VACCINATION OF SHEEP WITH PURIFIED SERINE PROTEASES FROM THE SECRETORY AND EXCRETORY MATERIAL OF LUCILIA-CUPRINA LARVAE

Sheep were vaccinated with two purified serine proteases, LCT25a and L CT25b, isolated from the secretory and excretory material from first i nstar larvae of Lucilia cuprina. The immunization produced a strong an tibody response to LCT25b and a weaker response to LCT25a as measured by ELISA. However, neither protease induced an ovine immune response w hich affected the development of first instar larvae growing on sera d erived from these sheep. Further, direct in vivo bioassays of larval g rowth on the backs of vaccinated sheep also indicated a lack of induct ion of an immune response which prevented establishment of the larvae. Sera from unvaccinated sheep which had previous experience of blowfly strike, in general, strongly recognised the serine protease LCT25b. I t was concluded from all of these results that serine proteases from t he secretory and excretory material of L. cuprina are unlikely to be e ffective antigens in a vaccine designed to protect sheep from blowfly strike.