Proteinases are known to be capable of prolonging the survival of endoparasites in a host. We were therefore interested in knowing whether immunization of lambs against a
proteasome (multisubunit
proteinases) preparation obtained from Trichostrongylus colubriformis infective third-stage larvae (L3) would have any effect on the immune response to a single challenge
infection with the same organism. A total of 21 penned lambs aged 8 months were divided into 3 equal groups. Group 1 was immunized on three occasions with increasing amounts of a
proteasome-enriched fraction obtained from infective L3. Group 2 was given a similar amount of
protein from the initial supernatant of homogenized larvae. Group 3 (controls) received adjuvant plus
saline solution only. All groups were challenged with 60,000 infective T. colubriformis larvae at 28 days after the last immunization. Significant protection was obtained only when the initial supernatant extract was used to immunize lambs. The
proteasome preparation seemed to have immunosuppressive effects through the stimulation of nonspecific
IgE production. Significantly lower levels of specific
IgE were observed in lambs immunized with the
proteasome-enriched fraction, and levels of specific
IgG antibodies were increased. We suggest that
proteasome fractions of T. colubriformis may serve as useful preparations for the study of mechanisms of
IgE production in parasitized sheep.