Infection of mice with Nematospiroides dubius: demonstration of neutrophil-mediated immunity in vivo in the presence of antibodies.

The ability of murine neutrophils to confer resistance to mice against infection by the helminth parasite Nematospiroides dubius has been investigated. Mice whose neutrophils had been 'altered' by an immunizing infection with third-stage larvae (L3) of N. dubius exhibited resistance to a challenge dose of L3 given 4 days after the immunizing infection, provided greater than 0.1 ml of immune mouse serum was passively transferred within 0-24 hr of challenge. Normal mouse serum was ineffective, as was immune serum given at the time of challenge to naive (unimmunized) mice. Neutrophils purified from the blood of mice infected 4 days previously were able to reduce the infectivity of exsheathed L3 when incubated with the latter in vitro in the presence of fresh immune serum. In contrast, peritoneal exudate cells collected at the same time were inactive in this test, indicating that activated macrophages capable of damaging L3 were not yet present and that the immunity of 4-day infected mice given immune serum was probably attributable to the presence of 'altered' neutrophils. The capacity of neutrophils to confer resistance to infection in vivo was unambiguously demonstrated by the passive transfer of 98 +/- 4% pure neutrophils, isolated from the blood of 4-day infected (C57Bl X BALB/c)F1 mice, to uninfected F1 mice. Only those mice which received both neutrophils and immune serum exhibited resistance to a challenge infection. In contrast, mice injected with an eosinophil-enriched cell preparation and immune serum were not resistant. These results indicate for the first time that neutrophils have the capacity to damage nematode parasites in vivo and that they are active against N. dubius in mice infected with this parasite.