Fibrinogen-related proteins in ixodid ticks

Fibrinogen-related proteins with lectin activity are believed to be part of the tick innate immune system. Several fibrinogen-related proteins have been described and characterised mainly on the basis of their cDNA sequences while direct biochemical evidence is missing. One of them, the haemolymph lectin Dorin M from the tick Ornithodoros moubata was isolated and characterised in more depth. Results Several fibrinogen-related proteins were detected in the haemolymph of ixodid ticks Dermacentor marginatus , Rhipicephalus appendiculatus , R. pulchellus , and R. sanguineus . These proteins were recognised by sera directed against the tick lectin Dorin M and the haemagglutination activity of the ticks R. appendiculatus and D. marginatus . Cross-reactivity of the identified proteins with antibodies against the fibrinogen domain of the human ficolin was also shown. The carbohydrate-binding ability of tick haemolymph was confirmed by haemagglutination activity assays, and this activity was shown to be inhibited by neuraminic acid and sialylated glycoproteins as well as by N-acetylated hexosamines. The fibrinogen-related proteins were shown to be glycosylated and they were localised in salivary glands, midguts, and haemocytes of D. marginatus . Hemelipoglycoprotein was also recognised by sera directed against the fibrinogen-related proteins in all three Rhipicephalus species as well as in D. marginatus . However, this protein does not contain the fibrinogen domain and thus, the binding possibly results from the structure similarity between hemelipoglycoprotein and the fibrinogen domain. Conclusions The presence of fibrinogen-related proteins was shown in the haemolymph of four tick species in high abundance. Reactivity of antibodies directed against ficolin or fibrinogen-related proteins with proteins which do not contain the fibrinogen domain points out the importance of sequence analysis of the identified proteins in further studies. Previously observed expression of fibrinogen-related proteins in haemocytes together with the results of this study suggest involvement of fibrinogen-related proteins in tick immunity processes. Thus, they have potential as targets for anti-tick vaccines and as antimicrobial proteins in pharmacology. Research on fibrinogen-related proteins could reveal further details of tick innate immunity processes.