Several lines of evidence indicate that immunologic effectors, particularly suppressor T cells and NK cells, may play a role in the pathogenesis of idiopathic repetitive abortions. To investigate the involvement of these immune cell populations, we determined the immunophenotypic characteristics of endometrial leukocytes from nonpregnant recurrent aborters. Habitual aborters with a negative investigation underwent an endometrial biopsy during their secretory phase and were followed prospectively to assess clinical outcome. Endometrial leukocytes were evaluated by two-color flow cytometric analysis. The percentage of endometrial CD8+ T lymphocytes was significantly decreased in recurrent aborters, and their CD4:CD8 ratio was increased. In contrast, the proportion of B lymphocytes (CD20+) was strikingly increased in these patients' endometria. The proportion of NK cells was identical in recurrent aborters and normal controls, but the CD16-CD56 bright NK cell subset, which is predominant in normal decidua and endometrium, was significantly decreased in favor of an important contingent of CD16+CD56 dim NK cells in all habitual aborters. Repetitive aborters who had normal CD8+ and CD20+ cell numbers and a normal CD4:CD8 ratio subsequently underwent successful pregnancies, while patients with continuing abortions presented lymphoid populations observed in the habitual aborters group. In conclusion, endometrial lymphocytes of recurrent spontaneous aborters harbor a distinct immunophenotypic profile that antedates implantation and suggests that endometrial immunologic conditions are intrinsically altered in recurrent aborters. Also, the prognostic impact of CD8 and CD20 expression supports their predominant role in the development of fetal tolerance. Finally, a role for NK cells in the abortion process is suggested by their altered subsets in all repetitive aborters.

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