IgE-positive cells in human intestinal mucosa are mainly mast cells.

Nine biopsy specimens from the jejunum of patients with a clinical history of food allergy and 10 from the rectal mucosa of patients with presumed 'allergic proctitis' were fixed in cold ethanol and further processed for paraffin embedding. Serial tissue sections were stained for IgE by direct (polyclonal antibody) and indirect (monoclonal antibody) immunofluorescence methods. Adjacent sections were subjected to conventional mast cell staining (astra blue). In all mucosal specimens from the jejunum and in 8 rectal ones, numerous cells were found to be positive both for astra blue by transmission microscopy and for IgE by fluorescence microscopy of the same section. With the monoclonal antibody all astra-blue-positive cells were IgE-positive; however, this was not always the case with the polyclonal reagent, probably because the fluorescence was weaker with the direct technique. Detection of IgE-positive mucosal mast cells may turn out to be of diagnostic interest in patients with adverse reactions to food.