Ticks alternately deposit saliva into and suck blood from the tick bite site and it was presumed that salivary immune modulators and anticoagulants deposited into the bite site, and absorbed into the gut along with the bloodmeal might provide essential functions both at the bite site and in the gut. However, a recent analysis of the gut transcriptome of Dermacentor variabilis by Anderson et al showed that about 6 of the sequenced transcripts encoded secreted proteins with putative antioxidant, anticoagulant and antimicrobial functions distinct from that observed in salivary glands. Consistent with this emerging active role for the tick gut in feeding, several reports demonstrate the expression of gut-specific anticoagulants in several Ixodid ticks. We now show that the I. scapularis adult gut elaborates an anticoagulant activity predominantly inhibiting the MEDChem Express MRT68921 (hydrochloride) thrombin step of the intrinsic pathway of host coagulation. The lack of activity against factor Xa is in clear contrast to the predominant factor Xa inhibitory activity observed in tick saliva. We observed minimal thrombin inhibitory activity in adult saliva collected from engorged adult ticks. Recently, a kDa protein was identified from a nymphal salivary gland yeast display library that appears to inhibit the formation of thrombin by targeting the activated factor Xa complex that precedes thrombin formation. A study by Chmelar et al has also shown that Ixodes ricinus salivary protein IRS-2 inhibits thrombin activity, albeit, at very high concentrations. We partially purified the thrombin inhibitory activity from adult tick guts by liquid chromatography. LC-MS/MS of the peptides in the active peak revealed the presence of a protein derived from the ISCW003862 locus. We named this protein Ixophilin on the basis of its strong homology with the thrombin. Temporal and spatial analysis of ixophilin expression showed that it was preferentially KS176 cost expressed in the adult and nymphal gut and was induced upon feeding, consistent with a potential role for Ixophilin in preventing the clotting of the blood meal in the gut. Ixophilin expression levels were higher in the nymphal gut compared to the adult gut ixophilin expression levels in fe
