Leukocyte function-associated antigen-1 expression on decidual natural killer cells in patients with early pregnancy loss

A large number of CD56(bright) natural killer (NK) cells, which comprise a very small fraction of peripheral blood lymphocytes, appear in the endometrium during the late secretory phase and early pregnancy. These cells are thought to immunologically maintain or inhibit pregnancy. However, the details regarding their contribution to the immuno-elimination systems of embryonic cells or decidual stromal cells remain unclear. Recently, leukocyte function-associated antigen-1 (LFA-1) was shown to play a critical role in the regulation of NK cytolysis in peripheral blood lymphocytes. We speculated that LFA-1 on the decidual CD56(bright) NK may be involved in the regulation of pregnancy. The expression of LFA-1 on the decidual CD56(bright) NK cells was analysed using flow cytometry with fluorescent monoclonal antibodies; CD56 (NKH1), CD16 (Fcg-R3) and CD11a (LFA-1 alpha-chain). In comparison with non-pregnant endometrium during the late secretory phase, the subpopulation of CD56(bright)CD16(-) cells in decidual lymphocytes was significantly increased during normal pregnancy, but was less than that in early pregnancy loss (P < 0.05). Furthermore, the number of CD56(bright) NK cells expressing LFA-1 was significantly higher in early pregnancy loss, and the late secretory phase, than during normal pregnancy (P < 0.05). Our results indicate that up-regulation of LFA-1 on CD56(bright) NK cells is related to spontaneous abortion or the onset of menstruation.