Stéphane M. Caucheteux

Tolerance of the fetus by the maternal immune system: role of inflammatory mediators at the feto-maternal interface

The adaptive immune system of placental mammals has evolved to tolerate the fetus. Rejection of the fetus by adaptive immune responses is therefore a rare event, with abortion being caused more frequently by inflammation in the placenta. This review will cover recent aspects of immune privilege and the innate immune system at the feto-maternal interface, citing examples of the role played by microbial infections in fetal demise.

Affinity-Dependent Alterations of Mouse B Cell Development by Noninherited Maternal Antigen

Abstract We have examined the passage of maternal cells into the fetus during the gestation and postpartum in mice. Using enhanced green fluorescent protein (EGFP)-transgenic females, we showed that maternal cells frequently gain access to the fetus, mostly in syngeneic pregnancies, but also in allogeneic and outbred crosses. EGFP-transgenic cells, including B, T, and natural killer cells, can persist until adulthood, primarily in bone marrow and thymus. We then asked whether maternal cells, bearing antigens not inherited by the fetus, influence the development of fetal and neonatal B lymphocytes. We have used the B cell receptor 3-83 µ/δ transgenic mouse model, whose B cells recognize the major histocompatibility complex class I molecules H-2Kk and H-2Kb, with a high or moderate affinity, respectively. The fate of transgenic B cells in animals exposed to noninherited H-2Kk or H-2Kb maternal antigens (NIMA) during gestation and lactation was compared with those of nonexposed controls. In H-2Kk-exposed fetuses, NIMA-specific transgenic B cells are partially deleted during late gestation. Nondeleted cells have downmodulated their B cell receptor. In contrast, in NIMA H-2Kb-exposed neonates, transgenic B cells present an activated phenotype, including proliferation, upregulation of surface CD69, and preferential localization in the T cell zone of splenic follicles. This state of activation is still clearly detectable up to 3 wk of age. Thus, we show that fetal and neonatal B cell development is affected by maternal cells bearing antigens noninherited by the fetus and that this phenomenon is highly dependent on the affinity of the B cell receptor for the NIMA.

Transgenic Major Histocompatibility Complex Class I Antigen Expressed in Mouse Trophoblast Affects Maternal Immature B Cells

Abstract We have produced transgenic mice using the mouse placental lactogen type II promoter to force and restrict the expression of the mouse major histocompatibility complex (MHC) class I molecule, H-2Kb, to the placenta. We show that the transgenic MHC antigen H-2Kb is expressed exclusively in trophoblast giant cells from Day 10.5 until the end of gestation. This expression affects neither the fetal development nor the maternal tolerance to the fetus in histoincompatible mothers. We have used the 3.83 B cell receptor (BcR) transgenic mouse line to follow the fate of H-2Kb-specific maternal B cells in mothers bearing H-2Kb-positive placentas. Our results suggest that transgenic H-2Kb molecules on trophoblast giant cells are recognized by 3.83 BcR-transgenic B cells in the bone marrow of pregnant females. This antigen recognition triggers the deletion of a bone marrow B cell subpopulation, including immature and transitional B cells. Their percentage decreases during the second half of gestation and is down to 8% on Day 17.5, compared to 22% in the (3.83 Tg female × Fvb) control group. This deletion might contribute to the process of maternal tolerance of the conceptus.

Antigen-stimulated CD4 T-cell expansion is inversely and log-linearly related to precursor number

Antigen-driven expansion of specific CD4 T cells diminishes, on a per cell basis, as infused cell number increases. There is a linear relation between log precursor number and log factor of expansion (FE), with a slope of ∼−0.5 over a range from 3 to 30,000 precursors. Cell number dependence of FE is observed at low precursor number, implying that the underlying process physiologically regulates antigen-driven T-cell expansion. FE of small numbers of transgenic precursors is not significantly affected by concomitant responses of large numbers of cells specific for different antigens. Increasing antigen amount or exogenous IL-2, IL-7, or IL-15 does not significantly affect FE, nor does FE depend on Fas, TNF-α receptor, cytotoxic T-lymphocyte antigen-4, IL-2, or IFN-γ. Small numbers of Foxp3-deficient T-cell receptor transgenic cells expand to a greater extent than do large numbers, implying that this effect is not mediated by regulatory T cells. Increasing dendritic cell number does result in larger FE, but the quantitative relation between FE and precursor number is not abrogated. Although not excluding competition for peptide/MHC complexes as an explanation, fall in FE with increasing precursor number could be explained by a negative feedback in which increasing numbers of responding cells in a cluster inhibit the expansion of cells of the same specificity within that cluster.

Placental Anomalies and Fetal Loss in Mice, After Administration of Doxycycline in Food for Tet-system Activation

During the course of a study aiming to obtain a tetracycline (Tet)-inducible transgene expression restricted to the placenta, we have observed a toxicity of doxycycline (dox) given in the food at doses of 2.5–10 mg/g to pregnant mice from two different inbred strains. During the second half of gestation, dox-fed non-transgenic mice presented placental anomalies and impaired fetal development proportional to the dose of antibiotic. Thus, dox administered in commonly used food doses can have an adverse effect on pregnancy. These observations are important for studies of placental or fetal development using inducible gene promoters.

Lipid phosphatases identified by screening a mouse phosphatase shRNA library regulate T-cell differentiation and protein kinase B AKT signaling.

Significance We identified a series of lipid phosphatases that regulate differentiation of naïve CD4 T cells to their major phenotypic states, T-helper (Th)1/Th2/Th17. Previously, phosphatase and tensin homolog (PTEN) was the only lipid phosphatase shown to function in this process. To identify these phosphatases, we used a unique “phosphatase-wide” screening procedure. Our results demonstrate that myotubularin-related protein (MTMR) 9 and MTMR7 play critical roles in Th differentiation. Knocking down MTMR9 enhances Th1 priming, and such Th1 cells show increased protein kinase B (PKB)/AKT phosphorylation. Knocking down MTMR7 increases Th2 and Th17 priming; these cells show enhanced AKT phosphorylation. Screening a complete mouse phosphatase lentiviral shRNA library using high-throughput sequencing revealed several phosphatases that regulate CD4 T-cell differentiation. We concentrated on two lipid phosphatases, the myotubularin-related protein (MTMR)9 and -7. Silencing MTMR9 by shRNA or siRNA resulted in enhanced T-helper (Th)1 differentiation and increased Th1 protein kinase B (PKB)/AKT phosphorylation while silencing MTMR7 caused increased Th2 and Th17 differentiation and increased AKT phosphorylation in these cells. Irradiated mice reconstituted with MTMR9 shRNA-transduced bone marrow cells had an elevated proportion of T-box transcription factor T-bet expressors among their CD4 T cells. After adoptive transfer of naïve cells from such reconstituted mice, immunization resulted in a greater proportion of T-box transcription factor T-bet–expressing cells. Thus, myotubularin-related proteins have a role in controlling in vitro and in vivo Th-cell differentiation, possibly through regulation of phosphatidylinositol [3,4,5]-trisphosphate activity.

Transplantation Tolerance to a Single Noninherited MHC Class I Maternal Alloantigen Studied in a TCR-Transgenic Mouse Model

The mechanisms underlying tolerance to noninherited maternal Ags (NIMA) are not fully understood. In this study, we designed a double-transgenic model in which all the offspring’s CD8+ T cells corresponded to a single clone recognizing the Kb MHC class I protein. In contrast, the mother and the father of the offspring differed by the expression of a single Ag, Kb, that served as NIMA. We investigated the influence of NIMA exposure on the offspring thymic T cell selection during ontogeny and on its peripheral T cell response during adulthood. We observed that anti-Kb thymocytes were exposed to NIMA and became activated during fetal life but were not deleted. Strikingly, adult mice exposed to NIMA accepted permanently Kb+ heart allografts despite the presence of normal levels of anti-Kb TCR transgenic T cells. Transplant tolerance was associated with a lack of a proinflammatory alloreactive T cell response and an activation/expansion of T cells producing IL-4 and IL-10. In addition, we observed that tolerance to NIMA Kb was abrogated via depletion of CD4+ but not CD8+ T cells and could be transferred to naive nonexposed mice via adoptive transfer of CD4+CD25high T cell expressing Foxp3 isolated from NIMA mice.

Analysis of naïve lung CD4 T cells provides evidence of functional lung to lymph node migration

The proportion of CD4 T cells with phenotypic and functional properties of naïve cells out of total CD4 T cells is similar in the lung parenchyma and lymph nodes. On treatment with a sphingosine-1-phosphate agonist, the frequency of these cells falls precipitously, but with a delay of ∼14 h compared with blood CD4 T cells; neither anti-CD62L nor pertussis toxin prevents entry of naïve CD4 T cells into the lung. Based on treatment with anti-CD62L and the use of CCR7−/− cells, lung naïve CD4 T cells appear to migrate to the mediastinal lymph nodes along a CD62L-independent, CCR7-dependent pathway. Cells that have entered the node in this manner are competent to respond to antigen. Thus, a portion (approximately one-half) of naïve CD4 T cells appears to enter the mediastinal lymph nodes through a blood-to-lung-to-lymph node route.