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* From the 2nd Division of Internal Medicine, Hamamatsu University School of Medicine (Drs. Suda, Chida, Hayakawa, Imokawa, Iwata, Nakamura), Hamamatsu, and Kyoto Preventive Medical Center (Dr. Sato), Kyoto, Japan.
| Abstract |
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Methods: The subjects included five patients with chronic hypersensitivity pneumonitis (CHP) diagnosed from clinical and histologic findings. We investigated histologically the development of BALT in these patients. Further, the cellular distribution of BALT was also examined by immunohistochemistry.
Results: BALT was present in three of five patients with CHP. Immunohistochemical examination revealed the follicular area of BALT to be composed mainly of B cells, while the parafollicular area comprised predominantly T cells. Centroblasts located in the germinal center of BALT expressed Ki-67 antigen, a marker of cell proliferation, suggesting that these cells were actively proliferating after antigenic stimulation. Cells expressing bcl-2, which is present primarily on memory B cells, were confined to the follicular area, devoid of any germinal centers. S-100-positive, CD1a-negative interdigitating dendritic cells were observed in the dome area of BALT.
Conclusions: These observations suggest that chronic antigenic stimulation and/or inflammation in CHP may cause BALT development, which, in turn, is likely to play an important role in the mucosal immune response of this disease.
Key Words: BALT bronchus-associated lymphoid tissues hypersensitivity pneumonitis
| Introduction |
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Chronic hypersensitivity pneumonitis (CHP) is an immunologically mediated disorder caused by continuous inhalation of specific environmental organic antigens.11 ,12 Patients with CHP manifest chronic inflammation predominantly around small airways caused by an antigen-specific immune reaction. As seen in DPB, it is possible that continuous antigenic stimulation and persistent airway inflammation in CHP may lead to the development of BALT. However, no data have been available on BALT in CHP.
In the present study, we investigated histological BALT development in patients with CHP. Further, the cellular distribution of BALT in CHP was also examined by immunohistochemistry. BALT was observed in three of five patients with CHP, suggesting that induced BALT may be involved in the mucosal immunity of this disease by functioning as its inductive site.
| Materials and Methods |
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Exposure leading to hypersensitivity pneumonitis was determined in all cases. We performed a challenge test exposing patients to either causative antigens or environments after hospitalization. Over the next 24 h after the challenge test, the patient's symptoms and signs were observed, and measurements were made of body temperature, leukocyte count, C-reactive protein, and pulmonary function. The challenge test was interpreted according to the criteria of Yoshida et al.13 One patient was a confectioner exposed to fine wheat flour. Provocation with emulsified wheat flour solution in phosphate-buffered saline solution for 10 min using a ultrasonic nebulizer gave a positive reaction. Another was a farmer who planted muskmelons in a greenhouse. The other three developed their symptoms in their homes. In these four patients, an environmental challenge was made by having the patients stay in the greenhouse or home for 3 to 12 h until a positive response was exhibited. Our institutional committee approved the challenge test and every patient tested gave informed consent.
Histologic Studies
Lung biopsy specimens were obtained from at least two lobes in
every case. They were fixed in 10% formaldehyde and embedded in
paraffin. Then 4-µm-thick sections were cut and stained with
hematoxylin-eosin or Elastica van Gieson. The histologic sections of
three or four lung tissues in each case were reviewed by two observers.
In this study, lymphoid follicle-like structures in the bronchiolar
wall, which were covered by a specialized lymphoepithelium, were
defined as BALT, as originally described by Bienenstock.14
The lymphoepithelium overlying the follicles is characterized by
nonciliated, cuboidal epithelial cells and intraepithelial
lymphocytes.1
,14
Immunohistochemistry
To study the cellular distribution of BALT, immunohistochemistry
was performed using a modified streptavidin-biotin-peroxidase complex
method with a Histofine SAB-PO kit (Nichirei; Tokyo, Japan). The
following antibodies were used: mouse monoclonal antibody O10
(anti-CD1a; Immunotech; Marseille, France), 144B (anti-CD8; Dako Japan;
Kyoto, Japan), L26 (anti-CD20; Dako Japan), 124 (anti-bcl-2; Dako
Japan), MIB1 (anti-Ki-67; Dako Japan), rabbit polyclonal antibody
anti-CD3 (Dako Japan), and anti-S-100a (Dako Japan). Briefly, 4-µm
sections were deparaffined in xylene and rehydrated in ethanol. For
staining against CD4, CD8, CD20, bcl-2, and Ki-67, nonspecific protein
staining was blocked with the rabbit serum. The sections were
autoclaved at 121°C for 20 min in a stainless steel pot filled with
10 mM citrate buffer (pH 6.0). The slides then were treated with 3%
hydrogen peroxidase in methanol for 20 min at room temperature, to
eliminate endogenous peroxidase, and incubated with the primary
antibody at 4°C overnight followed by biotinylated anti-mouse
immunoglobulin antibody for 20 min at room temperature. The slides then
were incubated with streptavidin-biotin-peroxidase complex for 15 min
at room temperature. They were developed with 3,3'-diaminobenzidine
tetrahydrochloride and counterstained with methyl green. For staining
against CD3 and S-100, biotinylated anti-rabbit immunoglobulin antibody
was used as the secondary antibody. The coexpression of different
antigens on the same cells was determined by staining the sequential
sections.
BAL
BAL was performed with a fiberoptic bronchoscope (Olympus Corp.;
Tokyo, Japan) in a segmental or subsegmental bronchus of the middle
lobe with 3 x 50 mL of sterile 0.9% saline solution. BAL fluid was
centrifuged at 800g for 10 min to obtain the cellular
components. Total cell count was determined using a hemocytometer and a
differential cell count was taken on Giemsa-stained cytocentrifuged
preparations. To characterize the phenotype of the T cells in the BAL
fluid, flow cytometric analysis was performed in a flow cytometer
(EPICS Profile; Coulter Electronics; Hialeath, France) using mouse
antibodies OKT3 (anti-CD3; Coulter Electronics), OKT4 (anti-CD4;
Coulter Electronics), and OKT8 (anti-CD8; Coulter Electronics).
Immunologic Studies
Serum samples obtained from patients were examined by the
Ouchterlony gel double immunodiffusion method for detecting
precipitating antibodies to various antigens: Aspergillus
fumigatus, Cephalosporium acremonium, Cryptostroma corticale,
Micropolyspora faeni, Pullularia pullulans, Sitophilus granarius,
Thermoactinomyces vulgaris, Trichoderma viride, pigeon droppings
and serum (Hollister-Stier Laboratories; Ontario, Canada),
Alternaria kikuchiana, Candida albicans, Cladosporium
cladosporoides, Penicillium lutem (Torii Corp; Tokyo, Japan),
Trichosporon cutaneum (which was a gift of Dr. M. Ando,
Kummamoto University; Kummamoto, Japan), Aspergillus niger,
and Sphaerotheca fuliginea prepared by Dr. K. Nishimura
(Research Center for Pathogenic Fungi and Microbial Toxicoses, Chiba
University, Chiba, Japan) as described by Ando et al.15
Isolation of Fungi
Cultures of indoor samples from the home or greenhouse were
performed by open plate culture on Sabouraud's agar media. All
isolated fungi were identified by Dr. K. Nishimura.
| Results |
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Although S-100-positive cells were found in both the dome area of the BALT and the bronchiolar epithelium, the cells in the dome area did not express CD1a (Fig 3 , top and middle). The S-100-positive, CD1a-negative cells in the dome area had irregular dendritic morphology (Fig 3 , bottom).
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| Discussion |
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All patients described herein presented with chronic respiratory symptoms related to their exposure to causative antigens or environments. The exposure causing CHP in each case was determined on the basis of a positive response in a challenge test. On histologic examination, two cases had a complete histologic triad of hypersensitivity pneumonitis, described by Coleman and Colby,18 including cellular bronchiolitis, interstitial infiltrates, and nonnecrotizing granulomas. Although no granuloma was found in the other three subjects, their histologic findings were compatible with hypersensitivity pneumonitis.
The lymphoid follicles seen in our patients had lymphoepithelium consisting of nonciliated, cuboidal epithelial cells and intraepithelial lymphocytes. In addition, they were composed of four distinct regions: lymphoepithelium, dome area, follicular area, and parafollicular area. These findings indicated that the lymphoid follicles in CHP had the characteristics of BALT.19 BALT is considered a major site of induction and amplification of the local immune response in the lungs of animals, because inhaled antigens can be taken up through its lymphoepithelium and presented to the lymphocytes in BALT.4 ,5 Thus, it is suggested that the BALT observed in our patients could act as an inductive site, resulting in amplification of the mucosal immune response in this disease, once it develops. In our previous report, BALT was observed in 12 of 17 patients with DPB.9 In DPB, we found that patients with BALT had a significantly higher level of serum IgA than did those without BALT. However, there was no difference in the clinical findings, including serum IgA levels, between patients with and without BALT in CHP.
Immunohistochemical examination showed the cellular distribution of the BALT in CHP to be similar to that in DPB.9 The follicular area was composed mainly of B cells, while the parafollicular area comprised predominantly T cells. The centroblasts located in the germinal center expressed Ki-67 antigen, which is expressed on cells during all active stages of the cell cycle, suggesting that they were proliferating after antigenic stimulation in BALT. Bcl-2-positive cells were confined to part of the follicular area. Since bcl-2 antigen is expressed mainly on memory B cells, the cells in the follicular area primarily were memory B cells. In the dome area, we found S-100-positive, CD1a-negative cells having a dendritic shape. These cells were considered to be phenotypically and morphologically identical to the interdigitating dendritic cells in other lymphoid tissues.20 ,21 Thus, it is likely that inhaled antigens taken up through the lymphoepithelium are translocated to the dome area, where, in turn, the interdigitating dendritic cells in the dome area process and present these antigens to the local T cells.
Little is known about the mechanism involved in the development of BALT. In DPB, persistent infection around the bronchioles and continuous microbial stimulation appear to be responsible for BALT development. In animals, chronic antigenic stimulation was reported to induce the full expression of organized BALT.1 ,2 ,22 On the other hand, systemic immunologic disorders are considered also to induce BALT formation as seen in rheumatoid arthritis.10 In CHP, it is possible that persistent respiratory inflammation elicited by antigen-specific immunologic reaction, in addition to repeated direct stimulation by a causative antigen, may lead to BALT development. However, further study is required to determine the precise mechanism and causative agents involved in BALT development, such as the cytokinetics over the period of BALT development.
The present study indicates BALT development in CHP. BALT is considered to be induced by chronic antigenic stimulation and/or inflammation in CHP, which, in turn, may play an important role in the mucosal immunity of this disease by acting as its inductive site.
| Acknowledgements |
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| Footnotes |
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Abbreviations:BALT = bronchus-associated lymphoid tissue; CHP = chronic hypersensitivity pneumonitis; DPB = diffuse panbronchiolitis; GALT = gut-associated lymphoid tissue
Received for publication June 1, 1998. Accepted for publication August 3, 1998.
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