Resistance or susceptibility of inbred mouse strains to the parasite L
eishmania major correlates with CD4(+) T cell responses of the Th1 or
Th2 subsets, respectively. To evaluate the genetic basis for this diff
erence, resistant B10.D2 mice were backcrossed onto susceptible BALB/c
mice for five generations with selection for resistance. Candidate re
sistance loci were identified by high frequency of heterozygosity in r
esistant N5 backcross mice. Loci on chromosomes 6, 7, 10, 11, 15, and
16 were associated with resistance, demonstrating the multigenic natur
e of this phenotype. The presence of all six loci was not necessary to
confer resistance and no single locus was required. Rather, a variety
of combinations of these loci may be capable of interacting to confer
resistance.