Memory T- and B-cell responses to trypanosome
antigens were measured in peripheral blood mononuclear cells, spleen and lymph node cells obtained from four trypanotolerant N'Dama cattle which had been exposed to six experimental
infections with Trypanosoma congolense. These cattle were treated with
trypanocidal drugs following each
infection and had remained aparasitemic for 3 years prior to this study. The
antigens used were whole trypanosome lysate, variable
surface glycoprotein, a 33-kDa
cysteine protease (
congopain) and a 70-kDa
heat-shock protein. As parameters of T-cell-mediated immunity, we measured T-cell proliferation and IFN-gamma production. Lymph node cells, spleen cells and peripheral blood mononuclear cells all proliferated to a mitogenic stimulus (
concanavalin A) but only lymph node cells responded to trypanosome
antigens. Similarly, IFN-gamma was produced by both lymph node and spleen cells stimulated with
concanavalin A but only by lymph node cells stimulated with variable
surface glycoprotein and whole trypanosome lysate. T. congolense-specific
antibodies were detected in sera and in supernatants of cultured lymph node and spleen cells after in vitro stimulation with
lipopolysaccharide and recombinant bovine
interleukin-2. In conclusion, we have demonstrated that memory T- and B-cell responses are detectable in various lymphoid organs in cattle 3 years following
infection and treatment with T. congolense.