A study recently published in the American Journal of Reproductive Immunology showed there are specialized immune cells in the placenta that can recognize and respond to fetal “allo-antigens,” or inherited proteins that come from the father and may be seen as foreign by the mother’s immune system.
Researchers identified two types of immune cells (CD4 TEM and TRM) that have these unique properties. These cells play a role in pregnancy-related diseases such as fetal and neonatal alloimmune thrombocytopenia (FNAIT).
Successful pregnancies require the maternal immune system to protect against diseases such as infections. CD4 T cells are examples of immune cells that work for this purpose.
Researchers sought to better understand the diversity and function of decidual (ie, of the uterus lining) CD4 T cells. To do so, they retrieved blood and placental tissues (from gestational age of over 37 weeks onwards) from healthy women after an uncomplicated pregnancy. They then isolated and purified decidual and peripheral blood CD4 T cells, which were then analyzed.
Researchers found that CD4 T cells obtained had distinct cell types that were not found in the maternal blood. This includes TREG and TRM. Furthermore, studies indicate that CD4 TEM and TRM cells have immune effector functions (ie, the activation of the protective function of the immune system).
Read more about FNAIT testing and diagnosis
Additionally, researchers found that decidual CD4 TEM and TRM cells express markers of antigen experience, with antigen experience referring to the first time an immune cell comes into contact with a foreign antigen, triggering an immune response.
Researchers also reported that both the frequency and phenotypes of CD4 T cells are influenced by important clinical variables, meaning that external influences determine some aspects of the CD4 T cell population size and how they manifest themselves. Importantly, decidual CD TEM and TRM cells can respond to cord blood allo-antigens.
“Further understanding of decidual CD4 TREG, TEM, and TRM functions, specificity, and clonality . . . will help define the beneficial roles of CD4 T cells in providing maternal–fetal tolerance and immunity to microbes in healthy pregnancy,” the authors of the study concluded.
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