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Infection and Immunity, June 2003, p. 3572-3577, Vol. 71, No. 6
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.6.3572-3577.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
* James G. Fox,2 Amy E. Juedes,3,
and Nancy H. Ruddle3
Section of Comparative Medicine, Yale University, New Haven, Connecticut 06510,1 Massachusetts Institute of Technology, Division of Comparative Medicine, Cambridge, Massachusetts 02139,2 Department of Epidemiology and Public Health and Section of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520-80343
Received 10 December 2002/ Returned for modification 10 February 2003/ Accepted 19 March 2003
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(14). The fact that LT plays a crucial role in the development of secondary lymphoid organs, in that LT-
-/- mice are devoid of lymph node and Peyers patches and exhibit defects in splenic organization (4), provides a unifying model for this concept. Recently it has become apparent that chronic inflammation associated with a few infectious diseases also exhibits some characteristics of tertiary lymphoid organs. These diseases include Lyme arthritis (23), hepatitis C-induced liver inflammation (9), and Propriobacterium acnes infection of mouse liver (27). Helicobacter pylori infection in humans can give rise to accumulations of lymphoid cells in the gastric mucosa with the expression of MAdCAM and PNAd (5). More recently, BLC has been noted in the H. pylori-infected gastric mucosa (17). In some cases, lymphomas also develop in the course of this infection, and they also retain some characteristics of lymphoid organs with PNAd, SLC, and accumulation of L-selectin (naïve) T cells. Experimental infection of mice (15) and guinea pigs (22) with H. pylori stimulates the appearance of gastric lymphoid follicles with prominent germinal centers. Chronic infection of mice with Helicobacter hepaticus (25) stimulates the development of large hepatic inflammatory infiltrates that have some morphological similarities to tertiary lymphoid tissue. A novel urease-negative Helicobacter sp. that leads to similar hepatic inflammation was recently described (21).
In this study, we have investigated the possibility that helicobacter infection in mice gives rise to accumulations of lymphoid cells with the characteristics of lymphoid organs. Infection with the novel Helicobacter sp. produces severe cholangiohepatitis after inoculation into susceptible strains of mice. We applied the same criteria of tertiary lymphoid organs that have been previously applied to autoimmune diseases and transgenic mice. Our observation that helicobacter infection in the mouse gives rise to tertiary lymphoid organs as defined by cellular composition, endothelial addressins, and lymphoid organ chemokines provides a new model to study the mechanism of this process. These data also suggest that lymphoid organ neogenesis is a process that is applicable in chronic inflammation in both autoimmune and infectious diseases and could play a role in pathogenesis and/or protection.
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Bacteria. The novel urease-negative Helicobacter sp. was grown from a stock originally isolated from the cecum of a clinically normal feral mouse (MIT 96-1001). It was grown under microaerobic conditions in vented jars containing N2, H2, and CO2 (80:10:10) at 37°C in brucella broth supplemented with 5% fetal calf serum. The bacteria were harvested after 24 to 48 h of growth, resuspended in phosphate-buffered saline (PBS), and visualized by Gram stain and phase microscopy for purity, morphology, and motility. The optical density at 600 nm was adjusted to 1.0, and 0.3 ml of this inoculum (corresponding to approximately 3 x 107 CFU) was used for each intraperitoneal injection or oral dose.
Infection status. To confirm infection status, cecal contents or liver collected at necropsy were cultured as previously described (21). Cecal contents were applied directly to blood agar plates containing cefoperazone, vancomycin, and amphotericin B (Remel, Lenexa, Kans.). Aseptically collected liver was ground and applied directly to blood agar plates for isolation of the Helicobacter sp. Although growth of the Helicobacter sp. was generally evident within 5 days, plates were maintained for 2 weeks before a determination of no growth was made. Presence of the Helicobacter sp. was determined by characteristic colony morphology, bacterial morphology, and urease and catalase tests. Selected cecal samples were analyzed by PCR to confirm positive or negative status. Samples were analyzed using helicobacter genus-specific primers as previously described (21).
Tissue sections for immunohistochemistry and in situ analysis. Liver tissue was obtained from mice that were confirmed to be infected or uninfected (controls) with the Helicobacter sp. Mice were euthanized for tissue harvest at 7 weeks (n = 20 controls and 20 infected), 14 weeks (n = 10 controls and 10 infected), or 24 weeks (n = 17 controls and 17 infected) postinfection. (Not all mice were used for all types of evaluation; see Results for details.) For immunohistochemistry, livers were embedded in Tissue-Tek OCT compound (VWR Scientific, Bridgeport, N.J.) and frozen or were fixed in formalin or Carnoy's fixative and embedded in paraffin. For in situ hybridization, livers were fixed overnight in 4% paraformaldehyde in PBS, then fixed for an additional 48 h in 4% paraformaldehyde-30% sucrose in PBS and then snap-frozen in Tissue-Tek OCT compound (VWR Scientific) and stored at -70°C. Slides made from frozen blocks were used for immunohistochemistry without further processing. Paraffin-embedded slides were de-paraffinized in 100% xylene (three 3-min washes followed by three 3-min washes in 100% ethanol). Carnoy's-fixed tissues were used immediately after deparaffinization. For formalin-fixed tissues, antigen recovery was aided by incubating slides for 30 min in a solution of Tris-buffered saline with 4 mM CaCl2 and 0.25% trypsin.
Cell suspensions for FACS. Infected (n = 3) or control (n = 3) A/J mice at 24 weeks postinfection were euthanized by CO2 asphyxiation, and their livers were perfused via the portal vein, as described by Mehal et al. (19), with RPMI 1640 medium (Life Technologies, Gaithersburg, Md.) containing collagenase II (Sigma, St. Louis, Mo.) at 1 mg/ml. The livers were then ground; the resulting cell suspensions were incubated at 37°C for 2 h, and mononuclear cells were isolated by discontinuous Percoll (PharMacia, Piscataway, N.Y.) gradient. After blocking with purified rat, hamster, and goat immunoglobulin G (Pierce, Rockford, Ill.), cells were incubated with directly conjugated antibodies in fluorescence-activated cell sorter (FACS) buffer (1% bovine serum albumin-0.1% sodium azide in PBS). Samples were analyzed with a FACScan flow cytometer (Becton Dickinson) with Cellquest software.
Immunohistochemical staining. Tissues were first blocked for 30 min with 3% serum of the species in which the secondary antibody was made, then incubated for 1 h with the primary antibody and then incubated for 30 min with the biotinylated secondary antibody at a dilution of 1:250. They were visualized with strepavidin-conjugated alkaline phosphatase (ABC kit; Vector Labs, Burlingame, Calif.) and the Vector Red kit (Vector Labs) or with strepavidin-conjugated horseradish peroxidase (ABC Elite; Vector Labs) and VIP kit (Vector Labs). Buffer was 100 mM Tris HCl (pH 8.2)-0.01% Triton X-1% bovine serum albumin (Sigma) for the alkaline phosphatase kits. PBS (pH 7.5) was used instead of Tris HCl for the ABC Elite kit. A nonspecific antibody of the same isotype as the primary antibody was used as a negative control.
Antibodies. (i) FACS. The CD4-fluorescein isothiocyanate (FITC), B220-phycoerythrin (PE), immunoglobulin M-FITC, CD69-PE, Mac-1-PE, L-selectin-PE, and CD44-Cychrome CD4-FITC, CD11b (Mac-1)-FITC, CD45-Cy-Chrome antibodies were all from Pharmingen (San Diego, Calif.).
(ii) Immunohistochemistry.
Primary antibodies (all obtained from Pharmingen) were monoclonal antibodies that react with MAdCAM-1 (MECA 367), PNAd (MECA 79), VCAM-1, B220, and CD3. MECA 79 was used at a concentration of 5 µg/ml; 3% mouse serum (Sigma) was used for blocking, the secondary antibody was biotinylated immunoglobulin-
light chains (Pharmingen), and unlabeled immunoglobulin-
light chains (Pharmingen) were used as a negative control. MECA 367 was used at a concentration of 5 µg/ml. Three percent goat serum (Sigma) was used to block, the secondary antibody was biotinylated goat anti-rat immunoglobulin G (Pharmingen), and the negative control was unlabeled Rat immunoglobulin G2a (Pharmingen). Anti-B220 and anti-VCAM-1 were used at a concentration of 2 µg/ml, and the block, secondary, and control antibodies used were identical to those for MECA 367. CD3 was used at a concentration of 2 µg/ml; the secondary antibody was biotinylated anti-hamster.
In situ hybridization. Digoxigenin (DIG)-labeled BLC and SLC antisense and sense probes were prepared by in vitro transcription from I.M.A.G.E. consortium expressed sequence tags 596050 and 389013, obtained from Genome Systems (St. Louis, Mo.), as previously described (11). Transcript yield and integrity of the probes were determined by comparison with control DIG-labeled RNA (Boehringer Mannheim, Mannheim, Germany). In situ hybridization was done as previously described with fixed frozen tissue sections of 5- to 10-µm thickness cut onto poly-L-lysine-treated glass slides (11). In brief, sections were fixed in 4% paraformaldehyde, pretreated with proteinase K (Boehringer Mannheim) and acetic anhydride, prehybridized, hybridized overnight at 58°C with the DIG-labeled riboprobes, washed at high stringency, incubated with anti-DIG antibody conjugated to alkaline phosphatase (Boehringer Mannheim), and developed with nitro blue tetrazolium/5-bromo-4-chloro-3-indole-phosphate.
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FIG. 1. Formation of lymphoid tissue in Helicobacter sp.-infected mouse livers. (A) Hematoxylin and eosin photomicrograph of a typical inflammatory infiltrate at 24 weeks postinfection. (B-C) Serial sections of mouse liver (7 weeks postinfection) stained for CD3-positive T cells (B) and B220-positive B cells (C). Clusters of CD3+ T cells are present, and B220 staining shows B-cell clusters colocalizing with, but separate from, T-cell clusters. (D) VCAM: dark red diffuse staining is visible in areas of intense inflammatory infiltrate (7 weeks postinfection). (E-F) Blood vessels develop a morphology resembling HEV and express MAdCAM-1 (E) and PNAd (F) (7 weeks postinfection). (G-H) In situ hybridization analysis of SLC mRNA expression mouse livers using DIG-labeled RNA probes. (G) Expression of SLC is indicated by purple staining of cells with SLC-antisense probes. (H) No staining is seen with SLC sense probe. Infiltrating cells are counterstained with methyl green. (I-J) In situ hybridization analysis of BLC mRNA expression mouse livers using DIG-labeled RNA probes. (I) Expression of BLC is indicated by purple staining of cells with BLC-antisense probes. (J) No staining is seen with BLC sense probe. Infiltrating cells are counterstained with methyl green.
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4ß7). Results are summarized in Fig. 2B. These data indicate that the hepatic inflammation in Helicobacter sp.-infected livers exhibits characteristics of lymphoid organs, namely cellular population (B, T, and antigen-presenting cells), compartmentalization into T and B cell areas, and the presence (though in low numbers) of cells with a naïve phenotype.
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FIG. 2. FACS analysis of mononuclear cells from liver infiltrates (results shown are the means of results of three experiments). (A) Cells isolated from infected and uninfected mice at 24 weeks postinoculation were labeled with Mac-1, CD4, CD8, and B220. Infected livers had quantitatively more cells than livers from uninfected controls. (B) Cells were gated for naïve T cells (low CD44 expression), and numbers of LPAM- or CD62L-positive cells are shown in the bottom right quadrant of each panel. L-selectin-positive cells, but not LPAM-positive cells, were actively recruited to the livers of infected mice.
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Helicobacter sp. liver infiltrates expressed chemokines characteristic of lymphoid organs. SLC and BLC are chemokines usually considered to be characteristic of secondary lymphoid organs, such as spleen or lymph nodes. SLC is capable of attracting dendritic cells and T cells, and BLC attracts B cells. In order to determine whether these chemokines characteristic of lymphoid organs were expressed in Helicobacter sp.-induced inflammatory lesions, selected fixed frozen liver sections were evaluated by in situ hybridization with anti-sense probes for SLC (Fig. 1G and H) and BLC (Fig. 1I and J). Both chemokine mRNAs were detected in regions of intense inflammatory infiltration but were not present in noninflamed areas of infected livers at 7 or 24 weeks postinfection (n = 3 at each time point) or in uninfected livers (n = 3 at each time point). The chemokines colocalized with B- and T-cell infiltrates. Thus, one more characteristic of lymphoid organs is present in the Helicobacter sp.-induced infiltrates.
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The inflammatory infiltrates expressed both MAdCAM and PNAd, which are endothelial cell addressins involved in the trafficking of naïve LPAM+ and L-selectin+ T cells into Peyer's patches and lymph nodes, respectively. PNAd was expressed in both the vessels and bile ducts in inflamed portal tracts. PNAd expression has not previously been reported to be expressed in any tissues other than HEVs, so finding it in inflamed bile ducts was not expected. However, in primary biliary cirrhosis, damaged bile ducts have been shown to express ICAM and in some cases VCAM (26). These authors suggest that the presence of these adhesion molecules facilitates recruitment of inflammatory cells to the bile ducts in primary biliary cirrhosis. Both MAdCAM and PNAd staining were detected in liver tissues from mice 7, 14, and 24 weeks postinfection with helicobacter. At 24 weeks postinfection (the only time point at which livers were available for FACS analysis), L-selectin-positive, but not LPAM-positive, T cells were present in numbers higher than in control mice, suggesting that the PNAd, but not MAdCAM, was actively recruiting relevant (L-selectin-positive) cells at this time point. It is possible that at earlier time points, MAdCAM was more important in recruitment but that at the later time point, much of the MAdCAM had been replaced by PNAd, as occurs in the development of secondary lymphoid organs (18). Future studies will evaluate the kinetics of addressin expression. VCAM was also detected, confirming that classical inflammation was also present. VCAM stained the endothelium of very few vessels but did exhibit a diffuse staining pattern in areas of lymphoid aggregates. This pattern is consistent with the VCAM staining pattern reported in stomach biopsies of patients infected with H. pylori (7).
The presence of B cells, T cells, and dendritic cells all could be due to recruitment by chemokines. We concentrated on lymphoid chemokines here, but it is likely that inflammatory chemokines are also expressed. The importance here is that SLC and BLC, which are lymphoid-specific chemokines, are expressed in Helicobacter infection, confirming that infection with these organisms can give rise to tissue with characteristics of tertiary lymphoid organs.
There are several possible mechanisms by which Helicobacter species could induce tertiary lymphoid tissue. Helicobacter may induce the formation of lymphoid tissue by causing inflammation and damage, by inducing lymphoid organ-promoting or chemokines directly, or even by mimicking the signals for lymphoid organogenesis. One fascinating possibility is that Helicobacter may express or direct the formation of an L-selectin ligand. The MECA79 (PNAd) epitope derives from modifications of a variety of core protein precursors, including CD34, GlyCAM, podocalyxin, and MAdCAM. H. pylori expresses a Lewis X analogue via a bacterial fucosyl transferase (24). Lewis X becomes an L-selectin ligand when modified by a GlcNac6 sulfotransferase (3). It is possible that cellular or bacterial proteins modify a Helicobacter Lewis X analogue to generate the MECA 79 epitope. One candidate sulfotransferase, HECGlcNAC6ST, is expressed primarily in HEVs (2, 10) and has been shown to be crucial for the luminal expression of the high-affinity L-selectin ligand MECA 79 epitope (8). An intriguing possibility is that HECGlcNAC6ST is activated in the context of Helicobacter species infection and induces the expression of an L-selectin ligand on Helicobacter so that the Helicobacter organisms themselves directly attract naïve T cells. MECA 79 detection in the bile ducts of infected mice may represent detection of L-selectin ligand-expressing Helicobacter organisms resident in the bile ducts. It is yet to be determined whether the Helicobacter sp. studied here in fact expresses a Lewis X analogue and whether that analogue could function as an L-selectin ligand.
In this report, we have presented further evidence that the development of tertiary lymphoid tissue in chronic inflammation involves the same mechanisms as lymphoid organogenesis during development, namely, induction of chemokines and adhesion molecules. Kratz et al. (14) have previously shown that LT is important for local recruitment of both lymphoid and antigen-presenting cells and orchestrates lymphoid neogenesis during the immune response through regulation of adhesion molecules and chemokines normally found in secondary lymphoid organs. It would be extremely interesting to determine whether LT knockout mice are able to form hepatic lymphoid aggregates such as those seen in the A/J mice used in this study. Yoneyama et al. (27) have recently reported on the presence of adhesion molecules and chemokines in granulomatous inflammatory infiltrate in mice infected with Propionibacterium acnes, suggesting that the process of lymphoid neo-organogenesis probably has some universal features independent of host cell type, gram negativity of the organism, or type of inflammation.
Formation of lymphoid follicles occurs in a number of chronic inflammatory diseases, including H. pylori gastritis. The function of this tissue is not clear: it may provide functional protection against the agent by allowing antigen presentation at the local site and priming of naïve cells. On the other hand, the tertiary lymphoid tissue may be detrimental to the health of the animal. For example, infection with H. hepaticus results in persistent infection, hepatic inflammation, and eventually hepatocellular carcinoma in A/J mice, but in C57BL/6 mice, it results in very little inflammation and no carcinoma (though the C57BL/6 remain persistently infected) (12). A detailed understanding of the processes leading to this lymphoid neogenesis, and determination of what protective role this tertiary lymphoid tissue provides, may provide a rationale for development of new therapeutics that can specifically target this process.
Future studies in the model described here will allow us to determine whether antigen presentation occurs in the liver infiltrate and whether this contributes to protection.
Present address: Boston University, Laboratory Animal Science Center, Boston, MA 02118. ![]()
Present address: LaJolla Institute of Allergy and Immunology, San Diego, CA 92121. ![]()
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