Development of immune responsiveness to Ascaris suum antigens in pigs vaccinated with ultraviolet-attenuated eggs.

Pigs fed Ascaris suum eggs attenuated by short wave ultraviolet-radiation developed resistance to challenge infection. Per os inoculation of pigs on three successive weeks with 10,000 eggs irradiated to total exposures of 150,100 and 75 microW-min/cm2, respectively, resulted in an 88% reduction in the number of larvae recovered from the lungs 7 days after challenge with 10,000 infective eggs. Peripheral blood lymphocytes (PBL) from vaccinated pigs were specifically stimulated in vitro to incorporate tritiated thymidine by egg hatching fluid (Ea) and by excretory-secretory products obtained from cultures and from cultures of third-stage larvae developing to fourth-stage (L3-4). PBL were also specifically stimulated by living L2. Ea and L2 stimulated pig PBL significantly at 7 days after the first inoculation; responses to L2-3 and L3-4 developed 7 days after a second inoculation. The antigen-responsive cells in the PBL population were non-immunoglobulin-bearing lymphocytes. Antibodies to Ea and L2-3 were not detected in the serum of vaccinated pigs, and only 3 of 7 pigs had low concentrations of serum antibodies to L3-4.