PEPTIDES BIND TO EOSINOPHILS IN THE RAT STOMACH

Background: An immunological role for eosinophils has been well establ ished. However, roles for eosinophils in the physiological functions o f the organs they populate are little explored. Methods: Fixed, frozen , then vibratomed sections of rat stomach were exposed to biotinylated 1-17 gastrin (bG17), biotinylated gastrin-releasing peptide (bGRP), b iotinylated neuromedin C (bNC), biotinylated vasoactive intestinal pep tide (bVIP), and biotinylated substance P (bSP). Binding sites were id entified using an avidin-biotin-glucose oxidase complex and tetranitro blue tetrazolium staining. Results: bG17, bGRP, and bNC all bound to c ells in the lamina propria and to a lesser extent in the submucosa. Ne ither bVIP nor bSP bound to cells in these sections. Stained cells wer e identified as eosinophils in the light microscope on the basis of th eir distribution and staining properties using the Luna stain for eosi nophils and in the transmission electron microscope (TEM) on the basis of a light/TEM matching process. Plastic sections viewed in the light microscope showed that stain was localized to a granular component in the cytoplasm of the eosinophils. No other cell type, specifically ne ither mast cells nor plasma cells, stained. G17 competed for the bG17 binding site better than did NC. A competition study in which polyglut amic acid failed to compete with bG17 for the binding site, and the ob servation that bG17, bGRP, and bNC did not bind to other positively ch arged sites (e.g., collagen, red blood corpuscles), demonstrated that binding was not due to nonspecific electrostatic interactions alone. B inding of bG17 to a CCKB/gastrin-type receptor was ruled out when spec ific receptor antagonists failed to block binding. Conclusions: The pa rticulate nature of the binding site suggests a secretory substance. I f so, eosinophils might use that substance to destroy, neutralize, or control the activity of peptide hormones bound to it in the extracellu lar space. (C) 1998 Wiley-Liss, Inc.