Interleukin 1 (IL-1) induces biosynthesis and cell surface expression of procoagulant activity in human vascular endothelial cells.

Human monocyte-derived interleukin 1 (IL-1) was found to be a potent inducer of procoagulant activity in cultured human vascular endothelium. IL-1-induced human umbilical vein endothelial cell procoagulant activity (HEC-PCA) was transiently expressed, manifest in intact cell monolayers, and required protein synthesis. Data obtained with coagulation factor-deficient plasma and a goat anti-human apoprotein III antiserum suggested that most, if not all, of IL-1-induced endothelial cell procoagulant activity is tissue factor-like. IL-1 induction of HEC-PCA may be important in the pathogenesis of intravascular coagulation in a variety of immunological and inflammatory conditions.

Proinflammatory responses are efficiently induced by homotrimeric but not heterotrimeric lymphotoxin ligands.

The cytokine, lymphotoxin [LT, tumor necrosis factor beta (TNF beta)] is a potent mediator of proinflammatory and tumoricidal activities. Soluble lymphotoxin is a complex of three LT alpha chains. Its receptors, TNF-R55 and TNF-R75, bind in clefts formed by adjacent identical LT alpha monomers. LT also exists as membrane anchored heterotrimers comprised of LT alpha and LT beta chains. The major and minor membrane forms, LT alpha 1 beta 2 and LT alpha 2 beta 1, respectively, bind a unique receptor, LT beta-R. As LT alpha 2 beta 1 expresses an LT alpha-alpha cleft, it also binds TNF-R. In this report we have compared the effects of ligand engagement of TNF-R and LT beta-R by evaluating the ability of soluble LT alpha beta complexes to initiate activities of human umbilical vein endothelial cells which are characteristically signalled by TNF. We recently reported that soluble LT alpha 1 beta 2 signals via LT beta-R to mediate cytotoxicity of a subset of gamma interferon (IFN-gamma) treated carcinomas. We now show that human LT alpha beta heterotrimers do not efficiently activate LT beta-R+, TNF-R+ human endothelial cells in vitro and only inefficiently mediates lethal toxicity in mice. We also show that neither LT alpha beta heterotrimer signals via TNF-R; in fact LT alpha 2 beta 1 trimers fail to activate NF-kappa B and rather inhibit ligand-induced TNF-R signalling supporting the role for aggregation in TNF-R signalling. Thus, the ability of LT alpha beta complexes to efficiently initiate tumoricidal but not inflammatory activities distinguishes the LT/LT beta-R from the LT/TNF-R pathways and suggest novel strategies for exploiting the LT ligands in tumor therapy and for inhibiting TNF-R-mediated inflammatory sequellae.

Mechanism of lymphocyte function-associated molecule 3-Ig fusion proteins inhibition of T cell responses. Structure/function analysis in vitro and in human CD2 transgenic mice.

Soluble ligands specific for cell surface molecules involved in APC-T cell interactions can signal cells and modulate immune responses. Recently, we reported that LFA3TIP, a fusion protein comprised of the first LFA-3 extracellular domain fused to the hinge, CH2, and CH3 regions of a human IgG1 inhibits proliferation of human T cells in vitro. We report herein the cell-based mechanism(s) of LFA3TIP in inhibition by studying the effects of structurally altered LFA3-Ig fusion proteins on proliferation of human PBL in vitro and on responses of mice transgenic for human CD2. We show that LFA3TIP inhibition requires expression of both the LFA-3 and CH2 domains of the fusion protein that bind CD2 and Fc gamma RI or Fc gamma RIII, respectively. LFA3TIP forms an intracellular Fc gamma R/CD2 bridge and directs cytolysis of CD2+ cells by freshly drawn human PBL in vitro as well as the non-C-mediated depletion of peripheral T cells of human CD2 transgenic mice. The cell-based mechanism(s) of LFA3TIP inhibition are discussed.

Low affinity binding of an LFA-3/IgG1 fusion protein to CD2+ T cells is independent of cell activation.

Quantitative analysis of binding of the bivalent recombinant soluble fusion protein, LFA-3/IgG1, shows that the fusion protein binds to human CD2+ PBLs primarily through low affinity (KD approximately 140 microM) but also through high avidity (90 nM) interactions. The concentration dependence for LFA-3/IgG1 PBL binding took the form of two overlapping bell-shaped curves separated by a clear and reproducible minimum. This was accounted for in part by minor heterogeneity in the LFA-3/IgG1 preparations, and potentially by the ability of the ligand to bind to both CD2 and Fc receptors (FcR), best evidenced by the distinct binding properties of the fusion protein to NK and T cells. The low affinity LFA-3/ IgG1 binding to T cells is consistent with binding to CD2 only, and is in agreement with the low affinity reported for interactions between soluble forms of LFA-3 and CD2 by surface plasmon resonance technology. Moreover, as the low affinity determinations are similar for CD2 on resting and activated T cells, although the CD2 molecule has been reported to be altered to reveal new epitopes upon T cell activation, the binding data argue against multiple cell activation-dependent affinity states of CD2 for LFA-3 binding. This is distinct from that observed with other adhesion partners, and suggests that the different adhesion pathways utilize distinct mechanisms to mediate cell adhesion.

Lymphotoxin but not tumor necrosis factor functions to maintain splenic architecture and humoral responsiveness in adult mice.

To compare the function of the tumor necrosis factor (TNF) and lymphotoxin (LT)alpha/beta systems in the mature immune system, these two pathways were blocked with soluble receptor-immunoglobulin (R-Ig) fusion proteins in normal adult mice. Inhibition of LT alpha/beta signaling using LT betaR-Ig or a blocking monoclonal antibody against murine LT beta had profound effects. The spleen lacked discrete B cell follicles and the marginal zone was altered. Less marked changes were detected in lymph nodes. LT alpha/beta inhibition also prevented germinal center formation in the spleen and impaired Ig production in response to sheep red blood cells (SRBC) immunization. These results show that the LT alpha/beta system is required for the maintenance of splenic architecture and normal immune responses, and not simply for the development of peripheral immune organs during ontogeny. In contrast, inhibition of the TNF/LT alpha pathway with TNF-R55-Ig did not affect the splenic architecture or the anti-SRBC response. Splenic defects and impaired antibody responses are seen in TNF-deficient mice, suggesting that TNF is important during development. Therefore relative to TNF, the LT system has the dominant influence on splenic organization and anti-SRBC Ig formation in the adult mouse.

Lymphotoxin beta receptor triggering induces activation of the nuclear factor kappaB transcription factor in some cell types.

NFkappaB is a pleiotropic transcription factor capable of activating the expression of a great variety of genes critical for the immunoinflammatory response. Tumor necrosis factor alpha (TNFalpha) and lymphotoxin alpha (LTalpha, originally TNFbeta) are potent nuclear factor kappaB (NFkappaB) activators in various cell types. The LTalpha molecule, in addition to being secreted as a soluble trimer, can also form membrane-anchored heterotrimers with the LTbeta chain, another member of the TNF family. The LTalpha1beta2 heterotrimer binds a specific receptor, called the LTbeta receptor (LTbeta-R), which is also a member of the TNF receptor family. Here, we show that engagement of LTbeta-R with a soluble form of LTalpha1beta2 or with a specific anti-LTbeta-R agonistic monoclonal antibody CBE11 quickly induces activation of NFkappaB in HT-29 and WiDr human adenocarcinomas. LTbeta-R triggering activates NFkappaB and induces proliferation in WI-38 human lung fibroblasts. No NFkappaB activation is observed in human umbilical vein endothelial cells, correlating with the inability of LTbeta-R activation to induce expression of NFkappaB-dependent cell surface adhesion molecules. Thus, like several other members of the TNF receptor family, the LTbeta-R can activate NFkappaB following receptor ligation in some but not all LTbeta-R-positive cells.

Recombinant tumor necrosis factor induces procoagulant activity in cultured human vascular endothelium: characterization and comparison with the actions of interleukin 1.

Human recombinant tumor necrosis factor (rTNF) was found to act directly on cultured human vascular endothelium to induce a tissue factor-like procoagulant activity (PCA). After a 4-hr incubation in rTNF (100 units/ml), serially passaged endothelial cells isolated from umbilical veins, saphenous veins, iliac arteries, and thoracic aortae demonstrated a dramatic increase (4- to 15-fold, 21 experiments) in total cellular PCA as measured with a one-stage clotting assay. rTNF-induced PCA was also expressed at the surface of intact viable endothelial monolayers. Induction of PCA by rTNF was concentration dependent (maximum, 500 units/ml), time dependent, reversible, and blocked by cycloheximide and actinomycin D, and it occurred without detectable endothelial cell damage. Actions of rTNF were compared with those of natural human interleukin 1 (IL-1) derived from stimulated monocytes and two distinct species of recombinant IL-1, each of which also induced endothelial PCA. The use of recombinant polypeptides and specific neutralizing antisera established the distinct natures of the mediators. The kinetics of the endothelial PCA responses to TNF and IL-1 were similar, demonstrating a rapid rise to peak activity at approximately equal to 4 hr, and a decline toward basal levels by 24 hr. This characteristic decline in PCA after prolonged incubation with TNF or IL-1 was accompanied by selective endothelial hyporesponsiveness to the initially stimulating monokine. Interestingly, the effects of TNF and IL-1 were found to be additive even at apparent maximal doses of the individual monokines. Endothelial-directed actions of TNF, alone or in combination with other monokines, may be important in the initiation of coagulation and inflammatory responses in vivo.

Stimulation of human monocyte/macrophage-derived growth factor (MDGF) production by plasma fibronectin.

Culture supernatants from human peripheral blood monocytes, isolated free of platelet contamination and cultured in the absence of serum, stimulate DNA synthesis and cell growth in Balb/c 3T3 fibroblasts and bovine aortic smooth-muscle cells. Monocytes cultured in serum-free medium for 24 hours with plasma fibronectin, added as either a surface-attached or soluble molecule, secrete significantly increased amounts of growth-promoting activity. Fibronectin also stimulates an increase in intracellular growth factor content and in protein synthesis by monocytes. Both the enhanced growth-promoting activity and protein synthesis are inhibited by cycloheximide. Thus, fibronectin-monocyte interactions may influence the production of growth-promoting activity by monocytes and contribute to fibroblast and smooth-muscle replication in wound healing, chronic inflammation and atherosclerosis.

The effects of an immunomodulatory LFA3-IgG1 fusion protein on nonhuman primates.

LFA3TIP, a fusion protein comprised of the first extracellular domain of LFA-3 fused to the hinge, CH2 and CH3 domains of human IgG1, inhibits proliferation of human T cells in vitro. LFA3TIP also inhibits responses of human CD2 transgenic mice by rapidly and totally depleting peripheral T cells. These effects require binding of the LFA-3 and CH2 domains of LFA3TIP to CD2+ T cells and Fc gamma R+ accessory cells, respectively. As CD2 is well conserved in primate species, we evaluated the effects of LFA3TIP in nonhuman primates. We report in vitro results leading to the selection of the baboon as a model for analysis of LFA3TIP, and in vivo effects of single and multidose regimens of LFA3TIP administration. This is the first report of the in vivo administration of an immunomodulatory fusion protein to primates. LFA3TIP is shown to mediate effects on primate T lymphocytes without apparent related toxicities or immunogenicity. Results are discussed in context of potential mechanisms of LFA3TIP immunotherapy.

Immunomodulation by LFA3TIP, an LFA-3/IgG1 fusion protein: cell line dependent glycosylation effects on pharmacokinetics and pharmacodynamic markers.

LFA3TIP, a fusion protein comprised of the first extracellular domain of LFA-3 fused to the hinge, CH2, and CH3 domains of human IgG1 inhibits responses of human and non-human primate T cells in vitro. In seeking to optimize the expression efficiency to prepare large quantities of LFA3TIP for primate studies, the protein was produced in both the CHO (Chinese hamster ovary) and murine NS-0 myeloma cell lines. Although LFA3TIP derived from these cell lines performs identically in vitro in CD2 receptor binding and T cell assays, examination of a pharmacodynamic marker-the reduction in CD2+ lymphocyte numbers-following the administration of equal doses of NS-0 or CHO derived LFA3TIP to baboons, suggested that the effect of the NS-0 derived material was less sustained. Pharmacokinetic analysis of the materials in baboons and mice shows that LFA3TIP produced by NS-0 cells is rapidly cleared from circulation relative to the product derived from CHO cells. The disparate clearance profiles correlate with distinct glycosylation patterns, with LFA3TIP derived from NS-0 cells being less extensively sialylated than that from CHO cells due in part to alpha-galactosyl capping of selected lactosamine moieties in the N-linked glycans of NS-0 derived LFA3TIP. Moreover, enzymatic desialylation of CHO derived LFA3TIP results in a glycoprotein with an evanescent serum profile when administered to mice and baboons. These results correlate the extent of N-acetylneuraminic acid capping with the clearance rates of LFA3TIP derived from the two distinct cell lines, and underscore the importance of evaluating glycosylation dependent PK parameters when choosing production cell lines for recombinant immunotherapeutics.

Characterization of lymphotoxin-alpha beta complexes on the surface of mouse lymphocytes.

The lymphotoxin-alpha beta complex (LT alpha beta) is found on the surface of activated lymphocytes and binds to a specific receptor called the LT beta receptor (LT beta R). In the mouse, signaling through this pathway is important for lymph node development and splenic organization, yet the biochemical properties of murine LT alpha and LT beta are essentially unknown. Here we have used soluble receptor-Ig forms of LT beta R and TNF-R55 and mAbs specific for murine LT alpha, LT beta, and LT beta R to characterize the appearance of surface LT alpha beta complexes and LT beta R on several common murine cell lines. Cells that bound LT beta R also bound anti-LT alpha and anti-LT beta mAbs in a FACS analysis. The ability of these reagents to discriminate between surface TNF and LT was verified by analysis of surface TNF-positive, LPS-activated murine RAW 264.7 monocytic cells. Primary mouse leukocytes from spleen, thymus, lymph node, and peritoneum were activated in vitro, and CD4+ and CD8+ T cells as well as B cells expressed surface LT ligand but not the LT beta R. Conversely, elicited peritoneal monocytes/macrophages were surface LT negative yet LT beta R positive. This study shows that on mononuclear cells, surface LT complexes and receptor are expressed similarly in mice and man, and the tools described herein form the foundation for study of the functional roles of the LT system in the mouse.