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-␥) Leishmaniasis is a neglected disease resulting in a global mortality rate of approximately 60,000 per year. Visceral leishmaniasis (VL) is almost always fatal if left untreated. VL accounts for the majority of mortalities from leishmaniasis, represents a serious public health problem in regions where leishmaniasis is endemic, and is rapidly emerging as an opportunistic infection in HIV patients (1). Patients who recover from VL are resistant to reinfection (2). The fact that recovery from VL protects individuals from disease indicates that it should be possible to develop a vaccine against VL. However, there is no vaccine available for VL. There is great interest in finding immunogenic molecules from Leishmania infantum with potential applications as a vaccine candidate or a diagnostic molecule. Many immunogenic molecules from Leishmania infantum have been reported (1).Antibody responses are parts of the immune response against Leishmania infantum in humans. The presence of anti-Leishmania antibodies has been documented in VL (3, 4). The roles of these antibodies in immunity against VL in humans are not clear (2). However, the regulatory (5) and exacerbating (6) roles of antibodies in murine visceral leishmaniasis have been reported. AntiLeishmania antibodies have been used as diagnostic tools for this disease (7,8).Lymphocyte proliferation against Leishmania antigens is associated with protective immunity to VL (9). Gamma interferon (IFN-␥) is necessary for resistance against VL (10). Interleukin 10 (IL-10) is a counterprotective cytokine in VL (10).LCR1 is an immunogenic molecule discovered through screening a cDNA library of Leishmania infantum chagasi (11). This antigen has reacted with sera from Brazilian VL patients, showing the presence of anti-LCR1 in VL patients (11). Vaccination with LCR1 in a murine model of VL has shown some degree of protection against the disease (11). We were interested in whether LCR1 has potential uses as a vaccine or a diagnostic molecule in Iranian individuals. To approach these goals, we studied antibody responses against LCR1 in Iranian VL p...