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Infection and Immunity, September 1999, p. 4921-4925, Vol. 67, No. 9
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of Local Cytokines in Increased Gastric
Expression of the Secretory Component in Helicobacter
pylori Infection
Ingela
Ahlstedt,1
Catharina
Lindholm,1
Hans
Lönroth,2
Annika
Hamlet,1,2
Ann-Mari
Svennerholm,1 and
Marianne
Quiding-Järbrink1,*
Departments of Medical Microbiology and
Immunology1 and of
Surgery,2 Göteborg University,
Göteborg, Sweden
Received 23 December 1998/Returned for modification 15 February
1999/Accepted 16 June 1999
 |
ABSTRACT |
Using immunohistochemical staining, we examined the presence of
secretory component (SC) on epithelial cells in gastric and duodenal
biopsy specimens collected from Helicobacter
pylori-infected individuals and healthy controls. Gastric
epithelial cells from healthy volunteers expressed low, but detectable,
levels of SC. In contrast, significantly higher level of expression of
SC (P < 0.001) was observed on epithelial cells in
the antra of H. pylori-infected individuals. The antral SC
expression correlated with staining for gamma interferon of
intraepithelial and lamina propria lymphocytes (rs = 0.76 and 0.69, respectively,
P < 0.001) and correlated weakly with production of
tumor necrosis factor alpha (rs = 0.43, P < 0.05), but it did not correlate at all with
interleukin-4 production.
 |
TEXT |
Infection with the noninvasive human
pathogen Helicobacter pylori gives rise to active chronic
gastritis as well as to substantial production of specific
immunoglobulin A (IgA) that can be detected both in serum and in
gastric aspirates (21, 23, 30, 31). Furthermore, we have
recently demonstrated large numbers of H. pylori-specific
IgA-secreting cells in the gastric mucosae of H. pylori-infected individuals (22). In spite of the local
immune response to H. pylori, the bacteria are rarely
cleared and the infection is usually lifelong. Nevertheless, several
animal studies demonstrated that it is possible to eradicate an already
established Helicobacter infection by means of oral,
therapeutic immunization (4, 9), and in some immunization
studies, protection has been correlated with mucosal IgA responses to
the bacterium (18, 25). On the other hand, it is possible to
protect antibody-deficient mice from H. pylori infection by
similar mucosal immunizations (11).
In mucosal tissues, IgA molecules are predominantly produced as dimers,
which are transported in endocytotic vesicles to the apical side of
epithelial cells bound to secretory component (SC), also known in its
uncleaved form as the polymeric immunoglobulin receptor (3).
Subsequent proteolytic cleavage of SC results in the release of
secretory IgA (S-IgA). Several cytokines have been shown to upregulate
SC expression in vitro, i.e., gamma interferon (IFN-
), tumor
necrosis factor alpha (TNF-
), and interleukin-4 (IL-4) (7, 16,
26). Conflicting results regarding the presence of SC in the
healthy human stomach have been published (13, 15, 17, 28,
29). An association between gastritis and increased gastric SC
expression has, however, been reported (13, 29), and
H. pylori infection also seems to be associated with increased expression of SC by gastric epithelial cells (10, 15). The influence of different components in the H. pylori-induced inflammation on SC expression has, however, not
been established. Therefore, we have examined the expression of SC in
gastric antra and corpora from H. pylori-infected subjects,
both duodenal ulcer (DU) patients and asymptomatic carriers, as well as
from uninfected healthy individuals. In parallel, gastric lymphocyte
and granulocyte infiltration, H. pylori cell density, and
local cytokine production were assessed on the individual level.
Volunteers and specimens.
The study was approved by the Human
Ethical Committee of the Medical Faculty, Göteborg, Sweden, and
comprised 17 subjects infected with H. pylori, of whom 9 had
DU disease (mean age, 52.7 years; five males and four females) and 8 were asymptomatic H. pylori carriers (mean age, 50.9 years;
seven males and one female) who had been identified among healthy blood
donors by using enzyme-linked immunosorbent assay (ELISA)
(12). In addition, nine healthy, uninfected subjects (mean
age, 39.8 years; three males and six females) with no gastrointestinal
disorders or symptoms were recruited to participate in the study. The
DU patients all had chronic relapsing DU disease confirmed by endoscopy
but were in clinical remission at the time of the investigation. The
asymptomatic and uninfected subjects had no history of gastrointestinal
disease or any other relevant illness. None of the subjects were on any
medication related to gastrointestinal symptoms at the time for the
study, and no premedication was used before endoscopy except for local anesthesia.
Gastric aspirates were collected at endoscopy and were immediately put
on ice and adjusted to pH 6 to 8; enzymatic degradation of
immunoglobulins was prevented by addition of bovine serum albumin, phenylmethylsulfonyl fluoride, and soybean trypsin inhibitor
(23). The aspirates were stored at
70°C until ELISA
analysis. Furthermore, biopsy specimens were collected from the
duodenal, antral, and corpus regions from each subject. One specimen
from each site was immediately fixed in formalin and sent for routine
histology at the Department of Pathology, Göteborg University,
where the presence of H. pylori and acute and chronic
inflammation were assessed blindly by an experienced pathologist
according to the Sydney classification system and scored from 0 to 3 (none, mild, moderate, or severe) (8). Four antral biopsy
specimens were immediately snap frozen in O.C.T. compound by using
liquid nitrogen and stored at
70°C until they were stained for
cytokine expression. Finally, fresh biopsy specimens from the antrum
were homogenized and inoculated on Skirrow blood agar plates containing
10% horse blood, which were examined for the presence of H. pylori-like colonies after 3-day incubation under microaerobic
conditions at 37°C. Only individuals who were positive by both
culture and histology were regarded as infected with H. pylori, and only individuals who were negative by both culture and
histology were included in the uninfected group.
SC expression.
Formalin-fixed mucosal biopsy specimens were
paraffin embedded and subsequently stained for SC by the
immunoperoxidase technique according to the manufacturer's
instructions, following trypsin digestion with 1 mg of Trypsin
(Boehringer Mannheim) per ml at 37°C for 30 min. Endogenous
peroxidase activity was blocked with 1% H2O2
and 0.02% NaN3 followed by incubation with 1% goat serum. Thereafter the sections were incubated with a preparation of polyclonal horseradish peroxidase (HRP)-labelled goat antibody to human SC (Nordic
Immunological Laboratories, Tilburg, Holland) at 1 µg/ml at room
temperature for 1 h. The sections were then incubated with
diaminobenzidine substrate (Vector Laboratories, Inc.,
Burlingame, Calif.) for 15 min, rinsed in distilled water,
counterstained with hematoxylin, dehydrated, and mounted with Mountex
(Histolab, Göteborg, Sweden). The intensity of SC staining was
scored on an arbitrary scale from 0 (negative) to 5 (very intense) and
was evaluated blindly by two independent investigators, whose
estimates correlated well (Pearson correlation coefficient
[r] = 0.87).
A polyclonal HRP-labelled goat antibody raised to mouse IgG
(Jackson Immuno Research Laboratories, Inc., West Grove, Pa.)
diluted to 1 µg/ml was used as a negative control, and sections
stained with this antibody were always completely negative. In
addition, the specificity of the SC-reactive antibody preparation
was
examined by absorption with 25 µg of S-IgA purified from human
colostrum (Sigma, St. Louis, Mo.) per ml at 4°C for 3 h. This
treatment completely abolished SC staining of both duodenal and
gastric
specimens, while a parallel incubation with human serum
IgA did not
affect the staining
intensity.
The ability of a single biopsy to represent the SC staining of the
different mucosal compartments was determined before the
start of the
study. From each of three volunteers (two
H. pylori-infected
individuals and one uninfected individual), three
specimens were
collected from each of the duodenum, antrum, and corpus
and stained
as described above. With one exception, all three specimens
collected
from the same site in one individual were judged to have the
same
staining intensity when evaluated blindly. Only the duodenal
specimens
from one
H. pylori-infected individual had
different staining
intensities, ranging from 2 to
4.
When the expression of SC in duodenal and gastric (antrum and corpus
mucosa) biopsy specimens was evaluated, the duodenal
epithelial cells
were usually found to have a higher intensity
of SC staining than the
gastric epithelial cells, either from
the antrum or the corpus (Fig.
1), from the same individual, and
H. pylori infection did not seem to affect duodenal SC
expression
(Fig.
1A). The SC staining of antral sections was always
more
intense on epithelial cells in the neck region of the gastric
glands than on the epitheliums at the surface or deeper in the
glands
(Fig.
2A). The same staining pattern,
although not as pronounced,
was seen also in corpus tissue, and has
also been observed in
previous studies of gastric inflammation
(
13,
29). Therefore,
the staining intensity reported for
gastric specimens is the value
obtained in the neck region. In healthy
individuals, the level
of gastric expression of SC was much lower than
the level seen
in the duodenum (Fig.
1B and C). Nevertheless, SC was
detected
on epithelial cells in the antrum for all but one of the
healthy
volunteers (Fig.
1B), indicating that translocation of locally
produced IgA and IgM across the gastric epithelium can occur in
healthy
individuals. When analyzing biopsy specimens from
H. pylori-infected
individuals, we found that the infection is
associated with an
increased expression of SC in the antrum region of
the stomach
compared to the expression in uninfected individuals
(
P < 0.001,
Wilcoxon rank sum test; Fig.
1B), but
increased expression was
not observed in the corpus (
P > 0.05; Fig.
1C). On the other hand,
there was no difference in
epithelial SC expression between asymptomatic
H. pylori
carriers and DU patients, suggesting that SC expression
and IgA
translocation are probably not important factors in determining
the
outcome of an
H. pylori infection.

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FIG. 1.
Expression of SC on epithelial cells in duodenal and
gastric mucosae. The expression of SC on duodenal (A), antral (B), and
corpus (C) epithelial cells was determined by using
immunohistochemistry, and the staining intensity was graded from 0 to 5 (negative to very intense). Tissues from DU patients (DU), asymptomatic
H. pylori carriers (AS), and H. pylori-negative
healthy volunteers (Hp ) were examined. Each dot represents the
individual value for one volunteer, and the horizontal bars denote the
medians for individual groups. The staining intensity for H. pylori-infected individuals (DU and AS) was significantly
different from that for uninfected individuals (P < 0.001) for the antrum but not (P > 0.05) for the
duodenum and corpus.
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FIG. 2.
Immunohistochemical staining of SC and IgA in
gastrointestinal tissues. (A and B), staining of SC in sections of the
antrum (A) and duodenum (B) from an H. pylori-infected
individual. (C and D), staining of IgA in sections of the antra from an
H. pylori-infected individual (C) and an uninfected healthy
individual (D). Original magnification, ×200.
|
|
IgA production.
Formalin-fixed antral biopsy specimens
were stained for IgA, using an HRP-conjugated goat antibody to
human IgA (Southern Biotechnology Inc., Birmingham, Ala.), according to
the protocols described for SC. S-IgA content in gastric juice was
determined by ELISA as previously described (23), using
commercially available S-IgA (Sigma) as a standard. The
immunohistochemical staining of IgA-positive cells demonstrated that
H. pylori infection is accompanied by a large increase in
the frequencies of IgA-positive cells in the antrum (Fig. 2C and D,
Table 1). The actual frequencies of
IgA-positive cells were difficult to determine, due to a strong staining of the entire lamina propria in specimens from some infected individuals, probably caused by extracellular IgA. The high frequencies of IgA-positive cells in H. pylori-infected volunteers are
in accordance with previous studies by our group documenting
substantially increased frequencies of IgA-secreting cells in the
gastric mucosa of H. pylori-infected individuals
(22), as well as studies by others showing increased amounts
of IgA in gastric tissue homogenates from H. pylori-infected
subjects (21, 31). Increased frequencies of IgA-positive
cells have also been shown in earlier studies of inflamed gastric
tissue (13, 29). Furthermore, total IgA production and
H. pylori-specific IgA production in the gastric mucosa are
very similar in asymptomatic carriers and DU patients (22),
again arguing that local S-IgA production in response to natural
infection does not seem to influence the outcome of H. pylori infection. It is surprising that the combined increase in
gastric IgA production and SC expression did not result in increased
levels of S-IgA in gastric aspirates of H. pylori-infected subjects compared to the levels in uninfected volunteers. This is
probably caused by the relatively small number of volunteers in the
study and by the fact that IgA concentrations were determined only at a
single time point. In addition, reflux of duodenal contents to the
stomach might conceal the differences in gastric S-IgA output between
H. pylori-infected and uninfected subjects.
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TABLE 1.
IgA in the stomachs of H. pylori-infected
subjects (both DU patients and asymptomatic carriers) and
uninfected healthy subjects
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Gastric inflammation.
The grade of acute and chronic
inflammation and presence of H. pylori in gastric biopsy
specimens were evaluated according to the Sydney system (8)
and scored from 0 to 3 (none, mild, moderate, or severe). The
inflammation scores were significantly higher in the antrum than in the
corpus for the H. pylori-infected individuals (P < 0.01, Wilcoxon signed rank test). The mean scores for chronic
gastritis were 1.8 (range, 1 to 3) for the antrum and 1.2 (range, 0 to
2) for the corpus, and the mean scores for active gastritis were 1.5 (range, 0 to 3) for the antrum and 0.8 (range, 0 to 3) for the corpus.
All but one of the uninfected subjects (who had grade 1 lymphocytic
gastritis in the corpus) had normal mucosa without inflammation. The
Helicobacter-like organism (HLO) density scores for both the
antrum and the corpus varied between 0 and 3 for the specimens from
infected subjects. The mean score for the antrum (2.5) was higher than
that for the corpus (1.8), but the difference was not statistically
significant. Expression of SC did not seem to be directly related to
the density of H. pylori or inflammatory cells in either the
antrum or the corpus. Thus, when the correlation of the SC score with
each of HLO density and lymphocyte and granulocyte scores was
evaluated, granulocyte infiltration and SC expression were found to
correlate weakly for the corpus (rs = 0.54, P < 0.05) but no other analysis revealed any
significant correlation. Furthermore, the observation that the
inflammation in the corpus of the H. pylori-infected volunteers was not accompanied by an increase in SC expression compared
to the expression in uninfected individuals suggests that the presence
of inflammatory cells per se is not a crucial factor influencing the
expression of SC. In accordance, it has been shown that SC expression
on dysplastic epithelial cells is actually inversely related to the
degree of inflammation in ulcerative colitis patients (27).
Antral cytokine production and SC expression.
Several in vitro
studies have shown that SC expression by intestinal epithelial cell
lines is upregulated by IFN-
, IL-4, and TNF-
, either alone or in
combinations (7, 16, 26). Since increased levels of IFN-
and TNF-
are hallmarks of H. pylori-associated gastritis
(5, 6, 14, 24), we examined if local cytokine production
might influence SC expression.
Cryopreserved antral biopsy specimens were analyzed for the presence of
cells containing IFN-

, TNF-

, or IL-4 according to
the protocol of
Andersson et al. (
1). Briefly, thin (8-µm)
cryosections
were fixed in 4% paraformaldehyde and permeabilized
with 0.1% saponin
(Sigma) before staining with cytokine-specific
monoclonal antibodies
(MAbs) (for IFN-

clone DIK 1, Chromogenix,
Mölndal,
Sweden; for TNF-

, clone mAb-1, Pharmingen, San Diego,
Calif.; for IL-4 clone 8F12, ImmunoKontakt, Bioggio, Switzerland),
followed by the stepwise addition of a biotinylated goat antibody
to
mouse IgG1 (Caltag Laboratories, South San Francisco, Calif.),
HRP-labelled avidin biotin complex (Vector), and diaminobenzidine
substrate. The specificity of the assay was ascertained by parallel
incubation with a control mouse IgG1 MAb. Cytokine expression
detected
by immunohistochemistry by to this procedure has previously
been shown
to correlate closely to in situ hybridization with
cytokine mRNA
(
20). IFN-

-, TNF-

-, and IL-4-containing cells
were
seen in the antral mucosae of most of the
H. pylori-infected
individuals. The individual variation in cytokine expression was
large,
but as a whole,
H. pylori-infected individuals had a
significantly
greater expression of IFN-

and TNF-

than healthy
ones, whereas
staining for IL-4 was similar for
H. pylori-infected and healthy
individuals (Table
2). These results have in part been
reported
previously (
19), but analyses have now been
extended. The correlation
between SC expression and IFN-

, TNF-

,
or IL-4 staining of lamina
propria and intraepithelial lymphocytes was
evaluated by using
Spearman's rank correlation. SC expression
correlated well with
the frequencies of IFN-

-positive lymphocytes,
both intraepithelial
cells and lamina propria cells
(
rs = 0.76 and 0.69, respectively,
P < 0.001). The expression of TNF-

by lamina
propria lymphocytes
also correlated weakly with SC expression
(
rs = 0.43,
P < 0.05).
In
contrast, IL-4 expression did not at all correlate with SC
expression
(
rs = 0.10). It is also interesting that in
our study,
as well as in previous studies of gastric inflammation
(
13,
29), the most intense staining for SC in the stomach is
found
in the neck region of the gastric glands, which is actually the
area where we detected the highest frequencies of IFN-

-containing
cells. These observations are the first in vivo correlates to
the
established capacity of IFN-

to enhance SC expression in
transformed
epithelial cell lines. In analogy with the findings
for the stomach,
several intestinal inflammatory diseases, such
as celiac disease and
Crohn's disease, which are strongly associated
with increased IFN-

production, also result in increased SC expression
by enterocytes
(
2).
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TABLE 2.
Frequencies of cytokine-expressing lymphocytes in the
antra of H. pylori-infected subjects (both DU patients
and asymptomatic carriers) and uninfected healthy subjects
|
|
In conclusion, our findings confirm that gastric epithelial cells have
the potential to translocate locally produced IgA across
the epithelium
by SC-mediated transcytosis. We also show that
this capacity is greatly
enhanced following infection with
H. pylori, possibly due to
gastric cytokine
production.
 |
ACKNOWLEDGMENTS |
We are grateful to Ulf Andersson, Huddinge Hospital,
Stockholm, for valuable help with establishing the cytokine
staining technique. We thank all volunteers who participated in this
study and the staff at the Gastroenterology unit at Sahlgrenska
University Hospital.
This study was supported by a grant from Astra Research Center, Boston.
 |
FOOTNOTES |
*
Corresponding author. Mailing address: Dept. of
Infectious and Tropical Diseases, London School of Hygiene and Tropical
Medicine, Keppel Street, London WC1E 7HT, United Kingdom. Phone:
44-171-927 2257. Fax: 44-171-323 5687. E-mail:
m.quiding{at}lshtm.ac.uk.
Editor:
J. R. McGhee
 |
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Infection and Immunity, September 1999, p. 4921-4925, Vol. 67, No. 9
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Copyright © 1999, American Society for Microbiology. All rights reserved.
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