A Trypanosoma brucei brucei‐Derived Factor that Triggers CD8+ Lymphocytes to Interferon‐γ 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‐γ has been purified from Trypanosoma brucei brucei (T.b. brucei). This was accomplished by raising monoclonal antibodies (MoAbs) against a fraction of T.h. brucei obtained by gel filtration, whieh contained high levels of material inducing rat mononuelear cells (MNC) to IEN‐y production. MoAbs from four hybridomas strongly inhibited trypanosome‐induced IFN‐γ 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‐γ‐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‐γ‐indueing activity. IFN‐γ 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‐γ production by splenocytes indueed by the infection and prolonged survival of the animals. The data support the hypothesis that TLTF and IFN‐γ have a erueial regulatory function in the parasite host interactions and that these moleeules influence the disease eourse during experimental African trypanosomiasis.