William C. Fanslow

ULBPs, Novel MHC Class I–Related Molecules, Bind to CMV Glycoprotein UL16 and Stimulate NK Cytotoxicity through the NKG2D Receptor

The human cytomegalovirus glycoprotein, UL16, binds to two members of a novel family of molecules, the ULBPs, and to the MHC class I homolog, MICB. The ULBPs are GPI-linked glycoproteins belonging to the extended MHC class I family but are only distantly related to MICB. The ULBP and MICB molecules are ligands for the activating receptor, NKG2D/DAP10, and this interaction is blocked by a soluble form of UL16. The ULBPs stimulate cytokine and chemokine production from NK cells, and expression of ULBPs in NK cell-resistant target cells confers susceptibility to NK cell cytotoxicity. Masking of NK cell recognition of ULBP or MIC antigens by UL16 provides a potential mechanism by which human cytomegalovirus-infected cells might evade attack by the immune system.

Herpesvirus Saimiri encodes a new cytokine, IL-17, which binds to a novel cytokine receptor

Herpesvirus Saimiri gene 13 (HVS13) exhibits 57% identity with the predicted sequence of a T cell-derived molecule termed CTLA8. Recombinant HVS13 and CTLA8 stimulate transcriptional factor NF-kappaB activity and Interleukin-6 (IL-6) secretion in fibroblasts, and costimulate T cell proliferation. An HVS13.Fc fusion protein was used to isolate a cDNA encoding a novel receptor that also binds CTLA8. This receptor is unrelated to previously identified cytokine receptor families. A recombinant soluble receptor inhibited T cell proliferation and IL-2 production induced by PHA, concanavalin A (conA), and anti-TCR MAb. These results define CTLA8 and HVS13 as novel cytokines that bind to a novel cytokine receptor. We propose to call these molecules IL-17, vIL-17, and IL-17R, respectively.

CD40 ligand gene defects responsible for X-linked hyper-IgM syndrome

The ligand for CD40 (CD40L) is a membrane glycoprotein on activated T cells that induces B cell proliferation and immunoglobulin secretion. Abnormalities in the CD40L gene were associated with an X-linked immunodeficiency in humans [hyper-IgM (immunoglobulin M) syndrome]. This disease is characterized by elevated concentrations of serum IgM and decreased amounts of all other isotypes. CD40L complementary DNAs from three of four patients with this syndrome contained distinct point mutations. Recombinant expression of two of the mutant CD40L complementary DNAs resulted in proteins incapable of binding to CD40 and unable to induce proliferation or IgE secretion from normal B cells. Activated T cells from the four affected patients failed to express wild-type CD40L, although their B cells responded normally to wild-type CD40L. Thus, these CD40L defects lead to a T cell abnormality that results in the failure of patient B cells to undergo immunoglobulin class switching.

CD30 antigen, a marker for Hodgkin's lymphoma, is a receptor whose ligand defines an emerging family of cytokines with homology to TNF

CD30 is a surface marker for neoplastic cells of Hodgkins lymphoma and shows sequence homology to members of the tumor necrosis factor (TNF) receptor superfamily. Using a chimeric probe consisting of the extracellular domain of CD30 fused to truncated immunoglobulin heavy chains, we expression cloned the cDNA cognate from the murine T cell clone 7B9. The encoded protein is a 239 amino acid type II membrane protein whose C-terminal domain shows significant homology to TNF alpha, TNF beta, and the CD40L. Cross-hybridization to an induced peripheral blood T cell cDNA library yielded the human homolog, which is 72% identical at the amino acid level. The recombinant human ligand enhances the proliferation of CD3-activated T cells yet induces differential responses, including cell death, in several CD30+ lymphoma-derived clones. The human and murine genes map to 9q33 and the proximal region of chromosome 4, respectively.

CD40 Ligand Is Required for Protective Cell-Mediated Immunity to Leishmania major

The CD40-CD40 ligand (CD40L) signaling process is a pivotal component of multiple immunoregulatory pathways. Although the role that CD40L plays in humoral immune responses is fairly well defined, its function(s) in cell-mediated responses in vivo has not been established. We investigated this issue by assessing the course of Leishmania major infection in CD40L knockout (CD40LKO) mice that were generated on a resistant background. In response to parasite challenge, CD40LKO mice developed ulcerating cutaneous lesions and failed to mount a vigorous Th1-like response. The impaired Th1-like response appears to be related to a defect in the ability of CD40LKO T cells to induce the production of IL-12 from macrophages. Treatment with exogenous IL-12 prevented disease progression in CD40LKO mice, and administration of recombinant CD40L provided partial protection against infection. Thus, a protective cell-mediated immune response to L. major appears to be dependent upon CD40L-induced IL-12 secretion by antigen-presenting cells.

A Novel TNF Receptor Family Member Binds TWEAK and Is Implicated in Angiogenesis

TWEAK is a member of the TNF ligand family that induces angiogenesis in vivo. We report cloning of a receptor for TWEAK (TweakR) from a human umbilical vein endothelial cell (HUVEC) library. The mature form of TweakR has only one hundred and two amino acids and six cysteine residues in its extracellular region. Five different assays demonstrate TWEAK-TweakR binding, and the interaction affinity constant (Kd) is within a physiologically relevant range of 2.3 +/- 0.1 nM. The TweakR cytoplasmic domain binds TRAFs 1, 2, and 3. Cross-linking of TweakR induces HUVEC growth, and mRNA levels are upregulated in vitro by a variety of agents and in vivo following arterial injury. Soluble TweakR inhibits endothelial cell migration in vitro and corneal angiogenesis in vivo.

CD40 ligand and its role in X-linked hyper-IgM syndrome

CD40 ligand (CD40L) on activated T cells binding to CD40 on B cells is of critical importance for Ig heavy-chain switching and rescue of B cells from apoptosis after somatic mutation in the germinal centre. Mutations in the CD40L gene are now known to cause X-linked hyper-IgM syndrome (HIGM1), an immunodeficiency characterized by the absence of serum IgG, IgA and IgE. In this review, we discuss how basic and clinical immunology have combined to provide major insights into the function of CD40 in T-B cell collaboration.

ULBP1, 2, 3: novel MHC class I‐related molecules that bind to human cytomegalovirus glycoprotein UL16, activate NK cells

New members of the extended MHC class I‐like family were identified based on their ability to bind human cytomegalovirus glycoprotein UL16 and/or their mutual homology. Soluble UL16 binding prteins (ULBP) competed with each other for binding to NK cells. Treatment of human and mouse NK cells with ULBP led to increased production of cytokines/chemokines, proliferation, cytotoxic activity and up‐regulation of activation‐associated surface molecules. The presence of ULBP during the stimulation phase of the CTL assay caused increased cytotoxic activity. Addition of soluble recombinant UL16 protein inhibited the biological activities mediated by ULBP, suggesting the existence of a novel mechanism utilized by CMV to evade elimination by the host immune system.

Effect of Nucleotide Restriction and Supplementation on Resistance to Experimental Murine Candidiasis

The influence of dietary nucleotides on susceptibility to candidiasis in mice was studied using two criteria: animal survival and recovery of viable Candida albicans organisms from the kidney and spleen. One-month-old mice were placed on one of five diets with varying nucleotide content. The results show that mice maintained on a nucleotide-free diet (NF) exhibit a significantly decreased mean survival time and a significantly increased viable organism recovery in the spleen following intravenous injection of graded inocula of C. albicans compared to mice fed diets containing RNA or uracil as a nucleotide source.

Incorporation of an Isoleucine Zipper Motif Enhances the Biological Activity of Soluble CD40L (CD154)

Recent progress in the understanding of immune function indicates that the interaction of CD40L with its receptor, CD40, plays a pivotal role in both humoral immunity and cell-mediated defense against pathogens. Functional studies of this interaction on both dendritic cells and malignant cells have demonstrated that CD40L also plays an important role in immune surveillance and anti-tumor immunity. CD40L exists in nature predominantly as a membrane-anchored molecule. To develop CD40L as a potential therapeutic, it is important to optimize soluble forms of this molecule that could be used in a clinical setting. Several reports have shown that soluble forms of CD40L, like CD40 antibodies, are biologically active. In the present report we demonstrate that the incorporation of an isoleucine zipper trimerization motif significantly enhances the biological activity of soluble CD40L.