CD4(-LYMPHOCYTES CONTRIBUTE TO PROTECTIVE IMMUNITY INDUCED IN SHEEP AND GOATS BY HAEMONCHUS-CONTORTUS GUT ANTIGENS() T)

Immunization with parasite antigens derived from the gut of adult Haem onchus contortus induces significant levels of protection against the parasite in sheep and goats. However, the mechanisms of immunity invol ved in this protection are riot clear. Here, we investigate the requir ement for CD4(+) T lymphocytes in gut antigen-induced immunity against H. contortus. Gut antigen immunized animals were depleted (>98%) of t heir CD4(+) T lymphocytes in peripheral blood by intravenous injection of an anti-CD4 MoAb. Depletion in peripheral blood persisted for at l east eight days, after which there was gradual recovery of CD4(+) T ly mphocytes. Serum antibody levels in gut antigen-immunized animals corr elated significantly with worm parameters, suggesting a contribution b y antibody to the immunity observed. By covariate analysis, using ELIS A OD as the covariate, CD4(+) T lymphocyte depletion was shown to part ially abrogate immunity induced by gut antigen immunization, against c hallenge infection with H. contortus. The greatest effect of CD4(+) T lymphocyte depletion was observed at 14 clays post-infection, with dif ferences between CD4(+) T lymphocyte depleted and intact animals less apparent between days 21 and 25. Collectively, our data indicate that CD4(+) T lymphocytes contribute to immunity induced by gut antigens. O ur results also suggest that antibody works synergistically with CD4() T lymphocytes to confer this immunity.