Single-Nucleus Analysis Reveals Tumor Heterogeneity of Aldosterone-Producing Adenoma.

BACKGROUND: Recent advances in omics techniques have allowed detailed genetic characterization of aldosterone-producing adenoma (APA). The pathogenesis of APA is characterized by tumorigenesis-associated aldosterone synthesis. The pathophysiological intricacies of APAs have not yet been elucidated at the level of individual cells. Therefore, a single-cell level analysis is speculated to be valuable in studying the differentiation process of APA. METHODS: We conducted single-nucleus RNA sequencing of APAs with KCNJ5 mutation and nonfunctional adenomas obtained from 3 and 2 patients, respectively. RESULTS: The single-nucleus RNA sequencing revealed the intratumoral heterogeneity of APA and identified cell populations consisting of a shared cluster of nonfunctional adenoma and APA. In addition, we extracted 2 cell fates in APA and obtained a cell population specialized in aldosterone synthesis. Genes related to ribosomes and neurodegenerative diseases were upregulated in 1 of these fates, whereas those related to the regulation of glycolysis were upregulated in the other fate. Furthermore, the total RNA reads in the nucleus were higher in hormonally activated clusters, indicating a marked activation of transcription per cell. CONCLUSIONS: The single-nucleus RNA sequencing revealed intratumoral heterogeneity of APA with KCNJ5 mutation. The observation of 2 cell fates in KCNJ5-mutated APAs provides the postulation that a heterogeneous process of cellular differentiation was implicated in the pathophysiological mechanisms underlying APA tumors.

Gene expression profiling of pancreatic neuroendocrine carcinoma and mixed neuroendocrine-non-neuroendocrine neoplasm.

Pancreatic neuroendocrine carcinoma (NEC) and mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) are rare pancreatic malignant tumors, and comprehensive gene analyses are scarce. In this study, six NECs and six MiNENs were collected, immunohistochemistry for synaptophysin, chromogranin A, INSM1, Ki-67, and Rb was conducted, and KRAS mutational status was examined. Among these cases, comprehensive gene expression analysis of oncogene pathways using nCounter® were performed with six NECs and four MiNENs, and those data were compared with that of three pancreatic ductal adenocarcinomas (PDACs), with that of three normal pancreatic ducts, and with each other. By dividing NEC and MiNEN cases into KRAS-mutated group and KRAS-wild group, the difference of clinicopathological data and gene expression profiling data were examined between the two groups. Compared to the data of normal pancreatic epithelium, all 13 cancer-related pathways were upregulated in PDAC, MiNEN, and NEC group with more upregulation in this order. Compared to the data of PDAC, genes of DNA Damage repair pathway was most upregulated both in NECs and MiNENs. Regarding the difference between KRAS-mutated and KRAS-wild groups, several genes were differentially expressed between the two, where MMP7 was the upregulated gene with highest p-value and NKD1 was the downregulated gene with highest p-value in KRAS-mutated group. From the extent of upregulation of 13 pathways, MiNEN was considered more progressed stage than PDAC, and NEC was considered more progressed than MiNEN. From the comparison of KRAS-mutated and KRAS-wild NECs and MiNENs, several differentially expressed genes were identified in this study.

High density and proximity of CD8+ T cells to tumor cells are correlated with better response to nivolumab treatment in metastatic pleural mesothelioma.

BACKGROUND: The efficacy of immune checkpoint inhibitors (ICIs) in pleural mesothelioma has recently been established. The response to ICIs can be predicted by quantitative analysis of cells and their spatial distribution in the tumor microenvironment (TME). However, the detailed composition of the TME in pleural mesothelioma has not been reported. We evaluated the association between the TME and response to ICIs in this cancer. METHODS: A retrospective analysis of 22 pleural mesothelioma patients treated with nivolumab in different centers was performed using surgical specimens. Four patients had a partial response to nivolumab (response group) and 18 patients had stable or progressive disease (nonresponse group). The number of CD4, CD8, FoxP3, CK, and PD-L1 positive cells, cell density, and cell-to-cell distance were analyzed by multiplex immunofluorescence. RESULTS: PD-L1 expression did not differ significantly between the response and nonresponse groups. The density of total T cells and of CD8+ T cells was significantly higher in the response than in the nonresponse group. CD8+ T cells were more clustered and located closer to tumor cells, whereas regulatory T cells were located further from tumor cells in the response than in the nonresponse group. CONCLUSIONS: High density and spatial proximity of CD8+ T cells to tumor cells were associated with better response to nivolumab, whereas the proximity of regulatory T cells to tumor cells was associated with worse response, suggesting that the distinct landscape of the TME could be a potential predictor of ICI efficacy in pleural mesothelioma.

A Primary Kidney Giant Cell Tumor of Soft Tissue Caused Peritoneal Dissemination, Considered to Be Malignant Transformation: A Case Report.

Giant cell tumor of soft tissue (GCTST) is a defined disease entity that has a morphology similar to giant cell tumor of bone (GCTB). The malignant transformation of GCTST has not been reported, and a kidney primary is extremely rare. We report the case of a 77-year-old Japanese male, who was diagnosed with primary GCTST of the kidney and showed peritoneal dissemination, considered to be a malignant transformation of GCTST, in 4 years and 5 months. Histologically, the primary lesion showed characteristics of round cells with not prominent atypia, multi-nucleated giant cells, and osteoid formation, and carcinoma components were not found. The peritoneal lesion was characterized by osteoid formation and round to spindle-shaped cells, but differed in nuclear atypia, and multi-nucleated giant cells were not detected. Immunohistochemical and cancer genome sequence analysis suggested these tumors were sequential. This is a first report of a case that we could diagnose as primary GCTST of the kidney and could be determined as malignant transformation of GCTST in the clinical course. Analysis of this case will be examined in the future when genetic mutations and the disease concepts of GCTST are established.

Immunohistochemical Differentiation between Western and East Asian Types of CagA-Positive Helicobacter pylori in Gastric Biopsy Samples.

Background: Cag A-positive Helicobacter pylori isolated from human gastric mucosa is categorized as a Western or East Asian allele-type based on whether the cagA gene encodes an EPIYA-C or EPIYA-D motif. We aimed to differentiate between the 2 types of H. pylori by immunohistochemistry (IHC) using formalin-fixed paraffin-embedded (FFPE) gastric biopsy samples. Materials and Methods: We developed 2 monoclonal antibodies (mAbs) that detect either the EPIYA-C or EPIYA-D motif of the H. pylori CagA protein by IHC using FFPE tissues. FFPE tissue sections from 30 Japanese and 39 Brazilian gastric biopsy samples with H. pylori infection confirmed by Giemsa staining (moderate/severe in the Sydney classification system) were examined by IHC with the novel mAbs followed by polymerase chain reaction (PCR) for EPIYA-C or EPIYA-D using DNA extracted from adjacent tissue sections. Results: Differentiation among Western and East Asian types and CagA-negative H. pylori was successful in most (97%) samples by IHC with the novel mAbs and commercially available mAbs that react with a species-specific lipopolysaccharide or a common CagA motif of H. pylori. The detection status of EPIYA-C/D motifs by IHC with the novel mAbs was consistent with the PCR results in 61 (88%) of 69 samples: EPIYA-C(+)/D(-) in zero Japanese and 26 Brazilian samples, EPIYA-C(-)/D(+) in 26 Japanese and 1 Brazilian sample, and EPIYA-C(-)/D(-) in 1 Japanese and 7 Brazilian samples. The detection sensitivity and specificity of IHC with each novel mAb compared with the PCR results were, respectively, 84% and 97% for EPIYA-C, and 97% and 95% for EPIYA-D. Conclusions: The novel mAbs specific to each EPIYA-C or EPIYA-D motif differentiated between Western and East Asian types of CagA-positive H. pylori by IHC using FFPE tissues. Applying these novel mAbs to large numbers of archived pathology samples will contribute to elucidating the association of these allele types with gastric cancer.

PHOX2B is a Sensitive and Specific Marker for the Histopathological Diagnosis of Pheochromocytoma and Paraganglioma.

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are non-epithelial neuroendocrine neoplasms originating from the adrenal medulla and paraganglion of the sympathetic and parasympathetic nervous system, respectively. PCCs and PGLs show histological similarities with other epithelial neuroendocrine neoplasms and olfactory neuroblastomas (ONBs), and the differential diagnosis of PGLs is particularly difficult. Therefore, we compared the sensitivity of PHOX2A, PHOX2B, and tyrosine hydroxylase (TH) in the histopathological diagnosis of PCCs and PGLs immunohistochemically using the tissue microarrays of 297 neoplasms including PCCs, PGLs, neuroblastomas, ganglioneuromas, epithelial neuroendocrine neoplasms, and ONBs. Using cutoff values of 25%, 5%, and 5% of tumor cells expressing PHOX2A, PHOX2B, and TH, respectively, as positive, 40 of 51 PCCs, 32 of 33 parasympathetic/head and neck PGLs (HNPGLs), 17 of 19 sympathetic/thoracoabdominal PGLs (TAPGLs), and 12 of 152 epithelial neuroendocrine neoplasms, including 123 well-differentiated and 29 poorly differentiated neuroendocrine neoplasms, were PHOX2A-positive. All 51 PCCs, 33 HNPGLs, and 19 TAPGLs were PHOX2B-positive, while all 152 epithelial neuroendocrine neoplasms were PHOX2B-negative. Moreover, 50 of 51 PCCs, 13 of 33 HNPGLs, all TAPGLs, and 12 of 152 epithelial neuroendocrine neoplasms were TH-positive. All ONBs were negative for PHOX2A, PHOX2B, and TH. PHOX2B was the most sensitive and specific diagnostic marker for PCCs and PGLs among PHOX2A, PHOX2B, and TH. PHOX2B can facilitate identification of PCCs and PGLs from epithelial neuroendocrine neoplasms and ONBs, especially in the case of HNPGLs, in which TH is often negative.

The implicated clinical factors for outcomes in 304 patients with salivary duct carcinoma: Multi-institutional retrospective analysis in Japan.

BACKGROUND: Salivary duct carcinoma (SDC) is a high-grade salivary malignancy that frequently occurs as the carcinomatous component of carcinoma ex pleomorphic adenoma. We herein examined the clinical factors affecting outcomes in a large cohort of SDC. METHODS: We selected 304 SDC cases and investigated clinical characteristics and the factors affecting outcomes. RESULTS: The median age of the cases examined was 68 years, the most common primary site was the parotid gland (238 cases), and there was a male predominance (M/F = 5:1). Outcomes were significantly worse when the primary tumor site was the minor salivary glands (SG) than when it was the major SG. Outcomes were also significantly worse in pN(+) cases (161 cases) than in pN0 cases, particularly those with a metastatic lymph node number ≥11. The cumulative incidence of relapse and distant metastases was significantly higher in stage IV cases than in stage 0-III cases. CONCLUSIONS: The absolute number of lymph node metastases, higher stages, and the minor SG as the primary tumor site were identified as factors affecting the outcome of SDC.

Left supraclavicular (Virchow's) node metastasis detected before primary infradiaphragmatic tumor: a case series.

BACKGROUND: Metastasis of infradiaphragmatic tumors to the left supraclavicular lymph node is reported to be rare. When metastasis is detected in the left supraclavicular node in patients with head and neck carcinoma, locating the primary cancer remains a difficult and time-consuming challenge despite the dramatic development of screening technologies and treatment methods. CASE PRESENTATION: We report three cases of malignant infradiaphragmatic tumor diagnosed following an initial finding of left supraclavicular node metastasis after surgery for tongue squamous cell carcinoma (follow-up period, range 18-62 months). In these cases, adenocarcinoma was diagnosed based on left supraclavicular node biopsies, and a second primary tumor was found, in a 78-year-old Japanese woman with a diagnosis of cholangiocarcinoma, a 64-year-old Japanese man with a diagnosis of bladder carcinoma, and a 61-year-old Japanese man with a diagnosis of prostate carcinoma. In the cholangiocarcinoma case, carbohydrate antigen 19-9 and alpha-fetoprotein levels helped to diagnose cholangiocarcinoma. Palliative care only was given, with survival for 11 months after diagnosis of lymph node metastasis. In the bladder carcinoma case, pathological analysis of fine-needle aspiration biopsy specimen of the metastatic cervical lymph node showed atypical cells with slight squamous differentiation. Hematoxylin-eosin staining of the bladder lesion did not identify a clear glandular or squamous component, and we could not make a definitive diagnosis of whether the lesion was poorly differentiated squamous cell carcinoma, adenocarcinoma, or high-grade urothelial carcinoma. GATA3 staining aided in the diagnosis of urothelial bladder cancer with left supraclavicular node metastasis. He survived for 2 months after diagnosis of left supraclavicular lymph node metastasis. In the prostate carcinoma case, 18F-fluorodeoxyglucose uptake was weak. Prostate-specific antigen levels and magnetic resonance imaging findings aided the diagnostic process. This patient underwent bilateral orchiectomy and adjuvant hormonal therapy and survived for 47 months after diagnosis of left supraclavicular node metastasis. CONCLUSIONS: Pathological diagnosis on the basis of immunohistochemistry and specific diagnosis methods such as radiological and serological assessments are important for providing rapid diagnosis and appropriate treatment.

Propionibacterium acnes-Derived Circulating Immune Complexes in Sarcoidosis Patients.

Propionibacterium acnes is a potential etiologic agent of sarcoidosis and a dysregulated immune response to the commensal bacterium is suspected to cause granuloma formation. P. acnes-derived insoluble immune complexes were recently demonstrated in sinus macrophages of sarcoidosis lymph nodes, suggesting local proliferation of the bacterium in affected organs. In the present study, we developed a method for detecting P. acnes-derived immune complexes in human blood by measuring the concentration of P. acnes-specific lipoteichoic acid (PLTA) detectable after an antigen retrieval pretreatment of plasma samples. Before pretreatment, anti-PLTA antibody was detected and PLTA could not be detected, in all plasma samples from 51 sarcoidosis patients and 35 healthy volunteers. After pretreatment, however, a significant level of PLTA (>105 ng/mL) was detected in 33 (65%) sarcoidosis patients and 5 (14%) control subjects, with 86% specificity and 65% sensitivity for sarcoidosis. In both groups, plasma anti-PLTA antibody titers did not differ between samples with and without detection of PLTA. PLTA levels were abnormally increased (>202 ng/mL) in 21 (41%) sarcoidosis patients. These findings suggest that P. acnes-derived circulating immune complexes present in human blood are abnormally increased in many sarcoidosis patients, presumably due to local proliferation of the bacterium in the affected organs.

Synovial sarcoma of the stomach: a case report and a systematic review of literature.

Worldwide, 5-10% of soft tissue sarcoma cases in adults have been attributed to synovial sarcoma. It is often reported to occur near the joints of the arm, neck, and leg but rarely in the gastrointestinal tract. In this study, we report a case of synovial sarcoma arising in the stomach of a 59-year-old woman. Gastrointestinal endoscopy revealed an ulcerative and hemorrhagic tumor with marginal elevation in the fundus. Histological study showed that the tumor was composed of tightly packed spindle cells in bundles, and one of its component demonstrated significant mitotic activity (> 40/10 high-power fields) in several areas. The diagnosis was confirmed by the evidence of SS18 gene rearrangement, according to immunohistochemistry study, (including a novel SS18-SSX fusion-specific antibody), fluorescent in situ hybridization, and the identification of the SS18-SSX1 and SS18-SSX1/2/4 fusion transcripts using reverse-transcript polymerase chain reaction. No evidence of local recurrence or distant metastasis has been found in the more than 5 years since. Distinguishing synovial sarcoma in the digestive tract from other mesenchymal neoplasms, such as gastrointestinal stromal tumor, may be difficult, especially when spindle-shaped cell proliferation is predominant, as in our patient. Therefore, morphological, immunohistological, and molecular evaluations are important for a comprehensive diagnosis.

Importance of Intestinal Environment and Cellular Plasticity of Islets in the Development of Postpancreatectomy Diabetes.

OBJECTIVE: To elucidate the pathogenesis of postpancreatectomy diabetes mellitus (PPDM). RESEARCH DESIGN AND METHODS: Forty-eight patients without diabetes undergoing either pancreatoduodenectomy (PD) (n = 20) or distal pancreatectomy (DP) (n = 28) were included. A 75-g oral glucose tolerance test was performed every 6 months. Microbiome composition and short-chain fatty acids (SCFAs) in feces were examined before and 6 months after surgery. The association of histological characteristics of the resected pancreas with PPDM was examined. RESULTS: During follow-up (median 3.19 years), 2 of 20 PD patients and 16 of 28 DP patients developed PPDM. Proteobacteria relative abundance, plasma glucagon-like peptide 1 (GLP-1), and fecal butyrate levels increased only after PD. Postsurgical butyrate levels were correlated with postsurgical GLP-1 levels. With no significant difference in the volume of the resected pancreas between the surgical procedures, both ß-cell and α-cell areas in the resected pancreas were significantly higher in DP patients than in PD patients. In DP patients, the progressors to diabetes showed preexisting insulin resistance compared with nonprogressors, and both increased α- and ß-cell areas were predictors of PPDM. Furthermore, in DP patients, α-cell and ß-cell areas were associated with ALDH1A3 expression in islets. CONCLUSIONS: We postulate that a greater removal of ß-cells contributes to the development of PPDM after DP. Islet expansion along with preexisting insulin resistance is associated with high cellular plasticity, which may predict the development of PPDM after DP. In contrast, PD is associated with alterations of gut microbiome and increases in SCFA production and GLP-1 secretion, possibly protecting against PPDM development.

Substantial Epstein-Barr virus reactivation in a case of severe refractory ulcerative colitis: a possible role in exacerbation.

Ulcerative colitis (UC) is an inflammatory bowel disease that causes chronic inflammation in the colon. 5-aminosalicylic acid and immunosuppressive medications such as corticosteroids, immunomodulators, and biologic agents are used to treat these patients. However, patients with UC who receive immunosuppressive medications may be at risk for certain opportunistic infections. Epstein-Barr virus (EBV) is one of those opportunistic infections, and its pathogenic role has been implicated in refractory UC, but its pathogenicity should be further investigated. Here, we report a surgical case of refractory UC that demonstrated a serologically post-infected pattern of EBV at admission but that later had a high load of EBV in both the peripheral blood and colonic mucosa. These findings suggest that EBV may have been reactivated in the colon, after which it damaged the colonic mucosa and aggravated inflammation in this patient with UC. Thus, EBV might lead to severity and a refractory response against corticosteroids and anti-TNFα agents, necessitating emergency surgery. Viral surveillance for EBV in patients with refractory UC may facilitate understanding of the patient's pathophysiology and predicting response to medications, and the development of antiviral intervention for those patients may improve their prognosis.

Islet cell dedifferentiation is a pathologic mechanism of long-standing progression of type 2 diabetes.

Dedifferentiation has been implicated in ß cell dysfunction and loss in rodent diabetes. However, the pathophysiological significance in humans remains unclear. To elucidate this, we analyzed surgically resected pancreatic tissues of 26 Japanese subjects with diabetes and 11 nondiabetic subjects, who had been overweight during adulthood but had no family history of diabetes. The diabetic subjects were subclassified into 3 disease stage categories, early, advanced, and intermediate. Despite no numerical changes in endocrine cells immunoreactive for chromogranin A (ChgA), diabetic islets showed profound ß cell loss, with an increase in α cells without an increase in insulin and glucagon double-positive cells. The proportion of dedifferentiated cells that retain ChgA immunoreactivity without 4 major islet hormones was strikingly increased in diabetic islets and rose substantially during disease progression. The increased dedifferentiated cell ratio was inversely correlated with declining C-peptide index. Moreover, a subset of islet cells converted into exocrine-like cells during disease progression. These results indicate that islet remodeling with dedifferentiation is the underlying cause of ß cell failure during the course of diabetes progression in humans.

Homeobox transcription factor engrailed homeobox 1 is a possible diagnostic marker for adenoid cystic carcinoma and polymorphous adenocarcinoma.

Diagnostic utility of a homeobox transcription factor, engrailed homeobox 1 (En1) in the histopathology of salivary gland neoplasms was studied. The expression of En1 was immunohistochemically examined in 51 cases of adenoid cystic carcinoma (AdCC) and 143 cases of other salivary gland neoplasms. In all 51 AdCCs, En1 was expressed in 30-100% of tumor cells. In eight of nine polymorphous adenocarcinomas (PACs), En1 was expressed in 40-100% of tumor cells. Less than 5% of tumor cells expressed En1 in three of 12 epithelial-myoepithelial carcinomas, one of 17 basal cell adenomas (BCAs), and one of 34 pleomorphic adenomas (PAs). Among 55 other carcinoma cases, 1-30% of tumor cells expressed En1 in three salivary duct carcinomas (SDCs) ex PA. None of the myoepitheliomas and Warthin tumors expressed En1. When the cut-off value of the percentage of En1-expressing cells was set to 25%, all 51 AdCCs, eight of nine PACs and one SDC ex PA were En1-positive and the others were En1-negative. En1 is expressed consistently in AdCCs, frequently in PACs, but rarely in other salivary gland neoplasms. En1 is a possible diagnostic marker for AdCC and PAC in the histopathology of salivary gland neoplasms.

Adenocarcinoma arising in the multiple heterotopic submucosal glands of the intestine in a Satoyoshi syndrome patient: A case report.

Satoyoshi syndrome is a rare multisystemic disorder of unknown etiology characterized by progressive muscle spasms, alopecia and diarrhea. Multiple protruding lesions with cystic glands, namely gastroenterocolitis cystica polyposa, manifest in the gastrointestinal tract. Since the first report of these lesions in 1977, which was unique to Satoyoshi syndrome, few studies have focused on their role, and the associated clinicopathological features are not well understood. Here, we report a 64-year-old Japanese woman with Satoyoshi syndrome who presented with multiple polypoid lesions in the stomach, duodenum, jejunum, ileum and colon. Histologically, the polypoid lesions in the intestine comprised multiple heterotopic submucosal glands containing cystically dilated glands and smooth muscle fibers in the lamina propria mucosa and/or submucosa. Additionally, we observed stromal changes, such as fibrosis, discontinuous and thinning muscularis mucosae, and diffuse neural fiber proliferation in the entire intestinal tract. Furthermore, multiple foci of adenocarcinomas were identified within several heterotopic submucosal glands. We hypothesized that multiple heterotopic submucosal glands in the present case corresponded to previously reported gastroenterocolitis cystica polyposa, suggesting that these lesions are essential in the histopathology and are a unique manifestation of Satoyoshi syndrome.

Intestinal phenotype is maintained by Atoh1 in the cancer region of intraductal papillary mucinous neoplasm.

Intraductal papillary mucinous neoplasm (IPMN) is a precancerous lesion of pancreatic cancer. Although there are 4 types of IPMN, among which intestinal-type IPMN is likely to progress into invasive cancer known as colloid carcinoma, no information regarding the involvement of the intestinal phenotype in the carcinogenesis of IPMN exists. The present study was conducted to explore how the intestinal differentiation system is maintained during the tumor progression of intestinal-type IPMN using surgical resection specimens. Results showed that Atoh1, a critical transcriptional factor for intestinal differentiation toward the secretory lineages of intestinal epithelial cells, was expressed in an invasive-grade IPMN. To determine the function of Atoh1 in pancreatic cancer, we generated a pancreatic ductal adenocarcinoma (PDAC) cell line overexpressing Atoh1. In a xenograft model, we successfully induced an IPMN phenotype in PDAC cells via Atoh1 induction. Finally, for the first time, we discovered that GPA33 is expressed in intestinal-type IPMN, thereby suggesting a novel target for cancer therapy. In conclusion, the intestinal differentiation system might be maintained during tumor progression of intestinal-type IPMN. Further analysis of the function of Atoh1 in IPMN might be useful for understanding the molecular mechanism underlying the malignant potential during the tumor progression of IPMN.

Disruption in the balance between apolipoprotein A-I and mast cell chymase in chronic hypersensitivity pneumonitis.

BACKGROUND: Apolipoprotein A-I (apoA-I) has an antifibrotic effect in idiopathic pulmonary fibrosis. Although pulmonary fibrosis is associated with poor prognosis of patients with hypersensitivity pneumonitis (HP), little is known regarding the role of apoA-I in the pathogenesis of HP. METHODS: Two-dimensional electrophoresis, immunoblotting, and enzyme-linked immunosorbent assays were performed for the identification and quantification of apoA-I in bronchoalveolar lavage fluid (BALF) from patients with acute and chronic HP. To investigate the degradation of apoA-I, apoA-I was incubated with BALF. Moreover, the role of apoA-I in TGF-ß1-induced epithelial-mesenchymal transition of A549 cells was examined. RESULTS: The concentration of apoA-I in the BALF was significantly lower in chronic HP (n = 56) compared with acute HP (n = 31). The expression level of apoA-I was also low in the lung tissues of chronic HP. ApoA-I was degraded by BALF from HP patients. The number of chymase-positive mast cells in the alveolar parenchyma was inversely correlated with apoA-I levels in the BALF of chronic HP patients. In vitro experiment using A549 cells, untreated apoA-I inhibited TGF-ß1-induced epithelial-mesenchymal transition, although this trend was not observed in the chymase-treated apoA-I. CONCLUSIONS: A decrease of apoA-I was associated with the pathogenesis of chronic HP in terms of pulmonary fibrosis and mast cell chymase attenuated the protective effect of apoA-I against pulmonary fibrosis. Furthermore, apoA-I could be a crucial molecule associated with lung fibrogenesis of HP.