THE GENE FOR A T-LYMPHOCYTE TRIGGERING FACTOR FROM AFRICAN TRYPANOSOMES

An early and essential event in the protective immune response against most viruses and protozoa is the production of interferon-gamma (IFN- gamma). In contrast, during infection with African trypanosomes, proto zoan parasites that cause human sleeping sickness, the increased level s of IFN-gamma do not correlate with a protective response, We showed previously that African trypanosomes ex-press a protein called T lymph ocyte triggering factor (TLTF), which triggers CD8(+) T lymphocytes to proliferate and to secrete IFN-gamma. Here, we isolate the gene for T LTF and demonstrate that the recombinant version of TLTF specifically induces CD8(+), but not CD4(+), T cells to secrete IFN-gamma. Studies with TLTF fused to the green fluorescent protein show that TLTF is loc alized to small vesicles that are found primarily at or near the flage llar pocket, the site of secretion in trypanosomes. TLTF is likely to be only the first example of a class of proteins that we designate as trypanokines, i.e., factors secreted by trypanosomes that modulate the cytokine network of the host immune system for the benefit of the par asite.