IMMUNE-RESPONSE OF SHEEP PREVIOUSLY IMMUN IZED AND CHALLENGED WITH TRICHOSTRONGYLUS-COLUBRIFORMIS

Changes in lymphocyte subsets and specific antibody production were ex amined in previously immunized New Zealand Romney sheep after challeng e with Trichostrongylus colubriformis. Groups of 10 mature sheep were immunized by 3 infections with T. colubriformis truncated at day 7 (gr oup 1) and day 3 (group 2), respectively or by non-abbreviated infecti ons (group 3). These groups and a nonimmunized control group (group 4) were challenged with 60.000 infective T. colubriformis larvae. Propor tions of lymphocyte subsets and specific antibody production were moni tored for the following 4 and 5 weeks, respectively. Groups 1 and 3 de veloped protective immunity and showed at week 1 an increase in propor tions of CD5(+) and CD4(+) cells, and a decline of CD45R(+) cells. The non-protected groups 2 and 4 showed declines in proportions of CD5(+) cells, and an increase in CD45R(+) cells at this time. At week 2 lymp hocyte subset proportions returned to baseline levels and thereafter n o consistent trends were observed. T. colubriformis specific antibody titre increased in groups 2 and 4, while those of groups 1 and 3 plate aued or declined.