| Current
Pharmaceutical Design
ISSN: 1381-6128
Current Pharmaceutical Design
Volume 12, Number 32, 2006
Contents
Toll-Like Receptors and Innate Immunity: Potential
Drug Targets for Treatment of Infectious, Inflammatory, and
Autoimmune Diseases
Executive Editor: Emilio Jirillo
Editorial Pp. 4089-4090
Evolution of A “Conserved” Amino Acid
Sequence: A Model Study of An In Silico Investigation
of the Phylogenesis of Some Immune Receptors Pp.
4091-4121
M.A. Panaro, A. Acquafredda, M. Sisto, S. Lisi, A.B. Maffione
and V. Mitolo
[Abstract]
TLR Signaling Pathways: Opportunities for Activation and Blockade
in Pursuit of Therapy Pp. 4123-4134
K. Hoebe, Z. Jiang, P. Georgel, K. Tabeta, E. Janssen,
X. Du and B. Beutler
[Abstract]
‘Toll’ Gates for Future Immunotherapy
Pp. 4135-4142
K.J. Ishii, S. Uematsu and S. Akira
[Abstract]
Negative Regulators of Toll-like Receptor 4-Mediated
Macrophage Inflammatory Response Pp. 4143-4153
J.P. Butchar, K.V.L. Parsa, C.B. Marsh and S. Tridandapani
[Abstract]
Molecular Basis for Invertebrate Innate Immune
Recognition of (1→3)-β-D-Glucan
as A Pathogen-Associated Molecular Pattern Pp. 4155-4161
T. Muta
[Abstract]
Enhancement of TLR-Mediated Innate Immune Responses
by Peptidoglycans through NOD Signaling Pp. 4163-4172
H. Takada and A. Uehara
[Abstract]
Toll-Like Receptors in Human Infectious Diseases
Pp. 4173-4184
S. de la Barrera, M. Alemán and M. del C. Sasiain
[Abstract]
TLR2 and TLR4 Expression During Bacterial Infections
Pp. 4185-4193
E. Lorenz
[Abstract]
Recognition of Fungal Pathogens by Toll-Like
Receptors Pp. 4195-4201
M.G. Netea, G. Ferwerda, C.A.A. van der Graaf, J.W.M.
Van der Meer and B.J. Kullberg
[Abstract]
Innate Immunity in the Mucosal Immune System
Pp. 4203-4213
T. Nochi and H. Kiyono
[Abstract]
Therapeutic Targeting of Toll-Like Receptors
in Gastrointestinal Inflammation Pp. 4215-4228
S. Ishihara, M.A.K. Rumi, C.-F. Ortega-Cava, H. Kazumori,
Y. Kadowaki, N. Ishimura and Y. Kinoshita
[Abstract]
Endotoxin, TLR4 Signaling and Vascular Inflammation:
Potential Therapeutic Targets in Cardiovascular Disease
Pp. 4229-4245
L.L. Stoll, G.M. Denning and N.L. Weintraub
[Abstract]
Toll-Like Receptor Signaling Mechanisms Involved
in Dendritic Cell Activation: Potential Therapeutic Control
of T Cell Polarization Pp. 4247-4254
L. Amati, M.T. Pepe, M.E. Passeri, M.L. Mastronardi, E.
Jirillo and V. Covelli
[Abstract]
Toll-Like Receptor-Positive Cells and Recognition
of Pathogens: How Human Myeloid Dendritic Cells Respond to
In Vitro Infection with Leishmania infantum
Pp. 4255-4262
M. Pepe, M. Altamura, R. Spinelli, R. Calvello, M. Saccia,
P. Cavallo, V. Covelli, E. Jirillo and O. Brandonisio
[Abstract]
In Vitro Infection of Human
Monocyte-Derived Dendritic Cells with Candida albicans:
Receptorial Involvement and Therapeutic Implications
Pp. 4263-4269
M. Pepe, E. Jirillo and V. Covelli
[Abstract]
Immunomodulating Effects of Flavonoids on Acute
and Chronic Inflammatory Responses Caused by Tumor Necrosis
Factor α
Pp. 4271-4279
Y. Kumazawa, K. Kawaguchi and H. Takimoto
[Abstract]
Abstracts
[Back
to top]
Editorial
Toll-Like Receptors and Innate Immunity: Potential
Drug Targets for Treatment of Infectious, Inflammatory, and
Autoimmune Diseases
In higher vertebrates and in mammals Toll- like receptors
(TLRs) represent a bridge between innate and adaptive immunity.
In this respect, a number of recent studies have led to the
discovery of various TLRs in mice and in men, as well as to
the characterization of structure and function of these receptors.
In virtue of TLR ability to trigger a cascade of inflammatory
and regulatory events, they are currently investigated as
specific targets for novel drugs potentially useful in the
treatment of various infectious and autoimmune diseases.
On these grounds, the present issue of Current Pharmaceutical
Design, entitled: "Toll-like receptors and innate immunity:
Potential drug targets for treatment of infectious, inflammatory,
and autoimmune diseases", will point out the main aspects
of biology, function and potential drug targeting of TLRs.
The in silico investigation of the phylogenesis of immune
receptors will be described by Panaro and associates [1],
demonstrating how some receptors are relatively conserved
from insects to mammals.
Hoebe and associates [2] and Ishi and associates [3] will
provide basic information on the structure-function of the
broad spectrum of TLRs, also emphasizing novel avenues for
future immunotherapy.
Butchar and associates [4] will review TLR4 activation by
endotoxin with special reference to the regulatory mechanisms
of TLR4 signaling.
Recognition of beta-glucan, a major component of the fungal
cell wall, will be described by Muta [5], as an example of
the phylogenesis of innate immunity.
Takada and Uehara [6] will consider another bacterial component,
peptidoglycan, for its capacity to enhance TLR-mediated responses
via the NOD pathway.
In two companion papers de la Barrera and associates [7] and
Lorenz [8] will describe the involvement of TLRs in infectious
diseases, even including bacterial infections with special
emphasis on novel therapeutic strategies.
Netea and associates [9] will review the mechanisms of TLR
activation by fungi and potential therapeutic approaches.
Nochi and Kiyono [10] and Ishihara and associates [11] will
provide information on the innate mucosal immune system and
on TLR-drug targeting in gastrointestinal inflammatory diseases.
Stoll and associates [12] will review the involvement of endotoxin
and TLR4 in vascular inflammation and potential therapeutic
targets.
In three consecutive papers Amati and associates [13], Pepe
and associates [14] and Pepe and associates [15] will describe
the TLR-mediated activation of dendritic cells, their involvement
in Leishmanmia infantum and Candida albicans
infections and novel protocols of TLR drug targeting.
Finally, Kumazawa and associates [16] will illustrate the
effects of flavonoids as therapeutic agents able to block
TLR-mediated pathways leading to production of proinflammatory
cytokines.
References
[1] Panaro, MA, Acquafredda A, Sisto M, Lisi S, Saccia M,
Mitolo V. Evolution of a "conserved" amino acid
sequence: a model study of an in silico investigation
of the phylogenesis of some immune receptors. Curr Pharm Design
2006; 12(32): 4091-4121.
[2] Hoebe K, Jiang Z, Georgel P, Tabeta K, Janssen E, Du X,
Beutler B. TLR signaling pathways: opportunities for activation
and blockade in pursuit of therapy. Curr Pharm Design 2006;
12(32): 4123-4134.
[3] Ishi KJ, Uematsu S, Akira S. "Toll" gates for
future immunotherapy. Curr Pharm Design 2006; 12(32): 4135-4142.
[4] Butchar JP, Parsa KVL, Marsh CB, Tridandapani, S. Negative
regulators of Toll-like receptor 4-mediated macrophage inflammatory
response. Curr Pharm Design 2006; 12(32): 4143-4153.
[5] Muta T. Molecular basis for invertebrate innate immune
recognition of (1-3)-β-D-glucan
as a pathogen -associated molecular pattern. Curr Pharm Design
2006; 12(32): 4155-4161.
[6] Takada H, Uehara A. Enhancement of TLR-mediated innate
immune responses by peptidoglycans through NOD signaling.
Curr Pharm Design 2006; 12(32): 4163-4172.
[7] de la Barrera S, Aleman M, Sasiain M del C. Toll-like
receptors in human infectious diseases. Curr Pharm Design
2006; 12(32): 4173-4184.
[8] Lorenz E. TLR2 and TLR4 expression during bacterial infections.
Curr Pharm Design 2006; 12(32): 4185-4193.
[9] Netea MG, Ferwerda G, van der Graaf CAA, Van der Meer
JWM, Kullberg BJ. Recognition of fungal pathogens by Toll
-like receptors. Curr Pharm Design 2006; 12(32): 4195-4201.
[10] Nochi T, Kiyono H. Innate immunity in the mucosal immune
system. Curr Pharm Design 2006; 12(32): 4203-4213.
[11] Ishihara S, Rumi MAK, Ortega-Cava C-F, Kazumori H, Kadowaki
Y, Ishimura N, Kinoshita Y. Therapeutic targeting of Toll-llike
receptors in gastrointestinal inflammation. Curr Pharm Design
2006; 12(32): 4215-4228.
[12] Stoll LL, Denning GM, Weintraub NL. Endotoxin, TLR4 signaling,
and vascular inflammation: potential therapeutic targets in
cardiovascular disease. Curr Pharm Design 2006; 12(32): 4229-4245.
[13] Amati L, Pepe MT, Passeri ME, Mastronardi ML, Jirillo
E, Covelli V. Toll-like receptor signaling mechanisms involved
in dendritic cell activation: potential therapeutic control
of T cell polarization. Curr Pharm Design 2006; 12(32): 4247-4254.
[14] Pepe M, Altamura M, Spinelli R, Calvello R, Saccia M,
Cavallo P, Covelli V, Jirillo E, Brandonisdio O. Toll-like
receptor-positive cells and recognition of pathogens: how
human myeloid dendritic cells respond to in vitro
infection with Leishmania infantum. Curr Pharm Design 2006;
12(32): 4255-4262.
[15] Pepe M, Jirillo E, Covelli V. In vitro infection
of human monocyte-derived dendritic cells with Candida albicans:
receptorial involvement and therapeutic implications. Curr
Pharm Design 2006; 12(32): 4263-4269.
[16] Kumazawa Y, Kawaguchi K, Takimoto H. Immunomodulating
effects of flavonoids on acute and chronic inflammatory responses
caused by tumor necrosis factor-α.
Curr Pharm Design 2006; 12(32): 4271-4279.
Emilio Jirillo
University of Bari and IRCCS De Bellis
Castellana Grotte
Bari, Italy
[Back to top]
Evolution of A “Conserved” Amino Acid
Sequence: A Model Study of An In Silico Investigation
of the Phylogenesis of Some Immune Receptors
M.A. Panaro, A. Acquafredda, M. Sisto, S. Lisi, A.B. Maffione
and V. Mitolo
In this paper we analyze a 55-amino acid (aa) sequence
which is relatively well conserved in several seven-transmembrane
receptor families (from Insects to Mammals) and in some Viruses.
This sequence, which covers the second transmembrane domain,
the first extracellular loop and the third transmembrane domain,
appears in its complete configuration in most of the seven-transmembrane
receptor families, as well as in the protein products of some
viruses. Other seven-transmembrane receptors and viruses exhibit
reduced configurations of the conserved sequence, lacking
either aa 31 or aa 30-31. 53-aa configurations are typically
found in most chemokine receptor (CKR) subfamilies, as well
as in some viral protein products. However, the CCR1, CCR3,
and CCR6 subfamilies comprise a 54-aa configuration and the
CKR-related protein products, ChemR23 and RDC1, include the
complete 55-aa sequence. For each CKR subfamily the “modal
sequence” of the conserved segment was constructed by
selecting the most frequently occurring aa at each position.
Then, pairwise alignments were made between: (i)
the modal CKR sequences, and (ii) the sequence (53-aa) of
the Yaba-like disease virus - 7L protein. From the alignments
two consensus matrices were derived: (i) the consensus 1 matrix
with reference to the whole conserved segment, and (ii) the
consensus 2 matrix with reference to aa 22-29, which appear
to be the most variable segment of the sequence. Based on
the obtained consensus values and with reference to this
specific conserved segment, the following conclusions
are proposed: (1) ChemR23 and RDC1 are probably the more primitive
CKR forms; (2) CCR1 and CCR3 may be grouped in a single cluster;
(3) CCRs 2, 4, and 5 are closely related to each other and
may be grouped in a cluster; CCR7 is likely to be evolutionarily
related to this cluster; (4) CXCRs 2, 3, and 4 and CCX CKR
appear to be evolutionarily related to each other and very
likely derived from an CCR6-like gene; (5) CCR2/4/5 and CCR7
may have derived either from CCR1/3-like or CCR6-like genes;
(6). The Yaba-like disease virus - 7L protein most likely
derived, through “molecular piracy”, from a CCR8-like
gene. We also discuss possible, more remote, evolutionary
links between CKRs, formylpeptide receptors, and possibly
the highly conserved 18S rRNA genes.
[Back to top]
TLR Signaling Pathways: Opportunities for Activation
and Blockade in Pursuit of Therapy
K. Hoebe, Z. Jiang, P. Georgel, K. Tabeta, E. Janssen,
X. Du and B. Beutler
The identification of the TLRs as key sensors of microbial
infection has presented a series of new targets for drug development.
The TLRs are linked to the most powerful inflammatory pathways
in mammals. The question arises from the start: do we wish
to stimulate TLR signaling in order to eradicate specific
infections and/or neoplastic diseases? Or do we wish to block
TLR signaling to treat inflammatory diseases? If we accept
that it would be useful to modulate TLR signaling, the next
step is to identify the correct molecular target(s) for the
task. Perhaps it might even be possible to exercise selectivity,
modulating some aspects of TLR signaling and not others. Classical
and reverse genetic analyses offer insight into the possibilities
that exist, and point to specific checkpoints within signaling
pathways at which modulation might normally be imposed.
[Back to top]
‘Toll’ Gates for Future Immunotherapy
K.J. Ishii, S. Uematsu and S. Akira
Toll-like receptors (TLRs) are evolutionary conserved transmembrane
proteins that recognize a unique pattern of molecules derived
from pathogens or damaged cells, triggering robust but defined
innate immune responses. TLR-mediated innate and/or adaptive
immune responses play an important role in a variety of diseases
including infectious diseases, sepsis, autoimmune diseases,
allergy, and atherosclerosis. Each TLR displays a differential
expression pattern, intracellular localization and signaling
pathway, resulting in distinct immune responses. A variety
of new TLR ligands including agonists (e.g. urinary Tamm-Horsfall
glycoprotein as a TLR4 ligand, siRNA as TLR3 or 7 ligand,
Plasmodium falciparum Hemozoin as a TLR9
ligand, Profilin-like protein in Toxoplasma gondii
as a TLR11 ligand) and antagonists (G-rich oligodeoxynucleotides
as antagonist for TLR9) have been identified, and some of
other TLR ligands are already under clinical trials. The manipulation
or intervention of TLR-mediated immune responses is a possible
multiple ‘Toll’ gate for future developments of
immunotherapies.
[Back to top]
Negative Regulators of Toll-like Receptor 4-Mediated
Macrophage Inflammatory Response
J.P. Butchar, K.V.L. Parsa, C.B. Marsh and S. Tridandapani
Activation of macrophages through TLR4, the receptor
for the bacterial endotoxin LPS, results in a potent inflammatory
response aimed at eliminating the invading pathogen. Excessive
production of inflammatory mediators is harmful to host tissue
and in extreme cases can result in fatal outcomes. This inflammatory
response is, therefore, tightly regulated by negative regulatory
mechanisms that act to maintain homeostasis. This review will
summarize recent advances in our current understanding of
molecular mechanisms that regulate macrophage TLR4 signaling.
[Back to top]
Molecular Basis for Invertebrate Innate Immune
Recognition of (1→3)-β-D-Glucan
as A Pathogen-Associated Molecular Pattern
T. Muta
Innate immunity responds to various pathogen-associated
molecular patterns (PAMPs) to evaluate the biological nature
of foreign materials by using limited numbers of receptors.
Analyses of interactions between PAMPs and its receptors are
essential to understand the molecular basis regarding how
we discriminate self and non-self materials. Upon infection
of horseshoe crabs, an arthropod species, rapid hemolymph
coagulation is induced to engulf invading microorganisms by
a cascade-type reaction. The reaction is very sensitive to
lipopolysaccharide and (1→3)-β-D-glucans
on Gram-negative bacteria and fungi, respectively, and hence
is utilized as assay reagents that detect and quantitate these
PAMPs with a name of “limulus test.” In this mini-review,
recognition of (1→3)-β-D-glucans
by a unique serine protease zymogen factor G of horseshoe
crab is described. Molecular dissection and detailed kinetic
analyses have revealed that multivalent binding to polymers
of a simple target structure is one of the principles that
allows stable and specific recognition of PAMPs by pattern
recognition receptors in innate immunity.
[Back to top]
Enhancement of TLR-Mediated Innate Immune Responses
by Peptidoglycans through NOD Signaling
H. Takada and A. Uehara
Toll-like receptors (TLRs) recognize common motifs, pathogen-associated
molecular patterns (PAMPs), in microorganisms. Bacterial PAMPs
are mainly distributed on cell-surfaces. Peptidoglycans (PGNs)
are ubiquitous constituents of bacterial cell walls. Muramyldipeptide
(MDP; N-acetylmuramyl-L-alanyl-D-isoglutamine) is
a common and key structure of PGNs and exhibits most the of
bioactivities of PGNs. Recently, the intracellular receptor
for MDP was revealed to be NOD2. Another bioactive moiety
of PGNs, diaminopimelic acid (DAP) containing desmuramylpeptides
(DMPs), senses another intracellular receptor, NOD1. MDP-primed
mice exhibited hyper-responses to endotoxin and other bacterial
components, which sense Toll-like receptors (TLRs), although
MDP itself does not exhibit apparent activity in mice. On
the other hand, DMPs exhibited definite activity in mice,
and the most powerful DMP, FK565, exhibited stronger priming
activity than MDP. In human monocytic cells, both MDP and
DMPs exhibited definite activities; marked synergistic interleukin
(IL)-8 secretion was induced by DMPs and MDP in combination
with synthetic TLR agonists, and suppression of the mRNA expressions
of NOD1 and NOD2, respectively, by RNA interference specifically
inhibited synergistic IL-8 secretion. In human dendritic cells
(DCs), synergistic T helper type 1 responses are induced by
combined stimulations of synthetic NOD and TLR agonists. Considering
these findings altogether, in host-bacteria interactions,
host cells should recognize bacteria via both TLRs
and NODs, which might induce synergistic innate and adaptive
immune responses.
[Back to top]
Toll-Like Receptors in Human Infectious Diseases
S. de la Barrera, M. Alemán and M. del C. Sasiain
Toll-like receptors (TLRs) have emerged as critical players
in immunity. They are capable of sensing organisms ranging
from protozoa to bacteria, fungi or viruses upon detection
of the pathogen as well as recognizing endogenous ligands,
and triggering transduction pathways. Following activation
of the innate immune system, strong inflammatory signals are
generated inducing inflammation and activation of the adaptive
immune response. However, the deregulation of TLRs signaling
pathways may be conducive to the pathogenesis of many infectious
diseases. Therefore, innate and adaptive immunity are not
simply sequential and complementary mechanisms of resistance
to pathogen, they regulate each other through cellular contacts
and the secretion of soluble mediators. Herein, we summarize
recent findings on TLRs signaling in infectious diseases and
how pathogens have developed strategies to evade these pathways.
In this context, a potential modulation of the innate immune
response could have therapeutic benefit through the development
of new drugs as well as vaccination strategies to be employed
in infectious diseases.
[Back to top]
TLR2 and TLR4 Expression During Bacterial Infections
E. Lorenz
The family of the toll-like receptors comprises a minimum
of 10 members identified in humans so far. These transmembrane
receptors act as important signaling intermediates between
the host and the invading pathogens. The following review
describes the complexities encountered by researchers studying
toll-like receptor (TLR) expression changes during bacterial
infections. Mutations in some of the TLRs, most prominently
TLR4 and TLR2, have been associated with increased susceptibility
to infectious diseases. While it is tempting to correct the
phenotypic effect of such mutations, in vitro and
in vivo research has shown that TLR activity and
function comprises a complex regulatory network. Heterodimer
formation, synergy, and cross-tolerance have previously been
described. More recently, interdependence of TLR2 and TLR4
expression has been identified. In addition, TLR expression
follows a specific timeline that may be dependent on the invading
pathogen. Lastly, mutations in invading pathogens have been
shown to alter the expression profile of TLR2 and TLR4, indicating
that therapies against bacterial pathogens will have to target
multiple TLRs.
Despite the complexities involved in TLR function, the significant
progress made in our understanding of the role these proteins
play in human diseases also indicates their potential value
as therapeutic agents.
[Back to top]
Recognition of Fungal Pathogens by Toll-Like
Receptors
M.G. Netea, G. Ferwerda, C.A.A. van der Graaf, J.W.M.
Van der Meer and B.J. Kullberg
Toll-like receptors (TLRs) have been identified as a
major class of pattern-recognition receptors. Recognition
of pathogen-associated molecular patterns (PAMPs) by TLRs,
either alone or in heterodimerization with other TLR or non-TLR
receptors, induces signals responsible for the activation
of innate immune response. Recent studies have demonstrated
a crucial involvement of TLRs in the recognition of fungal
pathogens such as Candida albicans, Aspergillus fumigatus
and Cryptococcus neoformans. By studying fungal infection
in knock-out mice deficient in either TLRs or TLR-associated
adaptor molecules, it appeared that specific TLRs such as
TLR2 and TLR4 play differential roles in the activation of
the various arms of the innate immune response. Recent data
also suggest that TLRs offer escape mechanisms to certain
pathogenic microorganisms, especially through TLR2-driven
induction of antiinflamatory cytokines. These recent developments
provide crucial information for understanding the mechanisms
of fungal recognition by cells of the immune system, and provide
hope for designing new therapeutical approaches to fungal
infections.
[Back to top]
Innate Immunity in the Mucosal Immune System
T. Nochi and H. Kiyono
The mucosal immune system is equipped with unique innate
and acquired defense mechanisms which provide a first line
of protection against ingested and inhaled infectious agents.
Peyer’s patches (PPs) and nasopharynx-associated lymphoid
tissue (NALT) have been shown to be important inductive sites
for the initiation of the acquired phase of antigen-specific
immune responses. In addition, the mucosal innate immune system
acts as both a physical and an immunological boundary, playing
a key role in the sensing and eliminating of pathogens and
in the creating of symbiosis. The mucus layer covering the
mucosal epithelium acts as a first physical and biochemical
barrier. An additional layer of physical protection against
microorganisms is provided by a tightly interlaced cell-to-cell
network of epithelial cells and intraepithelial lymphocytes.
Various antimicrobial peptides produced by the epithelium
and secreted into the mucosal lumen can directly kill the
invading pathogenic bacteria. Finally, Toll-like receptors
(TLRs) associated with the mucosal compartment have been shown
to recognize the pathogen-associated molecular patterns (PAMPs)
of a variety of pathogenic and commensal microorganisms. Therefore,
a greater understanding of the immunological progression from
mucosal innate to acquired immune systems should facilitate
the development of new generation of mucosal vaccines to prevent
and control infectious diseases.
[Back to top]
Therapeutic Targeting of Toll-Like Receptors
in Gastrointestinal Inflammation
S. Ishihara, M.A.K. Rumi, C.-F. Ortega-Cava, H. Kazumori,
Y. Kadowaki, N. Ishimura and Y. Kinoshita
Toll-like receptors (TLRs) are sensors of microbial products
that initiate host defense responses in multicellular organisms.
They are mainly linked to innate immunity and bridging to
adaptive immunity, signaling through different TLRs responsible
for a wide range of biological responses. The intracellular
signaling pathways through Toll/interleukin-1 receptor (IL-1R)
domains result in recruitment of the cytoplasmic adaptor molecules,
with subsequent activation of a signaling cascade leading
to nuclear factor-κB
(NF-κB).
TLR-signaling induces host inflammatory response and the inflammation
becomes more severe in the absence of several extra and intra
cellular negative regulators of TLR-signaling. In the intestine,
TLR-dependent activation of NF-κB
plays a vital role in maintaining epithelial homeostasis as
well as regulating infections and inflammation, while dysregulation
of TLR-signaling is associated with the pathogenesis of inflammatory
bowel diseases (IBD). Recent findings regarding innate immunity-mediated
regulation of intestinal patho-physiology prove that development
of new drugs targeting TLRs including antagonists of TLR-signaling
and agonists of their negative regulators has a potential
impact on therapeutic strategies for intestinal inflammatory
diseases.
[Back to top]
Endotoxin, TLR4 Signaling and Vascular Inflammation:
Potential Therapeutic Targets in Cardiovascular Disease
L.L. Stoll, G.M. Denning and N.L. Weintraub
Cardiovascular disease ranks among the leading causes
of morbidity and mortality in adult populations in the Western
world. Significant progress in understanding the etiology
of cardiovascular disease has come from recent recognition
that chronic inflammation plays a key role in its development.
The principal mediators of this inflammatory response, and
the mechanisms by which they work, however, are incompletely
understood. Moreover, the complex nature of the inflammatory
response poses significant challenges to the development of
effective and targeted treatments. Potentially promising targets
to reduce inflammation in atherosclerosis include Toll-like
receptor (TLR) pathways and anti-inflammatory factors that
modulate TLR signaling. In this review, we outline studies
that provide insight into the links be-tween cardiovascular
disease and inflammation, focusing on innate immunity and
endotoxin/TLR4 signaling. We also discuss the contribution
of specific host immune/inflammatory responses to atherogenesis,
and describe cellular signaling pathways (lipopolysaccharide-binding
protein [LBP], CD14, MD-2, TLR4, MyD88, and NF-κB,
among others) that play key roles in innate immune signaling.
Finally, we discuss the therapeutic potential of modulating
these cellular signaling pathways as future strategies for
the prevention and treatment of cardiovascular disease, including
such approaches as specific targeting of the TLR4 signaling
pathway, antibiotic therapy, drug classes with broad anti-inflammatory
activity (statins, thiazolidinediones), and the potential
of vaccine development. Because of the complexity of the links
between low-level chronic infections, inflammation, and atherosclerosis,
treatment and prevention of cardiovascular disease will likely
require an integrated approach that utilizes a combination
of these strategies to target the underlying inflammatory
processes.
[Back to top]
Toll-Like Receptor Signaling Mechanisms Involved
in Dendritic Cell Activation: Potential Therapeutic Control
of T Cell Polarization
L. Amati, M.T. Pepe, M.E. Passeri, M.L. Mastronardi, E.
Jirillo and V. Covelli
Dendritic cells (DCs) represent a bridge between innate
and adaptive immunity, being the maturation process dependent
on the binding of pathogen-associated molecular patterns (PAMPs)
to Toll-Like Receptors (TLRs) expressed on their surface.
TLRs associated to adaptor proteins, following binding to
PAMPs, are able to skew specific immune responses towards
the T helper (h)1- or the Th2-type according
to the antigenic stimulation involved. Of note, other receptors
different from TLRs are expressed on DCs which are also able
to recognize PAMPs. Among them, one should mention the DC-specific
ICAM-3-grabbing nonintegrin, the mannose receptor, Dectin-1
(the major β-glucan
receptor) and NOD2. Finally, the possibility to interfere
therapeutically with the TLR-dependent and -independent signaling
pathways in DCs is reviewed. According to current literature,
DC activation, their antigen uptake capacity and migration
can be enhanced with different experimental procedures whose
use in humans is still under evaluation. However, just recently
a probiotic cocktail VSL3, successfully used in patients with
pouchitis, seems to act on DCs, promoting abundant release
of Interleukin-10 in the gut.
These novel therapeutic strategies based on the modulation
of the signaling pathways in DCs seem to be encouraging for
the treatment of inflammatory and autoimmune diseases.
[Back to top]
Toll-Like Receptor-Positive Cells and Recognition
of Pathogens: How Human Myeloid Dendritic Cells Respond to
In Vitro Infection with Leishmania infantum
M. Pepe, M. Altamura, R. Spinelli, R. Calvello, M. Saccia,
P. Cavallo, V. Covelli, E. Jirillo and O. Brandonisio
Dendritic cells (DCs), instructed by the priming signals from
microbial factors, can produce interleukin (IL)-12p70 and
promote T helper (Th)1 proliferation and interferon (IFN)-γ
production. This event seems to be critical for the containment
of infections caused by intracellular pathogens, even including
Leishmania infection. In the present in vitro
study we have investigated: 1) phagocytic capacities and IL-12
production by human monocyte-derived DCs and macrophages (MØs),
infected with Leishmania infantum promastigotes;
2) IFN-γ
production by human CD4+ T cells coincubated with
DCs or macrophages pulsed with live promastigotes. Monocyte-derived
myeloid DCs and MØs from healthy donors were infected
with live metacyclic Leishmania infantum (MON-1)
promastigotes, previously opsonized with 5% autologous serum,
at 1:4 cell/parasite ratio. Percentage and index of phagocytosis
were calculated after 2, 24 and 48 h of incubation. IL-12
production was evaluated by an ELISA in supernatants from
48 h Leishmania-infected or lipopolysaccharides (LPS)-stimulated
DCs and MØs, also in the presence of phytohemagglutinin-activated
or inactivated CD4+ T cells. For IFN-γ
production, CD4+ T cells were repeatedly stimulated with DCs
or MØs, pulsed with live Leishmania promastigotes
or activated with LPS. The number of IFN-γ-secreting
cells was evaluated by an ELISpot assay. Results showed that
MØs have a higher phagocytic capacity towards L.
infantum promastigotes than DCs. Moreover, unlike MØs,
Leishmania-infected DCs were able to release IL-12p70;
this production significantly increased in the presence of
activated CD4+ T cells. Finally, DCs pulsed with live parasites
and added to autologous CD4+ T cells induced a higher number
of IFN-γ-secreting
cells than MØs, thus indicating their ability to polarize
Th cells toward the Th1 subset. These data indicate that DCs
are able to promote protective Th1 immune responses in our
experimental model of Leishmania infantum infection,
thus representing the grounds for initiating immunoterapeutic
and vaccinal strategies.
[Back to top]
In Vitro Infection of Human Monocyte-Derived
Dendritic Cells with Candida albicans: Receptorial
Involvement and Therapeutic Implications
M. Pepe, E. Jirillo and V. Covelli
Nowadays, infections with Candida albicans (C.
a.) are very frequent, mostly in the so-called immunocompromised
host. Therefore, research has been focused on the types of
immune response elicited by C. a., with the aim to
develop novel therapeutic strategies. Neutrophils and macrophages
(MØ) are deeply involved in the host defense against
C. a., and also dendritic cells (DCs) seem to be
very active in the host protection. In particular, DCs display
an array of surface receptors able to interact with fungal
components, even including Toll-like receptors.
Here, we will illustrate the in vitro immune response
of human monocyte-derived DCs infected with C. a..
In this test system, DCs exert phagocytic and killing activities
with a magnitude similar to that of MØ. Moreover, in
the presence of autologous CD4+ cells, DCs produce
T-helper (h) 1 type cytokines. This Th1 polarizing activity
is mediated by interleukin-12 released by infected CDs in
the presence of CD4+ cells.
Taken together, these data suggest a protective role played
by DCs in the course of C. a. infection and the possibility
to develop new strategies of immune intervention.
[Back to top]
Immunomodulating Effects of Flavonoids on Acute
and Chronic Inflammatory Responses Caused by Tumor Necrosis
Factor α
Y. Kumazawa, K. Kawaguchi and H. Takimoto
Flavonoids have beneficial activities which modulate oxidative
stress, allergy, tumor growth and viral infection, and which
stimulate apoptosis of tumor cells. In addition to these activities,
dietary flavonoids are able to regulate acute and chronic
inflammatory responses. Here we describe new aspects of regulatory
mechanisms by which flavonoids suppress production of tumor
necrosis factor-α
(TNF-α)
by macrophages, microglial cells and mast cells stimulated
with lipopolysaccharide (LPS) and others via toll-like
receptors (TLRs), and TNF-α-mediated
acute and chronic inflammatory responses. Treatment with flavonoids
such as luteolin, apigenin, quercetin, genistein, (-)-epigallocatechin
gallate, and anthocyanidin resulted in significant downregulation
of LPS-elicited TNF-α
and nitric oxide (NO) production and diminished lethal shock.
In chronic diseases, pathogenesis of collagen-induced arthritis
(CIA), a mouse model of rheumatoid arthritis which is triggered
by TNF-α,
was improved by the oral administration of flavonoids after
the onset of CIA. Here, we discuss that inhibitory effects
of flavonoids on acute and chronic inflammation are due to
regulation of signaling pathways, including the nuclear factor
κB
(NF-κB)
activation and mitogen-activated protein (MAP) kinase family
phosphorylation. FcεRI
expression by NF-κB
activation was also reduced by flavonoids; while accumulation
of lipid rafts, which is the critical step for signaling,
was blocked by flavonoids. The intake of dietary flavonoids
reduces acute and chronic inflammation due to blocking receptor
accumulation and signaling cascades, and would assist individuals
at high-risk from life-style related diseases.
|
