胰高糖素样肽-1受体激动剂通过JNK信号通路促进肝星形细胞凋亡的机制研究

目的 探讨胰高糖素样肽-1受体激动剂(GLP-1RA)通过JNK信号通路促进肝星形细胞(HSC)凋亡的机制.方法 体外培养人HSC并进行形态学鉴定,将HSC样本随机分成对照组(20份)、GLP-1RA组(20份)和JNK阻断组(20份).对照组HSC在常规培养基础上加入高糖(终浓度25 mmol/L),GLP-1RA组在对照组基础上加入GLP-1RA利拉鲁肽(终浓度10 mmol/L),JNK阻断组在GLP-1RA组基础上加入JNK信号通路阻断剂SP600125(终浓度20 μmol/L)进行培养;培养120 h后用流式细胞术检测各组的HSC凋亡情况.同时采用Western印迹法检测各组的p-JNK蛋白表达水平.结果 三组的平均凋亡率和平均p-JNK的表达水平差异均有统计学意义(F=19.412和66.451,P均＜0.01).GLP-1RA组的凋亡率和p-JNK蛋白表达水平分别为(30.61±4.07)％和(22.79±3.80)％,均高于对照组,差异均具有统计学意义(t=0.530和9.854,P均＜0.01);JNK阻断组的细胞凋亡率和p-JNK蛋白表达水平分别为(23.48±4.41)％和(10.66±4.15)％,均低于GLP-1RA组,差异有统计学意义(t=-5.428和-8.757,P均＜0.01).结论 JNK信号通路在GLP-1RA介导的HSC凋亡中起着关键作用,GLP-1RA可以通过JNK信号通路促成经高糖诱导活化的HSC发生凋亡.     

高糖对肾小管上皮细胞PTEN蛋白表达影响

目的 观察高糖条件下肾小管上皮细胞第10号染色体缺失的磷酸酶和张力蛋白同源基因(PTEN)蛋白的表达变化,探讨其在肾小管纤维化病变中的作用及可能机制.方法 体外培养大鼠肾小管上皮细胞株(NRK52E),随机分为对照组和高糖组,每组分别设2、12、24、48 h4个时间点进行动态观察;采用免疫荧光细胞化学染色检测E-钙黏素(E-cadherin)和α-平滑肌肌动蛋白(α-SMA)表达变化,Western blotting检测各组PTEN、磷酸化蛋白激酶B[p-Akt1 (Ser473)]、E-caderin和c-SMA蛋白表达变化.结果 与对照组比较,高糖组培养24、48 h时,PTEN、E-caherin蛋白表达量[分别为(1.15±0.13)、(1.10 ±0.13)和(1.23±0.11)、(1.22±0.11)]均减少(均P＜0.05),而p-Akt1(ser473)、α-SMA蛋白表达量[分别为(1.53±0.13)、(1.60±0.13)和(1.86±0.10)、(1.91±0.10)]均增多(均P ＜0.05);PTEN与E-cadherin蛋白表达量呈正相关(r=0.58,P＜0.05),与α-SMA蛋白表达量呈负相关(r=-0.61,P＜0.05).结论 高糖培养的肾小管上皮细胞中PTEN蛋白表达明显减少,可能通过PI3K/Akt信号通路参与了肾小管纤维化病变的发生发展过程.     

p38MAPK信号通路抑制剂对TNF-α诱导的乳腺癌细胞凋亡的影响

目的研究p38丝裂原活化蛋白激酶(p38MAPK)信号通路抑制剂对肿瘤坏死因子-α(TNF-α)诱导的乳腺癌细胞凋亡的影响。方法 TNF-α处理乳腺癌细胞MDA-MB-231,Western blot检测细胞中p38MAPK信号通路激活情况。p38MAPK信号通路阻断剂SB203580和TNF-α同时处理MDA-MB-231细胞,流式细胞术检测细胞凋亡,二氯二氢荧光素-乙酰乙酸酯(DCFH-DA)法检测细胞中活性氧(ROS)水平,Western blot检测细胞中p38MAPK、p-p38MAPK、Bid、Bcl-2相关X蛋白(Bax)水平。结果 TNF-α作用后的MDA-MB-231细胞中p-p38MAPK/p38MAPK蛋白水平由(0. 25±0. 03)升高至(0. 80±0. 07),两者比较差异有统计学意义(P<0. 05)。TNF-α处理后MDA-MB-231细胞凋亡率由(2. 28±0. 47)%升高至(19. 56±1. 33)%,SB203580处理后细胞凋亡率降低至(12. 14±1. 12)%。TNF-α处理后细胞中Bax和Bid水平明显升高,ROS水平升高,而SB203580处理后细胞中Bax、Bid水平和ROS水平有所降低,与对照MDA-MB-231细胞相比差异有统计学意义(P<0. 05)。结论 TNF-α诱导Bid、Bax介导的乳腺癌细胞凋亡,提高细胞中ROS水平,p38MAPK信号通路抑制剂可以减弱TNF-α的上述作用。     

双酚A对大鼠睾丸支持细胞P38丝裂原活化蛋白激酶及半胱氨酸天冬氨酸蛋白酶-3表达的影响

目的 研究双酚A (bisphenol A,BPA)对离体培养青春前期大鼠睾丸支持细胞P38丝裂原活化蛋白激酶(mitogen activated protein kinase,MAPK)、半胱氨酸天冬氨酸蛋白酶-3(caspase-3)及相关凋亡基因表达的影响.方法 将睾丸支持细胞分别暴露于0(溶剂对照)、30、50、70 μmol/L的BPA.采用MTT法检测离体培养细胞活力,采用RT-PCR的方法检测p38 MAPK、caspase-3、FasL、肿瘤坏死因子α(tumor necrosis factorα,TNF-α) mRNA的相对表达情况,采用western-blotting的方法检测细胞中P38 MAPK、磷酸化P38 MAPK和caspase-3酶原蛋白的表达情况.结果 与溶剂对照组相比,30 μmol/L BPA组支持细胞p38 MAPK mRNA的相对表达量升高,而50 μmol/L BPA组p38 MAPK的表达明显降低(P＜0.05);各浓度BPA染毒组caspase-3mRNA的相对表达量均较高(P＜0.05);仅50 μmol/L BPA组TNF-α mRNA的相对表达量增加(P＜0.05);50、70 μmol/LBPA组FasL mRNA的相对表达量增加(P＜0.05);各剂量BPA染毒组总P38MAPK蛋白的相对表达量无显著变化;50和70 μmol/LBPA组磷酸化P38 MAPK蛋白的相对表达量均明显升高(P＜0.05);仅70 μmol/L BPA组caspase-3酶原蛋白的相对表达量下降(P＜0.05).结论 BPA可激活离体培养青春前期大鼠睾丸支持细胞p38 MAPK,并诱发caspase-3活化,导致细胞凋亡,这可能是通过FasL凋亡途径介导的.     

PDCD4对SKO-V3细胞生长凋亡及p-p38MAPK、p-STAT3水平的影响

目的探讨程序性细胞死亡4 (PDCD4)对SKO-V3细胞生长、凋亡及p-STAT3、p-p38MAPK表达的影响。方法卵巢癌细胞SKO-V3转染PDCD4过表达载体(p DsRes2-N1-PDCD4)和对照载体(p DsRes2-N1),记为过表达组和阴性组,同时以不转染的细胞为对照组,Realtime PCR和Western blot检测PDCD4水平,噻唑蓝(MTT)和细胞克隆实验检测细胞增殖能力,流式细胞术检测细胞凋亡,Western blot检测磷酸化的p38MAPK (p-p38MAPK)、磷酸化的STAT3 (p-STAT3)水平。结果阴性组细胞中PDCD4 mRNA和蛋白水平、光密度值(OD值)、细胞克隆形成数目、凋亡率和p-p38MAPK、p-STAT3水平与对照组相比差异无统计学意义(P0. 05)。过表达组细胞中PDCD4 mRNA和蛋白水平明显高于对照组,并且细胞OD值和克隆形成数目明显低于对照组,而细胞凋亡率明显高于对照组(P0. 01)。过表达组p-STAT3/STAT3水平与对照组相比明显降低,p-p38MAPK/p38MAPK水平与对照组相比明显升高(P0. 01)。结论 PDCD4抑制卵巢癌细胞生长,促进卵巢癌细胞凋亡,这可能与抑制STAT3信号通路激活和促进p38MAPK信号通路激活有关。     

P38MAPK对变应性鼻炎患者外周血单核细胞IL-6及TNF-α的表达调控

目的探讨p38MAPK信号转导通路对变应性鼻炎(allergic rhinitis,AR)中细胞因子白细胞介素6(IL-6)和肿瘤坏死因子(TNF-α)表达的调控作用及p38MAPK与IL-6、TNF-α之间的相关性。方法变应性鼻炎(AR组)及正常者(正常组)各20例,分别从每位受试者的外周血中分离出单核细胞并分成3组培养。第1组为空白对照,第2组加入P38MAPK激动剂12-肉豆蔻酰-13-乙酸佛波酯(phorbol12-myristate13-acetate,PMA),第3组同时加入PMA和P38MAPK特异性抑制剂SB203580,将单核细胞进行培养,westernblot法检测核蛋白P38MAPK的表达,RT-PCR法检测IL-6和TNF-α的表达,ELISA法检测上清液中的IL-6和TNF-α蛋白含量。结果加入PMA培养的AR组T单核细胞P38MAPK蛋白表达、IL-6和TNF-αmRNA的表达及培养上清液中的IL-6和TNF-α蛋白表达与空白对照组比较均明显增加(均p<0.01);且与加入PMA培养的正常T淋巴细胞组比较上述指标也均明显增加(均p<0.01);而同时加入PMA和SB203580培养的AR组单核巴细胞的上述指标与加入PMA培养的AR组比较明显降低,但与AR空白对照组比较仍有增加(均p<0.01)。单核细胞P38MAPK蛋白表达与IL-6和TNF-α的mRNA表达均存在正相关(均p<0.01),与培养上清液中的IL-6和TNF-α蛋白含量也均存在正相关(均p<0.01)。结论p38MAPK信号转导途径参与调节AR的单核细胞活化及IL-6、TNF-α的基因表达。     

miR-150对角叉菜胶诱导慢性非细菌性前列腺炎模型炎症调控作用及机制

目的 分析微小RNA-150(miR-150)对角叉菜胶诱导慢性非细菌性前列腺炎(CNP)模型的炎症调控作用及相关机制。方法 选取60只SFP级雄性大鼠，随机分为A、B、C、D组各15只，A组不做任何处理，剩余三组大鼠建立角叉菜胶诱导的CNP模型。C组做miR-150沉默转染、D组做miR-150过表达转染，A组、B组注射生理盐水。对比分析各组指标。结果 与A、B组相比，C组miR-150表达量降低，D组miR-150表达量升高(P<0.05)。相比B组，C组体质量、前列腺湿质量较低，D组体质量、前列腺湿质量较高(P<0.05);相比C组，D组体质量、前列腺湿质量较高(P<0.05)。相比B组，C组白细胞介素(IL-1β、IL-6、IL-8)、肿瘤坏死因子-α(TNF-α)水平及p38丝裂原活化蛋白激酶(p38MAPK)、磷酸化p38丝裂原活性蛋白激酶(p-p38MAPK)、基质金属蛋白酶-9(MMP-9)蛋白表达量较高，D组IL-1β、IL-6、IL-8、TNF-α水平及p38MAPK、p-p38MAPK、MMP-9蛋白表达量较低(P<0.05);相比C组，D组IL-1β、IL-6、IL-8、TNF-α水平较低(P<0.05)。结论 miR-150过表达可能经作用于p38MAPK信号通路，最终发挥调控角叉菜胶诱导CNP局部炎症发挥作用。     

p38α丝裂原活化蛋白激酶在食管鳞癌细胞Eca109中的功能研究

目的 探讨p38α丝裂原活化蛋白激酶(MAPK)在食管鳞癌细胞Eca109中的可能作用.方法 构建p38α特异性的shRNA干扰载体,瞬时转染Eca109细胞,运用qRT-PCR、免疫印迹分别检测p38α干扰后在mRNA、蛋白水平上的沉默效果;运用MTT和流式细胞仪检测p38α干扰后Eca109细胞增殖,细胞周期和凋亡的变化;运用细胞划痕实验检测p38α干扰后细胞迁移能力的改变.作为平行反向验证,转染含有p38α全长cDNA的真核过表达质粒,运用免疫印迹检测p38α过表达后在蛋白水平上的表达效果;运用MTT和流式细胞仪检测p38α过表达后细胞增殖,细胞周期和凋亡的变化;运用细胞划痕实验检测p38α的变化后细胞迁移能力的改变.结果 p38α基因在受干扰后,测定其蛋白水平表达水平(22.970±2.857)较空质粒组(35.658 ±2.286)降低,差异具有统计学意义(t=-4.475,P＜0.01).观察Eca109细胞的增殖变化,发现干扰48 h后吸光度值(0.951±0.086)大于对照组细胞(0.811 ±0.012)(t=3.20,P＜0.05),表明Eca109细胞增殖加快.观察细胞周期和凋亡变化发现,干扰48 h后凋亡率(17.400±5.495)较空质粒组(1.000 ±0.721)增加(t=40.06,P＜0.01);干扰72 h后细胞迁移速度(0.034±0.031)较空质粒组(0.278±0.021)加快(t=-5.79,P＜0.01),表明浸润能力增加.p38α在过表达后,检测到其内源性p38α蛋白表达水平(41.170±2.357)高于对照组(35.658±2.286)(t=4.41,P=0.005);48 h过表达组吸光值(0.472±0.089)与对照组细胞吸光值(0.811±0.012)相比,细胞增殖受到抑制(t=-7.50,P＜0.01),细胞生长活动在G1期受阻(t=4.80,P＜0.01),并且其细胞凋亡(32.233±1.457)高于空质粒组(1.000±0.721)(t=17.20,P＜0.01),细胞迁移[(0.770±0.054) mm]较空质粒组[(0.278±0.021) mm]减慢并且浸润受到抑制(t=11.00,P＜0.01).结论 p38dMARK抑制食管鳞癌细胞Eca109的发生发展过程.     

纳米氧化锌对小胶质瘤BV2细胞炎症因子及p38MAPK蛋白磷酸化的影响

[目的]探讨纳米氧化锌(zinc oxide nanoparticle,nano-Zn O)对小胶质瘤BV2细胞炎症因子及p38丝裂原活化蛋白激酶(p38MAPK)磷酸化的影响。[方法]不同质量浓度nano-Zn O(0、5.0、10.0、15.0、20.0、30.0、50.0、75.0 mg/L)染毒小胶质瘤BV2细胞24 h,用MTT法测定细胞存活率后确定染毒剂量。以nano-Zn O(0、5.0、10.0、15.0、20.0 mg/L)染毒BV2细胞24 h,采用乳酸脱氢酶(LDH)检测试剂盒检测细胞培养液上清液中LDH活性,ELISA检测肿瘤坏死因子-α(TNF-α)、白细胞介素-1β(IL-1β)和白细胞介素-6(IL-6)的分泌水平,Western blot法检测磷酸化p38MAPK(p-p38MAPK)蛋白水平并用Image J软件对蛋白条带灰度值进行分析。应用Spearman相关分析炎症因子分泌与p38MAPK蛋白磷酸化水平的相关性。[结果]随nano-Zn O染毒剂量的增加,BV2细胞存活率降低(r=-0.994,P0.001),细胞培养液上清液中LDH活性增加(r=0.749,P0.001)。与对照组相比,10.0、15.0、20.0 mg/L nano-Zn O染毒组TNF-α、IL-1β、IL-6分泌水平增加(均Ps0.05)。Western blot检测结果发现各染毒组p-p38MAPK蛋白表达水平增高,且与炎症因子分泌水平的变化趋势一致(r TNF-α=0.836,P0.001;r IL-6=0.539,P0.001;r IL-1β=0.659,P=0.008);20.0 mg/L nano-Zn O染毒组p-p38MAPK与p38MAPK灰度值的比值较对照组高,差异有统计学意义(P0.05)。[结论]nano-Zn O可诱导BV2细胞炎症因子分泌水平和p38MAPK蛋白磷酸化水平增高。     

氯化镉对大鼠肾上皮细胞丝裂原活化蛋白激酶表达及其磷酸化的影响

目的 探讨氯化镉染毒大鼠正常肾上皮(normal rat kidney epithelial,NRK)细胞对丝裂原活化蛋白激酶(MAPK)表达及其磷酸化水平的影响.方法 应用不同剂量(0、1、5、10、20、40 μmol/L)氯化镉染毒NRK细胞24 h和同一剂量氯化镉(10 μmol/L)于不同时间(0、0.5、1.0、2.0、4.0、8.0 h)染毒NRK肾细胞.采用蛋白免疫印迹法检测氯化镉染毒后NRK细胞中MAPK表达水平,并用磷酸化抗体检测MAPK磷酸化水平.结果 不同氯化镉剂量和不同染毒时间染毒NRK细胞,发现MAPK表达无明显改变,但MAPK磷酸化蛋白表达量较对照组升高.氯化镉浓度在10 μmol/L时p-ERK1/2表达明显,表达量为1. 00±0.06;20 μmol/L和40 μmol/L剂量组表达量分别为2.58±0.11、2.76±0.23,比10 μmol/L组高1.58倍和1.76倍,差异有统计学意义(F=827.70,P＜0.01);氯化镉浓度为20 μmol/L(2.47±0.20)和40 μmol/L(3.73±0.25)时p-p38MAPK表达量比对照组(1.00±0.02)高1.47倍和2.73倍,差异有统计学意义(F=280.06,P＜0.01).p-ERK1/2和p-p38MAPK表达量与氯化镉浓度存在剂量-效应关系(p-ERK1/2相关系数为r=0.919,t=4.69,P=0.009;p-p38MAPK相关系数为r=0.945,t=5.79,P=0.004).MAPK磷酸化蛋白表达水平也与染毒时间相关,p-ERK1/2在染毒1 h(1.26±0.11)时表达明显,染毒4 h(1.51±0.07)和8 h(3.53±0.23)时表达量是对照组(1.00±0.02)的1.5倍和3.5倍,差异有统计学意义(F=427.82,P＜0.001);p-p38MAPK在染毒1 h(1.31±0.07)时表达也明显增加,染毒4 h(3.53±0.32)和8 h(4.41±0.38)时表达水平是对照组(1.00±0.03)的3.5倍和4.4倍,差异有统计学意义(F=280.06,P＜0.001).结论 氯化镉染毒NRK细胞可引起MAPK蛋白磷酸化水平明显升高,可能与MAPK的激活有关.     

Calcium intake in the elderly: validation of a dietary questionnaire

Epidemiological studies of calcium and osteoporosis have been hampered by the lack of a suitable tool for assessing calcium intake. This report describes a new frequency and amount questionnaire for measuring present and past calcium intake in the elderly. The validity of the questionnaire was tested against two commonly used standards of dietary assessment, five-day duplicate diets and seven-day weighed dietary inventories. The resulting correlation coefficients were, respectively, r = 0.76 and r = 0.69, while that for repeatability was r = 0.84. Furthermore, the questionnaire categorized subjects into thirds of the distribution of intake with almost no gross misclassification. It is suggested that the present findings may be extended to the majority of normal, healthy elderly subjects, implying wide application for the questionnaire in the assessment of calcium intake in the elderly.     

Self-reported health problems among Swedish miners one year after unemployment

Unemployment is considered to be a public health concern sincedeterioration in the health of the unemployed is often anticipated.However, for some groups, such as miners, unemployment mightimprove health due to a cessation of potentially harmful occupationalexposures. This study evaluates the health of 79 miners in oneSwedish iron-ore mine, and 226 age-matched controls from thegeneral population, during one year after the closure of themine. The participants received a questionnaire regarding medicalhistory and subjective symptoms at the beginning of the studyperiod, and after one year. Statistically significant negativeeffects on self-reported health attributable to unemploymentwere not found, although neuropsychiatric symptoms were morecommon among the unemployed miners. The miners reported a statisticallysignificant improvement in grip force (p=0.031). They had asignificantly higher prevalence of symptoms associated withmining related exposures when compared with the population controls;pain in the upper extremities [relative risk (RR)=2.27, 95%confidence interval (Cl)=1.44–3.59), back pain (RR=1.84;Cl=1.237–2.75), vasospastic disease of the fingers (RR=2.05;Cl=1.18–3.57) and obstructive respiratory symptoms (attacksof dyspnea and wheezing: RR=3.67; Cl=1.167–11.6).     

Excès de cas humains et animaux de tularémie en France au cours de l’hiver 2007–2008 : émergence ou phénomène isolé ?

Context

Tularemia is a zoonosis affecting humans and hares in France. We describe the results of surveillance in both species, in 2007 and 2008.

Methods

Human tularemia cases are mandatorily notifiable in France since 2003. In hares, surveillance relies on volunteer hunter associations in all districts of the country. Data from mandatory reports and volunteer surveillance in 2007/2008 were analyzed and compared with previous results.

Results

In 2007/2008, 144 cases were reported in humans and 117 cases in hares. This was a 100% increase compared to previous years. Human cases differed from those of previous years only by the frequency of contact with breeding animals. Human cases without any documented risk exposure were also more frequent.

Conclusion

An increase of tularemia cases occurred in 2007/2008 in both species. Complementary studies are needed to identify the species reservoir in France to understand the causes of this peak of cases.     

Occupational health hazards in mining: an overview

This review article outlines the physical, chemical, biological, ergonomic and psychosocial occupational health hazards of mining and associated metallurgical processes. Mining remains an important industrial sector in many parts of the world and although substantial progress has been made in the control of occupational health hazards, there remains room for further risk reduction. This applies particularly to traumatic injury hazards, ergonomic hazards and noise. Vigilance is also required to ensure exposures to coal dust and crystalline silica remain effectively controlled.     

Manufacture and use of nanomaterials: current status in the UK and global trends

This paper provides an overview of the production and use of nanomaterials (NMs), particularly in the UK. Currently, relatively few companies in the UK are identifiable as NM manufacturers, the main emphasis being the bulk markets in metals and metal oxides, and some niche markets such as carbon nanotubes and quantum dots. NM manufacturing in the UK does not reflect the global emphasis on fullerenes, nanotubes and fibres. Some assumptions have been made about the types of NM that are likely to be imported into the UK, which currently include fullerenes, modified fullerenes and other carbon-based NMs including nanotubes. Many university departments, spin-offs and private companies have developed processes for the manufacture of NMs but may only be producing small quantities for research and development (R&D) purposes. However, some have the potential to scale up to produce large quantities. The nanotechnology industry in the UK has strong R&D backup from universities and related institutions. This review has covered R&D trends at such institutions, and appropriate information has been added to a searchable database. While several companies are including NMs in their products, only a few (e.g. manufacturers of paints, coatings, cosmetics, catalysts, polymer composites) are using nanoparticles (NPs) in any significant quantities. However, this situation is likely to change rapidly. There is a need to collect more information about exposure to NPs in both manufacturing and user scenarios. As the market grows, and as manufacturers switch from the micro- to the nanoscale, the potential for exposure will increase. More research is required to quantify any risks to workers and consumers.     

深圳公立医院管理体制改革制度设计

深圳公立医院管理体制改革实行政事分开、管办分开,在理事会架构下按法定机构模式组建市医管中心,落实公立医院运营管理自主权.作者从当前公立医院管理体制的弊端入手,介绍了深圳市进行公立医院管理体制改革的基本思路及改革方案设计的主要举措,深入剖析了的改革方案的特点,并对改革效果进行了预测.     

Effects of nitrogen dioxide on red blood cells of rats: Changes in components of red cell membranes during in vivo exposure to NO2

Red cell membranes, prepared from red blood cells of rats exposed to 4, 10, or 20 ppm nitrogen dioxide (NO₂) for 1 to 10 days, were examined for evidence of changes in membrane components. Appreciable changes were not found in contents of phospholipid and cholesterol during exposure to 10 ppm NO₂. By contrast, protein content altered with the time of exposure. Moreover, changes in protein composition were observed by employing sodium dodecyl sulfate — polyacrylamide gel electrophoresis. Twenty-four-hour exposure to NO₂ at the concentration above 10 ppm resulted in a marked increase in the percentage of lysophosphatidylethanolamine (LysoPE) to the total phospholipids. The prolonged exposure to 10 ppm NO₂ gave rise to a further increase in LysoPE, whereas the percentage of phosphatidylethanolamine (PE) showed a gradual decrease. A 1-day exposure to 4.0 ppm NO₂ also caused an increase in sialic acid content and decreases in those of PE and hexose. In addition to contents of these components the percentage of LysoPE increased 5 days after exposure and the elevated values were maintained up to the end of exposure period. These results demonstrate that red blood cells in circulation exhibit different membrane properties in terms of lipid and carbohydrate composition during 10 days of exposure to 4.0 ppm NO₂.     

Investigating clusters in the workplace and beyond

Clusters of disease are common and occur in the workplace and in the general community. They often arouse considerable concern among the population. Investigations have sometimes lead to exciting new knowledge, but in general the investigation of clusters is difficult and often unrewarding, especially for community clusters. In the workplace, investigations are more likely to find associations and even new causes, but still many clusters remain enigmatic. Despite this, there are many reasons for investigating clusters, including allaying community concern and identifying uncontrolled exposures. A structure for investigating clusters in the workplace is suggested.