Decidual natural killer cells in recurrent spontaneous abortion with normal chromosomal content. 
The maternal local immune responses in unexplained recurrent spontaneous abortion (RSA) are not yet well known.  Maternal peripheral and decidual natural killer (NK) cells were evaluated in RSA with normal chromosomal content.  Maternal peripheral blood, villous trophoblast, and decidua were taken from 15 normal pregnancies and 9 RSA patients with normal chromosomes.  The NK cells in decidual lymphocytes were evaluated by flow cytometry using monoclonal antibodies for CD56, CD16, and CD3.  The percentages of CD56+ CD16- CD3- cells in decidual lymphocytes in RSA were lower than in normal pregnancies (P < 0.002).  The CD56+CD16+/CD56+CD16- cells ratio in RSA was higher than in normal pregnancies (P < 0.02).  The lower percentages of CD56+CD16-CD3- cells in RSA cases may show an inappropriate accumulation of NK cells in the decidua, and this finding may be a factor involved in RSA.