(A) Immunohistochemistry for M. bovis Vsp antigen in necrotic lesion; the centre of a caseonecrotic pulmonary lesions (N) is surrounded by mostly degenerate neutrophilic granulocytes and macrophages. Immunohistochemical labelling of extracellular accumulations of M. bovis antigens with mAb 1A1. Calf No. 5. ABC method. Bar = 46 μm; (B) Immunolabelling of M. bovis Vsp antigens with mAb 1A1 within the lumen of a bronchiole containing exudate. Calf No. 3. ABC method. Frozen section. Bar = 46 μm; (C) Immunolabelling of M. bovis variable antigen pMB67 with mAb I2. Sequential frozen section of the same location as in (B); (D) Numerous IgG1-positive plasma cells in the lamina propria of bronchial mucosa. Calf No. 8. ABC method. Bar = 92 μm; (E) Lower numbers of IgG2-positive plasma cells in the lamina propria of bronchial mucosa in a sequential paraffin section of the same location as in (D); (F) Immunohistochemistry for MHC class II in necrotic and perinecrotic lung area; caseonecrotic lung lesion with MHC class II immunoreactivity within the necrotic area (N) and within the perinecrotic region. The majority of macrophages surrounding the necrosis (asterisk) is negative for MHC class II. Calf No. 5. ABC method. Bar = 92 μm.