Figure 1.

Four stages of bovine tuberculoid granulomas. Stage I granulomas contain infiltrates of epithelioid macrophages, lymphocytes and multinucleated giant cells. Stage II granulomas resemble stage I but have variable degrees of central necrosis. Stage III granulomas are composed of a central necrotic core, surrounded by a zone of macrophages admixed with lymphocytes and multinucleated giant cells. Portions of the necrotic core may be mineralized. Encapsulation of the necrotic core and cellular infiltrate by a complete fibrous capsule distinguishes this stage from earlier stages. Stage IV granulomas represent a coalescence of stage III granulomas with multiple necrotic and partially mineralized centers, surrounded and subdivided by thick fibrous bands.