Usefulness of lymphocyte transformation test and in vitro cytokine release in differentiating between independent and cross‐reacting nickel/palladium allergy

Background Often concomitant patch test (PT) reactivity to palladium (Pd) and nickel (Ni) is found. Objectives To determine whether lymphocyte transformation test (LTT) could be useful in discrimination between cross‐reacting or distinct PT results, and to compare the results with in vitro cytokine production upon Pd or Ni stimulation. Materials and Methods The study population consisted of two groups: 13 individuals with Pd PT reactions (10 with concomitant Ni PT reaction, 3 individuals with only Pd PT reactivity) and 10 Ni/Pd PT negative individuals. LTT and assessment of cytokine release (interferon‐gamma, interleukin‐5 [IL‐5], IL‐8, IL‐17A, tumor necrosis factor alpha) by cytometric bead assay were performed. Results All 10 patients with positive PT to Ni and Pd showed positive LTT to Ni (P < .05) as compared with the 10 Pd/Ni PT negative patients—but had no significant LTT reaction to Pd. In all, 9 out of 10 Pd/Ni PT negative patients were also LTT negative to Ni and 10 out of 10 to Pd. In the 3 only Pd PT reactors 2 out of 3 remained LTT negative to Ni and 0 out of 3 to Pd. As a major finding, cytokine production gave clearly enhanced IL‐5 response to Ni in Ni PT positive individuals (P < .05), whereas Pd PT reactivity was not linked with such enhanced IL‐5 production in vitro to Pd. Conclusions Pd and Ni sensitization are mostly found concomitantly, and cross‐reactivity is questioned. By different LTT reactions and particularly IL‐5 production in vitro, predominant Ni sensitization becomes more evident