Immunohistochemical evidence for increased numbers of 'classic' CD57+ natural killer cells in the endometrium of women suffering spontaneous early pregnancy loss.

Despite increasing knowledge about the cell populations that exist in the decidualized endometrium in normal early human pregnancy, little is known about the decidual leukocyte populations in women suffering spontaneous early pregnancy loss. Decidual leukocytes were investigated in 40 cases of spontaneous abortion using a panel of monoclonal antibodies specific for leukocytes, macrophages, T cells, B cells and 'classic' CD57(+) natural killer (NK) cells and an avidin-biotin peroxidase immunohistochemical technique. Endometrial granulated lymphocytes (eGL), the predominant decidual leukocyte population in the first trimester of normal human pregnancy, were demonstrated with the phloxine-tartrazine stain. There were significantly fewer leukocytes in decidua in spontaneous abortion, but the numbers of eGL, macrophages and T cells did not differ significantly between normal and pathological pregnancies. eGL and macrophages accounted for a greater proportion of the decidual leukocyte population in spontaneous abortion. Of the 40 spontaneous abortion cases, 20 had significantly increased numbers of 'classic' CD57(+) NK cells when compared with normal human pregnancy. A proportion of spontaneous abortions may occur because of increased 'classic' CD57(+) NK cell numbers in the decidua, which could become activated by local cytokines to attack the trophoblast.