Lifestyle score is associated with cellular immune profiles in healthy Tanzanian adults

Immune system and vaccine responses vary across geographical locations worldwide, not only between high and low-middle income countries (LMICs), but also between rural and urban populations within the same country. Lifestyle factors such as housing conditions, exposure to microorganisms and parasites and diet are associated with rural-and urban-living. However, the relationships between these lifestyle factors and immune profiles have not been mapped in detail. Here, we profiled the immune system of 100 healthy Tanzanians living across four rural/urban areas using mass cytometry. We developed a lifestyle score based on an individual's household assets, housing condition and recent dietary history and studied the association with cellular immune profiles. Seventeen out of 80 immune cell clusters were associated with living location or lifestyle score, with eight identifiable only using lifestyle score. Individuals with low lifestyle score, most of whom live in rural settings, showed higher frequencies of NK cells, plasmablasts, atypical memory B cells, T helper 2 cells, regulatory T cells and activated CD4+ T effector memory cells expressing CD38, HLA-DR and CTLA-4. In contrast, those with high lifestyle score, most of whom live in urban areas, showed a less activated state of the immune system illustrated by higher frequencies of naïve CD8+ T cells. Using an elastic net machine learning model, we identified cellular immune signatures most associated with lifestyle score. Assuming a link between these immune profiles and vaccine responses, these signatures may inform us on the cellular mechanisms underlying poor responses to vaccines, but also reduced autoimmunity and allergies in low- and middle-income countries.

Tandem mass tag labeled quantitative proteomic analysis of differential protein expression on total alkaloid of Aconitum flavum Hand.-Mazz. against melophagus ovinus

Melophagus ovinus disease is a common ectoparasitosis, which can lead to a decrease in animal production performance, product quality, and even death. Aconitum flavum Hand.-Mazz. has many pharmacological activities including insecticidal, heat-clearing, analgesic, and dehumidifying. However, there are few researches focused on the effects and related mechanism of Aconitum flavum Hand.-Mazz. in killing Melophagus ovinus. In this study, 11 alkaloids of Aconitum flavum Hand.-Mazz. were detected, and its total alkaloid activity was determined. The results showed when the total alkaloid concentration was 64 mg/ml and the treatment time was 16 h, the killing rate of Melophagus ovinus reached 100%. Through the observation of the differences in the surface of Melophagus ovinus in each experimental group, it was found that the morphology of the posterior end of the female Melophagus ovinus in the alkaloid treatment group was significantly different from that of the blank and positive control groups, and most of the epidermal tissue was obsessive and missing. Moreover, the enzyme activity determination results of 64 mg/ml group were significantly different when compared with the normal control group, while there was no significant difference in other groups. Then, the Melophagus ovinus gene library was established by the unreferenced genome transcriptome sequencing, the proteomic comparison was performed using tandem mass tag labeled protein detection technology, and finally, the samples were quantitatively analyzed by liquid chromatography-mass spectrometry tandem and bioinformatics methods. Based on the above experimental results, it was speculated that Aconitum flavum Hand.-Mazz. total alkaloids may cause the imbalance of protein disulfide isomerase expressions by affecting the regulation of Hsp40 cellular protein homeostasis and the oxidation of protein disulfide isomerase and related proteins. This would affect the selective recognition of signal sequence, the targeted transport of Sec 61, and the correct folding of the three-dimensional structure of amino acid chain, weakening the clearance of amino acid chains that cannot be correctly folded and eventually resulting in the killing of Melophagus ovinus. This study preliminarily revealed the mechanism of Aconitum flavum Hand.-Mazz. total alkaloids against Melophagus ovinus and provided a theoretical basis for the screening of Melophagus ovinus action targets and the development of new veterinary drugs.

Immune responses of Cyprinus carpio induced by protein extracts of Lernaea cyprinacea Linnaeus, 1758

Lernaea cyprinacea Linnaeus, 1758 is an ectoparasite showing widespread infections in tropical aquaculture, and the present study aimed to determine the specific immune responses against this parasite. For the experiment, whole parasite extracts were injected intraperitoneally into Cyprinus carpio Linnaeus, 1758, and samples of epidermal mucus and blood were drawn at 0, 1, 7 and 14-days post-injection (DPI). The results revealed high levels of protein, protease and lysozyme activities in the experimental fish which were injected with L. cyprinacea protein extract. In the epidermal mucus, the total protein concentration of the control fish was 460 μg/mL, and the level raised significantly to 800 μg/mL in the experimental fish. The lysozyme activity increased from 741.5 u/mL to a peak level of 1448.5 u/mL at 7DPI. The protease activity was also found elated gradually from 2.91 u/μL to 4.49 u/μL at 1 to 14 DPI. In the serum samples, the protein concentration remained steady throughout the experiment period. However, all the experimental fish displayed statistically high levels of lysozyme and protease activity, from 890 u/mL to 1220 u/mL, and 6.10 u/μL to 11.88 u/μL, respectively. In the whole blood samples, the haemoglobin content and the red blood cells (RBC) count did not show any significant change in any of the experimental groups. But, the percentage of lymphocytes showed a marginal increase from 0.47 to 0.6 in the experimental groups. Overall, the immune responses induced by L. cyprinacea protein extracts depicts a pattern of specific responses, in which the local humoral responses dominate the systemic humoral/cellular response. The results further revealed the possibility of futuristic approaches to control freshwater ectoparasites.

Genome variation in tick infestation and cryptic divergence in Tunisian indigenous sheep

Background

Ticks are obligate haematophagous ectoparasites considered second to mosquitos as vectors and reservoirs of multiple pathogens of global concern. Individual variation in tick infestation has been reported in indigenous sheep, but its genetic control remains unknown.

Results

Here, we report 397 genome-wide signatures of selection overlapping 991 genes from the analysis, using ROH, LR-GWAS, XP-EHH, and F_ST, of 600 K SNP genotype data from 165 Tunisian sheep showing high and low levels of tick infestations and piroplasm infections. We consider 45 signatures that are detected by consensus results of at least two methods as high-confidence selection regions. These spanned 104 genes which included immune system function genes, solute carriers and chemokine receptor. One region spanned STX5, that has been associated with tick resistance in cattle, implicating it as a prime candidate in sheep. We also observed RAB6B and TF in a high confidence candidate region that has been associated with growth traits suggesting natural selection is enhancing growth and developmental stability under tick challenge. The analysis also revealed fine-scale genome structure indicative of cryptic divergence in Tunisian sheep.

Conclusions

Our findings provide a genomic reference that can enhance the understanding of the genetic architecture of tick resistance and cryptic divergence in indigenous African sheep.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08321-1.

Invasion history shapes host transcriptomic response to a body-snatching parasite

By shuffling biogeographical distributions, biological invasions can both disrupt long-standing associations between hosts and parasites and establish new ones. This creates natural experiments with which to study the ecology and evolution of host-parasite interactions. In estuaries of the Gulf of Mexico, the white-fingered mud crab (Rhithropanopeus harrisii) is infected by a native parasitic barnacle, Loxothylacus panopaei (Rhizocephala), which manipulates host physiology and behaviour. In the 1960s, L. panopaei was introduced to the Chesapeake Bay and has since expanded along the southeastern Atlantic coast, while host populations in the northeast have so far been spared. We use this system to test the host's transcriptomic response to parasitic infection and investigate how this response varies with the parasite's invasion history, comparing populations representing (i) long-term sympatry between host and parasite, (ii) new associations where the parasite has invaded during the last 60 years and (iii) naïve hosts without prior exposure. A comparison of parasitized and control crabs revealed a core response, with widespread downregulation of transcripts involved in immunity and moulting. The transcriptional response differed between hosts from the parasite's native range and where it is absent, consistent with previous observations of increased susceptibility in populations lacking exposure to the parasite. Crabs from the parasite's introduced range, where prevalence is highest, displayed the most dissimilar response, possibly reflecting immune priming. These results provide molecular evidence for parasitic manipulation of host phenotype and the role of gene regulation in mediating host-parasite interactions.

The salmon louse genome: Copepod features and parasitic adaptations

Copepods encompass numerous ecological roles including parasites, detrivores and phytoplankton grazers. Nonetheless, copepod genome assemblies remain scarce. Lepeophtheirus salmonis is an economically and ecologically important ectoparasitic copepod found on salmonid fish. We present the 695.4 Mbp L. salmonis genome assembly containing ≈60% repetitive regions and 13,081 annotated protein-coding genes. The genome comprises 14 autosomes and a ZZ-ZW sex chromosome system. Assembly assessment identified 92.4% of the expected arthropod genes. Transcriptomics supported annotation and indicated a marked shift in gene expression after host attachment, including apparent downregulation of genes related to circadian rhythm coinciding with abandoning diurnal migration. The genome shows evolutionary signatures including loss of genes needed for peroxisome biogenesis, presence of numerous FNII domains, and an incomplete heme homeostasis pathway suggesting heme proteins to be obtained from the host. Despite repeated development of resistance against chemical treatments L. salmonis exhibits low numbers of many genes involved in detoxification.

Keds, the enigmatic flies and their role as vectors of pathogens

Hippoboscid flies (Diptera: Hippoboscidae), commonly known as keds or louse flies, have been for long time overlooked by the scientific community, and their vector role of infectious agents to humans and domestic animals has been scantly investigated. This is partly due to the fact that the host range for most species is primarily restricted to wildlife, being rarely reported on domestic animals and humans. This led to a scarce scientific knowledge about their biology, ecology, behaviour, epidemiology as well as vector competence. However, the life history of some hippoboscid species, e.g., Melophagus ovinus, Lipoptena cervi and Hippobosca equina, suggests that these ectoparasites are important candidates to vector infectious disease agents (e.g., Rickettsia spp., Borrelia spp., Bartonella spp., Anaplasma phagocytophilum, Theileria ovis). Indeed, the peculiar biological and behavioural traits (i.e., obligatory blood sucking and reproductive physiology) of many ked species make them a suitable pabulum for pathogen's multiplication and for their transmission to receptive hosts. Therefore, studies focusing on the ked bio-ecological aspects as well as on their vector role are advocated along with the control of keds affecting different animal species. This review discusses current information on keds, highlighting their importance as vectors of pathogens of medical and veterinary concern to all animal species, with a special focus on mammals.

Salmon immunological defence and interplay with the modulatory capabilities of its ectoparasite Lepeophtheirus salmonis

The salmon louse Lepeophtheirus salmonis (Lsal) is an ectoparasitic copepod that exerts immunomodulatory and physiological effects on its host Atlantic salmon. Over 30 years of research on louse biology, control, host responses and the host-parasite relationship has provided a plethora of information on the intricacies of host resistance and parasite adaptation. Atlantic salmon exhibit temporal and spatial impairment of the immune system and wound healing ability during infection. This immunosuppression may render Atlantic salmon less tolerant to stress and other confounders associated with current management strategies. Contrasting susceptibility of salmonid hosts exists, and early pro-inflammatory Th1 type responses are associated with resistance. Rapid cellular responses to larvae appear to tip the balance of the host-parasite relationship in favour of the host, preventing severe immune-physiological impacts of the more invasive adults. Immunological, transcriptomic, genomic and proteomic evidence suggests pathological impacts occur in susceptible hosts through modulation of host immunity and physiology via pharmacologically active molecules. Co-evolutionary and farming selection pressures may have incurred preference of Atlantic salmon as a host for Lsal reflected in their interactome. Here, we review host-parasite interactions at the primary attachment/feeding site, and the complex life stage-dependent molecular mechanisms employed to subvert host physiology and immune responses.

Endocrine-immune signaling as a predictor of survival: A prospective study in developing songbird chicks

Immune function varies with an animal's endocrine physiology and energy reserves, as well as its abiotic and biotic environment. This context-dependency is thought to relate to adaptive trade-off resolution that varies from one context to the next; however, it is less clear how state- and environmentally-dependent differences in endocrine-immune signaling relate to survival in natural populations. We begin to address this question in a prospective study on a free-living passerine bird, the tree swallow (Tachycineta bicolor), by capitalizing upon naturally-occurring variation in ectoparasitism in 12-day old chicks. We measured body mass, hematological gene expression of the pro-inflammatory cytokine interleukin-6 (IL-6) as well as corticosterone (CORT) secretion at baseline and in response to 30 min of handling. We found that chicks with ectoparasites had smaller body mass and higher levels of IL-6 gene expression at this critical stage of post-natal growth and development. Mass and IL-6 were positively correlated, but only among parasitized chicks, suggesting that larger chicks mount stronger immune responses when necessary, i.e. in the presence of ectoparasites that are known to induce inflammation. IL-6 mRNA expression was negatively correlated with stress-induced CORT levels, suggesting that this proxy of inflammation may be co-regulated with or coordinated by glucocorticoids. More importantly, these endocrine-immune parameters predicted survival to fledging, which was positively associated with IL-6 mRNA abundance and, to a lesser degree, CORT reactivity. These results suggest a link between endocrine-immune interactions and performance in nature, and as a consequence, they shed light on the potentially adaptive, context-dependent interplay between body mass, immunity, and endocrine physiology during development.

A novel type I cystatin of parasite origin with atypical legumain-binding domain

Parasite inhibitors of cysteine peptidases are known to influence a vast range of processes linked to a degradation of either the parasites' own proteins or proteins native to their hosts. We characterise a novel type I cystatin (stefin) found in a sanguinivorous fish parasite Eudiplozoon nipponicum (Platyhelminthes: Monogenea). We have identified a transcript of its coding gene in the transcriptome of adult worms. Its amino acid sequence is similar to other stefins except for containing a legumain-binding domain, which is in this type of cystatins rather unusual. As expected, the recombinant form of E. nipponicum stefin (rEnStef) produced in Escherichia coli inhibits clan CA peptidases - cathepsins L and B of the worm - via the standard papain-binding domain. It also blocks haemoglobinolysis by cysteine peptidases in the worm's excretory-secretory products and soluble extracts. Furthermore, we had confirmed its ability to inhibit clan CD asparaginyl endopeptidase (legumain). The presence of a native EnStef in the excretory-secretory products of adult worms, detected by mass spectrometry, suggests that this protein has an important biological function at the host-parasite interface. We discuss the inhibitor's possible role in the regulation of blood digestion, modulation of antigen presentation, and in the regeneration of host tissues.

Variation of parasitism patterns in bats during hibernation: the effect of host species, resources, health status, and hibernation period

During critical periods of food shortage or variable climatic conditions, the choice of an appropriate host can increase the survival and reproductive performance of parasites. In turn, one of the unique adaptations to periodical food shortages is hibernation, which is often found among insectivorous bat species in the temperate zone. While hibernating, bats are completely defenseless against both predators and ectoparasites, their immune and endocrine systems are diminished, and survival is dependent on the accumulated fat reserves. Differences in the health status or in the rate of consumption of the resources might also explain species-specific differences in ectoparasite abundance, especially between closely related host species, such as the greater mouse-eared bat (Myotis myotis) and the lesser mouse-eared bat (M. blythii) during hibernation. In the present study, the abundance of two ecologically distinct (summer and winter) types of ectoparasites was examined in terms of its influence on the body condition and hemoglobin content of the two host species. The effects of demographic factors, such as host sex and age, were also investigated. Despite a similar pattern of deteriorating body condition and hemoglobin concentration, M. myotis was more parasitized than was M. blythii. The marked decrease in hemoglobin content in first-year females of both host species correlated with the highest parasite load and indicated a risk of anemia. At the intraspecific level, ectoparasite abundance was not correlated with body condition (resources), but it negatively affected hemoglobin content; however, this mostly concerned M. blythii, which had a lower parasite load. Therefore, it can be concluded that interspecific differences in ectoparasite abundance may result from parasites selecting the host species that is less sensitive to their activity. In turn, in summer ectoparasites, the preference for female hosts is probably attributable to the likelihood of reinfection rather than to an effect of host resources or health status. The absence of sex-based preferences in winter ectoparasites could be explained by equal host availability.

Pathological Changes Associated with Eggs and Larvae of Unionicola sp. (Acari: Unionicolidae) Infecting Strophitus connasaugaensis (Bivalvia: Unionidae) from Alabama Creeks

We detail gross and histopathological changes associated with infection by the eggs, larvae, and cuticular remnants of Unionicola sp. in the mantle, gill, and visceral mass of 25 Alabama creekmussels, Strophitus connasaugaensis, collected during May 2010 through July 2012 from 2 Alabama streams. A multitude (estimated mean intensity >100) of mite eggs and larvae typically infected mantle, gill, and visceral mass integument. Pathology associated with eggs (prevalence = 0.57) and larvae (prevalence = 0.39) typically consisted of localized distension of the infection site; a host response to these infections was indeterminate. However, larval mites embedded in suprabranchial connective tissues were typically encapsulated (prevalence = 0.89). Mite remnants (prevalence = 0.5) occurred in mantle, gill, visceral mass integument, foot, heart, pericardial gland, intestinal lamina propria, and were typically encapsulated. We speculate that S. connasaugaensis clears some infections but is recolonized by autoinfection or horizontal dispersal of mites in the stream. Noteworthy is that high-intensity infections seemingly do not markedly impact the histological picture of mussel tissues, indicating that mites are relatively benign symbionts that are of little concern to mussels under normal environmental conditions.

Evaluation of the murine immune response to Xenopsylla cheopis flea saliva and its effect on transmission of Yersinia pestis

Background/Aims

Arthropod-borne pathogens are transmitted into a unique intradermal microenvironment that includes the saliva of their vectors. Immunomodulatory factors in the saliva can enhance infectivity; however, in some cases the immune response that develops to saliva from prior uninfected bites can inhibit infectivity. Most rodent reservoirs of Yersinia pestis experience fleabites regularly, but the effect this has on the dynamics of flea-borne transmission of plague has never been investigated. We examined the innate and acquired immune response of mice to bites of Xenopsylla cheopis and its effects on Y. pestis transmission and disease progression in both naïve mice and mice chronically exposed to flea bites.

Methods/Principal Findings

The immune response of C57BL/6 mice to uninfected flea bites was characterized by flow cytometry, histology, and antibody detection methods. In naïve mice, flea bites induced mild inflammation with limited recruitment of neutrophils and macrophages to the bite site. Infectivity and host response in naïve mice exposed to flea bites followed immediately by intradermal injection of Y. pestis did not differ from that of mice infected with Y. pestis without prior flea feeding. With prolonged exposure, an IgG1 antibody response primarily directed to the predominant component of flea saliva, a family of 36–45 kDa phosphatase-like proteins, occurred in both laboratory mice and wild rats naturally exposed to X. cheopis, but a hypersensitivity response never developed. The incidence and progression of terminal plague following challenge by infective blocked fleas were equivalent in naïve mice and mice sensitized to flea saliva by repeated exposure to flea bites over a 10-week period.

Conclusions

Unlike what is observed with many other blood-feeding arthropods, the murine immune response to X. cheopis saliva is mild and continued exposure to flea bites leads more to tolerance than to hypersensitivity. The immune response to flea saliva had no detectable effect on Y. pestis transmission or plague pathogenesis in mice.

The saliva of blood-feeding arthropods contains a variety of components that prevent blood clotting and interfere with the immune system of the vertebrate host. These properties have been shown to enhance or inhibit the transmission of different pathogens transmitted by arthropods. Yersinia pestis, the bacterial agent of plague, is maintained in nature by flea to rodent transmission cycles. Most rodents live in close association with fleas and are constantly being bitten by them, but the influence this has on plague transmission is unknown - previous studies used laboratory animals which have never experienced a flea bite. We found that flea bites caused a mild inflammatory response in mice, and eventually an antibody response to components of flea saliva, but did not significantly affect pathogenesis. The transmission of Y. pestis by infected fleas and the incidence rate of bubonic plague mortality were the same in mice that had been exposed to frequent uninfected flea bites and mice with no prior exposure to fleas. Therefore, in contrast to what has been shown for many other arthropod-borne disease systems, vector saliva did not enhance or inhibit Y. pestis infection in mice, regardless of the immune status of the host to flea saliva.

The many roads to parasitism: a tale of convergence

Parasitic organisms account for a large portion of living species. They have arisen on multiple independent occasions in many phyla, and thus encompass a huge biological diversity. This review uses several lines of evidence to argue that this vast diversity can be reduced to a few evolutionary end points that transcend phylogenetic boundaries. These represent peaks in the adaptive landscape reached independently by different lineages undergoing convergent evolution. Among eukaryotic parasites living in or on animals, six basic parasitic strategies are identified based on the number of hosts used per parasite generation, the fitness loss incurred by the host, and the transmission routes used by the parasites. They are parasitoids, parasitic castrators, directly transmitted parasites, trophically transmitted parasites, vector-transmitted parasites and micropredators. These show evidence of convergence in morphology, physiology, reproduction, life cycles and transmission patterns. Parasite-host body size ratios, and the relationship between virulence and intensity of infection, are also associated with the different parasitic strategies, but not consistently so. At the population level, patterns of parasite distribution among hosts are not uniform across all parasitic strategies, but are distinctly different for parasitoids and castrators than for other parasites. To demonstrate that the above six strategies defined for animal parasites are universal, comparisons are made with parasites of plants, in particular, plant-parasitic nematodes and parasitic angiosperms; these are shown to follow the same evolutionary trajectories seen among animal parasites, despite huge physiological and ecological differences between animals and plants. Beyond demonstrating the inevitable convergence of disparate lineages across biological hyperspace towards a limited set of adaptive strategies, this synthesis also provides a unifying framework for the study of parasitism.

Characterization of the immunological response to Dermanyssus gallinae infestation in domestic fowl

Dermanyssus gallinae is a haematophagous ectoparasite of birds, which adversely affects both production and welfare of commercial poultry. Poultry in commercial production systems chronically exposed to D. gallinae do not appear to develop immunity to the mite. The objective of the current study was to determine the initial immune response of domestic fowl following exposure to D. gallinae. Two groups of birds (11 birds/group) had mite chambers secured to their backs. Controls received no mites, while infested birds received 200 unfed female D. gallinae on day 0 which were then removed on day 1 or 2. Spleen samples were collected on days -1, 1, 2 and 5. The expression of Th1 (IFNgamma, CXCLi2, IL6 and IL18), Th2 (IL4, IL10 and IL13) cytokines/chemokines normalized against a reference gene, GAPDH, were determined by semi-quantitative RT-PCR. Although there were no significant differences between treatments, numerical trends were observed. Th2 cytokine expression was not detected in any birds on any day. IL6, CXCLi2, IFNgamma and IL18 expression was increased on day 1 in the infested group, while on day 2 CXCLi2 and IFNgamma were lower and IL6 and IL18 levels were similar between treatments. The IL18 expression was similar between treatments on day 5, while IL6 and IFNgamma levels were increased and CXCLi2 expression was decreased in the infested group. Data suggest that D. gallinae feeding stimulates Th1 and pro-inflammatory cytokines/chemokines initially (day 1) followed by their subsequent down regulation. This study is the first report of the characterization of the immunological response of the domestic fowl to controlled numbers of D. gallinae.

Nestedness of ectoparasite-vertebrate host networks

Determining the structure of ectoparasite-host networks will enable disease ecologists to better understand and predict the spread of vector-borne diseases. If these networks have consistent properties, then studying the structure of well-understood networks could lead to extrapolation of these properties to others, including those that support emerging pathogens. Borrowing a quantitative measure of network structure from studies of mutualistic relationships between plants and their pollinators, we analyzed 29 ectoparasite-vertebrate host networks—including three derived from molecular bloodmeal analysis of mosquito feeding patterns—using measures of nestedness to identify non-random interactions among species. We found significant nestedness in ectoparasite-vertebrate host lists for habitats ranging from tropical rainforests to polar environments. These networks showed non-random patterns of nesting, and did not differ significantly from published estimates of nestedness from mutualistic networks. Mutualistic and antagonistic networks appear to be organized similarly, with generalized ectoparasites interacting with hosts that attract many ectoparasites and more specialized ectoparasites usually interacting with these same “generalized” hosts. This finding has implications for understanding the network dynamics of vector-born pathogens. We suggest that nestedness (rather than random ectoparasite-host associations) can allow rapid transfer of pathogens throughout a network, and expand upon such concepts as the dilution effect, bridge vectors, and host switching in the context of nested ectoparasite-vertebrate host networks.

SAAG-4 is a novel mosquito salivary protein that programmes host CD4 T cells to express IL-4

Mosquitoes represent the most important vector for transmitting pathogens that cause human disease. Central to pathogen transmission is the ability to divert the host immune system away from Th1 and towards Th2 responsiveness. Identification of the mosquito factor(s) critical for programming Th2 responsiveness should therefore lead to strategies to neutralize their function and thus prevent disease transmission. In the current study, we used a TCR transgenic adoptive transfer system to screen gene products present in the saliva of the mosquito Aedes aegypti for their ability to programme CD4 T cells to express the signature Th2 cytokine IL-4. The clone SAAG-4 encodes a secreted protein with a predicted size of 20 kDa whose function has previously been uncharacterized. Notably, SAAG-4 reduced host CD4 T cell expression of the signature Th1 cytokine IFN-gamma while simultaneously increasing expression of IL-4. SAAG-4 is therefore the first identified mosquito factor that can programme Th2 effector CD4 T cell differentiation.

Comparative immunogenicity of Haemaphysalis longicornis and Rhipicephalus (Boophilus) microplus calreticulins

The ticks Rhipicephalus (Boophilus) microplus and Haemaphysalis longicornis are blood-sucking ectoparasites of bovines, causing serious damages to the livestock production. The main control method for these ticks is based on acaricides. However, the use of vaccines has been studied as a promising control strategy. Calreticulin (CRT) is a multifunctional, predominantly intracellular protein present in almost all cells of animals. The secretion of CRT during feeding might be linked to the modulation of the parasite-host interaction. In the present study, recombinant CRTs of R. microplus (rBmCRT) and H. longicornis (rHlCRT) were expressed in Escherichia coli and purified by ion exchange chromatography and used for the immunization of bovines and mouse. ELISA demonstrated that both rCRTs are recognized by the sera of immunized bovines. In silico, despite the difference in amino acid sequences, antigenic index analysis of HlCRT and BmCRT using the Jameson-Wolf algorithm indicated that both proteins were very similar in antigenicity index, although six different epitopes between the tick CRTs have been inferred. These data were corroborated by competitive ELISA analyses, which suggest the presence of different epitopes within the proteins. Western blot analyses showed that anti-rBmCRT and anti-rHlCRT bovine sera also recognized the native proteins in larvae extracts and, moreover, sera of bovines immunized with saliva and extract of salivary glands recognized both recombinant CRTs. Thus, mouse and bovine immune system recognized rCRTs, resulting in the production of antibodies with similar specificity for both recombinant proteins, although different epitopes could be distinguished between rBmCRT and rHlCRT.

Haematophagous arthropod saliva and host defense system: a tale of tear and blood

The saliva from blood-feeding arthropod vectors is enriched with molecules that display diverse functions that mediate a successful blood meal. They function not only as weapons against host's haemostatic, inflammatory and immune responses but also as important tools to pathogen establishment. Parasites, virus and bacteria taking advantage of vectors' armament have adapted to facilitate their entry in the host. Today, many salivary molecules have been identified and characterized as new targets to the development of future vaccines. Here we focus on current information on vector's saliva and the molecules responsible to modify host's hemostasis and immune response, also regarding their role in disease transmission.

Immunotoxicology in wood mice along a heavy metal pollution gradient

We carried out an immunotoxicological field study of wood mice in three populations along a heavy metal pollution gradient. Heavy metal concentrations in liver tissue indicated that exposure to silver, arsenic, cadmium, cobalt and lead decreased with increasing distance from a non-ferrous smelter. Host resistance to the endoparasite Heligmosomoides polygyrus decreased with increasing exposure, while the abundance of tick larvae and the nematode Syphacia stroma was unrelated to heavy metal exposure. Spleen mass was increased at the intermediate and the most polluted sites and was positively correlated with the number of H. polygyrus and tick larvae. Proportion of early apoptotic leukocytes increased towards the smelter and was positively related to cadmium exposure. Red and white blood cell counts and lysozyme activity showed no relationship with metal exposure. All together, our observations suggest negative effects of heavy metal exposure on the immune function of wood mice under field conditions.

Immune response in demodicosis

BACKGROUND

Demodex folliculorum and Demodex brevis are obligatory parasites in the hair follicles and in the pilosebaceous glands. Although most people are infested with these mites, only a small number develop the clinical symptoms of demodicosis. The objective of this study was to determine the distinguishing features of the immune response to the infestation of the skin by Demodex mites.

METHODS

Twenty-nine patients with human demodicosis and 13 age- and sex-matched healthy subjects participated in the study. The presence of mites was determined by microscopic inspection of secretion from sebum glands. The immune response was evaluated in the peripheral blood by identifying membrane markers of different immune cells using monoclonal antibodies, while the concentration of immunoglobulin (Ig)A, IgM and IgG was calculated by simple radial immunodiffusion using anti-IgA, anti-IgM and anti-IgG. The level of circulating immune complexes and total haemolytic complement, as well as the preparatory and digestive function of neutrophils, and the functional activity of leucocytes were also studied.

RESULTS

The absolute number of CD95+ was higher in patients with demodicosis. The absolute number of CD3+, CD4+, CD8+ and CD16+ cells, the ratio CD3+/CD20+ and the functional activity of leucocytes were significantly lower in individuals infested with Demodex mites. No significant differences were found in the percentage and absolute number of CD20+ cells, the ratio of CD4+/CD8+ T-cell subpopulations, circulating immune complexes, level of serum complement activity (CH(50)), activity and index of phagocytosis and the levels of IgA, IgM and IgG antibodies between individuals infested with Demodex mites and the control group.

CONCLUSION

The readiness of lymphocytes to undergo apoptosis increases in parallel to the increasing density of the mites. This could be the result of local immunosuppression caused by the mites, which allows them to survive in the host skin.

Cloning and sequencing of putative calreticulin complementary DNAs from four hard tick species

Calreticulin (CRT) is a calcium-binding protein and has many functions in eukaryotic cells. CRT is possibly involved in parasite host immune system evasion. To better understand the molecular basis of CRT in ticks, we cloned and sequenced 4 full-length complementary DNAs (cDNAs) from the hard tick species, Dermacentor variabilis, Haemaphysalis longicornis, Ixodes scapularis, and Rhipicephalus sanguineus, using the technique of rapid amplification of cDNA ends. The deduced amino acid sequences share high identities (between 77 and 98%) with 3 known tick CRT sequences. The major characteristics of known CRTs are observed in all 4 of our deduced tick CRTs. These include 3 major domains, a signal peptide sequence at the beginning of the coding region, 2 triplets of conserved regions, cysteine sites providing disulfide bridges for N-terminal folding, and a nuclear localization signal. Remarkably, the replacement of the endoplasmic reticulum retention signal KDEL by HEEL, which is believed to be associated with secretion of CRT into the host during feeding and was previously recorded only in 2 ticks and a hookworm, is also present in all 4 of our tick putative CRTs. In addition, the CRT gene is potentially useful for tick phylogenetic reconstruction.

Modulation of bovine lymphocyte response by salivary gland extracts of the stable fly, Stomoxys calcitrans (Diptera: Muscidae)

The effect of salivary gland extract of the stable fly, Stomoxys calcitrans (L), on bovine lymphocyte proliferation was determined, and antibody reactivity to salivary gland proteins was characterized in cattle exposed to stable flies. Salivary glands were dissected from male and female flies (4-8 d after eclosion), and protein extracts were made by freeze-thaw cycles. Salivary gland extract (SGE, 1 and 5 microg) significantly inhibited mitogen-driven proliferation of bovine lymphocytes, compared with 1 and 5 microg of identically prepared midgut extract (ANOVA, P < 0.05). Phytohemagglutinin A (PHA) stimulated lymphocyte responses were suppressed by 61.7 and 79.5% (mean values) with 1 and 5 microg of SCE, whereas concanvalin A (Con A) stimulated responses were suppressed by 62.9 and 77.1% (1 and 5 microg). In contrast, midgut extract (1 and 5 microg) minimally suppressed PHA (12.7% +/- 12.6 and 18.7% +/- 15.5) and Con A-driven responses (13.8% +/- 20.5 and 24.6% +/- 14.9), respectively. Viability studies using propidium iodide and flow cytometry demonstrated that SGE was not cytotoxic. Two-color immunofluorescence studies identified T and B lymphocytes as the nonviable cells in the cultures. Western blot analysis of serum collected from five dairy cows during periods of low and high fly exposure identified an immunodominant 27 kDa protein among the salivary gland proteins. These results indicate that exposure of cattle to stable fly saliva during blood feeding results in an antibody response to salivary proteins and that the saliva has a potential to modulate T lymphocyte function.

Effect of salivary gland extracts from the tick, Boophilus microplus, on leucocytes from Brahman and Hereford cattle

The effect of salivary gland extract (SGE) from Boophilus microplus on peripheral blood lymphocytes, neutrophils and monocytes from Brahman (Bos indicus) and Hereford (Bos taurus) cattle was investigated. SGE (8 micro g) significantly inhibited the proliferation response of lymphocytes to concanavalin A from both Brahman and Hereford cattle by 89% and 41%, respectively. The difference in inhibition between the two breeds was highly significant (P < 0.01), whilst at 1 micro g of SGE, significant inhibition of lymphocytes occurred only in Hereford cattle (34%). Flow cytometric analysis of monocytes and neutrophils showed that SGE (40 micro g) significantly reduced both the proportion of cells actively phagocytosing Escherichia coli labelled with fluorescein isothiocyanate (E. coli-FITC) and the uptake of E. coli-FITC in Brahman cattle. However, in Hereford cattle, a significant depression in uptake was only observed in neutrophils. The proportion of monocytes and neutrophils with oxidative activity was significantly suppressed in the presence of SGE in both breeds of cattle. These results indicate that peripheral blood leucocytes from different breeds of cattle respond differently to SGE.

Cloning and partial characterization of a Boophilus microplus (Acari: Ixodidae) calreticulin

We report the cloning, sequence characterization and expression analysis of a calreticulin (CRT) coding cDNA of Boophilus microplus. CRT is a calcium-binding protein involved in multiple cell functions and possibly implicated in parasites host immune system evasion. The CRT cDNA sequence and its molecular characterization are described. Sequence similarity and phylogenetic analyses indicate a close relationship to other arthropod CRT sequences. The CRT cDNA was also expressed in a procariotic system and the recombinant protein (rBmCRT) was used to raise antibodies in a rabbit. Expression analyses of the corresponding gene in different developmental stages and tissues were performed by RT-PCR and Western-blot, which indicated a ubiquitous expression of the B. microplus calreticulin gene and demonstrated its presence in saliva. Sera of tick-infested bovines suggested that this protein may not be able to induce an IgG-based humoral response in its natural host.

Progress toward molecular characterization of ectoparasite modulation of host immunity

Ectoparasitic arthropods and vector-borne infectious agents are global medical and veterinary public health concerns. Economic impact due to direct effects of infestation and disease transmission are significant. These problems are increased by development of arthropod resistance to insecticides/acaricides; drug resistance of vector-borne pathogens; and, lack of effective vaccines to prevent many of these diseases. There is much to be gained from understanding the complex array of immunological interactions occurring at the arthropod-host-pathogen interface. One application of that knowledge is the development of novel vaccines for the control of both ectoparasitic arthropods and the diseases they transmit. We now realize that blood-feeding arthropods are not simply flying or crawling hypodermic needles and syringes. Ectoparasitic arthropods are not passive partners in their relationships with the immune systems of their hosts. These clever invertebrates produce numerous pharmacologically active molecules that help them migrate through tissues of their hosts or to successfully obtain blood meals. Arthropod parasites stimulate a spectrum of host immune responses that could potentially impair development, reduce feeding success, or kill the ectoparasite. Not unexpectedly, arthropods have developed sophisticated arsenals of countermeasures that modulate or deviate host immune responses. Not only does arthropod modulation of host immunity facilitate survival in tissues or increase the likelihood of obtaining a blood meal, but it is increasingly recognized as a critical factor in pathogen transmission. Those countermeasures to host immune defenses are the topics of this review. Emphasis is placed on our current understanding of the molecular bases of those changes; the molecules responsible for host immunomodulation; contemporary approaches for studying these complex relationships; and, the potential for using this information to develop innovative vaccine-based control strategies.

Protection against cutaneous leishmaniasis resulting from bites of uninfected sand flies

Despite the fact that Leishmania are transmitted exclusively by sand flies, none of the experimental models of leishmaniasis have established infection via sand fly bites. Here we describe a reproducible murine model of Leishmania major infection transmitted by Phlebotomus papatasi. Prior exposure of mice to bites of uninfected sand flies conferred powerful protection against Leishmania major that was associated with a strong delayed-type hypersensitivity response and with interferon-gamma production at the site of parasite delivery. These results have important implications for the epidemiology of cutaneous leishmaniasis and suggest a vaccination strategy against this and possibly other vector-borne diseases.

The biological and immunomodulatory properties of sand fly saliva and its role in the establishment of Leishmania infections

Sand fly saliva contains a rich array of pharmacologically active compounds whose primary function is to prevent the hemostatic mechanisms of the host. Several studies have ascribed immunosuppressive properties to sand fly saliva as well as an exacerbative effect on Leishmania infectivity for their mammalian hosts. This review provides a comprehensive account of sand fly salivary components, the immunomodulatory properties exhibited by some of its molecules, and describes the findings concerning the influence of saliva on Leishmania infections. The potential use of saliva as part of an anti-Leishmania vaccine for the mammalian host is also addressed.

Influence of repeated infestations with pathogen-free Ixodes scapularis (Acari: Ixodidae) on in vitro lymphocyte proliferation responses of C3H/HeN mice

In the United States, Ixodes scapularis Say has been implicated as the vector of at least three human pathogens. Tick induced modulation of host immunity is increasingly recognized as an important factor in successful transmission or establishment of tick-borne pathogens. This study was conducted to determine the effects of repeated infestations with pathogen-free I. scapularis nymphs on in vitro proliferative responses of splenic lymphocytes from C3H/HeN mice. Lymphocytes from repeatedly infested and uninfested mice were exposed to concanavalin A (Con A), Escherichia coli Castellini & Chalmers lipopolysaccharide (LPS), or I. scapularis salivary gland soluble proteins (SGSP), to determine if lymphocyte responses differed between tick-exposed and nonexposed mice. Female C3H/HeN mice were infested one to four times with pathogen-free I. scapularis nymphs, with a 14-d tick-free period between each exposure. After each infestation, tick biology parameters were measured and lymphocyte proliferative responses assessed. Acquired resistance to I. scapularis was not evident in mice subjected to tick feeding. Significant differences in the responses of lymphocytes exposed to I. scapularis SGSP were observed between infested and noninfested mice. In contrast, few differences between infested and noninfested mice were evident for lymphocytes exposed to Con A or LPS. Our results suggest that repeated exposure to I. scapularis nymphs does not affect Con A or LPS-induced proliferation of splenic lymphocytes, but significantly effects lymphocyte responses to tick salivary gland antigens.

Influence of soluble proteins from the salivary glands of ixodid ticks on the in-vitro proliferative responses of lymphocytes from BALB/c and C3H/HeN mice

In the U.S.A., Borrelia burgdorferi, the causative agent of Lyme borreliosis, is transmitted to humans by the ticks Ixodes scapularis and I. pacificus. Tick modulation of host immunity is an important factor in tick transmission of such pathogens. The proliferative responses of lymphocytes from BALB/c and C3H/HeN mice exposed to the salivary-gland soluble proteins (SGSP) of I. scapularis, I. pacificus or Dermacentor andersoni were therefore compared in vitro. This produced the present report, the first to describe the effects of I. pacificus SGSP on the proliferative responses of a host's lymphocytes in vitro. The effects of four concentrations of SGSP from each tick species were evaluated with unstimulated, and concanavalin-A-stimulated lymphocytes of each mouse strain. The responses of lymphocytes from both mouse strains were significantly effected when exposed to SGSP derived from each tick species. Responses of the unstimulated lymphocytes to SGSP indicated that the proteins from I. pacificus suppressed in-vitro lymphocyte proliferation to a greater degree than those from the other species investigated. For the concanavalin-A stimulated cells, however, suppression of the proliferative responses was greatest for cells exposed to I. scapularis SGSP.

Transmission of vesicular stomatitis virus from infected to noninfected black flies co-feeding on nonviremic deer mice

Vesicular stomatitis is an economically important arboviral disease of livestock. Viremia is absent in infected mammalian hosts, and the mechanism by which insects become infected with the causative agents, vesicular stomatitis viruses, remains unknown. Because infected and noninfected insects potentially feed on the same host in nature, infected and noninfected black flies were allowed to feed on the same host. Viremia was not detected in the host after infection by a black fly bite, but because noninfected black flies acquired the virus while co-feeding on the same host with infected black flies, it is concluded that a viremic host is not necessary for an insect to be infected with the virus. Thus co-feeding is a mechanism of infection for an insect-transmitted virus.