Primary culture and transfection of epithelial cells of human small intestine

OBJECTIVE: To evaluate perioperative and long-term morbidity in patients undergoing selective evaluation of coronary artery disease prior to abdominal aortic aneurysm (AAA) repair. DESIGN: Case series. SETTING: University and Veterans' Administration medical centers. PATIENTS: One hundred eighty-nine consecutive patients undergoing AAA repair between January 1989 and September 1996 were selectively evaluated for coronary artery disease and assigned to 1 of 3 groups: group 1, no abnormal cardiac history, normal electrocardiogram; group 2, minimal symptoms, history of myocardial infarction (MI), older than 70 years, diabetes mellitus, or congestive heart failure; or group 3, severe or unstable angina, ventricular dysfunction. INTERVENTIONS: Group 1 patients proceeded to AAA repair without further workup. Group 2 patients underwent pharmacologic or exercise stress testing followed by coronary angiography and intervention as required. Group 3 patients went directly to coronary angiography and intervention as needed. MAIN OUTCOME MEASURES: Perioperative MI, arrhythmias, or death. Long-term follow-up measures included MI and death. RESULTS: Adequate documentation was available on 171 patients. Twenty-four patients (14%) were in group 1. Of 136 patients (79.5%) in group 2, coronary angiography was performed in 36 (26%), followed by percutaneous transluminal coronary angioplasty (PTCA) in 9 (7%) and coronary artery bypass (CAB) in 5 (4%). Of 11 patients in group 3, 3 (27%) each received PTCA and CAB. Remote CAB or PTCA had been performed in 32 (19%) and 12 (7%) patients, respectively. Two perioperative deaths (1.1%) occurred in the 189 patients, one due to MI in a group 2 patient. There were 2 (1%) nonfatal MIs, both in group 2 patients who had no preoperative intervention. Arrhythmias and/or congestive heart failure occurred in 17 (9%) cases, 7 (39%) having had recent coronary revascularization (P = .001). By univariate analysis, only preoperative renal dysfunction predicted perioperative complications (P = .03) Overall survival by lifetable analysis was 87.9% and 69.7% at 3 and 5 years, respectively. CONCLUSION: Coronary artery disease is common in patients undergoing AAA repair, with 35.7% having preoperative coronary revascularization at some point. Selective preoperative coronary artery disease screening achieves excellent perioperative and late results in this population.     

Interactions of soluble recombinant integrin alphav beta5 with human adenoviruses

alphav integrins have been identified as coreceptors for adenovirus (Ad) internalization; however, direct interactions of these molecules with Ad have not been demonstrated. We report here the expression of soluble integrin alphav beta5, which retains the ability to recognize the Ad penton base as well as vitronectin, an Arg Gly Asp (RGD)-containing extracellular matrix protein. Soluble integrin alphav beta5 reacted with seven different Ad serotypes (subgroups A to E) in solid-phase binding assays. The soluble integrin exhibited different levels of binding to each Ad serotype; however, binding to multiple Ad types required the presence of divalent metal cations and was inhibited by a synthetic RGD peptide, indicating that RGD and cation-binding sequences regulate Ad interactions with alphav beta5. Incubation of Ad particles with soluble alphav beta5 integrin also inhibited subsequent Ad internalization into epithelial cells as well as virus attachment to monocytic cells. These findings suggest that soluble alphav integrins or antagonists of these coreceptors could be used to limit infection by multiple Ad types. The generation of soluble alphav integrins should also permit further detailed kinetic and structural analysis of Ad interactions with its coreceptors.     

Isolation and long-term maintenance of differentiated adult chicken hepatocytes in primary culture

Adult chicken hepatocytes were obtained by an adaptation of the two step in situ collagenase perfusion. Usually 0.5 to 1 x 10(9) cells were obtained, with 75 to 95% viability. Hepatocytes attached within 2 h when plated on plastic cell culture dishes and spread in 4 h, surviving for several months in a specific serum-free medium. These cells retained a typical parenchymal cell morphology and the ability to produce a specific protein (albumin) throughout the culture period. We hereby provide a suitable model for studying hepatic metabolism in birds.     

Time-course effects of human recombinant luteinizing hormone on porcine Leydig cell specific differentiated functions

Polymerase chain reaction (PCR)-based assays were developed to detect virulent Rhodococcus equi in transtracheal aspirate samples from sick foals showing respiratory signs. An oligonucleotide primer pair from the sequence of the virulence-associated 15- to 17-kDa antigen gene of the virulence plasmid in virulent R. equi was used to amplify a 564 bp region by PCR, and the result was confirmed by Southern blot hybridization. No positive reaction was seen in DNA from 13 different microorganisms typically found in the respiratory tract. In tracheal aspirates seeded with virulent R. equi, a visible band could detect 10 to 10(2) bacteria per PCR assay (10(3) to 10(4)/ml of the aspirate). Virulent R. equi was demonstrated in 31 of 42 transtracheal aspirates by culture and colony blot analysis, whereas a positive PCR result was observed in only 12 of the 31 culture positive samples. To prevent false-negative results, two methods were developed: a nested PCR and a PCR in combination with enrichment cultures of aspirates in the selective medium to increase the number of bacteria to 10(4)/ml or more. All of the PCR-negative and culture-positive samples were positive by the two methods. These results indicated that PCR-based assays provide a specific and sensitive means to detect virulent R. equi in tracheal aspirates of foals, and they are more rapid than the routine culture procedures for the diagnosis of R. equi pneumonia in foals.     

Induction of a differentiated ciliated cell phenotype in primary cultures of Fallopian tube epithelium

Human Fallopian tubal epithelial cells in culture lose morphological features associated with the epithelium in situ and the extent to which they retain their in-vivo phenotype or function is unknown. In order to address this question, immunocytochemical markers were identified which distinguish secretory (HMFG2+, LhS28-) from ciliated (HMFG2-, LhS28+) epithelial cells in tissue sections of Fallopian tube. These markers were used to analyse the phenotype of tubal cells in vitro. Primary cultures of human tubal epithelial cells were seeded onto glass and grown to confluence before addition of oestradiol-17beta. In the absence of hormone, tubal epithelial cells expressed cytokeratins and nuclear receptors for oestrogen and progesterone and adopted a homogeneous (HMFG2+, LhS28-) secretory cell phenotype. Following the addition of oestradiol-17beta, a proportion of cells became positive for LhS28. The induction of a ciliated epithelial cell phenotype was confirmed by scanning electron microscopy, where on permeable collagen membranes, approximately one-third of tubal epithelial cells became ciliated in the presence of oestradiol-17beta. We suggest that in vitro, tubal epithelial cells adopt an immature secretory-like phenotype and that oestrogen can induce differentiation to a ciliated epithelial cell phenotype.     

Immortalization of differentiated human hepatocytes by a combination of a viral vector and collagen gel culture

Adult human and chimpanzee hepatocytes, which have no proliferative potential in vitro, were immortalized by introducing an oncogene encoding simian virus 40 large tumor(T) antigen by means of infection with a recombinant adenovirus vector. The frequency of immortalization was enhanced by a suspension method for virus adsorption and especially by using a collagen gel culture. The replicating hepatocyte colonies were isolated and selected by albumin secretion which is specific for parenchymal hepatocytes, then continuously subcultured. The immortalized hepatocyte lines also secreted other hepatocyte-specific proteins (complement C3, transferrin, fibrinogen). However, the amount of protein secretion declined with subculture. The subline RY5, cloned from a human immortalized line, showed relatively stable albumin secretion. Therefore, chromosomal studies and anchorage-independent growth properties were discussed and compared with its original line.     

Aggrecan and link protein affect cell adhesion to culture plates and to type II collagen

Cartilage is a hypocellular tissue in which a balance of matrix molecules, especially aggrecan and link protein, play a critical role in maintaining structural integrity. To study the role of aggrecan and link protein in mediating cell activities, we have stably expressed them in NIH/3T3 fibroblasts and observed the effect on cell-substratum interactions. Overexpression of either protein destabilized the cell-substratum interaction. However, when both were co-expressed, the interaction between cell and substratum was less impaired. Similar results were obtained on type II collagen-coated plates. The addition of exogenous gene products into fibroblast cell lines and chondrocyte culture had the same effect as expression of the genes. The addition of exogenous hyaluronan to the growth medium or treatment of cells with hyaluronidase also decreased cell adhesion, indicating that hyaluronan also plays a role in the cell-substratum adhesion. The presence of aggrecan seems to increase the amount of link protein on the cell surface. Chondrocytes expressing high concentrations of aggrecan and link protein were maintained within a matrix network and were able to survive in suspended culture. Imbalances in aggrecan or link protein concentrations, or degradation of hyaluronan, disrupted the network and caused the chondrocytes to aggregate or adhere to the plates.     

Synthesis and conformational properties of a recombinant C-propeptide of human type III procollagen

A cDNA was prepared that coded for the signal peptide of type III procollagen linked to the complete C-propeptide of the protein. The cDNA was then used to express the protein in a baculovirus recombinant system. Recombinant protein was recovered as a trimer from the medium of transfected cells in a yield of 1 to 2.5 mg per liter. Mapping of peptide fragments with and without reduction indicated that the protein contained the expected interchain disulfide bonds. Analysis by circular dichroism suggested that the conformation of the protein corresponded to the native conformation. Therefore, the protein should be appropriate for further tests of its biological function and analysis of structure by X-ray diffraction.     

A new tool for efficient transfection of dog and human thyrocytes in primary culture

Basic research for designing a microplate which can be applied to determination of 32P by radioluminography was carried out. It was proven that 32P can be determined by using the microplate which has plural planchets placed at intervals on a thin plate and a brass collimator that fills the gaps between the planchets. The microplate is joined with the collimator, and exposed to an imaging plate for 24 h. The detection limit of the proposed method was estimated to be 6 m Bq. The cross-talk ratio was negligibly small (0.2%).     

Effects of recombinant human granulocyte colony-stimulating factor administration on neutrophil phenotype and functions

BACKGROUND AND OBJECTIVE: Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is currently used for treatment of various types of neutropenia, treatment of aplastic anemia, mobilization of peripheral blood progenitor cells. However, rhG-CSF is not only a growth factor for the myeloid lineage, but it also acts as a modulator of neutrophil behavior. The aim of the present review article is to examine the following aspects of rhG-CSF therapy: 1) does rhG-CSF influence neutrophil functions, and in particular their microbicidal properties? 2) does rhG-CSF modify neutrophil phenotype? 3) If so, what are the mechanisms potentially involved? EVIDENCE AND INFORMATION SOURCES: The author of the present article has been working in the field of rhG-CSF effects on neutrophil function, contributing original papers in peer-reviewed journals. In addition, the present review critically examines articles and abstracts published in journals covered by the Science Citation Index and Medline. STATE OF ART AND PERSPECTIVES: Treatment with rhG-CSF causes enhancement of functions such as phagocytosis, superoxide anion generation, chemiluminescence, bacterial killing, and ADCC. Neutrophil phenotype changes after rhG-CSF administration: immediate effects cause direct activation of circulating neutrophils, but delayed effects are characterized by increased surface expression of important effector molecules directly involved in neutrophil functions, such as CD14, CD32, CD64. These effects may have useful clinical consequence in patients who show an increased risk of infections, such as cancer patients, subjects with hematologic diseases (myelodysplasia, aplastic anemia), congenital diseases characterized by neutropenia, and patients with AIDS. Other changes which characterize neutrophils after rhG-CSF administration are represented by significant impairment of CD16 expression, chemotaxis, and reduced in vivo migration of neutrophils to inflammatory sites. These effects may be explained by bone marrow modification due to rhG-CSF therapy. In fact, treatment with rhG-CSF causes a significant acceleration of transit time of cells belonging to the myeloid lineage, along with amplification of the mitotic pool and a relative decrease of elements of the post-mitotic pool. It is possible that, because of the accelerated bone marrow transit time of myeloid cells, rhG-CSF causes a relative immaturity of circulating neutrophils. It is known that both CD16 expression and chemotaxis properties are acquired by neutrophils in the late stages of maturation, but the time necessary to acquire full functional maturity seems to be shortened by rhG-CSF administration, and this kinetic aspect may play a non-negligible role in the modification of neutrophil behavior.     

Adverse effects of recombinant human insulin-like growth factor I in obese insulin-resistant type II diabetic patients

Data from studies in diabetic rodents and evidence from clinical situations of severe resistance to insulin suggest that insulin-like growth factor I (IGF-I) is able to at least partly overcome insulin resistance. To assess the efficacy of recombinant human IGF-I in subjects with the most common form of insulin resistance, e.g., obese, type II diabetic patients, we administered recombinant human IGF-I (rhIGF) in doses of 120 and 160 micrograms/kg twice daily for 4-52 days to seven such individuals who had been treated previously with high doses of insulin (> 0.7 U.kg-1 x day-1). Four patients exhibited comparable or enhanced, whereas three had diminished, blood glucose control on rhIGF-I relative to that while on twice daily NPH insulin during the six-week control period. The occurrence of adverse effects in all patients compelled us to discontinue rhIGF-I administration before completing the 8-week treatment period. These adverse effects included edema primarily on the face and hands, mild weight gain, occasional dyspnea, bilateral jaw tenderness, arthralgias and myalgias, fatigue, tachycardia, flushing, orthostatic hypotension, and local burning at the injection site. We conclude that the frequency and severity of side effects associated with administering high-dose subcutaneous rhIGF-I to obese insulin-resistant diabetic patients make it an unacceptable therapeutic agent for these patients despite its ability to produce reasonable blood glucose control in approximately 50% of them.     

Postnatal development of type I and type II hair cells in the mouse utricle: acquisition of voltage-gated conductances and differentiated morphology

The type I and type II hair cells of mature amniote vestibular organs have been classified according to their afferent nerve terminals: calyx and bouton, respectively. Mature type I and type II cells also have different complements of voltage-gated channels. Type I cells alone express a delayed rectifier, gK,L, that is activated at resting potential. We report that in mouse utricles this electrophysiological differentiation occurs during the first postnatal week. Whole-cell currents were recorded from hair cells in denervated organotypic cultures and in acutely excised epithelia. From postnatal day 1 (P1) to P3, most hair cells expressed a delayed rectifier that activated positive to resting potential and a fast inward rectifier, gK1. Between P4 and P8, many cells acquired the type I-specific conductance gK,L and/or a slow inward rectifier, gh. By P8, the percentages of cells expressing gK,L and gh were at mature levels. To investigate whether the electrophysiological differentiation correlated with morphological changes, we fixed utricles at different times between P0 and P28. Ultrastructural criteria were developed to classify cells when calyces were not present, as in cultures and neonatal organs. The morphological and electrophysiological differentiation followed different time courses, converging by P28. At P0, when no hair cells expressed gK,L, 33% were classified as type I by ultrastructural criteria. By P28, approximately 60% of hair cells in acute preparations received calyx terminals and expressed gK,L. Data from the denervated cultures showed that neither electrophysiological nor morphological differentiation depended on ongoing innervation.     

Isolation and primary culture of murine alveolar type II cells

OBJECTIVES: The biotransformation of caffeine has been studied in vitro using human cytochrome P-450 isoenzymes (CYPs) expressed in human B-lymphoblastoid cell lines, namely CYP1A1, 1A2, 2A6, 2B6, 2D6-Val, 2E1 and 3A4, and microsomal epoxide hydroxylase (EH). In addition, CYP2D6-Met was also studied, in which a valine in the wild type (CYP2D6-Val) has been replaced by a methionine due to a G to A mutation in position 112. RESULTS: At caffeine 3 mmol center dot l-1, five CYPs (1A1, 1A2, 2D6-Met, 2E1 and 3A4) catalysed the biotransformation of caffeine. Among the enzymes studied, CYP1A2, which predominantly catalysed paraxanthine formation, had the highest intrinsic clearance (160 l center dot h-1 center dot mmol-1 CYP). Together with its high abundance in liver, it should be considered, therefore, to be the most important isoenzyme in caffeine metabolism. The affinity of caffeine for CYP1A1 was comparable to that of its homologue 1A2. CYP2D6-Met, which catalysed caffeine metabolism by demethylation and 8-hydroxylation, also had a relatively high intrinsic clearance (3.0 l center dot h-1 mmol-1 CYP), in particular for theophylline and paraxanthine formation, with kM values between 9-16 mmol center dot l-1. In contrast, the wild type, CYP2D6-Val, had no detectable activity. In comparison, CYP2E1 played a less important role in in vitro caffeine metabolism. CYP3A4 predominantly catalysed 8-hydroxylation with a kM value of 46 mmol center dot l-1 and an intrinsic clearance of 0.60 l center dot h-1 center dot mmol-1 CYP. Due to its high abundance in human liver, the latter CYP may contribute significantly to the in vivo formation of TMU. CONCLUSION: The findings of this study indicate that i) microsomes from transfected human B-lymphoblastoid cell lines give results close to those obtained with microsomes isolated from human liver, ii) at least four CYP isoforms are involved in caffeine metabolism, iii) at a substrate concentration <0.1 mmol center dot l-1, CYP1A2 and 1A1 are the most important isoenzymes, iv) at higher concentrations the participation of other isoenzymes, in particular CYP3A4, 2E1 and possibly also CYP2D6-Met, are important in caffeine metabolism, and v) the nucleotide composition at position 1120 of CYP2D6 determines the activity of this isoenzyme in caffeine metabolism.     

Characterization of recombinant type II collagen: arthritogenicity and tolerogenicity in DBA/1 mice

Using new nonisotopic and isotopic methods, we showed previously that fatty acid synthesis was markedly stimulated in weight-stable normal volunteers by a very-low-fat formula diet with 10% of energy as fat and 75% as short glucose polymers. In this study, we determined whether fatty acid synthesis was equally stimulated by a very-low-fat solid diet made with foods consumed typically. Four normal volunteers consumed the same very-low-fat formula diet for 25 d and then an isoenergetic solid food diet with 10% of energy as fat and 75% as starch, simple sugars, and fiber for 25 d. To measure fatty acid synthesis, the fatty acid compositions of the diets were matched to the composition of each subject's adipose tissue and compared with the composition of VLDL-triacylglycerol. In all subjects, the large increases in newly formed palmitate and decreases in linoleate in VLDL-triacylglycerol were quickly reversed by the solid food diet, and the fraction of de novo synthesized fatty acids in fasting VLDL-triacylglycerol decreased from 30-54% to 0-1%. In a second group of subjects, the stimulation of fatty acid synthesis by the formula diet with 75% glucose polymers was similarly reduced by a formula diet with amounts of fat, starch, and sugar chosen to mimic those of the solid food diet, but persisted after the addition of fiber or a diet with 75% sugar. In conclusion, an increase in fatty acid synthesis and palmitaterich, linoleate-poor VLDL-triacylglycerol induced by very-low-fat, high-sugar diets may be reduced by the substitution of dietary starch for sugar with potentially beneficial effects on cardiovascular health.     

Sustained nontumorigenic phenotype correlates with a largely stable chromosome content during long-term culture of the human keratinocyte line HaCaT

A temperature-dependent metastatic phenotype reported for a frog cell line, PNKT-4B, provided a means for studying potential mediators of cell-matrix interaction involved in metastatic invasion. Zymography revealed that these cells secreted enzyme species with properties and characteristics of mammalian metalloproteinases: collagenase, stromelysin, gelatinase A, and gelatinase B. These enzymes were produced by PNKT-4B cultures maintained at both invasive-permissive (28 degrees C), and invasion-restrictive (20 degrees C) temperatures. However, under the invasive-permissive culture condition cells produced more of the putative gelatinase B and A enzymes. In addition, an activated form of gelatinase A was produced only in invasion-permissive cultures. DNA synthesis bioassays (Mv1Lu cell line and mouse thymocytes) to detect growth promoting and/or inhibitory cytokines, revealed that PNKT-4B cultures kept at 28 degrees C released significantly higher levels of stimulatory (interleukin-1-like) and latent inhibitory (transforming growth factor-beta-like) substances into the medium compared to 20 degrees C cultures. Pre-absorption of media samples with heparin-sepharose indicated a second stimulatory cytokine as well. A corneal fibroblast bioassay that tests for mediators of collagenase synthesis, detected a stimulatory substance whose activity was greatly reduced in the presence of interleukin-1 receptor antagonist protein. Collagenase stimulatory activity present in 28 degrees C culture medium was significantly higher than equal samples from 20 degrees C cultures. These studies provide a molecular correlation between release of cytokines with properties of the metastatic phenotype seen in vivo. They further provide some of the first characterizations of frog MMPs and cytokines, which are likely to be involved in other tissue remodeling events.     

Repressor titration: a novel system for selection and stable maintenance of recombinant plasmids

The propagation of recombinant plasmids in bacterial hosts, particularly in Escherichia coli, is essential for the amplification and manipulation of cloned DNA and the production of recombinant proteins. The isolation of bacterial transformants and subsequent stable plasmid maintenance have traditionally been accomplished using plasmid-borne selectable marker genes. Here we describe a novel system that employs plasmid-mediated repressor titration to activate a chromosomal selectable marker, removing the requirement for a plasmid-borne marker gene. A modified E.coli host strain containing a conditionally essential chromosomal gene (kan) under the control of the lac operator/promoter, lac O/P, has been constructed. In the absence of an inducer (allolactose or IPTG) this strain, DH1 lackan , cannot grow on kanamycin-containing media due to the repression of kan expression by LacI protein binding to lac O/P. Transformation with a high copy-number plasmid containing the lac operator, lac O, effectively induces kan expression by titrating LacI from the operator. This strain thus allows the selection of plasmids without antibiotic resistance genes (they need only contain lac O and an origin of replication) which have clear advantages for use as gene therapy vectors. Regulation in the same way of an essential, endogenous bacterial gene will allow the production of recombinant therapeutics devoid of residual antibiotic contamination.     

Primary infection by type 1 human immunodeficiency virus: diagnosis and prognosis

Primary infection by type 1 human immunodeficiency virus (HIV) is symptomatic in about 70% of cases. The acute illness is a mononucleosis-like syndrome with characteristics such as mucosal ulcerations. The duration and severity of the symptoms appear to be related to the prognosis. After reviewing the most frequent signs and symptoms of primary HIV infection, we report different prognostic studies which examined the association between the acute illness and the progression of HIV disease.     

Upregulation of dynamin II expression during the acquisition of a mature pancreatic acinar cell phenotype

Members of the dynamin superfamily are GTPases which have been shown to support receptor-mediated endocytosis in vivo and bind to growth factor receptor-associated proteins in vitro. In acinar cells of the pancreas, receptor-mediated endocytosis is very important for the recycling of membranes after secretory granule release. Therefore, characterization of the molecular machinery responsible for this process is critical for a better understanding of this phenomenon. In this study we sought to determine the expression pattern of the endocytic GTPase dynamin II during pancreatic acinar cell differentiation in developing rat embryos and in dexamethasone-treated AR42J cells using Western blot, Northern blot, and immunocytochemical analyses. During pancreatic development, dynamin immunoreactivity is almost undetectable until day E17 but undergoes significant upregulation in acinar cells starting at E18. In addition, the levels of dynamin mRNA and protein in AR42J cells increase approximately threefold during dexamethasone-induced acinar differentiation. The increase in dynamin levels that occurs in both embryonic pancreatic cells and dexamethasone-treated AR42J cells correlates with the establishment of a more differentiated acinar phenotype. Therefore, these results suggest a potential role for dynamin in supporting receptor-mediated endocytosis in mature pancreatic acinar cells.     

Cell surface phenotype and ultramicroscopic analysis of purified human enterocytes: a possible antigen-presenting cell in the intestine

Epithelial cells of the intestine seem to act as antigen-presenting cells to surrounding lymphoid tissue and may be crucial to maintain the pool of peripheral T lymphocytes. The scope of this study was to carry out an immunophenotypic and ultramicroscopic analysis of purified human enterocytes to elucidate their role as antigen-presenting cells, in the immune responses in the gut-associated lymphoid tissue. A method has been developed to obtain purified and viable human enterocyte populations, later labeled with relevant monoclonal antibodies directed to leukocyte antigens and subjected to cytofluorometric analysis. Phenotypic analysis revealed the presence of markers common to "classical" antigen-presenting cells (CD14, CD35, CD39, CD43, CD63 and CD64), reinforcing the idea that enterocytes may act as such. Moreover, several integrins (CD11b, CD11c, CD18, CD41a, CD61 and CD29) were also found. CD25 (IL-2 receptor alpha chain) and CD28, characteristic of T cells, were detected on the surface of these cells; this latter finding rises the possibility that enterocytes could be activated by IL-2 and/or via CD28 through binding to its ligands CD80 or CD86. Finally, the presence of CD21, CD32, CD35 and CD64 that may bind immune complexes via Fc or C3, suggests their participation in the metabolism of immune complexes. Furthermore, the finding of a Birbeck's-like granule in the cytoplasm of the cells, shows that enterocytes contain an ultramicroscopic feature previously thought to be characteristic of Langerhans' cells, an antigen-presenting cell. The phenotype detected on the surface of enterocytes, along with their ultramicroscopic characteristics, suggests that they may play an important role in the immune responses elicited in the gut, presenting antigens to surrounding lymphoid cells, and establishing cognate interactions with them.