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 (Thmemhi ) cells identified individuals with a positive patch test for nickel with 100 % sensitivity [81%,100%] and 92% specificity [67%,100%]. Moreover, cobalt-specific Thmemhi 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 Thmemhi 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.