Four-stage categorization of the pulmonary lesions in infected guinea pigsa

Lesion stageExtent of lesions (% GF)bMacrophage typesLymphocyte organizationGranulocyte localizationStage sequelae
1Single (11: 0.1, 0.1)Histiocytes, epithelioidFew, scatteredProminent, scatteredAlveolitis
2Multifocal (21: 4.9, 19.1; 31: 7.1, 16.7)Histiocytes, epithelioidFew, scattered, with small aggregates at marginProminent, scattered around and in the coreKaryorrhectic debris, fibrin deposition in the core and surrounding mantle; fibroplasia; granulomatous lymphadenitis
3Multifocal (71: 45.7, 51.8)Epithelioid, foamyScattered plus a prominent halo surrounding macrophagesProminent, scattered around and in the core“Classical” granuloma; necrosis and fibroplasia; granulomatous lymphadenitis
4Coalescing (93: 42.9, 52.1; 99: 56.1)Epithelioid, foamyScattered aggregates or individual cellsProminent, scattered throughout macrophage focus, around and in the core, and amid airway debrisNecrosis, mineralization, marked fibroplasia; multinucleated giant cells; airway epithelium erosion and purulent airway exudate; granulomatous lymphadenitis
  • a Hematoxylin-and-eosin-stained lung sections were examined by standard light microscopy, and several parameters of the lesions were characterized. The parameters included morphometric assessment of the extent of the pulmonary involvement (granuloma fraction), the predominant macrophage types present, and the overall arrangement of lymphocytes and neutrophils in the lesions. Several sequelae of each stage were also noted in the infected lungs. Each lesion in a section was characterized individually, and stages were defined which encompassed the different types of lesions that were present.

  • b Bold values represent days postinfection. Values following these are percent granuloma fractions (GF) from individual animals.