A Trypanosoma brucei brucei-derived factor that triggers CD8+ lymphocytes to interferon-gamma secretion: purification, characterization and protective effects in vivo by treatment with a monoclonal antibody against the factor.

A protein factor that stimulates CD8+ lymphocytes to produce and secrete IFN-gamma has been purified from Trypanosoma brucei brucei (T.b. brucei). This was accomplished by raising monoclonal antibodies (MoAbs) against a fraction of T.b. brucei obtained by gel filtration, which contained high levels of material inducing rat mononuclear cells (MNC) to IFN-gamma production. MoAbs from four hybridomas strongly inhibited trypanosome-induced IFN-gamma production. One of them (MO1) was used for purification of the trypanosome-derived lymphocyte triggering factor (TLTF) by affinity chromatography. SDS electrophoresis of the purified TLTF displayed a band of 42-45 kDa MW. Gel filtration of homogenates of whole parasites yielded several peaks of IFN-gamma-inducing activity with a lowest MW of 41-46 kDa. Bioactivity of all peaks was blocked by MO1, suggesting that a single molecule, or a single epitope of additional molecules, is responsible for the different peaks with IFN-gamma-inducing activity. IFN-gamma released from MNC stimulates T.b. brucei growth. Blocking of TLTF in vitro with MO1 inhibited MNC-supported growth of the parasites. To study the in vivo relevance of TLTF in the course of experimental African trypanosomiasis, MO1 was used to treat rats and mice at different times after infection. Treatments instituted at different time-points after infection suppressed parasite growth, abrogated the IFN-gamma production by splenocytes induced by the infection and prolonged survival of the animals. The data support the hypothesis that TLTF and IFN-gamma have a crucial regulatory function in the parasite-host interactions and that these molecules influence the disease course during experimental African trypanosomiasis.