Correlation of parasitological and immunological parameters in sheep with high and low resistance to haemonchosis

Parasitological and immunological parameters of Blackbelly (Bb), a haemonchosis high-resistance sheep breed, and Columbia (Cb) a haemonchosis low-resistance breed were compared. Two experiments were performed: Bb and Cb lambs were infected weekly with 1000 third-stage larvae (L3) of Haemonchus contortus for 6 wk. In the first experiment, faecal egg counts (FEC) and blood eosinophils (BE) were determined for 15 wk. In the second experiment, the following parameters were measured weekly: FEC, plasma proteins, serum IgG to H. contortus L3 levels by ELISA and L3 antigens recognized by Western blot; animals were euthanized after 15 weeks and autopsies were performed to evaluate the total adult phases (AP), eosinophils and mast cells in the fundic abomasal region (FAR), pyloric abomasal region (PAR) and abomasal lymph node (ALN). Fecal egg counts and AP were significantly higher (P 0.05) in the number of mast cells per cm 2 in the sampled regions of both infected groups. The increase and maintenance of serum antibodies and circulating and local eosinophils in resistant animals agrees with the development and maintenance of a Th 2 type immune response. The initial increase and further reduction of serum antibodies and circulating and local eosinophils in the low-resistance lamb breed suggest an initial Th 2 type response and a subsequent change to a Th 1 type response. Key words: Haemonchus, immune response, breed resistence, eosinophils, antibodies, sheep