Rhipicephalus (Boophilus) microplus: distinct acute phase proteins vary during infestations according to the genetic composition of the bovine hosts, Bos taurus and Bos indicus

Two protocols using fluralaner for Rhipicephalus microplus strategic control on taurine cattle in a tropical region

BACKGROUND

The present study aimed to evaluate the effects of different treatment strategies using a new commercial formulation containing pour-on fluralaner on Rhipicephalus microplus infestation in cattle and in pastures in a tropical climate region where up to five generations of this tick species can occur per year.

METHODS

Forty-five naturally infested cattle were divided into three experimental groups: T01, treated with fluralaner (2.5 mg/kg) pour-on every 42 days; T02, the cattle received the first treatment with fluralaner on Day 0 but the next treatment involved a weekly visual evaluation; T03, control, received palliative treatment with a spray formulation when the group mean was ≥ 30 ticks. Counts of female R. microplus were performed weekly until day 343, and larval counts on pasture were performed on Days 0, 30, and 60 and every 30 days until Day 330.

RESULTS

Using fluralaner, six applications were performed in Group T01, and four were performed in Group T02. In the control group (T03), it was necessary to perform eight palliative acaricide treatments with the spray formulation. The animals in T01 and T02 showed lower mean tick counts (p ≤ 0.05) than the control group (T03) on 28 and 27 of the 49 evaluated dates, respectively. In the paddock where the animals were kept as controls, the R. microplus larvae counts increased to 1458. In the paddocks where the animals were treated with fluralaner, the number was ≤ 19 per paddock during the study.

CONCLUSIONS

The different strategic treatment protocols performed with pour-on fluralaner (2.5 mg/kg) over a year in taurine cattle in a tropical region with a history of up to five annual generations of cattle ticks were effective, maintaining levels of R. microplus infestations in animals and in pastures close to zero in most of the study. Depending on the retreatment criterion adopted, the number of applications per year may be lower, resulting in a reduction in the mean cost of acaricide treatment per year and lower exposure of R. microplus populations to the active ingredient, resulting in lower resistance and selection pressure.

Hematological Normality, Serum Biochemistry, and Acute Phase Proteins in Healthy Beef Calves in the Brazilian Savannah

The Brazilian savannah region, characterized by high average temperatures, well-defined rainy and dry seasons, soil with low productive potential, and high pressure for parasitic diseases, is home to the highest percentage of the beef herd, which is the world's largest commercial beef producer. Therefore, breeds that present rusticity combined with productivity are the focus of research in cattle breeding in the region. Considering their geographic particularities and their effects on the animals' blood parameters, the objective was to study the behavior of hematological variables, serum biochemistry, and acute phase proteins in beef calves at weaning age. Jugular blood samples were collected in a single day from 30 weaning calves (about eight months old and 200 kg of body weight) from the following breeds: Nellore, Senepol, Nellore × Aberdeen Angus cross, Nellore × Senepol cross, and Nellore × Aberdeen Angus × Senepol cross. Hematological data were obtained using an automatic cell counter, serum biochemical measurements were obtained using commercial kits, and the electrophoretogram was obtained using the SDS-page technique. In general, the results were consistent with data already published in similar situations regarding health status, age, and level of metabolic activity. However, differences observed between groups can be explained by differences observed in other concurrent variables like temperament. The pure zebu breed was more reactive than pure taurine. While crossbreds showed intermediate values, and parasitic infestation, the pure taurine breed with higher parasite infestation, while the zebu breed had lower values, which produced effects in some laboratory tests, and generated differences between breeds. In conclusion, the reference intervals available for healthy animals can be routinely used without interference from the geographic region for animals produced without nutritional failures as long as changes are recorded in pathological, infectious, metabolic, or nutritional deficiency situations. However, it is suggested that a study covering a larger number of herds may demonstrate a greater geographic effect on the studied variables.

Circulating oxidative stress and acute phase protein levels in horses infested with ticks

Ticks have saliva rich in immunoregulatory molecules that interfere with the host's physiology in order to feed. This study aimed to evaluate the concentration of acute phase proteins and circulating oxidative stress in response to infestation by Amblyomma sculptum and Dermacentor nitens in two breed horses, Mangalarga Marchador and Breton Postier, to define resistance or susceptibility to ticks. Among the oxidative stress markers, we observed lower malondialdehyde and nitric oxide in horses with tick infestation, consequently not altering the antioxidant enzymes. Breton Postier with tick infestation showed a reduction in the ferric reducing ability of plasma (FRAP), which may be due to lower feeding of the host due to the stress caused by the infestation or even to sequestration of components induced by the tick during blood feeding. The alpha-1-antitrypsin, an acute phase protein, showed an increase in Mangalarga Marchador with tick infestation; curiously it is related to a protective action against tissue damage, pathogens and parasites. We could assume that Mangalarga Marchador showed a better response to ticks when compared to Breton Postier. However, it is still early to define the resistance or susceptibility to ticks, as we did not observe significant changes in most of the analyzed variables. Further studies are needed to understand the compounds and mechanisms of action of the tick saliva in the acute phase proteins and the possible relationships of oxidative stress in the host and the tick during blood feeding.

Host Serum Proteins as Potential Biomarkers of Bovine Tuberculosis Resistance Phenotype

Eradication of bovine tuberculosis (bTB) continues to be a worldwide challenge. The lack of reliable vaccines dampens the control and eradication programs of Mycobacterium bovis infection and spread. Selection and breeding of cattle resistant to M. bovis infection would greatly enhance the effectiveness of bTB eradication programs. Here, we have evaluated the potential of serum proteins as biomarkers of cattle resistance to bTB in Holstein-Friesian cows, 6-8-year-old, born and raised in similar conditions in herds with bTB prevalence >30%. Serum proteins obtained from uninfected cows (bTB-resistant; R) were compared to those from infected cows (bTB-susceptible; S), defined by a negative or positive bTB diagnosis, respectively. bTB diagnosis included: (i) single intradermal (caudal fold) tuberculin test, (ii) whole blood IFN-gamma test, (iii) gross visible lesions in lymph nodes and lungs by inspection at the abattoir, and (iv) a bacteriological culture for M. bovis. Using 2D-GE and LC-ESI-MS/MS, we found higher expression levels of primary amine oxidase (AO), complement component 5 (C5), and serotransferrin (TF) in R cattle than S cattle. In-house developed and standardized ELISAs for these novel biomarkers showed the best sensitivities of 72, 77, 77%, and specificities of 94, 94, 83%, for AO, C5, and TF, respectively. AUC-ROC (95% CI) values of 0.8935 (0.7906-0.9964), 0.9290 (0.8484-1.010), and 0.8580 (0.7291-0.9869) were obtained at cut-off points of 192.0, 176.5 ng/ml, and 2.1 mg/ml for AO, C5, and TF, respectively. These proteins are involved in inflammatory/immunomodulatory responses to infections and may provide a novel avenue of research to determine the mechanisms of protection against bTB. Overall, our results indicate that these proteins could be novel biomarkers to help identify cattle resistant to bTB, which in turn could be used to strengthen the effectiveness of existing eradication programs against bTB.

Serum proteomes of Santa Gertrudis cattle before and after infestation with Rhipicephalus australis ticks

Previous studies have applied genomics and transcriptomics to identify immune and genetic markers as key indicator traits for cattle tick susceptibility/resistance; however, results differed between breeds, and there is lack of information on the use of host proteomics. Serum samples from Santa Gertrudis cattle (naïve and phenotyped over 105 days as tick-resistant [TR] or tick-susceptible [TS]) were used to conduct differential abundance analyses of protein profiles. Serum proteins were digested into peptides followed by identification and quantification using sequential window acquisition of all instances of theoretical fragment ion mass spectrometry. Before tick infestation, abundance of 28 proteins differed significantly (adjusted P < 10^-5 ) between TR and TS. These differences were also observed following tick infestation (TR vs TS) with a further eight differentially abundant proteins in TR cattle, suggesting possible roles in adaptive responses. The intragroup comparisons (TS-0 vs TS and TR-0 vs TR) showed that tick infestation elicited quite similar responses in both groups of cattle, but with relatively stronger responses in TR cattle. Many of the significantly differentially abundant proteins in TR Santa Gertrudis cattle (before and after tick infestation) were associated with immune responses including complement factors, chemotaxis for immune cells and acute-phase responses.

Network analysis uncovers putative genes affecting resistance to tick infestation in Braford cattle skin

Background

Genetic resistance in cattle is considered a suitable way to control tick burden and its consequent losses for livestock production. Exploring tick-resistant (R) and tick-susceptible (S) hosts, we investigated the genetic mechanisms underlying the variation of Braford resistance to tick infestation. Skin biopsies from four-times-artificially infested R (n = 20) and S (n = 19) hosts, obtained before the first and 24 h after the fourth tick infestation were submitted to RNA-Sequencing. Differential gene expression, functional enrichment, and network analysis were performed to identify genetic pathways and transcription factors (TFs) affecting host resistance.

Results

Intergroup comparisons of hosts before (Rpre vs. Spre) and after (Rpost vs. Spost) tick infestation found 51 differentially expressed genes (DEGs), of which almost all presented high variation (TopDEGs), and 38 were redundant genes. Gene expression was consistently different between R and S hosts, suggesting the existence of specific anti-tick mechanisms. In the intragroup comparisons, Rpost vs. Rpre and Spost vs. Spre, we found more than two thousand DEGs in response to tick infestation in both resistance groups. Redundant and non-redundant TopDEGs with potential anti-tick functions suggested a role in the development of different levels of resistance within the same breed. Leukocyte chemotaxis was over-represented in both hosts, whereas skin degradation and remodeling were only found in TopDEGs from R hosts. Also, these genes indicated the participation of cytokines, such as IL6 and IL22, and the activation of Wingless (WNT)-signaling pathway. A central gene of this pathway, WNT7A, was consistently modulated when hosts were compared. Moreover, the findings based on a genome-wide association study (GWAS) corroborate the prediction of the WNT-signaling pathway as a candidate mechanism of resistance. The regulation of immune response was the most relevant pathway predicted for S hosts. Members of Ap1 and NF-kB families were the most relevant TFs predicted for R and S, respectively.

Conclusion

This work provides indications of genetic mechanisms presented by Braford cattle with different levels of resistance in response to tick infestation, contributing to the search of candidate genes for tick resistance in bovine.

Distinct immune response profile during rhipicephalus (boophilus) microplus infestations of guzerat dairy herd according to the maternal lineage ancestry (mitochondrial DNA)

Rhipicephalus (Boophilus) microplus ticks cause major constraints to public and livestock health, and serious economic losses. It is well known that the immune response to infestations with cattle ticks is influenced by the host genetic background leading to distinct immunological profiles between bovine hosts genetically susceptible and resistant. The influence of Bos indicus (Bi) and Bos taurus (Bt) maternal lineage ancestry of mitochondrial DNA in the profile of the immune response of Zebu cattle to ticks remains unknown. The present work evaluated the hematological parameters and the immune response profile in the peripheral blood of a Guzerat dairy herd, further categorized into two maternal lineage ancestry subgroups (Bi-mtDNA and Bt-mtDNA) after experimental infestation with larvae of R. microplus. Our data demonstrated that although hematological and erythrogram analysis showed a similar profile throughout, some cell populations present a distinct profile between the groups. Especially MON, CD335⁺ and CD8⁺ T-cells are predominant in Bi-mtDNA. Moreover, an overall picture of R. microplus infestation demonstrated that Bi-mtDNA presented a more efficient and earlier innate immune response. Bi-mtDNA showed a greater number of connections with R. microplus counts and also with the CD25⁺ activation marker of the immune response. Bi-mtDNA showed greater number of connections, with an important participation of the innate immune while Bt-mtDNA showed a delay in the immune response. Elucidating the mechanisms by which resistant animals prevent heavy tick infestation is a crucial step in the development of predictive biomarkers for tick resistance for use in selective breeding programs, and is also potentially useful for the development of anti-tick vaccines.

Non-infectious illness after tick bite

Tick bites are common and may have non-infectious complications. Reactions range from local reactions to systemic syndromes, tick paralysis, mammalian meat allergy and tick anaphylaxis. Management revolves around prevention with vector avoidance and immediate removal of the tick if bitten. Treatment of bite reactions is usually symptomatic only with anti-histamines or corticosteroids. Adrenaline may be indicated for severe cases.

Bovine Immune Factors Underlying Tick Resistance: Integration and Future Directions

The mechanisms underlying tick resistance within and between cattle breeds have been studied for decades. Several previous papers on bovine immune parameters contributing to tick resistance discussed findings across DNA, RNA, protein, cellular, and tissue levels. However, the differences between bovine host species, tick species and the experimental layouts were not always taken into account. This review aims to (a) give a comprehensive summary of studies investigating immune marker differences between cattle breeds with varying degrees of tick resistance, and (b) to integrate key findings and suggest hypotheses on likely immune-regulated pathways driving resistance. Experimental issues, which may have skewed conclusions, are highlighted. In future, improved experimental strategies will enable more focused studies to identify and integrate immune markers and/or pathways. Most conclusive thus far is the involvement of histamine, granulocytes and their associated pathways in the tick-resistance mechanism. Interestingly, different immune markers might be involved in the mechanisms within a single host breed in contrast to between breeds. Also, differences are evident at each tick life stage, limiting the level to which datasets can be compared. Future studies to further elucidate immune molecule dynamics across the entire tick life cycle and in-depth investigation of promising markers and pathways on both molecular and cellular level are in dire need to obtain a scientifically sound hypothesis on the drivers of tick resistance.

Cattle Tick Rhipicephalus microplus-Host Interface: A Review of Resistant and Susceptible Host Responses

Ticks are able to transmit tick-borne infectious agents to vertebrate hosts which cause major constraints to public and livestock health. The costs associated with mortality, relapse, treatments, and decreased production yields are economically significant. Ticks adapted to a hematophagous existence after the vertebrate hemostatic system evolved into a multi-layered defense system against foreign invasion (pathogens and ectoparasites), blood loss, and immune responses. Subsequently, ticks evolved by developing an ability to suppress the vertebrate host immune system with a devastating impact particularly for exotic and crossbred cattle. Host genetics defines the immune responsiveness against ticks and tick-borne pathogens. To gain an insight into the naturally acquired resistant and susceptible cattle breed against ticks, studies have been conducted comparing the incidence of tick infestation on bovine hosts from divergent genetic backgrounds. It is well-documented that purebred and crossbred Bos taurus indicus cattle are more resistant to ticks and tick-borne pathogens compared to purebred European Bos taurus taurus cattle. Genetic studies identifying Quantitative Trait Loci markers using microsatellites and SNPs have been inconsistent with very low percentages relating phenotypic variation with tick infestation. Several skin gene expression and immunological studies have been undertaken using different breeds, different samples (peripheral blood, skin with tick feeding), infestation protocols and geographic environments. Susceptible breeds were commonly found to be associated with the increased expression of toll like receptors, MHC Class II, calcium binding proteins, and complement factors with an increased presence of neutrophils in the skin following tick feeding. Resistant breeds had higher levels of T cells present in the skin prior to tick infestation and thus seem to respond to ticks more efficiently. The skin of resistant breeds also contained higher numbers of eosinophils, mast cells and basophils with up-regulated proteases, cathepsins, keratins, collagens and extracellular matrix proteins in response to feeding ticks. Here we review immunological and molecular determinants that explore the cattle tick Rhipicephalus microplus-host resistance phenomenon as well as contemplating new insights and future directions to study tick resistance and susceptibility, in order to facilitate interventions for tick control.

Peripheral cellular and humoral responses to infestation with the cattle tick Rhipicephalus microplus in Santa Gertrudis cattle

Resistance to cattle tick infestation in single-host ticks is primarily manifested against the larval stage and results in the immature tick failing to attach successfully and obtain a meal. This study was conducted to identify immune responses that characterize the tick-resistant phenotype in cattle. Thirty-five tick-naïve Santa Gertrudis heifers were used in this study, thirty of which were artificially infested for thirteen weeks with tick larvae while five animals remained at a tick-free quarantine property to serve as a control group. Following thirteen weeks of tick infestation, the animals in this trial exhibited highly divergent tick-resistant phenotypes. Blood samples collected throughout the trial were used to measure peripheral immune parameters: haematology, the percentage of cellular subsets comprising the peripheral blood mononuclear cell (PBMC) population, tick-specific IgG₁ and IgG₂ antibody titres, IgG1 avidity for tick antigens and the ability of PBMC to recognize and proliferate in response to stimulation with tick antigens in vitro. The tick-susceptible cattle developed significantly higher tick-specific IgG₁ antibody titres compared to the tick-resistant animals. These results suggest that the heightened antibody response either does not play a role in resistance or might contribute to increased susceptibility to infestation.

Mining a differential sialotranscriptome of Rhipicephalus microplus guides antigen discovery to formulate a vaccine that reduces tick infestations

BACKGROUND

Ticks cause massive damage to livestock and vaccines are one sustainable substitute for the acaricides currently heavily used to control infestations. To guide antigen discovery for a vaccine that targets the gamut of parasitic strategies mediated by tick saliva and enables immunological memory, we exploited a transcriptome constructed from salivary glands from all stages of Rhipicephalus microplus ticks feeding on genetically tick-resistant and susceptible bovines.

RESULTS

Different levels of host anti-tick immunity affected gene expression in tick salivary glands; we thus selected four proteins encoded by genes weakly expressed in ticks attempting to feed on resistant hosts or otherwise abundantly expressed in ticks fed on susceptible hosts; these sialoproteins mediate four functions of parasitism deployed by male ticks and that do not induce antibodies in naturally infected, susceptible bovines. We then evaluated in tick-susceptible heifers an alum-adjuvanted vaccine formulated with recombinant proteins. Parasite performance (i.e. weight and numbers of females finishing their parasitic cycle) and titres of antigen-specific antibodies were significantly reduced or increased, respectively, in vaccinated versus control heifers, conferring an efficacy of 73.2%; two of the antigens were strong immunogens, rich in predicted T-cell epitopes and challenge infestations boosted antibody responses against them.

CONCLUSION

Mining sialotranscriptomes guided by the immunity of tick-resistant hosts selected important targets and infestations boosted immune memory against salivary antigens.

Immune recognition of salivary proteins from the cattle tick Rhipicephalus microplus differs according to the genotype of the bovine host

Background

Males of the cattle tick Rhipicephalus microplus produce salivary immunoglobulin-binding proteins and allotypic variations in IgG are associated with tick loads in bovines. These findings indicate that antibody responses may be essential to control tick infestations. Infestation loads with cattle ticks are heritable: some breeds carry high loads of reproductively successful ticks, in others, few ticks feed and they reproduce inefficiently. Different patterns of humoral immunity against tick salivary proteins may explain these phenotypes.

Methods

We describe the profiles of humoral responses against tick salivary proteins elicited during repeated artificial infestations of bovines of a tick-resistant (Nelore) and a tick-susceptible (Holstein) breed. We measured serum levels of total IgG1, IgG2 and IgE immunoglobulins and of IgG1 and IgG2 antibodies specific for tick salivary proteins. With liquid chromatography followed by mass spectrometry we identified tick salivary proteins that were differentially recognized by serum antibodies from tick-resistant and tick-susceptible bovines in immunoblots of tick salivary proteins separated by two-dimensional electrophoresis.

Results

Baseline levels of total IgG1 and IgG2 were significantly higher in tick-susceptible Holsteins compared with resistant Nelores. Significant increases in levels of total IgG1, but not of IgG2 accompanied successive infestations in both breeds. Resistant Nelores presented with significantly higher levels of salivary-specific antibodies before and at the first challenge with tick larvae; however, by the third challenge, tick-susceptible Holsteins presented with significantly higher levels of IgG1 and IgG2 tick salivary protein-specific antibodies. Importantly, sera from tick-resistant Nelores reacted with 39 tick salivary proteins in immunoblots of salivary proteins separated in two dimensions by electrophoresis versus only 21 spots reacting with sera from tick-susceptible Holsteins.

Conclusions

Levels of tick saliva-specific antibodies were not directly correlated with infestation phenotypes. However, in spite of receiving apparently lower amounts of tick saliva, tick-resistant bovines recognized more tick salivary proteins. These reactive salivary proteins are putatively involved in several functions of parasitism and blood-feeding. Our results indicate that neutralization by host antibodies of tick salivary proteins involved in parasitism is essential to control tick infestations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2077-9) contains supplementary material, which is available to authorized users.

Immune and biochemical responses in skin differ between bovine hosts genetically susceptible and resistant to the cattle tick Rhipicephalus microplus

Background

Ticks attach to and penetrate their hosts’ skin and inactivate multiple components of host responses in order to acquire a blood meal. Infestation loads with the cattle tick, Rhipicephalus microplus, are heritable: some breeds carry high loads of reproductively successful ticks, whereas in others, few ticks feed and reproduce efficiently.

Methods

In order to elucidate the mechanisms that result in the different outcomes of infestations with cattle ticks, we examined global gene expression and inflammation induced by tick bites in skins from one resistant and one susceptible breed of cattle that underwent primary infestations with larvae and nymphs of R. microplus. We also examined the expression profiles of genes encoding secreted tick proteins that mediate parasitism in larvae and nymphs feeding on these breeds.

Results

Functional analyses of differentially expressed genes in the skin suggest that allergic contact-like dermatitis develops with ensuing production of IL-6, CXCL-8 and CCL-2 and is sustained by HMGB1, ISG15 and PKR, leading to expression of pro-inflammatory chemokines and cytokines that recruit granulocytes and T lymphocytes. Importantly, this response is delayed in susceptible hosts. Histopathological analyses of infested skins showed inflammatory reactions surrounding tick cement cones that enable attachment in both breeds, but in genetically tick-resistant bovines they destabilized the cone. The transcription data provided insights into tick-mediated activation of basophils, which have previously been shown to be a key to host resistance in model systems. Skin from tick-susceptible bovines expressed more transcripts encoding enzymes that detoxify tissues. Interestingly, these enzymes also produce volatile odoriferous compounds and, accordingly, skin rubbings from tick-susceptible bovines attracted significantly more tick larvae than rubbings from resistant hosts. Moreover, transcripts encoding secreted modulatory molecules by the tick were significantly more abundant in larval and in nymphal salivary glands from ticks feeding on susceptible bovines.

Conclusions

Compared with tick-susceptible hosts, genes encoding enzymes producing volatile compounds exhibit significantly lower expression in resistant hosts, which may render them less attractive to larvae; resistant hosts expose ticks to an earlier inflammatory response, which in ticks is associated with significantly lower expression of genes encoding salivary proteins that suppress host immunity, inflammation and coagulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1945-z) contains supplementary material, which is available to authorized users.

Role of Rhipicephalus microplus cheliceral receptors in gustation and host differentiation

Rhipicephalus microplus is considered the most economically important ectoparasite of cattle worldwide. It is known that zebuine breeds of cattle are less susceptible to tick infestation than taurine breeds. Contact chemoreceptors in the cheliceral pit sensilla of ticks respond selectively to phagostimulant compounds, however their role in blood feeding relative to host susceptibility to infestation remains to be fully understood. We addressed this topic by conducting taste electrophysiology experiments with cheliceral pit sensilla preparations of R. microplus females. Solutions of five known ixodid tick phagostimulants were tested at different concentrations: sodium (NaCl), and potassium chloride (KCl) (10(-3)-10(-1)M); glucose (10(-4)-10(-1)M); adenosine triphosphate (ATP) (10(-6)-10(-2)M); and reduced l-glutathione (GSH) (10(-6)-10(-2)M). Serum samples from six susceptible animals of the Girolando breed (5/8 Bos indicus×3/8 B. taurus) and six resistant Nelore bovines (pure B. indicus) were also tested. A dose-dependent response of gustatory neurons associated with the chelicerae sensillum to NaCl, glucose, GSH, and ATP were observed. Responses by the cheliceral inner digit pit sensilla of R. microplus to KCl and glucose were also observed and they are reported here for the first time. In addition to an electrophysiological response to known phagostimulants, chemoreceptors in the chelicera of R. microplus responded differently to serum from cattle susceptible and resistant to infestation. The cheliceral pit neurons were more responsive to serum of R. microplus resistant bovines with a higher mean spike frequency (53.5±2spikess(-1)) than to serum samples from susceptible cattle (40.3±2spikess(-1)). The implications of chemosensation during tick blood feeding are discussed.

Microarray analysis of tick-infested skin in resistant and susceptible cattle confirms the role of inflammatory pathways in immune activation and larval rejection

Tick bites promote activation of an inflammatory process that is influenced by bovine genetic composition and its history of previous exposure. Taurine and indicine breeds are known to differ on its immune response development against Rhipicephalus microplus. Nevertheless, further investigation about the complex molecular pathways involved in the development of immune response to tick infestation in cattle presenting the same genetic background is mandatory. The aim of this work was to access the early immune response triggered by R. microplus larvae attachment in previously selected resistant and susceptible animals in a bovine F2 population derived from Gyr (Bos indicus)×Holstein (Bos taurus) crosses. Microarray data analysis of RNA samples from tick infested skin was used to evaluate the gene expression at 0, 24 and 48h after R. microplus larvae attachment. Our experimental design allowed us to deeply explore the immune response related to R. microplus infestation avoiding the innate differences between these breeds. The differentially expressed genes found reveal networks and pathways that suggest a key role of lipid metabolism in inflammation control and impairment of tick infestation in resistant animals. Acute phase response also seems to be impaired in susceptible animals. These results provide new insights about early immune response against ticks and raise the possibility of using immunomodulation processes to improve and develop novel tools for tick control.

Breeding strategies for tick resistance in tropical cattle: a sustainable approach for tick control

About 80 % of world cattle population is under the risk of ticks and tick borne diseases (TTBDs). Losses caused by bovine tick burdens in tropical countries have a tremendous economic impact on production systems. Chemical control of disease has been found to be ineffective and also involving large cost. To reduce our reliance on these chemical products, it is necessary to embark on programs that include habitat management, genetic selection of hosts, and development of a strain capable of inducing host resistance to ticks. Selection for disease resistance provide alternate method for sustainable control of TTBDs. Domestic livestock manifests tick-resistance by skin thickness, coat type, coat color, hair density and skin secretions etc. Zebu cattle have, on average, greater tick resistance than either European cattle or African cattle. Heritability for tick burden in cattle has been shown to range about 0.30, which is sufficient to result in the success of some programs of selection for tick resistance in cattle. To select animals at younger age, to reduce generation interval and to increase genetic gain, marker assisted selection is an important tool. There are also various MHC molecules which are associated with resistance to TTBDs.

Molecular genetic approaches for identifying the basis of variation in resistance to tick infestation in cattle

In recent years there has been renewed interest in the adaptation of cattle to challenging environments, largely driven by advances in genomic methods. The current interest in tick resistance is understandable given the major production and welfare implications of tick infestation in tropical and subtropical zones where around 70% of beef cattle are located. Heritability for tick burden in cattle has been shown to range about 0.30, which is sufficient to result in the success of some programs of selection for tick resistance in cattle. Gene-expression studies strongly indicate that both immune and non-immune mechanisms are associated with tick resistance in cattle. Recent quantitative-trait mapping studies have identified chromosome segments and single nucleotide polymorphisms associated with tick burden, but no causal variant has been identified so far. Most of the genetic markers identified for tick burden explain a relatively small proportion of the variance, which is typical of markers for quantitative traits. This leads to the conclusion that panels of multiple markers for tick resistance rather than a single marker will most likely be developed, possibly involving specific panels for zebu or taurine breeds, which could be used for future selection and breeding programs in cattle.

Rhipicephalus (Boophilus) microplus: clotting time in tick-infested skin varies according to local inflammation and gene expression patterns in tick salivary glands

Ticks deposit saliva at the site of their attachment to a host in order to inhibit haemostasis, inflammation and innate and adaptive immune responses. The anti-haemostatic properties of tick saliva have been described by many studies, but few show that tick infestations or its anti-haemostatic components exert systemic effects in vivo. In the present study, we extended these observations and show that, compared with normal skin, bovine hosts that are genetically susceptible to tick infestations present an increase in the clotting time of blood collected from the immediate vicinity of haemorrhagic feeding pools in skin infested with different developmental stages of Rhipicepahlus microplus; conversely, we determined that clotting time of tick-infested skin from genetically resistant bovines was shorter than that of normal skin. Coagulation and inflammation have many components in common and we determined that in resistant bovines, eosinophils and basophils, which are known to contain tissue factor, are recruited in greater numbers to the inflammatory site of tick bites than in susceptible hosts. Finally, we correlated the observed differences in clotting times with the expression profiles of transcripts for putative anti-haemostatic proteins in different developmental stages of R. microplus fed on genetically susceptible and resistant hosts: we determined that transcripts coding for proteins similar to these molecules are overrepresented in salivary glands from nymphs and males fed on susceptible bovines. Our data indicate that ticks are able to modulate their host's local haemostatic reactions. In the resistant phenotype, larger amounts of inflammatory cells are recruited and expression of anti-coagulant molecules is decreased tick salivary glands, features that can hamper the tick's blood meal.

Modulation of cutaneous inflammation induced by ticks in contrasting phenotypes of infestation in bovines

Tick saliva contains molecules that are inoculated at the site of attachment on their hosts in order to modulate local immune responses and facilitate a successful blood meal. Bovines express heritable, contrasting phenotypes of infestations with the cattle tick, Rhipicephalus (Boophilus) microplus: breeds of Bos taurus indicus are significantly more resistant than those of Bos taurus taurus. Tick saliva may contain molecules that interfere with adhesion of leukocytes to endothelium and resistant hosts may mount an inflammatory profile that is more efficient to hamper the tick's blood meal. We show in vitro that adhesion of peripheral blood mononuclear cells to monolayers of cytokine-activated bovine umbilical endothelial cells was significantly inhibited by tick saliva. The inflammatory response to bites of adults of R. microplus mounted by genetically resistant and susceptible bovine hosts managed in the same pasture was investigated in vivo. The inflammatory infiltrates and levels of message coding for adhesion molecules were measured in biopsies of tick-bitten and control skin taken when animals of both breeds were exposed to low and high tick infestations. Histological studies reveal that cutaneous reactions of resistant hosts to bites of adult ticks contained significantly more basophils and eosinophils compared with reactions of the susceptible breed. Expression of the adhesion molecules - intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P-selectin - was higher in adult-infested skin of susceptible hosts undergoing low infestations compared to resistant hosts; when host was exposed to high infestations expression of these adhesion molecules was down-regulated in both phenotypes of infestations. Expression of leukocyte adhesion glycoprotein-1 (LFA-1) was higher in skin from susceptible hosts undergoing low or high infestations compared to resistant hosts. Conversely, higher levels of E-selectin, which promotes adhesion of memory T cells, were expressed in skin of resistant animals. This finding may explain the resistant host's ability to mount more rapid and efficient secondary responses that limit hematophagy and infestations. The expression profiles observed for adhesion molecules indicate that there are differences in the kinetics of the inflammatory reactions mounted by resistant and susceptible hosts and the balance between tick and host is affected by the number of tick bites a host receives. We show that the contrasting phenotypes of infestations seen in bovines infested with R. microplus are correlated with differences in the cellular and molecular composition of inflammatory infiltrates elicited by bites with adult ticks.

Immunological profiles of Bos taurus and Bos indicus cattle infested with the cattle tick, Rhipicephalus (Boophilus) microplus

The cattle tick, Rhipicephalus (Boophilus) microplus, is a major threat to the improvement of cattle production in tropical and subtropical countries worldwide. Bos indicus cattle are naturally more resistant to infestation with the cattle tick than are Bos taurus breeds, although considerable variation in resistance occurs within and between breeds. It is not known which genes contribute to the resistant phenotype, nor have immune parameters involved in resistance to R. microplus been fully described for the bovine host. This study was undertaken to determine whether selected cellular and antibody parameters of the peripheral circulation differed between tick-resistant Bos indicus and tick-susceptible Bos taurus cattle following a period of tick infestations. This study demonstrated significant differences between the two breeds with respect to the percentage of cellular subsets comprising the peripheral blood mononuclear cell population, cytokine expression by peripheral blood leukocytes, and levels of tick-specific immunoglobulin G1 (IgG1) antibodies measured in the peripheral circulation. In addition to these parameters, the Affymetrix bovine genome microarray was used to analyze gene expression by peripheral blood leukocytes of these animals. The results demonstrate that the Bos indicus cattle developed a stabilized T-cell-mediated response to tick infestation evidenced by their cellular profile and leukocyte cytokine spectrum. The Bos taurus cattle demonstrated cellular and gene expression profiles consistent with a sustained innate, inflammatory response to infestation, although high tick-specific IgG1 titers suggest that these animals have also developed a T-cell response to infestation.