A newly identified three-domain C-type lectin associated with blood feeding in the tick Ixodes ricinus

Ixodes ricinus ticks are widely distributed throughout Europe and represent major vectors of tick-borne encephalitis virus and the Lyme borreliosis agent Borrelia burgdorferi sensu lato. In invertebrates, C-type lectins are commonly associated with innate immune functions, and several such lectins have been predicted in I. ricinus. Given the limited knowledge of lectin function in ticks, we characterized three carbohydrate-recognition domains (CRDs) of a novel C-type lectin identified in the I. ricinus transcriptome (IrCLec). The tertiary structures of CRD1, CRD2, and CRD3, predicted using the AlphaFold 3 program, corresponded to the typical structure of C-type lectins. Conserved carbohydrate-binding motifs were identified in CRD3, whereas non-canonical motifs were present in CRD1 and CRD2. Recombinant His-tagged CRDs were produced and analysed for carbohydrate-binding activity. Glycan array analysis revealed binding of all three domains to selected glycans, while hemagglutination assays demonstrated pronounced binding activity of CRD1 and CRD2 toward human erythrocyte antigens of blood groups A, B, and O. IrCLec expression was highest in the tick midgut and also detected in hemocytes, with expression levels increasing after blood feeding. RNAi-mediated silencing of IrCLec impaired blood feeding efficiency in tick nymphs. Together, these results indicate that IrCLec plays an important role in blood feeding and may additionally participate in lectin-mediated host-pathogen or host-blood component interactions.