Tumor necrosis factor-dependent segmental control of MIG expression by high endothelial venules in inflamed lymph nodes regulates monocyte recruitment.

Monocytes recruited from the blood are key contributors to the nature of an immune response. While monocyte recruitment in a subset of immunopathologies has been well studied and largely attributed to the chemokine monocyte chemoattractant protein (MCP)-1, mechanisms mediating such recruitment to other sites of inflammation remain elusive. Here, we showed that localized inflammation resulted in an increased binding of monocytes to perifollicular high endothelial venules (HEVs) of lymph nodes draining a local inflammatory site. Quantitative PCR analyses revealed the upregulation of many chemokines in the inflamed lymph node, including MCP-1 and MIG. HEVs did not express detectable levels of MCP-1; however, a subset of HEVs in inflamed lymph nodes in wild-type (but not tumor necrosis factor [TNF] null mice) expressed MIG and this subset of HEVs preferentially supported monocyte binding. Expression of CXCR3, the receptor for MIG, was detected on a small subset of peripheral blood monocytes and on a significant percentage of recruited monocytes. Most importantly, in both ex vivo and in vivo assays, neutralizing anti-MIG antibodies blocked monocyte binding to inflamed lymph node HEVs. Together, these results suggest that the lymph node microenvironment can dictate the nature of molecules expressed on HEV subsets in a TNF-dependent fashion and that inflammation-induced MIG expression by HEVs can mediate monocyte recruitment.

Id-2 regulates critical aspects of human cytotrophoblast differentiation, invasion and migration.

During early human placental development, the conceptus attaches itself to the uterus through cytotrophoblast invasion. Invasive cytotrophoblast cells differentiate from precursor villous cytotrophoblasts, but the essential regulating factors in this process are unknown. Basic helix-loop-helix (bHLH) transcription factor dimers are essential regulators of mouse trophoblast development. We therefore examined the importance of this family of factors in the human placenta. In many cell lineages, bHLH factors are sequestered by members of the Id family, HLH proteins that lack the basic DNA binding domain (Inhibitor of DNA binding proteins (Id-1 to Id-4)). During differentiation of some tissues, Id expression declines, allowing bHLH factors to dimerize, bind DNA and trans-activate lineage-specific genes. To begin to study the role of bHLH transcription factors in human placental development, we first characterized Id expression in cytotrophoblast cells. The cells expressed Id-3 constitutively; Id-2 was downregulated, at the mRNA and protein levels, as the cells differentiated in culture and in situ, respectively. In cases when cytotrophoblast differentiation was compromised (in placentas from women with preeclampsia, or in cells grown under hypoxic conditions in culture), Id-2 expression was maintained. To assess the functional relevance of these correlations, we used an adenovirus vector to maintain Id-2 protein expression in cultured cytotrophoblasts. Compared to control (lacZ-expressing) cells, cytotrophoblasts transduced to constitutively express Id-2 retained characteristics of undifferentiated cells: (alpha)1 integrin expression was low and cyclin B expression was retained. Furthermore, invasion through Matrigel was partially inhibited and migration was strikingly enhanced in Id-2-expressing cells. These results suggest that Id-2 and the bHLH factors that it partners play important roles in human cytotrophoblast development.

Human placental HLA-G expression is restricted to differentiated cytotrophoblasts.

Human placental trophoblasts lie at the maternal-fetal interface, a position in which they could play an important role in maternal tolerance of the fetal semi-allograft. Central to this hypothesis is their unusual MHC class I expression: they suppress class Ia production while expressing HLA-G, a class Ib molecule. We investigated human trophoblast HLA-G protein production in vivo and in vitro. We first used a synthetic peptide corresponding to the variable sequence of the alpha 1 domain to produce mAbs that recognized HLA-G. Ab specificity was demonstrated by immunoaffinity purification of a single protein with the same molecular mass (38 kDa) as HLA-G from choriocarcinoma cells. Use of these Abs to stain tissue sections of the maternal-fetal interface containing cytotrophoblasts in all stages of differentiation showed that HLA-G is expressed only by cytotrophoblasts that invade the uterus. Our previous in vitro studies showed that when early-gestation cytotrophoblast stem cells are cultured, they differentiate rapidly along the invasive pathway, as demonstrated by their expression of stage-specific markers. Here we show they also up-regulate HLA-G production. Cytotrophoblasts from term placentas, which have reduced invasive capacity in vitro, also had decreased ability to up-regulate HLA-G protein expression. We detected high levels of HLA-G mRNA in cytotrophoblasts isolated from first- and second-trimester placentas, but only trace amounts in term cells. Taken together, these results suggest that HLA-G production is a critical component of cytotrophoblast differentiation along the invasive pathway.

A repertoire of differentially expressed transcription factors that offers insight into mechanisms of human cytotrophoblast differentiation.

During human placental development, specialized cells allocated to the extraembryonic lineage (cytotrophoblasts) invade the uterus, anchoring the conceptus to the decidua and tapping a supply of maternal blood. This unusual behavior requires cytotrophoblasts to assume highly specialized characteristics; some are commonly associated with tumor cells, while others are typical of endothelia. Here we investigated the transcriptional mechanisms that control cytotrophoblast differentiation/invasion. Specifically, we examined the cells' expression of a number of transcription factors, at the RNA level, as they differentiated along the invasive pathway in vitro. Since basic helix-loop-helix (bHLH) proteins play important roles in murine trophoblast differentiation, we first examined their expression by cytotrophoblasts. As in murine placental development, expression of the human homologue of Mash-2 was confined to progenitor cells. But expression of Hand-1, which promotes differentiation of murine trophoblast giant cells, was not detected. We also found that cytotrophoblasts upregulated the expression of bHLH/PAS factors that function in adaptive responses to hypoxia, including hEPAS-1, which is expressed primarily in endothelial cells. Quite unexpectedly, we discovered that cytotrophoblasts express high levels of mRNA encoding the human homologue of the Drosophila neuronal fate gene, glial cells missing-1 (gcm-1). We also found evidence of crosstalk between the bHLH and GCM-1 regulatory networks. Together, these results offer insights into the transcriptional mechanisms that govern cytotrophoblast differentiation/invasion. Interestingly, these mechanisms suggest analogies with those that govern differentiation of murine stem cells allocated to both the intra- and extraembryonic lineages.

Membrane-bound TNF supports secondary lymphoid organ structure but is subservient to secreted TNF in driving autoimmune inflammation.

Mice without secreted TNF but with functional, normally regulated and expressed membrane-bound TNF (memTNF(Delta/Delta) mice) were created by knocking-in the uncleavable Delta 1-9,K11E TNF allele. In contrast to TNF-deficient mice (TNF(-/-)), memTNF supported many features of lymphoid organ structure, except generation of primary B cell follicles. Splenic chemokine expression was near normal. MemTNF-induced apoptosis was mediated through both TNF-R1 and TNF-R2. That memTNF is suboptimal for development of inflammation was revealed in experimental autoimmune encephalomyelitis. Disease severity was reduced in memTNF(Delta/Delta) mice relative to wild-type mice, and the nature of spinal cord infiltrates resembled that in TNF(-/-) mice. We conclude that memTNF supports many processes underlying lymphoid tissue structure, but secreted TNF is needed for optimal inflammatory lesion development.