Analysis of variables associated with promotion of resistance and its abrogation in T cell-reconstituted nude mice infected with Leishmania major

Upon intradermal challenge with the protozoan parasite Leishmania major, some mouse strains develop chronic cutaneous lesions, whereas other mouse strains show a resolving pattern of disease. The importance of T cell-dependent immunity in resistance to cutaneous leishmaniasis is substantiated by the susceptibility to infection of athymic nude mice of both resistant and susceptible strains. Small numbers of T lymphocytes from uninfected euthymic mice promote resistance in nude mice but T cells from chronically infected mice can impair this protective effect. In the present study we used an adoptive transfer system in which nude mice were reconstituted with T cells from normal or chronically infected mice in order to further investigate protection against disease or disease promotion. The results supported the following conclusions: (a) the host-protective activity of T cells from uninfected mice is highly effective even in long-term chronically infected nude mice, (b) T cell-mediated exacerbation of cutaneous disease does not involve enhancement of lesion development and is thus unlikely to be based on an accelerated proliferation of parasites in the lesion, (c) disease-promoting cells are not only found in genetically susceptible mice but can also be induced in genetically resistant mice, and (d) lymphoid organs of genetically susceptible mice chronically infected with L. major contain resistance-promoting cells in addition to disease-promoting cells. The data, together with those of others, continue to support the notion that recruitment with expansion and/or activation of different T cell subsets underlies genetically based resistance and susceptibility of mice to L. major.     

Pima Indians as a model to study the genetics of NIDDM.

More than half the Pima Indians over 35 years of age have non-insulin dependent diabetes mellitus (NIDDM). They have been the focus of prospective epidemiologic and metabolic studies for over two decades and the data collected during these studies are now proving invaluable in efforts to find genetic markers for NIDDM in humans. The Pima Indian model of this disease affords two major advantages. The population is genetically homogeneous compared to Caucasian populations, and therefore the causes of NIDDM are less heterogeneous, simplifying genetic linkage studies. Equally important, based on results from metabolic studies, two pre-diabetic phenotypes have been identified in the Pimas: insulin resistance and a low metabolic rate. Use of these phenotypes in genetic linkage analyses should greatly improve chances of finding genetic markers for NIDDM since these phenotypes may be more closely related to the putative abnormal gene products, and actual disease genes, than is the hyperglycemia of the fully developed phenotype of NIDDM.     

A novel cost of R gene resistance in the presence of disease

Resistance responses can impose fitness costs when pests are absent. Here, we test whether the induction of resistance can decrease fitness even in plants under attack; we call this potential outcome a net cost with attack. Using lines in which genetic background was controlled, we investigated whether susceptible Arabidopsis thaliana plants can outperform R gene resistant plants when infected with pathogens. For the R gene RPS2, there was a fitness benefit of resistance in the presence of intraspecific competition, but there was a net cost in the absence of competition: resistant plants produced less seed than susceptible plants even though infected with Pseudomonas syringae. This net cost was primarily due to overcompensation by susceptible plants, which occurred because of a developmental response to infection. For the R gene RPP5, there was no fitness effect of resistance without competition but a net cost when plants were infected with Peronospora parasitica in the presence of competition. This net cost was due to a reduction in the fitness of infected, resistant plants and complete compensation in susceptible plants. A spatially variable model suggests that a trade-off between net benefits and net costs with attack may help explain the persistence of individuals lacking R gene resistance to disease.     

Proof of concept of microbiome-metabolome analysis and delayed gluten exposure on celiac disease autoimmunity in genetically at-risk infants

Celiac disease (CD) is a unique autoimmune disorder in which the genetic factors (DQ2/DQ8) and the environmental trigger (gluten) are known and necessary but not sufficient for its development. Other environmental components contributing to CD are poorly understood. Studies suggest that aspects of gluten intake might influence the risk of CD occurrence and timing of its onset, i.e., the amount and quality of ingested gluten, together with the pattern of infant feeding and the age at which gluten is introduced in the diet. In this study, we hypothesize that the intestinal microbiota as a whole rather than specific infections dictates the switch from tolerance to immune response in genetically susceptible individuals. Using a sample of infants genetically at risk of CD, we characterized the longitudinal changes in the microbial communities that colonize infants from birth to 24 months and the impact of two patterns of gluten introduction (early vs. late) on the gut microbiota and metabolome, and the switch from gluten tolerance to immune response, including onset of CD autoimmunity. We show that infants genetically susceptible to CD who are exposed to gluten early mount an immune response against gluten and develop CD autoimmunity more frequently than at-risk infants in which gluten exposure is delayed until 12 months of age. The data, while derived from a relatively small number of subjects, suggest differences between the developing microbiota of infants with genetic predisposition for CD and the microbiota from infants with a non-selected genetic background, with an overall lack of bacteria of the phylum Bacteriodetes along with a high abundance of Firmicutes and microbiota that do not resemble that of adults even at 2 years of age. Furthermore, metabolomics analysis reveals potential biomarkers for the prediction of CD. This study constitutes a definite proof-of-principle that these combined genomic and metabolomic approaches will be key to deciphering the role of the gut microbiota on CD onset.     

Gene microarray analysis of multiple sclerosis lesions

Multiple sclerosis (MS) is an autoimmune disease affecting central nervous system white matter. The cause is unknown. It is thought that environmental factors trigger an immune response against myelin antigens in a genetically susceptible individual. The characteristic lesion of MS seen in the brain is a plaque, an area of inflammation, demyelination and glial reaction or ‘sclerosis’. Several recent studies have examined gene expression in MS plaques on a large scale using microarray technology. The involvement of immune-related genes has been confirmed, and many new genes not previously associated with MS lesions have been identified. Microarray studies are significant in identifying potential new targets for therapy.     

Disease spread in age structured populations with maternal age effects

Fundamental ecological processes, such as extrinsic mortality, determine population age structure. This influences disease spread when individuals of different ages differ in susceptibility or when maternal age determines offspring susceptibility. We show that Daphnia magna offspring born to young mothers are more susceptible than those born to older mothers, and consider this alongside previous observations that susceptibility declines with age in this system. We used a susceptible‐infected compartmental model to investigate how age‐specific susceptibility and maternal age effects on offspring susceptibility interact with demographic factors affecting disease spread. Our results show a scenario where an increase in extrinsic mortality drives an increase in transmission potential. Thus, we identify a realistic context in which age effects and maternal effects produce conditions favouring disease transmission.     

Genetic management of infectious diseases: a heterogeneous epidemio-genetic model illustrated with S. aureus mastitis

Given that individuals are genetically heterogeneous in their degree of resistance to infection, a model is proposed to formulate appropriate choices that will limit the spread of an infectious disease. The model is illustrated with data on S. aureus mastitis and is based on parameters characterizing the spread of the disease (contact rate, probability of infection after contact, and rate of recovery after infection), the demography (replacement and culling rates) and the genetic composition (degree of relationship and heritability of the disease trait) of the animal population. To decrease infection pressure, it is possible to apply non-genetic procedures that increase the culling (e.g., culling of chronically infected cows) and recovery (e.g., antibiotic therapy) rates of infected cows. But the contribution of the paper is to show that genetic management of infectious disease is also theoretically possible as a control measure complementary to non-genetic actions. Indeed, the probability for an uninfected individual to become infected after contact with an infected one is partially related to their degree of kinship: the more closely they are related, the more likely they are to share identical genes like those associated to the non-resistance to infection. Different prospective genetic management procedures are proposed to decrease the contact rate between infected and uninfected relatives and keep the number of secondary cases generated by one infected animal below 1.     

Evidence for a major gene controlling susceptibility to tegumentary leishmaniasis in a recently exposed Bolivian population.

Tegumentary leishmaniasis due to Leishmania braziliensis is a parasitic disease that occurs in two stages after the infected sandfly bite: (1) a primary cutaneous lesion followed by (2) a secondary mucosal involvement generally resulting in severe facial deformities. In order to investigate the genetic and environmental factors involved in the development of the cutaneous lesion, a familial study was performed in a region of Bolivia in which the disease is endemic. Complete selection of 118 nuclear families (703 subjects, with 241 patients), each with at least one cutaneous affected subject, was achieved; 41 families were of native origin, and 77 (herein designated "migrant") recently had settled in the area. For the analysis, the trait under study was the time to onset of the primary cutaneous lesion. The start of the follow-up was birth, for native population, or date of arrival in the endemic area, for migrant population. Segregation analysis was performed by use of a model based on survival analysis methods that allows joint estimation of genetic and environmental effects and accounts for gene x covariate interactions. A significant effect of gender, home-forest distance, and forest-related activity was found. In the 77 migrant families there was evidence for a recessive major gene controlling the onset of the primary cutaneous lesion, with residual familial dependences and age x genotype interaction. Penetrance estimations show that young subjects are genetically more susceptible than older subjects, suggesting that this genetic component could concern mechanisms involved in the development of individual protection during childhood. There was also a significant genetic heterogeneity of the sample according to the native/migrant origin of the families, and no major-gene effect was found in the native subsample.     

Interactions between genetic and reproductive factors in breast cancer risk in a French family sample.

Considerable progress has been made in the characterization of the genetic component of breast cancer (BC). However, BC still remains a complex disease involving a genetic component and many other risk factors essentially linked to reproductive-life factors. To search for interactions between genetic and reproductive-life factors in the etiology of BC, a systematic family study was performed in two French hospitals from December 1987 to January 1990 and led to recruitment of 288 families, the IGRC data ("IGRC" refers to the Institut Gustave Roussy and Institut Curie, where the data were obtained). Detailed information on reproductive factors was recorded for probands and female first-degree relatives. Segregation analysis of BC was conducted by taking into account a variable age at onset of disease, by use of the class D regressive logistic model, as implemented in the REGRESS computer program. Segregation analyses of BC in IGRC data showed evidence for the segregation of a dominant gene and additional sister-sister dependence, both when reproductive factors were ignored and when they were included. A significant interaction was detected between the dominant gene and age when reproductive factors were taken into account. Among the reproductive factors included in segregation analysis, parity was found to interact with the dominant-gene effect, and there was an indication of an interaction, albeit not significant, between the dominant gene and age at menarche. Whereas the usual protective effect conferred on breast-cancer risk by high parity remained in nonsusceptible women, it disappeared in susceptible women. The increased BC risk associated with a late age at menarche was higher in susceptible women than in nonsusceptible women. Interactions between inherited predisposition to BC and reproductive factors were detected here for the first time by segregation analysis. It would be of major interest to confirm these results by family studies in other populations.     

Transcriptional profiling reveals a possible role for the timing of the inflammatory response in determining susceptibility to a viral infection

Using a novel cDNA microarray prepared from sources of actively responding immune system cells, we have investigated the changes in gene expression in the target tissue during the early stages of infection of neonatal chickens with infectious bursal disease virus. Infections of two lines of chickens previously documented as genetically resistant and sensitive to infection were compared in order to ascertain early differences in the response to infection that might provide clues to the mechanism of differential genetic resistance. In addition to major changes that could be explained by previously described changes in infected tissue, some differences in gene expression on infection, and differences between the two chicken lines, were observed that led to a model for resistance in which a more rapid inflammatory response and more-extensive p53-related induction of apoptosis in the target B cells might limit viral replication and consequent pathology. Ironically, the effect in the asymptomatic neonatal infection is that more-severe B-cell depletion is seen in the more genetically resistant chicken. Changes of expression of many chicken genes of unknown function, indicating possible roles in the response to infection, may aid in the functional annotation of these genes.     

Genetic evidence for common pathways in human age‐related diseases

Aging is the single largest risk factor for chronic disease. Studies in model organisms have identified conserved pathways that modulate aging rate and the onset and progression of multiple age‐related diseases, suggesting that common pathways of aging may influence age‐related diseases in humans as well. To determine whether there is genetic evidence supporting the notion of common pathways underlying age‐related diseases, we analyzed the genes and pathways found to be associated with five major categories of age‐related disease using a total of 410 genomewide association studies (GWAS). While only a small number of genes are shared among all five disease categories, those found in at least three of the five major age‐related disease categories are highly enriched for apoliprotein metabolism genes. We found that a more substantial number of gene ontology (GO) terms are shared among the 5 age‐related disease categories and shared GO terms include canonical aging pathways identified in model organisms, such as nutrient‐sensing signaling, translation, proteostasis, stress responses, and genome maintenance. Taking advantage of the vast amount of genetic data from the GWAS, our findings provide the first direct evidence that conserved pathways of aging simultaneously influence multiple age‐related diseases in humans as has been demonstrated in model organisms.     

Entorhinal Cortex Lesions Transiently Alter Glucocorticoid but Not Mineralocorticoid Receptor Gene Expression in the Rat Hippocampus

Abstract: The mechanisms of delayed onset and cell death in Huntington's disease (HD) are unknown. One possibility is that a genetic defect in energy metabolism may result in slow excitotoxic neuronal death. Therefore, we examined the effects of age on striatal lesions produced by local administration of the mitochondrial toxin 3-nitropropionic acid in rats. In vivo chemical shift magnetic resonance imaging showed marked increases in striatal lactate concentrations that significantly correlated with increasing age. Histologic and neurochemical studies showed a striking age dependence of the lesions, with 4- and 12-month-old animals being much more susceptible than 1-month-old animals. Continuous systemic administration of low doses of 3-nitropropionic acid for 1 month resulted in striatal lesions showing growth-related changes in dendrites of striatal spiny neurons using the Golgi technique. These results show that a known mitochondrial toxin can produce selective axon-sparing striatal lesions showing both the age dependence and striatal spiny neuron dendritic changes that characterize HD.     

Evolution of microparasites in spatially and genetically structured host populations: The example of RHDV infecting rabbits

Several studies have shown that classical results of microparasite evolution could not extend to the case where the host species shows an important spatial structure. Rabbit haemorrhagic disease virus (RHDV), responsible for rabbit haemorrhagic disease (RHD), which recently emerged in rabbits, has strains within a wide range of virulence, thus providing an interesting example of competition between strains infecting a host species with a metapopulation structure. In addition, rabbits may show a genetic diversity regarding RHDV susceptibility. In the present paper we use the example of the rabbit-RHDV interaction to study the competition between strains of a same microparasite in a host population that is both spatially and genetically structured. Using metapopulation models we show that the evolution of the microparasite is guided by a trade-off between its capacity to invade subpopulations potentially infected by other strains and its capacity to persist within the subpopulation. In such a context, host genetic diversity acts by reducing the number of hosts susceptible to each strain, often favouring more persistent—and generally less virulent—strains. We also show that even in a stochastic context where host genes regularly go locally extinct, the microparasite pressure helps maintain the genetic diversity in the long term while reinforcing gene loss risk in the short term. Finally, we study how different demographic and epidemiologic parameters affect the coevolution between the rabbit and RHDV.     

Generation of isogenic pluripotent stem cells differing exclusively at two early onset Parkinson point mutations

Patient-specific induced pluripotent stem cells (iPSCs) derived from somatic cells provide a unique tool for the study of human disease, as well as a promising source for cell replacement therapies. One crucial limitation has been the inability to perform experiments under genetically defined conditions. This is particularly relevant for late age onset disorders in which in vitro phenotypes are predicted to be subtle and susceptible to significant effects of genetic background variations. By combining zinc finger nuclease (ZFN)-mediated genome editing and iPSC technology, we provide a generally applicable solution to this problem, generating sets of isogenic disease and control human pluripotent stem cells that differ exclusively at either of two susceptibility variants for Parkinson's disease by modifying the underlying point mutations in the α-synuclein gene. The robust capability to genetically correct disease-causing point mutations in patient-derived hiPSCs represents significant progress for basic biomedical research and an advance toward hiPSC-based cell replacement therapies.     

A strategy to identify positional candidate genes conferring Marek''s disease resistance by integrating DNA microarrays and genetic mapping

Marker-assisted selection (MAS) to enhance genetic resistance to Marek's disease (MD), a herpesvirus-induced T cell cancer in chicken, is an attractive alternative to augment control with vaccines. Our earlier studies indicate that there are many quantitative trait loci (QTL) containing one or more genes that confer genetic resistance to MD. Unfortunately, it is difficult to sufficiently resolve these QTL to identify the causative gene and generate tightly linked markers. One possible solution is to identify positional candidate genes by virtue of gene expression differences between MD resistant and susceptible chicken using deoxyribonucleic acid (DNA) microarrays followed by genetic mapping of the differentially-expressed genes. In this preliminary study, we show that DNA microarrays containing approximately 1200 genes or expressed sequence tags (ESTs) are able to reproducibly detect differences in gene expression between the inbred ADOL lines 63 (MD resistant) and 72 (MD susceptible) of uninfected and Marek's disease virus (MDV)-infected peripheral blood lymphocytes. Microarray data were validated by quantitative polymerase chain reaction (PCR) and found to be consistent with previous literature on gene induction or immune response. Integration of the microarrays with genetic mapping data was achieved with a sample of 15 genes. Twelve of these genes had mapped human orthologues. Seven genes were located on the chicken linkage map as predicted by the human-chicken comparative map, while two other genes defined a new conserved syntenic group. More importantly, one of the genes with differential expression is known to confer genetic resistance to MD while another gene is a prime positional candidate for a QTL.     

IL-10 is required for prevention of necrosis in the small intestine and mortality in both genetically resistant BALB/c and susceptible C57BL/6 mice following peroral infection with Toxoplasma gondii

The role for IL-10 in the immunopathogenesis of acute toxoplasmosis following peroral infection was examined in both genetically susceptible C57BL/6 and resistant BALB/c mice. C57BL/6-background IL-10-targeted mutant (IL-10-/-) mice all died in 2 wk after infection with 20 cysts of the ME49 strain, whereas only 20% of control mice succumbed. Histological studies revealed necrosis in the small and large intestines and livers of infected IL-10-/- mice. The necrosis in the small intestine was the most severe pathologic response and was not observed in control mice. Treatment of infected IL-10-/- mice with either anti-CD4 or anti-IFN-gamma mAb prevented intestinal pathology and significantly prolonged time to death. Treatment of these animals with anti-IL-12 mAb also prevented the pathology. Significantly greater amounts of IFN-gamma mRNA were detected in the lamina propria lymphocytes obtained from the small intestine of infected IL-10-/- mice than those from infected control mice. In common with C57BL/6-background IL-10-/- mice, BALB/c-background IL-10-/- mice all died developing intestinal pathology after infection. Control BALB/c mice all survived even after infection with 100 cysts and did not develop the intestinal lesions. Treatment with anti-IFN-gamma mAb prevented the pathology and prolonged time to death of the infected IL-10-/- mice. These results strongly suggest that IL-10 plays a critical role in down-regulating IFN-gamma production in the small intestine following sublethal peroral infection with Toxoplasma gondii and that this down-regulatory effect of IL-10 is required for prevention of development of IFN-gamma-mediated intestinal pathology and mortality in both genetically resistant BALB/c and susceptible C57BL/6 mice.     

Evaluation of Schistosome Promoter Expression for Transgenesis and Genetic Analysis

Schistosome worms of the genus Schistosoma are the causative agents of schistosomiasis, a devastating parasitic disease affecting more than 240 million people worldwide. Schistosomes have complex life cycles, and have been challenging to manipulate genetically due to the dearth of molecular tools. Although the use of gene overexpression, gene knockouts or knockdowns are straight-forward genetic tools applied in many model systems, gene misexpression and genetic manipulation of schistosome genes in vivo has been exceptionally challenging, and plasmid based transfection inducing gene expression is limited. We recently reported the use of polyethyleneimine (PEI) as a simple and effective method for schistosome transfection and gene expression. Here, we use PEI-mediated schistosome plasmid transgenesis to define and compare gene expression profiles from endogenous and nonendogenous promoters in the schistosomula stage of schistosomes that are potentially useful to misexpress (underexpress or overexpress) gene product levels. In addition, we overexpress schistosome genes in vivo using a strong promoter and show plasmid-based misregulation of genes in schistosomes, producing a clear and distinct phenotype- death. These data focus on the schistosomula stage, but they foreshadow strong potential for genetic characterization of schistosome molecular pathways, and potential for use in overexpression screens and drug resistance studies in schistosomes using plasmid-based gene expression.     

Cysteine protease B of Leishmania mexicana inhibits host Th1 responses and protective immunity

C3H mice infected with Leishmania mexicana fail to develop a protective Th1 response, and are unable to cure. In this study, we show that L. mexicana cysteine proteases suppress the antileishmanial immune response. Previous studies demonstrated that deletion of the entire multicopy cysteine protease B (CPB) gene array in L. mexicana is associated with decreased parasite virulence, potentially attributable to factors related to parasite fitness rather than to direct effects on the host immune response. We now show that C3H mice infected with the L. mexicana deletion mutant (Deltacpb) initially develop lesions that grow at rates comparable to those of wild-type L. mexicana-infected mice. However, in contrast to controls, Deltacpb-induced lesions heal with an accompanying Th1 immune response. Lesion resolution was Th1 dependent, as Deltacpb-infected IL-12p40(-/-) and STAT4(-/-) mice developed high parasite burdens and progressive disease. Moreover, when L. major was transfected with a cosmid expressing multiple L. mexicana CPB genes, this parasite induced a significantly lower IFN-gamma response compared with wild-type L. major. These data indicate that cysteine proteases of L. mexicana are critical in suppressing protective immune responses and that inhibition of CPB may prove to be a valuable immunomodulatory strategy for chronic forms of leishmaniasis.