Fibronectin synthesis in the harderian gland of the chicken.

Immunoelectron microscopic staining with a monoclonal antibody against fibronectin demonstrated the presence of this extracellular matrix glycoprotein in the avian Harderian gland. Fibronectin was detected as a component of the electron-dense material, which has been observed both between the epithelial cells lining the ducts of the gland and between the lymphoid cells within the subepithelial lymphoid tissue. Additionally, intracellular fibronectin was detected in the rough endoplasmic reticulum, Golgi complex, and secretory vacuoles in the cytoplasm of a cell, showing the ultrastructural features of a myofibroblast. These findings indicate that the Harderian gland myofibroblasts secrete and release fibronectin into the extracellular matrix.