Background: Unexplained recurrent spontaneous abortion (URSA) has been suggested being associated with the failure of fetal-maternal immunologic tolerance in which the regulatory T lymphocytes (Tregs) play a crucial role. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is expressed transiently on activated T cells and constitutively on Tregs. CTLA-4 interacts with the B7 cell surface molec...
