Genetic control of immune responses to parasites: selection for responsiveness and non-responsiveness to Trichuris muris in random-bred mice.

Populations of Schofield strain, random-bred mice were shown to have a bimodal variation in ability to bring about immune expulsion of the nematode Trichuris muris. This variation was genetically determined and independent of the size of infection experienced. The proportion of mice unable to achieve worm expulsion (non-responders) was relatively constant in various populations of the strain but was increased by selective breeding from mice of known status. Crosses made between non-responder and responder mice produced progeny that were almost all (92%) of responder phenotype, showing that the ability to achieve worm expulsion was inherited as a dominant characteristic. It is suggested that the genetic control involves a small number of genes; the possible immunological mechanisms by which control is mediated are briefly discussed.