The route of Leishmania tropica infection determines disease outcome and protection against Leishmania major in BALB/c mice

Abstract

Leishmania tropica is one of the causative agents of leishmaniasis in humans. Routes of infection have been reported to be an important variable for some species of Leishmania parasites. The role of this variable is not clear for L. tropica infection. The aim of this study was to explore the effects of route of L. tropica infection on the disease outcome and immunologic parameters in BALB/c mice. Two routes were used; subcutaneous in the footpad and intradermal in the ear. Mice were challenged by Leishmani major, after establishment of the L. tropica infection, to evaluate the level of protective immunity. Immune responses were assayed at week 1 and week 4 after challenge. The subcutaneous route in the footpad in comparison to the intradermal route in the ear induced significantly more protective immunity against L. major challenge, including higher delayed-type hypersensitivity responses, more rapid lesion resolution, lower parasite loads, and lower levels of IL-10. Our data showed that the route of infection in BALB/c model of L. tropica infection is an important variable and should be considered in developing an appropriate experimental model for L. tropica infections.

Keywords: Leishmania major; Leishmania tropica; disease outcome; immunity; intradermal; subcutaneous.

Fig. 1

The disease outcome is influenced by the route of Leishmania tropica infection. BALB/c mice were infected by subcutaneous (into the footpad) or intradermal (into the ear dermis) inoculation of 10⁵ stationary phase L. tropica promastigotes. Data represent the mean and SD of thickness increase of the footpad or ear of 6-15 mice per group from a representative experiment out of 2 replicate ones. Asterisks (^*) show statistically significant difference (P<0.05) as calculated by the Student's t-test.

Fig. 2

Lesion development after Leishmania major challenge in the footpad of L. tropica pre-infected BALB/c mice. Before challenge, mice were immunized by subcutaneous (into the footpad) or intradermal (into the ear dermis) inoculation of 10⁵ stationary phase L. tropica promastigotes. Data represent the mean and SD of the footpad thickness for 6-15 mice per group from a representative experiment out of 2 replicate ones. Asterisks (^*) show statistically significant difference (P<0.05) between subcutaneous vs. intradermal groups as calculated by the Student's t-test.

Fig. 3

Delayed type hypersensitivity (DTH) responses to Leishmania major challenge are significantly higher in mice pre-infected by L. tropica through the footpad subcutaneous route in comparison to the ear intradermal route. Mice were pre-infected by L. tropica through subcutaneously in the footpad or intradermally in the ear. Mice were then challenged with L. major in the footpad. Data represent the mean and SD of the footpad thickness for 6-15 mice from a representative experiment out of 2 replicate ones. Asterisks (^*) show statistically significant difference (P<0.05) as calculated by the Student's t-test.

Fig. 4

The percentage of IL-10 positive lymphocytes at week 1 after Leishmania major challenge in L. tropica pre-infected mice by ear intradermal or footpad subcutaneous routes. Data are mean and SD of percentages of IL-10 positive lymphocytes of 3 mice per group from 2 repeated experiments. The asterisk (^*) shows statistically significant difference between the 2 groups.

Fig. 5

Parasite loads after Leishmania major challenge in mice pre-infected with L. tropica through footpad subcutaneous or ear intradermal injection. Data are mean and SD of 3 mice per group. The asterisk (^*) shows statistically significant difference between the 2 groups.