Unique and common TCR repertoire features of Ni2+‐, Co2+‐, and Pd2+‐specific human CD154 + CD4+ T cells. Issue 1 (6th September 2022) - Riedel, Franziska
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 NiSO4, CoCl2, and PdCl2 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 non‐allergic 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. Abstract : Ni 2+ ‐, Co 2+ ‐, and Pd 2+ ‐specific CD4+ T cells can be detected by a short‐term CD154 upregulation assay. Overrepresentation of certain individual gene segments or a CDR3 histidine represent distinct TCR repertoire characteristics that underlie metal ion binding and cross‐reactivity. Frequent metal‐specific T cell activation in allergic and non‐allergic individuals challenges blood‐based allergy detection in vitro.Abbreviation: APC, antigen‐presenting cells; CDR3, complementarity determining region 3; Co, cobalt; HTS, high‐throughput sequencing; MHC, major histocompatibility complex; Ni, nickel; PBMC, peripheral blood mononuclear cells; Pd, palladium; TCR, T cell receptor; TRAV, TCR α‐chain V‐segment; TRBV, TCR β‐chain V‐segment