A poxvirus protein that binds to and inactivates IL-18, and inhibits NK cell response

IL-18 induces IFN-gamma and NK cell cytotoxicity, making it a logical target for viral antagonism of host defense. We demonstrate that the ectromelia poxvirus p13 protein, bearing homology to the mammalian IL-18 binding protein, binds IL-18, and inhibits its activity in vitro. Binding of IL-18 to the viral p13 protein was compared with binding to the cellular IL-18R. The dissociation constant of p13 for murine IL-18 is 5 nM, compared with 0.2 nM for the cellular receptor heterodimer. Mice infected with a p13 deletion mutant of ectromelia virus had elevated cytotoxicity for YAC-1 tumor cell targets compared with control animals. Additionally, the p13 deletion mutant virus exhibited decreased levels of infectivity. Our data suggest that inactivation of IL-18, and subsequent impairment of NK cell cytotoxicity, may be one mechanism by which ectromelia evades the host immune response.

Shared resources between the neural and immune systems: semaphorins join the ranks

The semaphorin family of molecules contains members known to deliver guidance cues to migrating axons during development. Semaphorins also have been identified on the surface of hematopoietic cells and, interestingly, in the genomes of certain lytic viruses. Recent studies indicate that semaphorins bind with high affinity to at least two different receptor families and are biologically active on immune cells as well as neuronal cells.

Plexin A is a neuronal semaphorin receptor that controls axon guidance

The Semaphorins comprise a large family of secreted and transmembrane proteins, some of which function as repellents during axon guidance. Semaphorins fall into seven subclasses. Neuropilins are neuronal receptors for class III Semaphorins. In the immune system, VESPR, a member of the Plexin family, is a receptor for a viral-encoded Semaphorin. Here, we identify two Drosophila Plexins, both of which are expressed in the developing nervous system. We present evidence that Plexin A is a neuronal receptor for class I Semaphorins (Sema 1a and Sema 1b) and show that Plexin A controls motor and CNS axon guidance. Plexins, which themselves contain complete Semaphorin domains, may be both the ancestors of classical Semaphorins and binding partners for Semaphorins.

The Epstein-Barr virus BARF1 gene encodes a novel, soluble colony-stimulating factor-1 receptor

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus associated with infectious mononucleosis and several tumors. The BARF1 gene is transcribed early after EBV infection from the BamHI A fragment of the EBV genome. Evidence shown here indicates that the BARF1 protein is secreted into the medium of transfected cells and from EBV-carrying B cells induced to allow lytic replication of the virus. Expression cloning identified colony-stimulating factor-1 (CSF-1) as a ligand for BARF1. Computer-assisted analyses indicated that subtle amino acid sequence homology exists between BARF1 and c-fins, the cellular proto-oncogene that is the receptor for CSF-1. Recombinant BARF1 protein was found to be biologically active, and it neutralized the proliferative effects of human CSF-1 in a dose-dependent fashion when assayed in vitro. Since CSF-1 is a pleiotropic cytokine best known for its differentiating effects on macrophages, these data suggest that BARF1 may function to modulate the host immune response to EBV infection.

A poxvirus-encoded semaphorin induces cytokine production from monocytes and binds to a novel cellular semaphorin receptor, VESPR

The vaccinia virus A39R protein is a member of the semaphorin family. A39R.Fc protein was used to affinity purify an A39R receptor from a human B cell line. Tandem mass spectrometry of receptor peptides yielded partial amino acid sequences that allowed the identification of corresponding cDNA clones. Sequence analysis of this receptor indicated that it is a novel member of the plexin family and identified a semaphorin-like domain within this family, thus suggesting an evolutionary relationship between receptor and ligand. A39R up-regulated ICAM-1 on, and induced cytokine production from, human monocytes. These data, then, describe a receptor for an immunologically active semaphorin and suggest that it may serve as a prototype for other plexin-semaphorin binding pairs.

Molecular characterization of the human interleukin (IL)-17 receptor

Human interleukin 17 (hIL-17) is a T-cell derived cytokine that exhibits 63% amino acid sequence identity to mouse IL-17 (mIL-17) and 57% identity to a viral protein encoded by the herpesvirus saimiri (HSV) gene 13 (HVS13). The IL-17 family of proteins binds to a unique mouse receptor (mIL-17R). Using nucleic acid hybridization techniques, a cDNA encoding a human homologue of the mIL-17R (hIL-17R) was isolated from a human T cell library. The predicted amino acid sequence of the hIL-17R is 69% identical to the mIL-17R, shares no homology with previously identified cytokine receptor families, and exhibits a broad tissue distribution. The hIL-17R gene was localized to chromosome 22. Monoclonal antibodies (mAbs) generated against the hIL-17R were able to block the IL-17-induced production of cytokine from human foreskin fibroblast (HFF) cells. Binding studies suggest that recombinant hIL-17 binds to the hIL-17R with low affinity.

Epstein-Barr virus uses HLA class II as a cofactor for infection of B lymphocytes

Infection of B lymphocytes by Epstein-Barr virus (EBV) requires attachment of virus via binding of viral glycoprotein gp350 to CD21 on the cell surface. Penetration of the cell membrane additionally involves a complex of three glycoproteins, gH, gL, and gp42. Glycoprotein gp42 binds to HLA-DR. Interference with this interaction with a soluble form of gp42, with a monoclonal antibody (MAb) to gp42, or with a MAb to HLA-DR inhibited virus infection. It was not possible to superinfect cells that failed to express HLA-DR unless expression was restored by transfection or creation of hybrid cell lines with complementing deficiencies in expression of HLA class II. HLA class II molecules thus serve as cofactors for infection of human B cells.

The extracellular domain of the Epstein-Barr virus BZLF2 protein binds the HLA-DR beta chain and inhibits antigen presentation

The Epstein-Barr virus BZLF2 gene encodes a glycoprotein that associates with gH and gL and facilitates the infection of B lymphocytes. In order to determine whether the BZLF2 protein recognizes a B-cell-specific surface antigen, a soluble protein containing the extracellular portion of the BZLF2 protein linked to the Fc portion of human immunoglobulin G1 (BZLF2.Fc) was expressed from mammalian cells. BZLF2.Fc was used in an expression cloning system and found to bind to a beta-chain allele of the HLA-DR locus of the class II major histocompatibility complex (MHC). Analysis of amino- and carboxy-terminal deletion mutants of the BZLF2.Fc protein indicated that the first 90 amino acids of BZLF2.Fc are not required for HLA-DR beta-chain recognition. Site-directed mutagenesis of an HLA-DR beta-chain cDNA and subsequent immunoprecipitation of expressed mutant beta-chain proteins using BZLF2.Fc indicated that the beta1 domain, which participates in the formation of peptide binding pockets, is required for BZLF2.Fc recognition. The addition of BZLF2.Fc to sensitized peripheral blood mononuclear cells in vitro abolished their proliferative response to antigen and inhibited cytokine-dependent cytotoxic T-cell generation in mixed lymphocyte cultures. Flow-cytometric analysis of Akata cells induced to express late Epstein-Barr virus antigens indicated that expression of BZLF2 did not result in reduced surface expression levels of MHC class II. The ability of BZLF2.Fc to bind to the HLA-DR beta chain suggests that the BZLF2 protein may interact with MHC class II on the surfaces of B cells.

Herpesvirus saimiri open reading frame 14, a protein encoded by T lymphotropic herpesvirus, binds to MHC class II molecules and stimulates T cell proliferation

Herpesvirus saimiri (HVS) is an oncogenic, lymphotropic, gamma-herpesvirus that transforms human and simian T cells in vitro and causes lymphomas and leukemias in various species of New World primates. Nucleotide sequence analysis of the HVS genome revealed an open reading frame with 22% amino acid identity to the mouse mammary tumor virus 7 superantigen. In this study, we demonstrate that this open reading frame, HVS14, encodes a heavily glycosylated protein that is secreted. Both the HVS14 present in the supernatant of transfected cells and a chimeric HVS14.Fc fusion protein were found to bind to heterodimeric MHC class II HLA-DR molecules. The supernatant from HVS14-transfected cells induced the proliferation of human PBMC, which could be specifically inhibited by HVS14-specific mAbs. Purified peripheral blood T cells were induced to proliferate in the presence of accessory cells and HVS14-containing supernatant. Whereas the HVS14 protein stimulated T cell proliferation, the HVS14.Fc fusion protein blocked proliferative responses to soluble Ags in vitro. Collectively, these data indicate that HVS14 can function as an immunomodulator that may contribute to the immunopathology of HVS infection.

Herpesvirus saimiri open reading frame 14, a protein encoded by T lymphotropic herpesvirus, binds to MHC class II molecules and stimulates T cell proliferation

Herpesvirus saimiri (HVS) is an oncogenic, lymphotropic, gamma-herpesvirus that transforms human and simian T cells in vitro and causes lymphomas and leukemias in various species of New World primates. Nucleotide sequence analysis of the HVS genome revealed an open reading frame with 22% amino acid identity to the mouse mammary tumor virus 7 superantigen. In this study, we demonstrate that this open reading frame, HVS14, encodes a heavily glycosylated protein that is secreted. Both the HVS14 present in the supernatant of transfected cells and a chimeric HVS14.Fc fusion protein were found to bind to heterodimeric MHC class II HLA-DR molecules. The supernatant from HVS14-transfected cells induced the proliferation of human PBMC, which could be specifically inhibited by HVS14-specific mAbs. Purified peripheral blood T cells were induced to proliferate in the presence of accessory cells and HVS14-containing supernatant. Whereas the HVS14 protein stimulated T cell proliferation, the HVS14.Fc fusion protein blocked proliferative responses to soluble Ags in vitro. Collectively, these data indicate that HVS14 can function as an immunomodulator that may contribute to the immunopathology of HVS infection.

One step ahead of the game: viral immunomodulatory molecules

For decades cell biologists have relied on viruses to facilitate the study of complex cellular function. More recently, the tragedy of the AIDS epidemic has focused considerable human and financial resources on both virology and immunology, resulting in the generation of new information relating these disciplines. As the miracle of the mammalian immune system unfolds in the laboratory, the elegance of the mechanisms used by co-evolving viruses to circumvent detection and destruction by the host becomes inescapably obvious. Although many observation of virus-induced phenomena that likely contribute to the virus's escape of immune surveillance are still empirical, many other such phenomena have now been defined at the molecular level and confirmed in in vivo models. Immune modulators encoded within viral genomes include proteins that regulate antigen presentation, function as cytokines or cytokine antagonists, inhibit apoptosis, and interrupt the complement cascade. The identification of such gene products and the elucidation of their function have substantially strengthened our understanding of specific virus-host interactions and, unexpectedly, have contributed to the recognition of potent synergy between viruses, which can result in an unpredictable exacerbation of disease in co-infected individuals. Because many viral immune modulators clearly have host counterparts, viruses provide a valuable method for studying normal immune mechanisms. It is conceivable that an improved understanding of virus-encoded immunomodulators will enhance our ability to design reagents for use in therapeutic intervention in disease and in vaccine development.

Human IL-17: a novel cytokine derived from T cells

A cDNA encoding human IL-17 (hIL-17) was cloned from a CD4+ T cell library. The predicted 155-amino acids sequence contains an N-terminal signal peptide and exhibits 72% amino acid identity with HVS13, an open reading frame from a T-lymphotropic Herpesvirus saimiri, and 63% with murine CTLA8. High levels of hIL-17 were induced from primary peripheral blood CD4+ T cells upon stimulation. When expressed in CV1/EBNA cells, recombinant hIL-17 was secreted in both glycosylated and nonglycosylated forms. A hIL-17.Fc fusion protein and supernatants from cells transfected with hIL-17 induced IL-6 and IL-8 production and enhanced the surface expression of the intracellular adhesion molecule-1 (ICAM-1) in human fibroblasts.

Human IL-17: a novel cytokine derived from T cells

A cDNA encoding human IL-17 (hIL-17) was cloned from a CD4+ T cell library. The predicted 155-amino acids sequence contains an N-terminal signal peptide and exhibits 72% amino acid identity with HVS13, an open reading frame from a T-lymphotropic Herpesvirus saimiri, and 63% with murine CTLA8. High levels of hIL-17 were induced from primary peripheral blood CD4+ T cells upon stimulation. When expressed in CV1/EBNA cells, recombinant hIL-17 was secreted in both glycosylated and nonglycosylated forms. A hIL-17.Fc fusion protein and supernatants from cells transfected with hIL-17 induced IL-6 and IL-8 production and enhanced the surface expression of the intracellular adhesion molecule-1 (ICAM-1) in human fibroblasts.

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-kappa B 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.

Structural characteristics of CD40 ligand that determine biological function

CD40 ligand (CD40L) is a 33 kDa type II glycoprotein which is transiently expressed on the surface of T cells following activation. The demonstration that signals delivered by CD40L are essential for the process of affinity maturation and immunoglobulin isotype switching following antigenic challenge came from the study of X-linked hyper-IgM patients whose T cells cannot express functional CD40L. While some of the biological activities of CD40L, especially on B cells, can be mimicked by monoclonal antibodies (MAb) specific for CD40, it is becoming increasingly clear that CD40L also mediates various functional effects on other cell types. Not only are there distinctions between the activities of CD40L and CD40 MAb, but the manner in which CD40 is ligated appears to play an important part in the biological outcome of signaling through this receptor. In this review, we compare and contrast the activities which can currently be ascribed to CD40L and CD40 MAb and consider the role that ligand oligomerization plays in CD40-mediated signal transduction.

Cytokine and cytokine receptor genes 'captured' by viruses

Viruses have historically been used as tools to understand basic cellular functions. Recently viruses have been shown to encode genes whose protein products function to modulate the host immune system. Viral immune modulators can now be exploited for the purpose of further understanding cellular immune phenomena. These studies promise to provide a rich source of information for the cellular immunologist, the basic virologist, and the clinic.

Inhibition of human B-cell lymphoma growth by CD40 stimulation

CD40 is a molecule present on B lymphocyte lineage cells that is important in B-cell differentiation and activation. Signaling through CD40 has been shown to exert costimulatory signals on normal B cells resulting in proliferative and differentiation responses. Examination of several B-cell lymphomas showed cell-surface expression of the CD40 molecule. Incubation of these lymphomas with anti-CD40 antibodies resulted in significant growth inhibition in vitro. Cross-linking of the CD40 antibodies resulted in even greater inhibition of proliferation. A recombinant soluble human CD40 ligand was also shown to inhibit lymphoma proliferation. When various human B-cell lymphomas were transferred into mice with severe combined immune deficiency, the treatment of the mice with anti-CD40 antibodies resulted in significant increases in survival showing that anti-CD40 is efficacious after in vivo administration. Thus, CD40 stimulation by either the antibody or soluble ligand directly inhibits human B-cell lymphoma growth and therefore, may be of significant clinical use in their treatment.

Recombinant CD40 ligand exerts potent biologic effects on T cells

Murine and human CD40 ligand (CD40L) were recently cloned, expressed, and shown to possess potent activity on human and murine B cells, including stimulation of proliferation and Ig secretion in the presence of cytokines. In addition to its action on B lymphocytes, this report demonstrates that CD40L induced both CD4+ and CD8+ T cells isolated from murine lymphoid tissues to proliferate in the presence of submitogenic dosages of Con A, PHA, CD3 mAb, and TCR-alpha beta mAb. The presence of CD40L during suboptimal TCR stimulation resulted in increased expression of the activation Ags IL-2R alpha and CD69 and increased IL-2 production. Taken together, these results show that CD40L is a potent activator of murine T cells and suggest that CD40L is involved in the regulation of T cell function mediated through T:T cell interaction.

Recombinant CD40 ligand exerts potent biologic effects on T cells

Murine and human CD40 ligand (CD40L) were recently cloned, expressed, and shown to possess potent activity on human and murine B cells, including stimulation of proliferation and Ig secretion in the presence of cytokines. In addition to its action on B lymphocytes, this report demonstrates that CD40L induced both CD4+ and CD8+ T cells isolated from murine lymphoid tissues to proliferate in the presence of submitogenic dosages of Con A, PHA, CD3 mAb, and TCR-alpha beta mAb. The presence of CD40L during suboptimal TCR stimulation resulted in increased expression of the activation Ags IL-2R alpha and CD69 and increased IL-2 production. Taken together, these results show that CD40L is a potent activator of murine T cells and suggest that CD40L is involved in the regulation of T cell function mediated through T:T cell interaction.

CD40 expression in malignant plasma cells. Role in stimulation of autocrine IL-6 secretion by a human myeloma cell line

Myeloma is a neoplasia characterized by the accumulation of malignant plasma cells in the bone marrow. In these studies, we have demonstrated that CD40 is expressed in human myeloma cells and have used a recently established IL-6-dependent myeloma cell line, ANBL-6, to examine the potential function of CD40 expression in myeloma cells. In addition to its expression on the ANBL-6 cells, we show that CD40 is expressed on freshly isolated myeloma cells from seven of seven patients tested. To address the role of CD40 expression in myeloma cells, we have examined the responsiveness of the ANBL-6 cell line to a CD40-specific mAb, G28-5. This cell line has previously been shown to proliferate only in response to IL-6. Of interest in this study, G28-5 also induced proliferation of the ANBL-6 cells. This proliferation was substantially inhibited by an IL-6-neutralizing mAb. Analysis of ANBL-6 cell culture supernatants by ELISA demonstrated that G28-5-stimulated cells secreted significant levels of IL-6, whereas unstimulated cell culture supernatants contained undetectable levels of IL-6. Furthermore, CV-1/EBNA cells expressing the human CD40 ligand also induced the proliferation of the ANBL-6 cell line, an effect that was inhibited by the anti-IL-6 mAb. Lastly, RNA blot analysis demonstrated an increase in IL-6 message in G28-5-stimulated ANBL-6 cells over unstimulated cells. These results indicate that the primary mechanism of anti-CD40-stimulated proliferation of the ANBL-6 cells is the induction of autocrine IL-6 production. Moreover, these data suggest that the expression of CD40 in malignant plasma cells may play a role in tumor cell expansion, possibly by stimulating the induction of autocrine IL-6 secretion.

CD40 expression in malignant plasma cells. Role in stimulation of autocrine IL-6 secretion by a human myeloma cell line

Myeloma is a neoplasia characterized by the accumulation of malignant plasma cells in the bone marrow. In these studies, we have demonstrated that CD40 is expressed in human myeloma cells and have used a recently established IL-6-dependent myeloma cell line, ANBL-6, to examine the potential function of CD40 expression in myeloma cells. In addition to its expression on the ANBL-6 cells, we show that CD40 is expressed on freshly isolated myeloma cells from seven of seven patients tested. To address the role of CD40 expression in myeloma cells, we have examined the responsiveness of the ANBL-6 cell line to a CD40-specific mAb, G28-5. This cell line has previously been shown to proliferate only in response to IL-6. Of interest in this study, G28-5 also induced proliferation of the ANBL-6 cells. This proliferation was substantially inhibited by an IL-6-neutralizing mAb. Analysis of ANBL-6 cell culture supernatants by ELISA demonstrated that G28-5-stimulated cells secreted significant levels of IL-6, whereas unstimulated cell culture supernatants contained undetectable levels of IL-6. Furthermore, CV-1/EBNA cells expressing the human CD40 ligand also induced the proliferation of the ANBL-6 cell line, an effect that was inhibited by the anti-IL-6 mAb. Lastly, RNA blot analysis demonstrated an increase in IL-6 message in G28-5-stimulated ANBL-6 cells over unstimulated cells. These results indicate that the primary mechanism of anti-CD40-stimulated proliferation of the ANBL-6 cells is the induction of autocrine IL-6 production. Moreover, these data suggest that the expression of CD40 in malignant plasma cells may play a role in tumor cell expansion, possibly by stimulating the induction of autocrine IL-6 secretion.

CD40L: a multi-functional ligand

B cells can be stimulated to proliferate and differentiate in response to cell-contact dependent signals provided by activated, but not resting, T cells. In the human system, antibodies specific for the surface antigen CD40 induce similar B cell responses. The cloning of a ligand for CD40, and the generation of reagents which can block the interaction of this ligand with its receptor, have demonstrated that the major component of the contact-dependent signal leading to B cell activation is CD40 ligand. Studies of individuals lacking functional CD40 ligand have indicated that signaling through CD40 is essential for immunoglobulin (Ig) heavy chain switching and the production of all isotypes other than IgM. In addition to its activities on B cells, CD40 ligand is stimulatory for cells of monocyte and T lineages suggesting a pleiotropic role for CD40 ligand 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.

CD40 ligand is a T cell growth factor

CD40 ligand (CD40L) is a 33-kDa type II membrane glycoprotein induced on T cells upon activation. CD40L has previously been shown to induce proliferation of resting B cells, immunoglobulin (Ig) secretion from B cells cultured with cytokines and cytokine secretion and tumoricidal activity from monocytes. In this report CD40L is shown to be stimulatory for human T cells, inducing CD25 (p55 IL-2R) and CD40L expression on resting peripheral blood T cells, enhanced expression of these molecules and CD69 on CD3-activated cells and secretion of interferon-gamma, tumor necrosis factor-alpha and interleukin (IL)-2 from T cells cultured in the presence of a sub-mitogenic concentration of phytohemagglutinin A (PHA). Furthermore, stimulation with CD40L induces proliferation of CD3- or PHA-activated T cells of blood, tonsillar or thymic origin. A similar proliferative response is observed with CD4+ and CD8+ T cells and this effect is largely IL-2 independent. A soluble construct of the extracellular domain of the CD40L has similar activity to that of membrane-expressed ligand in the induction of T cell surface antigens and proliferation. The results presented here taken together with the various activities ascribed for CD40L on B cells and monocytes demonstrate that CD40L has pleiotropic biological activity for cells of the hemopoietic lineage.

Suppression of apoptosis in normal and neoplastic human B lymphocytes by CD40 ligand is independent of Bc1-2 induction

The tendency of isolated germinal center (GC) B cells to undergo apoptosis was suppressed by recombinant cell-bound CD40 ligand (CD40L): after 2 days at 37 degrees C, > 80% of cells remained viable in the presence of CD40L as compared to < 1% in control cultures. CD40L sustained a high rate of DNA synthesis in GC cells and was more effective than monoclonal antibody to CD40 in this regard. Group I Burkitt lymphoma (BL) cell lines induced to undergo apoptosis with anti-immunoglobulin or calcium ionophore were also protected by CD40L. In BL cells, this route of rescue was not accompanied by induction of Bc1-2 protein, the expression of which has been linked to hemopoietic cell survival. Bc1-2 was induced in GC cells responding to CD40L, but its appearance was a relatively late event not reaching significant levels over controls until day 2 of culture. Thus induction of Bc1-2 appears to be secondary to the survival signal imparted by CD40L. These findings are discussed in relation to a potential role for CD40L in supporting B cell tumors in vivo and the discovery that the molecular defect in the X-linked Hyper-IgM syndrome is targeted to the CD40L gene.

CD40 expression by human monocytes: regulation by cytokines and activation of monocytes by the ligand for CD40

CD40 is a member of the tumor necrosis factor (TNF) receptor family of cell surface proteins and was originally described as a B cell restricted antigen. Treatment of primary human monocytes with granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3), or interferon gamma (IFN-gamma) resulted in the induction of CD40 mRNA and enhancement of cell surface protein expression. CD40 was found to mediate monocyte adhesion to cells expressing recombinant CD40 ligand. CD40 ligand-transfected cells provided a potent costimulus for monocyte TNF-alpha and IL-6 production in the presence of GM-CSF, IL-3, or IFN-gamma, and enhanced IL-8 production stimulated by GM-CSF or IL-3. In addition, CD40 ligand-transfected cells acting in the absence of a costimulus induced monocytes to become tumoricidal against a human melanoma cell target. Collectively, these data indicate that CD40 ligand is pleiotropic with potent biological activity on monocytes.

Identification of a distinct low-affinity receptor for human interleukin-4 on pre-B cells

Biotinylated interleukin-4 (IL-4) was used to examine IL-4 receptor (IL-4R) expression on a range of human B-cell lines by flow cytometry. Using high concentrations of biotinylated IL-4, we have identified a novel low-affinity IL-4 receptor expressed at high levels on pre-B lines. Expression of this low-affinity receptor did not correlate with detected mRNA levels for the previously cloned receptor or with reactivity of two anti-human IL-4R monoclonal antibodies (MoAb). Radiolabeled IL-4 cross-linking studies using pre-B lines showed a doublet of 65 to 75 Kd in contrast to the 110- to 130-Kd molecule detected on cells expressing the cloned IL-4R. A soluble IL-4 binding protein (IL-4bp) was purified from the supernatants of three pre-B lines expressing the low-affinity receptor on their surface. IL-4bp could block both IL-4-mediated CD23 induction on tonsil B cells and IL-4-induced inhibition of proliferation of the pre-B line JM1. Partial N-terminal amino acid sequence was obtained from purified IL-4bp that confirmed this protein to be novel. A 12 amino acid peptide based on the IL-4bp sequence was used to produce a polyclonal antiserum that was reactive with purified IL-4bp, and also bound to the surface of pre-B cells but not to murine CTLL cells transfected with the human IL-4R. Blocking MoAb against the previously characterized high-affinity receptor inhibited IL-4-mediated proliferation of hIL-4R+ CTLL cells but had no effect on IL-4-induced inhibition of JM1 cell proliferation, and only partially inhibited IL-4-mediated CD23 and sIgM induction and proliferation of tonsil B cells. The data presented here provide evidence for a novel cell-surface expressed low-affinity IL-4R that also exists as a biologically active soluble IL-4 binding protein.

Human B cell proliferation and Ig secretion induced by recombinant CD40 ligand are modulated by soluble cytokines

Recombinant human CD40 ligand (hCD40L) was expressed on the surface of CV1/EBNA cells and examined for its ability to induce proliferation and Ig secretion from human B cells in the presence or absence of soluble cytokines. hCD40L was directly mitogenic in a dose-dependent fashion for purified tonsil B cells with maximal proliferation occurring at days 5 to 7. Proliferation induced by CD40L was significantly enhanced in the presence of IL-2, IL-4, or IL-10 and strongly suppressed by transforming growth factor-beta. Although IL-5, TNF-alpha, and IFN-gamma had no stimulatory effect in the presence of hCD40L alone, if IL-4 was also present in cultures, these cytokines enhanced the proliferative response above that seen with IL-4 alone. Interestingly, in the absence of IL-4, IFN gamma had an inhibitory effect on hCD40L-induced proliferation. Although CD40L alone did not enhance Ig secretion, addition of IL-2 or IL-10 to the cultures significantly elevated the levels of IgM, IgG1, and IgA that were observed. Addition of IL-4 to the cultures did not enhance secretion of these isotypes but had a weak inhibitory effect. However, CD40L-mediated induction of IgG4 and IgE was dependent on the presence of IL-4. Of the cytokines examined, only IL-10 enhanced IgE secretion under these conditions. Although transforming growth factor-beta only partially inhibited secretion of IgM, IgG1, and IgA, it was strongly suppressive for IgG4 and IgE production. Our data demonstrate that proliferation and Ig secretion induced in the presence of CD40L can be modulated in a positive and negative fashion by soluble cytokines. IL-2 and IL-10 specifically enhance IgM, IgG1, and IgA production although IL-4, despite costimulating B cell proliferation, does not augment secretion of these isotypes but provided an essential cosignal with CD40L for the production of IgG4 and IgE.

Recombinant CD40 ligand stimulation of murine B cell growth and differentiation: cooperative effects of cytokines

The ligand for the B cell surface antigen CD40 was recently cloned from a murine thymoma cDNA library and shown to be expressed on activated T cells. In this study, we investigate the biological effects of murine recombinant CD40 ligand. The recombinant CD40 ligand expressed on the CV-1/EBNA monkey fibroblast cell line directly activated resting B cell to express elevated levels of cell surface class II major histocompatibility complex and CD23 molecules. CD40 ligand also stimulated B cell proliferation, reaching maximal levels on day 2 of culture and declining thereafter. This effect was positively regulated by other cytokines, most notably interleukin (IL)-4 and IL-5. By itself, CD40 ligand had no effect upon immunoglobulin secretion by B cells. However, when B cells were treated with CD40 ligand plus cytokines, immunoglobulin secretion was stimulated in a cytokine-dependent and isotype-specific manner. IL-4 was a potent co-stimulator of IgE and IgG1 in the presence of CD40 ligand, and IL-5 acted synergistically with IL-4 in these responses as well as in IgM and IgG3 production. Taken together, the results indicate that CD40 ligand is a potent regulatory molecule for B cell growth and differentiation, and its activities are potentiated in a cytokine-specific manner.

Human B cell proliferation and Ig secretion induced by recombinant CD40 ligand are modulated by soluble cytokines

Recombinant human CD40 ligand (hCD40L) was expressed on the surface of CV1/EBNA cells and examined for its ability to induce proliferation and Ig secretion from human B cells in the presence or absence of soluble cytokines. hCD40L was directly mitogenic in a dose-dependent fashion for purified tonsil B cells with maximal proliferation occurring at days 5 to 7. Proliferation induced by CD40L was significantly enhanced in the presence of IL-2, IL-4, or IL-10 and strongly suppressed by transforming growth factor-beta. Although IL-5, TNF-alpha, and IFN-gamma had no stimulatory effect in the presence of hCD40L alone, if IL-4 was also present in cultures, these cytokines enhanced the proliferative response above that seen with IL-4 alone. Interestingly, in the absence of IL-4, IFN gamma had an inhibitory effect on hCD40L-induced proliferation. Although CD40L alone did not enhance Ig secretion, addition of IL-2 or IL-10 to the cultures significantly elevated the levels of IgM, IgG1, and IgA that were observed. Addition of IL-4 to the cultures did not enhance secretion of these isotypes but had a weak inhibitory effect. However, CD40L-mediated induction of IgG4 and IgE was dependent on the presence of IL-4. Of the cytokines examined, only IL-10 enhanced IgE secretion under these conditions. Although transforming growth factor-beta only partially inhibited secretion of IgM, IgG1, and IgA, it was strongly suppressive for IgG4 and IgE production. Our data demonstrate that proliferation and Ig secretion induced in the presence of CD40L can be modulated in a positive and negative fashion by soluble cytokines. IL-2 and IL-10 specifically enhance IgM, IgG1, and IgA production although IL-4, despite costimulating B cell proliferation, does not augment secretion of these isotypes but provided an essential cosignal with CD40L for the production of IgG4 and IgE.

The regulation of T cell-dependent antibody formation in vitro by CD40 ligand and IL-2

Our study demonstrates the central role for the murine CD40 ligand and IL-2 in contact-dependent T cell help for Ag-specific primary antibody responses in vitro. Helper T cell clones were found to express CD40 ligand after activation with CD3 mAb. Membrane-bound recombinant CD40 ligand expressed on fixed CV1/EBNA cells had similar B cell-activating properties as T cell clones that had been activated and then fixed. These activities include the induction of B cell proliferation, induction of polyclonal secretion of multiple Ig isotypes in a cytokine-dependent manner, and induction of Ag-specific antibody responses by purified B cells. The induction of polyclonal Ig secretion by the recombinant CD40 ligand required IL-4 and IL-5 although optimal Ag-specific antibody formation required IL-2. Finally, soluble CD40.Fc inhibited the induction of Ag-specific antibody responses by fixed, activated Th cell clones. The requirement for both CD40 ligand and IL-2 for induction of Ag-specific antibody responses was mediated, in part, by the induction of B cell IL-2R expression by CD40 ligand. We conclude that the interaction of CD40 on B cells with its ligand on activated T cells is an integral event in the early activation of B cells to grow and differentiate to antibody formation.

The regulation of T cell-dependent antibody formation in vitro by CD40 ligand and IL-2

Our study demonstrates the central role for the murine CD40 ligand and IL-2 in contact-dependent T cell help for Ag-specific primary antibody responses in vitro. Helper T cell clones were found to express CD40 ligand after activation with CD3 mAb. Membrane-bound recombinant CD40 ligand expressed on fixed CV1/EBNA cells had similar B cell-activating properties as T cell clones that had been activated and then fixed. These activities include the induction of B cell proliferation, induction of polyclonal secretion of multiple Ig isotypes in a cytokine-dependent manner, and induction of Ag-specific antibody responses by purified B cells. The induction of polyclonal Ig secretion by the recombinant CD40 ligand required IL-4 and IL-5 although optimal Ag-specific antibody formation required IL-2. Finally, soluble CD40.Fc inhibited the induction of Ag-specific antibody responses by fixed, activated Th cell clones. The requirement for both CD40 ligand and IL-2 for induction of Ag-specific antibody responses was mediated, in part, by the induction of B cell IL-2R expression by CD40 ligand. We conclude that the interaction of CD40 on B cells with its ligand on activated T cells is an integral event in the early activation of B cells to grow and differentiate to antibody formation.

Independent binding of interleukin-1 alpha and interleukin-1 beta to type I and type II interleukin-1 receptors

Interleukin (IL)-1 refers to a group of three polypeptide hormones with a wide range of cellular targets. Two types of IL-1 receptor have been identified and characterized by cDNA cloning. Both human type I and type II IL-1 receptors contain extracellular domains of approximately 310 residues and a single membrane-spanning region. The type I receptor contains a cytoplasmic domain of 213 residues. The cytoplasmic region of the type II receptor is 29 residues in length. It has been found recently that a number of cells express both forms of receptor. By analogy with other cytokine receptor systems, the two IL-1 receptors might be expected to form a heterodimeric complex, the type II receptor being an alpha-chain-like structure, functioning only to bind ligand, and associating with the type I receptor (a beta-chain-like structure) which would transduce signals. In this report we show that this is not the case, but rather that IL-1, when complexed to type II receptor, cannot bind type I receptors, and vice versa. These data show that the complex patterns often observed for IL-1 binding to cells cannot be accounted for by the same type of mechanism that underlies the behavior of, for example, the IL-2 system.

Recombinant human CD40 ligand stimulates B cell proliferation and immunoglobulin E secretion

Signaling through the cell surface molecule, CD40, is known to play an important role in the proliferation and differentiation of B lymphocytes. Using the thymoma cell line EL4, we recently identified and cloned a cDNA encoding a murine ligand for the CD40 molecule (mCD40-L) and showed that it has biological activity in vitro. A cDNA encoding a human homologue of the mCD40-L was isolated using crosshybridization techniques from an activated peripheral blood T cell library. The predicted amino acid sequence indicates that this human ligand for CD40 (hCD40-L) is a 261 amino acid type II membrane protein that exhibits 78% amino acid identity with its murine counterpart. Northern blot and FACS analyses suggest that the hCD40-L is restricted in its expression to T lymphocytes, and that it is most abundant on the CD4+ T cell subpopulation. Cells transfected with hCD40-L caused the proliferation of human tonsil B cells in the absence of costimuli and, in the presence of interleukin 4, induced immunoglobulin E secretion from purified human B cells. A comparison of the efficacy of the hCD40-L and mCD40-L in these assays is presented.

Vaccinia and cowpox viruses encode a novel secreted interleukin-1-binding protein

Supernatants from vaccinia virus (VV)-infected CV-1 cells were examined and found to contain a 33 kd protein capable of binding murine interleukin-1 beta (mIL-1 beta). A VV open reading frame (ORF) that exhibits 30% amino acid identity to the type II IL-1 receptor was expressed in CV-1-EBNA cells and shown specifically to bind mIL-1 beta. A similar ORF from cowpox virus was expressed and also specifically bound mIL-1 beta. A recombinant VV was constructed in which this ORF was disrupted (vB15RKO). Supernatants from vB15RKO-infected cells did not contain an IL-1-binding protein. Supernatants from VV-infected CV-1 cells were capable of inhibiting IL-1-induced murine lymphocyte proliferation in vitro while supernatants from vB15RKO infected cells did not. Intracranial inoculation of mice with vB15RKO suggests that this ORF is involved in VV virulence. The possible role of a virus-encoded IL-1-binding protein in the pathology of a poxvirus infection and its relationship to other poxvirus-encoded immune modulators is discussed.

Beta 2-microglobulin-, CD8+ T-cell-deficient mice survive inoculation with high doses of vaccinia virus and exhibit altered IgG responses

Transgenic mice lacking an intact beta 2-microglobulin (beta 2m) gene fail to express major histocompatibility complex (MHC) class I proteins on the cell surface and, as a result, are virtually devoid of CD4- CD8+ lymphocytes. These animals provide a unique model system for directly assessing the role of CD8+ lymphocytes in the modulation of viral infection in vivo. beta 2m- CD8- mice and their normal littermates were inoculated at the base of the tail with the WR strain of vaccinia virus and monitored for serum antibody and lesion formation. Both groups developed similar lesions in response to a broad virus dose range, and all animals had completely recovered by day 28 after inoculation. Isotype-specific immunoglobulin levels were determined for each animal on day 7 and day 14 after primary inoculation, and again 7 days after a virus challenge. The virus-specific IgG1, IgG2a, and IgG2b levels were significantly different in the beta 2m-/- group (20-, 9-, and 30-fold lower, respectively, on day 7 after challenge) compared with the beta 2m+/- group. Virus-specific serum IgM levels for both groups remained similar throughout the experiment. In a separate experiment, beta 2m-/- mice were immunized with a nonviral antigen, 2,4,6-trinitrophenyl-conjugated keyhole limpet hemocyanin, and both total and antigen-specific isotype-specific immunoglobulin titers were determined. Total IgG1, IgG2a, IgG2b, and IgG3 tended to be lower overall in the beta 2m-/- mice compared with beta 2m+/- littermates. In contrast, total and antigen-specific IgE titers were similar in the two groups. These data indicate that CD8+ lymphocytes are not required to clear high doses of vaccinia virus, and they suggest that beta 2m-/- mice are less efficient at antigen-specific IgG production than their beta 2m+/- littermates.

Molecular characterization of the interleukin-1 receptor (IL-1R) on monocytes and polymorphonuclear cells

Primary human monocytes and monocytic cells express an interleukin 1 receptor (IL-1R) which is similar in molecular weight and IL-1 binding characteristics to the IL-1R expressed on B lymphocytes (type II). Northern blot analysis of monocytic cells using a cDNA probe from the recently isolated type II IL-1R indicates that this mRNA is detectable by 4 h and accumulates for at least 24 h following treatment with IL-1R inducing drugs. The time course of induction of this mRNA is slower than that of the type I IL-1R mRNA which is also transcribed in monocytic cells but does not appear to be translated. Sequence analysis of a monocyte-derived cDNA corresponding to the type II IL-1R mRNA shows that the monocyte and B-cell mRNAs are identical. Comparison of monocyte IL-1R peptide maps with those of the type II IL-1R suggests that the two surface IL-1R are identical. This was confirmed serologically using a polyclonal antiserum raised against the type II IL-1R. Data are presented which indicate that primary human neutrophils can also be induced to express abundant type II IL-1R.

Induction of an interleukin-1 receptor (IL-1R) on monocytic cells. Evidence that the receptor is not encoded by a T cell-type IL-1R mRNA

Primary human monocytes and the human monocytic cell line THP-1 were induced to express receptors for interleukin-1 alpha (IL-1 alpha) and IL-1 beta. Treatment of primary monocytes with dexamethasone resulted in a 10-fold increase in receptor number over untreated cells, to approximately 2,000 receptors/cell. Treatment of THP-1 cells with phorbol ester followed by prostaglandin E2 and dexamethasone resulted in the expression of approximately 30,000 receptors/cell. Competitive binding assays on THP-1 cells showed that both IL-1 alpha and IL-1 beta bind to the same receptor. The monocyte IL-1R is significantly smaller (63 kDa) than the T cell IL-1R (80 kDa) and is immunologically distinct. However, induction of monocytes and monocytic cell lines leads to the appearance of an abundant mRNA of approximately 5,000 bases which hybridizes to a cDNA probe from the T cell-type IL-1R. Sequence data obtained from a cDNA clone of this mRNA indicate that the message is identical to the T cell IL-1R mRNA throughout the coding region. A smaller mRNA, also homologous to the T cell IL-1R mRNA, accumulated in induced THP-1 cells and has a shorter 3'-untranslated region than the larger. Data are presented which suggest that neither form of this message encodes the 63-kDa IL-1R, but rather that this protein is the product of a separate nonhomologous mRNA.

Intracellular processing and transport of NH2-terminally truncated forms of a hemagglutinin-neuraminidase type II glycoprotein

Six amino-terminal deletion mutants of the NH2-terminally anchored (type II orientation) hemagglutinin-neuraminidase (HN) protein of parainfluenza virus type 3 were expressed in tissue culture by recombinant SV-40 viruses. The mutations consisted of progressive deletions of the cytoplasmic domain and, in some cases, of the hydrophobic signal/anchor. Three activities were dissociated for the signal/anchor: membrane insertion, translocation, and anchoring/transport. HN protein lacking the entire cytoplasmic tail was inserted efficiently into the membrane of the endoplasmic reticulum but was translocated inefficiently into the lumen. However, the small amounts that were successfully translocated appeared to be processed subsequently in a manner indistinguishable from that of parental HN. Thus, the cytoplasmic domain was not required for maturation of this type II glycoprotein. Progressive deletions into the membrane anchor restored efficient translocation, indicating that the NH2-terminal 44 amino acids were fully dispensable for membrane insertion and translocation and that a 10-amino acid hydrophobic signal sequence was sufficient for both activities. These latter HN molecules appeared to be folded authentically as assayed by hemagglutination activity, reactivity with a conformation-specific antiserum, correct formation of intramolecular disulfide bonds, and homooligomerization. However, most (85-90%) of these molecules accumulated in the ER. This showed that folding and oligomerization into a biologically active form, which presumably represents a virion spike, occurs essentially to completion within that compartment but is not sufficient for efficient transport through the exocytotic pathway. Protein transport also appeared to depend on the structure of the membrane anchor. These latter mutants were not stably integrated in the membrane, and the small proportion (10-15%) that was processed through the exocytotic pathway was secreted. The maturation steps and some of the effects of mutations described here for a type II glycoprotein resemble previous observations for prototypic type I glycoproteins and are indicative of close similarities in these processes for proteins of both membrane orientations.

Current approaches to the development of vaccines effective against parainfluenza and respiratory syncytial viruses

Vaccines against parainfluenza (PIV) and respiratory syncytial viruses (RSV) that are currently being developed include both live and subunit vaccines. Candidate live PIV vaccines that have been found to be attenuated and efficacious in rodents or primate models are (1) cold-adapted, temperature-sensitive mutants of PIV-type 3 that have been serially passaged at low temperature (20 degrees C) in simian kidney tissue culture; (2) protease-activation mutants (PIV-1-Sendai), which have mutations that decrease the cleavability of their F glycoprotein by host cell protease; (3) an animal virus, bovine PIV-3 virus, which is antigenically related to the human PIV-3 virus, and (4) vaccinia recombinant viruses bearing RSV or PIV-3 glycoproteins. Subunit RSV and PIV-3 viruses are being produced and evaluated as immunogens. A major concern with these vaccines is the possibility of disease potentiation following virus infection as occurred previously with formalin-inactivated measles and RSV vaccines. Studies indicate that PIV-3 and RSV glycoprotein vaccines are immunogenic and efficacious in animals but insufficient data exist to estimate their capacity to potentiate disease. However, since a cotton rat model is available to detect potentiated disease resulting from infection of cotton rats previously immunized with formalin-inactivated RSV vaccine, it is now possible to systematically evaluate new vaccines in experimental animals for disease potentiation before studies are initiated in humans. It is likely within the next several years that one or more of these PIV or RSV vaccines will be tested in humans for safety and immunogenicity.

Live viral vaccines for respiratory and enteric tract diseases

In its programme for accelerated development of vaccines for viral respiratory and enteric tract diseases the WHO has assigned a very high priority to respiratory syncytial virus (RSV), parainfluenza viruses and rotaviruses. There is also some interest in alternative approaches to immunization against influenza viruses because of the failure of inactivated vaccines to provide complete and reasonably durable immunity. Current attempts to develop satisfactorily attenuated viruses for use in prevention of disease caused by the above viral pathogens are described.

Immunization with vaccinia virus recombinants that express the surface glycoproteins of human parainfluenza virus type 3 (PIV3) protects patas monkeys against PIV3 infection

Patas monkeys (Eryphrocebus patas) were immunized intradermally with two vaccinia virus recombinants that individually express the hemagglutinin-neuraminidase glycoprotein or the fusion glycoprotein of human parainfluenza virus type 3 (PIV3). These immunizations induced a high titer of PIV3 serum-neutralizing antibodies. At 1 month after immunization, monkeys were challenged intratracheally with PIV3. Subsequent virus replication was reduced in these monkeys by 3.2 log10 and 1.9 log10 (mean peak virus titers) in the upper and lower respiratory tracts, respectively, compared with control animals. The average duration of virus shedding was also reduced from 9.0 to 3.4 days in the upper respiratory tract and from 5.3 to 1.2 days in the lower respiratory tract. These findings demonstrate that a single intradermal dose of live recombinant vaccinia viruses can significantly restrict the replication of a virus which primarily infects the epithelial cells of the respiratory tract.