Responses of NFR/N inbred mice to very low-dose infections with Ascaris suum.

Mice were evaluated for immunological responses and resistance to challenge infections after single infections. When given infections simultaneously with thiabendazole, larval migration to the liver and lungs was blocked but not when mice were given infections only. Enlargement of Peyer's patches was observed after infection followed by increased numbers of IgA-containing cells in the lamina propria of the intestines and increased levels of hepatobiliary IgA. Ig-containing cells were variable in the spleens during the early phase of infection. The observed changes quickly returned to normal control levels and did not change throughout the rest of the experiment. Serum Ig levels did not change dramatically. Challenge with high doses of eggs indicated that mice given single very low-dose infections became highly resistant.