Moreover, DC-HIL-SAP effectively inhibits an established CH response. == CH inhibition by DC-HIL-SAP is restricted to Ag at time of infusion == We next examined the immune reactivity of mice treated with DC-HIL-SAP to other haptens during their unresponsive state to the original hapten (Fig. produced almost total disappearance of SD-4+cells in haptenated skin and a 40% reduction of such cells within draining lymph nodes. Our results provide a strong rationale for exploring use of toxin-conjugated DC-HIL to treat activated T cell-driven disease in humans. Tlymphocyte activation is usually regulated by stimulatory and inhibitory signals transduced by binding of TCRs to corresponding ligands on APCs (1). Stimulatory receptors tend to be present constitutively even on resting T cells, whereas inhibitory receptors require activation for expression (2). Inhibitory receptors include CTLA-4 or CD152 (35), programmed cell death-1 (PD-1) (6,7), Rabbit Polyclonal to CHRNB1 B and T lymphocyte attenuator (810), and Tim-3 (1113). T cell expression profiles of these receptors overlap but are disparate; thus, CTLA-4 is expressed by almost all recently activated T cells, whereas PD-1 Mibefradil is restricted to effector T cells, and B and T lymphocyte attenuator and Tim-3 are expressed preferentially by Th1 cells. Moreover, because PD-1 is usually expressed at a sustained high-level by T cells undergoing exhaustion in chronic viral infections and in melanoma (1417), inhibitory receptors may serve as a marker for the functional state of T cells. We discovered and have characterized a novel inhibitory pathway composed of the highly glycosylated APC receptor dendritic cell-associated heparan sulfate proteoglycan-dependent integrin ligand (DC-HIL) and its exclusive T cell ligand syndecan-4 (SD-4) (1821). DC-HIL is also known as glycoprotein nmb (22), osteoactivin (23), and hematopoietic growth factor-inducible neurokinin-1 type (24). DC-HIL specifically recognizes a particular structure Mibefradil of heparan sulfate on SD-4 peculiar to T cells because it does not bind B cells, which constitutively express SD-4 at a high level (21). SD-4 shares with PD-1 a requirement for T cell activation for its expression (19). In the mouse contact hypersensitivity (CH) model for T cell-mediated immunity, SD-4 is usually expressed by CD4+and CD8+T cells within draining lymph nodes (DLNs) after hapten challenge (and not during hapten sensitization) (20). Inhibiting the DC-HIL/SD-4 pathway in this model by infusing soluble DC-HIL results in enhanced CH responses when DC-HIL is usually given during challenge (but not during sensitization), consistent with expression of SD-4 on activated (but not resting) T cells. In this study, we again use the CH model to show that SD-4 is usually expressed by some (but not all) activated T cells and preferentially by effector memory T cells within DLNs and especially hapten-challenged skin. Moreover, we show that toxin-conjugated DC-HIL can suppress an activated T cell-driven response by depleting SD-4+T lymphocytes. Our studies provide a foundation for manipulating the DC-HIL/SD-4 pathway Mibefradil to therapeutically deplete effector memory T cells. == Materials and Methods == == Mice == Female BALB/c (69 wk aged) mice were purchased from Harlan Breeders (Indianapolis, IN). Following National Institutes of Health guidelines, these animals were housed and cared for in the pathogen-free facility of the Institutional Animal Care Use Center of University of Texas Southwestern Medical Center, Dallas, TX. All animal protocols were approved by the institutional review table. == Production of Fc-fused recombinant proteins == A plasmid vector (pSTB-DC-HIL-Fc) encoding the extracellular domain name of DC-HIL fused to the Fc portion of human IgG1was constructed as reported previously (19). The Fc-fusion protein (DC-HIL-Fc) was produced in COS-1 cells and purified as explained previously (19). Purity of final preparations was high (19), as judged by a single band (120 kDa) in SDS-PAGE/Coomassie blue staining or in immunoblotting with goat anti-human IgG Ab or 1E4 rat antiDC-HIL mAb (19). == Conjugation of saporin with Fc protein == DC-HIL-Fc or human IgG1was biotinylated using EZ-link NHS-Biotin (Pierce, Rockford, IL) following manufacturer’s recommendations. Normally, one Fc protein molecule has one to two biotin molecules. Biotinylated Fc protein was then conjugated with streptavidin-saporin (SAP) (Advanced Targeting System, San Diego, CA) by mixing them with each other at a molecular ratio (Fc-protein:SAP) of 5:1. Resulting SAP conjugates are referred to as DC-HIL-SAP and Ig-SAP, respectively. == Abs == Mibefradil mAbs against CD4 (L3T4), CD8 (53-6.7), CD19 (eBio 1D3), and CD69 (H1.2F3).