Abstract: Objective To obtain the recombinant IgE-dependent histamine-releasing factors of Schistosoma japonicum and Clonorchis sinensis （rSjHRF and rCsHRF） and to study the effect of recombinant HRFs to induce histamine release from sensitized rat mast cells. Methods The complete coding regions of SjHRF and CsHRF were cloned separately， and the recombinant plasmids were respectively transformed and expressed in BL21 cells. The soluble recombinant rSjHRF and rCsHRF were purified. Aliquots of the mast cells obtained from the lungs of OVA-immunized rats were separately incubated with rSjHRF and rCsHRF and the released histamine was measured by the OPT spectrofluorometric procedure. The dose-dependent curves and the kinetics of histamine release induced by rSjHRF and rCsHRF were prepared. Results The recombinant plasmids pET-30-rSjHRF and pET-30-rCsHRF were constructed successfully and the purified soluble recombinant proteins rSjHRF and rCsHRF were obtained by affinity chromatography. rSjHRF and rCsHRF induced histamine release from sensitized mast cells in a dose-dependent manner. At the concentration of 150 mg/L， the average rate of histamine release from sensitized mast cells induced by rSjHRF and rCsHRF were 49.78% and 32.63%， respectively. Histamine release increased with prolonged reaction time and the maximal release occurred at 35min. Conclusion The recombinant parasite-originated IgE-dependent HRFs show an effect of inducing histamine release from sensitized mast cells， suggesting that this protein would play a role in type I hypersensitivity in hosts with parasitic infections.

Key words: Schistosoma japonicum, Clonorchis sinensis, IgE-dependent histamine-releasing factor, Mast cell, Histamine