Antibody-containing cells in the abomasal mucosa of sheep with genetic resistance to Haemonchus contortus.

The frequency distribution of parasite-specific antibody-containing cells (ACC) and total immunoglobulin-containing cells (ICC) in the abomasal mucosa was examined in genetically resistant and random-bred sheep, following infection with Haemonchus contortus, to determine whether the two genotypes differed in the development of a local immune response. Immunofluorescence staining was used to detect ACC and ICC of IgA, IgG1, IgG2 and IgM classes. No ACC were found in the abomasum of any of the sheep before infection. ACC were first detected in the abomasal mucosa of both the resistant and susceptible sheep seven days after infection, reached a peak level on day 21 and then declined. At all observation times, the majority of ACC in both genotypes were of the IgA isotype, followed by IgG1 and IgM. The IgG2-ACC response was negligible compared with the IgA and IgG1 response. The comparison of genotypes showed that the resistant sheep had significantly more IgA-ACC on days 14, 21, 28 and 35, and significantly more IgG1-ACC than random-bred sheep on days 14, 21 and 28. The numbers of IgG2- and IgM-ACC did not differ between the genotypes. The abomasal mucosa of the resistant sheep was also found to have significantly more ICC than the mucosa of random-bred sheep; IgA-ICC predominated at all the observation times followed by IgG1 and IgM. These results suggest that IgA and IgG1 antibodies, produced locally in response to infection, may play a role in mediating genetic resistance to haemonchosis in sheep.