Occludin expression and tight junction strand formation during replicative DNA synthesis in primary cultures of rat hepatocytes

Occludin, an integral membrane protein, is a candidate for forming the functional intercellular seal of the tight junction. In the present study, we examined the changes of occludin expression and tight junction strand in the cultured hepatocytes. In L-15 medium containing EGF with 2% DMSO and 10^–7M glucagon, the great majority of the cells were quiescent. Under this condition, occludin immunoreactivity was observed at cell-to-cell contacts. Tight junction strands formed well-developed networks in freeze-fracture replicas. When the cells entered S phase of the cell cycle, occludin immunoreactivity and the number of tight junction strands decreased. By contrast, when DNA synthesis was then inhibited by readdition of DMSO and glucagon, occludin immunoreactivity and the number of tight junction strands were restored. Regardless of DNA synthesis, however, there was no significant decrease in the protein and mRNA levels of occludin. These changes of occludin immunoreactivity were correlated to the organization of actin filaments. On the other hand, no change of ZO-1 immunoreactivity was observed. These results suggested that tight junctions of cultured hepatocytes regulated in a cell cycle-dependent fashion and correlated with the organization of circumferential actin bundles.     

Tight junction‐related human diseases

Tight junctions are intercellular junctions adjacent to the apical ends of paracellular spaces. They have two classical functions, the barrier function and the fence function. The former regulates the passage of ions, water and various molecules through paracellular spaces, and is thus related to edema, jaundice, diarrhea and blood‐borne metastasis. The latter function maintains cell polarity by forming a fence to prevent intermixing of molecules in the apical membrane with those in the lateral membrane. This function is deeply involved in cancer cell properties in terms of loss of cell polarity. Recently, two novel aspects of tight junctions have been reported. One is their involvement in signal transduction. The other is that fact that tight junctions are considered to be a crucial component of innate immunity. In addition, since some proteins comprising tight junctions work as receptors for viruses and extracellular stimuli, pathogenic bacteria and viruses target and affect the tight junction functions, leading to diseases. In this review, the relationship between tight junctions and human diseases will be described.     

A freeze-fracture electron microscopic study of tight junctions of epithelial cells in the human uterus

Summary Freeze-fracture electron microscopy has been used to study tight junctions of luminal epithelial cells of the human uterus. The junctions are deeper and more extensive in the middle of the menstrual cycle than they are later in the cycle. The results suggest that the contents of the uterine lumen may be more closely regulated at some times than at others.     

Claudin expression in gastric adenocarcinomas: a tissue microarray study with prognostic correlation

The claudins comprise a multigene family of integral membrane proteins, which play a major role in tight junction formation. Aberrations in the expression of certain claudins have been described in a number of malignancies. Our aims were to determine the expression pattern of claudins 1, 3, and 4 as well as ZO-1 in a large series of US patients with gastric cancer and to correlate expression with clinicopathologic and prognostic variables. Tissue microarrays were created from paraffinized samples from 146 patients with distal gastric adenocarcinomas (61 intestinal and 85 diffuse or mixed subtypes). In addition, cores of normal mucosa and intestinal metaplasia were taken from most cases. The microarrays were stained for claudins 1, 3, and 4 and ZO-1, and the intensity of staining was determined using a 3-point scale. Moderate claudin 1 and ZO-1 membranous staining were present, whereas only focal weak claudin 3 and 4 membranous staining was present in normal gastric epithelium. Moderate to strong staining of claudins 1, 3, 4, and ZO-1 was detected in 74%, 48%, 62%, and 74% of the intestinal but in only 46%, 24%, 45%, and 36% of the diffuse subtype of adenocarcinomas (P < .05). Cox multivariate analysis revealed that tumor stage, diffuse subtype, and moderate to strong claudin 4 staining were associated with decreased survival (P < .02). In conclusion, claudins 1, 3, and 4 and ZO-1 are strongly expressed in most gastric intestinal-type adenocarcinomas but less frequently in diffuse gastric cancers. The up-regulation of claudin expression during gastric carcinogenesis suggests their potential utility as diagnostic biomarkers and possible targets for therapeutic intervention.     

Tight junctions in the ependyma of the spinal cord of the urodele Pleurodeles waltlii

Summary The ependymal junction pattern in the spinal cord of postmetamorphic ribbed newts has been studied, using transmission electron microscopy of ultrathin sections of normal animals and of animals perfused through the IVth ventricle with lanthanum. Contrary to what has been observed in mammalian CNS, the ependyma of the urodelan spinal cord is furnished with tight junctions that seal the luminal border of the terminal bars. These occludens junctions are made up of two to seven punctate fusions of the plasma membranes. Lanthanum tracer remains restricted inside the lumen of the central canal, being stopped at the first punctate fusion on its way through the intercellular clefts. Beyond this point, the extracellular space contains no tracer material. Besides tight junctions, intermediate, desmosomal and gap junctions are also present. Gap junctions and desmosomes are not present in CSF-contacting neurons. It is suggested that ependyma with occluding junctions (special ependyma) overlay the regions of the CNS where the ependymal cells significantly modify the composition of both intercellular and cerebrospinal fluids, through secretory, transporting and permeability control activities.Dedicated to Dr. Jean Emmanuel Gruner     

Age-related changes in rat cerebral occludin and zonula occludens-1 (ZO-1)

The endothelial or epithelial tight junctions create a rate-limiting barrier to diffusion of solutes. A major determinant of the barrier function is the density of tight junction proteins. Since aging is associated with significant alterations in the blood-brain barrier (BBB) it is possible that specific tight junction proteins may be altered in the cerebrum of aging rats. To test this hypothesis, Western and Northern blot analysis were carried out to measure the steady-state level of occludin and zonula occludens-one (ZO-1) proteins and their mRNA in cerebral tissue of 3-, 12- and 24-month-old rats. The cerebral occludin content in 24-month-old rats (732.5+/-99.9 arbitrary units) was significantly reduced compared to 12-month-old rats (1043.4+/-131.8) or 3-month-old rats (1021.4+/-62.8), P<0.01. The cerebral ZO-1 protein content in 24-month-old rats (161.7+/-8.1 arbitrary units) and 12-month-old rats (144.3+/-35.9) were not significantly reduced compared to 4-month-old rats (189.0+/-27.2). The occludin mRNA content relative to G3PDH mRNA was 1.11+/-0.05, 1.11+/-0.07 and 1.00+/-0.05 in 3-, 12- and 24-month-old rats, respectively. The differences did not achieve statistical significance. The ZO-1 mRNA content of cerebral tissue relative to G3PDH mRNA was significantly increased in 24-month-old rats compared to 3-month-old rats (1.280+/-0.030 vs. 0.956+/-0.038), P<0.001. It is concluded that aging in rats may alter the molecular anatomy of the BBB by altering the content of select structural proteins of tight junctions.     

Tight junction proteins contribute to barrier properties in human pleura

The permeability of pleural mesothelium helps to control the volume and composition of the liquid lubricating pleural surfaces. Information on pleural barrier function in health and disease, however, is scarce. Tissue specimens of human pleura were mounted in Ussing chambers for measurement of transmesothelial resistance. Expression of tight junction (TJ) proteins was studied by Western blots and immune fluorescence confocal microscopy. Both visceral and parietal pleura showed barrier properties represented by transmesothelial resistance. Occludin, claudin-1, -3, -5, and -7, were detected in visceral pleura. In parietal pleura, the same TJ proteins were detected, except claudin-7. In tissues from patients with pleural inflammation these tightening claudins were decreased and in visceral pleura claudin-2, a paracellular channel former, became apparent. We report that barrier function in human pleura coincides with expression of claudins known to be key determinants of epithelial barrier properties. In inflamed tissue, claudin expression indicates a reduced barrier function.     

MicroRNA-21靶调控NCM460细胞ROCK1基因上调occludin表达

目的:探讨微小RNA-21(micro RNA-21,miR-21)对人正常结肠上皮细胞系NCM460中紧密连接相关蛋白——闭合蛋白(occludin)表达的影响,并分析其可能的靶基因。方法:利用miR-21过表达慢病毒建立miR-21过表达NCM460细胞系,q PCR检测miR-21表达水平,Western blot检测occludin表达情况。生物信息学方法预测miR-21的靶基因,根据评分和文献检索选择相应靶基因ROCK1进行进一步研究,利用miR-21 mimic和inhibitor转染NCM460细胞,同时检测miR-21以及ROCK1的表达水平;采用双萤光素酶报告基因实验验证ROCK1是miR-21的靶基因。结果:在NCM460细胞中过表达miR-21后可上调紧密连接相关蛋白occludin的表达。生物信息学分析预测ROCK1可能为miR-21的靶基因。在NCM460细胞中过表达miR-21可下调ROCK1的m RNA和蛋白水平,抑制miR-21可上调ROCK1的m RNA和蛋白水平。萤光素酶报告基因验证ROCK1为miR-21的靶基因。结论:在NCM460细胞中,miR-21能上调肠屏障功能相关蛋白occludin的表达。ROCK1是miR-21的靶基因,miR-21可能通过靶调控ROCK1促进occludin的表达。     

Pericyte endothelial gap junctions in human cerebral capillaries

Summary Human cerebral tissue has been ultrastructurally studied and gap junctions have been visualized between endothelial cells and pericytes that permit ion exchange. We propose that the functional interrelationship between endothelium and pericytes may play a role in the alteration of capillary diameter for the control of local cerebral blood flow.     

Enteropathogenic Escherichia coli changes distribution of occludin and ZO-1 in tight junction membrane microdomains in vivo

Diarrhea is a disease caused by enteropathogenic Escherichia coli (EPEC) infection, which caused the deaths of several hundred thousand children each year. However, the molecular mechanisms underlying EPEC infection in vivo are not fully understood. In the present study, we used the C57BL/6J mouse as an in vivo model of EPEC infection and investigated the effect of EPEC on tight junction (TJ) structure and barrier function. TJ ultrastructure was studied by transmission electron microscopy and a small molecule tracer biotin was used to examine the paracellular permeability of the colon. The distribution of TJ proteins occludin and ZO-1 in the epithelium was investigated by immunofluorescence microscopy. Our results demonstrated that TJ structure was disrupted following EPEC infection. And the morphological changes of TJ were accompanied by increased paracellular permeability which led to impairment of TJ barrier function. Immunofluorescency analysis revealed that occludin and ZO-1 were translocated from villous membrane to the cytoplasm in intestinal epithelial cells during EPEC invasion. Moreover, wild-type EPEC and the mutant EPEC strain, ΔespF, had similar effects on barrier function and TJ protein localization at 5 days postinfection. Our findings demonstrate that EPEC infection in vivo led to disruption of tight junction barrier function. These results may provide insights into the molecular mechanism of the pathogenesis of EPEC infection.     

CFTR and tight junctions in cultured bronchial epithelial cells

Airway epithelial salt and water transport takes place through paracellular and transcellular pathways. This transport depends critically on the epithelial sodium channel (ENaC) and the cystic fibrosis transmembrane conductance regulator (CFTR), operating in concert with the paracellular pathway through the tight junctions (TJ). Normal (16HBE14o-), cystic fibrosis (CFBE41o-), and corrected CFBE41o- (CFBE41o-pCep4 overexpressing wtCFTR) airway epithelial cell lines were cultured under isotonic conditions. Transepithelial electrical resistance (TEER) was measured as indicator of the tightness of the cultures. Morphology was investigated by immunofluorescence and paracellular permeability by lanthanum nitrate or [¹⁴C] mannitol as permeability markers.The CFTR-defective cell line CFBE41o- developed higher TEER than its corrected counterpart CFBE41o-pCep4. Addition of a specific inhibitor of CFTR (CFTR_inh-172) to 16HBE14o- and CFBE41o-pCep4 cells resulted in a time-dependent increase in TEER, whereas stimulation of CFTR by IBMX and forskolin caused a decrease. Permeability to lanthanum and [¹⁴C] mannitol was lower in CFBE41o- and in 16HBE14o- cells exposed to CFTR_inh-172, compared to untreated 16HBE14o- and CFBE41o-pCep4 cells, respectively. 16HBE14o- cells exposed to IBMX and forskolin showed higher permeability to lanthanum but lower permeability to [¹⁴C] mannitol compared to control. Immunofluorescence revealed a disorganization of F-actin and α-tubulin in 16HBE14o- cells and CFBE41o- pCep4 exposed to CFTR_inh-172 and in CFBE41o- cells. Changes in F-actin and α-tubulin in 16HBE14o- cells exposed to IBMX and forskolin were also seen. These results suggest the possibility of an interaction between CFTR and the TJ protein complex, probably via the cytoskeleton.     

Intercellular junctions in the human fetal membranes

Summary Freeze-fracture replicas of the human reflected and placental amnion and chorion laeve at term were studied in order to give a systematic survey of the nature and extension of the intercellular junctions in the fetal membranes. No differences could be detected between the reflected and placental amniotic epithelium. In both the replicas never displayed plasma membrane differentiations typical of occluding junctions, while communicating junctions were occasionally and desmosomes frequently seen. In the chorionic trophoblast maculae occludentes, communicating junctions and desmosomes were regularly encountered. It is assumed that the maculae occludentes are remnants of occluding junctions which early in gestation possibly seal off the chorionic cavity; it appears improbable that they contribute significantly to the permeability properties of the chorionic trophoblast, since it is known from previous ultrastructural studies that large open intercellular channels cross the chorionic trophoblast. Thus the absence of occluding junctions, which could act as effective permeability barriers, in both epithelial components of the fetal membranes suggests that the factors able to influence the amniotic fluid turnover or the paraplacental protein exchange are the geometrical relationships and physico-chemical properties of the intercellular channels in the amniotic epithelium and chorionic trophoblast. In addition, communicating junctions were present between fibroblasts in the chorion laeve but not in the amnion, possibly indicating differences in the functional state of these cells and/or their extracellular microenvironments.The results of this study have been presented in preliminary form at the 77. Versammlung der Anatomischen Gesellschaft, Hannover 31.5.-4.6.1982Supported by the DFG     

Tight junctions in lung cancer and lung metastasis: a review

Tight junctions are structures located in the apicobasal region of the cell membranes. They regulate paracellular solute and electrical permeability of cell layers. Additionally, they influence cellular polarity, form a paracellular fence to molecules and pathogens and divide the cell membranes to apical and lateral compartments. Tight junctions adhere to the corresponding ones of neighbouring cells and by this way also mediate attachment of the cells to one other. Molecules forming the membranous part of tight junctions include occludin, claudins, tricellulin and junctional adhesion molecules. These molecules are attached to scaffolding proteins such as ZO-1, ZO-2 and ZO-3 through which signals are mediated to the cell interior. Expression of tight junction proteins, such as claudins, may be up- or downregulated in cancer and they are involved in EMT thus influencing tumor spread. Like in tumors of other sites, lung tumors show changes in the expression in tight junction proteins. In this review the significance of tight junctions and its proteins in lung cancer is discussed with a focus on the proteins forming the membranous part of these structures.     

Sequential changes in intercellular junctions between hepatocytes during the course of acute liver injury and restoration after thioacetamide treatment

Sequential changes of gap junctions (GJs), tight junctions (TJs) and desmosomes (DSs) between hepatocytes during restorative proliferation were studied in rats after a single intraperitoneal administration of 200 mg/kg thioacetamide (TAA). Antibody against connexin 32 was used to demonstrate GJs; simultaneously the changes in TJs and DSs were studied using antibodies against 7H6 protein and desmoplakins. Propidium iodide and bromodeoxyuridine were used to recognize necrotic and proliferative cells. GJs were evenly distributed in early necrotic hepatocytes at 16 h after TAA treatment, then disappeared from necrotic and surrounding cells at 24 h. At 48 h, GJs had disappeared completely from hepatocytes in whole liver lobules, while many hepatocytes were heavily labelled with BrdU. At 72 h, GJs reappeared, firstly in perinecrotic areas. At 96 h after treatment, when the injured areas had disappeared and restorative proliferation ceased, GJs were distributed evenly throughout the lobules. Immunohistochemical observation of GJs in centrilobular, perinecrotic and periportal areas after TAA-induced hepatic necrosis was confirmed by counting the number of connexin-32-positive spots in the respective areas. TJs and DSs disappeared from necrotic cells at 24 h, but then increased between 24 and 48 h in perinecrotic areas, though the increased intensity of these junctions was more evident at 48 h. At 72 h, localization of TJs and DSs returned to normal. These results suggest that during the course of acute hepatic injury, GJs (cell-cell communication) behave differently from other intercellular junctions.     

Claudin 4 identifies a wide spectrum of epithelial neoplasms and represents a very useful marker for carcinoma versus mesothelioma diagnosis in pleural and peritoneal biopsies and effusions

We evaluated the usefulness of the tight-junction associated protein Claudin 4 (CL-4) in the diagnosis of mesothelioma and mimickers, analyzing biopsies from 454 tumors, including 82 mesotheliomas, 336 carcinomas of different origin (278 primary, 58 metastatic to serosae), 36 nonepithelial spindle cell neoplasms, as well as 97 cytological samples from reactive effusions (12), mesothelioma (23) and metastatic carcinomas (62). CL-4 was consistently negative in normal and reactive mesothelium, as well as in all 82 mesotheliomas. In contrast, strong reactivity was found in 57/58 serosal metastasis, and in 245/278 primary carcinomas, with uppermost expression (150/153) in those most frequently involved in the differential with mesothelioma (lung, breast, gastrointestinal tract, pancreas, ovary, primary serous papillary carcinoma of peritoneum). On effusions, reactive and neoplastic mesothelial cells were regularly negative, while metastatic tumor cells stained positively in 60/62 (96.8%) cases. Among spindle cell neoplasms, only 2/9 biphasic synovial sarcomas and 4/4 follicular dendritic cell sarcomas stained positively. Results indicate that CL-4 reacts with the majority of epithelial neoplasms that often metastasize to serous membranes, representing a pancarcinoma marker with extremely high sensitivity and specificity. CL-4 may be considered a primary immunohistochemical reagent to rule out the diagnosis of mesothelioma.     

Alterations of the blood-brain barrier in cerebral white matter lesions in the ageing brain

White matter lesions (WML) are associated with dementia and are common in brain ageing. In order to determine whether alteration of the blood-brain barrier (BBB) may contribute to the pathogenesis of WML we assessed albumin leakage and expression of the tight junction (TJ) proteins claudin-5 (Cln-5), zona occludin-1 (ZO-1) and occludin in cases derived from the Medical Research Council Cognitive Function and Ageing Study. Albumin extravasation was widespread in the ageing brain and enhanced in WML, suggesting dysfunction of the BBB may contribute to the pathogenesis of WML. This was not accompanied by significant changes in the endothelial expression of TJ proteins. However, ZO-1 and occludin were expressed by glial cells throughout the parenchyma of both control white matter and WML, suggesting these TJ proteins may have other functions in the brain.     

Intercellular localization of occludins and ZO-1 as a solute transport barrier of the mesothelial monolayer

A hyperpermeable state has been observed in patients on long-term peritoneal dialysis. To understand the causes of the structural or functional changes and the progression of the fibrotic process, it is important to determine which region of the peritoneum exhibits these changes. The objectives of this study were to determine the solute permeability associated with cell–cell adhesion of human peritoneal mesothelial cells (HPMCs), to study the relationship between solute permeability and localizations of tight junction-associated proteins (TJPs: occludins and ZO-1), and to assess the effect of exogenous H₂O₂ supplementation. HPMCs were cultured on a Transwell until the transmesothelial electrical resistance (TER) reached a plateau. Solute permeation tests were conducted using fluorescein isothiocyanate – labeled dextran (molecular weight: 4, 10, 70, and 150 kDa) to calculate the solute permeability coefficient (SPC). Localization of TJPs was observed by a confocal laser scanning microscope after immunofluorescent staining. TER levels increased steadily, beginning at 97.5 ± 0.7 ohms·cm² and leveling off at 128 ± 3.6 ohms·cm² (n = 4). This was accompanied by the confluence of cells and the appearance of localized TJPs. SPC levels of the HPMC monolayer on the Transwell were reduced compared to those of the Transwell itself, indicating that the HPMC monolayer provided resistance against solute permeation. Exogenous H₂O₂ supplementation revealed an increased permeability accompanied with delocalization of TJPs, particularly occludins. The delocalization of occludins and ZO-1 at the intercellular space led to a decrease in intercellular binding capacity and thus triggered an increase in the solute permeability.     

紧密连接蛋白-1、闭锁蛋白、白细胞介素-18在急性重症心肌炎心脏粘膜中的表达

目的 观察急性重症心肌炎大鼠心脏粘膜紧密连接蛋白(ZO-1)、闭锁蛋白(occludin)及白细胞介素(IL)-18的表达变化,探讨急性重症心肌炎时心脏屏障功能损伤的机制.方法 选择SD大鼠60只,随机分为三组,分别为对照组、假手术组、心肌炎组,每组各20只.心肌炎组制作急性重症心肌炎模型,假手术组大鼠麻醉后手术进腹,仅翻动心脏组织.对照组不进行腹部手术.术后24h处死各组大鼠,取心脏组织.光镜下观察心脏组织病理学改变,免疫组化检测各组心脏粘膜ZO-1、Occludin、IL-18蛋白的表达,实时荧光定量PCR检测各组心脏粘膜ZO-1、Occludin、IL-18 mRNA的表达.结果 光镜下可见心肌炎组心脏黏膜绒毛上皮坏死脱落,血管充血扩张,大量中性粒细胞浸润.对照组、假手术组、心肌炎组ZO-1阳性率分别为85％、70％、15％,心肌炎组ZO-1阳性率低于对照组及假手术组(P＜0.05).对照组、假手术组、心肌炎组Occludin阳性率分别为75％、65％、20％,心肌炎组Occludin阳性率低于对照组及假手术组(P＜0.05).对照组、假手术组、心肌炎组IL-18阳性率分别为15％、15％、80％,心肌炎组IL-18阳性率高于对照组及假手术组(P＜0.05).心肌炎组ZO-1、Occludin mRNA表达水平均低于对照组及假手术组(P＜0.05);,IL-18高于对照组及假手术组(P＜0.05).结论 急性重症心肌炎时,紧密连接相关蛋白Z0-1、Occludin表达降低,IL-18表达增加,可能共同参与了急性心肌炎心脏粘膜屏障功能损伤的病理过程.     

槲皮素增强肠易激综合征模型大鼠肠屏障功能的实验研究

目的：探讨槲皮素（Que）改善肠易激综合征（IBS）模型大鼠结肠上皮屏障功能的机制。方法：选择出生后2d的新生SD乳大鼠100只,随机分为对照组20只和模型组80只。模型组采用新生期乳大鼠母源性分离（NMS）联合醋酸（AA）灌肠法制作IBS模型（NMS＋AA）。造模结束后4～5周,选择满足条件的雄性幼鼠作为研究对象。其中对照组随机选择8只（生理盐水,10ml／kg）;模型组在造模成功者中随机选分成4组,即盐水组（10ml／kg）、培菲康组（210mg／只,含活菌数0．1×10。CFU）、Que低剂量组（50mg／kg）和Que高剂量组（200mg／kg）,每组8只。各组均予相应药物灌胃处理,每天1次,连续2周。采用腹壁撤退反射（AWR）评分评估结肠敏感性,”Cr—EDTA检测全消化道通透性,HE染色法检测结肠粘膜炎症细胞浸润,ELISA法检测结肠细胞因子TNF-a水平,Westernblot法检测结肠上皮紧密连接蛋白（TJs）occludin和claudin-l的表达。结果：采用NMS＋AA法可制作IBS大鼠模型,造模成功率达86．3％。模型鼠内脏敏感性提高,结肠通透性增加,大量炎细胞浸润远端结肠粘膜固有层,TNF-a含量增加,claudin-1和occludin表达下降。Que在结、直肠扩张（CRD）一定压力范围内可降低模型鼠的内脏敏感性（AWR评分降低）（P〈0．05）;高剂量Que可降低模型鼠全消化道通透性（P〈0．05）,减少结肠粘膜炎细胞的浸润水平和TNF-a含量（尸〈0．05）,并上调结肠claudin-1和occludin的表达（P〈0．05）。结论：采用NMS＋AA法可成功制作内脏高敏感伴结肠通透性增加的IBS大鼠模型。Que可通过调节IBS模型大鼠细胞因子TNF-a的含量和紧密连接蛋白claudin-1、occludin的表达,减少结肠粘膜炎症,降低消化道通透性,进而增强肠屏障功能,并可改善IBS模型大鼠的痛觉过敏。     

Cellular junctions in normal and inflammatory human synovial membrane revealed by tannic acid and freeze fracture

Summary Cellular junctions between synovial cells and endothelial cells of the microvasculature were examined in 10 normal and 20 inflammatory human synovial membranes by means of tannic acid and freeze fracture, Gap junctions and desmosomes predominated on synovial cells, and tight junctions in the microvasculature.Comparison between normal and inflammatory synovial membranes did not demonstrate changes in cellular contacts that might be caused by inflammation.