Characterization and synthesis of a macrophage inhibitory peptide from the second constant domain of human immunoglobulin G.

We have shown that IgG hydrolysed by Schistosoma mansoni schistosomula inhibited various macrophage functions, especially phagocytosis and anti-schistosome cytotoxicity. Here we show that a tripeptide, Thr289-Lys-Pro291, of the second constant domain of human immunoglobulin G (peptide 286-292) reproduced the inhibitory effect of a total hydrolysate. Indeed the beta-glucuronidase release from IgE-anti-IgE-stimulated rat and human macrophages decreased and its intracellular level did not rise after a prior incubation of the cells with Thr-Lys-Pro (500 nmol/ml). Moreover, the cell migration as well as the superoxide anion O2 generation were 50-80% reduced by the tripeptide. These results suggest that a single peptide set may be responsible for the decrease of the macrophage functions at the early stage of the parasite infection in the mammalian host. The pharmacologic properties of this tripeptide are under investigation.