Immunohistochemical staining of swine influenza virus antigens in lung tissue from a pig. Immunohistochemical detection of swine influenza virus (SIV) antigens using polyclonal rabbit anti-swine influenza antibody against A/swine/Denmark/4744/1981 (H1N1) and counterstaining with hematoxylin. A: Lung section from SIV H1N1 infected pig euthanized PID 4. SIV antigen positive (brown) epithelial cells (arrow) are seen in a bronchus. SIV antigen positive cells are also seen in the exudates in lumen of the bronchus (arrowhead). Original magnification x10. B: Lung section from SIV H1N2 infected pig euthanized PID 4. SIV antigen positive (brown) epithelial cells are seen in a bronchiole (b) and in alveolar septa (arrows). (Original magnification x10).