Actinobacillosis - microscopy image

This is the typical microscopic appearance of an actinobacillosis granuloma. It consists in an eosinophilic central area, called sulphur granule, (formed by the pathogen and by immune complexes synthesized as a response to the infection) enclosed in a neutrophilic cellular atmosphere. Peripherally, several mononuclear cellular elements can be found, namely macrophages, plasmocytes and lymphocytes (H&E, 100x). This inflammatory response causes a fibroblastic reaction that progressively isolates the granuloma from the surrounding tissue. On the right, radiated structures arranged in palisade, called clubs, form the periphery of the sulphur granule (H&E, 400X).