Small intestinal chromaffin cells and carcinoid tumours: a study with silver stains, formalin-induced fluorescence and monoclonal antibodies to serotonin.

The enterochromaffin cells of the human small intestinal mucosa were stained immunocytochemically with monoclonal antibodies against serotonin. The staining results were compared with those obtained with other methods for identifying serotonin-containing endocrine cells such as the argentaffin reaction, formalin-induced fluorescence and the argyrophil reaction of Grimelius. The different techniques gave similar, but not identical, results. The serotonin-immunoreactive cells outnumbered the argentaffin cells by 7%. Almost all (99%) serotonin-immunoreactive cells showed formalin-induced fluorescence but only a small population (5%) were fluorescent. In a subsequent study, these techniques were applied to 14 small intestinal carcinoids. It was shown that formalin-induced fluorescence and the argentaffin reaction were positive in 14 and 13 tumours, respectively, while the monoclonal serotonin antibodies failed to stain seven of the tumours. It is concluded that formalin-induced fluorescence and the argentaffin reaction are more useful techniques than serotonin immunocytochemistry for defining these tumours in routine formalin-fixed surgical specimens.