The Inflammatory Effects of Dietary Lipids Regulate Growth of Parasites during Visceral Leishmaniasis.

Visceral leishmaniasis is a potentially fatal disease caused by the protozoon Leishmania donovani or L. infantum (Li). Although previous studies revealed that high lipid intake reduces parasite burdens in Leishmania donovani-infected mice, the specific contributions of dietary lipids to Li-associated pathogenesis are not known. To address this, we evaluated parasite growth, liver pathology, and transcriptomic signatures in Li-infected BALB/c mice fed either a control, high-fat, high-cholesterol, or high-fat-high-cholesterol diet. Using quantitative PCR (qPCR), we observed significantly reduced liver parasite burdens in mice fed the high-fat-high-cholesterol diet compared to mice fed the control diet. In contrast to the liver, parasite expansion occurred earlier in the spleens of mice fed the experimental diets. Histological examination revealed an intense inflammatory cell infiltrate in livers predominantly composed of neutrophils caused by the high-fat-high-cholesterol diet specifically. After 8 weeks of infection (12 weeks of diet), Illumina microarrays revealed significantly increased expression of transcripts belonging to immune- and angiogenesis-related pathways in livers of both uninfected and Li-infected mice fed the high-fat-high-cholesterol diet. These data suggest that increased fat and cholesterol intake prior to Li infection leads to a hepatic inflammatory environment and thus reduces the parasite burden in the liver. Defining inflammatory signatures as well as pathology in the liver may reveal opportunities to modify the therapeutic approach to Li infection. IMPORTANCE Leishmaniasis is a spectrum of diseases caused by Leishmania species protozoa that is most common in warm climates, coinciding with impoverished regions. Visceral leishmaniasis is a potentially fatal disease in which parasites infect reticuloendothelial organs and cause progressive wasting and immunocompromise. The distribution and demographics of visceral leishmaniasis have changed over recent years, coinciding with modernizing societies and the increased availability of Western diets rich in lipid content. We report here that increased dietary fat and cholesterol intake affected disease pathogenesis by increasing inflammation and reducing localized parasite burdens in the liver. These diet-induced changes in disease pathogenesis might explain in part the changing epidemiology of visceral leishmaniasis. A relationship between diet and inflammatory responses may occur in leishmaniasis and other microbial or immune-mediated diseases, possibly revealing opportunities to modify the therapeutic approach to microbial infections.

Differential Activation of Human Keratinocytes by Leishmania Species Causing Localized or Disseminated Disease.

All Leishmania species parasites are introduced into mammalian skin through a sand fly bite, but different species cause distinct clinical outcomes. Mouse studies suggest that early responses are critical determinants of subsequent adaptive immunity in leishmaniasis, yet few studies address the role of keratinocytes, the most abundant cell in the epidermis. We hypothesized that Leishmania infection causes keratinocytes to produce immunomodulatory factors that influence the outcome of infection. Incubation of primary or immortalized human keratinocytes with Leishmania infantum or Leishmania major, which cause visceral or cutaneous leishmaniasis, respectively, elicited dramatically different responses. Keratinocytes incubated with L. infantum significantly increased expression of proinflammatory genes for IL-6, IL-8, tumor necrosis factor, and IL-1B, whereas keratinocytes exposed to several L. major isolates did not. Furthermore, keratinocyte-monocyte co-incubation studies across a 4 µM semipermeable membrane suggested that L. infantum-exposed keratinocytes release soluble factors that enhance monocyte control of intracellular L. infantum replication (P < 0.01). L. major-exposed keratinocytes had no comparable effect. These data suggest that L. infantum and L. major differentially activate keratinocytes to release factors that limit infection in monocytes. We propose that keratinocytes initiate or withhold a proinflammatory response at the site of infection, generating a microenvironment uniquely tailored to each Leishmania species that may affect the course of disease.

High-affinity caspase-4 binding to LPS presented as high molecular mass aggregates or in outer membrane vesicles.

Caspases of the non-canonical inflammasome (caspases -4, -5, and -11) directly bind endotoxin (LOS/LPS) and can be activated in the absence of any co-factors. Models of LPS-induced caspase activation have postulated that 1:1 binding of endotoxin monomers to caspase trigger caspase oligomerization and activation, analogous to that established for endotoxin-induced activation of MD-2/TLR4. However, using metabolically radiolabeled LOS and LPS, we now show high affinity and selective binding of caspase-4 to high molecular mass aggregates of purified endotoxin and to endotoxin-rich outer membrane vesicles without formation of 1:1 endotoxin:caspase complexes. Thus, our findings demonstrate markedly different endotoxin recognition properties of caspase-4 from that of MD-2/TLR4 and strongly suggest that activation of caspase-4 (and presumably caspase-5 and caspase-11) are mediated by interactions with activating endotoxin-rich membrane interfaces rather than by endotoxin monomers.

A Systematic Approach to Identify Markers of Distinctly Activated Human Macrophages.

Polarization has been a useful concept for describing activated macrophage phenotypes and gene expression profiles. However, macrophage activation status within tumors and other settings are often inferred based on only a few markers. Complicating matters for relevance to human biology, many macrophage activation markers have been best characterized in mice and sometimes are not similarly regulated in human macrophages. To identify novel markers of activated human macrophages, gene expression profiles for human macrophages of a single donor subjected to 33 distinct activating conditions were obtained and a set of putative activation markers were subsequently evaluated in macrophages from multiple donors using integrated fluidic circuit (IFC)-based RT-PCR. Using unsupervised hierarchical clustering of the microarray screen, highly altered transcripts (>4-fold change in expression) sorted the macrophage transcription profiles into two major and 13 minor clusters. Among the 1874 highly altered transcripts, over 100 were uniquely altered in one major or two related minor clusters. IFC PCR-derived data confirmed the microarray results and determined the kinetics of expression of potential macrophage activation markers. Transcripts encoding chemokines, cytokines, and cell surface were prominent in our analyses. The activation markers identified by this study could be used to better characterize tumor-associated macrophages from biopsies as well as other macrophage populations collected from human clinical samples.

Quantification of multiple infections of Plasmodium falciparum in vitro.

BACKGROUND: Human malaria infections caused by the parasite Plasmodium falciparum often contain more than one genetically distinct parasite. Despite this fact, nearly all studies of multiple strain P. falciparum infections have been limited to determining relative densities of each parasite within an infection. In light of this, new methods are needed that can quantify the absolute number of parasites within a single infection. METHODS: A quantitative PCR (qPCR) method was developed to track the dynamic interaction of P. falciparum infections containing genetically distinct parasite clones in cultured red blood cells. Allele-specific primers were used to generate a standard curve and to quantify the absolute concentration of parasite DNA within multi-clonal infections. Effects on dynamic growth relationships between parasites under drug pressure were examined by treating mixed cultures of drug sensitive and drug resistant parasites with the anti-malarial drug chloroquine at different dosing schedules. RESULTS: An absolute quantification method was developed to monitor the dynamics of P. falciparum cultures in vitro. This method allowed for the observation of competitive suppression, the reduction of parasites numbers due to the presence of another parasite, and competitive release, the improved performance of a parasite after the removal of a competitor. These studies demonstrated that the presence of two parasites led to the reduction in density of at least one parasite. The introduction of drug to a mixed culture containing both a drug resistant and drug sensitive parasites resulted in an increased proportion of the drug resistant parasite. Moreover, following drug treatment, the resistant parasite experienced competitive release by exhibiting a fitness benefit greater than simply surviving drug treatment, due to the removal of competitive suppression by the sensitive parasite. CONCLUSIONS: The newly developed assay allowed for the examination of the dynamics of two distinct clones in vitro; both competitive suppression and release were observed. A deeper understanding of the dynamic growth responses of multiple strain P. falciparum infections, with and without drug pressure, can improve the understanding of the role of parasite interactions in the spread of drug resistant parasites, perhaps suggesting different treatment strategies.

Quantitative trait loci mapping reveals candidate pathways regulating cell cycle duration in Plasmodium falciparum.

BACKGROUND: Elevated parasite biomass in the human red blood cells can lead to increased malaria morbidity. The genes and mechanisms regulating growth and development of Plasmodium falciparum through its erythrocytic cycle are not well understood. We previously showed that strains HB3 and Dd2 diverge in their proliferation rates, and here use quantitative trait loci mapping in 34 progeny from a cross between these parent clones along with integrative bioinformatics to identify genetic loci and candidate genes that control divergences in cell cycle duration. RESULTS: Genetic mapping of cell cycle duration revealed a four-locus genetic model, including a major genetic effect on chromosome 12, which accounts for 75% of the inherited phenotype variation. These QTL span 165 genes, the majority of which have no predicted function based on homology. We present a method to systematically prioritize candidate genes using the extensive sequence and transcriptional information available for the parent lines. Putative functions were assigned to the prioritized genes based on protein interaction networks and expression eQTL from our earlier study. DNA metabolism or antigenic variation functional categories were enriched among our prioritized candidate genes. Genes were then analyzed to determine if they interact with cyclins or other proteins known to be involved in the regulation of cell cycle. CONCLUSIONS: We show that the divergent proliferation rate between a drug resistant and drug sensitive parent clone is under genetic regulation and is segregating as a complex trait in 34 progeny. We map a major locus along with additional secondary effects, and use the wealth of genome data to identify key candidate genes. Of particular interest are a nucleosome assembly protein (PFL0185c), a Zinc finger transcription factor (PFL0465c) both on chromosome 12 and a ribosomal protein L7Ae-related on chromosome 4 (PFD0960c).