A soluble receptor for interleukin-1 beta encoded by vaccinia virus: a novel mechanism of virus modulation of the host response to infection

The ps/hr gene (B5R open reading frame homolog) of rabbitpox virus controls pock color, is a component of extracellular enveloped virus, and is secreted into the medium

Wild-type rabbitpox virus (RPV) produces red hemorrhagic pocks on the chorioallantoic membranes (CAMs) of embryonated chicken eggs. Like the crmA (SPI-2) gene of cowpox virus, disruption of the RPV ps/hr gene results in a mutant which produces white pocks on the CAMs. An examination of the properties of the RPV(ps/hr) mutant in cell culture also reveals a significantly reduced host range, defined as the inability to form plaques, compared with wild-type virus. One of several cell types on which RPV(ps/hr) mutants fail to produce plaques is chicken embryo fibroblasts, cells which have been traditionally used to propagate spontaneously arising white pock mutants isolated from CAMs. The inability of the RPV(ps/hr) mutant to form plaques in chicken embryo fibroblasts correlates with a failure of a low multiplicity of infection to spread to neighboring cells and to form extracellular enveloped virus (EEV), although the formation and yields of infectious intracellular naked virus appear relatively normal. The gene product of the ps/hr gene, initially synthesized as a 45-kDa glycoprotein, is found as a component of EEV, but not intracellular naked virus, and as a smaller, secreted soluble protein of 35 kDa. Production of the secreted 35-kDa protein was found to be independent of any viral morphogenesis, suggesting two distinct pathways for release of the ps/hr gene product from the cell, i.e., as a component of the EEV particle and as a separately secreted glycoprotein.

Cleavage of interleukin 1 beta (IL-1 beta) precursor to produce active IL-1 beta by a conserved extracellular cysteine protease from Streptococcus pyogenes

Streptococcal pyrogenic exotoxin B (SPE B), a conserved extracellular cysteine protease expressed by the human pathogenic bacterium Streptococcus pyogenes, was purified and shown to cleave inactive human interleukin 1 beta precursor (pIL-1 beta) to produce biologically active IL-1 beta. SPE B cleaves pIL-1 beta one residue amino-terminal to the site where a recently characterized endogenous human cysteine protease acts. IL-1 beta resulting from cleavage of pIL-1 beta by SPE B induced nitric oxide synthase activity in vascular smooth muscle cells and killed of the human melanoma A375 line. Two additional naturally occurring SPE B variants cleaved pIL-1 beta in a similar fashion. By demonstrating that SPE B catalyzes the formation of biologically active IL-1 beta from inactive pIL-1 beta, our data add a further dimension to an emerging theme in microbial pathogenesis that bacterial and viral virulence factors act directly on host cytokine pathways. The data also contribute to an enlarging literature demonstrating that microbial extracellular cysteine proteases are important in host-parasite interactions.

Virus infections in mice with targeted gene disruptions

The experimental dissection of the ways that the various cells and molecules of the immune system interact to promote virus clearance has been greatly facilitated by the availability of mice with targeted disruptions of key genes. New insights are emerging, and details of host resistance mechanisms that could only be inferred for the in vivo situation are now being clearly established.

Interleukin-1 type II receptor: a decoy target for IL-1 that is regulated by IL-4

Interleukin-1 (IL-1) interacts with cells through two types of binding molecules, IL-1 type I receptor (IL-1R I) and IL-1R II. The function of IL-1R II is unknown. In studies using monoclonal antibodies, IL-1 prolonged the in vitro survival of polymorphonuclear cells (PMN) through IL-1R I, and IL-4 antagonized the action of IL-1 by inducing expression and release of IL-1R II. Dexamethasone also induced expression and release of the IL-1R II in PMN. These results, together with the effect of antibodies to IL-1R on IL-1-induced production of cytokines in monocytes, indicate that IL-1 acts on myelomonocytic cells through IL-1R I and that IL-1R II inhibits IL-1 activity by acting as a decoy target for IL-1. The existence of multiple pathways of regulation emphasizes the need for tight control of IL-1 action.

Interleukin 1 signaling occurs exclusively via the type I receptor

Two receptors for the proinflammatory cytokine interleukin 1 (IL-1) have been cloned and characterized biochemically. While it has been well established that the type I (80-kDa) IL-1 receptor can mediate responses to IL-1, the function of the type II (60-kDa) IL-1 receptor has been unknown. In this manuscript we describe experiments designed to ask whether the type II receptor is capable of delivering a biological signal. We have examined two types of experimental situation: responses to IL-1 in cells which express predominantly the type II receptor, and responses to IL-1 which have been suggested previously in the literature to be mediated by type II receptors. In both situations we find that the responses instead are mediated via type I receptors. A blocking antibody against the type II receptor never inhibits, and in fact sometimes enhances, the responses. We conclude that a very small number of type I receptors is sufficient to mediate all of the actions of IL-1 which we have examined here and that the function of the type II receptor may not be to transduce signals.

Importance of interferons in recovery from mousepox

Gamma interferon is shown to be critical in recovery of C57BL/6 mice from mousepox. Anti-gamma interferon treatment of mice infected in the footpad with ectromelia virus resulted in enhanced spread to and efficient virus replication in the spleen, lungs, ovaries, and, especially, liver. All treated, infected mice died within a mean of 7 days, 2.5 days earlier than mice with severe combined immunodeficiency that were given a comparable infection. On the other hand, alpha interferon appeared not to have a major role in controlling virus replication in tissues examined, and beta interferon was important for virus clearance in the liver and ovaries but not the spleen. Either anti-alpha, beta interferon or anti-beta interferon antibody therapy resulted in only 25% mortality. Infected control mice survived but showed persistence of ectromelia virus at the site of infection (the footpad) and transient presence of the virus in the spleen, liver, lungs, and ovaries and in the fibroreticular but not lymphoid cells of the draining popliteal lymph node. Depletion of gamma interferon but not alpha and/or beta interferon resulted in a significant reduction in the numbers of splenic T (especially gamma delta-TCR+), B, and Mac-1+ cells, although the proportion of Mac-1+ cells in the spleen increased compared with control values. Depletion of alpha, beta, or gamma interferons did not severely affect the generation of virus-specific cytotoxic T-lymphocyte responses or natural killer cell cytolytic activity. This study, in which a natural virus disease model was used, underscores the crucial importance of gamma interferon in virus clearance at all stages of infection and in all tissues tested except the primary site of infection, where virus clearance appears to be delayed.

Presence of a novel primary response gene ST2L, encoding a product highly similar to the interleukin 1 receptor type 1

In the course of studying the ST2 gene, which was initially found to be expressed specifically at the G0/G1 transitional state in BALB/c-3T3 cells and was one of the primary response genes, we found another ST2-related mRNA, designated as ST2L, in serum-stimulated BALB/c-3T3 cells in the presence of cycloheximide. Nucleotide sequence analysis of the cloned ST2L cDNA revealed that it had an open reading frame encoding a polypeptide of 567 amino acids. A 5' region (1,028 nucleotides) of ST2L cDNA was identical with the ST2 cDNA, and a unique 3' region encoded a putative transmembrane domain of 24 amino acids and a cytoplasmic domain of 201 amino acids. The ST2 gene product is highly similar to the extracellular portion of IL-1 receptors type 1 and type 2, and the ST2L gene product shows a marked similarity with entire IL-1 receptor type 1.

African swine fever virus genome content and variability

A 55 kilobase pair (kb) region from the right end of the virulent African swine fever virus isolate, Malawi LIL20/1, has been sequenced. The 68 major open reading frames (ORFs) encoded are generally closely spaced and read from both DNA strands across the complete sequence. Comparison of the amino acid sequences of predicted ORFs with sequence databases identified 15 ORFs which encode proteins that are similar to proteins of known function. Two ORFs are homologous to copies of multigene family 360 (MGF360) and one ORF is homologous to copies of multigene family 110 (MGF110). Both of these multigene families have been described previously.

Interleukin-1 receptor antagonist

IL-1ra is the first described naturally occurring receptor antagonist of any cytokine or hormone-like molecule. IL-1ra is a member of the IL-1 family by three criteria: amino acid sequence homology of 26 to 30% to IL-1 beta and 19% to IL-1 alpha; similarities in gene structure; and common gene localization to human chromosome 2q14. Two structural variants of IL-1ra exist: sIL-1ra, a secretory molecule produced by monocytes, macrophages, neutrophils, fibroblasts, and other cells; and icIL-1ra, an intracellular molecule produced by keratinocytes and other epithelial cells, macrophages, and fibroblasts. IL-1ra production by monocytes, macrophages, and neutrophils may be regulated in a differential fashion with IL-1 beta. Human IL-1ra binds to both human IL-1RIs and IL-1RIIs on cell surfaces, although with 100-fold greater avidity to IL-1RIs. IL-1ra may bind preferentially to soluble IL-1RIs and not at all to soluble IL-1RIIs. IL-1ra competitively inhibits binding of both IL-1 alpha and IL-1 beta to cell surface receptors without inducing any discernible intracellular responses. All three forms of IL-1 may bind to IL-1 receptors in a similar fashion but IL-1ra may lack the secondary interactions necessary to trigger cell responses. A 100-fold or greater excess of IL-1ra over IL-1 may be necessary to inhibit biological responses to IL-1 both in vitro and in vivo. The roles of sIL-1ra and icIL-1ra in normal physiology or in host defense mechanisms remain unclear. The administration of IL-1ra blocks the effects of IL-1 in some animal models of septic shock, inflammatory arthritis, graft-versus-host disease, and inflammatory bowel disease. The preliminary results of clinical trials in humans indicate possible efficacy of IL-1ra in sepsis syndrome, rheumatoid arthritis, and GVHD.

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.