Experiment
L. tropica causes cutaneous leishmaniasis in humans and it can also visceralize. Experiments with mice revealed that manifestations of the disease after infection with L. tropica were strongly influenced by the geneotype of the host.
Mice from recombinant congenic strain CcS16, derived from a BALB/c-c-STS/A (CcS/Dem) panel, were crossed with BALB/c mice to create two experimental groups. The CcS16 strain carries 12.5% genes from the resistant parental STS/A strain and 87.5% from the susceptible BALB/c strain and is more susceptible to L. tropica than BALB/c mice. CcS16 was in more than 90 generations of inbreeding when used for these experiments.
The first experiment consisted of 111 mice, 51 mice from a (BALB/c x CcS16)F2 cross and 60 mice from the recprical cross, (CcS16 x BALB/c)F2. The second group contained a total of 134 mice, 64 from a (BALB/c x CcS16)F2 cross and 70 mice from the (CcS16 x BALB/c)F2 cross. Both F2 hybrid groups were derived from the same F1 parents. Infected mice from both experimental groups were genotyped and their linkage with pathological symptoms and systemic immune responses were determined, revealing eight Ltrp (Leishmania tropica response) loci. These loci are functionally heterogeneous - each influences a different set of responses to the pathogen.
In analysis of both the (BALB/c x CcS16)F2 mice and the (CcS16 x BALB/c)F2 mice, the authors identify a second, more distal, locus on Chr 2 of the CcS16/Dem mice, labeled Ltpr2, Leishmania tropica response 2 influencing control of multiple functions. Ltpr2, spans multiple peaks from D2Mit389 at 54.43 cM to D2Mit52 at 87.22 cM.
02.11.2016 Curator Note: We have retained the broader QTL identified in this study as Ltpr2. We have also assigned official nomenclature to each of the independent traits that map with significance within the broader Ltpr2 locus creating Ltpr2a, Ltpr2b, Ltpr2c, Ltpr2d, Ltpr2e, Ltpr2f and Ltpr2g.
A main effects QTL, Ltpr2a, controlling skin lesion development at week 19 after infection, mapped to D2Nds3 at 62.97 cM, corrected p=0.0004. STS/A alleles at Ltpr2a determined larger lesions and explained 20.9% of trait variance. [Table 1.]
Another main effects QTL, Ltpr2b, influenced the number of parasites in the liver 43 weeks after infection. Ltpr2b, was also linked with marker D2Nds3 at 62.97; corrected p=0.028. The STS/A allele at this locus was associated with a higher parasite load and accounted for 9.50% of trait variance. [Table 2.]
Ltpr2c, also a main effects QTL, controlling skin lesion development at week 31 after infection mapped to marker D2Mit389 at 54.43 cM, corrected p=0.015, with the STS/A allele contributing to larger lesions. Lptr2c explained 10.77% of trait variance. [Table 1.]
Ltpr2d, also linked with D2Mit389 at 54.43 cM, corrected p=0.0003, determined hepatomegaly. Less severe hepatomegaly was observed in heterozygotes at 43 weeks after infection. Ltpr2d accounted for 13.83% of trait variance. [Table 2.]
Ltpr2e, linked with D2Mit52 at 87.22 cM, corrected p=0.002, controlled serum chemokine levels (CCL7) after seven weeks of infection. Homozygosity for the STS allele at Ltpr2e determined higher CCL7 levels. The locus accounted for 9.06% of trait variance. [Table 5.]
Splenomegaly was influenced by gene-to-gene interaction at week 43 between Ltpr2f linked with D2Mit257 at 64.18 cM and Ltpr3g linked to D3Mit11 at 43.71 cM, corrected p=0.010. F2 mice with homozygous STS/A alleles at both Ltpr2f and Ltpr3g have the smallest splenomegaly. This interaction explained 9.05% of trait variance. [Table 3.]
Ltpr2g, linked with D2Mit257 was detected in interaction with Ltpr6b linked with D3Mit11, corrected p=0.002 at 7 weeks after infection. The highest serum levels of CCL7 were associated with homozygous STS/A alleles at Ltpr6b in combination with either heterozygotes or STS/A homozygotes at Ltpr2g. This interaction explained 6.66% of trait variance. [Table 6.]
Another main effect QTL, Ltpr2h, also linked with D2Nds3, corrected p=0.002, measured at 21 weeks after infection controlled skin lesion size. STS/A alleles at Ltpr2h determined larger lesions and explained 10.93% of trait variance. [Table 1.]
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