| Summary: | Visceral leishmaniasis (VL) is an infectious disease caused by parasitic protozoa of the genus <i>Leishmania</i> and manifests clinical symptoms such as splenomegaly, hepatomegaly, anemia, and fever. It has previously been shown that B-cell-activating factor (BAFF) is involved in splenomegaly during VL. Although BAFF is known to be expressed by a variety of cells, the mechanism of elevated BAFF expression in VL is not clear. In this study, we aimed to identify BAFF-producing cells in the spleens of mice infected with <i>Leishmania donovani</i>. Splenocytes of <i>L</i>. <i>donovani</i>-infected mice showed elevated BAFF expression compared to that of naive mice. In the infected spleen, the number of both CD11b<sup>+</sup> and F4/80<sup>+</sup> cells increased, and the major BAFF-producing cells were CD11b<sup>+</sup> cells, which did not serve as host cells of <i>Leishmania</i>. Immunohistochemical/immunofluorescent staining of spleens of infected mice revealed that the increased CD11b<sup>+</sup> cells were primarily MRP14<sup>+</sup> mononuclear cells. Together, these results suggest the increased BAFF expression in the spleen of <i>L</i>. <i>donovani</i>-infected mice involves a recruitment of inflammatory macrophages distinct from host macrophages for the parasites.
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