| Popis: |
The human fetoplacental unit may be considered as a true allograft in the immunologically competent mother and a graft rejection would be expected. However, there is essentially no evidence that this occurs, and the aim of this review is to present some basic mechanisms acting at the materno-fetal interface and contributing to successful survival of the fetoplacental unit. Recent advances have changed our traditional view on the trophoblast tissue as an immunologically inert barrier. HLA class I antigens are not generally suppressed on the trophoblast cells but rather less polymorphic HLA-G and HLA-C antigens are carefully selected (extravillous cytotrophoblast), and these molecules obviously play an important role in the maintenance of pregnancy. The decidua of pregnancy is heavily infiltrated by cells of bone marrow origin and the most prominent population are decidual granulated lymphocytes. These cells have NK like phenotype (CD56bright+ CD16). Perforin is a main mediator, at the molecular level, of the cytotoxic effector pathway mediated by cytotoxic T lymphocytes and natural killer cells. Both the percentage of perforin positive cells and the average content of perforin/cell is much higher in the decidual lymphocytes than in the peripheral blood lymphocytes, which shows that the human fetus elicits an increase in levels of perforin which, however, has a protective rather than a destructive role, since the level of perforin expression is significantly lower in pathological pregnancies. The role of hormones and humoral factors at the materno-fetal interface, particularly TH2 cytokines and progesterone induced blocking factor (PIBF), is emphasized. |
