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

Abstract

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 Cb lambs. BE showed a significant increase (P < 0.05) in both breeds at week 9 and, subsequently, Cb lambs presented a sudden decrease in these levels. The Bb lambs revealed a higher amount (P < 0.05) of antibodies between weeks 9 and 15 of the experiment, and Cb lambs showed a reduction in antibody levels at week 9. The Western blot revealed 11 bands of H. contortus L3 antigens; no differences were observed between breeds. The number of tissue eosinophils per cm2 in PAR and ALN was higher (P < 0.05) in the Bb lambs. No differences were found (P > 0.05) in the number of mast cells per cm2 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 Th2 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 Th2 type response and a subsequent change to a Th1 type response. Key words: Haemonchus, immune response, breed resistence, eosinophils, antibodies, sheep