The main rhinovirus respiratory tract adhesion site (ICAM-1) is upregulated in smokers and patients with chronic airflow limitation (CAL)
Shukla et al. Respiratory Research
The main rhinovirus respiratory tract adhesion site (ICAM-1) is upregulated in smokers and patients with chronic airflow limitation (CAL)
Shakti Dhar Shukla 0
Malik Quasir Mahmood 0
Steven Weston 0
Roger Latham 0
Hans Konrad Muller 0
Sukhwinder Singh Sohal 0 1
Eugene Haydn Walters 0
0 NHMRC Centre of Research Excellence for Chronic Respiratory Disease, School of Medicine, University of Tasmania , MS1, 17 Liverpool Street, Private Bag 23, Hobart, Tasmania 7000 , Australia
1 School of Health Sciences, University of Tasmania , Launceston, Tasmania 7248 , Australia
Background: ICAM-1 is a major receptor for ~60% of human rhinoviruses, and non-typeable Haemophilus influenzae, two major pathogens in COPD. Increased cell-surface expression of ICAM-1 in response to tobacco smoke exposure has been suggested. We have investigated epithelial ICAM-1 expression in both the large and small airways, and lung parenchyma in smoking-related chronic airflow limitation (CAL) patients. Methods: We evaluated epithelial ICAM-1 expression in resected lung tissue: 8 smokers with normal spirometry (NLFS); 29 CAL patients (10 small-airway disease; 9 COPD-smokers; 10 COPD ex-smokers); Controls (NC): 15 normal airway/lung tissues. Immunostaining with anti-ICAM-1 monoclonal antibody was quantified with computerized image analysis. The percent and type of cells expressing ICAM-1 in large and small airway epithelium and parenchyma were enumerated, plus percentage of epithelial goblet and submucosal glands positive for ICAM- 1. Results: A major increase in ICAM-1 expression in epithelial cells was found in both large (p < 0.006) and small airways (p < 0.004) of CAL subjects compared to NC, with NLFS being intermediate. In the CAL group, both basal and luminal areas stained heavily for ICAM-1, so did goblet cells and sub-mucosal glands, however in either NC or NLFS subjects, only epithelial cell luminal surfaces stained. ICAM-1 expression on alveolar pneumocytes (mainly type II) was slightly increased in CAL and NLFS (p < 0.01). Pack-years of smoking correlated with ICAM-1 expression (r = 0.49; p < 0.03). Conclusion: Airway ICAM-1 expression is markedly upregulated in CAL group, which could be crucial in rhinoviral and NTHi infections. The parenchymal ICAM-1 is affected by smoking, with no further enhancement in CAL subjects.
Intercellular adhesion molecule-1; Human rhinovirus; Epithelial adhesion; Chronic obstructive pulmonary disease; Chronic airflow limitation
Chronic obstructive pulmonary disease (COPD) is the
third leading cause of mortality worldwide. It is a disabling
condition resulting from damage inflicted by noxious
particles and gases, mainly from cigarette smoke leading to
airway remodeling and poorly-reversible airflow
obstruction . COPD patients are often prone to episodes of
acute exacerbations of COPD (AECOPD), which drive the
disease and are associated with higher mortality risks,
decreased quality of life, accelerated loss of lung function
and enormous health care costs .
COPD is seriously complicated by bacterial and viral
infections. Bacteria, viruses and co-infection with both,
have been shown to be important in precipitating
AECOPD, with viruses being detected in 40 to 60% in
PCR-based studies . Viral infections are also
associated with more severe exacerbations . Human
rhinoviruses (HRVs) make up approximately 50% of all
viruses isolated from COPD patients . The viral load
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at AECOPD is significantly higher than in the stable
state . The sputum viral load correlates with sputum
neutrophilia and interleukin-8 levels , i.e., the
activation of innate inflammation.
Respiratory tract epithelium is the primary target for
viral pathogens. Attachment of most HRV serotypes to
bronchial and alveolar airway epithelial cells is mediated
by intercellular adhesion molecule 1 (ICAM-1; CD54),
in more than 60%, and is essential for host-cell entry,
while low-density-lipoprotein receptor and related
molecules are receptors for only 10% of HRV serotypes .
ICAM-1 is a member of the immunoglobulin (Ig)
superfamily that contains five Ig-like domains, a
transmembrane domain, and a short cytoplasmic tail ; it is
expressed constitutively on a wide variety of cells
(including respiratory epithelial cells), but generally at a
low basal level , and further inducible by the
inflammatory mediators . Physiologically, ICAM-1 plays a
key role in stabilizing cell-cell interactions and it also
facilitates leukocyte per-endothelial transmigration from
blood into inflamed tissues .
Exposure of small-airway epithelial cells from
physiologically normal smokers to cigarette smoke causes
increased cell ICAM-1 expression . Clinical studies
have demonstrated elevated level of serum (soluble)
ICAM-1 in COPD-smokers compared to non-COPD
active smokers . HRV itself up-regulates
membranebound ICAM-1 expression via a NF-κβ-dependent
mechanism . However, the expression of ICAM-1
has not been directly investigated in large or small
airways in COPD patients, which could be crucial for
understanding their susceptibility to viral infections and
the natural history of COPD. Anti-ICAM-1 antibody has
been shown to inhibit major group HRV replication in
vitro, as well as HRV-induced inflammation and lung
virus RNA levels in a mice model .
Although most attention has been on HRV, ICAM-1
may serve as an adhesion molecule for Haemophilus
influenzae (via bacterial P5 fimbriae), which is the main
bacterial pathogen in COPD . Thus, ICAM-1 is an
Table 1 Demographic and lung function data for participants
Smoking history (pack years)
attractive target to block not only virus-receptor binding,
but also to check ICAM-1-mediated NTHi adhesion to
In the present study, we have taken a new direction
for human work, and test the potential for clinical
relevance of some of these previous observations. We have
investigated whether ICAM-1 expression is upregulated
in the epithelium of airways, and alveoli, in both
“normal” smokers and in patients with airflow obstruction.
This study has a cross-sectional analysis of data. A total
of 37 patients provided lung tissue at surgery. All had
primary non-small cell lung cancer (NSCLC), with an
approximately equal distribution of squamous and
adenocarcinoma. Patients were classified as current
smokers or ex-smokers (at least 12 months of smoking
cessation). Nineteen of these had demonstrated GOLD
stage I/II COPD on post-bronchodilator spirometry
(FER < 70%), and ten patients had small airway disease
(SAD) only, based on scalloping of the expiratory limb
of the flow-volume curve and FEF25-75 < 70% predicted.
In addition, there were eight individuals who were
current smokers with no evidence of airflow obstruction,
and hence designated as smokers with normal lung
function (NLFS). Because of the relatively small
numbers, and because of no obvious difference between
them in ICAM-1 expression, the small airway disease
(SAD) and definite COPD groups were merged as a
single chronic airflow limitation (CAL) group. Those with a
history of other chronic respiratory disorders were
excluded (Table 1), including anyone with a history or
clinical/physiological suggestion of asthma.
Resected lung sections from nine non-smoking,
nonCOPD subjects were included as a control group (NC)
for comparison of ICAM-1 expression in the small
airways. Large airway biopsies (n = 8) from our tissue
biobank were used as normal controls for the large
airway resected tissue.
FEF25–75% (L/sec)a N/A N/A 81.5 (70–116)
Data expressed as median and range
CAL chronic airflow limitation, FEV1 forced expiratory volume in 1 s, FVC forced vital capacity, FEF25–75% forced expiratory flow at 25–75%, LA large airway, NC
normal control, NLFS normal lung function smoker, N/A not any, SA small airway
aPost bronchodilator values after 400 μg of salbutamol
Tissue section acquisition and processing
Surgical resection material well away from the main
tumour, and containing non-cancer affected small
(<2 mm internal diameter) and large airways, were fixed
in formalin within minutes of surgery. At processing,
tissue blocks were embedded in paraffin for sectioning,
staining and further analyses, as previously described .
Sections were cut at 3 μm intervals from individual
paraffin embedded blocks, stained first with hematoxylin
and eosin for morphological assessment for quality and
lack of damage. Following removal of paraffin and
rehydration, immunostaining for ICAM-1 was done using an
anti-ICAM-1 monoclonal antibody (Merck Millipore
Corporation, Merck KGaA, Darmstadt, Germany,
Catalogue No MAB2130, 1/250 dilution for 90 min at 20 °C,
post heat retrieval). Appropriate negative and positive
controls were included in the study, as previously
outlined . To specifically co-localize Goblet Cells and
ICAM-1 staining serial sections from the same blocks
were taken; immunostaining for ICAM-1 performed as
above on one, and for the Goblet Cells a standard
Periodic acid (May & Baker, Dagenham, England) and
Schiff regent (Merck KGaA, Darmstadt, Germany)
protocol with haematoxylin as a nuclear stain was used.
Quantification of tissue sections
Computer-assisted image analysis was performed with a
Leica DM 2500 microscope (Leica Microsystems,
Wetzlar, Germany), Leica DFC495 camera (Leica
Microsystems, Wetzlar, Germany), and Image Pro Plus 7.0
(Media Cybernetics, Inc., Rockville, MD, USA) software.
An operator blinded to smoking and clinical status
assessed expression of ICAM-1 on randomized and
coded slides. For the epithelial analysis in both the large
and small airways, we randomly chose eight fields, all
without a tumor interface. ICAM-1 expression in both
the large and small airway epithelium was expressed as
the percentage of ICAM-1-expressing cells out of the
total cells. Moreover, ICAM-1 expression was
differentiated between being basal or global. An additional
quantification of ICAM-1 expression in the goblet cells and
sub mucosal glands was done in large airways only, with
staining intensity evaluated as: 0, negative; 1, weak; 2,
moderate for <20% of cells; 3, moderate for >20% of
cells; 4, strong for >20% of cells. ICAM-1-expressing
cells in airway reticular basement membrane (Rbm) were
also quantified and normalized over length of Rbm. For
alveolar ICAM-1 expression, the number of type I and
type II pneumocytes expressing the antigen were
quantified as percent of total alveolar epithelial cells. The
length of alveolar wall quantitated was approximately
Cell culture and qPCR
Bronchial epithelial cells from a commercial cell line
(BEAS-2B) (CellBank, Australia) were cultured as
described previously . At >80% confluency, cells were
stimulated with cigarette smoke extract (1%) for 4 h. RNA
was isolated from cells using the using the ReliaprepTM
Mini RNA cell Miniprep system (Promega, Australia).
Complementary DNA (cDNA) was then generated and
collected using the Promega cDNA synthesis kit
(Promega, Australia). The level of ICAM-1 (H_ICAM1_1,
Sigma Aldrich, USA) transcript was determined by qPCR
using the Corbett Rotor-Gene 6000 system (Qiagen,
Germany). Thermocycling controls were run as previously
described . The relative change of expression was
normalized to three-reference genes (18S rRNA, β-actin,
β2-microglobulin) using comparative analysis according
to the manufacturer’s guidelines (Qiagen, Germany). Data
were derived from two independent experiments, each
performed in duplicate.
Fixation and immunofluorescence
Cultured BEAS-2B cells were fixed and stained as
previously described . Briefly, post CSE-stimulation (or
controls), cells were fixed with 4% paraformaldehyde
(Sigma Aldrich, USA) for 20 min at room temperature
and rinsed. Blocking was done with 1% bovine serum
albumin (Sigma Aldrich, USA) and 1% Triton X-100 in
PBS, the cells were rinsed with PBS and incubated with a
1/250 dilution of anti-ICAM-1 antibody (Merck Millipore
Corporation, Merck KGaA, Darmstadt, Germany) in
blocking buffer overnight at 4 °C and then incubated with
a 1/500 dilution of AlexaFluor 498-conjugated goat
antimouse secondary antibody (Molecular Probes, USA) in
blocking buffer for 1 h at room temperature. The cells
were rinsed and then stained with 4′, 6-
diamidino-2phenylindole (DAPI; Life Technologies, USA), diluted
1:5000 in PBS, and then incubated in the dark at room
temperature for 15 min. The cells were washed three
times with PBS before slides were mounted with
Fluorescent-mounting Media (Dako, Australia).
Micrographs were analysed using an Olympus BX50
Fluorescence Microscope (Olympus; Tokyo, Japan) with
NIH elements microscopy software (Nikon; Tokyo,
Japan) and CoolSnap Hq2 CCD camera (Photometrics,
USA). Image merging was completed using Adobe
Photoshop C56 software (Adobe Systems, California,
USA). The percentage area of ICAM-1 cell expression
(green staining) was normalized by cell nuclei area (blue
staining), as neither nuclear nor cell area are likely to
have changed. This was measured using area of interest
using the cell-tracing capacity of our computer-aided
image analysis software (Image Pro Plus 7.0, Media
Cybernetics, Inc., USA), using a method previously
The distributions of these cross-sectional data were
generally skewed in an upward direction, so results are
presented as medians and ranges; non- parametric analyses
of variance was performed first (Kruskal-Wallis Test
comparing medians across all the groups of interest) and
specific group differences were then explored as
appropriate according to prior hypotheses (CAL verses
controls) using the Mann–Whitney U test. We also
performed regression analysis for ICAM-1 expression
against age, FEV1, and smoking history in both the
normal smoker controls and CAL groups separately.
Statistical analyses were performed using GraphPad Prism 6.0
(2012) for Windows, (GraphPad Software Inc., La Jolla,
CA, USA), with a two-tailed p-value ≤0.05 being
considered statistically significant.
ICAM-1 expression in epithelium of large and small
Compared to normal controls, epithelial staining was
increased in the apical areas in the NLFS group (large
airways: p < 0.006; small airways: p < 0.004), whereas in the
CAL group, heavy ICAM-1 expression was observed
throughout the airway epithelium (large airways: p <
0.001; small airways: p < 0.001), including both the apical
and basal cells, though basal cell staining was heaviest
(Figs. 1 and 2). CAL airways also had significantly greater
expression than the NLFS group (large airways: p < 0.007;
small airways: p < 0.02). For all current smoker groups
analyzed separately, there were positive relationships between
pack-year smoking history and ICAM-1 expression, for
both the large and small airways (r = 0.50; p < 0.03) (Fig. 3).
ICAM-1 positive cells in the airway reticular basement
The Rbm in smokers and especially in COPD have been
reported as hyper-cellular , and this was true in this study
also. However, the only significant increase in the number
of ICAM-1 expressing cells in the Rbm was observed in the
small airway walls of the CAL group (p < 0.02), in cells with
a fibroblast-like phenotype (Additional file 1: Figure S1).
ICAM-1 expression in the goblet cells and sub-mucosal
glands in the large airways
A novel finding that we did not expect, was that
Goblet Cells in the large airways of NLFS (p < 0.05)
and CAL (p < 0.004) patients seemed to show especially
intense ICAM-1 expression compared to control tissues
(Figs. 1, 4 and 5). That these cells were indeed Goblet
Cells was confirmed by the differential staining in serial
sections (Fig. 6). In addition, the Goblet Cell staining
Fig. 1 Intercellular adhesion molecule-1 (ICAM-1) expression in epithelium of large (a-c) and small airways (d-f). a, d Representative section of
small airway from a never smoker showing negligible ICAM-1 staining. b, e Typical normal lung function smoker showing positive staining
(showed by black arrow). c, f Typical COPD-smoker showing extensive ICAM-1 staining (black arrow). Magnification = x400. BC: basal cells; EC:
epithelial cells; GC; goblet cells
Fig. 2 Quantification of ICAM-1-expressing cells in cross-sectional study (a) large airway epithelium. b small airway epithelium. c lung alveolar
epithelial cells. Abbreviations: NC, normal control; CAL, chronic airflow limitation; ICAM-1, intercellular adhesion molecule-1; NLFS, normal
intensity was significantly higher for the CAL group (p <
0.04), compared with NLFS and NC groups combined.
Similarly, we observed increased ICAM-1 positivity in the
submucosal glands in tissues from the CAL group (p <
0.05) compared with NLFS group, and there was also
higher staining intensity (p < 0.03) (Figs. 4 and 5).
ICAM-1 expression in the alveolar cells in lung
Overall, approximately 15–30% of total epithelial cells, most
frequently but not exclusive type II cells, were found to be
positive in both the NLFS (p < 0.008) and CAL (p < 0.007)
groups, compared with normal tissue (Figs. 2 and 4).
Cigarette smoke extract (CSE) treatment upregulates
ICAM-1 expression in bronchial epithelial cells
Limited ICAM-1 expression was observed in control
BEAS-2B cells, although on a few cells only and at very
low levels (Fig. 7a). CSE exposure significantly increased
ICAM-1 protein expression per cell compared to
untreated cells (Fig. 7b, d). Further, ICAM-1 mRNA
expression (relative to three housekeeping genes)
wasincreased in BEAS-2B cells exposed to CSE (p < 0.03; n = 4)
compared to control cells (Fig. 7c).
This is the first comprehensive report of increased
ICAM-1 protein expression in epithelium of both the
large and small airways in smokers but especially in
patients with chronic airflow limitation. This group
consisted both of frank COPD plus individuals with small
airway obstruction only, but we combined them because
their data were very similar. There was some
upregulation in the alveolar epithelium, but this was less
marked than in the airways, and uniform between
smokers and all CAL groups. We also found increased
ICAM-1 expression in goblet cells in large airway
epithelium from smokers and CAL, but more marked in
CAL. Moreover, ICAM-1 expression, both at the mRNA
and protein level, was upregulated in cultured bronchial
epithelial cells exposed to cigarette smoke extract. These
findings, taken as a whole, may be crucial for
understanding the vulnerability of smokers and especially
patients with airflow obstruction to airway infections,
specifically with HRV and NTHi, although for the latter,
platelet-activating factor receptor (PAFr) upregulation
may be of even greater importance [18, 19].
Clinical relevance of increased ICAM-1 expression in
the pathogenesis of smoking-related airway diseases
including COPD has been suggested previously, but
mainly through indirect data, as discussed in
introduction [13, 25]. Moreover, higher ICAM-1 protein
expression was reported in the basal cells of bronchial
epithelium from individuals with “bronchitis”, compared
to normal individuals , but sputum concentrations of
sICAM-1 did not significantly correlate with FEV1 .
Fig. 3 Correlation between total epithelial cells positive for ICAM-1 with smoking history (pack years). a large airway epithelium. b small airway
epithelium. c lung alveolar epithelial cells. Abbreviations: ICAM-1, intercellular adhesion molecule-1
Fig. 4 Photomicrograph showing ICAM-1 expression. (a-b) lung alveolar epithelium. (c-d) submucosal glands. (a) Representative sections from a
never smoker. (b) Typical COPD-smoker showing positive staining in alveolar epithelial cells (mainly type II). (c) normal lung function smoker. (d)
COPD-smoker showing extensive ICAM-1 staining in submucosal glands. Magnification: A-B=x100; C-D=x200
Systemically, serum-sICAM-1 was higher in COPD
patients than either non-smoking healthy subjects or
smokers without COPD . Additionally, higher
concentrations of serum sICAM-1 in COPD did relate with
worsening spirometry . However, in contrast,
Noguera et al. showed lower serum levels of sICAM-1 in
patients with stable COPD than in healthy non-smokers
. In our study, we did not find any correlation
between cellular ICAM-1-expression in the airway and
either age or lung function in the CAL group, but
ICAM-1 expression in both the large and small airways
was significantly correlated with smoking history, with a
wide range of pack-years represented.
HRV has been detected in lower airway specimens
such as sputum from children with wheezy bronchitis
, and brushed cells from allergic volunteers
experimentally infected with RV16  by RT-PCR and
culture. Moreover, compared with normal control, cultured
airway epithelial cells from patients with COPD showed
increased susceptibility to RV infection, and also higher
levels of mRNAs encoding ICAM-1 . In normal
primary human bronchial epithelial cell cultures, HRV itself
upregulated membrane-bound ICAM-1 expression via
NF-κβ-dependent mechanisms , suggesting a
potential vicious cycle.
Interestingly, cultured epithelial basal cells were
found to be more susceptible to RV infection than
supra-basal cells, and basal cells also stained more for
ICAM-1 expression . The potential clinical
significance of ICAM-1 as a therapeutic target has been
shown by blocking the ICAM-1 receptor with
antiICAM-1 monoclonal antibodies (MAb) in an in vitro
cell-culture model . In addition, corticosteroid
pretreatment resulted in inhibition of HRV-induced ICAM-1
upregulation in both primary bronchial epithelial and
A549 cells . and one could speculate that this might
be one means by which corticosteroid therapy decreases
Although respiratory tract ciliated cells are thought to
be the major target for microbial pathogens, large airway
goblet cells, an integral part of respiratory epithelium,
and submucosal glandular cells, may also be involved.
Empirically, airway viral infection results in mucus
hypersecretion, which may play a role in the pathogenesis
of severe airway obstruction in AECOPD. Notably, we
showed increased ICAM-1 expression (both in number
and intensity) in goblet cells and submucosal glands in
the large airway of smokers, but especially in CAL
patients, which was further confirmed by staining
serially-sectioned airway wall-containing lung tissues
with a specific Goblet Cell marker, Periodic
acidSchiff (PAS). Previous research has shown that HRV
infection could upregulate ICAM-1-mRNA and
inflammatory cytokines in submucosal gland cells, and,
an anti-ICAM-1 antibody blocked both infection and
production of these cytokines . Thus, airway
goblet cells and submucosal glands may be important
potential targets of HRV induced mucus hypersecretion
via viral-epithelial interactions , and given that
there is marked hypertrophy of this glandular tissue
Fig. 5 Quantification of ICAM-1-expressing goblet cells (a-b) and submucosal glands (c-d) in the cross-sectional study. (a) ICAM-1 expressing
goblet cells in large airway epithelium. (b) Intensity of ICAM-1 staining of goblet cells in large airway epithelium. Only ICAM-1 positive goblet cells are
included in this comparison. (c) ICAM-1 expressing submucosal glands. (d) Intensity of ICAM-1 staining of submucosal glands. Abbreviations: NC,
normal control; CAL, chronic airflow limitation; ICAM-1, intercellular adhesion molecule-1; NLFS, normal lung-function smoker
Fig. 6 Resected lung tissue sections from a COPD-smoker showing goblet cells in of large airway epithelium. (a) ICAM-1 expression, stained with
anti-ICAM-1 antibody (brown). (b) goblet cell marker, stained with Periodic Acid-Schiff (purple). Block arrows showing goblet cells expressing both
ICAM-1 and PAS staining. Magnification=400x
Fig. 7 Photomicrograph showing ICAM-1 expression in bronchial epithelial cells. a BEAS-2B control cells. b BEAS-2B cells pretreated with CSE (1%,
4 h). c CSE 1% increases ICAM-1 transcript level, assessed by quantitative RT-PCR and normalized for three housekeeping genes. d CSE (1%) also
increases protein expression on epithelial cell culture, quantified by computerized image analysis software. Data is presented as mean ± SEM.
Magnification = 400x. (Blue: nuclear stain DAPI; Green: Alexa Fluor 488 showing ICAM-1 stain)
in COPD, it again adds to the vulnerability of these
patients towards HRV infections.
ICAM-1 may also serve as an adhesion receptor for
NTHi . Blocking cell surface ICAM-1 with specific
antibody significantly reduced the adhesion of NTHi to
epithelial cells . It has been shown that NTHi itself
upregulates ICAM-1 expression and HRV adherence
[41, 42]. These studies did not take into account the
possibility of co-regulation of ICAM-1 with Platelet
Activating Factor receptor (PAFr), which we have
previously suggested to be the main airway adhesion site for
pathogenic Haemophilus , with a tight correlation
between PAFr expression and NTHi adhesion to airway
epithelial cells . Work on potential reinforcing
interactions between these two adhesion systems is now
urgently needed, since novel non-antibiotic, broad
antiinfective therapeutic strategies could emerge.
Alveolar epithelial cell ICAM-1 expression was
increased equivalently in smokers and the CAL group,
with type II cells being the predominant cell type
affected. Empirically, staining was much less marked than
in the airways. Burns et al. also previously reported
increased ICAM-1 expression in type II pneumocytes in
mice lung tissue exposed to S. pneumoniae ,
emphasized the possibility of ICAM-1 upregulation increasing
neutrophilia, but not the possibility of increased
The strengths of the present study include the use of
abundant and relevant human tissue in well phenotyped
individuals with mild-to-moderate obstructive airway
disease, focusing on pathogenic mechanisms in relatively
early disease with few confounding factors such as
chronic bacterial infection or emphysema. We had
robust numbers to give sufficient power to detect these
findings, and this was confirmed by the strong statistical
There are also a few limitations. Firstly, the study was
cross-sectional and longitudinal studies of ICAM-1
expression are needed. Secondly, our control subjects were
somewhat younger on average, but ages over-lapped
substantially between groups and there was no
suggestion of a relationship between ICAM-1 expression and
age. Finally, we did not investigate viral adherence to in
relation to ICAM-1 expression.
In conclusion, epithelial ICAM-1 expression is
upregulated throughout the respiratory tract in smokers, but is
especially marked in the airway epithelium in subjects
with chronic airflow obstruction, even when mild.
ICAM-1 expression in Goblet Cells and sub-mucosal
glands in the airway wall is also markedly increased.
There is also an increase in the alveolar epithelium,
especially in Type-2 cells, but this is a smoking effect only,
and not further enhanced in COPD. Increased
expression of ICAM-1 in the respiratory tract, and mostly so
in the airways, could be a crucial risk factor for infection
here with the most common “respiratory” viral and
bacterial pathogens, and indeed such changes in pathogen
adhesion sites may underlie this vulnerability of smokers
and people with COPD to these specific infections which
is otherwise unexplained. Translational research in this
area is still in its infancy but has huge potential to
provide new therapeutic targets to modify clinical
management of smoking-related airflow limitation. Thus,
further clinical research on anti-ICAM-1 therapies and
therapies against other up-regulated microbial adhesion
sites is now warranted, and indeed urgently needed.
Additional file 1: Figure S1. ICAM-1-positive cells in reticular basement
membrane (Rbm) in the cross-sectional study. (A) large airway; (B) small
airway. Abbreviations: CAL: chronic airflow limitation; NC, normal control;
NLFS, normal lung-function smoker. (TIFF 924 kb)
Availability of data and material
The complete dataset is included in this manuscript.
Study design and conception: EHW, SDS and SSS; clinical assessment and
tissue collection: EHW and HKM; laboratory experiments and data acquisition:
SDS, SW and RL; data interpretation and analysis: SDS, MQM and EHW;
drafting of manuscript: All co-authors; critical revision of manuscript: EHW,
SDS and SSS. All authors read and approved the final manuscript.
Ethics approval and consent to participate
The Tasmania Health & Medical Human Research Ethics Committee
approved the study (EC00337 and H0013051). All subjects gave written,
informed consent to use their tissue, either prior to volunteer bronchoscopy
and biopsy, or prior to lung surgery.
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