Régis Josien

TRANCE is a TNF family member that regulates dendritic cell and osteoclast function.

Tumor necrosis factor (TNF)‐related activation‐induced cytokine (TRANCE) is a new member of the TNF family emerging as a key regulator of the immune system and of bone development and homeostasis. TRANCE is expressed on activated T cells and activates mature dendritic cells (DC), suggesting that it plays a role in the T cell‐DC interaction during an immune response. Furthermore, TRANCE is expressed on osteoblasts stimulated with vitamin D3, dexamethasone, and parathyroid hormone. TRANCE, when expressed on osteoblasts, induces osteoclastogenesis and osteoclast activation, suggesting that it links known calciotropic hormones to bone resorption. TRANCE mediates its effects via the TRANCE‐receptor (TRANCE‐R/RANK), whereas its activity can be inhibited by the soluble decoy receptor osteoprotegerin/osteoclast inhibitory factor (OPG/OCIF). OPG can be neutralized by another TNF‐family member, the TNF‐related apoptosis‐inducing ligand (TRAIL), suggesting that TRANCE is part of a complex cytokine network that regulates a diverse set of functions. We will discuss the current literature describing TRANCE and its receptors and its role in controlling DC and osteoclast function. J. Leukoc. Biol. 65: 715–724; 1999.

A novel member of the leukocyte receptor complex regulates osteoclast differentiation.

Osteoclasts (OCs) are multinucleated cells that resorb bone and are essential for bone homeostasis. They develop from hematopoietic cells of the myelomonocytic lineage. OC formation requires cell-to-cell interactions with osteoblasts and can be achieved by coculturing bone marrow precursor cells with osteoblasts/stromal cells. Two of the key factors mediating the osteoblast-induced osteoclastogenesis are macrophage–colony stimulating factor (M-CSF) and the tumor necrosis factor (TNF) family member TNF–related activation-induced cytokine (TRANCE) that are produced by osteoblasts/stromal cells in response to various bone resorbing hormones. In addition, other factors produced by osteoblasts/stromal cells further influence osteoclastogenesis. Here we report the identification and characterization of OC-associated receptor (OSCAR), a novel member of the leukocyte receptor complex (LRC)-encoded family expressed specifically in OCs. Genes in the LRC produce immunoglobulin (Ig)-like surface receptors and play critical roles in the regulation of both innate and adaptive immune responses. Different from the previously characterized members of the LRC complex, OSCAR expression is detected specifically in preosteoclasts or mature OCs. Its putative–ligand (OSCAR-L) is expressed primarily in osteoblasts/stromal cells. Moreover, addition of a soluble form of OSCAR in coculture with osteoblasts inhibits the formation of OCs from bone marrow precursor cells in the presence of bone-resorbing factors, indicating that OSCAR may be an important bone-specific regulator of OC differentiation. In addition, this study suggests that LRC-encoded genes may have evolved to regulate the physiology of cells beyond those of the immune system.

A critical role for transforming growth factor-beta in donor transfusion-induced allograft tolerance.

Donor-specific (DST) or nonspecific blood transfusions administered before transplantation can enhance survival of vascularized allografts both in humans and animals but the immunological mechanisms of this effect remain unclear. We have analyzed the expression and the role of endogenous TGF-beta1 in a model of heart allograft tolerance, induced by pregraft DST in adult rats. We reported previously that this tolerance occurs despite a strong infiltration of leukocytes into the graft that are unable to produce both Th1- and Th2-related cytokines in vivo. Allografts from DST-treated rats express high levels of TGF-beta1 mRNA and active protein. This phenomenon is correlated with the rapid infiltration of leukocytes producing high amounts of TGF-beta1. TGF-beta1-producing cells are virtually absent among early infiltrating cells in rejected grafts but are found at a later time point. The induction of allograft tolerance in vivo is abrogated by administration of neutralizing anti-TGF-beta mAb. Moreover, overexpression of active TGF- beta1 in heart allografts using a recombinant adenovirus leads to prolonged graft survival in unmodified recipients. Taken together, our results identify TGF-beta as a critical cytokine involved in the suppression of allograft rejection induced by DST and suggest that TGF-beta-producing regulatory cells are also involved in allograft tolerance.

Dendritic Cells as Killers: Mechanistic Aspects and Potential Roles

Dendritic cells (DC) are professional APC endowed with the unique capacity to activate naive T cells. DC also have important effector functions during the innate immune response, such as pathogen recognition and cytokine production. In fact, DC represent the crucial link between innate and adaptive immune responses. However, DC are quite heterogeneous and various subsets endowed with specific pathogen recognition mechanisms, locations, phenotypes, and functions have been described both in rodents and in humans. A series of studies indicated that rodent as well as human DC could also mediate another important innate function, i.e., cell-mediated cytotoxicity, mostly toward tumor cells. In this article, we will review the phenotypes of these so-called killer DC, their killing mechanism, and putative implication in the immune response.

Modulation of hyperoxia-induced TNF-alpha expression in the newborn rat lung by thalidomide and dexamethasone.

The effect of high oxygen concentrations on lungs of neonatal rats was studied. In addition, some oxygen-exposed animals were treated with either dexamethasone or thalidomide. No gross histologic changes were noted in the lungs following exposure to 95% oxygen nor were there changes in the total number or the phenotypic distribution of BAL cells obtained from these lungs compared to lungs from air exposed (control) neonatal rats. The majority of the BAL cells were CD45+ leukocytes (macrophages). However, when BAL cells were exposed to LPS in vitro, TNF-α production was higher in cells from rats exposed to 95% oxygen compared to cells from rats exposed to ambient air. In addition, lung TNF-α and IL-6 mRNA levels were increased after exposure to 95% oxygen. In the lungs of animals treated with either dexamethasone or thalidomide, TNF-α mRNA levels were reduced, while only dexamethasone treatment also reduced IL-6 mRNA levels.

CD95 ligand expression in dedifferentiated breast cancer

CD95 ligand expression has been observed in various malignancies. Studying the CD95 ligand (CD95L) and receptor (CD95) system in eight non‐malignant mammary tissues and 40 breast cancer tissues, mRNA and protein expression was determined by quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) and immunofluorescence. mRNA levels of CD95L correlated positively ( r=0·90; p< 0·01) and transmembrane CD95 inversely ( r=−0·88; p< 0·01) with histopathological grading of the breast tumours: CD95L mRNA levels were low in adenomas, but increased by 20‐fold in grade I, 120‐fold in grade II, and 310‐fold in grade III breast cancer. In contrast, CD95 mRNA levels were low in high‐grade carcinomas, but high in benign mammary tissues. Since CD95L acts as an efficient inducer of apoptosis in CD95+ cells, apoptotic cells were identified on the tissue sections. Tumour‐infiltrating lymphocytes and stromal cells in close proximity to CD95L‐expressing breast cancer underwent apoptosis. As a functional test, CD95+ target cells were cultured on breast cancer tissue sections. The target cells underwent apoptosis when cultured on breast cancer sections, but could be rescued when CD95L was specifically blocked by a CD95–Fc fusion molecule. The data suggest an inverse regulation of CD95 ligand and receptor expression during dedifferentiation of breast cancer. Killing of bystander cells by the CD95L‐expressing breast tumour could be involved in tissue invasion. Copyright