レセプターが母の免疫細胞の攻撃から胎児を守る　

1999/5/12　ロイター　胎児の細胞は母体の免疫系にとっては異物であるが、なぜか攻撃をまぬがれている。しかし、イタリアの研究グループによると胎児細胞の表面に存在するレセプター（HLA-G)は、子宮の脱落膜のkiller cell の表面に存在するレセプターに接触するとその攻撃力をなくすらしい。

Receptors shield fetus from mom's immune cells

NEW YORK, May 12 (Reuters Health) -- Fetal tissues are ''foreign'' to the mother's immune system -- but usually the fetus escapes attack by maternal immune cells.
Researchers in Italy have found a clue to this mystery. They report that receptors on the surface of fetal cells appear to turn off the maternal immune 'killer cells' that recognize ''non-self'' tissue. This system of receptor signaling may be ''an important mechanism to prevent the attack of fetal tissues by the (maternal) immune system,'' according to Dr. Marco Ponte, of Laboratorio di Immunopatologia, Centro Biotecnologie Avanzate, in Genova, Italy, and colleagues.
Although killer cells make up just 5% - 20% of all white blood cells, they comprise close to 95% of the white blood cells found in the decidua -- the part of the placenta that comes from the mother's uterine tissue.
The Italian researchers determined that these placental natural killer cells carry at least one of two unique receptors on their cell surface. When either of these two receptors come into contact with HLA-G -- a receptor found on the surface of fetal cells -- this contact leads to the attack capability of the killer cells being turned off.
These receptors appear to be exclusive to placental natural killer cells. All natural killer cells ``isolated from maternal decidua during the first trimester expressed either one or both of these receptors,'' the authors write in their report, published in the May issue of the Proceedings of the National Academy of Sciences.
In a commentary, Dr. Lewis Lanier, of the DNAX Research Institute of Cellular and Molecular Biology in Palo Alto, California, calls the finding ``a provocative association.'' But he notes that one infant born without functioning HLA-G ``did not suffer any dire consequences during fetal development.'' That outcome casts some doubt on the overall importance of HLA-G in the maternal immune system's relationship to the fetus, he explains.
SOURCE: Proceedings of the National Academy of Sciences USA 1999;96:5343-5345, 5674-5679.