A hemocyte-derived Kunitz-BPTI-type chymotrypsin inhibitor, HlChI, from the ixodid tick Haemaphysalis longicornis, plays regulatory functions in tick blood-feeding processes

► Haemaphysalis longicornis chymotrypsin inhibitor, HlChI, was expressed and localized in the cytoplasm of the hemocytes of the ticks. ► HlChI potently inhibited bovine α-chymotrypsin but weakly inhibited bovine trypsin and could not inhibit porcine elastase. ► HlChI was stable over the pH range 2-11 and heating up to 70 °C at pH 8.0. ► HlChI gene knockdown caused disruption of feeding, death of feeding ticks and impacted markedly on reproduction of ticks. ► HlChI might be a promising candidate for therapeutic agent/vaccine development for controlling ticks and tick borne diseases.