IL-1b

24 Pages·2000·0.383 MB·English

by  DinarcIIo C.

IL-1(cid:12)
Charles A. Dinarello*
Department of Infectious Diseases, University of Colorado Health Sciences Center,
4200 East Ninth Avenue, B168, Denver, CO 80262, USA
*corresponding author tel: [phone], fax: [phone], e-mail: [email protected]
DOI: 10.1006/rwcy.2000.04004.
BACKGROUND other biological properties. These are reviewed in
detail in Dinarello (1989). Before the molecular
Discovery cloning of IL-1(cid:12), this molecule was characterized by
itsisoelectricpointof7.0todistinquishitfromIL-1(cid:11)
which hadan isoelectric pointof5.2(Dinarelloet al.,
The ‘discovery’ of IL-1(cid:12) is found in the literature on
1974; Hanson and Murphy, 1984). After the cloning
the pathogenesis of fever. Although initially con-
of human, mouse, rabbit, and other species of IL-1(cid:12)
cernedwiththepyrogenicpropertiesofgram-negative
and IL-1(cid:11), the two members of the IL-1 family of
bacterial endotoxins, pyrogenic protein of endogen-
agonistswereidentifiedbytheiraminoacidsequences
ous origin and free of endotoxins was described in
which, indeed, reveal that IL-1(cid:12) and IL-1(cid:11) have
1948. The first studies were carried out by Paul
isoelectric points of 7 and 5, respectively.
Beeson in 1948 on the fever-producing properties of
rabbit peritoneal exudate cells (Beeson, 1948). The
historical events were reviewed by Atkins in 1960 Structure
(Atkins, 1960) and again more recently (Dinarello,
1999). Many people think that IL-1(cid:12) was first des-
IL-1(cid:12) is initially synthesized as a precursor molecule
cribedbyWaksmanandGery(1972),butthatimpor-
(31,000) without a signal peptide. Mature IL-1(cid:12) is a
tant discovery was related to the ability of IL-1(cid:12) to
17,500Da molecule. Although the IL-1(cid:12)-converting
act as a co-activator of lymphocyte proliferation, the
enzyme (ICE) is primarily responsible for cleavage of
least durable property of IL-1 compared to its role in
theprecursorintracellularly(Blacketal.,1988),other
inflammation. The fact remains that the most potent
proteases can process the IL-1(cid:12) precursor into an
endogenous pyrogen and inducer of the so-called
active cytokine (reviewed in Fantuzzi et al., 1997a).
‘acute phase response’ in rabbits and humans is, in
Proteinase 3 processes the IL-1(cid:12) precursor extra-
fact, IL-1(cid:12) and this molecule was first described for
cellularlytoanactivemolecule(Coeshottetal.,1999)
its role in fever and the acute phase response
(Figure 1).
(Merriman et al., 1977).
Main activities and
Alternative names
pathophysiological roles
IL-1(cid:12) was originally studied as an endogenous pyro-
gen (EP, fever production) (Murphy et al., 1974; The biological activities of IL-1(cid:12) are similar to those
Dinarello et al., 1977), leukocyte endogenous medi- of IL-1(cid:11) and the distinction should be made that IL-
ator (LEM, an inducer of hepatic acute phase 1(cid:12) is a secreted molecule (via ICE) whereas IL-1(cid:11) is
reactants) (Merriman et al., 1977), mononuclear cell primarily a cell-associated molecule. However, there
factor (MCF, an inducer of collagenases and PGE ) are no biological activities of IL-1(cid:12) that are not
2
(Dayer et al., 1977), lymphocyte-activating factor observed with IL-1(cid:11) and vice versa. Any reports of
(LAF, a costimulator of T and B lymphocyte differences between these two molecules in terms of
proliferation)(GeryandWaksman,1972)andseveral biological activities are due to species differences.
352 Charles A. Dinarello
Figure 1 Production and processing of IL-1(cid:12). obtained human blood monocytes and macrophage
cell lines derived from myelomonocytic leukemias.
The initial studies established that endotoxin triggers
transienttranscriptionandsteadystatelevelsofIL-1(cid:12)
mRNA which accumulate for 4 hours followed by a
rapid fall due to synthesis of a transcriptional
repressor (Fenton et al., 1987, 1988). Unlike most
cytokine promoters, IL-1(cid:12) regulatory regions can be
found distributed over several thousand base pairs
upstream and a few base pairs downstream from the
transcriptional start site. The topic of IL-1(cid:12) gene
regulation has recently been reviewed in detail,
concluding that IL-1(cid:12) gene expression is regulated
at different levels (Auron and Webb, 1994).
Studies have revealed sequences in the IL-1(cid:12)
promoter required for transcription using a reporter
gene transfected into human and mouse macrophage
celllines.Therearetwoindependentenhancerregions
((cid:255)2782 to (cid:255)2729) (Tsukada et al., 1994) and ((cid:255)2896
to (cid:255)2846) (Shirakawa et al., 1993) which appear to
act cooperatively. The latter contains a cAMP
response element, whereas the former is a composite
It is best to characterize the biological activities of cAMP response element/NF-IL6 which is responsive
IL-1(cid:12) as being proinflammatory. Moreover, the to LPS. The 80bp fragment ((cid:255)2782 to (cid:255)2729) is
biological importance of IL-1 in pathophysiological requiredfortranscriptionandcontains,inadditionto
roles is best revealed by examining the effect of IL-1 a cAMP response element, an NF(cid:20)B-like site.
blockade in animal models of disease. Since the IL-1 Activating protein 1 (AP-1) sites also participate in
receptor antagonist (IL-1Ra) blocks the IL-1R, any endotoxin-induced IL-1(cid:12) gene expression.
reductionindiseaseseverityassociatedwithIL-1Rais Proximal promoter elements between (cid:255)131 and
due to the role of IL-1 in that disease. These are (cid:135)14havealsobeenidentified(Shirakawaetal.,1993).
discussed in detail under Role in experiments of Sequences in this region contain the binding sites for
nature and disease states. the novel nuclear factor NF(cid:20)A (Buras et al., 1994)
which appears to be similar to nuclear factors termed
NF(cid:12)1 and NF(cid:12)2 (Shirakawa et al., 1993). This
GENE AND GENE REGULATION proximal promoter is required for maximal IL-1(cid:12)
gene expression. Recently, the nucleotide-binding
Sequence sequences of NF(cid:12)A were found to be identical to
those of the transcription factor Spi-1/PU.1 (Fenton
etal.,1994;Kominatoetal.,1995),awell-established
The sequence of the human IL-1(cid:12) gene can be found
NF in cells of myeloid and monocyte lineage. The
in Clark et al. (1986).
requirementforSpi-1/PU.1forIL-1(cid:12) geneexpression
imparts tissue specificity, since not all cells constitu-
Chromosome location
tively express this NF. Human blood monocytes,
which constitutively express Spi-1/PU.1, are exqui-
See Webb et al. (1986). sitelysensitivetogeneexpressionofIL-1(cid:12)by1–10pg/
mL of LPS. Interestingly, the IL-1Ra promoter
Regulatory sites and corresponding contains the proximal Spi-1/PU.1 site (Auron and
Webb, 1994), which is also highly sensitive to LPS.
transcription factors
Cells and tissues that express
Unlike the promoter of IL-1(cid:11), the promoter region
the gene
forIL-1(cid:12) contains aclear TATAbox, atypical motif
of inducible genes. The half-life of IL-1(cid:12) mRNA
depends upon the cell type and the conditions of Although the blood monocyte and tissue macro-
stimulation. The most studied cells are freshly phages are the primary sources of IL-1(cid:12), in health,
IL-1(cid:12) 353
thesecellsdonotconstitutivelyexpressIL-1(cid:12)(Mileno bindingsite(Evansetal.,1994).Theformationofthe
etal.,1995;ShapiroandDinarello,1997;Purenetal., heterodimer consisting of the IL-1RI and IL-1R
1999). Reports of constitutive expression of IL-1(cid:12) in accessoryprotein(IL-1RAcP)(Greenfederetal.,1995)
health are due to the activation of the IL-1(cid:12) probably explains the failure of IL-1Ra to trigger a
transcriptional process by surface contact (Schindler signal.Fromthestructuraldifferencesdescribedabove
etal.,1990a).However,thereseemstobeconstitutive between IL-1(cid:12) and IL-1Ra, one can propose that the
expression of IL-1(cid:12) in the human hypothalamus second binding site missing from the IL-1Ra is, in
(Brederetal.,1988).Manymalignanttumors,suchas fact, the site which binds the accessory protein. The
acute myelogenous leukemia (Cozzolino et al., 1989; crosslinked complex of radiolabeled IL-1Ra to the
Rambaldi et al., 1991; Estrov et al., 1993; Wetzler typeIreceptorwasnotprecipitatedbyaspecificanti-
et al., 1994) and juvenile myelogenous leukemia bodytotheaccessoryprotein(Greenfederetal.,1995).
(Schiro` et al., 1993), express IL-1(cid:12) as part of their Mutational analyses reveal two distinct areas
neoplastic nature. for binding to IL-1RI: site A and site B. For IL-1(cid:12),
site A is on the back side of the molecule (Gruetter
et al., 1994), whereas site B is at the open end of
PROTEIN the barrel. Site A on IL-1(cid:12) is shared with
Tyr16, Glu20, Tyr34, Glu36 and Tyr147 of IL-1Ra
Accession numbers (Evans et al., 1994). Site B, which in IL-1(cid:12)
comprises Arg4, Lys92/Lys94, Gln48/Glu51, Lys103,
and Glu105 and has been proposed to form the
P01584
receptor ‘trigger site’. This site is missing from IL-
1Ra. It is likely, however, that signal transduction
Sequence
for the two IL-1 agonists results in conformational
changes in the IL-1RI when both A and B sites bind.
The primary sequence of the human IL-1(cid:12) precursor Therefore, the possession of a single binding area on
can be found in Auron et al. (1984). IL-1Ra may account for its binding and receptor
occupancy. Most importantly, without the second
Description of protein binding site, the critical amino acids for receptor
triggering may not become engaged and receptor
conformationsremainunchanged.Thiswouldexplain
IL-1(cid:12) is primarily translated as a precursor (31,000)
the failure of IL-1Ra to transduce a signal.
lacking a signal peptide (Auron et al., 1984). The IL-
A nonapeptide within the mature IL-1(cid:12) structure
1(cid:12) precursor requires cleavage by the IL-1(cid:12)-convert-
which possesses immunostimulatory properties is
ing enzyme (ICE) (Black et al., 1988), also known
absent from IL-1Ra (Antoni et al., 1986, 1989). A
as caspase 1 (Alnemri et al., 1996). Mature IL-1(cid:12),
single point mutation in the carboxyl end of the
molecular weight 17,500Da, has a sequence N-
IL-1Ra molecule (lysine to aspartic acid) converts
terminus at alanine 117 and is biologically active.
IL-1Ra from an antagonist to a partial agonist
The propiece of IL-1(cid:12) is thought to have biological
(Ju et al., 1991) but this may be due to malfolding of
activities (Higgins et al., 1993).
the molecule. In general, it appears that no single
amino acid substitution accounts for the differences
Discussion of crystal structure
between the binding and signal transduction of IL-1
compared to IL-1Ra.
Crystal structural analysis of the mature form of
IL-1(cid:12) reveals that the molecule is comprised of all (cid:12)
Important homologies
sheets (Priestly et al., 1988). IL-1(cid:12) has two sites of
binding to IL-1 receptor type I (IL-1RI). There is a
primary binding site located at the open top of its The relevant homology of IL-1(cid:12) are to the acidic
barrel shape (Gruetter et al., 1994), which is similar fibroblast growth factor (Murzin et al., 1992) and to
but not identical to that of IL-1(cid:11) (Lambriola- IL-18 (Okamura et al., 1995). Also, IL-1(cid:12) shares
Tomkins et al., 1993). There is a second site on the homology to soybean trypsin inhibitor. The (cid:12)-barrel
back side of the IL-1(cid:12) molecule (Gruetter et al., structure of IL-1(cid:12) is closely related to that of
1994). IL-1Ra also has two binding sites similar to fibroblast growth factor (Murzin et al., 1992) which
thoseofIL-1(cid:12) (Evansetal.,1994;Vigersetal.,1994). possesses some IL-1-like activities. The primary
However, the back side site in IL-1Ra is more amino acid homology of mature human IL-1(cid:12) to
homologous to that of IL-1(cid:12) than the primary mature IL-1(cid:11) is 22%. Importantly, IL-1(cid:12) is more
354 Charles A. Dinarello
closely related to IL-1Ra than to IL-1(cid:11); the homo- discussion on the soluble IL-1 receptor type II, it is
logy of IL-1(cid:12) to IL-1Ra is 26%. Since each member pointed out that the affinity of proIL-1(cid:12) for this
of the IL-1 family binds to the same IL-1 receptors, constitutively produced soluble receptor is high and
it is not surprising that IL-1(cid:11), IL-1(cid:12), and IL-1Ra may prevent haphazard cleavage of the precursor by
share structural topology. For example, Arg4 and these enzymes in inflammatory fluids.
Arg12 of mature IL-1(cid:12) and IL-1(cid:11), respectively, The cDNA encoding ICE has been reported
are required for binding and biological activity (Cerretti et al., 1992). The 45kDa precursor of ICE
and both arginines occupy the same relative loca- requires two internal cleavages before becoming the
tion in their respective crystallographic structures enzymatically active heterodimer composed of a 10
(Nanduri et al., 1991). IL-1(cid:11) can act as a receptor anda20kDachain.Theactivesitecysteineislocated
antagonist of biological responses to IL-1(cid:12) (Boraschi on the 20kDa chain. ICE itself contributes to auto-
et al., 1990). Changing the aspartic acid at tyrosine processing of the ICE precursor by undergoing
151 in the mature IL-1(cid:11) results in loss of PGE oligomerization with itself or homologs of ICE
2
induction and fibroblast growth but the T cell (Wilson et al., 1994; Gu et al., 1995). In the presence
responses are unaffected (Yamayoshi et al., 1990). of a tetrapeptide competitive substrate inhibitor of
ICE, the generation and secretion of mature IL-1(cid:12)
is reduced and precursor IL-1(cid:12) accumulates mostly
Posttranslational modifications
inside but also outside the cell (Thornberry et al.,
1992). This latter finding supports the concept that
The primary translational product of the IL-1(cid:12) gene proIL-1(cid:12) can be released from a cell independent of
isaprecursor(31,000)lackingasignalpeptide(Auron processing by ICE. Methods for measuring IL-1(cid:12)
et al., 1984). The IL-1(cid:12) precursor requires intracel- detect primarily the mature form of IL-1(cid:12) (Herzyk
lular cleavage by the cysteine protease called the etal.,1992).Hence,agentsandconditionsreportedto
IL-1(cid:12)-converting enzyme (ICE) (Black et al., 1988), reducethesynthesisofIL-1(cid:12)may,infact,onlyinhibit
alsoknownascaspase1(Alnemrietal.,1966).Mature secretionofmatureIL-1(cid:12).Futhermore,preventionof
IL-1(cid:12), molecular weight 17,500Da, has a sequence the cleavage of the ICE precursor may also account
N-terminus at Ala117 and is biologically active. for an apparent inhibition of IL-1(cid:12) synthesis. Due to
Following synthesis, the IL-1(cid:12) precursor remains alternate RNA splicing, there are five isoforms of
primarily cytosolic until it is cleaved and transported humanICE (Alnemri et al., 1995): ICE(cid:11), (cid:12), (cid:13), (cid:14), and
out of the cell. The IL-1(cid:12) propiece (amino acids 1– ". ICE(cid:11) cleaves the ICE precursor and the IL-1(cid:12)
116) is myristoylated on lysine residues (Stevenson precursor; it is presumed that ICE(cid:12) and ICE(cid:13) also
et al., 1993). Some IL-1(cid:12) is found in lysosomes process precursor ICE. ICE" is a truncated form of
(Bakouche et al., 1987) or associated with micro- ICEwhichmayinhibitICEactivitybybindingtothe
tubules(Rubartellietal.,1990;Stevensonetal.,1992) p20 chain to form an inactive ICE complex.
andeitherlocalizationmayplayaroleinthesecretion Enhancement of processing and secretion can be
of IL-1(cid:12). In mononuclear phagocytes, a small alsoberegulated;addingATPtoLPS-stimulatedcells
amount of proIL-1(cid:12) is secreted from intact cells increases IL-1(cid:12) secretion whereas blocking anion
(Auron et al., 1987; Beuscher et al., 1990) but the transport reduces the secretion of mature IL-1(cid:12)
pathway for this secretion remains unknown. The (Laliberteet al., 1994),an effectwhich maybedueto
release of mature IL-1(cid:12) appears to be linked to inactivationofICE.Areductionincellularpotassium
processing by ICE (Black et al., 1988). is associated with increased processing of the IL-1(cid:12)
Although well-controlled in the setting of labora- precursor (Walev et al., 1995).
tory cell culture, death and rupture of inflammatory
cells is not an unusual occurrence in vivo. There are
several sites in the N-terminal 16kDa part of proIL-
1(cid:12)whicharevulnerabletocleavagebyenzymesinthe CELLULAR SOURCES AND
vicinityofAla117.Thesearetrypsin,elastase,chymo-
TISSUE EXPRESSION
trypsin, a mast cell chymase, and a variety of prote-
ases(Hazudaetal.,1990,1991),whicharecommonly
Cellular sources that produce
found in inflammatory fluids. Proteinase 3 also cuts
theIL-1(cid:12)precursorintoanactivemolecule(Coeshott
et al., 1999). The extent of the role that these prote- The primary sources of IL-1(cid:12) are monocytes,
ases play in the in vivo conversion of proIL-1(cid:12) to macrophages, and dendritic cells. B lymphocytes
mature forms is uncertain, but in each case a and NK cells are also sources. Keratinocytes will
biologically active IL-1(cid:12) species is produced. In the produce IL-1(cid:12) when stimulated, although these
IL-1(cid:12) 355
cells constitutively express IL-1(cid:11). Fibroblasts and alsoofTNF(cid:11)(Schindleretal.,1990a).Itappearsthat
epithelial cells generally do not produce IL-1(cid:12). theabovestimuliarenotsufficienttoprovideasignal
In health, circulating human blood monocytes or fortranslationdespiteavigoroussignalfortranscrip-
bone marrow aspirate do not constitutively express tion. Without translation, most of the IL-1(cid:12) mRNA
IL-1(cid:12) (Mileno et al., 1995; Shapiro and Dinarello, is degraded. Although the IL-1(cid:12) mRNA assembles
1997; Puren et al., 1999). Reports of constitutive into large polyribosomes, there is little significant
expressionofIL-1(cid:12)inhealthareduetotheactivation elongationofthepeptide(KasparandGehrke,1994).
of the IL-1(cid:12) transcriptional process by surface However, adding bacterial endotoxin or IL-1 itself to
contact (Schindler et al., 1990a). However, there cells with high levels of steady-state IL-1(cid:12) mRNA
seems to be constitutive expression of IL-1(cid:12) in the results in augmented translation (Schindler et al.,
human hypothalamus (Breder et al., 1988). Many 1990a, 1990c) in somewhat the same manner as the
malignant tumors express IL-1(cid:12) as part of their removal of cycloheximide following superinduction.
neoplastic nature, including acute myelogenous leuke- OneexplanationisthatstabilizationoftheAU-rich30
mia (Cozzolino et al., 1989; Rambaldi et al., 1991; untranslated region takes place in cells stimulated
Estrov et al., 1993; Wetzler et al., 1994) and juvenile with LPS. These AU-rich sequences are known to
myelogenous leukemia (Schiro` et al., 1993). suppress normal hemoglobin synthesis. The stabiliza-
tion of mRNA by microbial products may explain
why low concentrations of LPS or a few bacteria or
Eliciting and inhibitory stimuli, Borrelia organisms per cell induce the translation of
large amounts of IL-1(cid:12) (Miller et al., 1992).
including exogenous and
Another explanation is that IL-1 stabilizes its
endogenous modulators
own mRNA (Schindler et al., 1990b) by preventing
deadenylation as it does for the chemokine GRO(cid:11)
Nearly all microbes and microbial products induce (Stoeckle and Guan, 1993). Removal of IL-1 from
theproductionofIL-1(cid:12).Dependingonthestimulant, cells after 2 hours increases the shortening ofpoly(A)
IL-1(cid:12)mRNAlevelsriserapidlywithin15minutesbut and IL-1 apparently is an important regulator of
start to fall after 4 hours. This decrease is thought to gro synthesis because it prevents deadenylation. In
be due to the synthesis of a transcriptional repressor fact, of the several cytokines induced by IL-1, large
and/or a decrease in mRNA half-life (Fenton et al., amounts of the chemokine family are produced in
1988; Jarrous and Kaempfer, 1994). response to low concentrations of IL-1. For example,
Using IL-1 itself as a stimulant of its own gene 1pM of IL-1 stimulates fibroblasts to synthesize
expression, IL-1(cid:12) mRNA levels were sustained for 10nM of IL-8 (Shapiro et al., 1994).
over 24 hours (Schindler et al., 1990b; Serkkola and Studieshavetakenadvantageofpyridinyl-imidazol
Hurme, 1993). Raising cAMP levels in these same compounds which block the synthesis of IL-1(cid:12)
cells with histamine enhances IL-1(cid:11)-induced IL-1(cid:12) without affecting transcription or steady-state levels
gene expression and protein synthesis (Vannier and of mRNA. mRNA levels for either IL-1 or TNF(cid:11)
Dinarello, 1993). In human peripheral blood mono- in PBMCs stimulated with LPS in the presence of
nuclear cells (PBMCs), retinoic acid induces IL-1(cid:12) these compounds are indistinguishable from those in
geneexpression butthe primaryprecursor transcripts PBMCs stimulated with C5a, hypoxia, or adherence.
fail to yield mature mRNA (Jarrous and Kaempfer, In other words, there is ample cytokine mRNA but
1994). Inhibition of translation by cycloheximide nocytokineprotein.Theseareinterestingcompounds
results in enhanced splicing of exons, excision of whichhaveenteredclinicalmedicine.Somearecyclo-
introns, and increased levels of mature mRNA oxygenase/lipoxygenase inhibitors because, by classi-
(superinduction) by two orders of magnitude. Thus, fication, they block these enzymes. Hence they are
synthesis of mature IL-1(cid:12) mRNA requires an acti- oftencalled‘dualinhibitors’.However,theirmechan-
vation step to overcome an apparently intrinsic inhi- ismofactioninsuppressingIL-1andTNFhavenever
bition to process precursor mRNA. been linked to their ability to suppress either cyclo-
StimulantssuchasthecomplementcomponentC5a oxygenase or lipoxygenase (Sirko et al., 1991).
(Schindleretal.,1990c),hypoxia(Ghezzietal.,1991), These and other imidazol-like drugs have recently
adherence to surfaces (Schindler et al., 1990a) or been called ‘cytokine-suppressing anti-inflammatory
clotting of blood (Mileno et al., 1995) induce the drugs’orCSAIDs(Youngetal.,1994).TheseCSAID
synthesis of large amounts of IL-1(cid:12) mRNA in compoundsreduceIL-1andTNFtranslationbecause
monocytic cells without significant translation into they bind and inactivate a mitogen-activating protein
the IL-1(cid:12) protein. This dissociation between tran- (MAP) kinase (Lee et al., 1994). Like most MAP
scriptionandtranslationischaracteristicofIL-1(cid:12)but kinases, phosphorylation of serine/threonine residues
356 Charles A. Dinarello
on various proteins is observed; however, these large amounts of IL-1R AcP, the high-affinity bind-
CSAID-associated MAP kinases apparently phos- ing of the IL-1R/IL-1R AcP complex may explain
phorylate proteins which are required for translation why two classes of binding have been observed.
of cytokine mRNAs into their respective proteins Human, recombinant 17kDa IL-1(cid:12) binds more ad-
(Lee et al., 1994). They share homology with that of vidly to the nonsignal transducing type II receptor
the yeast hyperosmolarity glycerol 1 gene (HOG-1) (IL-1RII) at 100pM. IL-1(cid:12) binding to the soluble
and in the human are identical to the 38kDa MAP form of the IL-1RI is lower than to the cell-bound
kinase which is phosphorylated in cells stimulated receptor. However, the most dramatic differences in
with LPS or hyperosmolar concentrations of NaCl IL-1(cid:12) binding can be seen at the level of the soluble
(Galcheva-Gargova et al., 1994; Han et al., 1994, form of the type II receptor. Of the three ligands, the
1995). These HOG-1-related MAP kinases are also most avid binding is that of mature IL-1(cid:12) (500pM).
the same as those which are phosphorylated during By comparison, IL-1(cid:11) and IL-1Ra bind with 50-fold
IL-1 signal transduction (Freshney et al., 1994; or lower affinities. In addition to the highest affinity,
Kracht et al., 1994). Thus, these observations are IL-1(cid:12)bindingtoIL-1sRIIisnearlyirreversibledueto
consistent with the ability of IL-1 or LPS to augment a long dissociation rate (2 hours) (Arend et al., 1994;
the translation of cytokine mRNA (Schindler et al., Dower et al., 1994; Symons et al., 1994). Moreover,
1990c). Of relevance is that initiation factor eIF-4E pro-IL-1(cid:12) also preferentially binds to IL-1 soluble
requiresaMAP-likephosphorylationstepinorderto RII (Symons et al., 1991, 1993). Interactions of IL-1
dissociate from a translational regulatory molecule. with the receptors is summarized in Figure 2.
RECEPTOR UTILIZATION IN VITRO ACTIVITIES
In vitro findings
The high-affinity binding of IL-1(cid:12) for the IL-1RI
rangesfrom100to450pM.TheconcentrationsofIL-
1(cid:12) which can elicit a biological response are 10– IL-1(cid:12) stimulates cells in vitro in the picomolar to
100fM. There are two affinities: in cells expressing femtomolarrange. Thelist ofIL-1(cid:12) activities oncells
Figure2 CrosslinkingofIL-1RtypeIandIL-1RaccessoryproteinbyIL-1(cid:11)
or IL-1(cid:12) induces IL-1R signaling. IL-1Ra binds to IL-1R but does not
activate.TypeIIreceptor,eitheronmembraneorinsolution,actsasadecoy.
Ra
IL-1(cid:12) 357
in vitro is best understood at the level of gene expres- et al., 1992) and reviewed in (Arend et al., 1998). In
sion.AssummarizedinTable1,uponexposuretoIL- addition, the soluble form of the IL-1R type II has a
1(cid:12), gene expression is either increased or decreased. highaffinityforIL-1(cid:12) andtheIL-1(cid:12) precursorandis
produced in 5–10 molar excess.
Regulatory molecules: Inhibitors Enhancers of IL-1(cid:12) production are not common,
whereas natural inhibitors include IFN(cid:13) and IFN(cid:11).
and enhancers
For example, IFN(cid:13) inhibited IL-1-induced PGE in
2
human blood monocytes (Browning and Ribolini,
The most important regulatory molecule for IL-1(cid:12) is 1987). IFN(cid:13) also inhibited IL-1-induced IL-1
the IL-1Ra which is produced usually in 10- to 100- (Schindler et al., 1990b; Ghezzi and Dinarello, 1988).
fold molar excess (Granowitz et al., 1991; Fischer IFN(cid:11) also inhibits IL-1-induced IL-10 (Schindler
Table 1 Summary of the effect of exposure to IL-1(cid:12) on gene expression
Genes that increase following exposure to IL-1(cid:12)
Cytokines IL-1, IL-1Ra, TNF, IL-2, IL-3, IL-6, GM-CSF, TGF(cid:12)3,
G-CSF, M-CSF, steel factor, LIF, IFN, IL-8 and
chemokine family, MIP-1(cid:11)
Cytokine receptors IL-2 (p55), IL-2, IL-3, IL-5, GM-CSF ((cid:12)c receptor chain), c-kit
Proinflammatory mediators Cyclooxygenase type 2
Cytosolic and secretory phospholipase A , type 2
2
Nitric oxide synthase
Endothelin 1
Gammaglutamyltransferase
Hepatic acute phase reactants Mn superoxide dismutase
C-reactive protein (PTX3), serum amyloid A
Complement C2, C3, factor B
Metallothioneins, ceruloplasmin, lysozyme
Xanthine dehydrogenase, xanthine oxidase
Growth factors PDGF A chain, FGF, KGF
Hepatocyte growth factor
Nerve growth factor
MGSA (gro-(cid:11), (cid:12), (cid:13))
Insulin-like growth factor 1
Activin A
Clotting factors Fibrinogen
Urokinase plasminogen activator
Type 1 and 2 plasminogen activator inhibitor
Protease nexin 1
Tissue remodeling Stromelysin, gelatinases, elastase, collagenases
Tissue inhibitor of metalloproteinases 1, transin
Neuropeptides Pro-opiomelanocorticotropin, corticotropin-releasing factor
Lipid synthesis Triglyceride-increasing Apo CIII
Apolipoprotein J
Oncogenes c-jun, c-abl, c-fms, c-myc, c-fos
Adhesion molecules ICAM-1, ELAM, VCAM-1
Receptors Low-density lipoprotein
358 Charles A. Dinarello
Table 1 (Continued)
FGF
IL-1R type II
Extracellular matrix Aortic smooth muscle cell decorin
Collagen type IV
Beta amyloid precursor
Basement membrane protein 40
Laminin B1 and B2
Others Constitutive heat shock protein p70
Ornithine decarboxylase
Heme-oxygenase
G protein (cid:11) subunit
Aromatic 1-amino decarboxylase
Genes which decrease in steady-state levels following exposure to IL-1(cid:12)
Housekeeping genes Albumin, alkaline phosphatase
Cytochrome p450c17, p450 IIBI, IID
Receptors IL-1R type I
PDGF(cid:11)R
Cytokines TGF(cid:12)1, insulin-like growth factor I (in Leydig cells)
Extracellular matrix proteins Proteoglycans (chondroitin sulfate)
Type II collagen, fibronectin and thrombospondin
Others CD34 on endothelium
Thyroid peroxidase
Thyroglobulin
Glutaminase in fibroblasts
et al., 1990b). In cultured chondrocytes, IFN(cid:13) GM-CSF, G-CSF, M-CSF, MIP-1(cid:11), RANTES,
reduced IL-1-induced expression of collagenase LIF, and IL-10 itself. Explants of human rheuma-
(Andrews et al., 1989, 1990). Spontaneous produc- toid synovium release IL-1 and TNF(cid:11) as well as
tion of IL-1(cid:12) by synovial fluid macrophages from IL-10. However, specific neutralization of IL-10
patients with rheumatoid arthritis was inhibited by resulted in an increase in the production of IL-1
IFN(cid:13) (Ruschen et al., 1989). and TNF, suggesting that the IL-10 constitutively
Although IL-10 inhibits IL-1 synthesis, it does not produced in rheumatoid synovium acts as a natural
inhibitIL-1Raproduction.IL-10injectedintohumans suppressor of IL-1 and TNF production (Katsikis
inhibits the synthesis of IL-1 ex vivo (Chernoff et al., et al., 1994). Neutralization of IL-10 also resulted in
1995).Thereareanumberofreportsthatfocusonthe detectable IFN(cid:13).
ability of IL-10 to suppress gene expression and IL-13 and TGF(cid:12) inhibit IL-1(cid:12) production
synthesis of inflammatory cytokines (reviewed by (Vannier et al., 1996). Although IL-6 is found in a
Moore et al., 1993). Cell signaling following the variety of inflammatory, hematological, and infec-
engagement of IL-10 to its receptor includes tious diseases, IL-6 suppresses IL-1-inducible
phosphorylations of JAK1 and TYK2, very similar cyclooxygenase(Hauptmannetal.,1991);inaddition,
tothatofIFN(cid:11).SomestudieshaveshownthatIL-10 IL-6 suppresses gene expression and synthesis of
inhibits the translocation of NF(cid:20)B. Most studies on inflammatory cytokines (Aderka et al., 1989;
the anti-inflammatory properties of IL-10 have foc- Schindler et al., 1990d). Similarly to IL-6, CNTF
used on suppression of macrophage cytokines. IL-10 binds to its specific soluble receptor, and when
suppresses IL-1(cid:11), IL-1(cid:12), TNF(cid:11), IL-6, IL-8, IL-12, incubated with human blood PBMCs, the CNTF/
IL-1(cid:12) 359
soluble receptor complex suppresses IL-1-induced findings are consistent with those reported in the
IL-8 and PGE synthesis (Shapiro et al., 1994). same model using anti-IL-1R type I antibodies in
2
wild-type mice (Gershenwald et al., 1990). IL-1(cid:12)-
deficient mice also have reduced inflammation
Bioassays used following zymosan-induced peritonitis (Fantuzzi
et al., 1997b). Additional studies have also found
that IL-1(cid:12)-deficient mice have elevated febrile
There are several bioassays for IL-1(cid:12) in vitro.
responses to IL-1(cid:12) and IL-1(cid:11) (Alheim et al., 1997).
AlthoughtheearlystudiesfocusedonIL-1activation
In addition, there appears to be some reduction in
of murine thymocytes (Dinarello et al., 1986a) and
body temperature responses and behavioral changes
theTH2celllineD10(OrencoleandDinarello,1989),
in IL-1(cid:12) mice.
currently the best in vitro bioassay for IL-1(cid:12) is the
In contrast, IL-1(cid:12)-deficient mice have nearly the
induction of IL-8 or IL-6 from fibroblasts (Shapiro
sameresponsestoLPSasdowild-typemice(Fantuzzi
et al., 1994; Kaplanski et al., 1994). In addition,
et al., 1996) with one notable exception. IL-1(cid:12)-
IL-1 induction of PGE is also a reliable bioassay for
2 deficient mice injected with LPS have little or no
IL-1(cid:12).
expressionofleptinmRNAorprotein(Faggionietal.,
1998). In pregnant IL-1(cid:12)-deficient mice there is a
normal response to LPS-induced premature delivery;
IN VIVO BIOLOGICAL however, in these mice there are decreased uterine
ACTIVITIES OF LIGANDS IN cytokinelevels followingLPS(Reznikovet al., 1999).
The reduction in LPS-induced cytokines is not found
ANIMAL MODELS
in nonpregnant IL-1(cid:12)-deficient mice, suggesting that
the combination of the hormonal changes in preg-
Normal physiological roles
nancyandthestateofIL-1(cid:12)deficiencyacttogetherto
reducetheresponsivenesstoLPS.Themechanismfor
BecauseanullmutationintheIL-1(cid:12) generesultsina the reduced cytokine production in pregnant IL-1(cid:12)-
phenotypically normal mouse, there is probably no deficient mice appears to be a reduction in the
normal physiological role for IL-1(cid:12) in health. The constitutive level of the p65 component of NF(cid:20)B
IL-1(cid:12)-deficient mouse is now nearly 4 years in pro- (Reznikov et al., 2000).
ducing offspring and there are no signs of increased No differences were noted in plasma elevations of
susceptibility to disease or rapid aging. glucocorticoid steroids between IL-1(cid:12)-deficient and
wild-type mice following injection of LPS, indicating
that IL-1(cid:12) is not required for activation of the HPA
Species differences axis during endotoxemia (Kozak et al., 1998). The
data demonstrate that in the mouse, IL-1(cid:12) is critical
for the induction of fever during local inflammation.
In general, nearly all species tested respond to IL-1(cid:12).
Another characterized IL-1(cid:12) actvity was studied by
Human IL-1(cid:12) induces a variety of in vivo responses
feeding live influenza virus in IL-1(cid:12)-deficient mice.
in mice, rabbits, rats, etc. that are also observed with
Body temperature and activity were lower in IL-1(cid:12)-
mouse and rabbit IL-1(cid:12) (Cannon et al., 1989a).
deficient mice (Kozak et al., 1995). The anorexic
effects of influenza infection were similar in both
groups of mice. The mice deficient in IL-1(cid:12) exhibited
Knockout mouse phenotypes
a higher mortality to influenza infection than the
wild-type mice.
Asstatedabove,theIL-1(cid:12)-deficientmouseiswithout
abnormal findings after 4 years of continuous
Transgenic overexpression
breeding. However, upon challenge, IL-1(cid:12)-deficient
mice exhibit specific differences from their wild-type
controls. The most dramatic is the response to local There are no reports of mice overexpressing IL-1(cid:12).
inflammation followed by a subcutaneous injection
of turpentine (50–10mL). Within the first 24 hours,
Pharmacological effects
IL-1(cid:12)-deficient mice injected with turpentine do not
manifest an acute phase response, do not develop
anorexia, have no circulating IL-6 and have no fever UnlikeTNF(cid:11),evenlargedosesofIL-1(cid:12) donotresult
(Zheng et al., 1995; Fantuzzi et al., 1997a). These in death. However, adrenectomized mice have
360 Charles A. Dinarello
increased susceptibility to the lethal effects of IL-1(cid:12) PATHOPHYSIOLOGICAL ROLES
(Bertini et al., 1988). Injection of IL-1(cid:12) in primates
IN NORMAL HUMANS AND
induces neutrophilia and acute phase proteins. Injec-
tion of modest doses IL-1(cid:12) into mice (1–10mg/kg) DISEASE STATES AND
induces fever, anorexia, and circulating IL-6. Injec- DIAGNOSTIC UTILITY
tion of IL-1(cid:12) intravenously into rabbits induces a
shock-like state (Okusawa et al., 1988). The most
Normal levels and effects
dramatic responses to the pharmacological effects of
IL-1(cid:12) are observed in humans.
Highly sensitive assays for detecting IL-1(cid:12) in the
circulation of healthy humans reveals levels less than
Interactions with cytokine network 10pg/mL.FollowingachallengeinjectionofLPSinto
healthy humans, IL-1(cid:12) levels increase in the circula-
tionfrom3to6hoursandthenreturntothebaseline
Although there are many interactions of IL-1(cid:12) with
levels (Cannon et al., 1990). Increases are also seen
other cytokines, the most consistent and the most
afterexercise(Cannonetal.,1989b).However,unlike
clinically relevant is the synergism of IL-1 and TNF.
IL-6 or TNF(cid:11) or IL-8, levels of IL-1(cid:12) in human dis-
In rabbits, this synergism is manifested with a severe
easeareremarkablylow.Eveninpatientswithsevere
shock-like state and acute respiratory distress and
sepsis, the levels of circulating IL-1(cid:12) are low (Casey
death (Okusawa et al., 1988). In fact, there are few
et al., 1993). Nevertheless, these levels do correlate
examples in which the synergism between IL-1(cid:12) and
with severity of illness (Casey et al., 1993; Dinarello
TNF(cid:11) has not been demonstrated. These include
andCannon,1993).Whatistheexplanation?IL-1(cid:12) is
radioprotection, Shwartzman reaction, PGE synth-
2 averypotentmoleculewhenpresentinthecirculation
esis, sickness behavior, nitric oxide production, nerve
as evidenced by the response in humans to intra-
growthfactorsynthesis,insulinresistance,lossofmean
venously injected IL-1(cid:12) (see below). The levels of IL-
body mass, and IL-8 and chemokine synthesis. An
1(cid:12) measured in the circulation during disease are in
illustration of the molecular and cellular interactions
the femtomolar range, consistent with the levels that
initiated by IL-1 is shown in Figure 3.
would be reached following intravenous injection.
Endogenous inhibitors and Role in experiments of nature and
enhancers disease states
The endogenous inhibitors of IL-1(cid:12) activity are The role of IL-1(cid:12) in human disease states is best
TGF(cid:12), IL-10, IFN(cid:13), IFN(cid:11), IL-13, and members of revealed by two groups of experiments: (1) the
the gp130 family (IL-6 and CNTF). These are response of humans to parenterally administered IL-
described in the section on In vitro activities. 1(cid:12), and (2) the response of humans with pre-existing
Figure3 InteractionsbetweenIL-1andtheendotheliumleadtocapillary
leak and leukocyte recruitment.