Expression of recombinase-activating genes (RAG-1 and 2) in human decidual mononuclear cells.

Recombinase-activating genes (RAG-1 and RAG-2) are expressed in immature T or B lymphocytes and possess activity to induce V(D)J rearrangement in TCR and Ig genes. We examined their expression in human decidual and non-pregnant endometrial samples using a highly sensitive RT-PCR technique. Expression of RAG-1 and 2 was noted in all (13/13) pregnant decidual tissues obtained at different gestational stages. After anti-human Ig treatment to rule out the possibility of RAG-1,2 expression from decidual B-cells, strong expression of RAGs was still noted in B cell depleted decidual cells in contrast to lymph nodes and PBMC that lost RAG mRNA expression after this treatment. After FACS mediated cell sorting, strong expression of RAG-1,2 was noted in CD16-CD56bright cells and weak expression in CD3+ cells. Although CD16-CD56bright cells lack surface CD3, they express CD3 epsilon mRNA only detectable by RT-PCR. Our results suggest the nature of decidual CD16-CD56bright cells as a progenitor of extrathymic T cells that possess RAG-1 and 2 mRNA as markers of their immaturity, and possibly differentiate into CD3+ extrathymic T-cells in the decidua under the influence of trophoblastic cells. We propose the human decidua as a new site of extrathymic T-cells differentiation and propose possible roles of trophoblastic cells to attract progenitor lymphocytes of bone marrow origin and trigger their TCR rearrangement as thymic epithelial cells.