Enkephalin-like immunoreactivity in human skin is found selectively in a fraction of CD68-positive dermal cells: increase in enkephalin-positive cells in lesional psoriasis.

Opioid peptides are synthesized in neurons, endocrine cells, monocytes/macrophages and B and T lymphocytes. They interact with opioid receptors located on immune cells and nociceptive nerve terminals. Because opioid peptides might be of importance in inflammatory skin diseases, for example psoriasis, sections of skin from psoriatic patients were immunohistochemically stained with antisera against methionine and leucine enkephalin, CD68 (KP1, PG-M1), calprotectin (M747), M130 (Ber-MAC3), CD1a and CD3. Enkephalin-like activity was detected selectively in dermal CD68-positive macrophages/monocytes. The activity showed no association with the activation markers M747 and Ber-MAC3. There was a statistically significant increase in enkephalin-positive cells in involved psoriatic skin compared with uninvolved and normal skin. These results were confirmed by radioimmunoassay which showed elevated levels in extracts from involved psoriatic skin compared with uninvolved skin (81%) and normal skin (204%). Furthermore, preproenkephalin mRNA of an expected size was detected in involved psoriatic skin. If the increased levels of enkephalins present in monocytes/macrophages in psoriatic skin lesions reach the threshold for biological activity, they may play a role in the regulation of the inflammatory processes seen in this skin disease.