CD4⁺ cells are indispensable for ulcer development in murine cutaneous leishmaniasis

One of the most characteristic clinical features in cutaneous leishmaniasis is the development of nodules followed by ulcerations at the site of infection. Leishmania amazonensis-infected mice show similar ulcerative lesions. Leishmania-infected severe combined immunodeficiency (SCID) mice, however, have been shown to develop nonulcerative nodules. In the present study, the roles of T cells in ulceration were examined using SCID mice in cell reconstitution experiments. After development of nonulcerative nodules, SCID mice were inoculated with splenocytes from either Leishmania-infected or naive immunocompetent mice, resulting in ulceration in all mice. When naive splenocytes were depleted of CD4⁺, CD8⁺, or B220⁺ cell populations and the remaining cells were injected into Leishmania- infected SCID mice after the development of nodules, only SCID mice inoculated with splenocytes depleted of CD4⁺ cells did not show ulceration. The evidence obtained in this study clearly shows that the CD4⁺ cell population is indispensable for ulceration in leishmaniasis lesions of SCID mice.