Methylation patterns of human parathyroid hormone (PTH)/PTH-related peptide receptor gene promoters are established several weeks prior to onset of their function.

Expression of the human parathyroid hormone (PTH)/PTH-related peptide receptor (PTHR) gene is controlled by three promoters, P1-P3. P1 functions specifically in kidney, whereas P2 is ubiquitously active. P3 is also widely active, although more so in kidney than other tissues. However, only P2 functions at midgestation. We examined the role of methylation in controlling PTHR promoter activity. Function of all promoters was inhibited by CpG methylation in vitro. Significantly, P1 is selectively hypomethylated in adult kidney in vivo, strongly suggesting that demethylation is required for renal P1 function. Moreover, this pattern is established by 11. 75 weeks of fetal age, several weeks prior to the onset P1 activity. P3 is unmethylated at midgestation, although it is inactive at this stage of development, and thus exhibits characteristics of both tissue-specific and ubiquitously active promoters. These results show that adult methylation patterns of P1 and P3 are established several weeks prior to their induction, indicating that their function requires factors expressed late in development.

Developmental upregulation of human parathyroid hormone (PTH)/PTH-related peptide receptor gene expression from conserved and human-specific promoters.

The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR) functions in skeletal development and mediates an array of other physiological responses modulated by PTH and PTHrP. PTHR gene transcription in mouse is controlled by two promoters: P1, which is highly and selectively active in kidney; and P2, which functions in a variety of tissues. P1 and P2 are conserved in human tissue; however, P1 activity in kidney is weak. We have now identified a third human promoter, P3, which is widely expressed and accounts for approximately 80% of renal PTHR transcripts in the adult. No P3 activity was detected in mouse kidney, indicating that renal PTHR gene expression is controlled by different signals in human and mouse. During development, only P2 is active at midgestation in many human tissues, including calvaria and long bone. This strongly suggests that factors regulating well conserved P2 control PTHR gene expression during skeletal development. Our results indicate that human PTHR gene transcription is upregulated late in development with the induction of both P1 and P3 promoter activities. In addition, P2-specific transcripts are differentially spliced in a number of human cell lines and adult tissues, but not in fetal tissues, giving rise to a shorter and less structured 5' UTR. Thus, our studies show that both human PTHR gene transcription and mRNA splicing are developmentally regulated. Moreover, our data indicate that renal and nonrenal PTHR gene expression are tightly coordinated in humans.

Characterization of 5-oxo-L-prolinase in normal and tumor tissues of humans and rats: a potential new target for biochemical modulation of glutathione.

5-Oxo-L-prolinase (5-OPase) is an enzyme of the gamma-glutamyl cycle involved in the synthesis and metabolism of glutathione (GSH), which is known to protect cells from the cytotoxic effects of chemotherapy and radiation. Previous studies on rats have shown that administration of the cysteine prodrug L-2-oxothiazolidine-4-carboxylate, a 5-oxo-L-proline analogue that is metabolized by 5-OPase, preferentially increases the GSH content of normal tissues while paradoxically decreasing it in the tumor and results in an enhanced in vivo tumor response to the anticancer drug melphalan. These observations initiated the present study of 5-OPase in experimental models and clinical specimens to investigate the potential role of this enzyme in the selective modulation of GSH in normal and tumor tissues. First, 5-OPase activity was measured in tissues of tumor-bearing rats, in the peripheral mononuclear cells of normal human subjects, and in surgically resected tumor and the adjacent normal tissues from patients. We found that the activity of 5-OPase in human kidney, liver, and lung is significantly lower than that found in rats. Second, we have raised a polyclonal IgG anti-5-OPase antibody by immunizing rabbits with purified 5-OPase from rat kidney. This antibody has very high affinity (shown by immunoprecipitation) and specificity (shown by Western blot) and cross-reacts with human 5-OPase (shown by Western blot and immunohistochemistry). It was then used to examine the distribution of 5-OPase in paired normal and neoplastic human specimens using Western blot and immunohistochemistry. Examination of paired normal and neoplastic tissues of stomach and lung revealed a significantly lower level of 5-OPase in tumor tissues than in the paired normal tissues. In colon tissues, there is no significant difference in 5-OPase level between the normal and tumor tissues. These findings could have implications for both carcinogenesis and therapy.

Cell-surface levels of human carcinoembryonic antigen are inversely correlated with colonocyte differentiation in colon carcinogenesis.

Human carcinoembryonic antigen (CEA) is overexpressed in a wide variety of epithelial malignancies including colon cancer. CEA can function in vitro as a homotypic intercellular adhesion molecule and can block the terminal differentiation of rodent myoblasts, thus raising the possibility that deregulated expression of CEA might directly contribute to malignant progression. To address this question, the expression pattern and cell-surface levels of CEA were studied during malignant transformation of the colonic epithelium in sporadic and familial adenomatous polyposis-related neoplasms. The level of immunohistochemically detected CEA was higher in 30% to 62% of microadenomas and small adenomas from familial adenomatous polyposis patients compared with adjacent normal mucosa, and this proportion was positively correlated with lesion size and degree of dysplasia. Cytofluorometric analysis of highly purified single epithelial cell suspensions from freshly excised carcinomas versus adjacent normal tissue demonstrated up to a 20-fold increase of mean cell-surface CEA in a group of colon carcinomas representative of the overall majority of such tumors--from Dukes' stages A to D and ranging mainly from well to moderately differentiated, the degree of overproduction was inversely correlated with tumor differentiation and directly correlated with stage. A marked tendency toward nonpolarized versus apical cell-surface expression with progression was also noted. Nonspecific cross-reacting antigen (NCA), a CEA family member, is also a homotypic adhesion molecule and blocks terminal myogenic differentiation, whereas biliary glycoprotein is a CEA family adhesion molecule that does not. Cell-surface NCA showed even greater overexpression (up to 70-told) in dedifferentiated tumors, whereas total-cell biliary glycoprotein showed approximately 2-fold lower levels than was normal in more differentiated tumors and approximately 2-fold higher levels than in further progressed tumors. These results therefore support the suggestion that CEA and NCA can directly contribute to colon carcinogenesis by inhibiting colonocyte differentiation.

Relation of glutathione S-transferase alpha and mu isoforms to response to therapy in human breast cancer.

Glutathione S-transferase (GST) represents a multifunctional enzyme family consisting of four known cytosolic isoforms (alpha, mu, pi, and Phi) that detoxify a variety of xenobiotic chemicals and may confer resistance to both chemotherapeutic drugs and carcinogens in various experimental models. GST-pi has already been extensively studied in clinical specimens, including breast cancer. We studied the immuno-histochemical distribution and relative immunopositivity of GST-alpha and GST-mu, based on a grading system for immunointensity, in samples of 51 neoplastic and 46 normal breast samples and 12 lymph node metastases from patients treated with intensive chemotherapy and bone marrow transplant. In normal breast tissue, GST-alpha localized predominantly to the cytoplasm of scattered cells lining the luminal aspects of the ducts. Occasional cells showed both cytoplasmic and nuclear GST-alpha immunoreactivity. GST-mu was stained in myoepithelial cells preferentially as well as in occasional ductal cells (including apocrine epithelium), vascular smooth muscle, and plasma cells. GST-alpha and GST-mu were detected in 22 of 51 (43%) and 24 of 48 (50%) invasive cancers, respectively. In paired samples of normal and malignant tissue from the same patient, GST-alpha immunostaining in cancers was significantly less intense compared to that of normal breast tissue in 13 of 41 (32%) cases. No such trend was found for GST-mu in paired samples. Neither GST-alpha nor GST-mu immunopositivity in tumor or nonneoplastic breast was found to correlate with relapse-free or overall survival in this clinical context; however, the apparent decreased expression of GST-alpha in malignant versus normal breast epithelial cells could have important implications in breast carcinogenesis.

A metastasizing composite carcinoma of the thyroid with distinct medullary and papillary components.

Thyroid tumors with differentiation of both parafollicular and follicular epithelial cells are rare. The majority of those reported have been composed of a single cell population with combined features of the two cell types. We describe a 48-year-old man with a thyroid tumor composed of two discrete cell populations: thyroglobulin-positive papillary carcinoma intermixed with calcitonin-containing medullary carcinoma. The tumor metastasized to regional lymph nodes and maintained this composite differentiation. We propose that such tumors with two discrete intermingled cell populations be called composite thyroid carcinomas, as opposed to mixed thyroid tumors, which describes tumors with a single cell population that exhibits features of two cell types. Dual differentiation in thyroid neoplasms has been interpreted as indicative of a common stem cell origin. In this case, the presence of two mature, highly differentiated elements may suggest a proliferative response of two distinct cell populations to a common tumorigenic stimulus.

Non-specific fluorescent whitener stains in the rapid recognition of pulmonary dirofilariasis: a report of 20 cases.

BACKGROUND: Solitary lung nodules in humans caused by the dog parasite Dirofilaria immitis are steadily increasing in number. The organisms can be easily missed in haematoxylin and eosin stained tissue when they are degenerated and pale staining. METHODS: The value of Tinopal CBS-X (TCBS-X) and Calcofluor white (CFW), two rapid, inexpensive, simple non-specific fluorescent whitening stains, were assessed in the identification of these worms. Deparaffinised rehydrated tissue slides prepared from the pulmonary nodules were stained for one minute in 1% w/v aqueous solutions of TCBS-X or CFW, counterstained, coverslipped, and viewed with a fluorescent microscope. RESULTS: The stains demonstrated the intact worm and worm fragments in 20 cases of pulmonary dirofilariasis collected from hospitals in Houston. The filariae and fragments of filariae stained bright green while the background tissue stained red, delineating the internal structures of the worm. CONCLUSIONS: Dirofilariasis should be included in the differential diagnosis of subpleural masses, and non-specific fluorescent whitening stains can help in the rapid recognition of the fragmented organism in cytological or surgical material.

Endophytic malignant transformation within flat adenoma of the colon: a potential diagnostic pitfall.

A 74-year-old man was found to have a 1 cm, slightly elevated and flat, red mucosal lesion of the descending colon. An endoscopic biopsy showed a structure characteristic of a tubular adenoma. The surgical specimen revealed an inverted, transmural, solid and cystic lesion. The superficial (intra-mucosal) component of the neoplasm was histologically characteristic of a flat adenoma, showing epithelial dysplasia. However, the contiguous deep component was a well-differentiated adenocarcinoma extending to the serosa and demonstrating the unusual features of a circumscribed lobulated topography and the absence of an inflammatory/desmoplastic stromal reaction. Endophytic malignant transformation within a flat adenoma should be distinguished from conditions of misplaced glandular epithelium such as localized colitis cystica profunda. Complete and full mucosal thickness endoscopic snare removal is indicated in order to assess the degree of epithelial dysplasia and detect endophytic malignant transformation.

Characterization of a lung-cancer-associated auto-antigen.

An antigen, protein X (Px), was purified from immune complexes isolated from malignant pleural effusions from patients with adenocarcinoma of the lung by EDTA treatment, PEG 8000 precipitation, protein A affinity chromatography, and Sephadex G-200 separation in the presence of 3 M NaCl. The purified antigen had a M(r) 17,000 by SDS-PAGE, and consisted of isoelectric species of pI 6.3 and 6.6. Purified Px recombined with Ig isolated from pleural fluids from patients with lung adenocarcinoma, but not with Ig from patients with breast carcinoma. Using an autologous human and heterologous chicken antibody, Px was found, by immunohistology, in the cytoplasm of some of the well-differentiated lung adenocarcinoma cells, but was not seen in normal lung or a variety of other malignant tissues. A liquid-phase competitive-inhibition RIA was developed. Over 30 ng/ml of Px were found in 9 of 15 pleural fluids from patients with lung carcinoma, none of 20 from patients with breast, ovary, stomach or colon cancer, and in 3 of 15 patients with unknown primary tumor. Our data suggest that Px may be a lung-cancer-associated autoantigen which can elicit a host humoral response in vivo.

Heterotopic bone formation in rectal carcinoma. Case report and literature review.

A case of heterotopic bone formation in a primary rectal adenocarcinoma was recently observed in a 54-year-old woman. This unusual finding was present both in the diagnostic biopsy and in the subsequently resected bowel. Pertinent gross and microscopic features are presented. This report represents the twelfth case in the literature of heterotopic bone formation in a primary rectal adenocarcinoma and the first such finding in a colonic biopsy from one of these malignancies. The average age of these patients was 56 years (range 32-72) and the male-to-female ratio was 5:7. The rectum is the most common site of ossification in the gastrointestinal tract. The exact mechanism of heterotopic ossification is unknown, but it is probably the result of metaplasia of fibroblasts. Adenocarcinoma has been associated with 12 of the 16 reported cases of rectal glandular tumors with heterotopic bone.

Factors influencing the eradication of Helicobacter pylori with triple therapy.

Helicobacter pylori infection has been associated with gastritis, duodenal ulcer, gastric ulcer, and the epidemic form of gastric carcinoma. Eradication of H. pylori infection has proven to be difficult. Recently, combinations of antimicrobial drugs have been shown to eradicate greater than 50% of infections; however, the results have proven variable, and the factors influencing effectiveness of therapy are unclear. In the present study, the effectiveness of a triple therapy for eradication of H. pylori infection was evaluated. Triple therapy consisted of 2 g tetracycline, 750 mg metronidazole, and five or eight tablets of bismuth subsalicylate daily in 93 patients (70 with duodenal ulcer, 17 with gastric ulcer, and 6 with simple H. pylori gastritis). Combinations of a sensitive urea breath test, serology, culture, and histology were used to confirm the presence of infection, eradication, or relapse. Eradication was defined as inability to show H. pylori greater than or equal to 1 month after ending therapy. The overall eradication rate was 87%. The factors evaluated for their effect on predicting eradication included age, gender, type of disease, duration of therapy, amount of bismuth subsalicylate [five or eight Pepto-Bismol tablets daily (Procter & Gamble, Cincinnati, OH)], and compliance with the prescribed medications. Stepwise regression showed that compliance was the most important factor predicting success; the success rate was 96% for patients who took greater than 60% of the prescribed medications and 69% for patients who took less. For those taking greater than 60% of the prescribed therapy, the eradication rates were similar (a) for patients receiving therapy for 14 days or when tetracycline and bismuth subsalicylate were taken for an additional 14 days; (b) for patients with duodenal ulcer, gastric ulcer, and simple H. pylori gastritis; and (c) whether five or eight bismuth subsalicylate tablets were taken. It is concluded that triple therapy is effective for eradication of H. pylori and that future studies need to take compliance into account for comparisons between regimens.

Peripheral biphasic adenocarcinoma of the lung: light microscopic and immunohistochemical findings.

We report two cases of peripheral biphasic adenocarcinoma primary in the lung. To our knowledge, peripheral adenocarcinoma of the lung with a spindle-cell component has not been described previously. Diffuse positive cytokeratin and negative vimentin immunostaining of the spindle-cell components support an epithelial differentiation of the malignant spindle cells. Although study of additional cases is needed, our initial findings suggest that immunohistochemical staining pattern may help distinguish these neoplasms from other biphasic neoplasms primary or secondary to the lung, such as carcinosarcoma or malignant mesothelioma.

Pulmonary paragonimiasis. Report of a case with diagnosis by fine needle aspiration cytology.

We report a case of paragonimiasis in a Nigerian woman evaluated for symptoms of chronic respiratory disease five years after chemotherapy for primary lymphoma of the breast. Fine needle aspiration of one of two fibrocavitary pulmonary lesions yielded thick, brown material in which ova diagnostic of Paragonimus westermani were identified cytologically. This disease is unusual in natives of North America but is seen in travelers and immigrants from Asia, Africa, and South and Central America, where it is endemic. The infection can be fatal, especially if it involves the central nervous system. The clinical differential is broad, but an accurate diagnosis may be made by fine needle aspiration, thus allowing proper treatment.

Simple noninvasive method to test efficacy of drugs in the eradication of Helicobacter pylori infection: the example of combined bismuth subsalicylate and nitrofurantoin.

Eradication of Helicobacter pylori infections has proved to be difficult. There is a need both for improved therapies and for ways to rapidly identify therapies that show sufficient promise to be worth pursuing. The objectives of this study were to evaluate the value of a therapeutic regimen of a bismuth salt plus nitrofurantoin for eradication of infection by H. pylori and to determine the validity/utility of the urea breath test in monitoring the progress of a clinical trial. We used an 80% eradication rule to define a promising therapeutic regimen, i.e., a regimen that eradicated the infection (no evidence of infection by H. pylori 4 wk after termination of therapy) in at least 80% of the individuals treated. Eighteen men (median age 38) with documented infection by H. pylori completed the study. At the end-of-study evaluation, H. pylori infection was eradicated (negative urea breath test, culture, and histology) in only one of 18 (5.5%) subjects; 15 were positive by the urea breath test, 16 by culture, 15 by Warthin-Starry stain, and 16 by the presence of acute-on-chronic inflammation. Using the 80% eradication rule, any one of these tests alone would have identified that the combination of antimicrobials tested was not effective in the eradication of the infection. We conclude that the urea breath test is a simple, noninvasive, cost-effective method to separate promising from unpromising candidate therapies and for the evaluation of new therapeutic concepts.

Uterine lithiasis.

We report a case of uterine lithiasis in a 73-year-old Latin American woman. The patient underwent vaginal hysterectomy and colporrhaphy for complaints related to secondary uterine prolapse and cystocele. The 70-g, 8 x 5 x 3.5 cm uterus had a normal shape. Ten white, starlike, 0.5 x 0.5 x 0.2 cm, calcified structures were found within the endometrial cavity. Chemical analysis of one of these by x-ray diffraction showed it to be composed of calcite, one of the crystalline forms of calcium carbonate. To our knowledge, this is the first report of human uterine lithiasis in the literature.

Analysis of DNA in fresh and fixed tissue by the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to amplify viral or oncogene sequences from frozen or formalin-fixed, paraffin-embedded tissue sections. Methods for preparing fixed, embedded colonic tissue for PCR amplification of c-K-ras sequences from genomic DNA and for amplification of viral DNA from other tissues, including brain, lung, and liver, were evaluated. The effect of formalin fixation on the efficiency of amplification was also determined. While there seemed to be only a modest variation in the efficiency of the PCR for amplification of single-copy human genes, regardless of the methods used for tissue preparation, amplification of viral DNA sequences against a human genomic DNA background was more efficient when the DNA was purified to some degree before amplification of the tissue. We used the PCR to examine frozen and fixed embedded tissue sections for the presence of Epstein-Barr virus (EBV) and cytomegalovirus (CMV) DNA. One patient with a heart-lung transplant succumbed to a lymphoproliferative disorder, and EBV genome was present in tissues with abnormal lymphoid infiltrates. CMV was also present in bronchial lavages from the same patient, where cytologic diagnosis was not apparent. Another patient with a liver transplant showed CMV genome in multiple liver biopsies, with negative histologic results for CMV. In vitro DNA amplification with the PCR demonstrated sensitivity superior to that of histology in detecting CMV and EBV in the cases examined.

In vivo susceptibility of Campylobacter pylori.

Campylobacter pylori infection has been associated with duodenal ulcer, gastric ulcer, and non-ulcer dyspepsia. Although in vitro studies have shown that C. pylori is susceptible to most commonly used antibiotics, predictions from in vitro sensitivity studies have not led to a safe and generally effective therapy; C. pylori has proved to be very difficult to eradicate in vivo. We used the urea breath test to assess the susceptibility of C. pylori in vivo to various drugs. C. pylori was susceptible to bismuth subsalicylate, bismuth subnitrate, and furazolidone. C. pylori was not susceptible (i.e., urease activity remained despite administration of the drug) to the following drugs: 1) antiulcer agents (cimetidine, ranitidine, famotidine, omeprazole, misoprostol, sucralfate, liquid antacids); 2) NSAIDs (aspirin, indomethacin, ibuprofen, naproxen, tolmetin); 3) antibiotics (oral penicillin V, trimethoprim-sulfamethoxazole, dicloxacillin); 4) salts (lithium, ferrous sulfate, gold); 5) miscellaneous (acetaminophen, phenytoin, hydrochlorothiazide, propranolol, metoprolol, metoclopramide, ursodeoxycholic acid). Oral antimicrobials can be administered directly onto the site of infection, so that a very low oral dose will provide many multiples of the in vitro minimal inhibitory concentration. Furazolidone suspension (7 mg) was administered seven times daily (daily dose 49 mg) to three individuals infected by C. pylori during suppression of gastric acid secretion with famotidine (40 mg bid). After 4 days, all subjects had significant reductions in urease activity (two to normal and one to a borderline value). This response suggested that very low-dose therapy may be useful either alone or combined with bismuth. Conclusive establishment of an etiologic (or major contributory) relationship of C. pylori to ulcer disease will require a safe and reliable method to eradicate the organism from the stomach and duodenum.

Iatrogenic Campylobacter pylori infection is a cause of epidemic achlorhydria.

On a number of occasions, there have been descriptions of epidemic achlorhydria in subjects undergoing repeated gastric secretory studies, typically as part of research protocols. We observed a case in a 37-yr-old healthy man undergoing weekly gastric analyses, along with endoscopy and gastric biopsy, as part of a research protocol studying gastric adaptation to aspirin. In the middle of the 2nd wk of aspirin administration, he developed severe nausea and epigastric discomfort. Aspirin administration was discontinued, but, as per protocol, gastric analyses, endoscopies, and biopsies were continued. Compared to the week preceding the acute illness, biochemical analyses showed a transient 7.4-fold increase in basal gastric acid, 3.6-fold increase in pepsin secretion, 8.8-fold increase in DNA loss, 5.6-fold increase in mucus secretion, and 12-fold increase in gastric bleeding. Basal acid secretion was zero, and pepsin secretion was one-third of control during the 2nd wk of the infection. Endoscopy at the time of symptoms showed erosions in the gastric body and antrum, as well as numerous mucosal hemorrhages and an acute ulcer in the antrum. Endoscopy 7 days later revealed that the gastric mucosa had almost completely recovered, with only a shallow erosion seen at the site of the previous ulcer. Gastric biopsies were normal before and during the first 2 wk of aspirin ingestion. Gastric biopsies taken at the time of the acute illness (associated with increased basal acid secretion) showed marked acute inflammation of the antrum with many Campylobacter pylori bacilli. At that time, neither acute inflammation nor C. pylori were found in biopsies from the body of the stomach. Biopsies obtained 1 wk later (zero basal acid) showed acute inflammation of both the gastric body and antrum. One week later, biopsies from the gastric body showed mild focal acute inflammation, moderate chronic inflammation, and an occasional lymphoid follicle; the gastric antrum showed chronic inflammation. Antral biopsies obtained 2 yr later showed persistent chronic gastritis with prominent lymphoid follicles and scattered foci of acute inflammatory cells; C. pylori bacilli were still present, but were less apparent. We believe that the syndrome of acute (epidemic) gastritis is often iatrogenic C. pylori infection. Our case shows that increased basal acid and pepsin secretion occur before onset of basal acid hypochlorhydria in the acute phase of C. pylori infection.

Microcystic adenoma (serous cystadenoma) of the pancreas. A study of 14 cases with immunohistochemical and electron-microscopic correlation.

Microcystic adenoma (serous cystadenoma) of the pancreas (MA) is an unusual benign tumor of uncertain histogenesis. We have studied 14 cases of MA from 11 women and three men. The average age at diagnosis was 64 years. Six tumors were discovered incidentally. Tumors varied from 2.5 to 12 cm in greatest dimension and all were multicystic; eight tumors were located in the pancreatic head, two in the body, and three in the tail. Each tumor was composed of variably sized cysts lined by simple cuboidal or flattened, focally glycogen-rich epithelium. The stroma was variably collagenized and showed highly vascularized, delicate to broad fibrous septae, which focally contained dystrophic calcification, cholesterol clefts, and hemosiderin. Immunohistochemical studies were performed on eight cases to determine the cell of origin. Epithelial membrane antigen and a low-molecular-weight keratin, detected by monoclonal antibodies PKK1 or AE1/AE3, were diffusely seen in tumor cells of all cases. Tumor cells were uniformly negative for carcinoembryonic antigen, chromogranin, insulin, glucagon, somatostatin, vasoactive intestinal peptide, pancreatic polypeptide, and a low-molecular-weight keratin detected by monoclonal antibody PKK2. Tumor cell antigen reactivity most resembled that seen in normal centroacinar and ductal cells. Electron microscopy of seven cases showed primitive tumor cells with irregularly spaced, short, blunt microvilli, luminal occluding junctions and belt desmosomes, bundles of filaments including dense bodies in both apical and basal cell cytoplasm, sparse organelles, and variable but often pronounced amounts of glycogen. These ultrastructural features most closely resembled the normal pancreatic centroacinar cell. Based on both immunohistochemical and ultrastructural features described above, we conclude that the centroacinar cell is the cell of origin of MA.