Light and electron microscope localization of G-17- and G-34-like immunoreactivities of human gastrinomas.

Gastrin- 17 (G-17) and gastrin-34-like immunoreactivities of human gastrinoma cells were investigated at light and electron microscope level using N-terminally directed antisera. The procedure includes (a) the 24 hr/immunoperoxidase staining of Bouin-fixed paraffin embedded tissues, (b) the immunoelectron microscopic labelling of aldehyde-fixed Epon-embedded tissues according to the immunogold technique. On light microscopy, a variable number of tumor cells stained for G-34. In contrast, G-17 immunoreactivity was very low or undetectable in the tumor material, although it was easily detected in endocrine cells of similarly processed human pyloric mucosa. On electron microscopy, most of the tumor cell granules belonging to the round compact or dense-cored type exhibited a variable labelling for G-34, whereas the vacuolar/floccular type remained unlabelled. In contrast, the labelling for G-17 occurred over most of the tumor cell granules, whether compact or floccular. Dense granules of varying size and shape, previously shown to store C-terminal gastrin immunoreactivity, were only faintly labelled by the two antisera. When compared to the labelling pattern of human pyloric G-cells, the predominance of round dense granules with G-34 and G-17 immunoreactivity in gastrinoma cells suggests an incomplete or defective post-translational processing of the precursor peptide.