IMMUNOMORPHOLOGICAL STUDIES OF HUMAN DECIDUA-ASSOCIATED LYMPHOID-CELLS IN NORMAL EARLY-PREGNANCY

Human decidual lymphocytes from early, normal pregnancy were character ized in situ with respect to ultrastructure and distribution of subset s. The ultrastructure of isolated decidual gamma delta T cells was als o studied. CD45(+) cells comprised 11 +/- 2% of all decidual cells. Th e majority were localized in large lymphoid cell clusters (LCC), near endometrial glands, or as intraepithelial lymphocytes (IEL) in glandul ar epithelium. The major cell populations in LCC were CD56(+)TCR-gamma delta(+) cells, CD56(+) cells, TCR-alpha beta(+)CD4(+) cells, and TCR -alpha beta(+)CD8(+) cells. All expressed activation markers (CD45RO, Kp43, and/or HML-1) and MHC class II Ag (HLA-DR, HLA-DP, and/or HLA-DQ ). No B cells were found. Almost all IEL were activated TCR-gamma delt a(+) cells (CD56(+) and CD56(-)). The glandular epithelial cells expre ssed heat shock protein 60 at the basolateral side facing the TCR-gamm a delta(+) IEL. Decidual lymphocytes displayed cytoplasmic processes, microvilli, characteristic cytoplasmic granules, and had intimate cont act with neighboring cells. Lymphocytes in the outer rim of LCC and th e stroma showed signs of cellular movement. Two main morphotypes of ga mma delta T cells could be distinguished. One had single microvilli, m embrane-bound granules, and nuclear inclusions. The other had many mic rovilli, nonmembrane-bound granules and cytoplasmic multivesicular bod ies. Our data suggest that LCC are centers of immune reactivity where T and NK cells become activated. The activated cells may guard against infections and undue trophoblast invasion and/or be involved in modul ating the local maternal immune system toward unresponsiveness against the semiallogeneic fetus.