Unique and common TCR repertoire features of Ni²⁺‐, Co²⁺‐, and Pd²⁺‐specific human CD154 + CD4+ T cells

Abstract

Background: Apart from Ni 2+ , Co 2+ , and Pd 2+ ions commonly trigger T cell-mediated allergic contact dermatitis. However, in vitro frequencies of metal-specific T cells and the mechanisms of antigen recognition remain unclear.Methods: Here, we utilized a CD154 upregulation assay to quantify Ni 2+ -, Co 2+ -, and Pd 2+ -specific CD4+ T cells in peripheral blood mononuclear cells (PBMC). Involved αβ T cell receptor (TCR) repertoires were analyzed by high-throughput sequencing.Results: Peripheral blood mononuclear cells incubation with NiSO 4 , CoCl 2 , and PdCl 2 increased frequencies of CD154 + CD4+ memory T cells that peaked at ~400 μM.Activation was TCR-mediated as shown by the metal-specific restimulation of T cell clones. Most abundant were Pd 2+ -specific T cells (mean 3.5%, n = 19), followed by Co 2+ -and Ni 2+ -specific cells (0.6%, n = 18 and 0.3%, n = 20) in both allergic and nonallergic individuals. A strong overrepresentation of the gene segment TRAV9-2 was unique for Ni 2+ -specific TCR (28% of TCR) while Co 2+ and Pd 2+ -specific TCR favorably expressed TRAV2 (8%) and the TRBV4 gene segment family (21%), respectively. As a second, independent mechanism of metal ion recognition, all analyzed metal-specific TCR showed a common overrepresentation of a histidine in the complementarity determining region 3 (CDR3; 15% of α-chains, 34% of β-chains). The positions of the CDR3 histidine among metal-specific TCR mirrored those in random repertoires and were conserved among cross-reactive clonotypes.Conclusions: Induced CD154 expression allows a fast and comprehensive detection of Ni 2+ -, Co 2+ -, and Pd 2+ -specific CD4+ T cells. Distinct TCR repertoire features underlie the frequent activation and cross-reactivity of human metal-specific T cells.

Less efficient skin penetration of the metal allergen Pd2+ compared to Ni2+ and Co2+ from patch test preparations

“…Using the novel activation‐induced marker assay, our previous research has shown that T cell activation is highly concentration‐dependent, peaking at about 400 μM for all three metal ions 3 . Notably, at this concentration, Pd 2+ activates a large fraction of the T cell pool.…”

“…Of the three metals analysed, Pd 2+ had the lowest concentration in the remaining skin, regardless of whether PTPs or a metal salt solution were applied. This suggests that even though Pd 2+ has the ability to activate a large portion of the T cell pool, only a very small fraction of Pd 2+ ‐specific T cells become engaged at the low Pd 2+ concentrations in the skin 3 . This may explain why palladium allergies are less common than nickel allergies, in addition to a generally lower dermal exposure.…”

“…Using the novel activation-induced marker assay, our previous research has shown that T cell activation is highly concentrationdependent, peaking at about 400 μM for all three metal ions. 3 Notably, at this concentration, Pd 2+ activates a large fraction of the T cell pool. To ensure an accurate allergy diagnosis, PTPs must release metals to yield concentrations in the viable epidermis comparable to those that elicit ACD to re-activate tissue-resident memory T cells.…”

“…We recently quantified metal‐specific CD4+ T cells by an in vitro activation‐induced marker assay and identified the underlying interactions with conserved T cell receptor residues 2,3 . The particularly high frequencies we observed for Ni 2+ and Co 2+ were further exceeded by those of Pd 2+ ‐specific T cells at optimal concentrations (ca.…”