Impaired T-cell function in patients with novel ICOS

Interaction of ICOS - ICOS ligand is required for the germinal center formation, T-cell immune responses, and development of autoimmune diseases. Human ICOS deficiency with the identical ICOS mutation has been identified in nine patients worldwide. In vitro studies showed T-cell defect of the patients was mild, and in vivo autoimmunity was uncommon and mild. Here we report in-depth analysis of T-cell function in two siblings with novel ICOS deficiency. While the brother displayed mild skin infections, psoriasis-like skin region, and defective immunoglobulin class switching, the sister had more severe symptoms, which included immunodeficiency, rheumatoid arthritis, inflammatory bowel disease, interstitial pneumonitis, and psoriasis. Despite of normal CD3/CD28-induced proliferation and IL-2 production in vitro, peripheral blood T-cells from both patients demonstrated decreased percentage of CD4 central and effector memory T-cells and impaired production of Th1, Th2, and Th17 cytokines upon CD3/CD28 costimulation or upon PMA/ionophore stimulation. The defective polarization into effector cells were associated with impaired induction of T-bet, GATA3 and MAF and RORC. Reduced CTLA-4+CD45RO+ FoxP3+ regulatory T-cells and diminished induction of inhibitory cell surface molecules including CTLA-4 were also observed in the patients. Further analysis of the gene expression and immune functions of the patients demonstrated increased induction of RANKL, lack of IFN-g response, and loss of Itch expression upon activation in the female case with autoimmunity. Our study suggests extensive T-cell dysfunction and loss of balance between effector cells and regulatory cells in the ICOS-deficient patients may account for their immunodeficiency and/or autoimmune disorder.

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Takahashi N, Matsumoto K, Saito H, Nanki T, Miyasaka N, Kobata T, Azuma M, Lee SK, Mizutani S, Morio T