Dermal mast cell counts in F2 Holstein x Gir crossbred cattle artificially infested with the tick Boophilus microplus (Acari: Ixodidae)

Comparison of the differential regulation of T and B-lymphocyte subsets in the skin and lymph nodes amongst three cattle breeds as potential mediators of immune-resistance to Rhipicephalus microplus

Although varying natural resistance to ticks between highly resistant Brahman (Bos taurus indicus), resistant Bonsmara (5/8 B. t. indicus x 3/8 B. t. taurus) and susceptible Holstein-Friesian (B. t. taurus) breeds is documented in skin and blood, little information is available describing draining lymph nodes. To elucidate the cellular dynamics during Rhipicephalus microplus induced immune responses, this study analysed immune factors from these cattle breeds using histology, immunohistochemistry and flow cytometry. Following the collection of skin and lymph node samples before artificial tick infestation, cattle were infested with R. microplus larvae. Subsequent sampling coincided with the tick larvae and adult developmental stages. A significant influx of CD20+ B-lymphocytes in the dermis all cattle breeds was observed while CD3+ T-lymphocytes were significantly increased for more tick resistant breeds. Eosinophil infiltration in germinal centres of lymph nodes was significant for all cattle breeds while tingible body macrophages were significantly increased for adult infested Brahman animals. A negligible fluctuation in CD20+ and CD79α+ B-lymphocyte numbers was present in the lymph node of more resistant cattle breeds, while susceptible animals showed a decrease in B-lymphocytes after infestation, followed by an increase between larvae to adult infested time points. Increased variability of γd T-lymphocyte populations in lymph nodes was correlated with tick susceptibility. In addition, a more stable T helper lymphocyte population was identified in the lymph nodes for the Brahman cattle breed. Results suggest the association of tick susceptibility with differential B-lymphocyte regulation in lymph node tissues, increased variability of WC1+ γδ T-lymphocyte populations in the lymph node as well as a decrease in T helper lymphocytes in the lymph node.

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.

Modulation of host immunity by tick saliva

Next generation sequencing and proteomics have helped to comprehensively characterize gene expression in tick salivary glands at both the transcriptome and the proteome level. Functional data are, however, lacking. Given that tick salivary secretions are critical to the success of the tick transmission lifecycle and, as a consequence, for host colonization by the pathogens they spread, we thoroughly review here the literature on the known interactions between tick saliva (or tick salivary gland extracts) and the innate and adaptive vertebrate immune system. The information is intended to serve as a reference for functional characterization of the numerous genes and proteins expressed in tick salivary glands with an ultimate goal to develop novel vector and pathogen control strategies.

SIGNIFICANCE

We overview all the known interactions of tick saliva with the vertebrate immune system. The provided information is important, given the recent developments in high-throughput transcriptomic and proteomic analysis of gene expression in tick salivary glands, since it may serve as a guideline for the functional characterization of the numerous newly-discovered genes expressed in tick salivary glands.

Cellular responses to Rhipicephalus microplus infestations in pre-sensitised cattle with differing phenotypes of infestation

The blue tick, Rhipicephalus microplus, threatens cattle production in most tropical and subtropical areas of the world. Delayed skin hypersensitivity reactions are thought to cause Nguni cattle to be more resistant to R. microplus than Bonsmara cattle yet the cellular mechanisms responsible for these differences have not been classified. Tick counts and inflammatory cell infiltrates in skin biopsies from feeding sites of adult R. microplus ticks were determined in 9-month-old Nguni and Bonsmara heifers to determine the cellular mechanisms responsible for tick immunity. Nguni heifers (1.7 ± 0.03) had lower (P < 0.05) tick counts than the Bonsmaras (2.0 ± 0.03). Parasitized sites in Nguni heifers had higher counts of basophils, mast and mononuclear cells than those in the Bonsmara heifers. Conversely, parasitized sites in Nguni heifers had lower neutrophil and eosinophil counts than those in the Bonsmara heifers. Tick count was negatively correlated with basophil and mast cell counts and positively correlated with eosinophil counts in both breeds. In the Bonsmara breed, tick count was positively correlated with mononuclear cell counts. Cellular responses to adult R. microplus infestations were different and correlated with differences in tick resistance in Nguni and Bonsmara cattle breeds. It is essential to further characterise the molecular composition of the inflammatory infiltrate elicited by adult R. microplus infestation to fully comprehend immunity to ticks in cattle.

[Bovine disease-related DNA mutations and their genetic control strategies in breeding for disease resistance]

Bovine genomic DNA mutations and their genetic effects on gene expression and protein function influence disease susceptibility and resistance of cattle. The genetic loci related to cattle diseases are mainly divided into two types: single-locus-disease genes and multigenic-disease loci. The single-locus-disease genes are called causal mutations; their genetic basis is simply and normally detected in the coding and non-coding regions inducing substitution of amino acid, premature termination of translation, and complete deletion of entire exon(s). In contrast, the genetic basis of disease related to multiple genes is more complex since susceptibility or resistance of these diseases is affected by the interactions among host, pathogen, and environment. This article reviewed current research and application of the major diseases of cattle con-trolled by single gene or polygenic genes. The genetic control strategies of effective identification and control of these dis-eases in bovine breeding and production were also analyzed.

Differences in the behavior of Rhipicephalus sanguineus tested against resistant and susceptible dogs

To ascertain whether brown dog tick Rhipicephalus sp. infests resistant (beagle) and susceptible (English cocker spaniel) dogs differently, five animals of each breed were maintained in a kennel whose walls were infested with 7,000 larvae, 320 nymphs, 80 males and 80 females, in 3 infestations, at 10-day intervals. Five times more ticks were found on cocker spaniels (498) than on beagles (96). Substances were collected by rubbing pieces of clean flannel on the dogs for 15 min and these were tested for arrestment and attractiveness of ticks. Three choices were offered: cocker extract vs. control; beagle extract vs. control, and cocker extract vs. beagle extract. When allowed to choose between substances rubbed from dogs and a control, more ticks were arrested by extracts from the cockers than from beagles. In the arrestment tests with only a choice between substances from dogs of each breed, more ticks were arrested by cocker substances. To test for attraction, capsules containing adsorbent were used and the tests were carried out in a Y-olfactometer. Fifteen males and 15 females were tested, for each treatment. In the olfactometer, the ticks were not attracted to the odor of either breed, however the odor of the Beagle was apparently repellent. These results indicate that R. sanguineus can use substances from the dogs to differentiate susceptible English Cocker Spaniels from resistant Beagles.

The role of saliva in tick feeding

When attempting to feed on their hosts, ticks face the problem of host hemostasis (the vertebrate mechanisms that prevent blood loss), inflammation (that can produce itching or pain and thus initiate defensive behavior on their hosts) and adaptive immunity (by way of both cellular and humoral responses). Against these barriers, ticks evolved a complex and sophisticated pharmacological armamentarium, consisting of bioactive lipids and proteins, to assist blood feeding. Recent progress in transcriptome research has uncovered that hard ticks have hundreds of different proteins expressed in their salivary glands, the majority of which have no known function, and include many novel protein families (e.g., their primary structure is unique to ticks). This review will address the vertebrate mechanisms of these barriers as a guide to identify the possible targets of these large numbers of known salivary proteins with unknown function. We additionally provide a supplemental Table that catalogues over 3,500 putative salivary proteins from various tick species, which might assist the scientific community in the process of functional identification of these unique proteins. This supplemental file is accessble fromhttp://exon.niaid.nih.gov/transcriptome/tick_review/Sup-Table-1.xls.gz.

A critical analysis of disease-associated DNA polymorphisms in the genes of cattle, goat, sheep, and pig

Genetic variations through their effects on gene expression and protein function underlie disease susceptibility in farm animal species. The variations are in the form of single nucleotide polymorphisms, deletions/insertions of nucleotides or whole genes, gene or whole chromosomal rearrangements, gene duplications, and copy number polymorphisms or variants. They exert varying degrees of effects on gene action, such as substitution of an amino acid for another, shift in reading frame and premature termination of translation, and complete deletion of entire exon(s) or gene(s) in diseased individuals. These factors influence gene function by affecting mRNA splicing pattern or by altering/eliminating protein function. Elucidating the genetic bases of diseases under the control of many genes is very challenging, and it is compounded by several factors, including host x pathogen x environment interactions. In this review, the genetic variations that underlie several diseases of livestock (under monogenic and polygenic control) are analyzed. Also, factors hampering research efforts toward identification of genetic influences on animal disease identification and control are highlighted. A better understanding of the factors analyzed could be better harnessed to effectively identify and control, genetically, livestock diseases. Finally, genetic control of animal diseases can reduce the costs associated with diseases, improve animal welfare, and provide healthy animal products to consumers, and should be given more attention.

Towards the standardization of the abbreviations of genus names of ticks (Acari: Parasitiformes: Ixodida)

An abbreviation system for genus names of ticks of the world is proposed. This abbreviation system adopts two letters (typically, the first two), as previously proposed for Culicidae and more recently for Phlebotominae. I hope this abbreviation system will be useful for anyone interested in tick taxonomy and related areas.