Abstract: Objective To study the immunodiagnostic value and immune protection of the recombinant Ts21 protein of Trichinella spiralis. Methods ELISA using T. spiralis muscle larval excretory-ecretory （ES） antigens （Ts21-ELISA） or recombinant Ts21 protein （Ts21-ELISA） was applied to detect the anti-trichinella antibodies in sera from patients with trichinellosis and other parasitic infections as well as mice infected with 5 species of Trichinella （T1， T2，T3，T4 and T7）. Serum antibody level at different time interval after infection was observed in mice infected with different doses of T1 larvae. Mice were immunized by subcutaneous injection with recombinant Ts21 protein （20 μg/mouse）. Ten days after the last immunization， mice were orally infected each with 300 T. spiralis larvae. Mice were sacrificed 3.5 d and 42 d after challenge infection， the intestinal adult worms and muscle larvae were respectively collected and the reduction rate of parasite burden was calculated. Results When Ts21-LISA was used to assay the serum samples， the antibody positive rate of patients with trichinellosis，paragonimiasis，cysticercosis and echinococcosis was 94.7% （18/19）， 15.8% （3/19）， 9.1% （1/11） and 7.7% （1/13）， respectively； no cross reaction with sera from cases of schistosomiasis， clornochiasis and normal persons was observed. The difference of sensitivity and specificity between recombinant Ts21 protein and ES antigens for detecting the serum antibodies in cases with trichinellosis had no statistical significance （χ²=0， P＞0.05； χ²=0.358， P＞0.05）. The sensitivity between recombinant Ts21 protein and ES antigen for testing sera from mice infected T1 showed no significant difference （χ²=0.104， P＞0.05）， but the cross reaction rate of recombinant Ts21 protein with sera from mice infected with T2， T3， T4 and T7 was considerably lower than that of ES antigens （χ²=17.069， P＜0.05）. In mice infected with 300 T. spiralis larvae， the serum antibody positive rate detected by Ts21-LISA was 100% （10/10） at 4 weeks post infection. In mice infected with 5 larvae， the antibody positive rate was 100% （10/10） at 6 weeks post infection. In 3.5 days and 42 days after the immunized mice were challenged with T. spiralis larvae， the reduction rate of intestinal adult worms and muscle larvae was 42.7% and 49.8%， respectively. Conclusion The recombinant Ts21 protein may be applied to the serodiagnosis of trichinellosis，but its cross reaction with the sera of patients with paragonimiasis，cysticercosis and echinococcosis can not be neglected.

Key words: Trichinella spiralis, Recombinant Ts21 protein, ELISA, Serodiagnosis, Immune protection, Mouse