不同方式构建A20鼠B细胞淋巴瘤动物模型

目的探索多种方式构建A20鼠B细胞淋巴瘤动物模型及不同方式造模成瘤的特征。方法鼠源性B细胞淋巴瘤细胞株A20经皮下、尾静脉、脾脏和腹腔接种于同源BALB/c小鼠或先接种裸鼠成瘤后组织块移植BALB/c小鼠,观察动物成瘤时间、成瘤率、成瘤部位;取肿瘤组织和动物脏器行石蜡包埋、病理切片、HE染色观察其组织学特点。结果BALB/c鼠皮下注2×10^6组、2×10^7组和裸鼠瘤组织移植BALB/c小鼠组成瘤率皆为100%,成瘤时间分别为（15.29±3.2）d（、7.0±0.82）d和（6.29±0.49）d。BALB/c小鼠尾静脉注射2×106组、2×107组、脾脏注射组、腹腔注射组成瘤率分别为71.4%、100%、71.4%、14.3%,成瘤时间分别为（76.8±12.0）d、（26.1±7.99）d、（32.6±5.99）d和27 d。尾静脉成瘤部位播及肝脏、脾脏、胰腺、肾脏、食道、胃、肠、肠系膜、脑、淋巴结、骨、子宫、肌肉等多脏器和组织。BALB/c鼠A20成瘤组织学类似人弥漫大B细胞淋巴瘤。结论成功构建A20皮下移植瘤模型、血行播散性模型,为利用有免疫功能动物进行B淋巴瘤相关研究提供了实验平台。     

两品系小鼠食物过敏模型的比较

目的比较两种不同品系小鼠食物过敏模型的敏感性和肠道菌群变化的差异,旨在为食物过敏模型的建立提供依据。方法分别对30只4~5周龄BALB/c和KM雌鼠用卵清蛋白(ovalbumin,OVA)致敏建立食物过敏模型,ELISA法检测小鼠血清OVA特异性IgE水平;HE染色观察空肠组织形态;采用DGGE技术检测粪便菌群的变化。结果 (1)30只致敏的BALB/c小鼠中有27只血清OVA特异性IgE水平明显升高(P0.001),而30只致敏的KM小鼠中有21只,且BALB/c小鼠空肠绒毛炎症细胞浸润、上皮脱落及坏死比KM小鼠明显;(2)食物过敏造模后,BALB/c小鼠肠道菌群的改变明显(P0.001),而KM小鼠中仅有均匀度改变显著(P0.05);(3)BALB/c小鼠和KM小鼠对照组肠道菌群的丰富度、Shannon指数及均匀度都有差异。结论 BALB/c小鼠对OVA的敏感性高于KM小鼠,不同品系小鼠肠道菌群结构不同,OVA处理后,BALB/c小鼠菌群的改变比KM小鼠更明显。     

中性粒细胞弹性蛋白酶在小鼠实验性结肠炎中的表达及意义

目的：观察中性粒细胞弹性蛋白酶（NE）在葡聚糖硫酸钠（DSS）诱导的小鼠实验性结肠炎中的表达情况并探讨其表达的意义。方法：健康雄性BALB/c小鼠随机分为正常对照组、模型组。模型组小鼠予5%DSS溶液自由饮用制备小鼠急性实验性结肠炎模型,正常对照组小鼠予蒸馏水自由饮用。每日观察小鼠的一般状况及疾病活动指数（DAI）评分,于实验第5、9天分批处死小鼠,取小鼠结肠行组织学损伤评分;ELISA法检测小鼠血浆中性粒细胞弹性蛋白酶浓度;Western blot法检测远端结肠组织中NE蛋白的表达。结果：与正常对照组相比,模型组小鼠在实验第5天及第9天DAI评分显著升高（P〈0.001）、结肠组织学损伤评分明显升高（P〈0.01）、血浆NE浓度明显升高（P〈0.01）、远端结肠NE蛋白表达增加显著（P〈0.001）。在实验第5天及第9天,模型组小鼠DAI评分与组织学损伤评分呈显著正相关（P〈0.05）,血浆中NE浓度及结肠中NE蛋白的表达与DAI评分、组织学评分均呈显著正相关（P〈0.05）。结论：NE在实验性结肠炎小鼠血浆及结肠组织中表达明显增加,且与疾病活动指数及组织学评分呈正相关,提示NE可能参与实验性结肠炎小鼠的发病。     

哺乳期BALB/c小鼠胆道梗阻模型的探索

目的探讨新生BALB/c小鼠胆道梗阻模型的建立,并与报告的新生BALB/c小鼠感染猕猴轮状病毒(RRV)模型小鼠生存曲线进行比较。方法将出生后5～7 d的BALB/c小鼠随机分为实验组和对照组,实验组进行胆总管结扎,然后关腹。对照组打开腹部后关腹不结扎胆总管。实验完成后每天观察小鼠的体重变化、无毛区皮肤颜色变化、小鼠存活天数以及在术后第5、10天时分别取小鼠肝脏做病理及免疫组化。结果小鼠在结扎后随着时间的延长,小鼠的体重及肝体比、无毛区皮肤颜色、存活天数、肝脏病理等都存在一定变化。小鼠体重增长逐渐缓慢,术后第2天就会出现无毛区的皮肤变黄,在尿道口会有淡黄色的液体并随后出现陶土样便。在术后第5天及第10天时取肝脏做肝体比有统计学差异(P≤0.05),小鼠在术后第10天左右会出现死亡高峰。结论新生BALB/c小鼠胆总管结扎模型是研究胆道梗阻的可靠动物实验,其生存曲线与报告的猕猴轮状病毒致胆道闭锁大体类似。     

小鼠脊髓损伤模型的建立及神经干细胞移植后运动功能恢复情况的研究

目的制作小鼠脊髓损伤打击模型,观察神经干细胞(NSCs)移植对脊髓损伤小鼠运动功能恢复及Nestin表达的影响。方法将50只小鼠随机分为空白组(5只)、模型组(15只)、对照组(15只)、治疗组(15只),运用改良Allen's法制备小鼠T10脊髓损伤模型并立即在损伤节段进行NSCs移植,于损伤后1、3、7、14、21d进行BBB评分,并通过免疫荧光法及荧光定量PCR检测Nestin的表达情况。结果所有脊髓打击后小鼠均出现双后肢瘫痪,但随时间延长运动功能可有不同程度恢复,NSCs移植14d后治疗组较模型组及对照组BBB评分显著增高(P0.05),且治疗组Nestin表达量也高于模型组及对照组。结论成功建立了小鼠脊髓损伤打击模型;移植的外源性神经干细胞在脊髓损伤处存活并促进损伤后小鼠运动功能的恢复。     

体外修饰树突状细胞诱导免疫耐受的研究

目的:探讨体外联合应用白细胞介素10(interleukin 10,IL-10)和甲基强的松龙(methylprednisolone,Medron)修饰供体树突状细胞(dendritic cell,DC)对小鼠皮肤移植术后免疫耐受的诱导效果,为抗移植术后免疫排斥反应治疗提供依据。方法:以健康成年C57BL/6小鼠为供体。BALB/c小鼠为受体,随机分为6组。除A组外,其余各组均于皮肤移植前3d自尾静脉输入对应的供体DC。具体对应关系如下:A组为空白对照,尾静脉输入生理盐水;B组为输入未修饰的DC;C组为20μg/L IL-10处理组;D组为10mg/L Medron处理组:E组为20μg/L IL-10 10mg/L Medron处理组。同时设立F组,为BALB/c对BALB/c的同种同基因皮片移植。各组行皮肤移植术,观察受体移植皮片存活情况。结果:E组的移植皮片存活时间最长,与其它各处理组相比P＜0．05,存在统计学差异。结论:用IL-10和甲强龙修饰的供体树突状细胞对受体进行预处理,可明显延长移植皮片的存活时间。     

人鼠肝组织嵌合体模型的制备

目的研究制备人鼠肝组织嵌合小鼠模型。方法将人骨髓干细胞直接注射到一定日龄胎鼠肝组织,每只注射移植约1×109人骨髓干细胞。用免疫组化对出生一定日龄移植小鼠肝脏进行甲胎蛋白免疫组织化学检测,检定分析人肝细胞在小鼠体内嵌合生长情况。结果移植人骨髓干细胞胎鼠出生2月龄、12月龄可检测到甲胎蛋白。结论将人骨髓干细胞移植小鼠肝脏内能够存活并分化成人肝细胞并能够长期存活。     

IL-10在输血相关性移植物抗宿主病小鼠模型中的免疫调节作用

目的:IL-10在输血相关性移植物抗宿主病小鼠模型中的免疫调节作用。方法:取BALB/c实验小鼠免疫活性淋巴细胞,分别输注于BALB/c小鼠(设为A组)及BALB/c裸鼠(设为B组),建立TA-GVHD模型,观察小鼠症状,HE染色判断小鼠肝、肺、小肠、皮肤病理变化情况;采用双夹心酶联免疫吸附法(ELISA)检测两组小鼠血清IL-10浓度;用逆转录聚合酶链反应法RT-PCR检测移植后外周血单个核细胞中IL-10的表达。结果:A组中2只死亡(12.5%),B组中3只死亡(18.75%),共5只死亡,29只存活,两组死亡率比较无明显差异(P>0.05)。B组小鼠累及肝、肺、小肠和皮肤病理损伤程度较A组严重;存活小鼠IL-10浓度较死亡小鼠明显升高(P2<0.05);存活小鼠IL-10 mRNA表达阳性率96.55%明显高于死亡小鼠(20.00%)。结论:IL-10在输血相关的移植物抗宿主病小鼠模型中发挥负向免疫调节--免疫抑制作用。     

Listr1遗传位点影响小鼠对约氏疟原虫易感性的研究

探讨Listr1遗传位点影响小鼠对疟原虫易感性的可能性及其初步作用机制。致死型约氏疟原虫(Plasmodiumyoelii17XL,P.y17XL)感染C.B6By-Listr1小鼠(BALB/c小鼠基因背景下引入C57BL/6小鼠Lis-tr1遗传位点的同类系小鼠)和BALB/c小鼠,分析二者生存率和感染率的差异;HE染色分析P.y17XL感染后第5天C.B6By-Listr1小鼠和BALB/c小鼠肝脏组织损伤情况;定量PCR法检测P.y17XL感染后小鼠肝脏组织第1、2、5天IL-1β、IL-6、TNF-α、IFN-γ的表达含量。结果显示,P.y17XL感染后4~8dC.B6By-Listr1小鼠虫血症水平显著高于BALB/c小鼠(P<0.05)。C.B6By-Listr1小鼠于感染后7~9d全部死亡;而半数BALB/c小鼠于感染后8~9d死亡,其余BALB/c小鼠至感染后第13天仍存活,两种小鼠生存率差异具有统计学意义(P<0.01)。C.B6By-Listr1小鼠P.y17XL感染后第5天肝组织HE染色可见到明显的疟色素沉积;而BALB/c小鼠全片基本未见到疟色素的沉积。P.y17XL感染后第2天BALB/c小鼠肝组织IL-6(P<0.05)、TNF-α(P<0.05)mRNA水平显著高于C.B6By-Listr1小鼠。结果表明Listr1遗传位点可以影响小鼠对疟原虫的易感性,与肝脏固有免疫相关。     

探讨接种时间和剂量对小鼠肺炎支原体肺炎模型建立的影响

目的 用不同时间和剂量建立BALB/c小鼠的肺炎支原体肺部感染模型,探索小鼠急性肺炎支原体感染的过程.方法 BALB/c小鼠随机分为Ⅰ、Ⅱ两组,Ⅰ组在0、1、2 d滴鼻接种肺炎支原体菌液3次,Ⅱ组在0 d滴鼻接种小剂量肺炎支原体菌液1次后于8、9 d再接种和Ⅰ组相同的肺炎支原体菌液2次,均设立不同剂量、批次的生理盐水对照组.全部实验动物在3～18 d内分批处死.所有小鼠均取肺组织做病理切片.以组织病理学评分来确定小鼠的肺部炎症反应程度.取肺组织匀浆及肺泡灌洗液(BALF)进行肺炎支原体培养做病原学检测.结果 接种后实验动物全部存活无死亡.实验组动物均出现不同程度的肺炎支原体肺炎样病理改变,组织病理学评分为1.5～14.3分,分别于第5、6天和第11天达到最高,平均分为4.9分;Ⅰ组实验组动物多呈轻、中度改变,Ⅱ组实验组动物多呈中、重度改变.所有实验组动物肺组织匀浆及BALF的肺炎支原体培养在接种后1月内先后出现阳性结果.对照组动物未出现明显肺部炎症改变,组织病理学评分为0～1分,肺炎支原体培养为阴性.结论 成功建立BALB/c小鼠的肺部肺炎支原体感染模型;组织病理学评分方法可用以评价肺部炎症反应的严重程度;不同接种时间和剂量所致的病变程度不同.     

Comparative immunomodulatory properties of adipose‐derived mesenchymal stem cells conditioned media from BALB/c,C57BL/6, and DBA mouse strains

Adipose tissue‐derived mesenchymal stem cells (AD‐MSCs) have been shown to be capable of differentiating into multiple cell type and exert immunomodulatory effects. Since the selection of ideal stem cell is apparently crucial for the outcome of experimental stem cell therapies, therefore, in this study we compared AD‐MSCs conditioned media (CM) from BALB/c, C57BL/6, and DBA mouse strains. No significant difference was found in the morphology, cell surface markers, in vitro differentiation and proliferation potentials of AD‐MSCs isolated from C57BL/6, BALB/c, and DBA mice. The immunological assays showed some variation among the strains in the cytokines, nitric oxide (NO), and indoleamine 2,3‐dioxygenase (IDO) production and immunomodulatory effects on splenocytes functions. Our results indicated a suppression of splenocytes proliferation in the presence of AD‐MSC CM from the three inbred mouse strains. However, BALB/c CM exerted a higher suppression of splenocytes proliferation. AD‐MSCs isolated from C57BL/6 and BALB/c mice produced higher levels of TGF‐β than those from DBA mice. Furthermore, IL‐17 and IDO production was higher in AD‐MSCs isolated from BALB/c mice. Our results indicated an increased production of TGF‐β, IL‐4, IL‐10, NO, and IDO by splenocytes in response to CM from BALB/c AD‐MSCs. In conclusion, our results showed that the immunomodulatory properties of mouse AD‐MSCs is strain‐dependent and this variation should be considered during selection of appropriate stem cell source for in vivo experiments and stem cell therapy strategies. J. Cell. Biochem. 114: 955–965, 2013. © 2012 Wiley Periodicals, Inc.     

抗脐带间充质干细胞表面分子噬菌体ScFv抗体库的构建及初步鉴定

目的：利用噬菌体展示技术构建抗脐带间充质干细胞表面分子噬菌体ScFv抗体库。方法：收集P3代培养的UC-MSCs免疫BALB/c小鼠,提取其脾细胞总RNA,RT-PCR扩增全套VH和VL基因片段,将其先后克隆入噬菌粒pSEX81中,构建成完整的噬菌体ScFv抗体库。结果:构建的噬菌体ScFv抗体库的库容为2×107cfu,ScFv插入重组率为93％,BstN1酶切图谱呈不同多样性。ScFv抗体库经3轮初步筛选后插入重组率达100％,3个克隆出现了相同的酶切图谱,并且随着筛选次数的增加,输出/输入比明显提高,这说明抗体库得到了特异性富集。结论：成功地构建了抗脐带间充质干细胞表面分子噬菌体ScFv抗体库,这为将来筛选特异性抗体和进一步用于间充质干细胞表面特异性分子研究奠定了坚实的基础。     

Sex and Genetic Factors Determine Osteoblastic Differentiation Potential of Murine Bone Marrow Stromal Cells

Sex and genetic factors determine skeletal mass, and we tested whether bone histomorphometric parameters were sexually dimorphic in femurs from 1 to 6 month old C57BL/6 mice. Trabecular bone volume declined more rapidly in female mice than in male littermates because of enhanced bone resorption. Although bone formation was not different between sexes, female mice exhibited a higher number of osteoblasts than male littermates, suggesting that osteoblasts from female mice may have a reduced ability to form bone. To determine the impact of sex on osteoblastogenesis, we investigated the potential for osteoblastic differentiation of bone marrow stromal cells from C57BL/6, Friend leukemia virus-B (FVB), C3H/HeJ and BALB/c mice of both sexes. Bone marrow stromal cells from female FVB, C57BL/6 and C3H/HeJ mice exhibited lower Alpl and Osteocalcin expression and alkaline phosphatase activity, and formed fewer mineralized nodules than cells from male littermates. Proliferative capacity was greater in cells from male than female C57BL/6, but not FVB, mice. Sorting of bone marrow stromal cells from mice expressing an α-Smooth muscle actin-green fluorescent protein transgene, revealed a higher yield of mesenchymal stem cells in cultures from male mice than in those from female littermates. Sex had a modest impact on osteoblastic differentiation of mesenchymal stem cells. To determine the influence of sex and genetic factors on osteoblast function, calvarial osteoblasts were harvested from C57BL/6, FVB, C3H/HeJ and BALB/c mice. Alpl expression and activity were lower in osteoblasts from C57BL/6 and C3H/HeJ, but not FVB or BALB/c, female mice than in cells from littermates. Sex had no effect on osteoclastogenesis of bone marrow cultures of C57BL/6 mice, but osteoblasts from female mice exhibited higher Rankl and lower Opg expression than cells from male littermates. In conclusion, osteoblastogenesis is sexually dimorphic and influenced by genetic factors.     

Comparison of intestine and bone marrow radiosensitivity of the BALB/c and the C57BL/6 mouse strains and their B6CF1 offspring

The radiosensitivity as measured by LD50/6 or LD50/30 of the F1 hybrid B6CF1 (C57BL/6 X BALB/c) is similar to that of C57BL/6 mice but markedly different from BALB/c. The LD50/6 for BALB/c mice was about 8.8 Gy compared to 16.4 Gy for the B6CF1. The difference in LD50/6 between the parent strains or between BALB/c and the F1 hybrid could not be explained by any differences in crypt cell number, cell cycle time, or transit time. Likewise, the observed differences in the LD50/6 do not appear to result from marked differences in the radiosensitivity of marrow stem cells (CFU-S) since the D0's for the three genotypes of mice were similar. Also, there were no apparent differences in the red blood cell contents of several enzymes associated with antioxidant defenses. The microcolony assay was used to determine the D0 for the crypt clonogenic cells and the D0 values for 60Co gamma rays were about 0.8 Gy for BALB/c mice and 1.4 Gy for B6CF1 mice. However, the D0 values for JANUS fission neutrons were similar; 0.6 Gy for the BALB/c mice and 0.5 for the B6CF1 mice. A comparison of clonogenic cell kinetics, using prolonged colcemid block to distinguish between slowly and rapidly cycling cells suggest that, normally, the stem cells are slowly cycling in both the BALB/c and the B6CF1 hybrid. However, the stem cells of the B6CF1 appear to go into rapid cell cycle more rapidly than those of the BALB/c following irradiation or prolonged colcemid treatment. The more rapid recovery in intestinal epihelial cell production in the B6CF1 hybrid after irradiation may provide an increased mucosal barrier and may, in part, explain the difference in the response to radiation compared to that in the BALB/c.     

Effect of mouse genotype on the hematopoietic stem cell count. II. The number of hematopietic stem cells in BALB/c and CC57BR strain mice differing by the level of endogenous colony formation]

The number of stem hematopoietic cells in the hematopoietic organs of mice of BALB/c and CC57BR strains and (CC57BRXBALB/c)F1 hybrids was studied by the method of exogenous colony-forming units. The assay of migration of stem cells from the bone marrow to the spleen was carried out. It was found that the spleen and the bone marrow of mice of the studied genotypes contain approximately the same relative number of hematopoietic stem cells. The number of stem cells which migrate from the bone marrow to the spleen is greater in the mice of BALB/c strain than in the CC57BR mice.     

Effects of allogeneic bone marrow-derived mesenchymal stem cells on T and B lymphocytes from BXSB mice

Bone marrow-derived mesenchymal stem cells (bMSCs) can differentiate into a number of different cell/tissue types, and also possess immunoregulatory functions. The present study was undertaken to elucidate the exact immunoregulatory effects of allogeneic bMSCs on T- and B-lymphocyte proliferation, activation, and function maturation of BXSB mice, which has been considered as a experimental model for human systemic lupus erythematosus (SLE). We determined that bMSCs from BALB/c mice had inhibitory effects on BXSB mice T-lymphocyte proliferation, but no inhibitory effect on their activation. In addition, they had a significant inhibitory and stimulatory effect on IL-4- and IFN-gamma-producing T cells, respectively. Also, bMSCs had inhibitory effects on the proliferation, activation, and IgG secretion of B lymphocytes. In addition, BALB/c bMSCs had an enhancing effect on CD40 expression and inhibitory effects on CD40 ligand (CD40L) ectopic hyperexpression on B cells from BXSB mice.     

BALB／c小鼠胚胎干细胞系的建立及其嵌合体小鼠的获得

目的：建立BALB/c小鼠胚胎干细胞系,并用于制作嵌合体小鼠。方法：从BALB／c小鼠囊胚内分离培养内细胞团块。建系后,进行C57BL／6L小鼠受体囊胚腔注射,制作嵌合体小鼠,结果：建立了我国第一株BALB／c小鼠胚胎干细胞系,该细胞系具有典型的ES细胞形态,碱性磷酸酶强阳性,核型正常以及具有分化为三种胚层组织的能力,并已产生5只嵌合体小鼠,结论：建立的BALB／c小鼠胚胎干细胞系具有胚胎干细胞的各种特点,可用于体内外诱导分化研究,在进一步观察生殖系嵌合情况后,决定是否可应用于基因打靶等转基因动物的制作。     

Hypoxia increases erythropoiesis and decreases thrombocytopoiesis in mice: a comparison of two mouse strains

Several previous studies have shown that hypoxia increases erythropoiesis and decreases thrombocytopoiesis in mice. It has been postulated that the thrombocytopenia is caused by stem cell competition between the erythrocytic and megakaryocytic cell lines. In the present work, we compared the effects of severe hypoxia (5.5-6.0% O2) in both male and female C3H and BALB/c mice by measuring their abilities to produce red blood cells and platelets. All mice had significant increases in packed cell volumes and marked decreases in platelet production after hypoxia; however, there were significant differences in the degree of stimulation in the two mouse strains. After 14 days of hypoxia, the percentage of 35S incorporation into platelets, total circulating platelet counts and total circulating platelet masses were lower in C3H mice than in BALB/c mice, but platelet sizes were larger. Also, hypoxia caused greater changes in male mice than in female mice, with male C3H mice showing the greatest increase in packed cell volumes and the lowest platelet counts of all mice tested. The least responses were observed in female BALB/c mice. BALB/c mice had higher P50 (right-shifted O2 dissociation curves) and lower erythrocyte 2,3-diphosphoglycerate values than C3H mice, indicating a lower hemoglobin O2 affinity for BALB/c mice. The results indicate that the effects of hypoxia are not direct upon platelet production, but that the thrombocytopenia is a result of stimulation of erythropoiesis. These data support the stem cell competition hypothesis and illustrate that the degree of the inverse relationship between red blood cells and platelet production of hypoxic mice is dependent, to a large degree, upon the sex and strain of mice that are used.     

Immunoregulation of localized and disseminated murine myeloma: antigen-specific regulation of MOPC-315 stem cell proliferation and secretory cell differentiation.

Tumor development, MOPC-315 stem cells, and M315-secretory cells were quantitated in carrier-primed BALB/c mice that had been challenged subcutaneously or i.v. with mixtures of TNP-carrier and TNP-binding MOPC-315 cells. We observed that tumor incidence, myeloma stem cells, and secretory myeloma cells were: i) suppressed in mice in whom carrier-specific suppressor T cells had previously been induced and ii) initially ehnahced in mice with carrier-specific helper T cells. The early enhancement in mice with carrier-specific helper T cells was followed by progressively declining myeloma stem cell frequencies and regression of established tumors. These studies demonstrate that T cell-derived immunoregulators of host origin can be focused onto localized and disseminated malignant B cells and specifically regulate the expansion and differentiation of the neoplastic clone.     

Differences between IL-4- and IL-4 receptor alpha-deficient mice in chronic leishmaniasis reveal a protective role for IL-13 receptor signaling.

IL-4 receptor alpha-chain-deficient (IL-4Ralpha-/-) mice were generated by homologous and site-specific recombination, using the Cre/loxP system in BALB/c-derived embryonic stem cells. In vitro analysis of cells from these mice revealed impaired IL-4- and IL-13-mediated functions, demonstrating that the IL-4Ralpha-chain is an essential component of both the IL-4 and the IL-13 receptor. Whereas Leishmania major-infected BALB/c mice developed fatal progressive disease with type 2 Ab responses within 3 mo, both IL-4Ralpha-/- and IL-4-/- BALB/c mice contained infection with reduced footpad swelling, parasite load, moderate histopathology, and type 1 Ab responses during this time period. Conclusively, these results demonstrate an IL-4-dependent mechanism of susceptibility in BALB/c mice. Nevertheless, in contrast to mutant mice, infected C57BL/6 mice healed completely within 3 mo, indicating that additional factors are necessary for subsequent healing and elimination of the pathogen. During the further course of infection, IL-4Ralpha-/- mice developed progressive disease with massive footpad swelling. Lesions became ulcerative and necrotic with subsequent destruction of connective tissue and bones, as well as dissemination into organs and consequent mortality within the monitored 6 mo of chronic infection. In striking contrast, IL-4-/- mice maintained control of infection on a moderate level, but were unable to clear the pathogen. The distinct phenotypes of the BALB/c embryonic stem cell-derived IL-4-/- and IL-4Ralpha-/- mouse strains identify previously unsuspected mechanisms for maintaining host immunity to chronic infection with L. major, mediated by a functional IL-13 receptor.