A cytochemical marker for epidermal differentiation, Langerhans cells, skin resident macrophages and mitochondria.

Incubation of unfixed and unfrozen slices of skin in diaminobenzidine allows visualization of peroxidatic activity in the perinuclear envelope and endoplasmic reticulum of normal human Langerhans cells. A similar peroxidatic activity is observed in supra-basal keratinocytes undergoing orthokeratotic differentiation. Basal keratinocytes and melanocytes are always negative. This enzyme is absent in mucous and parakeratotic (psoriatic) differentiation. A peroxidatic activity was also found in the endoplasmic reticulum of normal resident skin macrophages. Mitochondria are also strongly stained by this technique and it was shown that the number of epidermal mitochondria is greatly increased in psoriatic lesions.