T Regulatory Cells in Early Pregnancy in Mice

Abstract

To accommodate the semi-allogeneic fetus, a state of maternal immune tolerance to paternally-derived conceptus alloantigens is required. Tolerance is initially established when the same antigens are contacted following seminal fluid exposure, and increases in tolerogenic CD4+Foxp3+ T regulatory (Treg) cells are elicited. Clinical studies demonstrate the importance of seminal fluid contact in human pregnancy, where pathologies of pregnancy including preeclampsia are more likely with a short period of sexual cohabitation. Despite the pivotal role of Treg cells in pregnancy, the factors which regulate their response are yet to be fully understood. In this thesis, we describe experiments using mouse models that investigate regulators of the Treg cell pool and their impact on pregnancy success. Initially, we examined the contribution of number of seminal fluid exposures to Treg cell generation. Our data demonstrate that repeated exposure to the same male alloantigens strengthens the Treg cell pool, and increases its stability. These changes were not observed after repeated mating to syngeneic males or following switching from syngeneic to allogeneic partners. Changes to the Treg cell population was also linked with greater resistance to inflammatory challenge in mid-gestation. These findings may provide a mechanistic explanation for clinical observations linking long-term seminal fluid exposure in women with improved outcomes of pregnancy. We then assessed the contribution of a number of key immune regulatory factors on the female Treg cell response in early pregnancy. Prominent among the tolerance-inducing cytokines is IL10, which protects against fetal loss and alters key immune cells in early gestation including Treg cells. In this study we demonstrate that maternal as opposed to fetal IL10 deficiency causes increases susceptibility to fetal loss following inflammatory challenge in mid-gestation. The transcriptome of Treg cells is altered in IL10 deficiency with increased Ctse (cathepsin E), Il1r1, Il12rb2 and Ifng. These findings highlight the pivotal contribution of maternal IL10 in facilitating robust Treg cell generation and immune protection of the fetus from inflammatory challenge. Recent studies demonstrate that microRNAs (miRNA) also play a role in Treg cell generation. miR-155 and miR-223 are both regulated by seminal fluid following coitus and are postulated to play important roles in the peri-conception immune environment. Using mir-155 null mutant mice, we demonstrate that miR-155 deficiency substantially alters the local Treg cell and antigen presenting cell populations after mating. Using mir-223 null mice, we demonstrate that miR-223 also contributes to the peri-conception immune environment with alterations to the Treg cell and antigen presenting cell populations after mating. Furthermore, deficiency in either miR-155 or miR-223 increases susceptibility to fetal loss following pro-inflammatory challenge in mid-gestation. These findings indicate that both miR-155 and miR-223 have pivotal roles in establishing the appropriate maternal immune environment during the peri-conception period, and in activating sufficient immune tolerance to protect against inflammatory challenge in later gestation. Collectively, these data build understanding of key factors contributing to Treg cell generation and function in the peri-conception environment. The findings may be beneficial in informing new approaches to diagnosis and treatment of human gestational disorders associated with immune dysregulation.