Fig. 2

a, b Early granuloma formation, surrounding small blood vessels marked by asterics (*). a Immunohistochemical staining for CD3⁺ T-lymphocytes (brown staining). Serial sections (not depicted here) disclose an identical distribution of predominating CD4⁺ T-helper cells. b Serial section of the same vessel as shown in (a) at a higher magnification with CD68⁺ macrophages gathering at subintimal and adventitial spaces. c, d Full-blown granulomas. c Haematoxylin-Eosin staining displays a dense plasmocytic infiltrate at the left upper corner. The right lower corner encompasses a tuberculoid granuloma dominated by epithelioid cells and multinucleated Langhans-type giant cells. d A large granulomatous complex is embedded into sharply confined neuropil, highlighted by immunohistochemical staining for glial fibrillary acidic protein (brown colour). e-h Miscellaneous aspects of granuloma histiocytes. e Enzyme-histochemical staining for tartrate-resistant acid phosphatase (red colour) discloses a high activity of this particular isoenzyme of acid phosphatase, typically upregulated in mature macrophages involved in chronic lysosomal lipid degradation. f Periodic acid Schiff staining (PAS, red colour). A centrally placed foam cell contains translucent lipid vacuoles and few PAS⁺ ceroid-like granules. Additional smaller-sized macrophages are storing ceroid-like granules exclusively, whithout visible lipid vauoles. At the periphery of the graph, there are several gemistocytic astrocytes with large swollen PAS-negative cytoplasm. g Clustering PAS⁺ ceroid-storing macrophages fuse to multinucleated giant cells, partially of Touton-type (Tt). h On Giemsa-staining, some giant macrophages adopt a phenotype of sea-blue histiocytes