Light and electron microscopy of rabbit testes infected with Treponema pallidum (Nichols strain): nature of deposited mucopolysaccharides and localisation of treponemes.

The mucopolysaccharide nature of the material deposited in rabbit testes infected with Treponema pallidum was confirmed by histochemical staining with alcian blue. Differential staining of mucopolysaccharides showed the presence of sulphated mucopolysaccharides as an almost constant feature, whereas in little more than half of the orchitic testes studied variable deposits of hyaluronic acid were seen. The treponemes were almost exclusively present in the areas rich in mucopolysaccharide. A combination staining with the Warthin-Starry method and alcian blue showed treponemes in close association with pre-existing fibrils and cells contained in these fibrils. The latter findings were confirmed by electron microscopy, and the fibroblasts to which treponemes adhered displayed the characteristics of activated cells. The close parallel between the histopathological changes observed here and their descriptions in published reports shows that our specific strain still behaves the same as the original Nichols pathogenic strain of T pallidum.