Fixation and staining of granules in mucosal mast cells and intraepithelial lymphocytes in the rat jejunum, with special reference to the relationship between the acid glycosaminoglycans in the two cell types.

Various fixation and staining procedures have been examined in order to obtain optimal numbers and acceptable morphology of the mucosal mast cells and granular intraepithelial cells in the rat jejunum. For subsequent staining with Alcian Blue, the best fixation of the jejunum was obtained with a methanol-formaldehyde-acetic acid mixture. Specific staining of the granules of these cells has been obtained using Alcian Blue at pH 5.8, at which hydrogen ion concentration more cells stain than in the usual very acid conditions. Specificity is achieved by the use of magnesium chloride concentrations above the critical electrolyte concentrations for staining of protein and nucleic acid by Alcian Blue, and by the use of Safranin O as a competitive counterstain. The critical electrolyte concentration technique has also been applied to a comparative study of the glycosaminoglycan in the two cell types. Evidence is presented that the glycosaminoglycan in the granular intraepithelial cell has either a lower degree of sulphation or a lower molecular weight or both than the material in mucosal mast cells. This finding may support the possibility that the granular intraepithelial lymphocyte is a precursor of the mucosal mast cell.