Purification, Cloning, and Expression of a Novel Salivary Anticomplement Protein from the Tick, Ixodes scapularis

Abstract

The alternative pathway of complement is an important defense against pathogens and in tick rejection reactions. The tick Ixodes scapularis is able to feed repeatedly on its natural host and has a salivary anticomplement activity that presumably facilitates feeding. In this study, we purified and then obtained the aminoterminal sequence of the I. scapularis salivary anticomplement (Isac). We found a full-length clone coding for Isac by random screening of a salivary gland cDNA library. Expressing Isac cDNA in COS cells reproduced the activity found in tick saliva, namely, inhibition of rabbit erythrocyte lysis by human serum in the presence of Mg 2؉ and EGTA, inhibition of C3b binding to agarose in the presence of Mg 2؉ and EGTA, and acceleration of factor Bb uncoupling from the C3 convertase generated by the alternative pathway. Recombinant Isac had no effect on the recalcification time of human platelet-poor plasma or in the classical complement pathway, indicating that it is a specific inhibitor similar to the regulators of complement activation of the alternative pathway such as factor H. Isac, however, has no similarity to any protein in the GenBank TM data base, indicating that it is a novel and relatively small (18.5 kDa) anticomplement molecule.

Disruption of Ixodes scapularis anticoagulation by using RNA interference

“…Characterizations of tick salivary antigens have, therefore, been based on their ability to (i) induce skin hypersensitivity reaction on tick-resistant animals, (ii) react with anti-tick immune serum, (iii) modulate host immune responses, and (iv) thwart host hemostatic mechanisms (28). Although these approaches have identified several tick salivary proteins (11,14,16,23,(28)(29)(30)(31), an effective vaccine against I. scapularis ticks remains elusive. Recently, random sequencing of clones from an adult I. scapularis salivary gland cDNA library identified Ϸ100 I. scapularis genes (17).…”

Borrelia burgdorferi complement regulator-acquiring surface proteins (BbCRASPs): Expression patterns during the mammal–tick infection cycle

“…When infected ticks begin to feed, B. burgdorferi begins production of Erp proteins , but BbCRASP-1 or -2 remain largely undetectable during this time Bykowski et al, 2007, and our unpublished results). Ingested host complement is ineffective inside the tick midgut, presumably due to components of tick saliva that block complement activation (Ribeiro, 1987;Lawrie et al, 1999;Wikel, 1999;Valenzuela et al, 2000;Rathinavelu et al, 2003;Schroeder et al, 2007).…”

Alboserpin, a Factor Xa Inhibitor from the Mosquito Vector of Yellow Fever, Binds Heparin and Membrane Phospholipids and Exhibits Antithrombotic Activity

“…In order to counteract host response to injury, salivary glands (SGs) of blood-sucking arthropods express a number of inhibitors of blood coagulation, platelet aggregation, host immunity, inflammation, angiogenesis, neutrophil function, wound healing, and vasodilation (1, 8 -16). Among anticoagulants, inhibitors targeting FVIIa/tissue factor, thrombin, FXa, FIXa, FXIIa, and high molecular weight kininogen have been reported (17)(18)(19)(20). Of note, members of different protein families, including Kunitz-, ascaris-, and antistasin-like, and SALP have been identified as FXa inhibitors (17,21).…”