Genetic control of immune responses to parasites: immunity to Trichuris muris in inbred and random-bred strains of mice.

A comparison has been made of the responses of random-bred CFLP and inbred NIH mice to infection with Trichuris muris. Random-bred mice showed greater variation in worm burdens and less uniformity in worm expulsion. Irradiation prior to infection reduced variation, but did not increase the mean level of infection above that shown by the most susceptible unirradiated mice. In NIH mice, however, irradiation raised the level of infection in all mice. The factors responsible for variation between CFLP mice and for the level of infection in NIH mice came into play after the fifth day of infection and were inactivated by cortisone acetate. It is suggested that these factors are immunologically mediated and under direct genetic control. Uniformity of infection and expulsion in NIH mice is therefore seen as a consequence of genetic uniformity; variability in CFLP mice as a consequence of genetic variation. The time of worm expulsion was found to differ markedly between inbred strains of mice. Hybrid progeny showed the expulsion time characteristic of the parental strain with the most rapid expulsion; greater resistance was therefore inherited as a dominant characteristic. The genetic control of immunity to T. muris is discussed in the context of the antibody- and cell-mediated components of the expulsion process.