Immune responses of sheep to the parasitic nematode Trichostrongylus colubriformis: infections in Thiry-Vella loops.

Some aspects of the local immune response to nematode infection were examined by introducing fourth-stage Trichostrongylus colubriformis larvae into Thiry-Vella loops in worm-free and T. colubriformis-resistant sheep. Approximately 15% of the larvae introduced into the worm-free sheep survived and matured into adult worms, whereas less than 1% survival in resistant sheep. The amount of IgG1, IgG2, IgM and albumin discharged from loops in worm-free but not resistant sheep all increased following infection with larvae. Secretions from resistant sheep contained approximately three times as much IgA as secretions from the worm-free group and, in addition, their plasma IgG1 level was significantly higher. Antibodies against T. columbriformis were found in both plasma and intestinal secretions, the highest titres being found in the resistant sheep. During worm expulsion from loops in the resistant sheep neither immunoglobulin levels nor antibody titres in the secretions increased significantly.