Bidirectional signalling between Trypanosoma brucei brucei and CD8+ T cells involves reciprocal action of the parasite-derived trypanosome derived lymphocyte triggering factor (TLTF) and lymphocyte-derived IFN-γ. Herein we further characterize this relationship and report quantitation of TLTF secretion into culture supernatants using a newly developed ELISA. Secretion is induced by IFN-γ in a dose–response manner, with 100 U/ml giving maximal yields of bioactive TLTF as assessed by ELISA and ELISPOT. This is a constitutive and active secretion. Furthermore, IFN-γ-induced secretion was dependent on tyrosine protein kinase activity. Specific blockers of this signalling system resulted in lower yields of TLTF in the culture supernatants.