Dermacentor andersoni: culture of whole salivary glands

How relevant are in vitro culture models for study of tick-pathogen interactions?

Although tick-borne infectious diseases threaten human and animal health worldwide, with constantly increasing incidence, little knowledge is available regarding vector-pathogen interactions and pathogen transmission. In vivo laboratory study of these subjects using live, intact ticks is expensive, labor-intensive, and challenging from the points of view of biosafety and ethics. Several in vitro models have been developed, including over 70 continuous cell lines derived from multiple tick species and a variety of tick organ culture systems, facilitating many research activities. However, some limitations have to be considered in the translation of the results from the in vitro environment to the in vivo situation of live, intact ticks, and vertebrate hosts. In this review, we describe the available in vitro models and selected results from their application to the study of tick-borne viruses, bacteria, and protozoa, where possible comparing these results to studies in live, intact ticks. Finally, we highlight the strengths and weaknesses of in vitro tick culture models and their essential role in tick-borne pathogen research.

Relative transcription of autophagy-related genes in Amblyomma sculptum and Rhipicephalus microplus ticks

Ticks endure stressful off-host periods and perform as vectors of a diversity of infectious agents, thus engaging pathways that expectedly demand for autophagy. Little is known of ticks' autophagy, a conserved eukaryotic machinery assisting in homeostasis processes that also participates in tissue-dependent metabolic functions. Here, the autophagy-related ATG4 (autophagin-1), ATG6 (beclin-1) and ATG8 (LC3) mRNAs from the human diseases vector Amblyomma sculptum and the cattle-tick Rhipicephalus microplus were identified. Comparative qPCR quantifications evidenced different transcriptional status for the ATG genes in the salivary glands (SG), ovaries and intestines of actively feeding ticks. These ATGs had increased relative transcription under nutrient-deprivation, as determined by validation tests with R. microplus embryo-derivative cells BME26 and A. sculptum SG explants incubations in HBSS. Starvation lead to 4-31.8× and ~ 60-500× increments on the ATGs mRNA loads in BME26 and A. sculptum SG explants, respectively. PI3K inhibitor 3MA treatment also affected ATGs expression in BME26. Some ATGs were more transcribed in the SGs than in the ovaries of cattle-ticks. Amblyomma sculptum/R. microplus interspecific comparisons showed that ATG4 and ATG6 were 0.18× less expressed in A. sculptum SGs, but ~ 10-100× more expressed in their ovaries when compared to R. microplus organs. ATG4 and ATG8a transcript loads were ~ 120× and ~ 40× higher, respectively, in A. sculptum intestines when compared to cattle-ticks of similar weight category. ATGs expression in A. sculptum intestines increased with tick weight, indicating Atgs contribution to intracellular blood digestion. Possible roles of the autophagy machinery and their organ-specific expression profile on vector biology are discussed.

Potentiation by spiperone and other butyrophenones of fluid secretion by isolated salivary glands of ixodid ticks

Isolated salivary glands from the ixodid tick, Amblyomma hebraeum Koch are stimulated to secrete fluid when exposed to dopamine (DA), the maximum response occurring at 10(-6) M. Spiperone, and a number of other butyrophenone derivatives, although lacking intrinsic activity, are able to potentiate the secretion elicited by supramaximal concentrations of DA; this potentiation by spiperone is evident at concentrations in the femtomolar range. Tranylcypromine, a potent, competitive inhibitor of monoamine oxidase (MAO) in tick salivary gland homogenates, has both intrinsic activity and potentiates DA-induced salivation. The fact that spiperone potentiates ergometrine-induced salivation that the prime mechanism of the butyrophenone effect is not by inhibiting catecholamine catabolism. The results also suggest that the receptor for DA and that for butyrophenones are distinct sites. Droperidol, benperidol and bromperidol, all potent neuroleptic drugs, failed (at 10(-9) M) to potentiate salivation. By contrast, R951, R27275 and R1187 (all at 10(-9) M) were very effective potentiators on the salivary gland system, despite the fact that they lack the basic structural requirements for neuroleptic activity. These results suggest that the butyrophenone site in tick salivary glands is different from butyrophenone binding sites in mammalian CNS.