The requirement of thymus competence for both humoral and cell-mediated steps in expulsion of Nippostorngylus brasiliensis from mice.

The worm damaging process (step 1 of Nippostrongylus brasiliensis expulsion from rodents) does not occur in congenitally thymus-deficient (nude) mice as determined by worm morphology, female worm fecundity, and kinetics of worm expulsion upon transfer into normal rats. Expulsion of damaged N. brasiliensis (step 2) does not occur subsequent to transfer of such worms from rats into nude mice. Morphological changes and reduced fecundity appeared in adult worms from normal thymus-bearing mice as early as the first day of patency (day 6 of infection). Thus, the worm damaging process is initiated several days earlier in mice than in rats and may, therefore, account for the reduced longevity of N. brasiliensis in mice compared with rats.