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).




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