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 is 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 (Ni), cobalt (Co), and chromium (Cr). Methods: Twenty‐one metal allergic patients with a positive patch test to Ni (n=16), Co (n=8), and Cr (n=3) and 13 controls were included. All were tested by a flow cytometric LPT. Results: Metal‐reactive cells were identified as T helper (Th) cells with high expression of the memory marker CD45RO. Skin‐homing (cutaneous lymphocyte‐associated antigen positive [CLA+]) Ni‐reactive memory Th (Thmemhi) cells identified individuals with a positive patch test for Ni with 100% sensitivity (95% confidence interval [CI] 81%‐100%) and 92% specificity (95% CI 67%‐100%). Moreover, Co‐specific Thmemhi cells expressing CCR6 identified patients with a positive patch test for Co with 63% sensitivity (95% CI 31%‐86%) and 100% specificity (95% CI 77%‐100%). In Cr allergic individuals, Cr‐reactive Thmemhi cells tended to increased CLA and CCR6 expression. Conclusion: Metal‐reactive Th cells with high expression of CD45RO and coexpression of CLA and CCR6 improved the LPT, making it an attractive supplement to the patch test. [ABSTRACT FROM AUTHOR]