Molecular cloning of the interleukin-1 beta converting enzyme

The role of cytokines in the pathophysiology of chronic liver diseases

Many of the biological activities of cytokines are similar to clinical manifestations and abnormalities of laboratory parameters observed in chronic liver diseases (CLD). Evidence of impaired cytokine synthesis in CLD comes from studies of serum or plasma levels, supernatants of peripheral blood mononuclear cells stimulated with various agents and from studying cytokine expression locally in the liver. Circulating levels of several cytokine-regulated molecules such as neopterin, soluble IL-2 receptor, adhesion molecules, and metabolites of the nitric oxide pathway are elevated in patients with CLD. Thus inhibition of cytokine synthesis or modulation of their activity could provide not only important information about their pathophysiologic relevance but also have a profound impact on disease progression in CLD. These studies will also show whether prolonged anti-cytokine treatment with interleukin-1- or tumor necrosis factor-inhibitors interferes with host defense mechanism.

U937 cells can utilize plasminogen activator to regulate human interferon-gamma

Urokinase-type plasminogen activator (uPA) converts the proenzyme plasminogen to plasmin and thereby contributes to processes like cell migration, tissue remodeling, and cytokine processing. We report here that uPA produced by the human U937 promonocytic cell line also initiated the inactivation of recombinant interferon-gamma (rIFN-gamma) by plasmin-mediated proteolysis. When cultured serum-free with plasminogen, U937 promonocytic cells generated measurable levels of plasmin activity and destroyed the antiviral activity of exogenously added rIFN-gamma. This effect was not seen in the absence of plasminogen, was prevented by inhibitors of uPA and plasmin, and was accompanied by changes in the electrophoretic mobility of rIFN-gamma on polyacrylamide gels, consistent with limited proteolysis of the lymphokine. Culturing U937 cells or blood monocytes for 48 h led to an elevated expression of their surface uPA and an increase in their capacity to produce plasmin and inactivate rIFN-gamma. The ability of rIFN-gamma to induce Fc receptors on U937 cells could also be prevented by providing the cells with a source of exogenous plasminogen, indicating that U937 cells could control their own activation in vitro through the action of uPA. The results of these studies support the conclusion that mononuclear phagocytes have the capacity to use uPA to regulate cytokine activity in vitro.

Production of interleukin-1 alpha and interleukin-2 by separate, phenotypically different leukaemia and human T cell lymphotropic virus-1-transformed T cell clones

The relationship between interleukin-1 (IL-1) and interleukin-2 (IL-2) production and immunophenotype marker profiles was studied in a panel of 29 leukaemia and human T cell lymphotropic virus-1 (HTLV-1)-transformed T cell lines. Culture supernatants from six of the 29 T cell lines tested increased IL-2 production by the MOLT-16 cell line in a manner similar to that of rIL-1 alpha or rIL-1 beta. The enhancing activity in the cell culture supernatants was inhibited by antibody against IL-1 alpha. Anti-IL-1 beta antibody had no inhibitory effect. All the cell lines producing IL-1 alpha had characteristics of activated mature T cells. They were terminal deoxyribonucleotidyl transferase (TdT)-, CD4+, CD8-, HLA-DR+ and all were strongly positive for IL-2R alpha (Tac antigen) expression. However, none of the IL-1 alpha producing cell lines secreted detectable IL-2. A significant quantity of IL-2 was found, after stimulation with phytohaemagglutinin, in supernatants from nine of the 29 cell lines tested. The majority of IL-2 producing cell lines originated from less mature, non-activated T cells, as they were characterized by the expression of TdT, lack of HLA-DR antigens and > 50% had no detectable IL-2R alpha. The results thus show that separate, phenotypically different leukaemia and HTLV-1-transformed T cell clones produce IL-1 alpha and IL-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the leucocyte in the pathogenesis of vascular disease

The leucocyte plays a key role in the local and systemic tissue injury that results from peripheral arterial disease and chronic venous insufficiency. Despite the apparent dissimilarities between limb ischaemia and chronic venous ulceration, in both diseases macrovascular abnormalities lead to microvascular leucocyte trapping and activation. Activated leucocytes adhere to and damage adjacent endothelium by expressing adhesion molecules and releasing harmful moieties such as proteases and free radicals. Subsequent loss of endothelial integrity and the migration of activated leucocytes outwith the circulation leads to destruction of surrounding tissue. Leucocytes and their products are also involved in the systemic manifestations of ischaemia such as multiple organ failure and coagulopathy. An overview of leucocyte biology as it pertains to peripheral arterial and venous disease is presented. The opportunities for novel therapeutic interventions based on a better understanding of this biology are also discussed.

Processing proIL-1 beta decreases detection by a proIL-1 beta specific ELISA but increases detection by a conventional ELISA

Recent investigations have noted that conventional IL-1 beta enzyme linked immunoassays (ELISA) may underestimate proIL-1 beta concentrations. In an attempt to circumvent this problem, we have devised a proIL-1 beta specific ELISA which sandwiches proIL-1 beta between a carboxy-terminus specific, capture antibody, and an amino-terminus specific, detection antibody. The amino-terminus specific antibody was generated against amino acids 3-21 of the intact proIL-1 beta molecule. This sandwich ELISA does not recognize mature 17 kDa IL-1 beta and is not inhibited by the coexistence of mature, 17 kDa IL-1 beta. We compared this proIL-1 beta specific ELISA (amino-terminus ELISA) to the conventional IL-1 beta ELISA (carboxy-terminus ELISA) on test samples that contained either proIL-1 beta or mature IL-1 beta. When purified proIL-1 beta is cleaved by increasing concentrations of IL-1 beta converting enzyme or porcine pancreatic elastase, there is a dose dependent increase in the signal from the conventional IL-1 beta ELISA and a concurrent decrease in signal from the proIL-1 beta specific ELISA. Furthermore, when the proIL-1 beta specific ELISA is used to quantify cellular sources of IL-1 beta, there is no detectable release of proIL-1 beta into the supernatants from either fresh blood monocytes or alveolar macrophages, despite detectable mature IL-1 beta. The cell associated compartment of IL-1 beta is largely proIL-1 beta and the relative amounts of IL-1 beta that remain intracellularly are quite large. Specifically, when assayed at 18 h, the proIL-1 beta ELISA detected 4.6 +/- 1.4 ng/ml per 10(6) monocytes and 13.8 ng/ml per 10(6) macrophages vs. 0.8 +/- 0.3 ng/ml/10(6) monocytes and 1.6 ng/ml/10(6) macrophages by conventional IL-1 beta ELISA. Thus, the 5-10-fold deficit in the detection of intracellular IL-1 beta by a conventional IL-1 beta ELISA, combined with the enhanced detection after enzymatic processing of proIL-1 beta, confirms that a proIL-1 beta specific ELISA is needed to accurately quantify proIL-1 beta.

Effects of serine protease inhibitor, TAME, on IL-1 beta in LPS-stimulated human monocytes: relationship between synthesis and release of a 33-kDa precursor and the 17-kDa biologically active species

LPS stimulation of human monocytes in vitro induced release of the 17-kDa mature IL-1 beta (mIL-1 beta) but did not result in release of precursor IL-1 beta (pIL-1 beta). In contrast, the presence of a serine protease inhibitor, N alpha-(p-toluene sulfonyl)-L-arginine methyl ester (TAME; 10 mM) for 6 or 18 h was associated with the LPS-stimulated release of the 33-kDa pIL-1 beta as well. These effects were initially discerned from observations that the fraction of the total IL-1 beta produced (as detected by ELISA) that was released from monocytes increased in the presence of TAME, and immunoblot assays confirmed that this fraction was predominantly 33-kDa IL-1 beta. A global decrease in monocyte protein synthesis was also observed after prolonged (18-h) exposure to TAME and was associated with a decrease in IL-1 beta synthesis, predominantly affecting 31-kDa pIL-1 beta, and a dose-dependent inhibition of TNF-alpha production. Parallel examination of lactate dehydrogenase (LDH) release indicated that pIL-1 beta release was unrelated to cell lysis. These results demonstrate that TAME-inhibitable serine proteases are probably involved in the production and eventual proteolysis of the 33-kDa pIL-1 beta in situ but are probably not mechanistically related to either maturation of the IL-1 beta molecule or signaling of IL-1 beta release. IL-1 beta release appears to be dependent on the amount of total IL-1 beta synthesized. Serine proteolysis may constitute a degradative pathway for excess precursor, which, if interfered with, could result in release of the higher-molecular-weight forms of IL-1 beta.

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.

The 31-kDa precursor of interleukin 1 alpha is myristoylated on specific lysines within the 16-kDa N-terminal propiece

The cytokine interleukin 1 alpha (IL-1 alpha) is a critical mediator of the immune and inflammatory responses. A unique determinant of its activity as compared with IL-1 beta may be its association with the plasma membrane. While the biologic activity of "membrane IL-1" has been extensively reported, the mechanism of membrane binding remains unclear. We report that the N terminus of the 31-kDa IL-1 alpha precursor is myristoylated on specific internal lysine residues. Immunoprecipitation of [3H]myristic acid-radiolabeled human monocyte lysates with IgG antibodies to the 31-kDa IL-1 alpha precursor recovered a protein with the physicochemical properties of the IL-1 alpha N-terminal propiece (16 kDa, pI 4.45). Glycyl N-myristoylation of this protein is precluded by the absence of a glycine residue at position 2, suggesting that the propiece is myristoylated on epsilon-amino groups of lysine. To determine which lysine(s) are acylated, a series of synthetic peptides containing all lysines found in the IL-1 alpha N-terminal propiece were used in an in vitro myristoylation assay containing peptide, myristoyl-CoA, and monocyte lysate as enzyme source. Analysis of the reaction products by reverse-phase HPLC and gas-phase sequencing demonstrated the specific myristoylation of Lys-82 and Lys-83, yielding predominantly monoacylated product. A conserved sequence in the IL-1 beta propiece was myristoylated with at least 8-fold less efficiency. Acylation of the IL-1 alpha precursor by a previously unrecognized lysyl epsilon-amino N-myristoyl-transferase activity may facilitate its specific membrane targeting.

Role of interleukin-1 inhibitory molecules in therapy of acute and chronic myelogenous leukemia

The poor outcome of conventional therapy of acute and chronic myelogenous leukemias (AML and CML) has prompted several groups to investigate new therapeutic directions. Data from various laboratories, including our own, indicate that both normal and leukemia precursors proliferate in response to growth factors. Furthermore, it has been shown that AML blasts, low-density cells from CML patients with advanced disease, and cultured bone marrow-adherent layers from CML blast crisis patients produce interleukin 1 (IL-1); this molecule may play a pivotal role in driving leukemia cell proliferation through autocrine or paracrine pathways. We have therefore hypothesized that interruption of the IL-1-mediated growth-stimulatory mechanism may suppress leukemia precursor multiplication. In searching for IL-1-inhibitory molecules that may be used clinically, we have investigated the in vitro effects of various IL-1 inhibitors including IL-1 receptor antagonist, soluble IL-1 receptors, and interleukin 4. Our studies suggest that IL-1 inhibitors can suppress clonogenic growth of cultured AML and CML progenitors and may hence be exploitable in clinical trials.

Regulation of the interleukin-1 beta (IL-1 beta) gene by mycobacterial components and lipopolysaccharide is mediated by two nuclear factor-IL6 motifs

The cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF-alpha) are released by mononuclear phagocytes in vitro after stimulation with mycobacteria and are considered to mediate pathophysiologic events, including granuloma formation and systemic symptoms. We demonstrated that the Mycobacterium tuberculosis cell wall component lipoarabinomannan (LAM) is a very potent inducer of IL-1 beta gene expression in human monocytes and investigated the mechanism of this effect. We localized the LAM-, lipopolysaccharide (LPS)-, and TNF-alpha-inducible promoter activity to a -131/+15 (positions -131 to +15) DNA fragment of the IL-1 beta gene by deletion analysis and chloramphenicol acetyltransferase assay. Within this DNA fragment, there were two novel 9-bp motifs (-90/-82 and -40/-32) with high homology to the nuclear factor-IL6 (NF-IL6) binding site. Site-directed mutagenesis demonstrated that the two NF-IL-6 motifs could be independently activated by LAM, LPS, or TNF-alpha and that they acted in an orientation-independent manner. DNA mobility shift assay revealed specific binding of nuclear protein(s) from LAM-, LPS-, or TNF-alpha-stimulated THP-1 cells to the NF-IL6 motifs. We conclude that the two NF-IL6 sites mediate induction of IL-1 beta in response to the stimuli LAM, LPS, and TNF-alpha.

Regulation of the interleukin-1 beta (IL-1 beta) gene by mycobacterial components and lipopolysaccharide is mediated by two nuclear factor-IL6 motifs

The cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF-alpha) are released by mononuclear phagocytes in vitro after stimulation with mycobacteria and are considered to mediate pathophysiologic events, including granuloma formation and systemic symptoms. We demonstrated that the Mycobacterium tuberculosis cell wall component lipoarabinomannan (LAM) is a very potent inducer of IL-1 beta gene expression in human monocytes and investigated the mechanism of this effect. We localized the LAM-, lipopolysaccharide (LPS)-, and TNF-alpha-inducible promoter activity to a -131/+15 (positions -131 to +15) DNA fragment of the IL-1 beta gene by deletion analysis and chloramphenicol acetyltransferase assay. Within this DNA fragment, there were two novel 9-bp motifs (-90/-82 and -40/-32) with high homology to the nuclear factor-IL6 (NF-IL6) binding site. Site-directed mutagenesis demonstrated that the two NF-IL-6 motifs could be independently activated by LAM, LPS, or TNF-alpha and that they acted in an orientation-independent manner. DNA mobility shift assay revealed specific binding of nuclear protein(s) from LAM-, LPS-, or TNF-alpha-stimulated THP-1 cells to the NF-IL6 motifs. We conclude that the two NF-IL6 sites mediate induction of IL-1 beta in response to the stimuli LAM, LPS, and TNF-alpha.

Modalities for reducing interleukin 1 activity in disease

The therapeutic advantage of reducing the activity of interleukin 1 (IL-1) resides in preventing its deleterious biological effects without interfering with homeostasis. As such, methods attempting to block the production or activity of IL-1 have now entered clinical trials. For example, IL-1 induction of prostaglandins is one target in treating disease, and drugs preventing the production of inhibiting cyclooxygenase have well-known toxicities because they block the normal synthesis of prostaglandins in many tissues. IL-1 blockading agents, in contrast, affect only that portion of prostaglandin synthesis due to elevated IL-1, sparing the synthesis of these molecules for homeostasis. Here we review the unique pharmacological advantages of manipulating IL-1.

Mechanisms of stimulation of interleukin-1 beta and tumor necrosis factor-alpha by Mycobacterium tuberculosis components

The granulomatous immune response in tuberculosis is characterized by delayed hypersensitivity and is mediated by various cytokines released by the stimulated mononuclear phagocytes, including tumor necrosis factor-alpha (TNF alpha) and IL-1 beta. We have demonstrated that Mycobacterium tuberculosis cell wall component lipoarabinomannan (LAM), mycobacterial heat shock protein-65 kD, and M. tuberculosis culture filtrate, devoid of LPS as assessed by the Amebocyte Lysate assay, stimulate the production of TNF alpha and IL-1 beta proteins and mRNA from mononuclear phagocytes (THP-1 cells). The effect of LAM on the release of these cytokines was specific, as only LAM stimulation was inhibited by anti-LAM monoclonal antibody. Interestingly, we found that LAM and Gram-negative bacterial cell wall-associated endotoxin LPS may share a similar mechanism in their stimulatory action as demonstrated by inhibition of TNF alpha and IL-1 beta release by monoclonal antibodies to CD14. Anti-CD14 monoclonal antibody MY4 inhibited both TNF alpha and IL-1 beta release with LAM and LPS but no effect was observed with other mycobacterial proteins. An isotype antibody control did not inhibit release of cytokines under the same experimental conditions. M. tuberculosis and its components upregulated IL-1 beta and TNF alpha mRNAs in THP-1 cells. Nuclear run-on assay for IL-1 beta demonstrated that LAM increased the transcription rate. The induction of IL-1 beta was regulated at the transcriptional level, in which these stimuli acted through cis-acting element(s) on the 5' flanking region of the IL-1 beta genomic DNA. M. tuberculosis cell wall component LAM acts similarly to LPS in activating mononuclear phagocyte cytokine TNF alpha and IL-1 beta release through CD14 and synthesis at the transcriptional level; both cytokines are key participants in the host immune response to tuberculosis.

Modalities for reducing interleukin 1 activity in disease

The therapeutic advantage of reducing the activity of interleukin 1 (IL-1) resides in preventing its deleterious biological effects without interfering with homeostasis. As such, methods attempting to block the production or activity of IL-1 have now entered clinical trials. For example, IL-1 induction of prostaglandins is one target in treating disease, and drugs preventing the production of inhibiting cyclooxygenase have well-known toxicities because they block the normal synthesis of prostaglandins in many tissues. IL-1 blockading agents, in contrast, affect only that portion of prostaglandin synthesis due to elevated IL-1, sparing the synthesis of these molecules for homeostasis. Charles Dinarello reviews the unique pharmacological advantages of manipulating IL-1.

Identification of a serine protease which activates the mouse heart adenosine 5',5"',P1,P4-tetraphosphate receptor

We have previously demonstrated that a serine protease dependent processing step is required for activation of the 30-kDa adenosine 5',5"',P1,P4-tetraphosphate (Ap4A) receptor. However, monoclonal antibodies (Mabs) against a 212-kDa polypeptide inhibit Ap4A binding to its receptor [Walker et al. (1993) Biochemistry 32, 1264-1269]. SDS-PAGE followed by autoradiography of [3H]diisopropylfluorophosphate (DIPF) covalently attached to membrane fractions reveals that the serine protease is the 212-kDa polypeptide or a proenzyme. Mabs against the 30-kDa Ap4A receptor are identified that inhibit Ap4A binding to its membrane receptor. These Mabs do not recognize the 212-kDa membrane protein but recognize four membrane proteins with molecular masses of 67, 55, 42, and 30 kDa. These data suggest that the precursor for the Ap4A receptor is a 67-kDa polypeptide which undergoes multiple cleavage events, at least one by the 212-kDa protein.

Post-translational regulation of interleukin 1 beta secretion

In view of the key role played by interleukin 1 (IL-1) beta in inflammation, its production is likely to be precisely regulated. Previous studies have shown that IL-1 beta biosynthesis is controlled at the transcriptional and translational levels. We have investigated whether post-translational events also play a role in regulating the production of bioactive IL-1 beta. IL-1 beta, which lacks a signal sequence, is released by activated monocytes through a novel pathway of secretion, alternative to the classical endoplasmic reticulum-Golgi route. Secretion of mature 17 kDA IL-1 beta is increased when pulse-labelled activated monocytes are chased in the presence of heat-aggregated immunoglobulins or of various drugs. Febrile temperatures inhibit secretion of mature IL-1 beta, but only reduce its synthesis: treatment with cycloheximide restores secretion. Processing of the 33 kDa precursor to the 17 kDa mature molecule is inhibited when the external pH is 8 or higher: under these conditions, release of unprocessed, biologically inactive 33 kDa IL-1 beta is observed. Thus, secretion of IL-1 beta is regulated by post-translational mechanisms which operate at the level of both proteolytic processing and extracellular export.

Retinal pigment epithelial cells produce interleukin-1 beta and granulocyte-macrophage colony-stimulating factor in response to interleukin-1 alpha

The retinal pigment epithelium (RPE) is clinically involved in diverse ocular inflammatory diseases. Because perturbed RPE cells produce a variety of inflammatory substances, RPE cells may play an integral part in these diseases. Interleukin-1 (IL-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are pleiotropic cytokines with the ability to trigger numerous inflammatory responses. This report shows that cultured human RPE cells synthesize interleukin-1 beta (IL-1 beta) and GM-CSF in response to the potentially inflammatory cytokine, IL-1 alpha, but not to E. coli endotoxin. Control RPE cells made little or no mRNA or protein for either IL-1 beta or GM-CSF. Upon stimulation of the cells by IL-1 alpha, both IL-1 beta and GM-CSF mRNAs were readily apparent by 3 hours, persisted for over 24 hours, and were translated into immunologically detectable proteins. GM-CSF protein was secreted into the culture medium, whereas IL-1 beta protein remained cell associated. The IL-1 alpha-induced mRNA and protein production were inhibited by dexamethasone. These observations provide additional evidence that RPE cells are capable of playing a pivotal role during ocular inflammation.

Interleukin 1 beta (IL-1 beta) processing in murine macrophages requires a structurally conserved homologue of human IL-1 beta converting enzyme

Murine interleukin 1 beta (IL-1 beta) convertase (mICE) was identified in cytosolic extracts of peritoneal exudate cells (PECs) and macrophage cell lines. mICE cleaves both the human and mouse IL-1 beta precursors (pIL-1 beta) at sites 1 and 2 but fails to cleave a human pIL-1 beta (Asp116 to Ala) mutant at site 2, indicating that Asp is required to the left of the scissile bond. Ac-Tyr-Val-Ala-Asp-amino-4-methyl coumarin, patterned after site 2 of human pIL-1 beta, is a fluorogenic substrate for mICE, while the tetrapeptide aldehyde Ac-Tyr-Val-Ala-Asp-CHO is a potent inhibitor (Ki = 3 nM) that prevents generation and release of mature IL-1 beta by PECs (IC50 = 7 microM). Cloning of a full-length 1.4-kb cDNA shows that mICE is encoded as a 402-aa proenzyme (p45) that can be divided into a prodomain (Met1-Asp122), followed by a p20 subunit (Gly123-Asp296), a connecting peptide (Ser297-Asp314), and a p10 subunit (Gly315-His402). At the amino acid level, p45, p20, and p10 are 62%, 60%, and 81% identical with human IL-1 beta convertase (hICE). The active site Cys284 lies within a completely conserved stretch of 18 residues; however, Ser289 in hICE, which aligns with the catalytic region of serine and viral cysteinyl proteases, is absent from mICE. Expression in Escherichia coli of a truncated cDNA encoding Asn119-His402 generated active enzyme, which was autocatalytically processed at three internal Asp-Xaa bonds to generate a p20 subunit (Asn119-Asp296) complexed with either p11 (Ala309-His402) or p10. Recombinant mICE cleaves murine pIL-1 beta accurately at the Asp117-Val118 bond. The striking similarities of the human and murine enzymes will make it possible to assess the therapeutic potential of hICE inhibitors in murine models of disease.

Activation of the mouse heart adenosine 5',5"'-P1-P4-tetraphosphate receptor

We have previously demonstrated that mouse brain membrane fractions have a specific, saturable receptor for diadenylated nucleotides. Binding is specific for two adenosines, and the length of the phosphate bridge is critical, with four phosphates being optimal [Hilderman et al. (1991) J. Biol. Chem. 266, 6915-6918]. In this report, we demonstrate that adenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) binding to its receptor is dependent upon an activation step that requires divalent cations and a serine protease. Monoclonal antibodies (Mabs) are identified that inhibit Ap4A binding to its membrane receptor. These antibodies recognize a 212-kDa membrane protein. However, SDS-PAGE analysis of Ap4A cross-linked to membrane fractions reveals that Ap4A is not attached to the 212-kDa peptide but to a 30-kDa polypeptide. Appearance of the 30-kDa polypeptide is dependent on the activation step, and one of the inhibitory antibodies blocks its appearance. We suggest that the protease-dependent processing step involves cleavage of the 212-kDa component with the appearance of an active 30-kDa receptor.

Immunosuppressive therapy

Although Cyclosporin A has improved transplant outcome, its use has serious limitations due to its narrow therapeutic window. New approaches to broaden this window exploit alternative drug formulations, pharmacokinetic profiling and new immunosuppressive agents, such as Rapamycin and Brequinar, which act in a synergistic fashion. There is no evidence to suggest that the pharmacological alternative to Cyclosporin A, FK-506, displays a broader therapeutic window, although it may be tenfold more potent. Similarly, despite the specificity of the IgG2a mouse anti-human CD3 monoclonal antibody, it displays a significant range of clinical side effects, delayed therapeutic action and frequently stimulates generation of human anti-mouse monoclonal antibodies. Recent advances in monoclonal antibody technology seek not only to produce antibodies against determinants involved in alloactivation, but also to 'humanize' the antibodies for reduced side effects. The availability of this array of potential agents highlights the need to develop guidelines for clinical trial methodologies to address the unique needs and demands of organ transplantation.

Viral inhibition of inflammation: cowpox virus encodes an inhibitor of the interleukin-1 beta converting enzyme

Cowpox virus effectively inhibits inflammatory responses against viral infection in the chick embryo. This study demonstrates that one of the viral genes necessary for this inhibition, the crmA gene (a cytokine response modifier gene), encodes a serpin that is a specific inhibitor of the interleukin-1 beta converting enzyme. This serpin can prevent the proteolytic activation of interleukin-1 beta, thereby suppressing an interleukin-1 beta response to infection. However, the modification of this single cytokine response is not sufficient to inhibit inflammatory responses. This suggests that cowpox virus encodes several cytokine response modifiers that act together to inhibit the release of pro-inflammatory cytokines in response to infection. These viral countermeasures to host defenses against infection may contribute significantly to the pathology associated with poxvirus infections.