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 activat es CD8(+) cells to produce iinterferon-gamma (IFN-gamma) that in turn stimu lates parasite growth. The gene for TLTF was recently cloned, and recombina nt TLTF (rTLTF) showed bioactivity that was similar to native TLTF. In this work, we employed two anti-TLTF monoclonal antibodies (mAbs) to detect lev els of TLTF during Trypanosoma brucei brucei (T. b. billcei) infections in mice. Furthermore, rTLTF was utilized to assess levels of anti-TLTF antibod ies. Mice with intact genes (wild type), and knockout mice with disrupted I FN-gamma (IFN-gamma(- / -)) or IFN-gamma R (IFN-gamma R- / -) genes were st udied. The knockout mice were used in order to illustrate the role of IFN-g amma in the production of antibodies to TLTF. While wild-type mice showed h igh parasitaemia accompanied by high TLTF levels and low anti-TLTF antibodi es at day 3 postinfection (p.i.). low TLTF was measured together with incre ased anti-TLTF antibodies at day 21 p.i. IFN-y(- / -) mice exhibited very l ow parasitaemia, TLTF and anti-TLTF antibody levels. In contrast, IFN-gamma R- / - mice revealed very high parasitaemia, increased TLTF levels, but de creased anti-TLTF antibodies. In a biological assay for TLTF, Fab' fragment s of anti-TLTF antibodies dose dependently inhibited the TLTF-induced IFN-g amma production by splenocytes, suggesting a regulatory importance of these antibodies. Our data demonstrate a role of IFN-gamma 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 t rypanosomiasis.