Genetic control of immunity to Trichinella spiralis infections of mice. Hypothesis to explain the role of H-2 genes in primary and challenge infections

H-2 congenic strains of mice were compared for their ability to expel T. spiralis infections from the small intestine and for their ability to limit the reproduction of adult female worms. B10.M mice (H-2(f)) expelled both primary and challenge infections more quickly than did the strains B10.Q(H-2(q)) and B10.BR(H-2(k)). During a primary infection, expulsion of worms from B10.M mice began before Day 9 post-infection and worm counts differed significantly (P < .05 Student's t-test) from counts in B10.BR mice on each of Days 12 and 15. B10.Q mice expelled worms more rapidly than B10.BR but worm counts did not differ significantly until Day 15. Whereas B10.M mice responded most quickly to expel worms from the gut, B10.Q mice were most effective in limiting worm reproduction. Female worms harvested from B10.Q mice and cultured for 24 hr in vitro produced significantly fewer newborn larvae than did worms from B10.M or B10.BR mice. Worms from B10.M mice were less fecund than worms from B10.BR, but this difference was not apparent before Day 9 post-infection, and worms from B10.M were always more fecund than worms from B10.Q. Challenge infections 21 days following a priming dose of 200 T. spiralis muscle larvae were rejected very quickly. B10.M mice expelled 65% of their worms during the first 24 h. By Day 6 after challenge, B10.M mice had expelled 84% of their worms; B10.Q and B10.BR expelled 75% and 37% respectively. These results suggest that a rapid expulsion response may be expressed in many different strains of mice depending on how the mice are immunized and the size of the infecting dose. Fecundity of female worms 6 days following a challenge infection was reduced for all strains tested when compared to primary infection controls; however, worms from B10.Q mice were less fecund than worms from B10.M or B10.BR. Results of these experiments demonstrate that H-2 genes play an important role in controlling the immune response which expels worms from the gut and the response which limits worm reproduction. These H-2-controlled differences are expressed during both primary and challenge infections. As the present results conflict somewhat with results published elsewhere, we have proposed a new hypothesis to explain the data collected in our laboratories thus far. According to this hypothesis, the anti-adult response, the anti-fecundity response, and the rapid expulsion response are under independent genetic control and influenced by the interacting products of both H-2 and non-H-2 genes.