Herpesvirus entry mediator ligand (HVEM-L), a novel ligand for HVEM/TR2, stimulates proliferation of T cells and inhibits HT29 cell growth.

Herpesvirus entry mediator (HVEM), a member of the tumor necrosis factor (TNF) receptor family, mediates herpesvirus entry into cells during infection. Upon overexpression, HVEM activates NF-kappaB and AP-1 through a TNF receptor-associated factor (TRAF)-mediated mechanism. Using an HVEM-Fc fusion protein, we screened soluble forms of novel TNF-related proteins derived from an expressed sequence tag data base. One of these, which we designated HVEM-L, specifically bound to HVEM-Fc with an affinity of 44 nM. This association was confirmed with soluble and membrane forms of both receptor and ligand. HVEM-L mRNA is expressed in spleen, lymph nodes, macrophages, and T cells and encodes a 240-amino acid protein. A soluble, secreted form of the protein stimulates proliferation of T lymphocytes during allogeneic responses, inhibits HT-29 cell growth, and weakly stimulates NF-kappaB-dependent transcription.

A newly identified member of the tumor necrosis factor receptor superfamily with a wide tissue distribution and involvement in lymphocyte activation.

The tumor necrosis factor receptor (TNFR) superfamily consists of approximately 10 characterized members of human proteins. We have identified a new member of the TNFR superfamily, TR2, from a search of an expressed sequence tag data base. cDNA cloning and Northern blot hybridization demonstrated multiple mRNA species, of which a 1.7-kilobase form was most abundant. However, TR2 is encoded by a single gene which, maps to chromosome 1p36.22-36.3, in the same region as several other members of the TNFR superfamily. The most abundant TR2 open reading frame encodes a 283-amino acid single transmembrane protein with a 36-residue signal sequence, two perfect and two imperfect TNFR-like cysteine-rich domains, and a short cytoplasmic tail with some similarity to 4-1BB and CD40. TR2 mRNA is expressed in multiple human tissues and cell lines and shows a constitutive and relatively high expression in peripheral blood T cells, B cells, and monocytes. A TR2-Fc fusion protein inhibited a mixed lymphocyte reaction-mediated proliferation suggesting that the receptor and/or its ligand play a role in T cell stimulation.

Differential recognition by CD28 of its cognate counter receptors CD80 (B7.1) and B70 (B7.2): analysis by site directed mutagenesis.

CD28, which is a member of the immunoglobulin superfamily of molecules (IgSF), is a homodimer of two polypeptides containing a single V-like domain with short transmembrane and cytoplasmic regions. It serves as a co-signalling molecule for T cell activation through binding to its cognate counter-receptors CD80 and B70, expressed on antigen presenting cells. In the current study, we investigated the regions of CD28 which are involved in its interactions with CD80 and B70, using site directed mutagenesis, CD28 mAb epitope mapping, receptor based adhesion assays and direct binding of Ig-fusion proteins to cell surface receptors. Truncation or substitution of a stretch of a proline rich "hallmark" sequence, "MYPPPY", abrogates binding to CD80 or B70, while retaining CD28 mAb epitopes and cell surface expression. On an Ig-fold model of the CD28 V-domain, this fully conserved motif localizes to a CDR3-like region. Mutations introduced into other loops, including the CDRI-like and CDR2-like regions, had very little effect on CD80 or B70 binding. Mutations introduced within the predicted beta-strand regions caused loss of receptor expression. Conservative substitution of both the flanking tyrosine residues within the "MYPPPY" motif with phenylalanine, caused loss of binding to B70 but not to CD80. These results show that, although the same overall region on CD28 may be involved in the interactions with CD80 and B70, subtle but important differences distinguish recognition by the two molecules. These finding, along with previous observations on the differential pattern of expression and tissue distribution of CD80 and B70, support the contention that these molecules play distinct roles in the regulation of immune responses in vivo.