A serial study of rejection of Trichostrongylus colubriformis by immune sheep.

Host responses and the rejection of worms were measured at intervals following challenge of immune and susceptible sheep with T. colubriformis infective larvae. Immune sheep rejected most of their larvae within the first day after infection. This early rejection was associated with local appearance of globule leucocytes and increased concentration of T. colubriformis-specific IgG1 and IgG2 in intestinal mucus. Rejection of the remaining worms occurred between 3 and 14 days after infection and was associated with increased T. colubriformis-specific IgA and IgG2 in intestinal mucus, local T cell infiltration, activation, differentiation and epithelial necrosis. Local T cell changes included expansion of the T19- gamma delta+ populations in the villous lamina propria and epithelium.