Receptor-mediated internalization of tuftsin by human polymorphonuclear leukocytes.

A high-performance liquid chromatography (HPLC) purified fluorescein-labeled analogue of tuftsin was prepared, which retains the full biological activity of the native molecule. Characterization of the derivatization site by amino acid analysis, N-terminal cleavage, and dansylation revealed a monofluorescinated derivative at the alpha-amino terminus. Binding of the fluorescent tuftsin to living polymorphonuclear leukocytes (PMN) was observed by means of video intensification microscopy. At 37 degrees C, diffuse membrane fluorescence was seen initially, followed by rapid aggregation and internalization. The latter was demonstrated by saltation of intracellular fluorescent aggregates. These processes are temperature-dependent and rely on specific binding to the tuftsin receptor.