The course of human Leishmania chagasi infections appears to be
determined by the balance between type 1 (T1) CD4+ and CD8+ T suppressor (Ts) cell
activities. Skin test positive adults living in hyperendemic areas who have no history of visceral
leishmaniasis (VL) have T1 CD4+ T cell immunodominant responses against L.
chagasi. The cytokines they secrete during anti-leishmania responses are a probable source
of cytokines which inhibit the CD8+ Ts cells associated with VL. The ability of supernatants
generated from peripheral blood mononuclear cells derived from skin test positive adults to
reverse immune responses which appear to be mediated by CD8+ Ts cells was assessed in
three sets of screening assays. The supernatants displayed three candidate factors. One, which
could be explained by Leishmania antigens in the supernatant, decreased high
endogenous IL-10 secretion characteristic of one class of VL patients. A second activity
decreased high endogenous proliferation characteristic of the same class of patients without
decreasing antigen specific proliferation. The third activity inhibited or killed CD8+ T cells but
not CD4+ T cells. These activities might be useful in treating VL.
