Identification of FIPV antigens in inflamed omentum from a cat with experimentally-induced FIP. A OCT embedded and cryostat sectioned omentum from cat with experimentally-induced effusive FIP stained by DIFA using cat globulin from FIPV infected cats. Intense fluorescence was seen in most monocyte/macrophage appearing cells within a pyogranuloma, ×400, Evan’s blue counterstain. B A formalin-fixed and paraffin embedded section from the identical diseased region of omentum as shown in A. The section was reacted with mouse monoclonal antibody to the N protein of FIPV followed by goat anti-mouse Ig conjugated to horse radish peroxidase, ×40, hematoxylin counterstain. C High power view of region outlined in B. Staining for FIPV N protein was concentrated in cytoplasm of large multi-vacuolated macrophages with faint staining in smaller monocyte/macrophage appearing cells, ×400, hematoxylin counterstain.