title: Tick Thioester-Containing Proteins and Phagocytosis Do Not Affect Transmission ofBorrelia afzeliifrom the Competent VectorIxodes ricinus.
abstract: The present concept of the transmission of Lyme disease fromBorrelia-infectedIxodessp. ticks to the naïve host assumes that a low number of spirochetes that manage to penetrate the midgut epithelium migrate through the hemocoel to the salivary glands and subsequently infect the host with the aid of immunomodulatory compounds present in tick saliva. Therefore, humoral and/or cellular immune reactions within the tick hemocoel may play an important role in tick competence to act as a vector for borreliosis. To test this hypothesis we have examined complement-like reactions in the hemolymph of the hard tickIxodes ricinusagainstBorrelia afzelii(the most common vector and causative agent of Lyme disease in Europe). We demonstrate thatI. ricinushemolymph does not exhibit borreliacidal effects comparable to complement-mediated lysis of bovine sera. However, after injection ofB. afzeliiinto the tick hemocoel, the spirochetes were efficiently phagocytosed by tick hemocytes and this cellular defense was completely eliminated by pre-injection of latex beads. As tick thioester-containing proteins (T-TEPs) are components of the tick complement system, we performed RNAi-mediated silencing of all nine genes encoding individual T-TEPs followed byin vitrophagocytosis assays. Silencing of two molecules related to the C3 complement component (IrC3-2 andIrC3-3) significantly suppressed phagocytosis ofB. afzelii, while knockdown ofIrTep (insect type TEP) led to its stimulation. However, RNAi-mediated silencing of T-TEPs or elimination of phagocytosis by injection of latex beads inB. afzelii-infectedI. ricinusnymphs had no obvious impact on the transmission of spirochetes to naïve mice, as determined byB. afzeliiinfection of murine tissues following tick infestation. This result supports the concept thatBorreliaspirochetes are capable of avoiding complement-related reactions within the hemocoel of ticks competent to transmit Lyme disease.
authors.affiliation: Biology Centre of the Czech Academy of Sciences, Institute of Parasitology Ceske Budejovice, Czechia.
authors.forename: Veronika
authors.initials: V
authors.lastname: Urbanová
authors.affiliation: Biology Centre of the Czech Academy of Sciences, Institute of Parasitology Ceske Budejovice, Czechia.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Hajdušek
authors.affiliation: Biology Centre of the Czech Academy of Sciences, Institute of Parasitology Ceske Budejovice, Czechia.
authors.forename: Helena
authors.initials: H
authors.lastname: Hönig Mondeková
authors.affiliation: Biology Centre of the Czech Academy of Sciences, Institute of Parasitology Ceske Budejovice, Czechia.
authors.forename: Radek
authors.initials: R
authors.lastname: Šíma
authors.affiliation: Biology Centre of the Czech Academy of Sciences, Institute of Parasitology Ceske Budejovice, Czechia.
authors.forename: Petr
authors.initials: P
authors.lastname: Kopáček
mesh_terms: D000818:Animals; D001096:Arachnid Vectors / Q000276:immunology / Q000382:microbiology*; D060829:Arthropod Proteins / Q000378:metabolism; D015748:Borrelia burgdorferi Group / Q000276:immunology*; D003165:Complement System Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D018562:Disease Transmission, Infectious; D006434:Hemocytes / Q000276:immunology*; D018884:Ixodes / Q000276:immunology / Q000382:microbiology*; D008193:Lyme Disease / Q000635:transmission*; D051379:Mice; D010587:Phagocytosis
chemical_list: D060829:Arthropod Proteins; D003165:Complement System Proteins
keywords: Borrelia; Ixodes; complement; phagocytosis; thioester-containing proteins