Expression of acquired immunity to Heligmosomoides polygyrus in mice concurrently infected with Trypanosoma congolense.

The effects of concurrent Heligmosomoides polygyrus and Trypanosoma congolense infection on the expression of acquired resistance to homologous nematode challenge were studied in female outbred TO mice. Mice were infected with 500 infective larvae (L3) of H. polygyrus and the infection was terminated by anthelminthic treatment on Day 12, when the worms were adults. Eight days later sub-groups of these pre-exposed mice, and of similar mice which had not experienced the previous infection with H. polygyrus, were either simultaneously infected with 500 L3 of H. polygyrus and 10(4) bloodstream forms of T. congolense, or with only one of these parasites, or were not infected. The experiment was monitored by routine parasitological and immunological techniques, including quantitative assessment of worm burden, trypanosome parasitaemia, growth of nematodes and measurement of the parameters reflecting pathological and antibody responses for 30 days after immunization. Concurrent H. polygyrus and T. congolense infection resulted in abrogation of the partial immunity against challenge infection with H. polygyrus in the pre-exposed mice, and in depressed humoral antibody responses following infection. Mortality was greatly reduced in pre-exposed mice infected with T. congolense alone compared to naive mice. The growth of male H. polygyrus worms was not affected by either the immune or infection status of their host. Although the increased size of the female worms from pre-exposed and then concurrently infected mice compared to similar mice infected only with H. polygyrus was significant, the egg production per worm was not affected.