Laparoscopic versus hybrid approach for treatment of incisional ventral hernia: a 5-10-year follow-up of the randomized controlled multicenter study.

PURPOSE: In this long-term follow-up of a prospective, randomized, and multicenter study, we compare the results of a group receiving laparoscopic incisional ventral hernia repair using intraperitoneal onlay mesh (LG) to a group receiving a hybrid hernia repair where open closure of fascial defect was added to intraperitoneal mesh placement (HG). METHODS: Originally, 193 patients with 2-7 cm incisional hernias were randomly assigned to either the LG or HG during the 30-month recruitment period in 2012 to 2015. Long-term follow-up was conducted 5-10 years after surgery to evaluate hernia recurrence rate and quality of life (QoL). RESULTS: In all, 65 patients in the LG and 60 in the HG completed the long-term follow-up with a median follow-up period of 87 months. Recurrent hernia was detected in 11 of 65 patients (16.9%) in the LG and 10 of 60 patients (16.7%) in the HG (p > 0.9). Kaplan-Meier analysis demonstrated a recurrence rate approaching 20% in both groups, with similar curves. Three patients in the LG (4.6% and five patients in the HG (8.1%) had undergone re-operation due to recurrence (p = 0.48). There was no difference in patient-reported QoL measured using the SF-36 questionnaire. Mean pain scores were similar between groups, mean numeric rating scale (NRS) 0 to 10 being 1.1 in the LG and 0.7 in the HG (p = 0.43). CONCLUSION: Fascial closure did not reduce hernia recurrence rate in this study population, even though it has been shown to be beneficial and recommended in surgery guidelines. In the long term, recurrence rate for both groups is similar.

Blood Transfusions in Major Pancreatic Surgery: A 10-Year Cohort Study Including 1404 Patients Undergoing Pancreatic Resections in Finland.

BACKGROUND: Despite guidelines on blood transfusion (TF) thresholds, there seems to be great variation in transfusion policies between hospitals and surgeons. In order to improve and unify blood transfusion policies, the Finnish Red Cross Blood Service carried out a project concerning the optimal use of blood products (Verivalmisteiden optimaalinen käyttö) between 2002 and 2011. In this study, we determined the blood transfusion trends in major pancreatic surgery in Finland. METHODS: Initially, 1337 patients who underwent major pancreatic resections between 2002 and 2011 were classified into the TF+ or TF- groups. Centers were divided into high-, medium-, and low-volume centers. The blood transfusion trends and the trigger points for blood transfusions in these patients were determined. RESULTS: There were no differences between high-, medium- and low-volume centers in blood usage, trigger points or the use of reserved blood units after pancreatoduodenectomy or total pancreatectomy. However, the trigger points were lowered significantly during the study period at high-volume centers (p = 0.003), and a better use of reserved blood units was found in high- (p < 0.001) and medium-volume (p = 0.043) centers. In addition, a better use of reserved blood units was found in high-volume centers after distal pancreatectomy (p = 0.020). CONCLUSION: Although only minor changes in blood transfusion trends after pancreatoduodenectomy or total pancreatectomy were found generally, the lowering of the transfusion trigger point and the best use of reserved blood units during the study period occurred in high-volume centers.

Histological damage of colonic epithelium is associated with clinical severity and outcome in colectomized critically Ill patients.

BACKGROUND: Severe intestinal mucosal damage and organ failure has been associated in experimental models. Our purpose was to determine whether there is any association between histopathological findings and postoperative mortality among ICU patients undergoing emergency colectomies for various illnesses. METHODS: In a retrospective case control study, total colectomy specimens from 50 patients in a mixed ICU were analysed: 18 had sepsis, 11 vascular operations, and 21 Clostridium difficile colitis. Overall thickness, the width of epithelial defects, and presence of cryptal damage were assessed. Extent of necrosis and amount of neutrophils were separately evaluated in the layers of the colonic wall. Clinical features, including sequential organ failure assessment (SOFA) scores and survival, were registered. RESULTS: The histopathological findings for the three clinical entities were similar, except for the abundance of characteristic pseudomembranes in the Clostridium group. Mucosal height (maximum) showed a negative correlation with SOFA score on admission (ρ = -0.296, P = 0.037), and with preoperative blood lactate level (ρ = -0.316; P = 0.027). The nonsurvivors had wider enterocyte defects (60 vs. 40.8, P = 0.002) and more severe crypt damage (61 vs. 27 %; P = 0.024) than the survivors. CONCLUSIONS: The histopathological damage involves all layers of the colon wall among ICU patients being largely similar in sepsis, C. difficile infection, and ischemia after vascular operations. Mucosal epithelial damage is associated with clinical severity of the illness and mortality.

Treatment of esophageal perforation in octogenarians: a multicenter study.

Esophageal perforation is associated with significant mortality, and this may markedly increase with advanced age. This multicenter study investigates this issue in patients older than 80 years. Data on 33 patients >80 years old who underwent conservative (10 patients), endoclip (one patient), stent grafting (11 patients), or surgical treatment (11 patients) for esophageal perforation were collected from nine centers. Surgical repair consisted of repair on drain in one patient, primary repair in seven patients, and esophagectomy in two patients. Among patients who underwent stent grafting, one required repeat stenting and another stent graft repositioning. One patient was converted to surgical repair after stent grafting. Thirteen patients (39.4%) died during the 30-day and/or in-hospital stay. Their mortality was significantly higher than in a series of patients<80 years old (13.0%, 21/161 patients, P=0.001). Three patients (30.0%) died after conservative treatment, one (100%) after treatment with endoclips, five (45.5%) after stent grafting, and four (36.4%) after surgical repair (P=0.548). Early survival with salvaged esophagus was 42.4% (conservative treatment: 70.0% endoclips 0%, stent grafting: 54.5%, and surgical repair: 54.5%, respectively, P=0.558). Estimated glomerular filtration rate<60 mL/minute/1.73 m2 (70.0% vs. 25.0%, P=0.043) and sepsis (100% vs. 32.1%, P=0.049) at presentation were associated with increased risk of early mortality in univariate analysis. Esophageal perforation in octogenarians is associated with very high early and intermediate high mortality irrespective of the treatment method used.

Claudins 1, 3, 4, 5 and 7 in esophageal cancer: loss of claudin 3 and 4 expression is associated with metastatic behavior.

The aim of the study was to elucidate the significance of claudins in surgically treated esophageal carcinoma. The expression of claudins 1, 3, 4, 5 and 7 was studied by immunohistochemistry. Tumor proliferation was assessed with Ki67 immunostaining and apoptosis by the TUNEL method and immunostaining of fragmented caspase 3. Adenocarcinomas showed significantly more cases with moderate or strong claudin 3 (p<0.001) and claudin 5 positivity (p=0.031) compared to squamous cell carcinomas. Loss of claudin 3 expression was associated with the presence of distant metastases (p=0.039). Claudins 3, 4 and 7 had a significant association with either a high apoptotic index or a high number of caspase 3-positive cells, while claudin 5 was associated with increased proliferation. In esophageal carcinoma, claudin expression may vary along with the histology of the tumor. Claudin expression may also be associated with apoptosis or proliferation, suggesting that claudins may contribute to tumor behavior and growth.

Continuous retention suture for the management of open abdomen: a high rate of delayed fascial closure.

BACKGROUND AND AIMS: Open abdomen is most often a consequence of damage control surgery, abdominal decompression or intra-abdominal infections. Ventral hernia after unsuccessful closure of open abdomen causes marked disability to the patient. Several methods for delayed fascial closure have been developed. Patients treated with continuous retention suture were evaluated to find out how often fascial closure was achieved, and what complications were related to the technique. METHOD: A retrospective analysis of 16 open abdomen patients treated with continuous retention suture. RESULTS: The most common cause of open abdomen was abdominal infection. Complete fascial closure was achieved in nine of the eleven surviving patients. Closure failed in one patient. Partial closure was also achieved in one patient. The median time between leaving the abdomen open and starting the process of closure was twelve days. The longest period of open abdomen before successful fascial closure was 29 days. Five patients died before the process of closure was complete. CONCLUSION: Delayed fascial closure can be accomplished by using the retention suture method described here.

Expression of transmembrane carbonic anhydrases IX and XII in ovarian tumours.

AIMS: Carbonic anhydrase (CA) isozymes IX and XII have been suggested to play a role in oncogenic processes. The aim of the present study was to investigate CA IX and XII expression in patients with ovarian tumours. METHODS AND RESULTS: A series of ovarian tumours was immunostained for CA IX and XII and the results were correlated with histopathological and clinical parameters. Most cases of borderline mucinous cystadenomas, mucinous cystadenocarcinomas and serous cystadenocarcinomas were moderately or strongly positive for CA IX. In malignant tumours, the staining was most prominent in hypoxic regions. Expression of CA XII was detected in all tumour categories, although the mean staining intensity was weaker than for CA IX in all groups except for clear cell carcinomas. CONCLUSIONS: The wide expression of CA IX and XII in ovarian tumours suggests that these isozymes could represent potential targets in ovarian cancer therapy. The expression pattern of CA IX suggests that it could also serve as a useful histopathological marker protein for hypoxia in malignant ovarian tumours.

Organ system dysfunction following open cholecystectomy for acute acalculous cholecystitis in critically ill patients.

BACKGROUND: Acute acalculous cholecystitis (AAC) refers to cholecystitis without gallstones and is a serious complication of critical illness. We describe the time course of organ system dysfunction associated with cholecystectomy in critically ill patients with AAC. METHODS: The data of all intensive care unit (ICU) patients who had operatively confirmed AAC during their ICU stay between 2003 and 2004 were analyzed. Patients who also had other intra-abdominal pathologies were excluded. The Sequential Organ Failure Assessment (SOFA) scores were recorded 3 days before, on the day of operation and on the first, second, third and seventh post-operative day after cholecystectomy. The impact of open cholecystectomy on organ dysfunction was evaluated on the basis of the change in the total and individual organ SOFA scores. RESULTS: Twenty-four patients underwent open cholecystectomy for AAC with no other intra-abdominal pathology. Sepsis was the most common admission diagnosis, followed by cardiovascular surgery. The mean (standard deviation, SD) Acute Physiology and Chronic Health Evaluation (APACHE II), Simplified Acute Physiology Score (SAPS) II and SOFA scores on admission were 24.7 (5.8), 44.3 (12.3) and 9.4 (3.2), respectively. The median (25th, 75th percentiles) total SOFA score 3 days before cholecystectomy was 7.5 (1.3, 8.0), which increased to 10.5 (8.3, 13.0) (P < 0.0001) by the day of cholecystectomy, indicating developing multiorgan dysfunction. After the operation, the score decreased to 5.5 (3.3, 10.8) (P = 0.004) by the seventh post-operative day. The change was most obvious in cardiovascular and respiratory SOFA scores. CONCLUSIONS: AAC is associated with multiorgan dysfunction in critically ill patients. Open cholecystectomy seems to alter the course of multiorgan dysfunction in these patients.

Histopathology of acute acalculous cholecystitis in critically ill patients.

AIMS: To illustrate the histopathological features of acute acalculous cholecystitis (AAC) of critically ill patients and to compare them with those of acute calculous cholecystitis (ACC) and normal gallbladders. METHODS AND RESULTS: We studied 34 gallbladders with AAC and compared them with 28 cases of ACC and 14 normal gallbladders. Histological features were systematically evaluated. Typical features in AAC were bile infiltration, leucocyte margination of blood vessels and lymphatic dilation. Bile infiltration in the gallbladder wall was more common and extended wider and deeper into the muscle layer in AAC compared with ACC. Epithelial degeneration and defects and widespread occurrence of inflammatory cells were typical features in ACC. Necrosis in the muscle layer was also more common and extended wider and deeper in ACC. There were no differences in the occurrence of capillary thromboses, lymphatic follicles or Rokitansky-Aschoff sinuses between the AAC and ACC samples. CONCLUSIONS: There are characteristic differences in histopathology between AAC and ACC, although due to overlap, none appeared to be specific as such for either condition. These results suggest that AAC is largely a manifestation of systemic critical illness, whereas ACC is a local disease of the gallbladder.

Acute acalculous cholecystitis in critically ill patients.

BACKGROUND: Acute acalculous cholecystitis (AAC) is a serious complication of critical illness. We evaluated the underlying diseases, clinical and diagnostic features, severity of associated organ failures, and outcome of operatively treated AAC in a mixed ICU patient population. METHODS: The data of all ICU patients who had operatively confirmed AAC during their ICU stay between 1 January 2000 and 31 December 2001 were collected from the hospital records and the intensive care unit's data management system for predetermined variables. RESULTS: Thirty-nine (1%) out of 3984 patients underwent open cholecystectomy for AAC during the two-year period. Infection was the most common admission diagnosis, followed by cardiovascular surgery. The mean APACHE II score on admission was 25, and 64% of the patients had three or more failing organs on the day of cholecystectomy. The mean length of ICU stay before cholecystectomy was 8 days, and the mean total length of ICU stay was 19 days. Most patients (85%) received norepinephrine infusion, and 90% suffered respiratory failure before cholecystectomy. Hospital mortality was 44%. The non-survivors had higher Sequential Organ Failure Assessment (SOFA) scores on the day of cholecystectomy compared to the survivors (12.9 vs. 9.5, P = 0.007). CONCLUSION: Acute acalculous cholecystitis was associated with severe illness, infection, long ICU stay, and multiple organ failure. Mortality was related to the degree of organ failure. Prompt diagnosis and active treatment of AAC can be life-saving in these patients.

The quality of life of gastroesophageal reflux disease patients waiting for an antireflux operation.

BACKGROUND: The purpose of this trial was to measure the health-related quality of life (HRQL) of gastroesophageal reflux disease (GERD) patients waiting for an antireflux operation. METHODS: A total of 120 patients waiting for a laparoscopic fundoplication were sent questionnaires measuring their symptoms and quality of life. RESULTS: Ninety-five of the patients still needing an operation returned the questionaires and were included in the analysis. Thirty-one of 84 patients (37%) felt that the symptoms had worsened, and 51/90 (57%) were unsatisfied. Thirty percent suffered from throat or airway infections, 25% from swallowing difficulties, 48% from retrosternal pain, and 18% had asthma. The mean GERD HRQL score (0-45) was 21.7 (95% confidence interval, 19.7-23.7). Short Form-36 scores of this population were significantly worse when compared to patients with inguinal hernia or moderate asthma. CONCLUSIONS: Patients waiting for a fundoplication seem to have a significantly decreased health-related quality of life due to poor symptom control regardless of continuous medical treatment.

Transmembrane carbonic anhydrase, MN/CA IX, is a potential biomarker for biliary tumours.

BACKGROUND/AIMS: Carbonic anhydrase isoenzyme IX (MN/CA IX) is a transmembrane protein with a suggested function in maintaining the acid-base balance and intercellular communication. Previous studies have demonstrated that MN/CA IX is expressed in the basolateral plasma membrane of normal biliary epithelial cells, but not in hepatocytes. This study was designed to examine the expression of MN/CA IX in hepatobiliary neoplasms and to elucidate its value as a marker for biliary differentiation. METHODS: Fifty-seven hepatobiliary lesions were immunostained for MN/CA IX using biotin-streptavidin complex method. Twenty samples containing normal biliary epithelium and five containing normal liver tissue were used as controls. RESULTS: In the biliary epithelial tumours, immunostaining for MN/CA IX was mainly localized at the basolateral surface of the epithelial cells, like in normal mucosa. All non-invasive dysplastic lesions and 57% of invasive lesions of gall-bladder expressed MN/CA IX. In liver, 78% of cholangiocellular malignant lesions showed a positive reaction for MN/CA IX, whereas only 33% of hepatocellular carcinomas showed a weak immunoreaction. CONCLUSIONS: Our results suggest that abnormal expression of MN/CA IX may be linked to malignant transformation of hepatobiliary cells. In addition, it seems to be a promising marker for biliary differentiation in hepatobiliary neoplasms.

Differential expression of cytoplasmic carbonic anhydrases, CA I and II, and membrane-associated isozymes, CA IX and XII, in normal mucosa of large intestine and in colorectal tumors.

This study compares the localization of carbonic anhydrase isozymes (CA) I and II and that of IX and XII in normal large intestine and in colorectal tumors. Immunohistochemical studies were performed on 69 colorectal lesions. While the normal mucosa of the large intestine showed high expression for CA I and II, the intensity of the immunostaining for both isozymes decreased in benign lesions and was very weak in malignant tumors. The reciprocal pattern of expression observed for these cytoplasmic isozymes and transmembrane CA IX and XII in intestinal tissue specimens supports the suggestion that CA IX and XII may be functionally involved in tumor progression to malignancy and/or in invasion. By contrast, while CA I and II are prominent in normal colorectal mucosa, where they play a role in regulation of pH homeostasis and water and ion transport, loss of expression of these cytoplasmic isozymes consistently accompanies progression to malignant transformation.

Expression of the membrane-associated carbonic anhydrase isozyme XII in the human kidney and renal tumors.

Carbonic anhydrase isozyme XII (CA XII) is a novel membrane-associated protein with a potential role in von Hippel-Lindau carcinogenesis. Although Northern blotting has revealed positive signal for CA XII in normal human kidney, this is the first study to demonstrate its cellular and subcellular localization along the human nephron and collecting duct. Immunohistochemistry with a polyclonal antibody (PAb) raised against truncated CA XII revealed distinct staining in the basolateral plasma membrane of the epithelial cells in the thick ascending limb of Henle and distal convoluted tubules, and in the principal cells of the collecting ducts. A weak basolateral signal was also detected in the epithelium of the proximal convoluted tubules. In addition to the normal kidney specimens, this immunohistochemical study included 31 renal tumors. CA XII showed moderate or strong plasma membrane-associated expression in most oncocytomas and clear-cell carcinomas. The segmental, cellular, and subcellular distribution of CA XII along the human nephron and collecting duct suggests that it may be one of the key enzymes involved in normal renal physiology, particularly in the regulation of water homeostasis. High expression of CA XII in some renal carcinomas may contribute to its role in von Hippel-Lindau carcinogenesis.

Expression of transmembrane carbonic anhydrase isoenzymes IX and XII in normal human pancreas and pancreatic tumours.

Carbonic anhydrase (CA) IX and XII are transmembrane isoenzymes which are expressed in several epithelia and overexpressed in some carcinomas. They have recently been linked to von Hippel-Lindau gene-mediated carcinogenesis in that both isoenzymes are downregulated by the product of the wild-type von Hippel-Lindau tumour suppressor gene. This paper describes the localisation of CA IX and XII in the normal human pancreas and pancreatic tumours. Both isoenzymes showed positive reaction in the basolateral plasma membrane of the normal acinar and ductal epithelia. The hyperplastic ductal epithelium in tumour specimens generally showed an increased staining for CA IX. Of 29 malignant tumours of exocrine pancreas, 10 showed moderate or strong immunoreaction for CA IX. The signal for CA XII remained weak in most malignant lesions. The present results show that both CA IX and XII are unevenly expressed in the ductal and acinar compartments of the human pancreas. The expression of these isoenzymes in a relatively low number of malignant tumour specimens suggests that they have a limited value in diagnostic evaluation of pancreatic carcinoma. However, the increased expression of CA IX in hyperplastic ductal epithelium may contribute to the pancreatic tumourigenesis.

Expression of a novel transmembrane carbonic anhydrase isozyme XII in normal human gut and colorectal tumors.

Carbonic anhydrase isozyme XII is a recently discovered member of the alpha-carbonic anhydrase gene family with a suggested role in von Hippel-Lindau gene-mediated carcinogenesis. Increased expression of its mRNA has been observed in renal and lung carcinomas. This paper presents the localization of CA XII in the normal human gut and in colorectal tumors. Immunohistochemistry performed using a polyclonal antibody raised against truncated CA XII revealed prominent polarized staining for CA XII in the basolateral plasma membrane of the enterocytes of the normal large intestine, the reaction being most intense in the surface epithelial cuff region. Most colorectal tumors displayed abnormal expression of CA XII; the most dramatic change was observed in the deep parts of the adenomatous mucosa, where the positive immunoreaction clearly increased along with the grade of dysplasia. Adenomas with severe dysplasia and carcinomas showed an equal, diffuse staining pattern. The results indicate region-specific regulation of CA XII expression along the cranial-caudal axis of the human gut, whereas its diffuse expression in the most malignant tumors seems to correlate with their biological behavior.

Cell-specific expression of mitochondrial carbonic anhydrase in the human and rat gastrointestinal tract.

Mitochondrial carbonic anhydrase V (CA V) in liver provides HCO3- to pyruvate carboxylase for the first step in gluconeogenesis and HCO3- to carbamyl phosphate synthetase I for the first step in ureagenesis. Because carbamyl phosphate synthetase I and ornithine transcarbamylase are also expressed in enterocytes, we tested the hypothesis that CA V is expressed in the gastrointestinal tract in addition to liver. Polyclonal rabbit antisera were raised against a polypeptide of 17 C-terminal amino acids of human CA V and against purified recombinant mouse isozyme and were used in Western blotting and immunoperoxidase staining of human and rat tissues. Immunohistochemistry showed that CA V is expressed cell-specifically in the alimentary canal mucosa from stomach to rectum. Immunoreactions for CA V were detected in the parietal cells and gastrin-producing G-cells of the stomach and in intestinal enterocytes. Western blotting of human and rat gastrointestinal tissues with isozyme-specific antibodies showed positive signals for CA V with the expected molecular mass. The findings in human tissues paralleled those in rat. The cell-specific pattern of CA V expression suggests a role for CA V in alimentary canal physiology. We propose that mitochondrial CA V participates in the detoxification of ammonia produced in the gastrointestinal tract by providing bicarbonate to carbamyl phosphate synthetase I. (J Histochem Cytochem 47:517-524, 1999)

Association of HFE protein with transferrin receptor in crypt enterocytes of human duodenum.

In hereditary hemochromatosis (HH), intestinal absorption of dietary iron is increased, leading to excessive iron accumulation in tissues and resultant organ damage. The HFE protein, which is defective in HH, normally is expressed in crypt enterocytes of the duodenum where it has a unique, predominantly intracellular localization. In placenta, the HFE protein colocalizes with and forms a stable association with the transferrin receptor (TfR), providing a link between the HFE protein and iron transport. In the present study, we examined the relationship of the HFE protein to the TfR in enterocytes of the human duodenum and measured the uptake of transferrin-bound iron and ionic iron by isolated crypt and villus enterocytes. Immunocytochemistry showed that the HFE protein and TfR both are expressed in the crypt enterocytes. Western blots showed that, as was the case in human placenta, the HFE protein in crypt enterocytes is physically associated with the TfR and with beta2-microglobulin. The crypt cell fraction exhibited dramatically higher transferrin-bound iron uptake than villus cells. On the other hand, the villus cells showed 2-3 times higher uptake of ionic iron than crypt cells. We propose that the HFE protein modulates the uptake of transferrin-bound iron from plasma by crypt enterocytes and participates in the mechanism by which the crypt enterocytes sense the level of body iron stores. Impairment of this function caused by HFE gene mutations in HH could provide a paradoxical signal in crypt enterocytes that programs the differentiating enterocytes to absorb more dietary iron when they mature into villus enterocytes.

Immunohistochemical study of colorectal tumors for expression of a novel transmembrane carbonic anhydrase, MN/CA IX, with potential value as a marker of cell proliferation.

Carbonic anhydrase isoenzyme IX, MN/CA IX, is a recently discovered member of the carbonic anhydrase (CA) gene family with a suggested function in acid-base balance, intercellular communication, and cell proliferation. Increased expression of MN/CA IX has been observed with certain epithelial tumors. We investigated the expression of MN/CA IX in 69 colorectal neoplasms, consisting of 1 juvenile polyp, 8 hyperplastic polyps, 39 adenomatous lesions, 21 carcinomas, and 7 metastases. Tissue sections were immunostained with a monoclonal antibody specific to MN/CA IX. The proliferative activity of the tumor cells was evaluated by Ki-67 antigen immunoreactivity. The hyperplastic polyps showed a weak or moderate reaction for MN/CA IX only in the cryptal epithelium, as did the normal intestinal mucosa. The adenomas showed immunoreactivity mainly in the superficial part of the mucosa, whereas the distribution in the carcinomas and metastases was more diffuse. Comparative immunostaining of serial sections for Ki-67, a well established marker of cell proliferation, confirmed that MN/CA IX is expressed in areas with high proliferative capacity. Our results show abnormal MN/CA IX expression in colorectal neoplasms, suggesting its involvement in their pathogenesis. The co-occurrence of MN/CA IX and Ki-67 in the same tumor cells indicates its potential for use as a marker of increased proliferation in the colorectal mucosa.

Immunohistochemistry of carbonic anhydrase isozyme IX (MN/CA IX) in human gut reveals polarized expression in the epithelial cells with the highest proliferative capacity.

MN/CA IX is a recently discovered member of the carbonic anhydrase (CA) gene family that has been identified in the plasma membranes of certain tumor and epithelial cells and found to promote cell proliferation when transfected into NIH3T3 cells. This study presents localization of MN/CA IX in human gut and compares its distribution to those of CA I, II, and IV, which are known to be expressed in the intestinal epithelium. The specificity of the monoclonal antibody for MN/CA IX was confirmed by Western blots and immunostaining of COS-7 cells transfected with MN/CA IX cDNA. Immunohistochemical stainings of human gut revealed prominent polarized staining for MN/CA IX in the basolateral surfaces of the enterocytes of duodenum and jejunum, the reaction being most intense in the crypts. A moderate reaction was also seen in the crypts of ileal mucosa, whereas the staining became generally weaker in the large intestine. The results indicate isozyme-specific regulation of MN/CA IX expression along the cranial-caudal axis of the human gut and place the protein at the sites of rapid cell proliferation. The unique localization of MN/CA IX on the basolateral surfaces of proliferating crypt enterocytes suggests that it might serve as a ligand or a receptor for another protein that regulates intercellular communication or cell proliferation. Furthermore, MN/CA IX has a completely conserved active site domain of CAs suggesting that it could also participate in carbon dioxide/bicarbonate homeostasis.