To Örebro University

During pregnancy, immunological tolerance toward the semiallogeneic fetus needs to be established while at the same time an effective immune defense must be maintained.1 The pregnancy-associated thymic involution reported in rodents2 has been suggested to support maternal immune regulation by reducing the output of potentially harmful TH cells. However, the functional importance of this thymic involution remains unclear and it is not known whether it even occurs in humans.3 In fact, the role of thymus during human pregnancy and in pregnancy-associated tolerance remains largely unknown,4 albeit a role for thymic-derived regulatory T (Treg) cells in pregnancy complications has been suggested,4 supporting a role for thymus in immune regulation during human pregnancy. The aim of this study was to assess the role of thymus in TH-cell regulation during human pregnancy by analyzing the output of different TH-cell populations.