Histopathology and antigen expression in selected tissues from infected gulls. By immunohistochemistry, influenza virus antigen expression is visible as a red staining. (A, B): Bronchus of 2 dpi infected gull without histologic lesions (A), and scarce bronchial epithelial cells showing positivity on the immuno-stained consecutive section (arrows) (B). (C, D): Pancreas of 4 dpi infected gull showing multiple foci of lytic necrosis (C), and intense positivity associate to necrotic foci in the immune-stained consecutive section. (E, F): Cerebral cortex showing necrotic neurons, and satellitosis (E), and intense positivity in neurons and associated glial cells in the immune-stained consecutive section. HE stain (A, C, E) and immunoperoxidase counterstained with hematoxylin (B, D, F). All the pictures are at 10x power fields.