Extracellular pH affects the proliferation of cultured human T cells and their expression of the interleukin-2 receptor

Ex vivo expansion of T cells is an important aspect of many cellular immunotherapy protocols, and the effects of the culture environment on the cells must be understood to produce large numbers of functional cells. Extracellular pH is a fundamental parameter that has many different effects on cultured cells. In this study, peripheral blood mononuclear cells were stimulated with phytohemagglutinin and cultured at pH values of 7.0, 7.2, or 7.4. The effects of pH on the cells were studied during the 2 to 3 weeks of proliferation resulting from phytohemagglutinin stimulation, in order to examine the culture kinetics over realistic time scales for ex vivo expansion. The proliferation capacity of the T cells increased more than three-fold for the pH 7.0 and 7.2 cultures compared with the pH 7.4 cultures. The culture pH also affected the kinetics of the interleukin-2 receptor down-regulation process. The faster receptor down-regulation in both the pH 7.2 and 7.4 cultures resulted in a more than twofold greater fraction of interleukin-2 receptor(+) cells in the pH 7.0 cultures. Although the fraction of apoptotic cells (using the Annexin V flow-cytometric method) remained less than 10%, we observed 27% more apoptosis in the pH 7.4 cultures than in the 7.2 cultures and 49% more apoptosis in the pH 7.4 cultures than in the 7.0 cultures. These effects on interleukin-2 receptor expression and cellular apoptosis may partially explain the observed effects of pH on T-cell proliferation.     

Barrett's esophagus in children

Barrett's esophagus (BE) is a condition of esophageal dysplasia in which the tubular esophagus is lined with columnar instead of squamous mucosa--not with just any type of columnar mucosa, but with a specialized type with goblet cells. It is considered to be an acquired phenomenon secondary to acid exposure from gastro-esophageal reflux (GER). This report shows a review of BE of children and our data about BE from the study of 19 handicapped children with GER. 3 had intestinal dysplasia with goblet cells (BE). The % time of pH under 4 on 24-hour pH monitoring was significantly lower in the patients with esophagitis including BE than in them with normal esophagus. BE of our study seemed to be reversible after the surgery and anti-acid therapy. It is suggested that BE is not a rare condition even in children and biopsy specimens should be taken to establish the diagnosis.     

Bimodal effects of platelet-derived growth factor on rat mesangial cell proliferation and death, and the role of lysophosphatidic acid in cell survival.

Although mesangial cell death has been shown to be correlated with mesangial cell mitosis in vivo, little is known about how these two apparently opposite events are regulated. We show that the addition of platelet-derived growth factor (PDGF; 10-50 ng/ml) to primary cultured rat mesangial cells for 24 h caused continuous proliferation along with simultaneous cell death. This process was accompanied by the fragmentation of DNA into nucleosomal oligomers, the development of apoptotic morphological changes in the nucleus, and increased expression of p53. Accumulation of lactate dehydrogenase (LDH) was also observed in the culture medium, suggesting that both apoptosis and necrosis are involved in the cell death mechanisms observed. We also observed that addition of 30 microM lysophosphatidic acid (LPA) to the culture medium greatly suppressed PDGF-induced cell death, leading to synergistically enhanced mesangial cell proliferation. DNA fragmentation, p53 expression and LDH release were all suppressed by LPA. We suggest that PDGF is a bifunctional molecule in mesangial cells that evokes both cell proliferation and cell death simultaneously, whereas LPA is a survival factor. We speculate that PDGF and LPA may play important roles in the progression or exacerbation of proliferative glomerulonephritis.     

Esophageal epithelial response to gastroesophageal reflux. A quantitative study.

Exposure of the distal esophageal mucosa to acid gastric juice was quantitated by 24-hr pH monitoring in 100 individuals and was correlated with morphologic data derived from esophageal biopsies. The degree of acid exposure to the distal esophagus correlated directly with increases in both relative and absolute length of the subepithelial papillae and to relative basal zone hyperplasia. Both papillary length and basal zone hyperplasia decreased after antireflux surgery had reduced acid exposure to normal. Reflux in the recumbent position resulted in prolonged exposure of the mucosa to acid because of poor acid clearing from the esophagus. This caused longer papillae than did upright reflux, where there were more frequent reflux episodes, but with rapid acid clearance. The presence of a hiatal hernia was associated with longer papillae, lower DES pressure, increased reflux frequency, and prolonged recumbent acid clearance. Twenty-four hour pH monitoring correlated better with papillary length than did symptoms or other clinical measures of gastroesophageal reflux.     

人骨髓间充质干细胞与脐血CD34+细胞体外扩增

为了研究骨髓间充质干细胞(MSC)及细胞因子对脐血CD34 造血祖细胞体外扩增的作用,及其扩增作用 对细胞黏附分子的影响,用免疫磁珠富集脐血CD34 细胞,然后接种到含有或不含有MSC和细胞因子的24孔培 养板,体外培养1周,观察不同指标并进行组间比较。结果表明:①SDF-1α SCF TPO FL因子组合与SCF TPO FL因子组合对脐血CD34 细胞的扩增作用无显著性差异(无论有无MSC细胞层存在)(P>0.05);②MSC 与上述细胞因子共存的培养体系优于相应的单纯细胞因子培养体系(P<0.05);③扩增前与扩增后脐血造血祖 细胞黏附分子CD44的表达没有明显变化。结论:趋化因子SDF-1α对SCF TPO FL因子组合的扩增作用无显 著影响;MSC增加细胞因子的脐血细胞体外扩增的作用;体外扩增不影响跻血细胞黏附分子CD44的表达。     

Fibronectin and alpha5 integrin regulate keratinocyte cell cycling. A mechanism for increased fibronectin potentiation of T cell lymphokine-driven keratinocyte hyperproliferation in psoriasis.

In addition to being T lymphocyte-driven, psoriasis may be due in part to abnormal integrin expression. Normal-appearing (uninvolved) skin from psoriatic patients was examined to determine whether altered fibronectin or its receptor expression is detectable before development of psoriatic lesions. In contrast to skin from normal subjects, we detect by immunofluorescence the abnormal presence of plasma fibronectin in the basal cell layer of the epidermis of psoriatic uninvolved skin. Furthermore, increased fibronectin exposure superinduces the in vitro cell cycle induction and expansion of psoriatic nonlesional keratinocytes in response to a cocktail of T cell lymphokines. Fibronectin alone also appeared to increase cell cycle entry among uninvolved but not normal keratinocytes. Concordantly, the alpha5 integrin fibronectin receptor, but not alpha2 or alpha3, is overexpressed in the in vivo nonlesional psoriatic epidermis. The involvement of alpha5beta1 in the early outgrowth of clonogenic keratinocytes in the ex vivo culture was demonstrated by the ability of anti-alpha5 mAb to inhibit keratinocyte growth on fibronectin. Thus, the fibronectin receptor appears to be one of the components required for the development of the hyperresponsiveness of psoriatic keratinocytes to signals for proliferation provided by lymphokines produced by intralesional T lymphocytes in psoriasis.     

Continuous proliferation of murine antigen-specific helper T lymphocytes in culture.

Murine helper T cells activated to sheep or horse erythrocyte antigens in vivo have been established as continuous cell lines in culture. T cells require the presence of a T-cell growth factor (TCGF) for continuous proliferation. TCGF purified from murine, rat, or human sources all stimulate murine T-cell growth. The T-cell mitogens concanavalin A and phytohemagglutinin do not stimulate cell proliferation in continuous T-cell lines. All cells that grow in the presence of TCGF express Thy-1 antigens. Helper activity of T-cell lines is both antigen specific and effective for syngeneic or F1 B cells. Supernates from T-cell lines do not contain antigen-specific or nonspecific helper factors. Although several T-cell lines have shown stable helper activity for greater than 50 wk in culture, other cell lines have shown a gradual decline in effector function. The procedure used to establish and maintain proliferation of T cells in culture should be suitable for the selection and growth of antigen-specific effector T cells from each subclass.     

幽门螺杆菌感染与反流性食管炎及Barrett食管的相关性

目的 探讨幽门螺杆菌的根除与反流性食管炎(RE)及Barrett食管(BE)的相关性及临床意义.方法 262例患者(RE177例、BE 85例)分为无幽门螺杆菌感染组139例(A组),有幽门螺杆菌感染组123例(B组);B组又随机分成2个亚组,B1组62例,B2组61例.A组及B1组给予洛赛克20 mg/次,2次/d,多潘立酮10 mg/次,3次/d,果胶铋100 mg/次,3次/d,疗程为8周;B2组在A组、B1组治疗方法的基础上加用阿莫西林500 mg/次,2次/d,克拉霉素500 mg/次,2次/d或替硝唑500 mg/次,2;A/d,其中三种抗生素选两种,应用2周.治疗前及治疗后行内镜、病理及24 h食管pH及胆红素监测检查.结果 治疗后3组患者症状改善总有效率均达95.0%以上[分别为A组97.8%(136/139)、B1组96.8%(60/62)、B2组98.4%(60/61)],与治疗前比较差异有统计学意义(P<0.05),但3组间比较,差异无统计学意义(P>0.05);内镜下3组反流性食管炎患者总有效率分别为92.9%(78/84)、91.8%(45/49)、88.6%(39/44),差异有统计学意义(P<0.05),Barrett食管患者未见明显效果,有效率约35.0%,与治疗前比较差异无统计学意义(P均>0.05);3组患者24 h食管pH及胆红素监测与治疗前比较均有显著改善(P<0.05),但3组间比较无明显差异(P>0.05).结论 幽门螺旋杆菌感染的RE及BE患者,可进行抗HP治疗但须同时进行抑制胃酸减少胃液,促进胃排空及保护食道黏膜的系统治疗,短期内可有效预防RE及BE的进展,长期效果还有待长期、大量的临床病例观察.     

Release of interleukin 1 inhibitory activity (contra-IL-1) by human monocyte-derived macrophages infected with human immunodeficiency virus in vitro and in vivo.

Infection of monocyte-macrophages with human immunodeficiency virus may be central to the pathogenesis of the acquired immunodeficiency syndrome. The ability of infected macrophages to prime T cells through IL-1 production was investigated in vitro. Purified human monocytes maintained in suspension culture were infected with strain HIV-DV. Intracellular expression of virus p24 antigen increased from undetectable levels immediately after infection to 13-59% of cells by 10-14 d; infected macrophages remained viable for up to 60 d. Supernatants collected between 14 and 20 d after infection were examined in the murine thymocyte co-mitogenesis assay and demonstrated to contain a potent IL-1 inhibitor, designated contra-IL-1. Contra-IL-1 activity was present in all supernatants examined after 4 d of infection, and peaked coincident with peak p24 antigen expression. Inhibitory activity was not present in uninfected cells. Contra-IL-1 activity eluted after gel filtration with an approximate molecular weight of 9 kD. Inhibitory activity was removed by exposure to heat or acid pH, or by incubation with chymotrypsin or staphylococcal V8 protease. Contra-IL-1 did not inhibit IL-2- or IL-4-dependent proliferation of murine T cell lines. Despite its ability to inhibit IL-1 activity, contra-IL-1 did not interfere with the binding of recombinant IL-1 beta to a fibroblast cell line. Contra-IL-1 inhibited the proliferation of normal peripheral blood mononuclear cells to both concanavalin A and tetanus toxoid; inhibition could be attenuated by the addition of exogenous IL-1. Messenger RNA extracted from infected macrophages was examined by Northern analysis for the presence of message to IL-1 beta. No message was apparent, suggesting that the presence of contra-IL-1 was not obscuring the concomitant release of IL-1. Infected macrophages stimulated with endotoxin generated readily detectable message for IL-1 beta. Spleen macrophages purified from two patients with AIDS complicated by immune thrombocytopenia spontaneously expressed p24 antigen in vitro and released contra-IL-1 activity into the media. Contra-IL-1 may contribute to the immune dysfunction of AIDS.     

54例Barrett食管临床研究

目的 分析Barrett食管（barrecc esophagus，BE）患者的临床特点，尤其是胃镜下表现度食管动力改变，以提高BE的诊断率，以期早期治疗。方法 回顾分析54例BE患者的临床资料。结果 22例行食管动力检查提示LESP厦屏障压（LESP-GS）明显降低，酸反流总时间、酸反流总次数以度食管下段pH〈4时间百分比均明显增加。系统治疗后，41例患者在该院行胃镜复诊，21例（51．22％）仍为BE，19例（46．34％）患者恢复正常食管上皮，1例（2．44％）进展为食管腺癌。结论 BE是胃食管反流痛（gastroesophageal reflux disease，GERD）严重的并发症；内镜下治疗联合抑酸治疗为BE治疗提供新的方法。     

Gastroesophageal reflux disease: presentation and assessment of a common, challenging disorder

Although gastroesophageal reflux disease (GERD) is frequently referred to as a continuous spectrum, it is more useful to consider GERD as 2 discrete entities with several subsets that differ in pathophysiology, clinical presentation, natural history, and therapy. One entity is classic severe acid reflux with erosive esophagitis and its complications. Barrett's esophagus is an important subset of this group, with markedly increased acid exposure and an increased risk of adenocarcinoma. The second entity is nonerosive reflux disease (NERD) with minimal or no esophagitis. Patients with NERD do not develop local mucosa complications, like stricture or Barrett's esophagus, but their symptom severity can equal that of erosive esophagitis. Acid is involved in the symptoms of many but not all NERD patients. This acid dependence is evident either as an increase in esophageal acid reflux or a hypersensitivity to acid, and both generally respond well to proton pump inhibitor (PPI) therapy. NERD patients who are not acid-dependent have what is called functional heartburn; GERD-like symptoms are present, but there is no obvious involvement of refluxed acid. An important subset of GERD is refractory GERD, which consists of patients who fail aggressive PPI therapy. Parallel findings with other refractory syndromes can be anticipated; however, there are indications that psychosocial factors play a major role in refractory GERD, and these patients may benefit more from an integrated biopsychosocial approach. Diagnosis of GERD is usually made on clinical grounds, often supplemented by a therapeutic trial with antisecretory agents. Endoscopy is reserved for patients with alarm symptoms, such as dysphagia, anemia, or weight loss, or to detect Barrett's esophagus. Endoscopy is not useful to exclude the diagnosis of GERD because it will be negative in 70% of cases in primary care. Ambulatory 24-hour esophageal pH monitoring is necessary only when the diagnosis is in doubt, the patient fails medical management, or surgery is contemplated.     

P物质在BARRETT食管黏膜组织中的表达

目的研究P物质在BARRETT食管（BE）黏膜组织中的表达,探讨其在BE发病中的作用。方法应用免疫组织化学方法测定P物质在正常对照组（n=25）及BE组（n=58）中的表达,并比较P物质在不同化生程度、伴或不伴胆汁反流BE组中表达的差异。结果 P物质在BE中的表达低于对照组,且胃化生（＋）BE组P物质表达高于肠化生（＋）BE组,差异均有显著性（t=9.98、3.25,P〈0.05）;伴胆汁反流BE组P物质表达明显低于不伴胆汁反流BE组（t=3.04,P〈0.05）,而伴胆汁反流BE组肠化生阳性率高于不伴胆汁反流BE组,差异有显著性（χ2=4.99,P〈0.05）。结论 BE组存在P物质分泌失调,其可能在BE的发生发展中起着一定作用;胆汁反流可能影响BE黏膜P物质的分泌,而与肠化生的发生可能有关。     

Epidermal growth factor improves lentivirus vector gene transfer into primary mouse hepatocytes

Partial resistance of primary mouse hepatocytes to lentiviral (LV) vector transduction poses a challenge for ex vivo gene therapy protocols in models of monogenetic liver disease. We thus sought to optimize ex vivo LV gene transfer while preserving the hepatocyte integrity for subsequent transplantation into recipient animals. We found that culture media supplemented with epidermal growth factor (EGF) and, to a lesser extent, hepatocyte growth factor (HGF) markedly improved transduction efficacy at various multiplicities of infection. Up to 87% of primary hepatocytes were transduced in the presence of 10 ng EGF, compared with ~30% in standard culture medium (SCMs). The increased number of transgene-expressing cells correlated with increased nuclear import and more integrated pro-viral copies per cell. Higher LV transduction efficacy was not associated with proliferation, as transduction capacity of gammaretroviral vectors remained low (<1%). Finally, we developed an LV transduction protocol for short-term (maximum 24 h) adherent hepatocyte cultures. LV-transduced hepatocytes showed liver repopulation capacities similar to freshly isolated hepatocytes in alb-uPA mouse recipients. Our findings highlight the importance of EGF for efficient LV transduction of primary hepatocytes in culture and should facilitate studies of LV gene transfer in mouse models of monogenetic liver disease.     

Gastroesophageal reflux disease and Barrett's esophagus

Gastroesophageal reflux disease (GERD) is a common clinical problem. Circumstantial evidence continues to suggest that infection with Helicobacter pylori may protect some patients from developing GERD and its complications. An empirical trial of a proton-pump inhibitor may now be a reasonable alternative to endoscopy or 24-hour pH testing for the diagnosis of GERD. Long-term follow-up data covering more than over a decade indicate that proton-pump inhibitors are effective and safe agents for the treatment of GERD. Furthermore, a strategy of proton-pump inhibitors first may be the most cost-effective approach to GERD. It remains unclear why some patients with GERD develop Barrett's esophagus, whereas others do not. Recent studies demonstrate the importance of pulses of acid or bile in increasing cell proliferation and cyclooxygenase-2 expression in Barrett's epithelium cell cultures. Short-segment Barrett's esophagus is now clearly associated with an increased risk of dysplasia or cancer compared to intestinal metaplasia of the cardia, and the cancer risk in this condition is similar to that with long-segment Barrett's esophagus. However, the overall cancer risk in patients with Barrett's esophagus is lower than previously estimated, at approximately 0.5% annually. Ablation techniques continue to show promise, but are not yet ready for routine clinical use. Endoscopic mucosal resection is a new treatment option for selected patients with high-grade dysplasia or superficial esophageal adenocarcinoma.     

Butyric acid prodrugs are histone deacetylase inhibitors that show antineoplastic activity and radiosensitizing capacity in the treatment of malignant gliomas

Histone modification has emerged as a promising approach to cancer therapy. We explored the efficacy of a novel class of histone deacetylase inhibitors in the treatment of malignant gliomas. Treatment of glioma cell lines with two butyric acid derivatives, pivaloylomethyl butyrate (AN-9) and butyroyloxymethyl butyrate (AN-1), induced hyperacetylation, increased p21(Cip1) expression, inhibited proliferation, and enhanced apoptosis. Histone deacetylase inhibitor-induced apoptosis was mediated primarily by caspase-8. Treatment of cells with AN-1 or AN-9 for 24 hours before exposure to gamma-irradiation potentiated further caspase-8 activity and resultant apoptosis. Clonogenic survival curves revealed marked reductions in cell renewal capacity of U251 MG cells exposed to combinations of AN-1 and radiation. Preliminary in vivo experiments using human glioma cell lines grown as xenografts in mouse flanks suggest in vivo efficacy of AN-9. The data suggest that novel butyric acid prodrugs provide a promising treatment strategy for malignant gliomas as single agents and in combination with radiation therapy.     

长期培养对基质细胞衍生因子1/CXCR4介导间充质干细胞迁移的影响

背景:人外源性的间充质干细胞能特异性地向损伤部位迁移,参与多种组织的损伤修复,然而其定向迁移的机制尚不清楚.目的:观察基质细胞衍生因子1对骨髓间充质干细胞定向迁移的影响.方法:体外培养不同个体的骨髓间充质干细胞,培养至第10代,检测细胞衰老状态.RT-PCR和细胞免疫荧光检测骨髓间充质干细胞CXCR4受体表达情况;体外迁移体系(Transwell)检测基质细胞衍生因子1对骨髓间充质干细胞迁移的影响.结果与结论:骨髓间充质干细胞在体外长期增殖后生长逐渐缓慢,在第6,7代衰老细胞增多,其CXCR4受体表达减少.基质细胞衍生因子1对骨髓间充质干细胞的趋化作用呈剂量依赖性.     

长期培养对基质细胞衍生因子1/CXCR4介导间充质干细胞迁移的影响

背景：人外源性的间充质干细胞能特异性地向损伤部位迁移,参与多种组织的损伤修复,然而其定向迁移的机制尚不清楚。目的：观察基质细胞衍生因子1对骨髓间充质干细胞定向迁移的影响。方法：体外培养不同个体的骨髓间充质干细胞,培养至第10代,检测细胞衰老状态。RT-PCR和细胞免疫荧光检测骨髓间充质干细胞CXCR4受体表达情况;体外迁移体系（Transwell）检测基质细胞衍生因子1对骨髓间充质干细胞迁移的影响。结果与结论：骨髓间充质干细胞在体外长期增殖后生长逐渐缓慢,在第6,7代衰老细胞增多,其CXCR4受体表达减少。基质细胞衍生因子1对骨髓间充质干细胞的趋化作用呈剂量依赖性。     

Icodextrin effluent leads to a greater proliferation than glucose effluent of human mesothelial cells studied ex vivo.

OBJECTIVE: To compare the effect of glucose (Glu) and icodextrin (Ico) dialysate on in vitro culture of mesothelial cells (MC) from peritoneal dialysis (PD) patients. DESIGN: Prospective, controlled comparative study on the effects of two PD solutions. SETTING: A tertiary-care public university hospital. PATIENTS: Sixteen PD patients regularly using Glu dialysate were asked to collect an 8-hour dwell peritoneal effluent on 2 different days, with an interval shorter than 7 days. In the first collection, 2.27% Glu solution and in the last, 7.5% Ico solution was infused. Human MC were isolated from the nocturnal peritoneal effluent bags and grown ex vivo. MAIN OUTCOME MEASURES: Mesothelial cell proliferative capacity ex vivo. RESULTS: Mesothelial cells were present in all patient dialysates except that of a single patient's Glu dialysate. The number of MC drained was similar with both solutions. After the initial culture reached confluence, MC were identified in 14 and 12 patients receiving Ico and Glu, respectively. However, in 1 patient using Ico and in 2 using Glu, the MC count at this stage was so low that further subculture could not be performed. Cells from Ico-derived solutions exhibited a higher degree of proliferation than cells from Glu-derived solutions. The morphology of MC was also different. Cells from drained effluent were typical in 11 patients using Glu solution in contrast with 14 patients using Ico. At confluence, the percentages of typical appearance were 50% and 92.9% (p < 0.05) in Glu and Ico respectively. CONCLUSIONS: Mesothelial cells taken from icodextrin effluent show a greater proliferation ex vivo than those taken from glucose effluent.     

复合结扎加抑酸治疗Barrett食管

目的观察抑酸加复合结扎治疗Barrett食管(BE)的临床效果。方法对40例经内镜和病理诊断为BE的病人,分别采取抑酸加复合结扎(治疗组)和抑酸加抗反流(对照组)治疗。于治疗后3、6、12个月分别进行内镜和病理检查,观察两组BE病人治疗情况。结果治疗组20例BE病人,治疗后3、6、12个月时的有效率分别为65%、70%、80%,而对照组则分别为0、0、25%。治疗组除出现短暂的吞咽疼痛、低热外,无出血、穿孔、狭窄等并发症。结论抑酸加复合结扎治疗BE,疗效高,见效快,长疗程抑酸加抗反流对BE治疗有一定作用。     

Chinese hamster ovary cell adhesion to human platelet thrombospondin is dependent on cell surface heparan sulfate proteoglycan.

Thrombospondin is a 420-kD platelet alpha-granule glycoprotein that binds specifically to heparin. We examined adhesion to thrombospondin of CHO K1 cells and three mutant CHO lines with varying deficiencies in glycosaminoglycan (GAG) synthesis. In an experiment in which the parent line (K1) had 78% adherence to thrombospondin adsorbed to tissue culture plastic, CHO S745 cells, with less than 6% normal GAG synthesis had 11% adherence. CHO S677 cells, with decreased heparan sulfate proteoglycan but increased chondroitin sulfate proteoglycan, had 42% adherence. CHO S803 cells, with decreased heparan sulfate proteoglycan and normal chondroitin sulfate proteoglycan, had 31% adherence. Heparin inhibited K1 cell adhesion to thrombospondin, but not fibronectin, in a concentration-dependent manner. Dermatan sulfate but not chondroitin sulfate was also inhibitory. There was markedly decreased K1 cell adhesion to a thrombospondin core fragment that lacked the heparin binding NH2-terminal domain. Purified heparin binding domain, although poorly adhesive when adsorbed to substratum, inhibited cell adhesion to intact thrombospondin. Adhesion was better for all cell lines tested, including three human tumor cell lines, when thrombospondin was adsorbed at pH 4.0 compared with pH 7.4. When adsorption of thrombospondin was done at pH 7.4, cell adhesion was better when thrombospondin was adsorbed in the presence of greater than or equal to 0.6 mM calcium, compared to 0.1 mM calcium or EDTA. These findings suggest that thrombospondin can adsorb to plastic with varying degrees of exposure of a cell adhesion domain. We conclude that the thrombospondin cell adhesion receptor on CHO cells is a heparan sulfate proteoglycan, and that cell adhesion to thrombospondin depends on conformation of adsorbed thrombospondin.