人参皂甙Rb1抑制Aβ25-35诱导皮层神经元tau蛋白的过度磷酸化

目的：探讨人参皂甙Rb1对凝聚态Aβ25-35诱导的胎鼠皮层神经元tau蛋白过度磷酸化的影响及其可能的作用机制。方法通过蛋白免疫印迹法和免疫细胞化学染色法检测胎鼠皮层神经元tau蛋白在Ser396、Ser199／202和Thr231位点的磷酸化水平、总tau蛋白水平和糖原合成酶3B(GSK-3β)的蛋白表达水平。结果20μmol／L     

p25/cdk5可能参与人参皂苷Rb1减轻Aβ_(25-35)诱导的tau蛋白过度磷酸化

目的探讨在Aβ25-35诱导的皮层神经元tau蛋白过度磷酸化中,人参皂苷Rb1对周期依赖性蛋白激酶(cyc lin-de-pendent k inase 5,CDK 5)的激动亚基p35/p25的影响。方法通过蛋白免疫印迹法和免疫细胞化学染色法检测胎鼠皮层神经元CDK 5的两个亚基cdk5和p35/p25的蛋白水平,以及CDK 5的磷酸化底物tau蛋白在Ser199/202、Thr205、Ser396和Ser404位点的磷酸化水平。结果凝聚态Aβ25-35(20μmol.L-1)作用于皮层神经元12 h,可使皮层神经元中p25的数量增多,以及tau蛋白在Ser199/202、Thr205、Ser396和Ser404位点的磷酸化水平增高,但对cdk 5亚基表达水平影响并不明显。Rb1和calpain特异性抑制剂calpeptin可减少皮层神经元p25的生成,同时人参皂苷Rb 1和CDK 5特异性抑制剂roscovitine可减轻凝聚态Aβ25-35诱导的皮层神经元tau蛋白的过度磷酸化水平。结论p25/cdk 5可能参与人参皂苷Rb1减轻Aβ25-35诱导的tau蛋白过度磷酸化。     

NGF对局灶性脑缺血/再灌注大鼠海马tau蛋白磷酸化作用的影响

目的探讨外源性神经生长因子(NGF)对局灶性脑缺血/再灌注大鼠海马神经元tau蛋白过度磷酸化的影响。方法用线栓法制作局灶性脑缺血/再灌注模型,应用免疫组织化学SABC法、Westernblot和图像分析方法检测大鼠海马CA1区tau蛋白在Ser199/202位点磷酸化程度和总tau蛋白表达,以及NGF对tau蛋白过度磷酸化的影响。结果缺血/再灌注组海马CA1区tau蛋白在Ser199/202位点磷酸化水平和总tau蛋白明显升高(P<0·05);NGF组大鼠海马tau蛋白在Ser199/202位点磷酸化水平明显低于缺血/再灌注组,总tau也下降(P<0·05)。结论NGF明显减轻局灶性脑缺血/再灌注大鼠海马tau蛋白磷酸化程度,降低tau蛋白磷酸化水平可能对缺血神经元起保护作用。     

MANF对神经细胞中tau蛋白过度磷酸化的抑制作用

目的观察MANF是否可以抑制冈田酸诱导的N2a细胞中tau蛋白的过度磷酸化,以了解MANF神经保护作用的机制。方法采用体外培养小鼠神经母瘤细胞株N2a,以冈田酸(okadaic aicd,OA)作为诱导剂诱导N2a细胞中tau蛋白过度磷酸化,在加入重组人MANF蛋白干预或转染MANF过表达质粒及siRNA后,用MTT法检测细胞增殖活性的变化,并用AT-8抗体检测tau蛋白ser202/Thr205位点的磷酸化水平变化。结果 N2a细胞在加入重组人MANF蛋白预处理4 h后加入OA诱导24 h后,经Western blot和MTT法检测发现,重组人MANF蛋白能明显抑制N2a细胞中tau蛋白的过度磷酸化,并可促进N2a细胞的增殖活性;在转染MANF过表达质粒后,N2a细胞中OA诱导的过度磷酸化tau蛋白减少,且细胞活性增加;与此相反,转染siRNA下调内源性的MANF的表达则能促进N2a细胞中的tau蛋白过度磷酸化,并抑制细胞活性。结论 MANF可以抑制神经细胞中tau蛋白过度磷酸化,这可能是其发挥神经保护作用的原因之一。     

复智散通过细胞周期依赖性蛋白激酶5通路减轻皮层神经元Tau蛋白过度磷酸化

目的探讨复方中药复智散(FZS)能否通过抑制细胞周期依赖性蛋白激酶5(CDK5)通路,减轻Aβ_(25-351)诱导的新生鼠皮层神经元Tau蛋白过度磷酸化。方法选用24 h内新生Wistar大鼠,分离纯化皮层神经元,进行体外培养。皮层神经元在体外培养7 d后,应用20μmol·L-1Aβ_(25-351)作用于皮层神经元24 h。药物治疗组则应用FZS(20 mg·L~(-1))、CDK5抑制剂Roscovitine(15μmol·L~(-1))、钙蛋白酶(calpain)制剂Calpeptin(20μmol·L~(-1))预处理24 h,然后用20μmol·L~(-1)Aβ_(25-351)作用24 h。用Western blot检测Tau蛋白Ser396、Ser202和Thr231位点磷酸化水平和CDK5的激活蛋白p25/p35的蛋白水平;荧光酶标仪测定荧光强度来反映calpain活性;免疫沉淀法检测CDK5激酶活性。结果 20μmol·L~(-1)Aβ_(25-351)作用于皮层神经元24 h后,Tau蛋白在Ser396、Ser202、Thr231位点磷酸化水平增加,CDK5激酶活性升高,CDK5激活蛋白p25水平升高,calpain活性升高。20 mg·L-1FZS治疗组则明显抑制了Aβ_(25-351)导致的Tau蛋白在Ser396、Ser202、Thr231位点磷酸化水平增加,抑制了CDK5激酶活性、p25蛋白水平以及calpain活性升高。CDK5抑制剂roscovitine和calpain抑制剂calpeptin作为阳性对照药物也显示了抑制Tau蛋白过度磷酸化的作用。结论复智散可能通过calpain-p25/CDK5通路抑制Aβ_(25-351)导致的皮层神经元Tau蛋白过度磷酸化。     

氯化锂对冈田酸所致SK-N-SH神经元突触萎缩的保护作用

目的考察氯化锂(LiCl)对蛋白磷酸酶抑制剂冈田酸(OA)诱导的SK-N-SH细胞分化神经元损伤的保护作用和tau蛋白Ser-~(262)位点磷酸化水平的影响。方法利用全反式维甲酸(ATRA)诱导SK-N-SH细胞分化为成熟的神经元细胞;采用OA诱导成熟神经元细胞建立AD模型;采用磺酰罗丹明B(SRB)比色法考察LiCl对成熟的神经元细胞增殖的抑制作用;Giemsa染色观察SK-N-SH细胞形态学变化;并采用Image-Proplus软件测定神经元细胞的突触长度;采用Western blot检测synaptophysin蛋白和tau蛋白Ser-~(262)位点磷酸化水平。结果 10μmol·L~(-1)ATRA连续处理7 d,可诱导SK-N-SH细胞突触生长和synaptophysin蛋白表达等典型分化神经元的特征。20~100 nmol·L~(-1)OA作用于分化神经元,可浓度和时间依赖性抑制细胞增殖,同时致分化神经元突触萎缩,tau蛋白Ser-~(262)位点磷酸化水平也明显升高。10 mmol·L~(-1)LiCl预处理可维持synaptophysin蛋白高表达,抑制tau蛋白Ser-~(262)位点磷酸化水平(P<0.01)。结论LiCl能够改善OA所致分化神经元的突触损伤,并伴随着synaptophysin表达的升高、tau蛋白Ser-~(262)位点异常磷酸化水平的降低。     

金钗石斛总生物碱抑制海马tau蛋白的过度磷酸化

目的研究金钗石斛总生物碱(DNLA)对衰老小鼠及痴呆模型大鼠脑内tau蛋白过度磷酸化的影响。方法以SAMP8小鼠作为衰老小鼠模型,SAMR1小鼠作为正常对照,自4月龄始给予DNLA(20和40 mg·kg~(-1)),每天灌胃1次,连续6个月;SD大鼠双侧侧脑室注射链脲佐菌素(STZ)作为痴呆模型,侧脑室注射溶媒大鼠作为正常对照,术后给予DNLA,每天1次,连续28 d。Morris水迷宫及Y迷宫检测各组动物学习记忆功能;HE和Nissl染色观察海马神经元形态及数量;Western印迹法检测海马组织tau蛋白表达及Ser199,Ser396,Ser404,Ser422和Thr231位点的磷酸化水平;GSK-3β蛋白表达及Ser9和Y216位点的磷酸化水平;以及PP2A的蛋白表达水平。结果 DNLA可改善SAMP8小鼠和STZ大鼠的学习记忆功能(P<0.05);减少模型小鼠和大鼠海马组织神经元形态的损伤和数量的丢失(P<0.01);并降低tau蛋白Ser199,Ser396,Ser404,Ser422和Thr231位点的磷酸化水平(P<0.05),提高GSK-3β在Ser9位点的磷酸化水平(P<0.05),对GSK-3β的Y216位点磷酸化、PP2A、总tau蛋白及总GSK-3β的蛋白表达无明显的影响。结论 DNLA对脑内tau蛋白的过度磷酸化的具有抑制作用。     

人参皂苷对蛋白磷酸酶抑制剂冈田酸拟阿尔采末病细胞模型的影响

目的探讨人参皂苷(ginsenoside,GS)对蛋白磷酸酶抑制剂冈田酸(OA)诱导拟Alzheimer病(AD)细胞模型神经细胞tau蛋白的磷酸化、微管、细胞凋亡和凋亡调节因子的影响。方法GS与人神经母细胞瘤细胞系SK-N-SH细胞预孵育24h,弃去培养基,然后用OA10nmol·L-1与SK-N-SH细胞共孵育6h;用倒置显微镜观察细胞形态的变化,激光共聚焦显微镜观察微管变化,Western blot方法观察磷酸化tau蛋白、凋亡因子Bcl-2、Bax和Caspase-3的表达,用TUNEL法观察凋亡细胞的变化。结果正常SK-N-SH神经细胞铺展良好,OA模型组细胞突起断裂,GS显示了细胞保护作用。通过激光共聚焦显微镜观察,正常SK-N-SH细胞微管粗壮、连续,而OA模型组微管断裂、消失;GS能够减少OA引起的微管破坏作用。OA模型组tau蛋白Ser-199/202和Ser-404位点磷酸化水平较正常对照组明显增高,非磷酸化水平较正常对照组明显下降;GS 50mg·L-1和100mg·L-1组使神经细胞tau蛋白Ser-199/202和Ser-404位点磷酸化水平较OA模型组明显下降,GS 50mg·L-1和100mg·L-1组的tau蛋白Ser202非磷酸化水平较模型组则明显升高;正常对照组未见凋亡细胞;OA模型组凋亡细胞明显增多,Bax和Caspase-3表达水平较正常对照组明显增高,Bcl-2水平明显下降;GS能够明显抑制OA诱导的细胞凋亡,减少Bax和Caspase-3表达。结论人参皂苷对蛋白磷酸酶抑制剂OA所致的神经细胞病理变化有明显的保护作用,可能是通过抑制tau蛋白过度磷酸化,防止细胞凋亡来发挥作用的,提示该药在防治AD方面可能具有良好的应用前景。     

人参皂苷Rb1可能通过CDK5途径减轻Aβ25-35诱导的胎鼠海马神经元tau蛋白过度磷酸化

观察人参皂苷Rb1对Aβ_25-35诱导的海马神经元tau蛋白过度磷酸化的影响，并探讨其对周期依赖性蛋白激酶(cyclin-dependent kinase 5，CDK5)及激动亚基p25/p35的可能作用。通过蛋白免疫印迹法和免疫细胞化学染色法检测胎鼠海马神经元tau蛋白在Thr²⁰⁵、Ser³⁹⁶和Ser⁴⁰⁴位点的磷酸化水平，及CDK5的两个亚基cdk5和p25/p35的蛋白水平。20 μmol·L^-1凝聚态Aβ_25-35作用于海马神经元12 h，可使海马神经元tau蛋白在Thr²⁰⁵、Ser³⁹⁶和Ser⁴⁰⁴位点的磷酸化水平增高，p25的数量增多，但并不影响cdk5亚基的表达。人参皂苷Rb1可减轻凝聚态Aβ_25-35诱导的海马神经元tau蛋白的过度磷酸化，抑制p35的降解并减少海马神经元p25的生成。人参皂苷Rb1可能通过CDK5途径减轻Aβ_25-35诱导的胎鼠海马神经元tau蛋白过度磷酸化。     

自噬参与神经细胞中过表达tau和异常磷酸化tau蛋白的降解

目的观察自噬对神经细胞内源性tau、过表达tau和异常磷酸化tau蛋白水平的影响,探讨不同形式tau蛋白降解的可能机制。方法体外培养小鼠神经瘤母细胞株N2a和敲除Atg5基因的小鼠胚胎成纤维细胞株MEF,分别转染GFP-tau质粒,并用蛋白磷酸酯酶抑制剂冈田酸(okadaic acid,OA)诱导tau蛋白过度磷酸化,自噬诱导剂雷帕霉素(rapamycin)和溶酶体抑制剂氯化铵(NH4Cl)处理细胞,Western blot法检测tau、磷酸化tau以及自噬相关蛋白LC3和p62的表达;放线菌酮(cycloheximide,CHX)示踪法观察tau和磷酸化tau的降解;GFP-tau和RFP-Lamp1质粒共转染N2a细胞,观察tau和溶酶体的定位;免疫荧光染色和DAB染色观察自噬抑制对表达tau细胞形态的影响。结果与溶媒对照组相比,NH4Cl和rapamycin处理组细胞内源性tau蛋白水平无明显变化;过表达tau的细胞中,NH4Cl能增加tau和OA诱导的磷酸化tau蛋白水平,而rapamycin处理组细胞中tau和磷酸化tau水平降低,尤其是高分子量的磷酸化tau寡聚体明显减少;CHX实验证明自噬抑制能减缓tau和磷酸化tau的降解;tau和溶酶体在细胞内存在共定位;过表达tau的N2a细胞经NH4Cl处理后,胞质中出现大量tau聚集体,细胞核变小、固缩甚至消失。结论自噬参与神经细胞中过表达tau和异常磷酸化tau蛋白的降解,抑制自噬能增加tau的细胞毒作用。     

Aluminum-induced neuropathology: Transient changes in microtubule-associated proteins

In susceptible species, aluminum induces cytoskeletal changes in which neurofilaments accumulate in neuronal cell bodies and proximal axonal enlargements. To determine if microtubule-associated proteins (MAPs) are altered in this model, we examined the spinal cords of aluminum- and saline-treated control rabbits at several time points after treatment. Transient decreases in tau and MAP2 immunoreactivity in neurons in aluminum-intoxicated rabbits were demonstrated with immunocytochemistry. An antibody directed against Alzheimer's disease paired helical filaments labeled neurons in aluminum-treated rabbits but not controls. MAP5 immunoreactivity in the cell body cytoplasm was displaced by aluminum-induced tangles. The transient decreases in MAP2 and tau immunoreactivity did not reflect alterations in protein levels measured using immunoblotting. The transient antigenic changes in tau and MAP2 may reflect conformational changes in these cytoskeletal proteins. Aluminum-induced pathology provides a model for studying perturbations in MAPs and neurofilament proteins that are characteristic of many human neurodegenerative diseases such as Alzheimer's disease, diffuse Lewy body disease, Parkinson's disease, and amyotrophic lateral sclerosis.     

The effects of an anti-CD18 antibody (R15.7) in antigen-induced airway hyperresponsiveness (AH) and cell influx in guinea pigs.

Aerosol ovalbumin challenge (OA) of sensitized guinea pigs induced airway hyperreactivity (AH) to i.v. acetylcholine (Ach) and serotonin (5-HT) 24 hr post OA. Bronchoalveolar lavage fluid 24 hrs after OA showed increased leukocytes compared to unsensitized unchallenged animals. Treatment with monoclonal antibody R15.7 (3 mg/kg i.v.,) 1 hr prior and 4 hours after OA prevented the induction of AH to Ach but not to 5-HT and reduced influx of leukocytes. We conclude: 1) antigen inhalation induces an increase in AH with an increase in proinflammatory cell influx and 2) treatment with anti-CD18 antibody inhibits cell influx and airway hyperreactivity.     

Tau-Directed Immunotherapy: A Promising Strategy for Treating Alzheimer’s Disease and Other Tauopathies

Immunotherapy directed against tau is a promising treatment strategy for Alzheimer’s Disease (AD) and tauopathies. We review initial studies on tau-directed immunotherapy, and present data from our laboratory testing antibodies using the rTg4510 mouse model, which deposits tau in forebrain neurons. Numerous antibodies have been tested for their efficacy in treating both pathology and cognitive function, in different mouse models, by different routes of administration, and at different ages or durations. We report, here, that the conformation-specific antibody MC-1 produces some degree of improvement to both cognition and pathology in rTg4510. Pathological improvements as measured by Gallyas staining for fully formed tangles and phosphorylated tau appeared 4 days after intracranial injection into the hippocampus. We also examined markers for microglial activation, which did not appear impacted from treatment. Behavioral effects were noted after continuous infusion of antibodies into the lateral ventricle for approximately 2 weeks. We examined basic motor skills, which were not impacted by treatment, but did note cognitive improvements with both novel object and radial arm water maze testing. Our results support earlier reports in the initial review presented here, and collectively show promise for this strategy of treatment. The general absence of extracellular tau deposits may avoid the opsonization and phagocytosis mechanisms activated by antibodies against amyloid, and make anti tau approaches a safer method of immunotherapy for Alzheimer’s disease.     

人参皂苷Rg1对Aβ_(25-35)诱导大鼠海马神经元tau蛋白异常磷酸化的影响

目的探讨人参皂苷Rg1对Aβ2535所致大鼠海马神经tau蛋白异常磷酸化的抑制作用及其可能机制。方法应用脑立体定向技术向成年大鼠海马背侧注射凝聚态Aβ25355nmol制备AD样大鼠模型,术后分别给予腹腔内注射不同浓度的人参皂苷Rg1(625、125、25μmol·kg-1)处理,14d后处死,采用镀银染色方法观察海马组织神经元病理改变;免疫组织化学染色方法和免疫蛋白印迹技术显示大鼠脑内[pS396]tau、[pSpS199/202]tau、[pT231]tau的表达水平情况,以及总tau蛋白的水平(tau5);免疫蛋白印迹技术检测海马组织中GSK3β和磷酸化GSK3β的水平变化。结果凝聚态Aβ2535注射组神经元纤维走行紊乱,增粗、肿胀密集成宽带状,轴突深染;而人参皂苷Rg1对神经元具有明显的保护作用,脑内总tau的水平下降,[pS396]tau、[pSpS199/202]tau、[pT231]tau的表达明显低于Aβ2535注射组(P<001),以25μmol·kg-1保护作用最明显;GSK3β和磷酸化GSK3β的水平亦明显低于Aβ2535注射组,与正常和假注射组差异无显著性(P>005),以25μmol·kg-1作用最明显。结论人参皂苷Rg1对Aβ2535诱导的AD样大鼠海马神经元具有保护作用,其机制可能是通过阻断GSK3β的活性而降低磷酸化tau蛋白的表达而实现的。     

山茱萸环烯醚萜苷对蛋白磷酸酶抑制剂冈田酸拟阿尔采末病细胞模型的作用

目的探讨中药山茱萸环烯醚萜苷(COIG)对蛋白磷酸酶2A和1(PP2A和PP1)抑制剂冈田酸(okadaicacid,OA)拟阿尔采末病细胞模型tau蛋白过度磷酸化水平和细胞微管的影响。方法COIG与人神经母细胞瘤细胞系SKNSH细胞预孵育24h,再用OA10nmol·L-1与SKNSH细胞共孵育6h,在显微镜下观测细胞形态变化,用Westernblot方法观察磷酸化和非磷酸化tau蛋白表达,用间接免疫荧光法观察神经细胞微管的变化。结果正常SKNSH细胞铺展良好,OA模型组细胞变圆,突起断裂;OA模型组tau蛋白ser199/202和ser404位点磷酸化水平较正常对照组明显增高,非磷酸化水平下降;OA模型组细胞微管平均面积较正常对照组明显减少。COIG(100和200mg·L-1)给药组细胞形态基本恢复正常,tau蛋白ser199/202和ser404位点磷酸化水平较OA模型组明显下降、非磷酸化水平升高,细胞微管平均面积比模型组明显增大。结论山茱萸环烯醚萜苷能够抑制神经细胞tau蛋白过度磷酸化,保护细胞微管结构,因此可能具有治疗AD的应用前景。     

Mechanisms of the spatial memory deficits induced by injection of okadaic acid into the Meynert nucleus basalis of rats

We previously reported that the injection of okadaic acid (OA) into the Meynert nucleus basalis of rats induced spatial memory deficits. The present study was designed to further explore the underlying mechanisms. We found that the level of acetylcholine (Ach) in the hippocampus significantly decreased 24 h after injection of OA into the Meynert nucleus basalis of rats. Simultaneously, spatial memory deficit, PP-2A inhibition and tau hyperphosphorylation at Ser-198/Ser-199/Ser-202 (Tau-1 epitope) and Ser-396/Ser-404 (PHF-1 epitope) were observed. With the restoration of hippocampus Ach to normal levels at 48 and 72 h after the injection, the spatial memory deficits, PP-2A inhibition and tau hyperphosphorylation were reversed. It is suggested that injection of OA into the Meynert nucleus basalis of rats may impair the hippocampus-dependent spatial memory through damaging the cholinergic projection between the Meynert nucleus basalis and the hippocampus and the selective inhibition of PP-2A and tau hyperphosphorylation may be at least part of the underlying mechanisms.     

Prolonged arsenic exposure increases tau phosphorylation in differentiated SH-SY5Y cells: The contribution of GSK3 and ERK1/2

Arsenic is a metalloid that has been hypothesized to be an environmental risk factor for Alzheimer’s disease (AD), a disease having hyperphosphorylated tau aggregate as a marker. The present study demonstrated that prolonged exposure to sodium arsenite at low micromolar range (1−10 μM) reduced Tau 1 (recognizing dephosphorylated tau at residues 189–207) and elevated pS202 tau in differentiated human neuroblastoma SH-SY5Y cells indicating that arsenic increases tau phosphorylation in neurons. Sodium arsenite elevated GSK3β kinase activity, while GSK3 inhibitors, BIO, SB216763, and lithium, reversed the Tau 1 reduction by sodium arsenite. Additionally, sodium arsenite increased levels of active phosphorylation of ERK1/2, and inhibition of ERK1/2 by U0126 partially improved the Tau1 reduction. These results suggest that arsenic may cause tau hyperphosphorylation in neurons through the activation of GSK3 and ERK1/2. Furthermore, sodium arsenite augmented tau phosphorylation in the membrane and cytosolic fractions. Inductions of GSK3 activity by sodium arsenite treatment were observed in the membrane fraction, as evidenced by a reduction of β-catenin, a protein signaled for degradation following phosphorylation by GSK3. An enhancement of ERK1/2 phosphorylation by sodium arsenite was also witnessed in the cytosol. Additionally, sodium arsenite increased insoluble tau aggregation. These results suggest that arsenic induces tau hyperphosphorylation in the membrane fraction which may lead to its redistribution from the membrane fraction to the cytosol, where it promotes neurofibrillary formation. Collectively, we demonstrate that prolonged arsenic exposure increases tau phosphorylation, partly through GSK3 and ERK1/2 activation, and insoluble tau aggregates, hence possibly contributing to the development of sporadic AD.     

The effect of disodium 4-chloro-2-iminodibenzoate (CCA) on IgE levels and anaphylactic shock

The effect of disodium 4-chloro-2,2-iminodibenzoate (CCA) on IgE antibody response was examined in C3H/A and (BALB/c x C57BL/6J) F1 hybrid mice immunized with low doses of ovalbumin (OA) adsorbed on aluminium hydroxide gel. CCA administered orally at the doses of 5 and 50 mg/kg/day reduced IgE antibody production in these mice as determined by PCA test. High doses of CCA (100 mg/kg/day) given from day 7 before immunization of C57BL mice and during 1 week after immunization of mice with OA and Bordetella Pertussis Vaccine reduced the mortality of these mice subjected to anaphylactic shock on day 7 of immunization. CCA treatment was ineffective in anaphylactic shock of C57BL mice immunized with very high dose of OA, known to elicit little or no IgE antibody production but high IgG antibody response. The treatment of OA-immunized Guinea pigs with one oral dose of CCA (100 mg/kg) did not reduce mortality in protracted anaphylactic shock. Our results demonstrate that CCA inhibits IgE production as well as IgE mediated hypersensitivity reactions in mice.