Protective Role of Purified Cysteine Proteinases against Infection in Experimental Animals

Fascioliasis is one of the public health problems in the world. Cysteine proteinases (CP) released by $Fasciola$ $gigantica$ play a key role in parasite feeding, migration through host tissues, and in immune evasion. There has been some evidence from several parasite systems that proteinases might have potential as protective antigens against parasitic infections. Cysteine proteinases were purified and tested in vaccine trials of sheep infected with the liver fluke. Multiple doses (2 mg of CP in Freund's adjuvant followed by 3 booster doses 1 mg each at 4 week intervals) were injected intramuscularly into sheep 1 week prior to infect orally with 300 $F.$ $gigantica$ metacercariae. All the sheep were humanely slaughtered 12 weeks after the first immunization. Changes in the worm burden, ova count, and humoral and cellular responses were evaluated. Significant reduction was observed in the worm burden (56.9%), bile egg count (70.7%), and fecel egg count (75.2%). Immunization with CP was also found to be associated with increases of total IgG, $IgG_1$, and $IgG_2$ ($P$<0.05). Data showed that the serum cytokine levels of pro-inflammatory cytokines, IL-12, IFN-${\gamma}$, and TNF-${\alpha}$, revealed significant decreases ($P$<0.05). However, the anti-inflammatory cytokine levels, IL-10, TGF-${\beta}$, and IL-6, showed significant increases ($P$<0.05). In conclusion, it has been found that CP released by $F.$ $gigantica$ are highly important candidates for a vaccine antigen because of their role in the fluke biology and host-parasite relationships.