Expression of a prostaglandin E2 synthase in the salivary glands of the blacklegged tick, Ixodes scapularis

Ticks are obligatory ectoparasites that feed exclusively on the blood of vertebrates and often transmit a number of pathogens, including viruses, bacteria, and protozoa, resulting in substantial economic loss in the animal industry and presenting risks to human health.  The blacklegged tick, Ixodes scapularis, is known to transmit the important tick-borne pathogen, Borrelia burgdorferi, the causative agent of Lyme Disease.  Tick salivary glands, and their secretions, contain various bioactive components that aid in the manipulation of hosts' defenses.  Ticks secrete large amounts of prostaglandin E₂ (PGE₂) into the host, where it impacts the host’s hemostatic response and facilitates blood feeding.  PGE₂ is also known to have an autocrine or paracrine function in tick salivary glands, likely through a PGE₂ receptor, leading to the secretion (exocytosis) of other salivary proteins.  We have identified and cloned a gene encoding a PGE synthase ortholog (PGES2) in I. scapularis, which is involved in the biosynthesis of PGE₂.  The expression pattern, examined by quantitative reverse transcription PCR and immunohistochemistry, supports that this gene is expressed in the salivary glands constitutively throughout tick feeding.  PGES2 levels were also examined in ticks fed on naive versus immune challenged hosts, exploring the effects of host acquired immunity to ticks on PGES2 expression in tick salivary glands.  The identification and functional study of PGES2, along with the description of its expression patterns, provides critical information into the biosynthetic pathway of PGE₂ in the tick salivary glands, and opens the door to future studies into the disruption of tick feeding.