Variation in responsiveness to Trichinella spiralis infection in inbred rat strains

An analysis of interstrain variation between 12 inbred and 4 congenic rat strains in the expression of immunity against Trichinella spiralis is reported. All rat strains expressed strong rapid expulsion which resulted in the elimination of 88-98% of a challenge infection of muscle larvae. In contrast, substantial interstrain variation in the rate of adult worm expulsion in the primary infection was evident. By day 10 after infection, BUF and YO strains had less than 50 worms left in the intestine whereas BI and WKA strain rats had barely begun rejection, with approximately 1000 worms present in the gut for both strains. All other rat strains fell within these extremes in a continuous gradation. There was no clustering of rat strains into phenotypic groups with comparable worm burdens as seen with mice. The number of muscle larvae that established after the primary infection showed less variation than had adult worm burden in the primary infection and there was only a weak correlation of muscle larvae burden with numbers of intestinal adults present at 10 days. Comparison of MHC-matched or MHC-disparate rat strains on a PVG background suggested that non-MHC genes determined the principal adult worm rejection characteristics of a given strain. The absence of phenotypic variation in the expression of rapid expulsion in rats reinforces the biological distinction between rat rapid expulsion and the 'rapid expulsion' defined for mice.