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* Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research and
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892;
Department of Microbiology, Colorado State University, Fort Collins, CO 80523; and
Department of Pathology, George Washington University, Washington, D.C. 20037
| Abstract |
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and
IL-1, and adhesion molecules. Associated with this rapid initial
up-regulation of recruitment and amplification molecules was enhanced
expression of transcription factors and signaling molecules. By 24
h, this proinflammatory response subsided, and after 4 days, when some
bacteria were being degraded, others escaped destruction to replicate
within intracellular vacuoles. Under these conditions, inducible NO
synthase was not up-regulated and increased transferrin
receptors may facilitate iron-dependent mycobacterial growth. Sustained
adhesion molecule and chemokine expression along with the formation of
multinucleated giant cells appeared consistent with in vivo
events. Thus, in the absence of T lymphocyte mediators, macrophages are
insufficiently microbicidal and provide a nonhostile environment in
which mycobacteria not only survive and replicate, but continue to
promote recruitment of new macrophages to perpetuate the
infection. | Introduction |
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In HIV-1-negative individuals, susceptibility to pulmonary infections
often occurs in the context of predisposing lung conditions (10, 13). MAC has been shown to present as pulmonary infections in
immunocompetent patients including elderly women and smokers, as well
as immunocompromised individuals who have undergone organ
transplantation or with inheritable defects in IFN-
(10, 14). Cutaneous manifestations of MAC in immunocompetent
individuals also occur, especially in children (15, 16).
All of these manifestations of MAC have in common infiltration by
mononuclear cells and granuloma formation.
Although enhanced susceptibility to M. avium infection generally reflects reduced T cell numbers and/or functional deficiencies, it is the macrophage that represents the primary host. The interaction between M. avium and macrophages, initiated via cell surface receptors, results in subsequent internalization and residence as an intracellular pathogen. The evidence that multiple macrophage receptors may be involved in the initial bacterium-host cell encounter (17), including complement receptors, vitronectin receptors, CD14, mannose receptors, CD43, and Toll-like receptors (TLR) (13, 18, 19, 20, 21, 22, 23), underscores the need for M. avium to be internalized to survive. Once within the macrophage, this facultative intracellular pathogen must commandeer the host cell machinery to enable its own multiplication and survival. However, the mechanisms by which this is accomplished are largely unknown.
Whereas only a few mycobacteria may initiate the infection, over time,
enormous numbers of microorganisms may be found locally or at
dissemination sites as a consequence of intracellular replication and
reinfection in susceptible macrophages. Little is known regarding how
macrophages either kill M. avium or become its breeding
ground. For example, controversy exists over whether reactive oxygen or
nitrogen intermediates are toxic to M. avium (24, 25), although inducible NO synthase (iNOS) is considered
essential in defense against experimental Mycobacterium
tuberculosis (26). However, many of these studies
have been performed using rodent macrophages or cell lines which do not
necessarily parallel human macrophage responses to mycobacteria. To
explore the mechanisms whereby M. avium enters macrophages
and takes up residence in the absence of molecular signals derived from
T lymphocytes, notably IFN-
, we have infected human peripheral blood
monocyte-derived macrophages with M. avium in vitro, and
evaluated host cell gene expression by cDNA expression arrays from
2 h to 7 days postinfection. Multiple genes encoding transcription
factors, signal transduction molecules, and proteins involved in
regulation of inflammatory and immune responses were differentially
expressed. The immediate early response was consistent with immune
activation, but this response was reversed once the mycobacteria were
safely internalized. By comparing intact mycobacteria, M.
avium Ag, and purified cell wall lipoarabinomannan (LAM), a TLR2
agonist (23), we identify a complex profile of overlapping
gene expression, reflecting involvement of a TLR2 signal cascade.
| Materials and Methods |
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Tissue biopsies were obtained with consent from HIV-1-seropositive patients with MAC and from HIV-1-seronegative donors and processed as described (3, 4). M. avium was visualized following staining with acid-fast New Fuchsin (Sigma-Aldrich, St. Louis, MO) (3). Glutaraldehyde-fixed tissues or cells were postfixed in OsO4, dehydrated through graded ethanol and propylene oxide, embedded in Spurrs epoxy, and thick- and thin-sectioned. Thin sections were placed on copper grids, stained with uranyl acetate and lead citrate, and viewed in a Zeiss EM10 microscope (LEO electron microscope; Oberkochen, Germany) (3).
Purification of human monocytes by counterflow centrifugal elutriation
Human peripheral blood cells were obtained by leukapheresis of normal volunteers at the Department of Transfusion Medicine (National Institutes of Health, Bethesda, MD), diluted in endotoxin-free PBS without Ca2+ and Mg2+ (BioWhittaker, Walkersville, MD) and density-sedimented on lymphocyte separation medium (LSM; ICN Pharmaceuticals, Aurora, OH). The monocytes in the mononuclear cell layer were purified as described (4), suspended in DMEM (BioWhittaker) with 2 mM L-glutamine and 10 µg/ml gentamicin (complete medium), and plated in 6-well (6 x 106 cells/well) or 48-well (1.5 x 106 cells/well) plates (Corning, Cambridge, MA). After an initial adherence for 46 h at 37°C in 5% CO2, 10% human AB- serum (Department of Transfusion Medicine) was added to the culture medium. Cells were cultured 7 days to enable differentiation into macrophages.
Macrophage M. avium infection or treatment with M. avium Ag (MAg) and LAM
Adherent macrophages were infected with viable M. avium at a ratio of 5:1 for 2 h at 37°C (4). The M. avium is a virulent smooth transparent strain passaged in immune-deficient animals to maintain virulence (27). Unbound bacteria were removed by washing the cells three times with PBS and refeeding with complete medium containing 10% FCS. Control populations of adherent macrophages were mock-infected and cultured in parallel. For visualization of mycobacteria-macrophage binding, green fluorescent protein (GFP)-tagged mycobacteria (28) were added to macrophage monolayers for indicated times and evaluated by confocal microscopy. Macrophages from five different donors were infected or not with M. avium, and cells and supernatants were harvested at indicated times from 2 h to 7 days after infection. In additional cultures, 0.550 µg/ml MAg prepared from a M. avium lysate (4) or 0.110 µg/ml M. avium LAM (29) was added for 2 h at 37°C. After incubation with MAg or LAM, cells were washed three times with PBS, and fresh complete medium with 10% FCS was added before culture for the indicated times.
cDNA expression array
Total cellular RNA was extracted from adherent control or infected macrophages using the Qiagen RNeasy minikit (Chatsworth, CA) (4). The Atlas cDNA Expression Array (Clontech Human Array 1.2I, catalog no. 7850-1; Clontech Laboratories, Palo Alto, CA; complete 1200 gene list at http://atlasinfo.clontech.com) was performed using 5 µg of DNase-digested total RNA. The RNA was converted into first-strand cDNA, labeled with [32P]dATP, and purified by column chromatography (NucleoSpin Extraction Spin Column; Clontech Laboratories). The labeled probe was mixed with denaturing solution (1 M NaOH, 10 mM EDTA) for 20 min, then C0t-1 DNA and neutralizing solution (1 M NaH2PO4, pH 7.0) were added for 10 min at 68°C. The nylon membranes were hybridized in a solution of Express Hyb (Clontech Laboratories) and sheared salmon testes DNA for 30 min at 68°C. The probe was added to the membrane and hybridized overnight at 68°C. The membranes were then washed, exposed to phosphor screens, and analyzed with a PhosphorImager (Molecular Dynamics, Sunnyvale, CA). Arrays were analyzed using AtlasImage 1.01a software (Clontech Laboratories). From each donor, macrophage cultures were mock-infected and incubated in parallel with the cells exposed to M. avium and harvested at the same time intervals. The gene expression in infected cells was then compared with the corresponding control population from the same donor expressed as a ratio (fold change) after normalization to housekeeping genes.
Ribonuclease protection assay (RPA)
Total cellular RNA was extracted using the RNeasy minikit (Qiagen) from 6 x 106 control or treated macrophages per well in a six-well plate. Total RNA (3 µg) was used with the hCK-2 template of the Riboquant MultiProbe RPA system (BD PharMingen, San Diego, CA). Band densities were normalized to the GAPDH housekeeping gene using ImageQuant (Molecular Dynamics).
Cytokine ELISA
The supernatants from the M. avium-infected LAM- or
MAg-stimulated macrophages were analyzed for TNF-
production by
ELISA (R&D Systems, Minneapolis, MN).
| Results |
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In immunocompromised hosts, M. avium invades the
intestinal mucosa and is initially taken up by macrophages in the
lamina propria (Fig. 1
A), from
where it can disseminate to lymph nodes (Fig. 1
B) and other
tissues. Enormous numbers of acid fast, deep red-stained mycobacteria
can be readily identified within tissue macrophages. Once inside
macrophages, many, but not all mycobacteria survive and replicate
within phagocytic vacuoles (Fig. 1
C) to eventually be
released to reinfect a new macrophage host. As evident, large numbers
of macrophages accumulate at these sites of infection (Fig. 1
, A and B), largely due to induction of chemokine
synthesis by infected macrophages (30). In the absence of
adequate T cells, this cycle of recruitment and infection appears to
progress unchecked.
|
|
The morphological and structural changes of macrophages early
after exposure to M. avium and during the evolution of
infection demonstrated a bacterial influence on phenotype and function.
To determine the transcriptional impact of the initial interaction
between M. avium and macrophages which may underlie
mycobacterial persistence, the cells were exposed to M.
avium at a ratio of 5:1 for 2 h when RNA was collected and
processed for cDNA expression array. Although all isolated monocytes
were adhered and differentiated under parallel conditions for 7 days
before infection, and individual cultures were synchronously exposed to
mycobacteria, heterogeneity in donor macrophage responses to M.
avium was noted (not shown). As data from individual donors were
reproducible, the heterogeneity, at least in part, stems from the level
of constitutive activation/differentiation of the control macrophages
from each donor upon which the fold change was based, but may also
reflect differential donor susceptibility to the pathogen. We present
data (Table I![]()
![]()
) in which macrophages from
five separate donors were infected
with M. avium. Only those genes which were
reproducibly up-regulated in a minimum of three donors with a mean
2.0-fold increase above parallel donor control macrophages are
represented in Table I![]()
![]()
. For assessment of transcriptional suppression,
we set our cutoff as a mean decrease of 2-fold in infected compared
with uninfected macrophage cultures from the same donor, again in at
least three replicate experiments.
|
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(GNB) subunit 1, and the rap1 GTPase-GDP
dissociation stimulator, as well as kinases, phosphatases, and other
signal regulatory molecules (Table I
and
components, TNFR1, CD40 ligand receptor, IL-6R
, the
Herpes virus entry protein C, and the transferrin receptor were
increased. Associated with enhanced receptors and signaling molecules,
transcription-related genes were also increased, particularly those
involved in the NF-
B pathway, as well as NF-AT cytoplasmic,
activating transcription factor 4, and IFN regulatory factor
(IRF)1.
|
B pathway constituents
(4), a dramatic increase in downstream proinflammatory
gene expression occurred. With this initial engagement of an apparent
host defense response, increased expression of genes for recruitment of
immune cell reinforcements, cell-cell interactions, and cell activation
were observed (Table I
1,
8,
3,
6,
7,
v, and CD11b and
c, in addition to ICAM1 and CD44. In addition to adhesion molecules,
up-regulated chemokines (IL-8, macrophage-inflammatory protein
(MIP)1
, MIP1
, MIP2
, RANTES) (30) and TGF-
would foster leukocyte recruitment and granuloma formation. Multiple
cytokines were also increased early after exposure to M.
avium. Although levels of gene expression were variable between
monocyte donors (n = 5), IL-1
(average 18-fold) and
TNF-
(average 143-fold) were consistently highly elevated within
2 h. Besides IL-1
and TNF-
, the cytokines, B94, LIF,
placenta growth factor (PLGF), IL-15 and IL-6, were typically enhanced
(Table I
. At later
intervals (see below), additional genes were observed to be
down-regulated during mycobacterial growth within the macrophages. Macrophage activation by mycobacterial components
Following the initial infection and in the absence of T
cell activation, M. avium replicates within the cultured
macrophages, although some are killed, degraded, and/or released (Figs. 1
and 2
). To establish whether bacterial constituents such as MAg or
the M. avium LAM stimulated a similar profile of cytokine
genes, cultured macrophages were treated with intact microorganisms,
MAg or purified LAM for 23 h and gene induction was compared with
parallel unstimulated cell populations (Fig. 3
). With one exception (Rap1), the most
highly up-regulated genes in macrophages exposed to live mycobacteria
and to purified LAM were identical at 2 h. Both TNF-
and IL-8
were dominant genes, whether triggered by M. avium or LAM.
Chemokines and adhesion molecules maximally increased by purified LAM
paralleled those induced by viable bacteria interactions with the
macrophage. MAg, representing a complex mycobacterial lysate, also
enhanced expression of these genes, but in a less defined pattern (Fig. 3
). However, by RPA, both LAM and MAg, similar to live mycobacteria,
significantly elevated IL-1
in a dose-dependent fashion (Fig. 4
, A and C) as
determined by densitometric analysis of the blots (Fig. 4
, B
and D) with smaller increases in IL-1Ra and IL-6. A higher
concentration of the crude lysate (MAg) was required compared with the
purified glycolipid to induce a comparable response. IL-1
, IL-12p40,
and IL-10 were nominally affected in this RPA from a
representativedonor within the 23 h interval following exposure
and no induction of IFN-
was detected, confirming the array results
with viable microorganisms.
|
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protein
To further compare the macrophage response to M. avium,
MAg, and LAM, we monitored expression of TNF-
as a representative
gene product. Supernatants from M. avium-infected
macrophages expressed very high levels of TNF-
protein within hours
after exposure to the mycobacteria (4), which declined
precipitously, but remained minimally elevated above uninfected
controls after infection (Fig. 5
A). Both LAM and MAg induced
a dose-dependent release of TNF-
, although purified LAM was
typically a 50100 times more potent stimulus (Fig. 5
B).
Thus, M. avium-induced gene regulation in infected
macrophages identified by cDNA expression array, as represented by
TNF-
, is consistent with and reproducible by RPA (4)
and protein assessment (Fig. 5
), and may represent a key
mycobacterial-induced transient mediator associated with host
defense.
|
The transient release of TNF-
by macrophages infected with
viable microorganisms prompted a kinetic analysis of M.
avium-induced genes beyond the initial binding-signal transduction
event registered at 2 h. In this regard, we monitored macrophage
gene expression 24 h and 4 and 7 days after infection with
M. avium as compared with mock-infected parallel cultures
from the same donors. The initial macrophage response, which appears to
favor signaling and transcription factors, in addition to mediators of
recruitment and activation of the cellular components of host defense
(Table I![]()
![]()
), changes strikingly with time. Over the next 7 days, genes
associated with inflammation and immunity recede, although some were
more stably induced (IL-1
, GNB1, migration inhibitory factor-related
protein (MRP)8/14, and MMPs) based on the means of individual donors
(Table II
, Fig. 6
). Moreover, a new
spectrum of genes was impacted during days 17 postinfection as shown
in Table II
(top 20 up-regulated genes are shown for days 1, 4, and 7
postinfection). Signal-related GNB1 and ERBB3, so strikingly
up-regulated within 2 h, remained elevated for 4 days after
infection (Fig. 6
A). IL-8, which increased >30-fold within
2 h, increased further by 24 h and although it declined
thereafter, remained elevated during the subsequent week. Monocyte
chemoattractant protein (MCP)-1 levels, albeit donor-dependent
(30), were elevated from day 1 through 7 (Fig. 6
B). The migration inhibitory factor-related S100
proteins or calgranulins, particularly MRP8/calgranulin A,
progressively increased through the 7 days evaluated (Fig. 6
C). Sustenance of adhesion molecule expression (Fig. 6
D) may facilitate formation of multinucleated giant cells.
Several of the MMPs rapidly increased and remained elevated after
infection with M. avium, while antiproteases, such as tissue
inhibitor of MMP (TIMP)1 (Table II
), cytoplasmic antiproteinase
(CAP)2 and
1 antitrypsin (Fig. 7
B) also increased. Notable is
a lack of induction of iNOS or defensins at any time point evaluated
after infection in this lymphocyte-depleted population.
|
|
3, cathepsin D and DNase
through day 7 (Fig. 7| Discussion |
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B (4, 31, 33, 34) (N. Vázquez, T. Greenwell-Wild, and S. M. Wahl,
manuscript in preparation). In our transcriptional analyses,
multiple MAP kinase and NF-
B-dependent genes were rapidly and
dramatically elevated by 2 h after infection. Up-regulation of
Rac1 is consistent with recent reports that this Rho family GTPase is
involved in TLR2 signaling (35), as well as cytoskeletal
changes (36) and possibly, autocrine IL-6 signaling linked
to STAT3 (37). Signal transduction leads to rapid up-regulation of a panoply of chemokine mRNAs and proteins (30), similarly up-regulated by other bacteria (38, 39), and likely effective in mediating leukocyte recruitment and initiation of the adaptive immune response. The rapidity with which some of these chemokines are released (30) and their known interactions with cognate seven transmembrane domain G protein-coupled receptors suggests the possibility that the increased gene expression of G protein-associated signaling molecules might be a secondary consequence of engagement of this pathway. Also evident is the persistence of these molecules, particularly IL-8, a week after infection, which is consonant with granulomagenic congregation of inflammatory cells, essential as new bacterial hosts (30). Beyond recruitment of leukocytes, chemokines, in recent times, have been shown to have multiple additional activities in angiogenesis, matrix deposition, and proliferation (reviewed in Ref. 40).
Pathogenicity may also be fostered via enhanced transcription of adhesion molecules to facilitate migration through the endothelial barrier to the site of infection, promote cell-cell interactions, and formation of multinucleated giant cells (4, 5, 41, 42, 43). The regulation of macrophage trafficking may also be a function of elevated MRP8 and MRP14. The production of these myeloid S100 calcium-binding proteins has been associated with fast migrating cells that express high CD11b and preferentially use ICAM-1-dependent mechanisms of transendothelial migration (44, 45). Recruitment and activation of inflammatory cells at the site of infection would not only involve the orchestrated expression of leukocyte and vascular adhesion molecules, and the generation of chemotactic gradients, but also the production of multiple MMPs, essential to dissolution of basement membrane and matrix components.
Along with M. avium-mediated NF-
B activation
(4) and abundant gene expression of TNF-
and IL-1
,
an extensive repertoire of cytokines and other mediators transiently
escalate subsequent to infection. Early, but unsustained increases in
IL-10 and TGF-
may share in dampening the initial activation
response (46, 47). TNF-
and IL-1
, proinflammatory
cytokines that activate multiple signal transduction pathways to
influence both immune and nonimmune cell function, also inhibit
macrophage apoptosis (48). This is in keeping with the
observations that infection with M. avium appears to protect
macrophages from apoptosis, thereby maintaining the pool of infected
and infectible targets (5, 6, 30). Avirulent mycobacteria
reportedly more effectively promote macrophage apoptosis than virulent
strains (49), consistent with our observations that
phagocytic uptake and internalization of M. avium induced
expression of apoptosis regulatory genes. The enhanced expression of
immediate early gene X (IEX)-1L, Bcl-2A1, and Bcl-x may
counteract apoptotic protease-activating factor 1 and Bax with
the balance of pro- and antiapoptotic pathways favoring survival.
During the 7-day postinfection interval monitored, morphologic
integrity and function appeared uncompromised, and apoptosis was not
frequently encountered (assessed by TUNEL staining; H. Hale-Donze,
unpublished observation) in these infected monocyte-derived
macrophages, consistent with the mycobacterial need for prolonging the
functional longevity of their hosts.
The meek IL-12 response observed in this study does not conjure up an
image of a robust Th1 response considered essential to eliminate the
mycobacteria (50). IL-12 is reportedly a key cytokine in
host defense against mycobacteria (51) and the absence of
IL-12 increases infectibility in animals and humans (39, 52, 53). TLR2 signaling in murine macrophages was also recently
shown to not induce IL-12p40, IFN-
, or IL-6 mRNA compared with a
TLR4 agonist (54). And in fact, the initial M.
avium signaling response and generation of inflammatory mediators
by macrophages is transient, suggesting that once internalization
occurs, the mycobacteria suppress the response which allows them to
establish an infectious niche before recognition by the adaptive immune
response. The virulence of strains of M. tuberculosis is
considered inversely proportional to its efficacy in inducing
proinflammatory cytokines (55) such as TNF-
, and the
massive induction of TNF-
by M. avium and LAM could fit
this pattern in an immune competent host. Further insight into the
mechanisms of mycobacterial subversion may be found in the suppression
of certain macrophage genes by the pathogen. In the second phase, when
many of the initially enhanced genes have returned to control levels,
evidence of microbicidally relevant genes implies an attempt to limit
growth of ingested mycobacteria, but macrophages continue to harbor the
M. avium. M. avium is transported to phagosomes, which in
the absence of IFN-
-mediated activation (31), do not
fuse with protease-bearing lysosomes, enabling mycobacterial survival.
Although lysosomal cathepsins D and L transcripts are initially
increased, mycobacteria suppress those lysosomal enzymes which may
otherwise contribute to their demise. Cathepsin D, an acidic protease
up-regulated within hours in response to M. avium, is
synthesized as an inactive 51-kDa proform and typically processed to a
30-kDa mature form in acidic lysosomal compartments (56).
However, viable M. avium-harboring phagosomes, with retarded
acidification, do not process procathepsin D (56, 57),
blocking its proteolytic potential. M. avium inhibition of
cathepsin D activity plus suppression of its transcription, together
with enhanced expression of
1 antitrypsin, may contribute to
mycobacterial escape from degradation. In contrast, MMP7 (matrilysin),
MMP11, MMP14, and MMP9, which increase early, remain variably elevated
through 7 days after infection. MMP9 has previously been shown to be
up-regulated in M. avium-infected PBMC and to facilitate
HIV-1 replication (58). At least at the transcriptional
level, the corresponding modest increase in TIMPs may implicate a
proteolytic imbalance. Whether persistence of MMPs subserves some
mycobacterial need, in addition to facilitating recruitment, cytokine
processing, and granuloma formation (58, 59), is under
evaluation.
Increased virulence may also be associated with increased gene
expression of the transferrin receptor for requisite iron transport
(60), and transient increases in the free radical
scavenging enzyme superoxide dismutase (2 h) may represent a potential
mode of macrophage self-preservation, but also protect the
mycobacteria. Decreased ADORAs, which reportedly regulate TNF-
and
IL-6 (61) and suppress IL-12 production (62),
could also support a less hostile environment. It is conceivable that
the mycobacteria may incorporate multiple cellular mechanisms for their
survival, enabling replication within a safe haven and eventual release
by apoptotic or necrotic macrophages to begin the reinfection process.
Depending on whether pro- or anti-inflammatory-driven responses
prevail, the mycobacteria will be cleared or protective granuloma will
evolve. Evidence for increased platelet-derived growth factor (PDGF),
observed early after infection and elevated again after a week may be
contributory to fibrogenesis.
Whereas M. tuberculosis infects individuals with apparently
normal immune function, M. avium is an opportunistic
pathogen. Our findings with M. avium may provide insight
into unique and/or shared inducible host factors involved in the
differential virulence between M. avium and M.
tuberculosis. Comparing our data for 1200 potential M.
avium-regulated genes in primary macrophages with that for 375
immunoregulatory genes evaluated for M. tuberculosis in a
cell line (63) and in macrophages (39)
revealed not only considerable overlap, but also differences at
early time points. Our study also uniquely monitors gene expression at
later time points consonant with mycobacterial survival and
intracellular growth. Moreover, analysis of M.
tuberculosis-induced changes in gene expression in murine
macrophages (64) revealed both shared and unique
transcriptional pathways. Comparison of M. avium- and
M. tuberculosis-induced gene expression in parallel
macrophage cultures will provide important insight into
virulence-related genes. In addition to host factors, environmental
factors and bacterial genotype and phenotype all influence the outcome
of infection and evolution of disease. These M. avium
opportunists, to which many individuals are exposed, but which
typically cause no symptoms or pathology as they are rapidly cleared,
can become life-threatening in the context of HIV-1 infection or by
other modes of immune suppression (3, 4, 5). Engagement of
adaptive immunity and T cell function is essential to bacterial
containment (65). The requisite IFN-
signal is
deficient in HIV-1-induced immunodeficiency as well as in our purified
macrophage cultures. Whether due to a lack of IFN-
or an inability
to respond to IFN-
, as occurs in macrophages infected with virulent
M. tuberculosis (66), the microorganisms have a
survival advantage. Unraveling the intricacies of M. avium
entry and intracellular cohabitation with macrophages provides new
insights into disarming mycobacterial invasion and evasion of host
defense.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Abbreviations used in this paper: MAC, M. avium complex; TLR, Toll-like receptor; iNOS, inducible NO synthase; MAg, M. avium Ag; LAM, lipoarabinomannan; GFP, green fluorescent protein; RPA, ribonuclease protection assay; MAP, mitogen-activated protein; GNB, guanine nucleotide-binding protein; IRF, IFN regulatory factor; MIP, macrophage-inflammatory protein; PLGF, placenta growth factor; MMP, matrix metalloproteinase; MRP, migration inhibitory factor-related protein; MCP, monocyte chemoattractant protein; TIMP, tissue inhibitor of MMP; CAP, cytoplasmic antiproteinase; ADORA, adenosine A1 receptor; PKC, protein kinase C; PDGF, platelet-derived growth factor; PP, protein phosphatase; ITG, integrin; HSP, heat shock protein; GST, glutathione S-transferase; ERBB, epidermal growth factor; IEX, immediate early gene X. ![]()
Received for publication January 18, 2002. Accepted for publication September 17, 2002.
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J. S. Philalay, C. O. Palermo, K. A. Hauge, T. R. Rustad, and G. A. Cangelosi Genes Required for Intrinsic Multidrug Resistance in Mycobacterium avium Antimicrob. Agents Chemother., September 1, 2004; 48(9): 3412 - 3418. [Abstract] [Full Text] [PDF] |
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S. M. Wahl, T. Greenwell-Wild, G. Peng, G. Ma, J. M. Orenstein, and N. Vazquez Viral and host cofactors facilitate HIV-1 replication in macrophages J. Leukoc. Biol., November 1, 2003; 74(5): 726 - 735. [Abstract] [Full Text] [PDF] |
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