Antimicrobial activity of three tick defensins and four mammalian cathelicidin-derived synthetic peptides against Lyme disease spirochetes and bacteria isolated from the midgut

In this study, chemically synthesized tick defensins and cathelicidin-derived mammalian peptides were used to investigate the activity spectrum against Borrelia garinii and symbiotic Stenotrophomonas maltophila. Synthetic tick defensins showed antimicrobial activity against Staphylococcus aureus but not B. garinii and S. maltophila. Mammalian peptides which have cationic property similar to tick defensins, showed antimicrobial activity similar to tick defensins. The antimicrobial peptides in ticks and mammalian hosts have common characteristics against microbial invasion in the innate immune system.     

A tick antioxidant facilitates the Lyme disease agent's successful migration from the mammalian host to the arthropod vector

The tick Ixodes scapularis is an efficient vector for microbes, including the Lyme disease agent Borrelia burgdorferi. Ticks engorging on vertebrates induce recruitment of inflammatory cells to the bite site. For efficient transmission to the vector, pathogens have to traffic through this complex feeding site while avoiding the deleterious effects of immune cells. We show that a tick protein, Salp25D, plays a critical role-in the mammalian host-for acquisition of Borrelia burgdorferi by the vector. Silencing salp25D in tick salivary glands impaired spirochete acquisition by ticks engorging on B. burgdorferi-infected mice. Immunizing mice against Salp25D also decreased Borrelia acquisition by I. scapularis. Salp25D detoxified reactive oxygen species at the vector-pathogen-host interface, thereby providing a survival advantage to B. burgdorferi at the tick feeding site in mice. These data demonstrate that pathogens can exploit arthropod molecules to defuse mammalian responses in order to successfully enter the vector.     

Adaptation of Borrelia burgdorferi in the tick and the mammalian host

Borrelia burgdorferi, the causative agent of Lyme disease, shows a great ability to adapt to different environments, including the arthropod vector, and the mammalian host. The success of these microorganisms to survive in nature and complete their enzootic cycle depends on the regulation of genes that are essential to their survival in the different environments. This review describes the current knowledge of gene expression by B. burgdorferi in the tick and the mammalian host. The functions of the differentially regulated gene products as well as the factors that influence their expression are discussed. A thorough understanding of the changes in gene expression and the function of the differentially expressed antigens during the life cycle of the spirochete will allow a better control of this prevalent infection and the design of new, second generation vaccines to prevent infection with the spirochete.     

Adaptation of the Lyme disease spirochaete to the mammalian host environment results in enhanced glycosaminoglycan and host cell binding

The Lyme disease spirochaete, Borrelia burgdorferi, is transmitted to mammals by Ixodes ticks and can infect multiple tissues. Host cell attachment may be critical for tissue colonization, and B. burgdorferi cultivated in vitro recognizes heparin- and dermatan sulphate-related glycosaminoglycans (GAGs) on the surface of mammalian cells. To determine whether growth of the spirochaete in the mammalian host alters GAG binding, we assessed the cell attachment activities of B. burgdorferi grown in vitro or in dialysis membrane chambers implanted intraperitoneally in rats. Host-adapted B. burgdorferi exhibited approximately threefold better binding to purified heparin and dermatan sulphate and to GAGs expressed on the surface of cultured endothelial cells. Three B. burgdorferi surface proteins, Bgp, DbpA and DbpB, have been demonstrated previously to bind to GAGs or to GAG-containing molecules, and we show here that recombinant derivatives of each of these proteins were able to bind to purified heparin and dermatan sulphate. Immunofluorescent staining of in vitro-cultivated or host-adapted spirochaetes revealed that DbpA and DbpB were present on the bacterial surface at higher levels after host adaptation. Recombinant Bgp, DbpA and DbpB each partially inhibited attachment of host-adapted B. burgdorferi to cultured mammalian cells, consistent with the hypothesis that these proteins may promote attachment of B. burgdorferi during growth in the mammalian host. Nevertheless, the partial nature of this inhibition suggests that multiple pathways promote mammalian cell attachment by B. burgdorferi in vivo. Given the observed increase in cell attachment activity upon growth in the mammalian host, analysis of host-adapted bacteria will facilitate identification of the cell binding pathways used in vivo.     

Stage‐specific effects of bone morphogenetic proteins on the oligodendrocyte lineage

Oligodendrocyte maturation is regulated by multiple secreted factors present in the brain during critical stages of development. Whereas most of these factors promote oligodendrocyte proliferation and survival, members of the bone morphogenetic protein family (BMPs) recently have been shown to inhibit oligodendrocyte differentiation in vitro. Oligodendrocyte precursors treated with BMPs differentiate to the astrocyte lineage. Given that cells at various stages of the oligodendrocyte lineage have distinct responses to growth factors, we hypothesized that the response to BMP would be stage‐specific. Using highly purified, stage‐specific cultures, we found that BMP has distinct effects on cultured oligodendrocyte preprogenitors, precursors, and mature oligodendrocytes. Oligodendrocyte preprogenitors (PSA‐NCAM+, A2B5−) treated with BMP2 or BMP4 developed a novel astrocyte phenotype characterized by a morphological change and expression of glial fibrillary acidic protein (GFAP) but little glutamine synthetase expression and no labeling with A2B5 antibody. In contrast, treating oligodendrocyte precursors with BMPs resulted in the accumulation of cells with the traditional type 2 astrocyte phenotype (GFAP+, A2B5+). However, many of the cells with an astrocytic morphology did not express GFAP or glutamine synthetase unless thyroid hormone was present in the medium. The addition of fibroblast growth factor along with BMP to either oligodendrocyte preprogenitor or the oligodendrocyte precursor cells inhibited the switch to the astrocyte lineage, whereas platelet‐derived growth factor addition had no effect. Treatment of mature oligodendrocytes with BMP elicited no change in morphology or expression of GFAP. These data suggest that as cells progress through the oligodendrocyte lineage, they show developmentally restricted responses to the BMPs. © 2000 John Wiley & Sons, Inc. J Neurobiol 43: 1–17, 2000     

Molecular individuality and adaptation of the tick Rhipicephalus appendiculatus in changed feeding environments

The tick Rhipicephalus appendiculatus Neumann (Acari: Ixodidae) naturally infests many host species. However, the mechanisms that enable it to feed on such a wide range of hosts are unclear. One possibility is that a tick population maintains molecular (genotypic and/or phenotypic) diversity among individuals such that individuals vary in their competency in taking bloodmeals under different feeding conditions. As a first step in testing this hypothesis, we showed that the polymorphism of salivary gland proteins, previously demonstrated in unfed ticks, was maintained during feeding on guinea-pigs. We then compared feeding performance under standard laboratory rearing conditions: one instar (adults or nymphs) feeding on guinea-pigs, with three changed conditions: (1) two instars (adults and nymphs) feeding together on guinea-pigs; (2) one instar (adults or nymphs) feeding on hamsters; and (3) two instars (adults and nymphs) feeding together on hamsters. The mean engorged weight of adult females was significantly reduced under all changed conditions, indicating that most of the adult individuals were significantly challenged by the changed conditions. However, some individuals achieved successful engorgement, indicating competence to the changed condition, and demonstrating variation in adaptive ability among individuals. Engorged females produced egg masses positively correlated to the engorged weights. More interestingly, the correlation coefficient (R) increased when feeding condition was changed. This may lead to more efficient selection for population adaptation under the changed conditions. As the feeding success of ixodid ticks depends on the efficiency of the cocktail of immunomodulatory saliva, the relevance of the polymorphism of salivary gland proteins and host adaptation is discussed.     

Stage‐ and thermal‐specific genetic architecture for preadult viability in natural populations of Drosophila melanogaster

Studying the processes affecting variation for preadult viability is essential to understand the evolutionary trajectories followed by natural populations. This task requires focusing on the complex nature of the phenotype–genotype relationship by taking into account usually neglected aspects of the phenotype and recognizing the modularity between different ontogenetic stages. Here, we describe phenotypic variability for viability during the larval and pupal stages in lines derived from three natural populations of Drosophila melanogaster, as well as the variability for phenotypic plasticity and canalization at two different rearing temperatures. The results indicate that the three populations present significant phenotypic differences for preadult viability. Furthermore, distinct aspects of the phenotype (means, plasticity, canalization, plasticity of canalization) are affected by different genetic bases underlying changes in viability in a stage‐ and environment‐specific manner. These findings explain the generalized maintenance of genetic variability for this fitness trait.     

Characterization of Lyme disease spirochetes isolated from ticks and vertebrates in North Carolina

Borrelia burgdorferi isolates obtained from numerous locations and from different hosts in North Carolina, were compared to previously characterized strains of the Lyme disease spirochete and other Borrelia spp. The spirochete isolates were confirmed to be B. burgdorferi sensu stricto based on immunofluorescence (IFA) using a monoclonal antibody to outer surface protein A (Osp A [H5332]) and polymerase chain reaction (PCR) using a species-specific nested primer for a conserved region of the gene that encodes for flagellin. In addition, the isolates tested positive in Western blots with species-specific monoclonal antibodies for outer surface protein A and OspB (84c), and the genus-specific, monoclonal antibody to flagellin (H9724). Infectivity studies with several of these isolates were conducted using Mus musculus and Oryzomys palustris and the isolates exhibited markedly different levels of infectivity. This study demonstrates that B. burgdorferi sensu stricto is present and naturally transmitted on the Outer Banks and in the Coastal Plain and Piedmont regions of North Carolina.     

Discovery of the Lyme disease spirochete and its relation to tick vectors.

The various hypotheses concerning the etiologic agent of erythema chronicum migrans of Europe and of Lyme disease in the United States are reviewed, and an account of events that led to the discovery of the causative spirochetal agent in Ixodes dammini is presented. Spirochetes morphologically and antigenically similar, if not identical to, the organism detected in I. dammini were also found for the first time in Ixodes pacificus and Ixodes ricinus, the vectors hitherto incriminated, respectively, in western United States and Europe. In most infected ticks, spirochetal development was found to be limited to the midgut. Ticks with generalized infections were shown to transmit spirochetes via eggs, but infections decreased in intensity and became restricted to the central ganglion as filial ticks developed to adults. Although the mechanisms of transmission to a host are still under investigation, the spirochetes may be transmitted by saliva of ticks with generalized infectious and possibly also by regurgitation of infected gut contents, or even by means of infected fecal material.     

Loss of adaptation following reversion suggests trade‐offs in host use by a seed beetle

Experimental evolution has provided little support for the hypothesis that the narrow diets of herbivorous insects reflect trade‐offs in performance across hosts; selection lines can sometimes adapt to an inferior novel host without a decline in performance on the ancestral host. An alternative approach for detecting trade‐offs would be to measure adaptation decay after selection is relaxed, that is, when populations newly adapted to a novel host are reverted to the ancestral one. Lines of the seed beetle Callosobruchus maculatus rapidly adapted to a poor host (lentil); survival in lentil seeds increased from 2% to > 90% in < 30 generations. After the lines had reached a plateau with respect to survival in lentil, sublines were reverted to the ancestral host, mung bean. Twelve generations of reversion had little effect on performance in lentil, but after 25–35 generations, the reverted lines exhibited lower survival, slower development and smaller size. The most divergent pair of lines was then assayed on both lentil and mung bean. Performance on lentil was again much poorer in the reverted line than in the nonreverted one, but the lines performed equally well on mung bean. Moreover, the performance of the nonreverted line on mung bean remained comparable to that of the original mung‐bean population. Our results thus present a paradox: loss of adaptation to lentil following reversion implies a trade‐off, but the continued strong performance of lentil‐adapted lines on mung bean does not. Genomic comparisons of the reverted, nonreverted and ancestral lines may resolve this paradox and determine the importance of selection vs. drift in causing a loss of adaptation following reversion.     

The glycerol-3-phosphate dehydrogenases GpsA and GlpD constitute the oxidoreductive metabolic linchpin for Lyme disease spirochete host infectivity and persistence in the tick

We have identified GpsA, a predicted glycerol-3-phosphate dehydrogenase, as a virulence factor in the Lyme disease spirochete Borrelia (Borreliella) burgdorferi: GpsA is essential for murine infection and crucial for persistence of the spirochete in the tick. B. burgdorferi has a limited biosynthetic and metabolic capacity; the linchpin connecting central carbohydrate and lipid metabolism is at the interconversion of glycerol-3-phosphate and dihydroxyacetone phosphate, catalyzed by GpsA and another glycerol-3-phosphate dehydrogenase, GlpD. Using a broad metabolomics approach, we found that GpsA serves as a dominant regulator of NADH and glycerol-3-phosphate levels in vitro, metabolic intermediates that reflect the cellular redox potential and serve as a precursor for lipid and lipoprotein biosynthesis, respectively. Additionally, GpsA was required for survival under nutrient stress, regulated overall reductase activity and controlled B. burgdorferi morphology in vitro. Furthermore, during in vitro nutrient stress, both glycerol and N-acetylglucosamine were bactericidal to B. burgdorferi in a GlpD-dependent manner. This study is also the first to identify a suppressor mutation in B. burgdorferi: a glpD deletion restored the wild-type phenotype to the pleiotropic gpsA mutant, including murine infectivity by needle inoculation at high doses, survival under nutrient stress, morphological changes and the metabolic imbalance of NADH and glycerol-3-phosphate. These results illustrate how basic metabolic functions that are dispensable for in vitro growth can be essential for in vivo infectivity of B. burgdorferi and may serve as attractive therapeutic targets.     

Benefits and potential trade‐offs associated with yeast‐like symbionts during virulence adaptation in a phloem‐feeding planthopper

Insect herbivores form symbioses with a diversity of prokaryotic and eukaryotic microorganisms. A role for endosymbionts during host feeding on nutrient‐poor diets – including phloem – is now supported by a large body of evidence. Furthermore, symbiont‐herbivore associations have been implicated in feeding preferences by host races (mainly aphids) on multiple plant species. However, the role of symbionts in mediating herbivore preferences between varieties of the same plant species has received little research attention despite the implications for virulence adaptation to resistant crops. This study investigates the role of yeast‐like symbionts (YLS) in virulence adaptation and host plant switching among populations of the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), that were selected on various rice [Oryza sativa L. (Poaceae)] lines differing in their resistance against herbivores. Planthopper fitness (nymph weight) declined where YLS densities were depleted through heat treatment. However, compared to normal symbiotic planthoppers, the depletion of symbionts did not generally change the relative fitness of planthoppers (each ‘adapted’ to a single natal host) when switched to feed on a range of rice lines (exposed hosts). In some cases, this occurred despite differences in YLS density responses to the various hosts. Furthermore, we detected no fitness costs associated with YLS in adapted populations. Therefore, the results of this study suggest that, whereas YLS are essential for planthopper nutrition, changes in YLS density play little role during virulence adaptation and host plant switching by the brown planthopper.     

A novel iron‐ and copper‐binding protein in the Lyme disease spirochaete

Iron and copper are transition metals that can be toxic to cells due to their abilities to react with peroxide to generate hydroxyl radical. Ferritins and metallothioneins are known to sequester intracellular iron and copper respectively. The Lyme disease pathogen Borrelia burgdorferi does not require iron, but its genome encodes a ferritin‐like Dps (D NA‐binding p rotein from s tarved bacteria) molecule, which has been shown to be important for the spirochaete's persistence in the tick and subsequent transmission to a new host. Here, we show that the c arboxyl‐terminal c ysteine‐r ich (CCR) domain of this protein functions as a copper‐binding metallothionein. This novel fusion between Dps and metallothionein is unique to and conserved in all Borrelia species. We term this molecule BicA for B orrelia i ron‐ and c opper‐binding protein A . An isogenic mutant lacking BicA had significantly reduced levels of iron and copper and was more sensitive to iron and copper toxicity than its parental strain. Supplementation of the medium with iron or copper rendered the spirochaete more susceptible to peroxide killing. These data suggest that an important function of BicA is to detoxify excess iron and copper the spirochaete may encounter during its natural life cycle through a tick vector and a vertebrate host.     

Genetic correlations and sex‐specific adaptation in changing environments

Females and males have conflicting evolutionary interests. Selection favors the evolution of different phenotypes within each sex, yet divergence between the sexes is constrained by the shared genetic basis of female and male traits. Current theory predicts that such “sexual antagonism” should be common: manifesting rapidly during the process of adaptation, and slow in its resolution. However, these predictions apply in temporally stable environments. Environmental change has been shown empirically to realign the direction of selection acting on shared traits and thereby alleviate signals of sexually antagonistic selection. Yet there remains no theory for how common sexual antagonism should be in changing environments. Here, we analyze models of sex‐specific evolutionary divergence under directional and cyclic environmental change, and consider the impact of genetic correlations on long‐run patterns of sex‐specific adaptation. We find that environmental change often aligns directional selection between the sexes, even when they have divergent phenotypic optima. Nevertheless, some forms of environmental change generate persistent sexually antagonistic selection that is difficult to resolve. Our results reinforce recent empirical observations that changing environmental conditions alleviate conflict between males and females. They also generate new predictions regarding the scope for sexually antagonistic selection and its resolution in changing environments.     

Response of nymphal Ixodes scapularis, the primary tick vector of Lyme disease spirochetes in North America, to barriers derived from wood products or related home and garden items.

Forest products were tested to see if they functioned as a barrier to nymphal Ixodes scapularis. These products could potentially be used to define a border between high density and low density tick zones on residential properties in Lyme disease endemic regions of North America. Common home and garden items were also tested. Three wood products effectively acted as barriers to nymphal I. scapularis: Alaska Yellow Cedar sawdust, Alaska Yellow Cedar woodchips, and cellulose. These three products were then weathered to determine how long they remained active. Cellulose and Alaska Yellow Cedar woodchips lost their activity almost immediately (within three days); in contrast, Alaska Yellow Cedar sawdust impeded crossing by nymphal ticks for up to one month. Creating barriers at the woods-lawn interface may someday play a role in integrated campaigns to prevent Lyme disease but will not serve as a stand-alone measure to block transmission of Lyme disease spirochetes.     

Finding disease specific alterations in the co-expression of genes

MOTIVATION: Standard analysis routines for microarray data aim at differentially expressed genes. In this paper, we address the complementary problem of detecting sets of differentially co-expressed genes in two phenotypically distinct sets of expression profiles. RESULTS: We introduce a score for differential co-expression and suggest a computationally efficient algorithm for finding high scoring sets of genes. The use of our novel method is demonstrated in the context of simulations and on real expression data from a clinical study.     

Advances in the treatment of acute graft‐versus‐host disease

Allogeneic hematopoietic stem cell transplantation (HSCT) has been widely used for the treatment of hematologic malignant and non‐malignant hematologic diseases and other diseases. However, acute graft‐versus‐host disease (GVHD) is a life‐threatening complication of allogeneic transplantation. Acute GVHD may occur in 30% of transplant recipients, which is a syndrome of erythematous skin eruption, cholestatic liver disease and intestinal dysfunction, resulting from the activation of donor T lymphocytes by host antigen‐presenting cells, resulting in an immune‐mediated inflammatory response. Recent scientific advances in the understanding of the pathogenesis involved in the development of acute GVHD and clinical investigation have provided more effective therapeutic strategies for acute GVHD. This review focuses on major scientific and clinical advances in the treatment of acute GVHD.