Alpha-endorphin-like immunoreactivity in plasma cells of the canine colonic mucosa.

During immunocytochemical investigations on the presence of opioid peptides in gastrointestinal endocrine cells it was found that a subpopulation of plasma cells located in the lamina propria of the canine colonic mucosa showed immunoreactivities for alpha-endorphin. All immunohistochemical specificity controls proved the specificity of the reaction. Circumstantial evidence suggest, however, that no authentic alpha-endorphin is present within this cell type. Possibly sequence homologies between alpha-endorphin and the amino acid composition of a certain immunoglobulin are responsible for the immunocytochemically specific alpha-endorphin-like immunoreactivity of plasma cells.