ABSTRACT.    The hard tick Ixodes ricinus is a serious disease vector in Europe, known especially for transmitting the spirochete Borrelia burgdorferi causing Lyme disease and the tick borne-encephalitis virus. Transmitted pathogens have to be capable to evade both humoral and cellular immune reactions of the invertebrate host. The broad-spectrum protease inhibitors of α₂-macroglobulin family are believed to be important components of the innate immunity since they guard organism against undesired action of proteases of different origin, including those from invading pathogens. A closely related thiol-ester protein from the malaria vector Anopheles gambiae was shown to be a determinant of Plasmodium transmission (Blandin et al., Cell 116, 661--670, 2004). In this work, we have focused on the role of IrAM in phagocytosis of a model Gram-negative Chryseobacterium indologenes by tick hemocytes. Elimination of IrAM activity by inactivation of its reactive thiol-ester with methylamin or depletion of IrAM from tick hemolymph by dsRNA interference led to a significant decrease of phagocytic activity of tick hemocytes. Indirect immunofluorescent microscopy revealed that IrAM binds to the surface of bacteria. These results indicate that IrAM functions as an opsonin. Similar ongoing experiments are performed on phagocytosis of the Borrelia spirochetes.
The project was supported by the Grant Agency ASCR No. IAA 60022603 and Research Centre No. LC06009.