The Langerhans cells in healed patch tests reactions, before and after oral administration of nickel.

Langerhans cells (LC) were studied at the light and electron microscopic levels in normal skin and in positive patch test areas after long-term healing before and after the flare-up reaction induced by oral administration of nickel. A number of reactive changes indicating increased cell activity, similar to those found in positive patch tests 72 hours after allergen application, were registered in the test areas. Thus, strong reactive changes persist in the LC system after a fulminant contact allergic dermatitis, even beyond clinical healing. Some cellular reactions, especially pronounced after oral nickel provocation, indicate that much of the LC activity takes place on a superficial level of the epidermis. Oral nickel administration induced, among other things, an intense formation of lipid-like inclusions in the LC, formerly observed only in contact allergic reaction to nickel. Goniometric analysis of the LC cytomembrane showed that the concept "spotty damage" is probably erroneous and that the LC are not targets of destruction in contact allergy. Keratinocytes adjacent to LC exhibited membrane and cytoplasmic changes indicative of interaction between these two cell types. Combined fluorescence and electron microscopic analyses of contact allergic dermatitis using long series of sections have disclosed a variety of reactive changes in, and an increased activity of, the Langerhans cell system (1, 2). In the present study Langerhans cells (LC) have been scrutinized for reactive changes after long-term healing of challenged epidermis and after oral nickel provocation causing a flare-up reaction of healed patch test areas.