γ－干扰素在淋巴细胞介导的子宫颈角化上皮细胞毒作用中的意义

本研究以子宫颈角化上皮为靶细胞，用试管培养技术及非同位素细胞毒性试验，探讨了干扰素（ＩＦＮ－γ）对淋巴细胞介导的对宫颈角化上皮细胞毒作用的影响及细胞间吸附分子１（ＩＣＡＭ－１）与白细胞功能相关抗原１（ＬＦＡ－１）在细胞毒作用中的意义。结果显示ＣａＳｋｉ、ＳｉＨａ、ＨｅＬａ、Ｗ１２及ＮＣｘ均为ＮＫ抵抗、ＬＡＫ敏感细胞。ＩＦＮ－γ预处理靶细胞明显增加ＬＡＫ细胞的杀伤活性，但对ＮＫ活性影响不大；ＩＦＮ－γ预处理效应细胞可增强ＬＡＫ细胞对上述靶细胞的溶解作用，但并不改变ＮＫ对靶细胞的选择性；抗ＩＣＡＭ－１与ＬＦＡ－１单克隆抗体能有效地降低ＬＡＫ细胞对靶细胞的杀伤作用，而抗ＨＬＡＡＢＣ及ＨＬＡＤＲ则无此作用。提示ＩＦＮ－γ仅对ＬＡＫ细胞介导的对宫颈角化上皮的细胞毒作用有明显增强作用，而对ＮＫ细胞无明显影响；ＩＣＡＭ－１－ＬＦＡ－１通路为ＬＡＫ细胞结合并溶解靶细胞的主要通路，且这种细胞毒作用是非ＭＨＣ限制的。     

N—CWS激活小鼠巨噬细胞抗肿瘤作用的研究

Ｎ－ＣＷＳ在线只鼠体内１００－２００μｇ可明显抑制Ｂ１６黑色素瘤细胞在Ｃ５７ＢＬ／６小鼠体内的生长。Ｎ－ＣＷＳ腹腔给药后３天可明显增强小鼠脾脏自然钉伤细胞（ＮＫ）和腹腔巨噬细胞的杀伤活性，认为Ｎ－ＣＷＳ的抑制Ｂ１６黑色素瘤作用与其激活小鼠细胞免疫功能有关。体外实验结果表明，当有ＩＦＮ－γ存在的条件下，Ｎ－ＣＷＳ对小鼠腹腔Ｍψ释放ＮＯ及ＴＮＦ都具有显著促进作用，认为这一作用与Ｎ－ＣＷＳ激活小鼠腹腔Ｍ     

γ—干扰素在淋巴细胞介导的子宫颈角化上皮细胞毒…

本研究以子宫颈角化上皮为靶细胞，用试管培养技术及非同位素细胞毒性试验，探讨了干扰素（ＩＦＮ－γ）对淋巴细胞介导的对宫颈角化上皮细胞毒作用的影响及细胞间吸附分子１（ＩＣＡＭ－１）与白细胞功能相关抗原１（ＬＦＡ－１）在细胞毒作用中的意义。结果显示ＣａＳｋｉ、Ｓｉｈａ、ＨｅＬａ、Ｗ１２及ＮＣｘ均为ＮＫ抵抗、ＬＡＫ敏感细胞。ＩＦＮ－γ预处理靶细胞明显增加ＬＡＫ细胞的杀伤活性，但对ＮＫ活性影响不大；ＩＦＮ－     

CHANGES OF 6-K-PGF_(1a) RELEASE FROM THE LUMINAL SURFACE OF DACRON SEEDED WITH AUTOLOOUS VENOUS TISSUE FRAGMENTS

ＣＨＡＮＧＥＳＯＦ６－Ｋ－ＰＧＦ１ａＲＥＬＥＡＳＥＦＲＯＭＴＨＥＬＵＭＩＮＡＬＳＵＲＦＡＣＥＯＦＤＡＣＲＯＮＳＥＥＤＥＤＷＩＴＨＡＵＴＯＬＯＯＵＳＶＥＮＯＵＳＴＩＳＳＵＥＦＲＡＧＭＥＮＴＳＣＨＡＮＧＥＳＯＦ６－Ｋ－ＰＧＦ１ａＲＥＬＥＡＳＥＦＲＯＭＴＨ...     

白细胞介素4基因转移的肿瘤细胞体内诱导杀伤细胞活性及细胞因子产生的实验研究

观察了小鼠接种高分泌ＩＬ－４的黑色素瘤细胞后体内免疫效应细胞（包括ＣＴＬ、ＮＫ细胞及ＬＡＫ细胞）抗肿瘤活性及其分泌的细胞因子（包括ＩＬ－２、ＩＦＮ－ｒ、ＴＮＦ及ＧＭ－ＣＳＦ）水平的变化，荷瘤后第１５天小鼠脾细胞ＮＫ活性及经诱导后的ＬＡＫ活性有所降低，而经诱导后的ＣＴＬ杀伤活性显著升高，荷瘤小鼠腹腔内巨噬细胞杀伤活性及其分泌的ＩＬ－１水平也明显升高；在荷瘤后第４天及第１２天出现两个高峰，实验结果表明，高分泌ＩＬ－４的黑色素瘤细胞体内生长受抑制是因为ＩＬ－４基因的导入及ＩＬ－４的分泌使体内ＣＴＬ及巨噬细胞杀伤活性提高，因而使机体抗肿瘤免疫功能得以增强。     

TNF基因转染的肿瘤细胞体内诱导免疫细胞杀伤活性的研究

本文观察了小鼠接种高分泌ＴＮＦ－α的Ｂ１６黑色素瘤细胞后体内免疫细胞杀伤活性的变化。实验结果发现：接种Ｂ１６－ＴＮＦ－α＾＋后第１５天，小鼠脾细胞ＮＫ活性和诱导后的ＬＡＫ活性显著高于对照组，而经诱导后的ＣＴＬ杀伤活性则无显著变化。     

双歧杆菌表面分子对LPS在小鼠体内调节胸腺细胞凋亡的观察

目的研究双歧杆菌表面分子细胞壁肽聚糖（ＷＰＧ）、脂磷壁酸（ＬＴＡ）对ＬＰＳ体内诱导小鼠胸腺细胞凋亡的调节。方法用ＤＮＡ凝胶电泳、ＴＵＮＥＬ法检测ＷＰＧ、ＬＴＡ对ＬＰＳ体内诱导小鼠胸腺细胞凋亡的影响,并分别用生物活性法和Ｇｒｉｅｓｓ反应测定ＷＰＧ、ＬＴＡ、ＬＰＳ体外诱生ＴＮＦ－α、ＮＯ２－的含量。结果ＷＰＧ、ＬＴＡ可显著抑制ＬＰＳ体内诱导的小鼠胸腺细胞的凋亡。ＷＰＧ、ＬＴＡ单独刺激巨噬细胞时所诱生的ＴＮＦ－α、ＮＯ的量显著低于ＬＰＳ刺激时所产生的这两种活性介质的量,而ＷＰＧ、ＬＴＡ与ＬＰＳ共同应用时可显著降低ＬＰＳ诱导巨噬细胞产生的ＴＮＦ－α、ＮＯ的量;诱生型一氧化氮合成酶抑制剂Ｓ－甲基异硫脲硫酸盐体外可抑制巨噬细胞产生的ＮＯ的量,在体内可部分抑制ＬＰＳ诱导的小鼠胸腺细胞的凋亡。结论ＷＰＧ、ＬＴＡ与ＬＰＳ共同应用时,可抑制ＬＰＳ诱导的巨噬细胞产生的ＴＮＦ－α、ＮＯ的量,从而下调ＬＰＳ体内诱导小鼠胸腺细胞的凋亡     

人重组粒细胞集落刺激因子突变体的构建、表达和其体内外生物学活性研究

目的为提高人重组粒细胞集落刺激因子（ｈｕｍａｎｒｅｃｏｍｂｉｎａｎｔｇｒａｎｕｌｏｃｙｔｅｃｏｌｏｎｙ－ｓｔｉｍｕｌａｔｉｎｇｆａｃｔｏｒ,ｒｈＧ－ＣＳＦ）的稳定性和活性,对ｒｈＧ－ＣＳＦ进行改造和体内、外活性研究。方法利用定向点突变技术,将人重组粒细胞集落刺激因子第１７位游离的半胱氨酸编码序列突变为丙氨酸序列,ＤＮＡ序列分析证明后,在大肠杆菌中表达突变蛋白。利用Ｇ－ＣＳＦ依赖细胞株ＮＦＳ－６０,对在不同温度及在人血浆中保存的Ｇ－ＣＳＦ蛋白（Ｇ－ＣＳＦ－Ａｌａ１７）和野生型的Ｇ－ＣＳＦ进行活性测定。腹腔注射后小鼠外周血白细胞计数检测其体内生物学活性。结果ＤＮＡ序列分析表明１７位半胱氨酸突变为丙氨酸,并在大肠杆菌中表达成功Ｇ－ＣＳＦ－Ａｌａ１７。纯化的突变蛋白对ＮＦＳ－６０细胞具有刺激活性;与野生型Ｇ－ＣＳＦ相比,在各种温度储存的突变蛋白保留更高的活性,与人血浆孵育５０小时后突变蛋白仍保持活性;小鼠一次性体内注射突变蛋白后外周血白细胞数明显高于野生型Ｇ－ＣＳＦ。结论Ｇ－ＣＳＦ突变体（Ｇ－ＣＳＦ－Ａｌａ１７）较野生型的Ｇ－ＣＳＦ具有更高的体外稳定性和体内造血刺激活性。     

IL－12－NK细胞剌激因子的研究进展

ＩＬ－１２又称ＮＫ细胞刺激因子（ＮＫＳＦ），是最近才被纯化、鉴定的一种新型细胞因子。它是由二硫键相连的异二聚体，其分子量为７０ｋＤ，它的基因也已被克隆。ＮＫＳＦ其有多种生物学功能，它能诱导外周血淋巴细胞（ＰＢＬ）产生ＩＦＮ－γ，增强ＮＫ细胞介导的细胞毒活性，增强丝裂原激活的Ｔ细胞增殖，增强ＩＬ－２对ＬＡＫ活性的诱导。由于ＮＫＳＦ对免疫活性细胞的诱导和调节功能，提示它在肿瘤和病毒性疾病的生物免疫治疗中起着重要作用。     

人胎脾抗癌效应细胞及相关细胞因子的胚胎发育动力学研究

对不同胎龄胎脾抗癌效应细胞及相关细胞因子的胚胎发育动力学进行了系统观测。结果显示：２０周龄前基本无ＮＫ活性和Ｍ杀伤功能，但可随胎龄增长而逐渐加强，至出生前后已接近成人水平，ＬＡＫ活性在１６周龄即与成人基本相同。ＩＬ－２，ｒＦＮ－α和ＩＬ－６能分别促进ＮＫ和ＬＡＫ活性。胎脾Ｍ２０周龄即合成高水平ＩＬ－６，出生前已显著高于成人，３２周龄时分泌ＩＬ－１的能力达成人水平，ＴＮＦ活性达高峰。ＦＳＭＣ合成ＩＬ－２的能力在３６周龄才达成人水平，合成的ＩＬ－６至出生前仍低于成人。ＦＳＭＣ的ＨＬＡ－ＤＲ抗原表达显著低于成人。因此以胎脾细胞作为抗癌效应细胞来源是安全、有效、可行的。     

Isolation and characterisation of herpes simplex virus type 1 mutants which fail to induce dUTPase activity

The herpes simplex virus (HSV) type 1 dUTPase gene was inactivated by insertion of HindIII oligonucleotide linker sequences into the KpnI site within the coding region of the cloned gene. The mutated gene was introduced into wild type herpes simplex virus by marker rescue and the recombinants were identified by the acquisition of a HindIII site within genome map coordinates 0.69 to 0.70 and the failure to induce virus-specific dUTPase activity. A spontaneous dUTPase deficient mutant, which had an identical restriction endonuclease DNA pattern to wild type virus, was also isolated from this transfection experiment. Both types of dUTPase-negative mutants failed to induce a virus-specific 39,000 mol wt polypeptide. Cells infected with the insertional mutant contained instead a novel polypeptide about 40,000 mol wt. No abnormal virus specific polypeptide was detected in cells infected with the spontaneous mutant. We conclude that the 39,000 mol wt polypeptide induced by wild type HSV-1 is the virus-coded dUTPase. Since both types of mutants grew well in exponentially growing and serum-starved tissue culture cells in the absence of wild type helper virus, the dUTPase is not required for virus replication under these conditions. Thymidine kinase deficient, dUTPase deficient double mutants were constructed by recombination of a thymidine kinase insertional mutation into dUTPase deficient virus. These mutants also grew as well as wild type virus both in normal tissue culture cells and cells lacking the cellular thymidine kinase.     

常见乙型肝炎病毒表面抗原突变体的抗原性分析

目的：研究乙型肝炎病毒（HBV）表面抗原突变株和野毒株对表面抗体结合能力的差异,探讨免疫漏检基因变异株的机制及对策。方法：应用基因重组技术构建HBsAg常见基因突变株和野毒株表达质粒,分别在COS－7细胞中瞬时表达,定量后用常规HBsAg免疫诊断试剂盒检测,观察重组抗原与不同抗－HBs的结合能力。结果：T126 S变异与单克隆抗体的结合力增高,G145R,K141 E和2株三位点同时变异株则明显下降,对M133T变异与单克隆抗体的结合力影响不大。变异株与多克隆抗体的结合力也有变化,但仍能检测到大部分变异株抗原。结论:“a”抗原决定簇氨基酸的置换影响了HBsAg与抗－HBs的结合能力,并且氨基酸的置换位置和特性对抗原性的影响各有不同。因此,建议应用HBsAg多克隆抗体或开发研制“免疫逃逸突变株”的特异性抗体,以完善HBsAg免疫诊断试剂的抗体组成,减少免疫诊断对常见基因变异株的漏检。     

Isolation and characterization of mini-Tn5Km2 insertion mutants of enterohemorrhagic Escherichia coli O157:H7 deficient in adherence to Caco-2 cells

Adherence of enterohemorrhagic Escherichia coli (EHEC) to intestinal epithelium is essential for initiation of the infection. To identify genes involved in adherence, an EHEC O157:H7 strain (O157Sakai) was mutagenized by mini-Tn5Km2, where Km refers to kanamycin resistance, and 4,677 insertion mutants were screened for their ability to form microcolonies (MC) on Caco-2 cells. The less adherent mutants were divided into three groups: those with no adherent ability (designated as class 1 mutants, n = 10), those less adherent than the wild type (class 2 mutants, n = 16), and those unable to form MC but which adhered in a diffuse manner (class 3 mutants, n = 1). The sites of insertion in class 1 mutants were all found within genes of the locus for enterocyte effacement (LEE) thought to be required for type III protein secretion. Indeed, the class 1 mutants failed to secrete type III secreted proteins such as EspA and Tir into the culture medium. The insertions in class 2 mutants were outside the LEE, and all the mutants except one were able to secrete type III proteins into the culture medium. The class 3 mutant had the insertion in the tir gene in the LEE and was deficient in Tir and intimin expression, suggesting that in the absence of intimin-Tir, O157Sakai can still adhere to Caco-2 cells but in a diffused manner. This was confirmed by construction of a nonpolar eae (encoding intimin) mutant. Examination of the eae mutant together with O157Sakai and one of the class 1 mutants for the ability to form MC revealed that EHEC initially adhered diffusely at 1.5 h after infection. Following washing out of the nonadherent bacteria, while wild-type EHEC bacteria developed MC for another 2 to 3 h on Caco-2 cells, the eae mutant diffusely adhered throughout the infection without forming MC. MC with O157Sakai but not the diffusely adherent eae mutant could evoke F-actin condensation beneath the bacterium. Our results suggest that EHEC encodes additional adherence-associated loci and that the type III secreted proteins are involved in the initial diffuse adherence, while the intimin-Tir interaction is required for the subsequent development of MC.     

G145R突变后HBsAg"a"决定簇合成肽的免疫学特性分析

目的研究G145R突变后乙肝表面抗原(HBsAg)"a"决定簇合成肽的免疫学特性改变情况. 方法首先合成2条短肽P1-wt和P2-145R,分别代表野毒株和G145R突变后HBsAg"a"决定簇合成肽.然后用β-巯基乙醇(2-ME)变性试验以及用乙肝疫苗标准品制备的小鼠多抗血清研究2条合成肽的空间构象以及抗原性异同.最后用等量合成肽免疫小鼠,用酶免疫法、竞争抑制试验和Western blot试验等研究G145R突变后"a"决定簇合成肽的免疫原性改变.结果合成肽P1-wt和P2-145R用2-ME温和变性后,PAGE结果表现为相对分子质量(Mr)为4×103左右的单一条带,而变性前2条合成肽均表现为Mr是从4×103到30×103的弥漫条带,主带位置在5×103和10×103,分别相当于二聚体和四聚体位置;用HBsAg的多克隆抗体(anti-HBs)检测合成肽的抗原性,结果在固定抗原量的前提下,在抗体1∶32 000稀释时仍可检测到P1-wt的阳性结果,而当同一抗体稀释到1∶8000时,P2-145R检测结果即为阴性.合成肽P2-145R免疫小鼠产生的抗体与P1-wt合成肽的反应滴度比与P2-145R合成肽本身的反应低4～8倍. 结论针对HBsAg"a"决定簇合成肽可自发形成一定的空间构象,G145R突变株的HBsAg"a"决定簇的抗原性和免疫原性与野毒株相比发生了明显改变,为正确评价G145R变异株的流行危害以及现行疫苗的保护效果提供了实验依据.     

Cold-passaged human parainfluenza type 3 viruses contain ts and non-ts mutations leading to attenuation in rhesus monkeys.

Cold-passaged (CP) mutants derived from the JS strain of wild type wt parainfluenza type 3 virus (PIV3) are being evaluated as candidate live virus vaccines. The wt virus was serially passaged 45 times at low temperature and mutant clones with the cold-adapted (CA), temperature-sensitive (ts), and attenuation (ATT) phenotypes were selected following passage levels 12, 18 and 45 (cp12, cp18, and cp45). The cp45 virus was more ts than the cp12 or cp18 mutants, although all 3 mutant viruses were clearly attenuated in rhesus monkeys compared to wild type virus. The mean peak titers of the cp12 and cp18 viruses administered by the intratracheal route were at least 6000-fold lower than JSwt in both the upper and lower respiratory tracts. The cp45 virus was not recovered from monkeys administered virus by the i.t. route alone; however, when the cp45 virus was administered by the intranasal route, it replicated in the upper respiratory tract to a level comparable to that of the cp12 and cp18 viruses, but continued to be markedly restricted in the lower respiratory tract. These data indicate that the cp12 and cp18 viruses contain predominantly non-ts attenuating mutations whereas the cp45 mutant has both non-ts and ts attenuating mutations. Each of the CP mutants induced a high level of resistance to wild type virus challenge. Also, the ATT phenotype of the cp12 and cp18 viruses as measured in rhesus monkeys was stable after replication in chimpanzees or humans, respectively, although the ts phenotype was not. Based on its greater level of temperature sensitivity in vitro and its greater degree of attenuation in rhesus monkeys, the cp45 virus appears to be the most promising vaccine candidate for humans.     

Poxvirus deletion mutants: virulence and immunogenicity

Post-vaccinial encephalitis and disseminated vaccinia are major concerns with the use of vaccinia virus recombinants as immunization vectors in man. To identify and characterize possible attenuated poxvirus vectors, rabbitpox virus (RPV) (closely related to vaccinia) and four deletion mutants of RPV were studied for organ tropism, neurovirulence, and protection from wild-type challenge in BALB/c mice. Intraperitoneal (IP) inoculation with 10(7) PFU wild-type (wt) RPV or with two mutants 8 sm and 28 (containing approximately 12 kilobase deletions) showed titers of greater than 10(3) PFU/g tissue in multiple organs. In contrast, IP inoculation of 10(7) PFU of mutants 31 or 23 (containing approximately 30 kilobase deletions) showed markedly reduced growth in all organs. Neurovirulence of wt and mutant RPV was determined by intracerebral (IC) inoculation of mice. Wt and mutants 8 sm, and 28 RPV had LD50 less than 10(2) PFU; in contrast, 31 and 23 had LD50 greater than 10(5) PFU. Finally, 10(6) PFU of mutants 31 or 23, were administered to mice by scarification, the normal route of vaccinia immunization. Both 31 and 23 grew locally in the skin and protected mice challenged IC at 21 days with 100 LD50 of wt RPV, while all unimmunized controls died. We conclude that deletion mutants 31 and 23 demonstrate markedly reduced invasiveness and neurovirulence while retaining immunogenicity. Similar deletion mutations in vaccinia may create avirulent, but effective vaccine vectors for man.     

Generation of Yersinia pestis attenuated strains by signature-tagged mutagenesis in search of novel vaccine candidates

In a search for novel attenuated vaccine candidates for use against Yersinia pestis, the causative agent of plague, a signature-tagged mutagenesis strategy was used and optimized for a subcutaneously infected mouse model. A library of tagged mutants of the virulent Y. pestis Kimberley53 strain was generated. Screening of 300 mutants through two consecutive cycles resulted in selection of 16 mutant strains that were undetectable in spleens 48 h postinfection. Each of these mutants was evaluated in vivo by assays for competition against the wild-type strain and for virulence following inoculation of 100 CFU (equivalent to 100 50% lethal doses [LD50] of the wild type). A wide spectrum of attenuation was obtained, ranging from avirulent mutants exhibiting competition indices of 10(-5) to 10(-7) to virulent mutants exhibiting a delay in the mean time to death or mutants indistinguishable from the wild type in the two assays. Characterization of the phenotypes and genotypes of the selected mutants led to identification of virulence-associated genes coding for factors involved in global bacterial physiology (e.g., purH, purK, dnaE, and greA) or for hypothetical polypeptides, as well as for the virulence regulator gene lcrF. One of the avirulent mutant strains (LD50, >10(7) CFU) was found to be disrupted in the pcm locus, which is presumably involved in the bacterial response to environmental stress. This Kimberley53pcm mutant was superior to the EV76 live vaccine strain because it induced 10- to 100-fold-higher antibody titers to the protective V and F1 antigens and because it conferred efficacious protective immunity.     

Different Glycosylation Pattern of Human IgG1 and IgG3 Antibodies Isolated from Transiently as well as Permanently Transfected Cell Lines

The effector functions of IgG depend on the presence of carbohydrates attached to asparagine 297 in the Fc‐portion. In this report, glycosylation profiles of recombinant wild‐type and mutant IgG1 and IgG3 antibodies produced from three cell lines were analysed using LC‐ESI‐Orbitrap. Clear differences were detected between IgG1 and IgG3 glycoforms, where IgG1 generally contained fucosylated glycoforms, whilst IgG3 mainly were non‐fucosylated. When using NS‐0 and J558L cells for permanent transfection, IgG1 wt glycoforms differed between the two cell lines, whilst IgG3 wt glycoforms did not. Transiently transfected HEK 293E cells were used to produce IgG1 and IgG3 wt and mutants, affecting complement activation. Cell supernatants were harvested at early and late time points and analysed separately. IgGs harvested late showed simpler and less developed glycosylation structure compared to those harvested early. The IgG harvested early was slightly more effective in complement activation than those harvested late, whilst the antibody‐dependent cell‐mediated cytotoxicity was unaltered. Generally, the glycosylation pattern of the mutants tested, including a hinge truncate mutant of IgG3, did not differ significantly from the wild‐type IgGs. The striking difference in glycosylation pattern of IgG1 compared to IgG3 therefore appears not to be due to the long hinge region of IgG3 (62 amino acids) relative to the IgG1 hinge region (15 amino acids). Furthermore, mutation variants at or near the C1q binding site showed similar glycosylation structure and difference in their complement activation activity observed earlier is thus most likely due to differences in protein structure only.     

Enterohemorrhagic Escherichia coli O157:H7 gal mutants are sensitive to bacteriophage P1 and defective in intestinal colonization

Enterohemorrhagic Escherichia coli (EHEC), especially E. coli O157:H7, is an emerging cause of food-borne illness. Unfortunately, E. coli O157 cannot be genetically manipulated using the generalized transducing phage P1, presumably because its extensive O antigen obscures the P1 receptor, the lipopolysaccharide (LPS) core subunit. The GalE, GalT, GalK, and GalU proteins are necessary for modifying galactose before it can be assembled into the repeating subunit of the O antigen. Here, we constructed E. coli O157:H7 gal mutants which presumably have little or no O antigen. These strains were able to adsorb P1. P1 lysates grown on the gal mutant strains could be used to move chromosomal markers between EHEC strains, thereby facilitating genetic manipulation of E. coli O157:H7. The gal mutants could easily be reverted to a wild-type Gal(+) strain using P1 transduction. We found that the O157:H7 galETKM::aad-7 deletion strain was 500-fold less able to colonize the infant rabbit intestine than the isogenic Gal(+) parent, although it displayed no growth defect in vitro. Furthermore, in vivo a Gal(+) revertant of this mutant outcompeted the galETKM deletion strain to an extent similar to that of the wild type. This suggests that the O157 O antigen is an important intestinal colonization factor. Compared to the wild type, EHEC gal mutants were 100-fold more sensitive to a peptide derived from bactericidal permeability-increasing protein, a bactericidal protein found on the surface of intestinal epithelial cells. Thus, one way in which the O157 O antigen may contribute to EHEC intestinal colonization is to promote resistance to host-derived antimicrobial polypeptides.