Leishmania tropica infection, in comparison to Leishmania major, induces lower delayed type hypersensitivity in BALB/c mice

Abstract

Leishmania tropica and L. major are etiologic agents of human cutaneous leishmaniasis. Delayed type hypersensitivity (DTH) is an immunologic response that has been frequently used as a correlate for protection against or sensitization to leishmania antigen. In BALB/c mice, L. tropica infection results in non-ulcerating disease, whereas L. major infection results in destructive lesions. In order to clarify the immunologic mechanisms of these 2 different outcomes, we compared the ability of these 2 leishmania species in induction of DTH response in this murine model. BALB/c mice were infected with L. major or L. tropica, and disease evolution and DTH responses were determined. The results show that the primary L. major infection can exacerbate the secondary L. major infection and is associated with DTH response. Higher doses of the primary L. major infection result in more disease exacerbation of the secondary L. major infection as well as higher DTH response. L. tropica infection induces lower DTH responses than L. major. We have previously reported that the primary L. tropica infection induces partial protection against the secondary L. major infection in BALB/c mice. Induction of lower DTH response by L. tropica suggests that the protection induced against L. major by prior L. tropica infection may be due to suppression of DTH response.

Fig. 1

Effect of parasite dose of L. major infection on ear thickness in BALB/c mice. L. major at doses of 10⁵, 10⁴, and 10³ were injected into the ear intradermally. Ear thickness increase was defined as thickness of infected ear minus thickness of contralateral uninfected ear. Data are mean + SD of 5-10 mice per group. Symbol "#" shows statistically significant differences (P < 0.05) between doses of 10⁵ and 10⁴. Symbol "*" shows statistically significant differences (P < 0.05) between all the three doses (10⁵, 10⁴, and 10³).

Fig. 2

Effect of primary L. major infection on secondary L. major infection of BALB/c mice. Mice were infected by 10⁵ L. major in the ear as the primary infection followed by 10⁶ L. major in footpad as the secondary infection. The secondary infection was done 2-3 mo after the primary infection. Footpad thickness increase was defined as thickness of infected footpad minus thickness of contralateral uninfected footpad. Data are mean + SD of footpad increase of 5-10 mice per group after the secondary infection. Asterisk (*) shows statistically significant difference (P < 0.05) between the 2 groups.

Fig. 3

Effect of primary L. major infection on delayed type hypersensitivity (DTH) response to secondary L. major infection in BALB/ mice. Mice received 10⁵ L. major in the ear as the primary infection followed 2-3 mo later by 10⁶ L. major in the footpad as the secondary infection. DTH were determined in the footpad after the secondary infection. Footpad thickness increase was defined as thickness of infected footpad minus thickness of contralateral uninfected footpad. Data are footpad increase of individual mice.

Fig. 4

Effect of dose of primary L. major infection on secondary L. major infection in BALB/c mice. Mice received the primary infection of 10⁵ or 10³ L. major in the ear followed by 10⁶ L. major in footpad as the secondary infection 2-3 mo later. Footpad thickness increase was defined as thickness of infected footpad minus thickness of contralateral uninfected footpad. Data are mean + SD of footpad increase of 5-10 mice per group. Asterisk (*) shows statistically significant difference (P < 0.05) between the 3 groups.

Fig. 5

Effect of dose of primary L. major infection on delayed type hypersensitivity (DTH) response of BALB/c mice to secondary L. major infection. Mice received 10⁵, 10⁴, and 10³ doses of L. major in the ear as the primary infection followed by 10⁶ L. major in footpad as the secondary infection 2-3 mo later. Footpad thickness increase was defined as thickness of infected footpad minus thickness of contralateral uninfected footpad. Data are mean + SD of footpad increase of 5-10 mice per group after the secondary infection. Asterisk (*) shows statistically significant difference (P < 0.05) between doses of 10⁵, 10⁴, and 10³.

Fig. 6

Effect of primary infection of L. major or L. tropia on delayed hypersensitivity (DTH) response against secondary L. major or L. tropica infection in BALB/c mice. Mice received 10⁵ L. major or L. tropica in the ear as the primary infection followed by the secondary infection of 10⁶ L. major or L. tropica in footpad 3-4 mo later. Footpad thickness increase was defined as thickness of infected footpad minus thickness of contralateral uninfected footpad. Data are mean + SD of footpad increase of 5-10 mice per group 18-24 hr after the secondary infection. Asterisk (*) shows statistically significant difference (P < 0.05) between the groups inside the brackets.