Histological and immunohistochemical detection of different Helicobacter species in the gastric mucosa of cats

Detailed histopathological evaluation of the gastric mucosa of Helicobacter -infected cats is complicated by the difficulty of recognizing Helicobacter organisms on hematoxylin and eosin (HE)-stained sections and the ability o f multiple Helicobacter species to infect cats. In this study, the presence and localization of different species of Helicobacter in the stomachs of c ats was investigated using silver staining and immunohistochemistry. Five g roups containing 5 cats each were established (group 1: urease negative and Helicobacter free; groups 2, 3, 4, and 5: urease positive and infected wit h Helicobacter heilmannii, unclassified Helicobacter spp., Helicobacter fel is, and Helicobacter pylori, respectively). Gastric samples were evaluated by HE and silver staining and by immunohistochemistry with 3 different anti -Helicobacter primary antibodies. Helicobacter were detected by Steiner sta in in all infected cats at the mucosal surface, in the lumen of gastric gla nds, and in the cytoplasm of parietal cells. In silver-stained sections, H. pylori was easily differentiated from H. felis, H. heilmannii, and unclass ified Helicobacter spp., which were larger and more tightly coiled. No orga nisms were seen in uninfected cats. Helicobacter antigen paralleled the dis tribution of organisms observed in Steiner-stained sections for 2 of the 3 primary antibodies tested. The antisera were not able to discriminate betwe en the different Helicobacter species examined. A small amount of Helicobac ter antigen was present in the lamina propria of 3 H. pylori-, 3 H. felis-, and 1 H. heilmannii-infected cat. Minimal mononuclear inflammation was pre sent in uninfected cats and in those infected with unclassified Helicobacte r spp. and H. heilmannii cats. In H. fells-infected cats, lymphoid follicul ar hyperplasia with mild pangastric mononuclear inflammation and eosinophil ic infiltrates were present. The H. pylori-infected cats had severe lymphoi d follicular hyperplasia and mild to moderate mononuclear inflammation acco mpanied by the presence of neutrophils and eosinophils. These findings indi cate that Steiner staining and immunohistochemistry are useful for detectin g Helicobacter infections, particularly when different Helicobacter species can be present. Monoclonal antibodies specific for the different Helicobac ter species could be important diagnostic aids. There appear to be differen ces in the severity of gastritis in cats infected with different Helicobact er species.