Immune exclusion and mucus trapping during the rapid expulsion of Nippostrongylus brasiliensis from primed rats.

AThe phenomenon of rapid expulsion (RE) of Nippostrongylus brasiliensis was examined in Wistar rats. Within 4 hr of intraduodenal challenge with 4 day old N. Brasiliensis greater than 85% of the worms were expelled from rats immunized by infection 18 days previously with 4000-6000 third stage larvae. Rapid expulsion was unaffected by the challenge dose but waned with time after primary infection. Histological observations suggested that the parasites were excluded from their predilection site between the villi in immune rats and that they were separated from the mucosa by a superficial layer of mucus. A newly developed intestinal wash-out technique demonstrated that the 70%-80% of worms in previously uninfected controls were adherent to the mucosa whereas in immune rats 28%-36% of the parasites were adherent and 3%-23% were trapped in mucus. These experiments establish that immune exclusion and mucus trapping are early events in the expulsion process. The possible mechanisms controlling these phenomena are discussed.