THE EFFECT OF IMMUNIZATION OF SHEEP WITH DRUG-ABBREVIATED INFECTIONS OF TRICHOSTRONGYLUS-COLUBRIFORMIS ON IN-VITRO LYMPHOCYTE BLASTOGENIC RESPONSES

Sixty 15-month-old ewes were randomly allocated to six groups of 10 sh eep each; the first four groups were infected three times with 20,000, 40,000 and 60,000 T. colubriformis 3rd stage larvae (L3) at 21 day in tervals and infections in each group were terminated with Oxfendazole at different times. Group 1, 2 and 3 infections were terminated 15, 7 and 3 days respectively after each infection and 21 days after the thi rd infection for only Group 4. Groups 1-5 were then challenged with 60 ,000 L3 T. colubriformis. Group 6 was left as uninfected control. All sheep were bled before and after the immunization procedure and then a t weekly intervals after the challenge infection. The blastogenic resp onses of peripheral blood lymphocytes to Con A, PHA, PWM and LPS, as w ell as responsiveness to L3 and adult T. colubriformis antigens, were evaluated using tritiated thymidine incorporation into DNA. The greate st changes in blastogenic response were observed in Group 2 immunized by successive infections terminated 7 days after infection; the smalle st in Groups 1 and 4 immunized by early L5 (immature 15 days) and L5 ( mature 21 days) stages of T. colubriformis, respectively. Lymphocyte r esponsiveness to L3 and adult parasite ES antigens, assessed for all g roups on the day challenge infection was given, were variable amongst groups.