Non-specific immunodepression by larval and adult Nematospiroides dubius.

Mice infected with Nematospiroides dubius generate weaker immune responses to concurrently administered sheep red blood cells (SRBC), than non-infected controls. The experiments described in this paper demonstrate that both adult and larval stages of N. dubius cause non-specific immunodepression of the response to SRBC. Mice which had been infected with larvae exposed to 25 krad. of irradiation, which prevents development to the adult luminal stages, produced as weak haemagglutination responses to SRBC as mice infected with normal worms even when SRBC were administered 6 weeks after infection. The removal of adult N. dubius by treatment with pyrantel 9, 11 and 15 days after infection with normal larvae did not restore the host's ability to respond to SRBC given on day 14. It was only when the mice had been without worms for 17 days that their capacity to respond normally to SRBC was restored. Mice infected with 60 or 400 transplanted adult worms produced depressed haemagglutination and plaque-forming responses to concurrently injected SRBC when compared with normal or sham-operated controls. The significance of these results is discussed in relation to the possible role of non-specific immunodepression in facilitating the survival of N. dubius in the host.