[Immune cell functionality during pregnancy].

Immunological recognition of the fetus is the prerequisite of successful pregnancy. Decidualization enables the formation of embryo-competent tissue environment. The decidua is an independent organ performing endocrine and immunological function. On the other hand, the embryo itself is also an active participant of fertilization through the strictly regulated bidirectional communication between embryonic and maternal tissues. Immunological properties of fetomaternal interface dynamically change and pregnancy can be characterized by immunological stages. Chronology of pregnancy may be represented by the three phases “immune clock”: the implantation period is associated with the previously unimaginable inflammatory milieu, which is replaced by the anti-inflammatory environment essential to fetal growth, and followed by a second inflammatory state, which helps in labor. Adaptation to pregnancy requires great flexibility of the immune system in order to simultaneously achieve tolerance to paternal alloantigens, optimal development of the placenta and fetus, and protection against infections/xenobiotics. All this can only be achieved if a special and closely cooperating immune milieu develops at the fetal–maternal interface, where the cellular and soluble components of natural and adaptive immunity are attuned to the hormonal environment, cooperate with the microbiome and respond appropriately to the immunomodulatory effects of the trophoblasts. Characterization of the maternal immune system during pregnancy is important to understand how we can diagnose or treat immune dysregulation associated pregnancy complications, including infertility, implantation failure or pregnancy complications. Orv Hetil. 2023; 164(51): 2006–2015.