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Infection and Immunity, April 2003, p. 2041-2046, Vol. 71, No. 4
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.4.2041-2046.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Jana Badalová,1,2 Milena Svobodová,3 Helena Havelková,1 Augustinus A. M. Hart,4 Hana Bla
ková,1 Peter Demant,5,
and Marie Lipoldová1,2*
Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 166 37 Prague 6,1 3rd Faculty of Medicine, Charles University, 100 00 Prague 10,2 Department of Parasitology, Faculty of Science, Charles University, 128 44 Prague 2, Czech Republic,3 Division of Radiotherapy,4 Division of Molecular Genetics, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands5
Received 21 October 2002/ Returned for modification 9 December 2002/ Accepted 9 January 2003
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To dissect the multigenic control of response to L. major infection, we used a special tool for genetic analysis of multigenically controlled biological traits, the recombinant congenic (RC) strains (5, 27). A series of 20 RC strains is derived from two inbred strains, a background strain and a donor strain. Each of the 20 RC strains contains a different random set of about 12.5% genes from the donor strain and 87.5% genes from the background strain. As a consequence, the individual donor strain genes contributing to the control of a biological trait (e.g., resistance to infection) were distributed among different RC strains. In our study we have used the RC strains of the BALB/c-c-STS/Dem (CcS/Dem) mouse series which were derived from the susceptible background strain BALB/cHeA (BALB/c) and the resistant donor strain STS/A (STS).
By this approach, we have dissected the genetic and functional aspects of susceptibility to leishmaniasis using, in place of two contrasting inbred strains, the set of 20 CcS/Dem RC strains. Strain CcS-5/Dem turned out to be highly resistant (5a), whereas RC strain CcS-16/Dem (CcS-16) is highly susceptible. The latter developed skin lesions earlier and had a tendency to develop larger skin lesions than BALB/c (13). By linkage analysis of the F2 hybrids between the most-resistant RC strain CcS-5 and the susceptible strain BALB/c, we mapped five novel loci, Lmr3 to Lmr7 (for L. major response), each of which appears to be associated with a different combination of pathological symptoms and immunological reactions (14). In the present study we have analyzed the control of skin lesions and visceral pathology in the most-susceptible strain, CcS-16.
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Parasites. L. major LV 561 (MHOM/IL/67/LRC-L137 JERICHO II) was maintained in rump lesions of BALB/c females. Amastigotes were transformed to promastigotes using SNB-9 (6). A total of 107 promastigotes from 6-day- old subculture 2 were inoculated in 50 µl of sterile saline subcutaneously into mouse rump.
Disease phenotype. The size of the primary skin lesions was measured weekly using a vernier caliper gauge. The mice were killed 8 weeks after infection and body, spleen, and liver weights were recorded.
Genotyping of F2 mice by PCR. DNA was isolated from tails using a standard proteinase procedure. The strain CcS-16 differs from BALB/c at STS-derived segments on nine chromosomes (24). These differential segments were typed in the F2 hybrid mice between CcS-16 and BALB/c using 23 microsatellite markers (Research Genetics, Huntsville, Fla.): D2Mit156, D2Mit389, D2Mit102, D2Nds3, D2Mit283, D2Mit51, D3Mit25, D3Mit11, D4Mit153, D6Mit48, D6Mit320, D10Mit67, D10Mit103, D11Mit139, D11Mit242, D11Mit37, D16Mit126, D17Mit38, D17Mit130, D18Mit120, D18Mit35, D18Mit40, and D18Mit49. The maximum distance between any two markers in the chromosomal segments derived from the strain STS or from the nearest BALB/c-derived markers was 20 centimorgans (cM). The PCR genotyping was performed as described elsewhere (10).
Statistical analysis.
The role of genetic factors in control of skin lesions, splenomegaly, and hepatomegaly induced by L. major infection was examined by analysis of variance (ANOVA) (Number Cruncher Statistical System [NCSS]). Marker, gender, and age were fixed factors, and the experiment was considered a random parameter. In order to obtain normal distribution required for ANOVA, the obtained values were transformed as shown in the footnotes to Table 1. The normality of data was tested by Martinez-Iglewitz and Kolmogorov-Smirnov normality tests in the NCSS. Markers and interactions with a P of <0.05 were combined in a single comparison. The time course of skin lesion development was evaluated on the basis of weekly measurements of lesion size in each mouse in week 4 to 8 after infection. Covariance analysis (general linear model ANOVA [GLM ANOVA]) (NCSS) with marker as the fixed variable and the week of observation as the covariate has been used to evaluate the linkage. To obtain whole genome significance values (corrected P) the observed P (
T) values were adjusted according to the method of Lander and Kruglyak (11) using the formula
T*
[C + 2
Fh(T)]
T, where G = 2 M (the length of the segregating part of the genome: 12.5% of 16 M); C = 9 (number of chromosomes segregating in cross between CcS-16 and BALB/c);
= 1.5 for F2 hybrids; and h(T) = the observed statistics (F ratio).
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TABLE 1. Linkage analysis of visceral disease in L. major-infected F2 hybrids between BALB/c and CcS-16a
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FIG. 1. Effects of genotype at Lmr13 on size of cutaneous lesions weeks 4 to 8 after infection. The means and standard errors of means (error bars) for each of the three genotypes at different time points are given (n = 565). C and S indicate the presence of BALB/c and STS allele, respectively. The numbers of mice of individual D18Mit35 genotypes are as follows: for CC ( ), n = 144; for CS ( ), n = 285; for SS (), n = 136. The P corrected for multiple testing is 0.00000125. Lesion sizes at week 8 after infection (mean ± standard deviation) were 158.34 ± 11.92 mm2 in strain BALB/c (n = 19), 220 ± 11.61 mm2 in strain CcS-16 (n = 20), and 171.84 ± 2.19 mm2 in the all F2 hybrids (n = 576); in the F2 hybrids, means ± standard deviations in the individual experiments were 152.20 ± 4.35 mm2 (n = 137), 170.56 ± 4.12 mm2 (n = 140), 175.49 ± 4.33 mm2 (n = 150), and 189.12 ± 4.67 mm2 (n = 149) in the experiment 1, 2, 3, and 4, respectively.
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(ii) Lmr14 on chromosome 2 controls splenomegaly and hepatomegaly. Splenomegaly is linked with the markers on chromosome 2 (D2Mit389, D2Mit102, and D2Nds3 [corrected P < 0.0177, 0.00282, and 0.0000728, respectively]), and hepatomegaly is linked with the markers D2Mit389, D2Mit102, D2Nds3, D2Mit283, and D2Mit51 (corrected P < 0.0168, 0.00000348, 0.000000137, 0.00209, and 0.0146, respectively). The STS allele is associated with larger spleno- and hepatomegaly. A weak influence on size of the skin lesions linked to the marker D2Mit283 was observed (data not shown).
(iii) Lmr15 on chromosome 11 controls hepatomegaly. Lmr15 is linked to the markers D11Mit242 and D11Mit37 (corrected P < 0.00741 and 0.0255, respectively), and the STS allele is associated with less pronounced hepatomegaly.
The influence of the experimental group on skin lesions was pronounced (P < 10-7 for Lmr13), and it was obvious for splenomegaly (P < 0.0008 for Lmr14) and hepatomegaly (P < 0.017 and 0.0086 for Lmr14 and Lmr15, respectively). However, there is no interaction between the experiment (or age) and any of the markers exhibiting linkage, indicating that the differences between the experimental groups do not affect the observed linkage and that the observed linkages are not artifacts due to unequal distribution of phenotypes and markers in different experiments, or to other untraceable causes.
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FIG. 2. Position of the loci that control cutaneous or visceral leishmaniasis in CcS-16. The regions of STS origin are represented as dark, the regions of undetermined origin are shaded. Only the BALB/c markers at the position between BALB/c and STS markers and STS markers that were used for typing are shown. The markers that exhibit significant P values (corrected P < 0.05) are shown in boxes.
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TABLE 2. Summary of Lmr loci that control pathological parameters in CcS-16 and potential candidate genes
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Locus Lmr14 on chromosome 2 controls the visceral symptoms (splenomegaly and hepatomegaly) (Table 1; Fig. 2). However, as the mapping of these effects appears to be spread over a broader region of chromosome 2 (>25 cM) with a peak of linkage at D2Nds3, it cannot be ruled out that the visceral pathologies are caused by two or more linked loci. Near D2Nds3 are candidate genes in the Il1 complex. Interleukin-1 (IL-1) was shown to play an important role in the development of cutaneous leishmaniasis (26).
CcS-16 has on chromosome 11 four short STS-derived regions. Lmr15 is linked to two of them, which are localized on the central part. The most distal one contains genes involved in defense against infection with Nos2 (which codes for nitric oxide synthase 2) and a cluster of several Scya (small inducible cytokine) genes. Nos2 was described as playing a central role in defense against L. major (4). Lmr15, which influences visceral pathology in our experiments, overlaps with Scl1, which was described to control cutaneous leishmaniasis (20). More experiments are necessary to establish the relationship and precise position of Lmr15 and Scl1. In the central part of chromosome 11 are located the candidate gene encoding interferon regulatory factor 1 and locus Tmp1, which were reported to influence in vitro IL-12 responsiveness and Th1 versus Th2 development, respectively (8, 9). However, no role of these loci in response to L. major in vivo has been demonstrated. The locus influencing skin lesions described by Beebe et al. (3) maps to the centromeric part of chromosome 11 that is not polymorphic between the two strains tested here and therefore cannot play a role in the effects we describe.
The present observations of the distinct gene effects on cutaneous and visceral components of leishmaniasis extend our previous data on the heterogeneous effects on pathology and immunology of the differential loci (Lmr3 to Lmr12) (1, 14). For example, the locus Lmr3 (chromosome 5) predominantly affects the visceral manifestations, Lmr4 (chromosome 6) affects the cutaneous lesions, and Lmr5 (chromosome 10) affects both cutaneous and visceral pathology. Organ-specific control of antiparasite response to L. major were also observed in functional analysis of inducible nitric oxide synthase control, where inhibition of the Nos2 product, inducible nitric oxide synthase, in resistant C57BL/6 mice led to parasite reactivation in the skin and draining lymph nodes but not in the spleen (25). Similar genetic heterogeneity was observed in response to another pathogen, the bacterium Borrelia burgdorferi, in which different loci controlled swelling of the ankle, tendon sheath thickness, and the amount of B. burgdorferi in heart tissue (21). Our data also indicate that the extent of pathological changes in organs does not directly correlate with the L. major parasite load but that the relation between the two is to a large degree strain-dependent, i.e., related to the host genome (J. Badalová et al., unpublished data).
Our results are compatible with the extensive genetic effects on the clinical heterogeneity of the disease caused by L. major revealed by the RC strains (13). Whereas the strain BALB/c develops both the cutaneous and visceral manifestations and the strain STS develops barely any signs of disease, the 20 RC strains, each carrying a different subset of 12.5% of STS genes on a BALB/c genetic background, differ widely in both clinical and immunological effects of L. major infection.
Collectively, these findings show that the effects of host genotype on the disease are complex and heterogeneous but also that they can be successfully dissected into the effects of individual genes that can be further characterized in detail. This genetic and functional dissection of the infectious disease will ultimately lead to the understanding of the specific effects of genes of the host on the pathogenesis and prognosis of the disease in the affected individuals, thus providing the possibilities for individualized medicine (22).
We acknowledge the permission of P. Kodym and K. Zitek (State Institute for Health, Prague) to use their laboratory and animal facilities for part of these experiments.
Present address: Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298. ![]()
Present address: Roswell Park Cancer Institute, Buffalo, NY 14263. ![]()
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ková, J. Engová, T. Pil
ík, P. Volf, P. Demant, and M. Lipoldová. 2002. Separation and mapping of multiple genes that control IgE level in Leishmania major infected mice. Genes Immun. 3:187-195.[CrossRef][Medline]
nková, A. A. M. Hart, D. Schlegel, P. Volf, and P. Demant. 2002. Mouse genetic model for clinical and immunological heterogeneity of leishmaniasis. Immunogenetics 54:174-183.[CrossRef][Medline]
nková, V. Holán, A. A. M. Hart, P. Volf, and P. Demant. 2000. Susceptibility to Leishmania major infection in mice: multiple loci and heterogeneity of immunopathological phenotypes. Genes Immun. 1:200-206.[CrossRef][Medline]
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