Humoral and cellular responses following local immunization with a surface antigen of the gastrointestinal parasite...

A purified, larval specific antigen of the abomasal parasite Haemonchus contortus was used to immunize sheep. In an attempt to induce a local immune response in the abomasum, the antigen was injected twice into the abomasal wall after one peripheral immunization. Serum antibody responses were boosted by each intra-abomasal immunization but not by the challenge infection given 3.5 weeks after the last immunization. Examination of the specific antibody secreting cells (ASC) recirculating in the peripheral blood indicated that there was an increase in blood ASC 5 days after local stimulation. This increase was maintained only after immunization and not after infection, probably reflecting the different responses induced when antigen is presented by injection in an adjuvant or by the parasite during infection. High proliferative T cell responses in the abomasal lymph nodes were only observed in one of the five sheep immunized with antigen; this was also the only sheep in this group to maintain an adult parasite burden at postmortem corresponding with the lowest antibody response. Peak faecal egg counts after infection were reduced by 54% in the immunized group compared to control sheep. Egg counts in the control sheep were, however, variable and dropped quickly, probably as a consequence of the inflammatory response induced by the injection of aluminium hydroxide into the abomasal wall.