The structural basis of maternal-fetal immune interactions in the human placenta

Peripheral CD300a+CD8+ T lymphocytes with a distinct cytotoxic molecular signature increase in pregnant women with chronic chorioamnionitis

PROBLEM

  CD300a is an immunomodulatory molecule of the immunoglobulin receptor superfamily expressed in the leukocytes of myeloid and lymphoid lineages. However, its biological function on CD8+ T lymphocytes remains largely unknown. This study was conducted to assess the biological significance of CD300a expression in T lymphocytes and to determine whether its expression in peripheral T lymphocytes changes in pregnant women presenting with antifetal rejection.

METHODS OF STUDY

Microarray analysis was performed using total RNA isolated from peripheral CD300a+ and CD300a- T lymphocytes. Flow cytometric analysis of the peripheral blood samples of pregnant women and pathologic examination of the placentas were conducted.

RESULTS

  A large number of genes (N = 1245) were differentially expressed between CD300a- and CD300a+ subsets of CD8+ T lymphocytes, which included CCR7, CD244, CX3CR1, GLNY, GZMB, GZMK, IL15, ITGB1, KLRG1, PRF1, and SLAMF7. Gene ontology analysis of differentially expressed genes demonstrated enrichment of biological processes such as immune response, cell death, and signal transduction. CD300a expression in CD8+ T lymphocytes was coupled to a more cytotoxic molecular signature. Of note, the proportion of CD300a+CD8+ T lymphocytes increased in pregnant women with chronic chorioamnionitis (antifetal rejection of the chorioamniotic membranes; P < 0.05).

CONCLUSION

  The findings of this study strongly suggest an increase in systemic T-lymphocyte-mediated cytotoxicity in pregnant women with chronic chorioamnionitis as a manifestation of maternal antifetal rejection.

T cell recognition and immunity in the fetus and mother

All multi-cellular organisms protect themselves from invasion by allogeneic organisms and cells by mounting immune responses. While protective, allogeneic immune responses present a threat to successful reproduction in eutherian mammals in which the maternal immune system is exposed to the semi-allogeneic fetus. Thus, successful reproduction in eutherian mammals depends on mechanisms that control the potentially hostile maternal immune system without hindering immune responses to potentially deadly infectious organisms. Three general mechanisms have been proposed to explain successful reproduction in mammals: (i) the formation of an anatomical barrier between mother and fetus; (ii) expression of allogeneic antigens at a very low level by the fetus; and (iii) hindrance of the maternal immune system responding to fetal antigens. These mechanisms explain in part how the fetus evades the maternal immune system; however, they do not explain fully the survival of the fetus. We hypothesize that site-specific immune suppression may play an important role in successful eutherian reproduction in conjunction with other mechanisms. Site-specific immune suppression at the fetal-maternal interface would protect the fetus while allowing peripheral maternal immune responses to continue unabated.