The role of somatostatin in schistosomiasis: a basis for immunomodulation in host-parasite interactions?

This review explores the possible modulatory role of the neuropeptide somat ostatin in the outcome of Schistosoma-caused morbidity in man. Somatostatin could play an important role in Schistosoma mansoni-man interactions via i ts influence on intersystem signalling; therapeutically, via its direct eff ect on Schistosoma-caused morbidity (fibrosis, granuloma size, portal hyper tension, variceal bleeding); and via immunomodulation of Schistosoma-induce d inflammatory responses in the liver and intestines. In schistosomiasis-en demic regions two interesting patterns of infection emerge. First, the inte nsity of infection is higher in children than in adults; secondly, at any g iven time, only a fraction of Schistosoma-infected individuals develop Symm er's pipe-stem fibrosis. These morbidity patterns cannot be explained on th e basis of acquired immunity alone. Somatostatin has an inhibitory effect o n hormone, immune and physiological body functions like growth hormone secr etion, Interferon (IFN) gamma production, collagen I and III formation and hepatic stellate cell activation. Levels of somatostatin secreted endogenou sly by man upon the onset of Schistosoma infection may be one factor regula ting the activity of the above, and thereby fibrosis in the host. The neuro peptide hormone somatostatin may determine pre-disposition to Schistosoma-c aused morbidity.