STRONGYLOIDES-STERCORALIS - EOSINOPHIL-DEPENDENT IMMUNE-MEDIATED KILLING OF 3RD STAGE LARVAE IN BALB CBYJ MICE/

Challenge worm survival was significantly reduced when BALB/cByJ mice were vaccinated against Strongyloides stercoralis infective third stag e larvae (L3) regardless of whether the challenge infections consisted of systemically migrating L3 or L3 implanted in diffusion chambers. T he only cell type that increased in number in diffusion chambers in im munized mice, 1 week after booster immunizations, was the eosinophil, and maximal levels of eosinophils were coincident with parasite killin g. Mice were treated with mAb to eliminate IL-5 or granulocytes to ass ess the role that eosinophils play in larval killing. Treated animals showed no decrease in immunity when challenge infections consisted of systemically migrating L3 administered 3 weeks after booster immunizat ions. Eosinophil numbers in immunized mice decreased to control levels when measured 3 weeks post-booster immunization, both in diffusion ch ambers and in the peripheral blood, whereas they were elevated at 1 we ek after booster immunizations. Direct contact between host cells and L3 was, however, still required for larval killing in immunized hosts 3 weeks after booster immunizations. Elimination of eosinophils by tre atment with mAb to IL-5 or granulocytes significantly reduced protecti ve immunity, when L3 were implanted in diffusion chambers at 1 and 3 w eeks post-booster. However, as systemically migrating L3 were still ki lled in immunized, eosinophil-depleted animals, other cell types may p lay a role in larval destruction. Two human eosinophil granule product s were found to be toxic for host-adapted L3(+), but had no effect on infective L3, indicating that host-adapted larvae are possible targets for eosinophil-mediated destruction of third stage larvae. These find ings suggest that inactivation of eosinophils by mAb treatment abolish es protective immunity to L3 contained within diffusion chambers and t hat small numbers of eosinophils are sufficient for immune-mediated ki lling of S. stercoralis L3. (C) 1996 Academic Press, Inc.