Immunity to Heligmosomoides polygyrus induced by subcutaneous vaccination with post-infection larvae

The objective of this study was to investigate, using the Heligmosomoides polygyrus (= Nematospiroides dubius)-mouse model, whether live post-infection trichostrongylid larvae recovered from the intestinal wall of donor animals and placed subcutaneously would serve as vaccine protecting against oral challenge by third-stage (infective) larvae (L3). Experiments were conducted to determine the effect of number and age of post-infective larvae as well as age and sex of host on vaccination. Vaccinated BALB/cByJ mice were challenged with 30 L3 and total adult worm burdens compared between vaccinated groups and sham-treated controls (> 90% infection rates). All mice subcutaneously vaccinated with either five or 10 larvae harbored significantly fewer challenge parasites in their intestines than did sham-treated controls ( P < 0.001). Both young and mature mice were significantly protected against challenge by the subcutaneous larval vaccine. Adult female mice had significantly ( P < 0.05) fewer parasites than adult male mice. The age of the larvae (indicated as the days between infection and harvesting of the larvae) was important in that day-4 or day-6 larvae (L4) were significantly more protective ( P < 0.001) than day-2 (L3) or day-8 larvae (L5-preadult). Reduction in worm burden for young vaccinated animals ranged from 31 to 39% ( P < 0.001) and for mature animals from 88 to 100% ( P < 0.001). Passive transfer to serum resulted in the reduction of worm burdens by 26–40% ( P < 0.05). Results of the above experiments demonstrated that significant immunity to gastrointestinal nematodes may be induced by the subcutaneous implantation of low numbers of post-infective larvae. When L4 were used as vaccine, this immunity frequently reached 100%.