Fig. 4. Representative light micrographs of gill sections from killifish that demonstrate the localization of COX2 protein. Gill sections were incubated with antibody 160126 (A,C), antibody 160126 and antigen (B), or antibody 5 (D). Peroxidase substrates used to label antibodies were brown (160126=COX2) and blue (Na⁺/K⁺-ATPase). No immunolabeling was observed in negative control sections that were incubated with antibody 160126 and excess antigen followed by multilink (anti-mouse, rabbit and donkey) secondary antibodies (B); however, strong immunolabeling occurred in a population of epithelial cells with antibody 160126 (A). In serial sections, immunolabeling with antibody 160126 was always in cells with Na⁺/K⁺-ATPase (C,D); arrows mark cells that stained with both antibodies. Lamellae are numbered for clarity. Scale bars, 50 µm.