A transcriptome and proteome of the tick Rhipicephalus microplus shaped by the genetic composition of its hosts and developmental stage.

The cattle tick, Rhipicephalus microplus, is a monoxenous tick that co-evolved with indicine cattle on the Indian subcontinent. It causes massive damage to livestock worldwide. Cattle breeds present heritable, contrasting phenotypes of tick loads, taurine breeds carrying higher loads of the parasite than indicine breeds. Thus, a useful model is available to analyze mechanisms that determine outcomes of parasitism. We sought to gain insights on these mechanisms and used RNA sequencing and Multidimensional Protein Identification Technology (MudPIT) to generate a transcriptome from whole larvae and salivary glands from nymphs, males and females feeding on genetically susceptible and resistant bovine hosts and their corresponding proteomes. 931,698 reads were annotated into 11,676 coding sequences (CDS), which were manually curated into 116 different protein families. Male ticks presented the most diverse armamentarium of mediators of parasitism. In addition, levels of expression of many genes encoding mediators of parasitism were significantly associated with the level and stage of host immunity and/or were temporally restricted to developmental stages of the tick. These insights should assist in developing novel, sustainable technologies for tick control.

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.

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

Tick bites may trigger acute phase responses. Positive and negative acute phase proteins were measured in infested cattle genetically resistant and susceptible to ticks. During heavier infestations levels of haptoglobin increased significantly in susceptible bovines; levels of serum amyloid A increased in resistant bovines; levels of alpha-1-acid glycoprotein decreased significantly in resistant bovines; levels of transferrin decreased significantly in susceptible bovines. In conclusion, tick infestations trigger acute phase responses and enhancement of specific acute phase proteins differs according to the genetic composition of hosts. Acute phase proteins may constitute useful biological signatures for monitoring the stress induced by tick infestations.