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 LCT25b, isolated from the secretory and excretory material from first instar larvae of Lucilia cuprina. The immunization produced a strong antibody response to LCT25b and a weaker response to LCT25a as measured by ELISA. However, neither protease induced an ovine immune response which affected the development of first instar larvae growing on sera derived from these sheep. Further, direct in vivo bioassays of larval growth on the backs of vaccinated sheep also indicated a lack of induction 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. It was concluded from all of these results that serine proteases from the secretory and excretory material of L. cuprina are unlikely to be effective antigens in a vaccine designed to protect sheep from blowfly strike.