Heterogeneous Specificities of Nickel Presentation to Nickel Specific CD4 T Cells

Sensitization to nickel (Ni2+) is the most common T cell mediated type IV hypersensitivity, although the mechanisms by which Ni2+ alters antigen presentation are not understood. To study how the TCR then recognizes Ni2+ bound to the MHC molecule, we performed paired single cell RNA sequencing of PBMCs from two highly Ni2+ sensitized subjects to orthopedic implants and characterized three Ni2+ specific CD4+ T cell clones. One Ni2+ specific CD4+ T cell is highly restricted to HLA-DR7. But the other highly cross-reactive CD4+ T cell clones was restricted to multiple HLA alleles, including HLA-DR, HLA-DP, and HLA-DQ expressing antigen presenting cells. We identified a HLA-DQ8 restricted Ni2+ dependent mimotope reactive to the highly cross-reactive T cell clone. This mimotope appeared to present Ni2+ ions with the Glu at P2 position, involving βH81. The mutational studies of HLA-DP2 molecule showed that the same T cell recognized the Ni2+ ion bound to a completely different location in the P4-P7 pocket. Ni2+ ion was also can be presented efficiently by HLA-DR53 to the same T cells. mutational and structural study of HLA-DR53 molecules suggested that HLA-DR53 presented Ni2+ in the P4-P7 pocket. This is the first evidence showing that a metal ion can be presented by HLA using the different sites. The metal binding sites are HLA and peptide dependent. The heterogeneous specificities of Ni2+ specific TCRs are determined by different alleles of HLAs together with particular self-peptides. Sensitization to nickel (Ni2+) is the most common T cell mediated type IV hypersensitivity, although the mechanisms by which Ni2+ alters antigen presentation are not understood. To study how the TCR then recognizes Ni2+ bound to the MHC molecule, we performed paired single cell RNA sequencing of PBMCs from two highly Ni2+ sensitized subjects to orthopedic implants and characterized three Ni2+ specific CD4+ T cell clones. One Ni2+ specific CD4+ T cell is highly restricted to HLA-DR7. But the other highly cross-reactive CD4+ T cell clones was restricted to multiple HLA alleles, including HLA-DR, HLA-DP, and HLA-DQ expressing antigen presenting cells. We identified a HLA-DQ8 restricted Ni2+ dependent mimotope reactive to the highly cross-reactive T cell clone. This mimotope appeared to present Ni2+ ions with the Glu at P2 position, involving βH81. The mutational studies of HLA-DP2 molecule showed that the same T cell recognized the Ni2+ ion bound to a completely different location in the P4-P7 pocket. Ni2+ ion was also can be presented efficiently by HLA-DR53 to the same T cells. mutational and structural study of HLA-DR53 molecules suggested that HLA-DR53 presented Ni2+ in the P4-P7 pocket. This is the first evidence showing that a metal ion can be presented by HLA using the different sites. The metal binding sites are HLA and peptide dependent. The heterogeneous specificities of Ni2+ specific TCRs are determined by different alleles of HLAs together with particular self-peptides.