Location: Livestock Arthropod Pests ResearchTitle: Tick salivary acetylcholinesterase: A probable immunomodulator of host-parasite interactions
Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2015
Publication Date: 5/1/2016
Citation: Temeyer, K.B., Tuckow, A.P. 2016. Tick salivary acetylcholinesterase: A probable immunomodulator of host-parasite interactions. Journal of Medical Entomology. 53:500-504.
Interpretive Summary: The southern cattle tick, Rhipicephalus (Boophilus) microplus, transmits at least two fatal diseases to cattle and is the most important ectoparasite affecting cattle in the world. Although eradicated from the United States, these ticks remain in many countries and continue to threaten U.S. cattle producers despite careful inspection and pesticide treatment of all imported cattle in addition to quarantine and eradication of ticks from infested premises. Organophosphate pesticides are preferred for tick eradication and function by inhibiting the activity of acetylcholinesterase (AChE), an enzyme essential to function of the central nervous system of ticks and other animals. Unlike mammals, there are several different AChEs expressed in the brain of ticks that differ in structure and biochemical properties. A new scientific study reports the presence of an active AChE enzyme in tick saliva. It is proposed that the tick salivary AChE may protect the tick by hydrolyzing excess acetylcholine present in the large quantity of host blood consumed during tick engorgement. In addition, tick salivary AChE may have an important function in protecting the tick by altering the immune response of the host animal.
Technical Abstract: The southern cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini), is the most economically important ectoparasite affecting cattle in the world. Although eradicated from the United States, R. microplus and R. annulatus (Say) continue to threaten U.S. cattle producers despite maintenance of an importation barrier based on inspection, dipping of imported cattle in organophosphate (OP) acaricide and quarantine of infested premises. OP acaricides inhibit acetylcholinesterase (AChE), an enzyme essential to tick central nervous system function. Unlike vertebrates, ticks possess at least three genes encoding AChEs that differ in amino acid sequence and biochemical properties. The genome of the related tick, Ixodes scapularis, may contain many genes encoding different AChEs. The present work reports a salivary AChE in R. microplus, and discusses the complexity of the cholinergic system in ticks and the functional significance of tick salivary AChE at the tick-host interface. It is the first report of tick salivary AChE and provides evidence that it likely functions to hydrolyze acetylcholine present in the host blood thereby detoxifying the blood meal and modulating the innate and adaptive immune response of the host.