Emphasis on peanut lectin as a marker for granular cells.

Peanut lectin (PNL) binding to a total of 13 granular cell tumours was examined by means of the peroxidase antiperoxidase technique. The tumours included six tumourettes of the neurohypophysis, one malignant granular cell tumour of the brain, and six peripheral tumours of distinct locations. Every tumour studied showed intracytoplasmic fine granular PNL binding; after pretreatment with neuraminidase, the weakly positive reaction was enhanced to a great extent. In all tumours simultaneous examination for the detection of lysozyme and glial fibrillary acidic protein (GFAP) was also carried out. Lysozyme was negative in all cases, whereas GFAP expression could be demonstrated at the periphery of the malignant granular cell tumour of the brain. The data presented clearly demonstrate that PNL can be used as a histochemical marker for granular cells regardless of their location. The fact that the presence of lysozyme could not be proved does not support the view of a histiocytic origin for granular cells, whereas the expression of GFAP in some immature granular cells of the brain tumour examined is considered to be an argument in favor of its glial origin.