Tim-3: An inhibitory immune checkpoint is associated with maternal-fetal tolerance and recurrent spontaneous abortion

The establishment and maintenance of pregnancy are involved in maternal-fetal immune tolerance whose imbalance can lead to recurrent spontaneous abortion (RSA). RSA is defined as two or more clinically recognized pregnancy losses within 20-24 weeks of gestation with the same partner, including embryonic and fetal losses. However, approximately half of RSA cases are idiopathic, which may be related to immune aberrations. T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) is an inhibitory checkpoint protein that plays a critical role in immune tolerance. Several studies have reported that Tim-3 expression in immune cells is important for maintaining maternal-fetal immune tolerance and that the abnormal expression of Tim-3 may be associated with RSA. To further understand the etiology and pathogenesis of RSA and inspire novel strategies for its diagnosis and treatment, we reviewed the research progress on the Tim-3-induced regulation of natural killer cells, T cells, macrophages, dendritic cells, and myeloid-derived suppressor cells in maternal-fetal immune tolerance and RSA.