Decidual CD8+CD28- T cells express CD103 but not perforin.

Maternal lymphocytes at the fetal-maternal interface play a key role in the immune acceptance of the allogeneic fetus. Decidual NK cells have shown to contain immune modulatory properties and may facilitate fetal trophoblast invasion into maternal tissue. More recently, CD4+CD25(bright)FOXP3+ Treg cells have been shown to be concentrated in decidual tissue and to be able to suppress both fetus-specific and nonspecific responses. However CD8+ T cells form the largest fraction of T cells at the fetal-maternal interface and are the main candidates to recognize and respond to fetal-maternal HLA differences. So far limited data are available on the phenotype and function of decidual CD8+ T cells during pregnancy. Phenotypic analysis of peripheral blood and decidual CD8+ T cells showed the presence of activated CD8+ T cells as well as a population of CD8+CD103+ T cells in decidual tissue. Unlike peripheral CD8+CD28- T cells, decidual CD8+CD28- T cells do not express the cytolytic molecule perforin. The lack of perforin expression may indicate that decidual CD8+ T cells are not able to elicit a cytotoxic response, and supports the hypothesis that decidual CD8+ T cells play a role in local immune regulation. Defects in decidual CD8+ T-cell regulation or differentiation may lead to placental pathologic conditions whereby placental and fetal growth are impaired.