Mast Cells, Neutrophils, and Eosinophils in Prurigo Nodularis

Background and Design.—Prurigo nodularis is a disease of unknown cause. To characterize the involvement of mast cells, neutrophils, and eosinophils in lesional tissue, we analyzed seven skin biopsy specimens by an indirect immunofluorescence technique for localization of mast cell tryptase, neutrophil elastase, and eosinophil granule major basic protein, eosinophil cationic protein, and eosinophilderived neurotoxin. Results.—Mast cells were detected in all of the specimens, with prominent numbers of mast cells in three specimens; there was minimal or no extracellular deposition of tryptase in any of the tissues. Neutrophil infiltration was observed in all specimens, but few cells were observed in four; extracellular elastase was minimal or absent in all but one specimen in which prominent dermal elastase deposition was found. Scanty eosinophil infiltration was present in all specimens; however, extracellular deposition of the eosinophil granule proteins including major basic protein, eosinophil-derived neurotoxin, and eosinophil cationic protein was present in all but one specimen and striking deposition of at least one eosinophil granule protein was present in six of the seven specimens. Conclusions.—These studies suggest that mast cell numbers are increased in prurigo nodularis and that eosinophil degranulation as evidenced by striking extracellular deposition of granule proteins is prominent in lesions. In contrast, extracellular deposition of mast cell and neutrophil proteins is absent. The distinctive proteins of the eosinophil granule have potent effects on tissues; the toxicity of these proteins and their deposition in lesional tissue suggest a pathogenic role for the eosinophil in prurigo nodularis.