FIG. 4.

Phenotypic characterization of the primary duck IBDE cultures. At various days of culture, coverslips of primary IBDE cultures were fixed in 100% methanol for 5 min and processed for immunoperoxidase staining using CAM 5.2. After reactivity with the substrate, DAB, the cells were counterstained with Mayer's hematoxylin. Cytokeratin staining was detected as dark brown precipitates in the cytoplasm of cells at 2 (A and B) and 5 (C) days of culture. (A and B) Early in culture, IBDE cells grew as cell clusters which often contained a lumen (arrow). (C) By day 5 of culture, duct-like structures (arrow) were observed in IBDE colonies.