Loss of immune tolerance is controlled by ICOS in Sle1 mice

Abstract

Abstract ICOS, a member of the CD28 family, represents a key molecule that regulates adaptive responses to foreign Ags. ICOS is prominently expressed on T follicular helper (TFH) cells, a specialized CD4+ T cell subset that orchestrates B cell differentiation within the germinal centers and humoral response. However, the contribution of ICOS and TFH cells to autoAb profiles under pathological conditions has not been thoroughly investigated. We used the Sle1 lupus-prone mouse model to examine the role of ICOS in the expansion and function of pathogenic TFH cells. Genetic deletion of ICOS impacted the expansion of TFH cells in B6.Sle1 mice and inhibited the differentiation of B lymphocytes into plasma cells. The phenotypic changes observed in B6.Sle1-ICOS–KO mice were also associated with a significant reduction in class-switched IgG and anti-nucleosomal IgG-secreting B cells compared with B6.Sle1 animals. An upregulation in the IFN gene signature early in the life of B6.Sle1 mice modestly correlated with increased levels of autoAbs. The level of VCAM-1, a molecule that was shown to be elevated in patients with SLE and in lupus models, was also increased in an ICOS-dependent manner in Sle1 mice and correlated with autoAb levels. The elimination of ICOS-expressing CD4+ T cells in B6.Sle1 mice, using a glyco-engineered anti-ICOS–depleting Ab, resulted in a significant reduction in anti-nucleosomal autoantibodies. Our results indicate that ICOS regulates the ontogeny and homeostasis of B6.Sle1 TFH cells and influences the function of TFH cells during aberrant germinal center B cell responses. Therapies targeting the ICOS signaling pathway may offer new opportunities for the treatment of lupus and other autoimmune diseases.