Changes in parietal and mucous cell mass in the gastric mucosa of normal subjects with age: a morphometric study

A systematic review with meta-analysis: Efficacy and safety of potassium-competitive acid blocker compared with proton pump inhibitor in the maintenance of healed erosive esophagitis

Introduction

Proton pump inhibitor (PPI) is the mainstay therapy for the maintenance of healed erosive esophagitis (EE). It is unknown whether potassium-competitive acid blockers (PCABs) are more efficacious and safer than PPIs.

Methods

Only randomized controlled trials (RCTs) comparing PCABs to PPIs in the maintenance of healing rates of endoscopically proven healed EE and indexed in MEDLINE, EMBASE, and CENTRAL until 3 February 2024, were included. A fixed-effects model meta-analysis was performed to pool primary efficacy outcome (maintenance of healing rates at week 24) and safety data (any treatment-emergent adverse event or TEAE). The risk of bias was assessed using Cochrane's Risk of Bias 2 (RoB2) tool.

Results

Four RCTs with a total of 2554 patients were eligible for inclusion. All trials were of low risk of bias. Compared to lansoprazole 15 mg, the maintenance rates of healed EE at week 24 were significantly higher with vonoprazan 10 mg (RR 1.13; 95% CI 1.07-1.19) and vonoprazan 20 mg (RR 1.15; 95% CI 1.10-1.21). Likewise, compared to lansoprazole 15 mg, any TEAEs were significantly greater with vonoprazan 20 mg (RR 1.10; 95% CI 1.01-1.20) but not vonoprazan 10 mg.

Conclusion

Vonoprazan 10 and 20 mg were superior to lansoprazole 15 mg in the maintenance of the healing of EE. Any TEAEs were greater with vonoprazan 20 mg.

Mucus interaction to improve gastrointestinal retention and pharmacokinetics of orally administered nano-drug delivery systems

Oral delivery of therapeutics is the preferred route of administration due to ease of administration which is associated with greater patient medication adherence. One major barrier to oral delivery and intestinal absorption is rapid clearance of the drug and the drug delivery system from the gastrointestinal (GI) tract. To address this issue, researchers have investigated using GI mucus to help maximize the pharmacokinetics of the therapeutic; while mucus can act as a barrier to effective oral delivery, it can also be used as an anchoring mechanism to improve intestinal residence. Nano-drug delivery systems that use materials which can interact with the mucus layers in the GI tract can enable longer residence time, improving the efficacy of oral drug delivery. This review examines the properties and function of mucus in the GI tract, as well as diseases that alter mucus. Three broad classes of mucus-interacting systems are discussed: mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems. For each class of system, the basis for mucus interaction is presented, and examples of materials that inform the development of these systems are discussed and reviewed. Finally, a list of FDA-approved mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems is reviewed. In summary, this review highlights the progress made in developing mucus-interacting systems, both at a research-scale and commercial-scale level, and describes the theoretical basis for each type of system.

H+ /K+ ATPase expression in human parietal cells and gastric acid secretion in elderly individuals

OBJECTIVE

To investigate whether the ultrastructure and hydrogen potassium adenosine triphosphate (H+ /K+ ATPase) expression of human parietal cells were associated with aging.

METHODS

In all, 50 participants who underwent gastroscopy due to dyspepsia were divided into two age groups, with 19 in the younger group (YG, aged 20-59 years) and 31 in the elder group (EG, aged ≥60 years). The ultrastructure of their parietal cell was determined by electron microscopy (EM), and the expressions of H+ /K+ ATPase α-subunit mRNA and β-unit protein were detected. Furthermore, 24-h esophageal pH monitoring was performed in the two groups.

RESULTS

EM images showed no distinct difference in the morphology and distribution of parietal cells or the acid secretion-related organelle between the two groups. There were no differences between YG and EG in the proportion of mitochondria and the tubulovesicular system area. The expressions of H+ /K+ ATPase α-subunit mRNA and β-subunit protein showed no age-related alteration between YG and EG. The expression of H+ /K+ ATPase α-subunit mRNA in EG was higher than that in YG, whereas the expression of β-subunit protein was significantly higher in those aged ≥80 years than in the YG. No significant difference was found in the 24-h esophageal pH monitoring between YG and EG.

CONCLUSION

Acid secretion-related organelles in parietal cells do not degenerate with aging, the expression of H+ /K+ ATPase even shows a trend to increase, indicating the existence of intact molecular biological basis for acid secretion in healthy elderly individuals.

Telomere shortening is associated with reduced duodenal HCOFormula secretory but normal gastric acid secretory capacity in aging mice

The incidence of duodenal ulcer, especially Helicobacter pylori-negative duodenal ulcer, strongly increases with age. In humans, telomere length shortening is considered to be one critical factor in cellular senescence and organ survival. In this study, we compared basal and stimulated gastric acid and duodenal HCO(3)(-) secretory rates in aged late-generation (G(3)) telomerase-deficient (mTERC(-/-)) mice, which are characterized by severe telomere dysfunction due to the inability to elongate telomeres during cell division. We found that basal and forskolin-stimulated HCO(3)(-) secretion and short-circuit current (I(sc)) in isolated duodenal mucosa of G(3) mTERC(-/-) mice were markedly reduced compared with age-matched wild-type mice. In contrast, basal and forskolin-stimulated acid secretory rates in isolated G(3) mTERC(-/-) gastric mucosa were not significantly altered. Correspondingly, duodenal mucosa of G(3) mTERC(-/-) mice showed slimming and shortening of villi, whereas gastric mucosal histology was not significantly altered. However, the ratios of cystic fibrosis transmembrane conductance regulator (CFTR) and solute-linked carrier 26 gene family (Slc26a6) mRNA expression in relation to cytokeratin-18 were not altered in duodenal mucosa. The further knockout of p21, which is a downstream effector of telomere shortening-induced senescence, rescued villus atrophy of duodenal mucosa, and basal and forskolin-stimulated duodenal HCO(3)(-) secretion and I(sc) in mTERC(-/-) p21(-/-) double-knockout mice were not different from wild-type controls. In conclusion, genetic ablation of telomerase resulted in p21-dependent duodenal mucosal atrophy and reduced duodenal HCO(3)(-) secretory capacity, whereas gastric morphology and acid secretory function were preserved. This suggests that telomere shortening during aging may result in an imbalance between aggressive and protective secretions against duodenal mucosa and thus predispose to ulcer formation.

Morphometric features and glycoconjugate pattern of rabbit intestine are affected by particle size of pelleted diets

Feed particle size effects on morphology and glycoconjugate pattern was investigated in the rabbit intestine. Rabbits fed with fine particles (2 mm) displayed more irregularly shaped, higher duodenal villi and deeper crypts in distal colon as well as higher number of goblet cells than coarse (8 mm) fed ones. Brush border expressed: (i) in duodenum, neutral/sulfated glycoconjugates and glycans binding MAL II, SNA, Con A than KOH-sialidase-PNA and DBA reactivity in fine and coarse fed rabbits, respectively, (ii) in cecum, mainly sulfoglycans in coarse fed rabbits, MAL II and PNA staining in all samples, and (iii) in distal colon few sulfoglycans and MAL II reactivity. Enterocytes bound MAL II in duodenum, Con A in cecum, DBA, and Con A in distal colon of all rabbits, SNA in distal colon of coarse fed ones. Brunner's glands displayed high presence of acidic/sulfated mucins in fine fed rabbits, neutral glycoconjugates and reactivity with MAL II, SNA, PNA, KOH-sialidase-PNA, and Con A in all rabbits. Goblet cells exhibited: (i) in duodenum neutral and sulfomucins as well as MAL II and KOH-sialidase-PNA staining, than SNA and DBA in fine and coarse fed rabbits, respectively, (ii) in cecum sulfated glycans, MAL II, SNA, KOH-sialidase-PNA, DBA reactivity, and (iii) in distal colon acidic/sulfomucins, MAL II and SNA staining, and DBA reactivity in fine fed specimens. Crypt cells exhibited neutral and PNA reactive glycoconjugates in the cecum. In the distal colon also acidic/sulfated glycans, and MAL II, KOH-sialidase-PNA, DBA; SNA staining showed weaker reactivity in fine fed rabbits, which bound Con A.

Cell division and aging of the organism

The capacity to regenerate cell compartments through cell proliferation is an important characteristic of many developed metazoan tissues. Pre- and post-natal development proceeds through the modifications occurring during cell division. Experiments with cultivated cells showed that cell proliferation originates changes in cell functions and coordinations that contribute to aging and senescence. The implications of the finite cell proliferation to aging of the organism is not the accumulation of cells at the end of their life cycle, but rather the drift in cell function created by cell division. Comparative gerontology shows that the regulation of the length of telomeres has no implications for aging. On the other hand there are interspecies differences in regard to the somatic cell division potential that seem to be related with the "plasticity" of the genome and with longevity, which should be viewed independently of the aging phenomenon. Telomeres may play a role in this plasticity through the regulation of chromosome recombination, and via the latter also in development.

Qualitative and quantitative alterations in the parietal cell domain in chronic gastritis

Hematoxylin and eosin (H&E) is not an optimal stain to discriminate between parietal and chief cells in gastric biopsies; modified Giemsa (G) and toluidine blue (TB) were found more suitable stains to characterize these two cell phenotypes. Sixty-eight well-oriented sections from the fundic mucosa were stained with H&E, and with G or TB. With G or TB the normal fundic mucosa clearly displayed a parietal cell domain (PCD) and a chief-cell domain (CCD). The continuity of these two cell domains was assessed in the entire section at ×4 magnification and the thickness of the PCD. The total mucosal thickness (TMT) was measured in three different HPF at ×20 magnifications. Qualitative observations indicated that the PCD and CCD were (a) continuous in normal fundic mucosa or having slight chronic gastritis, (b) fragmented in moderate chronic gastritis, in focal glandular atrophy or focal IM or (c) absent in severe chronic gastritis, including autoimmune gastritis and extensive IM. Quantitative measurements showed that the thickness of the PCD in chronic gastritis could be (a) normal, (b) reduced by partial destruction of the parietal cell population by chronic inflammation, or (c) absent, in extensive IM or total glandular atrophy (p < 0.05). Toluidine blue gave a better contrast between the two cell phenotypes than modified Giemsa stain. Future studies might elucidate whether qualitative and quantitative studies of toluidine blue-stained sections of the fundic mucosa are useful in monitoring the results of therapy in individual patients with chronic gastritis.

Age-related changes in immune function: effect on airway inflammation

Immunosenescence is defined as changes in the innate and adaptive immune response associated with increased age. The clinical consequences of immunosenescence include increased susceptibility to infection, malignancy and autoimmunity, decreased response to vaccination, and impaired wound healing. However, there are several immune alterations that might facilitate persistence of asthma into late adulthood or development of asthma after the age of 50 to 60 years. Asthma in older patients is not uncommon, and this is a growing population as the average lifespan increases. Specific innate changes that might affect severity of asthma in older patients or be involved in the development of late-onset asthma include impaired mucociliary clearance and changes in airway neutrophil, eosinophil, and mast cell numbers and function. Additionally, age-related altered antigen presentation and decreased specific antibody responses might increase the risk of respiratory tract infections. Respiratory tract infections exacerbate asthma in older patients and possibly play a role in the pathogenesis of late-onset asthma. Furthermore, cytokine profiles might be modified with aging, with some investigators suggesting a trend toward T(H)2 cytokine expression. This review examines specific innate and adaptive immune responses affected by aging that might affect the inflammatory response in older adults with asthma.

Treatment and management of epilepsy in the elderly demented patient

Epilepsy and seizures are more frequent in the elderly population than in any other age group. The number of individuals older than 65 is constantly increasing, and dementia is a process that predominantly affects this age group. Several studies have shown that dementia is an important risk factor for developing seizures and epilepsy. Seizure semiology in the elderly demented might differ from that of younger age groups and diagnosis can be complicated further by the variety of other causes of transient changes of alertness and behavior that affects these patients. The pharmacokinetic changes of antiepileptic drugs in the elderly make this group a major therapeutic challenge. Side effects and drug interactions play a major role in the choice of antiepileptic agents. This review intends to summarize the existing data to see whether this can help guide the clinician in the treatment and management of epilepsy in the elderly patient with dementia. Nonpharmacologic therapeutic options are also briefly considered.

Clinical and diagnostic relevance of Meckel's diverticulum in children

Meckel's diverticulum (MD) has varied clinical manifestations and is a diagnostic challenge for pediatricians. This study investigates the clinical and diagnostic characteristics of MD in children with different presentations. We retrospectively reviewed the medical records of pediatric patients diagnosed with MD from 1988 to 2008. The data including the age, sex, clinical features, laboratory data, sensitivity of diagnostic methods, and pathological finding were recorded. These patients were classified into three groups: diverticulitis, intestinal obstruction, and intestinal bleeding. A total of 47 children (35 boys and 12 girls) with a median age of 5.6 years were enrolled and categorized as follows: diverticulitis (n = 12), obstruction (n = 12), bleeding (n = 21), and two diagnosed incidentally. Patients with intestinal obstruction were significantly younger than those with bleeding (3.7, 95% CI, 1.6-5.7 vs. 6.6, 95% CI, 4.5-8.7, P = 0.04). In the obstruction group, intussusception was found in eight of 12 patients, of whom 62.5% were aged older than 3 years. Heterotopic tissues were found in 46.3% of surgical specimens and more frequently existed in patients with bleeding than those with diverticulitis (P = 0.02) and obstruction (P = 0.047). Tc-99m scans yielded a diagnostic sensitivity of about 65% in bleeding patients. Repeated Tc-99m scans and red blood cell (RBC) scans can be good supplementary tools in Tc-99m scan-negative bleeding patients. In conclusion, manifestations of childhood MD are variable and may depend on the presence of heterotopic tissues and the patients' age. Tc-99m scans supplemented with RBC scans are appropriate to diagnose childhood MD with bleeding.

Analyses of human colonic mucus obtained by an in vivo sampling technique

BACKGROUND

The mucus layer is an important dynamic component of the epithelial barrier. It contains mucin glycoproteins and other compounds secreted by the intestinal epithelium, such as secretory IgA. However, a standardized in vivo sampling technique of mucus in humans is not yet available.

AIM

To assess the validity and feasibility of mucin and protein determinations in human colonic mucus collected under physiological conditions.

SUBJECTS AND METHODS

Triplicate colonic mucus samples were collected in 11 healthy volunteers using cytology brushes during sigmoidoscopy. As an indication of the quantity of collected mucus, total protein and mucin concentrations were determined by measuring oligosaccharide equivalents and monosaccharides. Also secretory IgA and sialic acid concentrations were determined and proteomic analysis was performed using surface enhanced laser desorption/ionization-time of flight-mass spectrometry.

RESULTS

Mean values of secretory IgA and sialic acid corrected for the amount of mucus ranged from 0.16 to 1.81 g secretory IgA/mmol oligosaccharide equivalents and from 12.6 to 48.6g sialic acid/mmol oligosaccharide equivalents. Proteomic analysis of mucus is feasible and cluster analysis showed subject specific profiles.

CONCLUSION

Using cytology brushes, human colonic mucus can be sampled and under physiological conditions. These samples could give information on the composition and quality of the mucus layer.

Gastric emptying, diabetes, and aging

Gastric emptying is mildly slowed in healthy aging, although generally remains within the normal range for young people. The significance of this is unclear, but may potentially influence the absorption of certain drugs, especially when a rapid effect is desired. Type 2 diabetes is common in the elderly, but there is little data regarding its natural history, prognosis, and management. This article focuses on the interactions between gastric emptying and diabetes, how each is influenced by the process of aging, and the implications for patient management.

Assessment of Age-Related Changes in Abdominal Organ Structure and Function With Computed Tomography and Positron Emission Tomography

With the size of the aged population in the United States expected to grow considerably during the next several decades, the number of imaging studies performed on such aged individuals will similarly increase. Thus, it is important to understand normal age-related changes in the structural and functional imaging appearance of the abdominal organs. We therefore present preliminary data and a review of the literature relevant to structural and functional changes in the abdominal organs of children and older adults. In a retrospective study of both adult and pediatric populations, we used computed tomography (CT), positron emission tomography (PET), and PET/CT imaging to investigate age-associated changes in size, attenuation, and metabolic function of the abdominal organs. Organs of interest include the liver, spleen, pancreas, kidneys, adrenal glands, stomach, small bowel, colon, and rectum. Although volumes of adult liver, spleen, pancreas, and kidneys do not change significantly with age, adult left and right adrenal gland volumes do significantly increase with age (r = 0.2823, P = 0.0334, and r = 0.3676, P = 0.0049, respectively). Also, the attenuation of adult liver (r = -0.2122, P = 0.0412), spleen (r = -0.4508, P < 0.0001), pancreas (r = -0.5124, P = 0.0007), and left and right adrenal gland (r = -0.5835, P < 0.0001 and r = -0.6135, P < 0.0001, respectively) decrease significantly with increasing age. Every organ studied in the pediatric population demonstrates a positive association between organ volume and age. Significant age-related changes in organ function are noted in the adult liver and small bowel, with the liver demonstrating a positive association between metabolic activity and age (r = 0.4434, P = 0.0029) and the small bowel showing an inverse association between mean small bowel standardize uptake value and age (r = -0.2435, P = 0.0174). Also, the maximum overall small bowel and colon metabolic activity in children increases with age (r = 0.6478, P = 0.0008). None of the other organs studied (ie, spleen, pancreas, adrenal glands, stomach, colon, rectum) demonstrate significant changes in metabolism with advancing age. The metabolic volumetric product (calculated as the product of organ volume and mean organ SUV) of the liver and spleen does not change significantly with age. In conclusion, various abdominal organs demonstrate differential changes in volume, attenuation, and/or metabolism with increasing age in pediatric and adult populations.

Improving the gastrointestinal tolerability of aspirin in older people

Interventions to reduce mortality and disability in older people are vital. Aspirin is cheap and effective and known to prevent cardiovascular and cerebrovascular disease, many cancers, and Alzheimer dementia. The widespread use of aspirin in older people is limited by its gastrointestinal side effects. Understanding age-related changes in gastrointestinal physiology that could put older people at risk of the side effects of aspirin may direct strategies to improve tolerance and hence lead to greater numbers of older people being able to take this effective intervention.

Effect of age-related changes in gastric physiology on tolerability of medications for older people

Studies specifically examining the effect of age upon the stomach are limited and frequently uncontrolled for the high prevalence of Helicobacter pylori in this age group. Age-related changes in gastric physiology such as reduced mucosal protection, gastric blood flow and impaired repair mechanisms may all impact upon gastrointestinal adverse effects and how older people tolerate medicines. Understanding how the upper gastrointestinal tract changes with advancing age could allow interventions that lead to more appropriate prescribing for older people, potentially reduce adverse effects, increase compliance with treatment regimens, and may allow older people to take medications that they would not otherwise tolerate. This review emphasises how the stomach changes with age, and how understanding this will aid clinicians when prescribing medications with potential gastrointestinal adverse effects to older people.

Changes in upper gastrointestinal physiology with age

Diseases of the upper gastrointestinal tract such as peptic ulceration and gastric cancer become more common and more severe with advancing age. In the normal stomach and duodenum, there is a balance between mucosal protective mechanisms and endogenous (gastric acid and pepsin) and exogenous aggressive factors. The high incidence of gastrointestinal pathology seen in older age groups is not related to increase in the secretion of endogenous aggressive factors. Recent work suggests that gastrointestinal mucosal protective mechanisms are impaired with age. The roles in the gastrointestinal tract of molecules that have been implicated in mucosal repair, such as trefoil peptides and matrix components, are beginning to be elucidated and their study in older people is essential to ensure appropriate, efficient, cost-effective management of gastric pathology in the elderly. Strategies to improve the management of upper gastrointestinal diseases in older people will reduce mortality and improve quality of life.

Review article: the ageing bowel and intolerance to aspirin

Aspirin has a role in the prevention of cardiovascular and cerebrovascular disease, Alzheimer's dementia and several cancers. Encouraging all 50 year olds to take low-dose aspirin doubles their chances of living a healthy life into their nineties. The widespread use of aspirin, however, is limited as many older subjects are currently unable to take aspirin because of gastrointestinal side-effects. This review explores why gastrointestinal events occur with aspirin use and how a net benefit from prophylactic aspirin might be achieved in older subjects. It is suggested that, by understanding the age-related changes in upper gastrointestinal physiology and the mechanisms by which aspirin leads to the risk reductions associated with its use, it may be possible to direct interventions to improve tolerability in older subjects. This would allow greater numbers of older subjects to gain the benefits associated with aspirin use.

Gastro-Oesophageal reflux in the elderly: role of drug therapy in management

Gastro-oesophageal reflux disease (GORD) is common in the elderly. The presenting symptoms of heartburn and regurgitation, so common in the young, are less frequent in the elderly. Common symptoms of GORD in the elderly are dysphagia, vomiting and respiratory problems. Because of the higher risk of associated pathological oesophageal lesions in the older person presenting with symptoms suggestive of GORD, oesophagogastroduodenoscopy must be performed earlier in their clinical course. There is only a poor correlation between the severity of the symptoms and the severity of the associated oesophagitis. Whereas lifestyle modifications are important in individuals with GORD, the use of proton pump inhibitors is recommended to heal the underlying pathology, to resolve the patient's symptoms, to prevent complications, and to improve the quality of life.

Visualization of areae gastricae on double-contrast upper gastrointestinal radiography: relationship to age of patients

OBJECTIVE

The purpose of this study was to determine whether the frequency of visualization of areae gastricae on double-contrast upper gastrointestinal tract examinations is related to a patient's age.

MATERIALS AND METHODS

A total of 141 double-contrast upper gastrointestinal tract examinations with normal findings were reviewed for the presence or absence of areae gastricae on double-contrast images of the stomach. All images were evaluated by two radiologists who were blinded to the age of the patients. The data were then analyzed to determine if the frequency of visualization of areae gastricae on double-contrast studies was significantly related to the age of patients.

RESULTS

The frequency of visualization of areae gastricae increased significantly with increasing age (p = 0.008). The youngest age group (20--29 years old) exhibited areae gastricae in only four (19%) of 21 cases, whereas the oldest age group (> or = 70 years old) exhibited areae gastricae in 19 (76%) of 25 cases. On average, the rate of visualization of areae gastricae on double-contrast studies increased by 9% per decade.

CONCLUSION

Our data show that the frequency of visualization of areae gastricae on double-contrast upper gastrointestinal tract examinations increases significantly with increasing patient age. It is important for radiologists to be aware of the effect of aging on the delineation of areae gastricae on double-contrast studies.

Rapid quantitative assessment of gastric corpus atrophy in tissue sections

BACKGROUND/AIMS

Grading of Helicobacter pylori induced atrophic gastritis using the updated Sydney system is severely limited by high interobserver variability. The aim of this study was to set up a quantitative test of gastric corpus mucosal atrophy in tissue sections and test its reproducibility and correlation with the Sydney scores of atrophy.

METHOD

Mucosal atrophy was assessed in 124 haematoxylin and eosin stained corpus biopsy specimens by two experienced gastrointestinal pathologists (EB, JL) according to the updated Sydney system as none (n = 33), mild (n = 33), moderate (n = 33), or pronounced (n = 25). In each specimen, the proportions of glands, stroma, infiltrate, and intestinal metaplasia in the glandular zone were measured as volume percentages using a point counting method. The optimal point sample size, intra-observer and interobserver reproducibility, discriminative power for degrees of atrophy, and correlations with H pylori status were evaluated.

RESULTS

Counting 400 points in 200 fields of vision provided the smallest sample size that still had excellent intra-observer and interobserver reproducibility (r > or = 0.96). Overall, the volume percentage of glands (VPGL), infiltrate (VPI), and stroma (VPS) correlated well with the Sydney scores for atrophy (p < or = 0.003). However, no differences were found between non-atrophic mucosa and mild atrophy. No correlation was found between age and either the Sydney grade of atrophy or the VPGL or VPS. In non-atrophic mucosa and mild atrophy, H pylori positive cases showed a significantly higher VPI than did H pylori negative cases. A lower VPGL was seen in H pylori positive cases than in H pylori negative cases in the mild atrophy group. VPS did not correlate with H pylori status within each grade of atrophy.

CONCLUSION

Point counting is a powerful and reproducible tool for the quantitative analysis of mucosal corpus atrophy in tissue sections. These data favour the combination of "none" and "mild" atrophy into one category, resulting in a three class grading system for corpus atrophy, when using the updated Sydney system.

Concomitant staining of mast and parietal cells in human gastric mucosa

A simple technique for concomitant staining of mast and parietal cells in the same section is described. Mast cells were stained by alcian blue or astra blue in methanol-formalin-acetic acid fixed biopsies of gastric mucosa. Parietal cells were visualized by Dolichos biflorus lectin binding.