Immune responses of Iranian patients with visceral leishmaniasis and recovered individuals to LCR1 of Leishmania infantum

Visceral leishmaniasis is a serious public health problem. Leishmania infantum is one of its causative agents. LCR1 is an immunogen from L. infantum. Antibodies against this protein have been detected in visceral leishmaniasis patients. The aim of this study was to define the antibody and cellular immune responses against LCR1 in Iranian visceral leishmaniasis patients and recovered individuals. The LCR1 protein was produced in recombinant form. Antibody responses against this protein were studied in Iranian individuals with a recent history of visceral leishmaniasis. Responses of peripheral blood mononuclear cells to this protein were studied in Iranian individuals who had recovered from visceral leishmaniasis. Our data show that (i) there was an antibody response to LCR1 in each individual with a recent history of visceral leishmaniasis studied, (ii) there was neither a proliferative response nor production of gamma interferon (IFN-γ) or interleukin 10 in response to LCR1 by mononuclear cells from individuals who had recovered from visceral leishmaniasis, and (iii) individuals who have recovered from visceral leishmaniasis show ongoing immune responses long after recovery from the disease. These data show that there are no detectable cellular memory responses to LCR1 in Iranian individuals who have recovered from visceral leishmaniasis, while there are detectable antibody responses in patients with this disease. Our data suggest that LCR1 has potential applications for the diagnosis of leishmaniasis through antibody detection, while the application of LCR1 alone for induction of IFN-γ in individuals who recovered from this disease is not supported. The presence of long-lasting immune reactivities in individuals who recovered from the disease may show the necessity of extended medical surveillance for these individuals.

Viscerotropic growth pattern of Leishmania tropica in BALB/c mice is suggestive of a murine model for human viscerotropic leishmaniasis

Leishmania (L.) tropica is a causative agent of cutaneous leishmaniasis, and occasionally of visceral or viscerotropic leishmaniasis in humans. Murine models of Leishmania infection have been proven to be useful for elucidation of mechanisms for pathogenesis and immunity in leishmaniasis. The aim of this study was to establish a murine model for human viscerotropic leishmaniasis, and the growth pattern of L. tropica was studied in different tissues of BALB/c mice in order to find out whether the parasite visceralizes in this murine model. L. major was used as a control as this species is known to cause a progressive infection in BALB/c mice. L. tropica or L. major was injected into the footpad of mice, and thickness of footpad, parasite loads in different tissues, and the weight of the spleen and lymph node were determined at different intervals. Results showed that L. tropica visceralizes to the spleen and grows there while its growth is controlled in footpad tissues. Dissemination of L. tropica to visceral organs in BALB/c mice was similar to the growth patterns of this parasite in human viscerotropic leishmaniasis. The BALB/c model of L. tropica infection may be considered as a good experimental model for human diseases.

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

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.