Pathogenesis of orally induced flare-up reactions at old patch sites in nickel allergy.

The flare-up reaction of old patch test sites following oral intake of antigen have been shown to be site and antigen specific reactions. Using enzyme and immunohistochemistry, the morphology of 6- to 8-week-old patch test sites, before and after oral challenge with nickel, was investigated. Before oral challenge, small scattered perivascular cell infiltrates consisting of macrophages, mast cells, T-lymphocytes, and OKT6+ dendritic cells were found in old patch test sites. In early and strong flare-up reactions combined with systemic toxicoderma-like reactions, polymorphonuclear leukocytes and lysed granular fragments from these cells were prominent. In slower flare-up reactions with little systemic involvement, T-lymphocytes predominated. We conclude that cells, probably macrophages, which are able to secrete inflammatory mediators promoting chemotaxis for polymorphonuclear leukocytes and/or T-lymphocyte proliferation, may play an important role in initiation of the flare-up reaction.