Genetics of host response to Leishmania tropica in mice - different control of skin pathology, chemokine reaction, and invasion into spleen and liver

Abstract

Background: Leishmaniasis is a disease caused by protozoan parasites of genus Leishmania. The frequent involvement of Leishmania tropica in human leishmaniasis has been recognized only recently. Similarly as L. major, L. tropica causes cutaneous leishmaniasis in humans, but can also visceralize and cause systemic illness. The relationship between the host genotype and disease manifestations is poorly understood because there were no suitable animal models.

Methods: We studied susceptibility to L. tropica, using BALB/c-c-STS/A (CcS/Dem) recombinant congenic (RC) strains, which differ greatly in susceptibility to L. major. Mice were infected with L. tropica and skin lesions, cytokine and chemokine levels in serum, and parasite numbers in organs were measured.

Principal findings: Females of BALB/c and several RC strains developed skin lesions. In some strains parasites visceralized and were detected in spleen and liver. Importantly, the strain distribution pattern of symptoms caused by L. tropica was different from that observed after L. major infection. Moreover, sex differently influenced infection with L. tropica and L. major. L. major-infected males exhibited either higher or similar skin pathology as females, whereas L. tropica-infected females were more susceptible than males. The majority of L. tropica-infected strains exhibited increased levels of chemokines CCL2, CCL3 and CCL5. CcS-16 females, which developed the largest lesions, exhibited a unique systemic chemokine reaction, characterized by additional transient early peaks of CCL3 and CCL5, which were not present in CcS-16 males nor in any other strain.

Conclusion: Comparison of L. tropica and L. major infections indicates that the strain patterns of response are species-specific, with different sex effects and largely different host susceptibility genes.

Figure 1. Skin lesion caused by Leishmania tropica in female of CcS-16 strain at week 43 after infection.

Figure 2. Kinetics of skin lesion development of CcS/Dem strains after infection with L. tropica.

Individual strains are marked with different colors. The columns show median values of lesion size in females (A) and males (B). Figure summarizes data from two independent experiments.

Figure 3. Number of parasites cultivated from lymph nodes of mouse strains 21 and 43 weeks after infection.

Mice were killed at week 21 (A) and week 43 (B) after infection. Asterisks show strains that exhibited parasite load significantly different from BALB/c. Brackets indicate strains with differences between males and females. Data are presented as mean ± SD.

Figure 4. Leishmania tropica parasites inside the macrophage.

A smear of the inguinal lymph node of BALB/c male was stained with the anti-Leishmania lipophosphoglycan monoclonal antibody (CLP003A, Cedarlane, Hornby, Canada) and TRITC labeled IgM (115-025-020, Jackson Immunoresearch, West Grove, PA, United States of America), all diluted 1∶100. Nuclei of the cells were stained with DAPI. Parasites are shown with arrows.

Figure 5. Parasites in hematoxylin-eosin stained spleen smears.

Arrows show a group of parasites among spleen cells in infected BALB/c male (A); noninfected control BALB/c male without parasites (B).

Figure 6. Relationship between chemokine expression and lesion size development during the course of L. tropica infection.

Kinetics of skin lesion development (median, left y axis) and serum levels of CCL2, CCL3 and CCL5 (median values; right y axis) in females are shown. Figure summarizes data from two independent experiments (21 and 43 weeks of infection).

Figure 7. Comparison of kinetics of serum level of CCL3 and CCL5 in females and males of strains CcS-16 and BALB/c.

Kinetics of CCL3 levels (median values) in serum of BALB/c (A) and CcS-16 (B) and serum levels of CCL5 (median values) in BALB/c (C) and CcS-16 (D) mice is shown. Figure summarizes data from two independent experiments (21 and 43 weeks of infection).