Memory T helper cells identify patients with nickel, cobalt and chromium metal allergy.

Background Patch testing is the gold standard for identifying culprit allergens in allergic contact dermatitis; however, it's laborious and positive reactions are difficult to quantitate. Development of complementary in vitro tests is, therefore, of great importance. Objectives This study aimed to improve the in vitro lymphocyte proliferation test (LPT) to detect allergic responses to nickel, cobalt and chromium. Methods Twenty-one metal-allergic patients with a positive patch test to nickel (16), cobalt (8) and chromium (3) and thirteen controls were included. All were tested by a flow cytometric LPT. Results Metal-reactive cells were identified as Th cells with high expression of the memory marker CD45RO. Skin-homing (CLA+ ) nickel-reactive memory Th (Thmem hi ) cells identified individuals with a positive patch test for nickel with 100 % sensitivity [81%,100%] and 92% specificity [67%,100%]. Moreover, cobalt-specific Thmem hi cells expressing CCR6 identified patients with a positive patch test for cobalt with 63% sensitivity [31%,86%] and 100% specificity [77%,100%]. In chromium allergic individuals, Chromium-reactive Thmem hi cells tended to increased CLA and CCR6 expression. Conclusion Metal-reactive Th cells with high expression CD45RO and co-expression of CLA and CCR6 improved the LPT, making it an attractive supplement to the patch test. This article is protected by copyright. All rights reserved.