12月5日的《科学》杂志报道说，在孕妇体内，来自母亲的细胞会进入胎儿体内，而胎儿的免疫系统则会学着来容忍它们，而不是像日后攻击其它外来异物那样对它们发动攻击。这种耐受性至少会持续到成年期之初，这可解释为什么那些需要器官移植的患者，容易对那些与他们母亲的组织相类似的组织有耐受性。

    科学家很早就知道，发育中的胎儿免疫系统会对异物具有不同寻常的耐受性。可是，除此之外，人们对有关人类胎儿免疫系统却所知甚少。一些研究是在小鼠上进行的，但小鼠与人类免疫系统的发育速度不同，因此在子宫中对外来物质的反应也有很大差异。

    加州大学旧金山分校Jeff Mold及同事报告说，他们通过研究人类组织发现，有令人惊诧的大量的孕妇细胞会进入胎儿的淋巴结。这些细胞在那里会诱导一群调节性的T细胞来抑制胎儿对母体细胞的免疫反应。与小鼠的免疫系统相反，人类胚胎的T细胞看来在受到母体抗原的刺激时非常容易成为调节性的T细胞。研究人员表示，在出生之后，这些调节性的T细胞会继续抑制针对母体细胞的免疫反应。

推荐原始出处：

Science，Vol. 322. no. 5907, pp. 1562 - 1565，Jeff E. Mold，Joseph M. McCune

Maternal Alloantigens Promote the Development of Tolerogenic Fetal Regulatory T Cells in Utero

Jeff E. Mold,1,2 Jakob Micha?lsson,3 Trevor D. Burt,1,4 Marcus O. Muench,5 Karen P. Beckerman,6* Michael P. Busch,5 Tzong-Hae Lee,5 Douglas F. Nixon,1 Joseph M. McCune1

As the immune system develops, T cells are selected or regulated to become tolerant of self antigens and reactive against foreign antigens. In mice, the induction of such tolerance is thought to be attributable to the deletion of self-reactive cells. Here, we show that the human fetal immune system takes advantage of an additional mechanism: the generation of regulatory T cells (T_regs) that suppress fetal immune responses. We find that substantial numbers of maternal cells cross the placenta to reside in fetal lymph nodes, inducing the development of CD4+CD25^highFoxP3+T_regs that suppress fetal antimaternal immunity and persist at least until early adulthood. These findings reveal a formof antigen-specific tolerance in humans, induced in utero and probably active in regulating immune responses after birth.

1 Division of Experimental Medicine, Department of Medicine, University of California at San Francisco (UCSF), San Francisco, CA 94110, USA.
2 Biomedical Sciences Graduate Program, UCSF, San Francisco, CA 94143, USA.
3 Center for Infectious Medicine, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, 141 86, Stockholm, Sweden.
4 Department of Pediatrics, Division of Neonatology, UCSF, San Francisco, CA 94143, USA.
5 Blood Systems Research Institute and Department of Laboratory Medicine, UCSF, San Francisco, CA 94118, USA.
6 Department of Obstetrics, Gynecology, and Reproductive Sciences, UCSF, San Francisco, CA 94143, USA.