Induction of the trypanosome lymphocyte-triggering factor (TLTF) and neutralizing antibodies to the TLTF in experimental African trypanosomiasis

We have demonstrated that African trypanosomes secrete a novel trypanokine, the trypanosome-derived lymphocyte-triggering factor (TLTF), which activates CD8+ cells to produce interferon-γ (IFN-γ) that in turn stimulates parasite growth. The gene for TLTF was recently cloned, and recombinant TLTF (rTLTF) showed bioactivity that was similar to native TLTF. In this work, we employed two anti-TLTF monoclonal antibodies (mAbs) to detect levels of TLTF during Trypanosoma brucei brucei (T. b. brucei) infections in mice. Furthermore, rTLTF was utilized to assess levels of anti-TLTF antibodies. Mice with intact genes (wild type), and knockout mice with disrupted IFN-γ (IFN-γ−/−) or IFN-γR (IFN-γR−/−) genes were studied. The knockout mice were used in order to illustrate the role of IFN-γ in the production of antibodies to TLTF. While wild-type mice showed high parasitaemia accompanied by high TLTF levels and low anti-TLTF antibodies at day 3 postinfection (p.i.), low TLTF was measured together with increased anti-TLTF antibodies at day 21 p.i. IFN-γ−/− mice exhibited very low parasitaemia, TLTF and anti-TLTF antibody levels. In contrast, IFN-γR−/− mice revealed very high parasitaemia, increased TLTF levels, but decreased anti-TLTF antibodies. In a biological assay for TLTF, Fab′ fragments of anti-TLTF antibodies dose dependently inhibited the TLTF-induced IFN-γ production by splenocytes, suggesting a regulatory importance of these antibodies. Our data demonstrate a role of IFN-γ in the generation of neutralizing antibodies to TLTF. Furthermore, the induction of TLTF and its antibodies may constitute a new approach for future diagnosis of African trypanosomiasis