Intestinal infusion of soluble larval antigen stimulates rejection of heterologous nematode larvae by immune sheep

Abstract.

Sheep immunised by multiple truncated infections with Trichostronglyus colubriformis were highly resistant to subsequent challenge with homologous exsheathed larvae, administered via a surgically implanted duodenal cannula. The duration of immunity after truncated infections was 12–14 weeks against challenge with T. colubriformis or Cooperia curticei, but there was little cross-protection against challenge with Nematodirus spathiger. When immune sheep were given booster doses of T. colubriformis larvae before challenge with N. spathiger, there were 97% fewer N. spathiger larvae in the first 5 m of small intestine, and an overall 79% reduction of N. spathiger larvae in immunised sheep, compared with naive controls. Boosting T. colubriformis immune sheep with killed T. colubriformis larvae plus soluble T. colubriformis L3 antigen, or with soluble antigen alone, also caused significant displacement of N. spathiger challenge larvae (98% and 100% respectively), indicating a non-specific expulsion process. These results indicate that N. spathiger can be used as an indicator species in T. colubriformis immune sheep, to quantify the effects of stimulating mucosal immunity with specific antigens, which may lead to identification of the antigens required for immunisation against nematodes.