PD-1 and PD-L1 expression in peripheral CD4/CD8+ T cells is restored in the partial remission phase in type 1 diabetes.

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Partial remission (PR) in type 1 diabetes (T1D) is accompanied by downregulation of the immune response. Programmed cell death-1 (PD-1) and its ligand (PD-L1) are important immunosuppressive molecules, but their changes in PR phase are unclear.We investigated the dynamic changes of PD-1/PD-L1 expression on T cells around the PR phase in T1D.Ninety-eight T1D patients were recruited cross-sectionally and grouped according to PR status into non-remitters (individuals who did not undergo PR during the disease course, n=39), pre-PR (n=15), mid-PR (n=30) or post-PR (n=14) subgroups. PR was defined according to C-peptide level ≥300 pmol/L or index of insulin-adjusted hemoglobin A1c (IDAA1c) ≤9 as recommended. Among all the 98 patients, 29 newly diagnosed individuals were prospectively followed up for one year. The dynamic changes of PD-1/PD-L1 expression, frequency of Tregs and IL-35+ Tregs among peripheral CD4/CD8+ T cells were determined.PD-1/PD-L1 on CD4+/CD8+ T cells showed a dynamic change around the PR phase: lowest in pre-PR phase, restored in mid-PR phase, and declined again in post-PR phase. Conversely, this pattern did not occur for non-remitters. Notably, PD-1 expression on CD8+ T cells in mid-PR was positively correlated with the length of the PR phase. The percentages of circulating Tregs and IL-35+ Tregs showed no relation to PR.The PR phase is associated with restoration of PD-1/PD-L1 on CD4+ and CD8+ T cells, suggesting that PD-1/PD-L1 may be a potential target for prolonging this phase in T1D.

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