 variants (either allele or haplotype specific) with asthma, atopy, or serum immunoglobulin E levels. These results demonstrate that, in spite of direct involvement of Nramp1 in a murine asthma model, in human populations NRAMP1 is not likely to be a major contributor to the genetic etiology of asthma and asthma-related phenotypes.

A preliminary study of possible genetic influences on the susceptibility of sheep to Johne's disease

OBJECTIVE

To investigate possible genetic influences on susceptibility or resistance of sheep to Johne's disease.

DESIGN

A field and laboratory study of two fine-wool Merino flocks with a high prevalence of disease due to Mycobacterium avium subsp paratuberculosis infection.

PROCEDURE

Adult sheep were phenotypically classified as having severe, mild or no disease on the basis of clinical, pathological and cultural tests for paratuberculosis, and as positive or negative in tests for humoral immunity (agar gel immunodiffusion test) or cell mediated immunity (skin test for delayed type hypersensitivity). Correlations with phenotype were sought for polymorphisms at loci within selected immune function genes (NRAMP, MHC complex, IFN-gamma, lysozyme, leukaemia inhibiting factor).

RESULTS

Possible associations of particular NRAMP and MHC alleles with susceptibility or resistance to Johne's disease were detected.

CONCLUSION

If the results of this preliminary study are confirmed in further work, then the use of rams with "resistant" genotypes may assist in the control of Johne's disease in infected flocks.

Variants of the natural resistance-associated macrophage protein 1 gene (NRAMP1) are associated with severe forms of pulmonary tuberculosis

Although genetic factors may affect susceptibility to tuberculosis, studies that have assessed variants of the natural resistance-associated macrophage protein 1 gene (NRAMP1) and their association with tuberculosis in humans have yielded conflicting results. It is likely that NRAMP1 polymorphisms may be associated with progression to severe forms of pulmonary tuberculosis rather than with susceptibility to Mycobacterium tuberculosis infection. To test this possibility, we examined NRAMP1 variants at the INT4 and D543N loci, as well as their association with severe forms of pulmonary tuberculosis, in 127 patients with active pulmonary tuberculosis and in 91 ethnically matched, healthy control subjects in areas of China where tuberculosis is endemic. We found that NRAMP1 polymorphisms at these 2 loci were significantly associated with 2 severe forms of pulmonary tuberculosis: sputum smear-positive tuberculosis and cavitary tuberculosis. The NRAMP1 variants were not associated with pulmonary M. tuberculosis infection, when analyses of all patients with tuberculosis and all control subjects were performed. The findings of the present study support the hypothesis that genetic variants of NRAMP1 may have an effect on bacilli growth and on outcomes of pulmonary tuberculosis, but not on susceptibility to M. tuberculosis infection.

Dictyostelium as host model for pathogenesis

The haploid social soil amoeba Dictyostelium discoideum has been established as a host model for several pathogens including Pseudomonas aeruginosa, Cryptococcus neoformans, Mycobacterium spp. and Legionella pneumophila. The research areas presently pursued include (i) the use of Dictyostelium wild-type cells as screening system for virulence of extracellular and intracellular pathogens and their corresponding mutants, (ii) the use of Dictyostelium mutant cells to identify genetic host determinants of susceptibility and resistance to infection and (iii) the use of reporter systems in Dictyostelium cells which allow the dissection of the complex host-pathogen cross-talk. The body of information presented in this review demonstrates that the availability of host cell markers, the knowledge of cell signalling pathways, the completion of the genome sequencing project and the tractability for genetic studies qualifies Dictyostelium for the study of fundamental cellular processes of pathogenesis.

Johne's disease, inflammatory bowel disease, and Mycobacterium paratuberculosis

Johne's disease is a chronic diarrhea affecting all ruminants. Mycobacterium avium subsp. paratuberculosis (MAP), a slowly growing mycobacteria, is the etiologic agent. There is also a concern that MAP might be a causative agent of some cases of inflammatory bowel disease in humans, especially Crohn's disease. Food products including pasteurized bovine milk have been suggested as potential sources of human infection. This review addresses microbial factors that may contribute to its pathogenicity. In addition, the experimental evidence defining MAP as the cause of Johne's disease and the issues and controversies surrounding its potential pathogenic role in humans are discussed.

Association of CXCR2 polymorphisms with subclinical and clinical mastitis in dairy cattle

The ability to identify objectively cows that are more or less susceptible to mastitis has been a long-standing goal. Genetic markers associated with inflammatory responses during mastitis could aid in selection of these cattle. One potential marker is CXCR2, a chemokine receptor required for neutrophil migration to infection sites, which contains single nucleotide polymorphisms (SNP) within the gene. The objective of this experiment was to evaluate the association of CXCR2 SNP genotypes with subclinical and clinical mastitis. Thirty-seven Holstein and 42 Jersey cows that completed at least 2 full lactations were used. Quarter foremilk samples were collected for bacteriological examination quarterly and when cows exhibited clinical mastitis. Subclinical mastitis was defined as the presence of the same pathogen in the same quarter in at least 2 of 3 consecutive samples. A significant association was detected between CXCR2 SNP +777 genotype and percentages of subclinical mastitis cases in Holsteins. Holsteins expressing genotype GG had decreased percentages of subclinical mastitis, but genotype CC cows had increased percentages of subclinical mastitis. Significant differences in clinical mastitis incidence were not detected between genotypes for either breed. This approach of genetically identifying mastitis resistant cows may represent an effective means of marker-assisted selection for mastitis and other inflammatory diseases involving neutrophils.

Correlation of virulence, lung pathology, bacterial load and delayed type hypersensitivity responses after infection with different Mycobacterium tuberculosis genotypes in a BALB/c mouse model

One of the most intriguing aspects of tuberculosis is that the outcome of an infection with M. tuberculosis (TB) is highly variable between individuals. The possibility of differences in virulence between M. tuberculosis strains or genotypes has only recently been studied. There is evidence of multifactorial genetic predisposition in humans that influences the susceptibility to tuberculosis. A better understanding of differences in virulence between M. tuberculosis genotypes could be important with regard to the efforts at TB control and the development of improved antituberculosis vaccines. Survival, lung pathology, bacterial load and delayed type hypersensitivity (DTH) responses of BALB/c mice after intratracheal infection with any of 19 different M. tuberculosis complex strains of 11 major genotype families were studied. The results indicate that among genetically different M. tuberculosis strains a very broad response was present with respect to virulence, pathology, bacterial load and DTH. 'Low'-responders were the H37Rv, Canetti, Beijing-1 strains, while Beijing-2,3, Africa-2 and Somalia-2 strains were 'high'-responders. A severe pathological response correlates with a high mortality and a high CFU counts in lungs, but poorly with the degree of the DTH response.

Structure of the bovine natural resistance associated macrophage protein (NRAMP 1) gene and identification of a novel polymorphism

The NRAMP 1 gene is a major candidate gene influencing the outcome of infections with intracellular pathogens in numerous species. NRAMP 1 is highly conserved in many mammalian species and the NRAMP 1 gene shows considerable conservation in structure between mice and humans. The association of NRAMP 1 gene polymorphisms with disease in cattle has been limited to a single microsatellite located within the 3'-non coding region of the bovine NRAMP 1 gene. In order to facilitate further studies on this important gene, we now report the nearly complete structure of the bovine NRAMP 1 gene, including sizes and positions of 13 introns relative to the bovine NRAMP 1 gene coding sequence and the DNA sequence of intron-exon junctions. Comparison of the bovine, murine and human NRAMP 1 gene structures revealed a high degree of conservation in intron placement, though the lengths of several introns were less-well conserved. In general, the greatest divergence in intron lengths occurred in regions of the NRAMP 1 gene displaying the lowest coding sequence conservation. In addition, mutations near intron-exon junctions could account for 25 of the 75 total amino acid differences between murine and bovine NRAMP 1. Using information gained through this study, it was possible to rapidly identify a novel polymorphism within the bovine NRAMP 1 gene intron X. This polymorphism was shown by direct DNA sequence analysis to consist of insertion of three guanine nucleotides at positions 37,40 and 98 relative to the intron X start point. Initial scans of several cattle breeds suggest that the two intron X alleles identified here are stable and widespread in the Bos taurus population.

Genetic susceptibility to infectious disease

Our understanding of the variation in individual clinical responses to pathogens has become increasingly relevant, particularly in the face of new emerging epidemics as well as the increasing number of multi-drug-resistant organisms. An effective immune response to infection has contributed to the development of host genetic diversity through selective pressure, with an increasing number of studies characterizing the role that host genetics plays in disease susceptibility. Knowledge of the role host mechanisms play in the pathogenesis of infectious disease can contribute to the design of new therapeutic strategies. Rapid advances in the field of human genomics offer great opportunities for adopting this approach to find new insights into pathogenesis.