Subcellular localization of transforming growth factor-α in human eosinophil granulocytes

Eosinophils are involved in the inflammatory response seen in allergy and helminthic infestations. Eosinophils synthesize transforming growth factor- α (TGF-α), which may play a role in the development of the characteristic fibrosis seen in longstanding high eosinophilia. Using immunoelectron microscopic techniques, eosinophils from peripheral blood of healthy individuals and from one patient with high eosinophilia showed presence of TGF-α in matrix of the specific crystalloid-containing granules. In cryosections, TGF-α was also visualized in a vesicular compartment of the cytoplasm. In double-labeling experiments, the TGF-α of this latter compartment did not colocalize with CD63, a marker for lysosomes, nor with albumin of secretory vesicles. In extracts from eosinophils, obtained from healthy donors, immunoreactive TGF-α could be detected by enzyme-linked immunosorbent assay-technique. In addition, sera from two patients with high eosinophilia showed TGF-α concentrations of 1.5 ng/mL and 164 pg/mL, respectively, whereas TGF-α could not be detected in serum from healthy controls. In conclusion, TGF-α is present in the specific granules, and in an additional vesicular compartment of the cytoplasm of eosinophils.