Using a cell sorter, CD16-CD56bright natural killer (NK) cells were sorted from decidual mononuclear cells at an early stage of pregnancy. These cells were examined by the reverse transcriptase-polymerase chain reaction (RT-PCR) method for their expression of mRNA coding for the following 12 cytokines: IL-1 beta, IL-2, IL-3, IL-4, IL-5, IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and leukemia inhibitory factor (LIF). Although mRNA coding for every cytokine was detected in decidual mononuclear cells, mRNAs coding for only G-CSF, GM-CSF, M-CSF, TNF-alpha, IFN-gamma, and LIF were detected in CD16-CD56bright NK cells. Also, the supernatant of CD16-CD56bright NK cell cultures was found to contain G-CSF, GM-CSF, M-CSF, TNF-alpha, IFN-gamma, and LIF. These findings indicate that CD16-CD56bright NK cells produce many different cytokines and that these cytokines may play an important role in a successful pregnancy.

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The amount of TGF-beta contained in human whey was studied by the colony formation of NRK47F cells. It was noted that a factor inducing colony formation did exist in human whey, and its action was neutralized when anti-TGF-beta antibodies were introduced. This suggests that TGF-beta does exist in human whey. In colostrum, the total amount of TGF-beta was 1365.7 +/- 242.9 ng/ml, of which the active form comprised 728.1 +/- 248.7 ng/ml (n = 21). In late milk, the total TGF-beta was 952.5 +/- 212.6 ng/ml, with an active form of 178.7 +/- 157.3 ng/ml. Thus human milk contains a large amount of active TGF-beta. Furthermore, it was revealed by the reverse transcriptase polymerase chain reaction that mRNAs coding TGF-beta 1 and TGF-beta 2 exist in human milk cells. These results suggest that both TGF-beta 1 and TGF-beta 2 exist in human milk.

Most human peripheral blood natural killer (NK) cells express the phenotype CD16+CD56+. However, a very minor subset of NK cells express CD16-CD56+, and these NK cells bear both interleukin 2 receptor (IL-2R)alpha (p55) and IL-2R beta (p75) (high affinity IL-2 receptors). In this report, we demonstrate that in human early pregnancy decidua--an interface between maternal immunocompetent cells and fetus (placenta)--abundant (approximately 83%) CD16-CD56+ NK cells with high affinity IL-2 receptors were present, and these cells responded to low amounts of IL-2 (4.5 pM). These CD16-CD56+ NK cells significantly expressed an early activation antigen, CD69, in vivo, whereas peripheral CD16-CD56+ NK cells did not express CD69. These findings suggest that CD16-CD56+ NK cells in early pregnancy decidua may be activated in vivo, and may play an important role in immunoregulation during early pregnancy. Also, decidual lymphocytes may be useful materials to study the mechanism of MHC-unrestricted cytotoxicity of this type of NK cells.

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