[PMC free article] [PubMed] [Google Scholar] 31. conversation of mouse LIGHT with its receptors expressed on transfected cells. An antibody with the desired specificity was evaluated in a short-term allogeneic cytotoxic assay and tested for its ability to detect endogenous mouse LIGHT. Results We provide evidence for the first time that in mice, as previously described in humans, LIGHT protein is usually rapidly and transiently expressed after T cell activation, and this expression Isosilybin was stronger on CD8 T cells than on CD4 T cells. Two anti-LIGHT antibodies prevented interactions of mouse LIGHT with its two known receptors HVEM and LTR. administration of anti-LIGHT antibody (clone 10F12) ameliorated host anti-donor short-term cytotoxic response in WT B6 mice, although to a lesser extent than that observed in LIGHT-deficient mice. Conclusions The therapeutic targeting of LIGHT may contribute to achieve a better control of cytotoxic responses refractory to current immunosuppressive drugs in transplantation. Keywords: HVEM (TNFRSF14), LIGHT (TNFSF14), LTR (TNFRSF3), DcR3 (TNFRSF6b), co-stimulation, transplantation, alloreactivity, graft rejection, graft versus host disease, cytotoxicity Introduction Human LIGHT (homologous to lymphotoxin, exhibits inducible expression and competes with HSV glycoprotein D for binding to herpesvirus entry mediator, a receptor expressed on T lymphocytes) is usually a member of the TNF superfamily transiently detected on human T cells upon activation (1,2) and immature dendritic cells (3,4). Mouse LIGHT Isosilybin is usually a type II transmembrane protein of 239 amino acids, with an extracellular region 74% comparable in amino acid sequence to human LIGHT (1,5). LIGHT can act as a costimulatory molecule independently of CD28 (3,4), fostering T cell proliferation in the mixed lymphocyte reaction and promoting the process of DC maturation as well (6). It can even augment antitumor activity directly (7) or indirectly through enhancing CTL activity against tumor cells (4). In line with the costimulatory activity of LIGHT, constitutive transgenic expression of LIGHT under the control of a T cell-specific promoter led to chronic inflammation of mucosal tissues (8,9). In contrast, gene deletion of LIGHT results in defective CD8 T cell proliferation and acquisition of CTL effector function, which is usually associated with prolonged graft survival in several allogeneic mouse models of transplantation (10-13). One of the LIGHT receptors is usually HVEM (TNFRSF14), which is usually broadly expressed on hematopoietic and non hematopoietic cells (14,15). HVEM is usually a type I transmembrane molecule with an extracellular portion divided into cysteine-rich domains (CRD1-4) (16-18) with distinct binding Isosilybin sites for its ligands. BTLA and CD160 bind to the CRD1 and part of the CRD2 of HVEM, and so does the viral protein gD of Herpes Simplex Virus (HSV) (19,20), whereas LIGHT interacts with CRD2 and CRD3 on opposite sides of the extracellular a part of HVEM (21). Furthermore, membrane LIGHT can be released by the action of a metalloprotease (22) and the soluble form of LIGHT binds to BTLA/HVEM complex and strengthens the molecular conversation, whereas engagement of membrane anchored HVEM by LIGHT in displaces BTLA from its conversation with HVEM and allows bidirectional co-stimulatory contacts between HVEM and LIGHT (1,23,24). The other well-characterized receptor of LIGHT is the LTR, which is usually expressed on follicular dendritic cells (FDCs), dendritic cells (DCs), macrophages, stromal cells and high endothelial venules (HEV) (25). LT CD4+CD3? inducer cells interact with LTR on stromal organizer cells to guide lymphoid organogenesis during development and, later on, stroma-derived LTR signaling is still essential for the maintenance of the lymphoid tissue structure (26,27). LT expression on activated CD4+ helper T cells (28) and LTR on DCs and B cells follows a similar pattern to that of CD40L and CD40 expression Isosilybin on T cells and antigen presenting cells respectively, suggesting that LT/LTR pathway may regulate the exchange of information between antigen presenting cells and T cells, and therefore participate in T cell activation and differentiation. LIGHT expressed on activated T cells may provide a licensing signal upon conversation with LTR expressed on DC (6) or on stromal cells that would in turn change the lymphoid tissue environment to achieve proper T cell priming. So far, there have been no reagents available capable to Rabbit Polyclonal to EPHA3/4/5 (phospho-Tyr779/833) specifically recognize conformational epitopes around the extracellular region of the mouse LIGHT, although reagents against human LIGHT are available (6), (29). In an attempt to define the therapeutic potential of targeting LIGHT in animal model systems, and to detect and follow membrane LIGHT expression, rat monoclonal antibodies against mouse LIGHT were raised and selected.