NO release by monocyte-derived macrophages eight months after diagnosis of Leishmania infection. CTL: uninfected macrophages (controls). LEISH: L. infantum-infected macrophages. A, macrophages from symptomatic dogs incubated without lymphocytes; B, macrophages from symptomatic dogs incubated with autologous lymphocytes; C, macrophages from asymptomatic dogs without lymphocytes; D, macrophages from asymptomatic dogs with autologous lymphocytes. Results are expressed as means ± SE.