D3.475 - Long-term retention of mouse blood proteins in Ixodes ricinus suggests residual host blood as a potential source of α-Gal

The α-Gal syndrome (AGS), characterized by a delayed hypersensitivity reaction to mammalian meat and by-products, has been repeatedly linked to bites from hard ticks. Although ticks are known to induce α-Gal sensitization, the precise origin of the α-Gal carrying sensitizing molecules is still debated. They might be produced by the tick itself or persist as remnants of the previous blood meal. To address this question, we examined whether host-derived blood proteins remain detectable for prolonged time in Ixodes ricinus, after feeding and moulting.

I. ricinus larvae were fed on BALB/c mice under controlled laboratory conditions. Following engorgement, larvae were reared until they moulted into nymphs and subsequently maintained unfed for 0, 10, or 20 weeks. Protein extracts from both larval and nymphal stages were subjected to LC-MS/MS analysis to monitor the presence of host-derived proteins over time.

Mouse‑derived peptides were identified at all sampling points, demonstrating that host proteins survive moulting and remain detectable during extended starvation up to 20 weeks. Peptide mapping showed high sequence coverage for mouse albumin (76%) and hemoglobin subunits (>85%), indicating the presence of intact protein at all stages. A relative quantification of mouse and tick proteins suggested that the concentration of host blood protein is relatively high compared to total tick protein content. Six of the detected proteins contain predicted N-glycosylation sites. Notably, mouse serine protease inhibitors and Muc5ac were detected after starvation and are described to have 3-4 and 5 N-glycosylation sites, respectively. Although the glycan structures of these proteins are not known so far, these characteristics could make them potential candidates for an α-Gal source in residual host blood.

This study provides the first detailed characterization of residual host blood proteins in I. ricinus, the predominant European tick species. Mouse blood proteins survive the moulting process and remain detectable in nymphs for up to 20 weeks of starvation. While glycosylation patterns were not examined directly, we suggest that residual host glycoproteins, apart from endogenously produced α-Gal, is a plausible source of α-Gal. These findings have implications for further research on the evolution of the tick-host relationship and the immunological mechanisms that evade host immune responses.