We undertook an investigation in which flow cytometry was used to characterize immune cell populations in the decidua of first-trimester normal pregnancies, spontaneous abortions, and ectopic pregnancies in comparison to the nonpregnant endometrium to demonstrate how the proportions of immunocompetent cell populations at the fetomaternal interface are influenced by the presence and state of a fetoplacental allograft. No significant differences were found in the decidua of the different types of first-trimester pregnancy in the proportions of the CD45+, CD14+, CD3+, CD4+, CD8+, CD19+, CD3-/Cd+ and/or CD56+, CD3+/ CD16+ and/or CD56+, CD4+/Leu-8+, CD4+/ Leu-8-, CD8+/CD11b+, CD8+/CD11b-, and CD3+/HLA-DR- decidual leukocyte subsets. However, the percentage of decidual CD3+/HLA-DR+ cells, which are characteristic of activated T cells, was significantly higher in spontaneous abortions than in normal pregnancies (p < 0.05). This suggests that the accumulation of decidual leukocytes may be regulated mainly by hormones and/or cytokines rather than by the presence and stage of an intrauterine conceptus and that on/off-switching of activation of decidual T cells may be associated with successful maintenance of the implanted embryo.
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