肠毒素大肠埃希菌载体活菌疫苗的安全性和免疫性研究

目的 研究肠毒素大肠埃希菌活菌载体疫苗FE3、FE16的安全性和免疫原性。方法 通过肠毒素大肠埃希菌肠毒素毒力试验、新西兰大白兔免疫试验、小鼠口服和鼻饲途径免疫试验，检测载体疫苗的毒性、免疫原性和免疫效果。结果 毒力试验中所有检测均为阴性；免疫4次后大白兔血清对福氏2a型茵的凝集效价均不低于1：640，对肠毒素大肠埃希菌菌毛抗原的凝集效价均不低于1：1280；通过口服和鼻饲方式免疫小鼠后，血清中IgG显著升高，同时能够在粪便中检测到分泌型IgA，而灭活苗免疫未能检测到分泌型IgA。结论 活菌载体疫苗株FE3和FE16具有良好的安全性和免疫原性，同时能够刺激机体产生体液免疫和黏膜免疫反应。     

幽门螺杆菌免疫奶羊的免疫应答机制及其应用前景分析

目的观察Hp全菌抗原免疫奶羊中特异性抗体产生规律。方法采用菌液浓度为6×109cfuml全菌抗原,通过滴鼻、多点皮下注射、妊娠期肌肉注射三种途径免疫3只产奶山羊。前2组都于0、14、21、28天接受4次免疫接种,妊娠组于分娩前后1个月每隔两周注射1次。收集血清、乳清样本,并以酶联免疫吸附试验进行样本中的IgA、IgG抗体测定。结果3种途径免疫奶羊后都激发了奶羊的系统免疫,产生了血清循环抗体。血清中IgA变化幅度不大,三组血清中IgG较免疫前都有很大升高。羊奶中IgA抗体较免疫前都有升高,且抗体水平滴鼻组>妊娠组>皮下组,羊奶中IgG抗体升高幅度妊娠组>皮下组>滴鼻组。结论3种途径都能激发奶羊机体的免疫应答,使羊奶中抗HpIgA、抗HpIgG抗体水平升高,血清中IgG抗体水平升高,尤其是滴鼻免疫能够诱导机体同时产生不同部位的粘膜免疫和系统免疫,且所需的抗原量远远少于其他两组,是一个敏感、安全、可行有效的免疫途径。     

重组Calpain蛋白的免疫原性及其诊断上的应用研究

目的研究在大肠杆菌中表达的日本血吸虫Calpain蛋白的免疫原性及其在日本血吸虫诊断上的应用. 方法用重组Calpain蛋白免疫BALB/c小鼠,ELISA法测定特异性IgG抗体的动态变化及其IgG亚型(IgG1, IgG2a, IgG2b, IgG3)产生特征;同时用重组Calpain蛋白作为诊断抗原,粪检血吸虫病阳性患者血清作为一抗,肝吸虫阳性患者血清作为考核交叉反应血清. 结果重组Calpain抗原免疫小鼠后,产生了一个极高的抗Calpain特异性抗体,免疫4周后IgG类抗体达到高峰,与对照组鼠相比较,免疫鼠血清中IgG1, IgG2a, IgG2b特异性抗体也有显著性的上升; Calpain重组抗原血清诊断日本血吸虫和粪检的符合率为100%, 粪检阳性EPG低的个体抗Calpain抗体滴度高, EPG高的患者抗Calpain抗体滴度反而低, 与肝吸虫的交叉反应率为37%. 结论日本血吸虫Calpain是一个具有免疫原性的蛋白,能够激发宿主产生高水平的免疫球蛋白,能够敏感地测定日本血吸虫的感染, 说明Calpain可以发展成为日本血吸虫病的诊断抗原和日本血吸虫疫苗候选分子.     

neuB1失活空肠弯曲菌突变株灭活全菌苗经鼻免疫小鼠的实验研究

[目的]探讨neuB1失活空肠弯曲菌0:19突变株灭活全菌苗的免疫原性及其对抗野生株攻击的免疫保护性.[方法]以neuB1失活空肠弯曲菌0:19突变株灭活菌体,经鼻途径以不同剂量免疫Balb/C小鼠,ELISA法检测小鼠肠腔灌洗液和血液中的抗体滴度;并以5×109 cfu野生株进行攻击,计算疾病指数.[结果]免疫后7 d肠腔灌洗液中的抗CJ特异性slgA和21 d血清中特异性IgG及IgA滴度均显著增高;免疫组的疾病指数分别由0.90降至0.30～0.34,保护率为62%～67%.[结论]neuB1失活CJ 0:19突变株灭活全菌苗经鼻免疫,能诱导动物产生有效的体液免疫应答,具有显著的免疫原性;能有效保护免疫小鼠免受野生株的攻击,基于该突变株良好的免疫活性且无分子模拟所致的神经毒性,有望成为理想的全菌候选疫苗.     

免疫乳抗炎作用研究

目的:研究免疫乳的抗炎症作用。方法:以24株人肠道病原菌(包括病原性大肠杆菌12株、沙门菌8株、志贺菌3株、小肠结肠炎耶尔森菌1株)作为抗原,对乳牛进行系统免疫,免疫乳与非免疫乳乳中IgG含量无显著差异。结果:系统免疫并不增加乳中IgG的含量,但IgG的抗体特异性大大增强;免疫乳(immunemilk,IM)中乳抗体对24种不同病原菌的凝集价为128,为普通乳(regularmilk,RM)中乳抗体凝集价的64倍。结论:免疫乳对角叉菜胶和甲醛致炎引起的大鼠足趾肿胀具有显著的抑制作用,同时可显著降低炎性组织中PGE2的含量。免疫乳粉对小鼠肉芽肿也具有显著的抑制作用。     

抗幽门螺杆菌不同免疫途径免疫奶羊的研究

目的:以幽门螺杆菌(Helicobacterpylori,H.polyri,Hp)全菌抗原免疫奶羊,观察羊奶中特异性抗体产生规律。方法:采用菌液浓度为60亿cfu/ml全菌抗原,通过滴鼻、多点皮下注射、妊娠期肌肉注射三种途径免疫3只产奶山羊。前两组都于0、14、21、28d接受四次免疫接种,妊娠组于分娩前后1个月每隔2w注射1次。收集血清、乳清样本,以酶联免疫吸附试验测定IgA、IgG抗体。结果:经滴鼻、多点皮下注射、妊娠期肌注三种途径免疫奶羊后产生了抗体。血清中IgA变化幅度不大,三组血清中IgG较免疫前都有很大升高。羊奶中IgA抗体较免疫前都有升高,抗体水平:滴鼻组>妊娠组>皮下组,羊奶中IgG抗体水平:妊娠组IgG>皮下组>滴鼻组。结论:滴鼻粘膜免疫、多点皮下注射、妊娠期肌肉注射三种途径都能激发奶羊机体的免疫应答,使羊奶中抗Hp-IgA、抗Hp-IgG抗体水平升高,血清中IgG抗体水平升高,尤其是滴鼻免疫能够诱导机体同时产生不同部位的粘膜免疫和系统免疫,且所需的抗原量远远少于其他两组,是一个敏感、安全、可行有效的免疫途径。     

大肠杆菌不耐热肠毒素中和试验

产肠毒素大肠株菌是引起急性腹泻病的主要病原苗，目前已引起全球许多国家的重视。为了探讨我省分离产肠毒素大肠杆菌（ETEC）其不耐热肠毒素（LT）与抗毒血清的中和状况。近年来，我们对一些苗杆的LT与抗毒血清进行中和试验。现将结果报告如下。一、材料与方法1．菌株来源：ETEC菌株是从我省霍乱样腹泻病人分离的：吕乱邓首569BN株是中国预防医学科学院流行病防治研究所赠送的。2．肠毒素液的制备：产生肠毒素菌株接种于pH7．6的3％脉际水20～30ml中，大肠杆菌于37”C孵育4天；吕乱弧菌569BN株孵育1天。其培养液加人1／万硫柳汞后…     

STAg、蜂胶和IFN-γ联合滴鼻免疫对小鼠抗体影响

目的 观察弓形虫可溶性速殖子抗原(STAg)联合蜂胶和γ干扰素(IFN -γ)滴鼻免疫BALB/c小鼠后诱导血清IgG,粪便、鼻咽冲洗液和阴道冲洗液中IgA特异性抗体动态变化,探讨抗弓形虫感染作用机制.方法 将5～6周龄雌性BALB/c小鼠96只随机分为免疫组和对照组,免疫组以弓形虫复合黏膜疫苗(20 μg STAg+ 40 μg蜂胶+ 1000U IFN -γ)滴鼻免疫,对照组以磷酸盐缓冲液滴鼻.分别于滴鼻2次(间隔2周)后第1、2、3、4、6、8、10和12周处死小鼠,收集血清、粪便、鼻咽冲洗液和阴道冲洗液,采用酶联免疫吸附法检测血清IgG,粪便、鼻咽、阴道冲洗液中IgA抗体.结果 免疫组小鼠血清IgG,粪便、鼻咽、阴道冲洗液中IgA均高于对照组,血清IgG水平第3周达高峰(吸光度A值0.257),第1、2、3、4、6周IgG水平明显高于对照组(F=5.87,P＜0.05);粪便IgA抗体第2周达高峰(吸光度A值0.054),第2、3、4周明显高于对照组(F=5.32,P＜0.05);鼻咽、阴道冲洗液中IgA第1周即达高峰(吸光度A值分别为0.0313,0.0533),之后逐渐降低,至第12周仍明显高于对照组(F =6.15,P＜0.05).结论 STAg联合蜂胶和IFN -γ滴鼻免疫小鼠可诱导高水平特异性抗体,且可持续较长时间.     

检出产肠毒素性大肠杆菌的滤膜分析法

产肠毒素性大肠杆菌(ETEC)是儿童腹泻的一种主要病原菌。本文介绍一种检出产不耐热肠毒素(LT)大肠杆菌的滤膜分析法。当生长有菌落的滤膜置于含抗霍乱毒素的琼脂培养基上孵育时,菌落所产生的LT就通过滤膜扩散,与抗体结合而在琼脂中形成一沉淀区。将4株待检菌和2株对照菌(阳性及阴性株)点种于49mm醋酸纤维滤膜(孔径0.45μm)上,再把滤膜放在浸透了为产毒素而改良的大肠杆菌选择性肉汤的载体上培养,此肉汤含(g/L):胰酶大豆     

产毒性大肠杆菌疫苗

在一次世界卫生组织召开的专家会议上讨论了产毒性大肠杆菌疫苗的问题。在发展中国家,10～50%的腹泻可能由产毒性大肠杆菌(ETEC)所致。ETEC的重要抗原是定居因子和肠毒素。定居因子抗原主要有CFA/Ⅰ、CFA/Ⅱ和CFA/Ⅳ。动物和人体试验表明,口服     

Prime-boost vaccine regimen confers protective immunity to human-derived enterotoxigenic Escherichia coli

Development of effective vaccines against diarrhea caused by enterotoxigenic Escherichia coli (ETEC) strains is still a priority for those living at or traveling to endemic regions. In this work, we evaluated the protective role of an anti-ETEC vaccine regimen based on parenteral priming with a DNA vaccine, pRECFA, followed by oral boosting with a recombinant attenuated Salmonella Typhimurium vaccine strain, HG3, both encoding the same antigen, the structural subunit (CfaB) of the ETEC CFA/I fimbriae. The DNA-priming Salmonella-boosting protocol enhanced both murine anti-CfaB serum IgG and fecal IgA antibody responses and increased the ability of serum antibodies to inhibit the adhesive properties of the CFA/I fimbriae expressed by live bacteria, as compared to mice immunized with only one vaccine type. Addition of a mucosal adjuvant (LTR192G) to the Salmonella vaccine strain further enhanced the synergic effects of the vaccine regimen on the induced CfaB-specific antibody responses. DBA/2 dams submitted to the prime-boost regimen transferred complete passive protection to suckling neonates challenged with a virulent ETEC strain. Detection of milk anti-CfaB IgA antibodies and protection conferred by vaccinated dams to neonates born from non-vaccinated dams indicated that secretion of antigen-specific IgA is the immune response induced by the protective vaccine regimen. These results demonstrate that priming with a DNA vaccine and boosting with a Salmonella strain enhances both quantitatively and qualitatively the antibody responses to the CfaB antigen and represents an alternative for either active or passive immunization approach to ETEC-associated diarrhea.     

Boosting systemic and secreted antibody responses in mice orally immunized with recombinant Bacillus subtilis strains following parenteral priming with a DNA vaccine encoding the enterotoxigenic Escherichia coli (ETEC) CFA/I fimbriae B subunit

Recombinant Bacillus subtilis strains, either spores or vegetative cells, may be employed as safe and low cost orally delivered live vaccine vehicles. In this study, we report the use of an orally delivered B. subtilis vaccine strain to boost systemic and secreted antibody responses in mice i.m. primed with a DNA vaccine encoding the structural subunit (CfaB) of the CFA/I fimbriae encoded by enterotoxigenic Escherichia coli (ETEC), an important etiological agent of diarrhea among travelers and children living in endemic regions. DBA/2 female mice submitted to the prime-boost immunization regimen developed synergic serum (IgG) and mucosal (IgA) antibody responses to the target CfaB antigen. Moreover, in contrast to mice immunized only with one vaccine formulation, sera harvested from prime-boosted vaccinated individuals inhibited adhesion of ETEC cells to human red blood cells. Additionally, vaccinated dams conferred full passive protection to suckling newborn mice challenged with a virulent ETEC strain. Taken together the present results further demonstrate the potential use of recombinant B. subtilis strains as an alternative live vaccine vehicle.     

Over-expression of major colonization factors of enterotoxigenic Escherichia coli, alone or together,on non-toxigenic E. coli bacteria

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrheal disease and deaths among children in developing countries and the major cause of traveller's diarrhea. Since surface protein colonization factors (CFs) of ETEC are important for pathogenicity and immune protection is mainly mediated by locally produced IgA antibodies in the gut, much effort has focused on the development of an oral CF-based vaccine. We have recently described the development of recombinant strains over-expressing CFA/I; the most prevalent CF among human clinical ETEC isolates. Here, non-toxigenic recombinant E. coli strains over-expressing Coli surface antigen 2 (CS2), CS4, CS5, and CS6, either alone, or each in combination with CFA/I were constructed by cloning the genes required for expression and assembly of each CF into expression vectors harboring a strong promoter. Immunological assays showed that recombinant strains expressing single CFs produced those in significantly larger amounts than did corresponding naturally high producing reference strains. Recombinant strains co-expressing CFA/I together with another CF also expressed significantly larger amounts of both CFs compared with the corresponding references strains. Further, when tested in mice, oral immunization with formalin-killed recombinant bacteria co-expressing one such double-expression CF pair, CFA/I + CS2, induced specific serum IgG + IgM and fecal IgA antibody responses against both CFs exceeding the responses induced by immunizations with natural reference strains expressing CFA/I and CS2, respectively. We conclude that the described type of recombinant bacteria over-expressing major CFs of ETEC, alone or in combination, may be useful as candidate strains for use in an oral whole-cell CF-ETEC vaccine.     

Antibodies derived from an enterotoxigenic Escherichia coli (ETEC) adhesin tip MEFA (multiepitope fusion antigen) against adherence of nine ETEC adhesins: CFA/I,CS1, CS2, CS3, CS4, CS5, CS6, CS21 and EtpA

Diarrhea continues to be a leading cause of death in children younger than 5 years in developing countries. Enterotoxigenic Escherichia coli (ETEC) is a leading bacterial cause of children's diarrhea and travelers’ diarrhea. ETEC bacteria initiate diarrheal disease by attaching to host receptors at epithelial cells and colonizing in small intestine. Therefore, preventing ETEC attachment has been considered the first line of defense against ETEC diarrhea. However, developing vaccines effectively against ETEC bacterial attachment encounters challenge because ETEC strains produce over 23 immunologically heterogeneous adhesins. In this study, we applied MEFA (multiepitope fusion antigen) approach to integrate epitopes from adhesin tips or adhesive subunits of CFA/I, CS1, CS2, CS3, CS4, CS5, CS6, CS21 and EtpA adhesins and to construct an adhesin tip MEFA peptide. We then examined immunogenicity of this tip MEFA in mouse immunization, and assessed potential application of this tip MEFA for ETEC vaccine development. Data showed that mice intraperitoneally immunized with this adhesin tip MEFA developed IgG antibody responses to all nine ETEC adhesins. Moreover, ETEC and E. coli bacteria expressing these nine adhesins, after incubation with serum of the immunized mice, exhibited significant reduction in attachment to Caco-2 cells. These results indicated that anti-adhesin antibodies induced by this adhesin tip MEFA blocked adherence of the most important ETEC adhesins, suggesting this multivalent tip MEFA may be useful for developing a broadly protective anti-adhesin vaccine against ETEC diarrhea.     

Construction of a non-toxigenic Escherichia coli oral vaccine strain expressing large amounts of CS6 and inducing strong intestinal and serum anti-CS6 antibody responses in mice

Coli surface antigen 6 (CS6) is one of the most prevalent non-fimbrial colonization factors (CFs) of enterotoxigenic Escherichia coli (ETEC) bacteria, which are the most common cause of diarrhea among infants and children in developing countries. Since immune protection against ETEC is mainly mediated by locally produced IgA antibodies in the gut, much effort is focused on the development of an oral CF-based vaccine. Previous work has described the preparation of candidate E. coli vaccine strains expressing immunogenic amounts of fimbrial CF antigens such as CFA/I and CS2, which are retained after formalin treatment. However, attempts to generate E. coli expressing immunogenic amounts of CS6 and to preserve the immunological activity of the CS6 protein in a killed whole-cell vaccine have failed until now. Here we describe the construction of a recombinant non-toxigenic E. coli strain, with thyA as a non-antibiotic-based selection, which expresses large amounts of CS6 antigen on the bacterial surface, and show that phenol inactivation of the bacteria does not destroy the CS6 antigen properties. Oral immunization of mice with such phenol-killed CS6 over-expressing E. coli bacteria induced strong fecal and intestinal IgA and serum IgG + IgM antibody responses to CS6 that exceeded the responses induced by an ETEC reference strain naturally expressing CS6 and previously used as a vaccine strain. Our data indicate that the described phenol-inactivated non-toxigenic and CS6 over-expressing E. coli strain may be a useful component in an oral ETEC vaccine.     

Immune responses elicited against multiple enterotoxigenic Escherichia coli fimbriae and mutant LT expressed in attenuated Shigella vaccine strains

Shigella and enterotoxigenic Escherichia coli (ETEC) continue to be important causes of diarrheal disease in infants and young children in developing countries and are major etiologic agents of traveler's diarrhea. Since attenuated strains of Shigella have been developed as live oral vaccines against shigellosis, we have adapted these attenuated Shigella strains to serve as carriers of ETEC antigens, thereby constituting a hybrid vaccine. Since protective immunity against ETEC is largely directed against fimbrial antigens (of which there are multiple antigenic types), we have individually expressed four different ETEC fimbriae, including CFA/I, CS2, CS3, and CS4, using deltaguaBA attenuated Shigella vaccine strain CVD 1204 as a prototype live vector. Following mucosal (intranasal) immunization of guinea pigs, serum IgG and mucosal IgA responses were elicited against each fimbrial type. An additional strain was constructed expressing a detoxified version of the human ETEC variant of heat labile toxin (LThK63). Following mucosal immunization of guinea pigs with a mixed inoculum containing five Shigella strains each expressing a different ETEC antigen, immune responses were observed against each ETEC antigen plus the Shigella vector.     

Immunogenicity and protective efficacy of orally or intranasally administered recombinant Lactobacillus casei expressing ETEC K99

In an effort to develop a safe and effective vaccine for the prevention of enterotoxigenic Escherichia coli (ETEC) K99 infections, we have developed a surface antigen display system using pgsA (poly-γ-glutamate synthetase A) as an anchoring matrix. The recombinant fusion proteins comprised of pgsA and fimbriae protein of ETEC K99 were stably expressed on Lactobacillus casei. Surface localization of the fusion protein was verified by immunoblotting, immunofluorescence microscopy and flow cytometry. Specific Pathogen Free (SPF) BALB/c mice orally or intranasally vaccinated with recombinant L. casei resulted in high levels of serum immunoglobulin G (IgG) and mucosal IgA against ETEC K99, as demonstrated by enzyme-linked immunosorbent assays using purified fimbriae peptides. The serum antibody isotypes elicited were predominantly IgG1 and IgG2a. Vaccinated SPF BALB/c mice were evaluated by oral challenge with standard-type ETEC C83912 after the last booster immunization. More than 80% of immunized mice survived regardless of the immune route. The antibody titers elicited following oral immunization were lower than those following intranasal immunization but the protective efficacy was in the same order of magnitude. These results indicate that mucosal immunization with recombinant L. casei expressing ETEC K99 fimbriae protein on its surface provides an effective means for eliciting a protective immune response against the ETEC K99.     

Oral rice-based vaccine induces passive and active immunity against enterotoxigenic E. coli-mediated diarrhea in pigs

Enterotoxigenic Escherichia coli (ETEC) causes severe diarrhea in both neonatal and weaned pigs. Because the cholera toxin B subunit (CTB) has a high level of amino acid identity to the ETEC heat-labile toxin (LT) B-subunit (LTB), we selected MucoRice-CTB as a vaccine candidate against ETEC-induced pig diarrhea. When pregnant sows were orally immunized with MucoRice-CTB, increased amounts of antigen-specific IgG and IgA were produced in their sera. CTB-specific IgG was secreted in the colostrum and transferred passively to the sera of suckling piglets. IgA antibodies in the colostrum and milk remained high with a booster dose after farrowing. Additionally, when weaned minipigs were orally immunized with MucoRice-CTB, production of CTB-specific intestinal SIgA, as well as systemic IgG and IgA, was induced. To evaluate the cross-protective effect of MucoRice-CTB against ETEC diarrhea, intestinal loop assay with ETEC was conducted. The fluid volume accumulated in the loops of minipigs immunized with MucoRice-CTB was significantly lower than that in control minipigs, indicating that MucoRice-CTB-induced cross-reactive immunity could protect weaned pigs from diarrhea caused by ETEC. MucoRice-CTB could be a candidate oral vaccine for inducing both passive and active immunity to protect both suckling and weaned piglets from ETEC diarrhea.     

Passive antibodies derived from intramuscularly immunized toxoid fusion 3xSTaN12S-dmLT protect against STa+ enterotoxigenic Escherichia coli (ETEC) diarrhea in a pig model

Enterotoxigenic Escherichia coli (ETEC) strains are among the most common causes of children’s diarrhea and travelers’ diarrhea. Developing effective vaccines against ETEC associated diarrhea becomes a top priority. ETEC heat-labile toxin (LT) and heat-stable toxin (STa) toxoid fusion 3xSTa_N12S-dmLT was demonstrated recently to induce neutralizing antitoxin antibodies in intraperitoneally or subcutaneously immunized mice. However, whether antibodies derived from this toxoid fusion are protective against ETEC diarrhea has not been examined. In this study, we intramuscularly immunized pregnant gilts with toxoid fusion 3xSTa_N12S-dmLT, challenged suckling piglets with a STa-positive ETEC strain, and assessed protective efficacy of passive acquire antitoxin antibodies against ETEC diarrhea. Data showed all three immunized gilts developed anti-STa IgG and IgA antibodies, and piglets born to the immunized dams acquired anti-STa and anti-LT antibodies. When challenged with a STa+ ETEC strain, none of the piglets born to the immunized dams developed watery diarrhea, with 20 piglets remained normal and the other 8 piglets developed mild diarrhea indicated with stained butt. In contrast, the control dams and born piglets had no anti-STa or anti-LT antibodies detected, and 26 out 32 piglets developed watery diarrhea after challenge of the STa+ ETEC strain. These results indicated that passive acquired anti-STa antibodies are protective against ETEC diarrhea, and suggested potential application of toxoid fusion 3xSTa_N12S-dmLT in ETEC vaccine development.     

Different kinetic of antibody responses following infection of newly weaned pigs with an F4 enterotoxigenic Escherichia coli strain or an F18 verotoxigenic Escherichia coli strain

To develop a vaccine against Escherichia coli-induced post-weaning diarrhea and edema disease, insights in the induction of the protective immune response following infection with these pathogenic E. coli is needed. Therefore, the fimbriae-specific antibody response of newly weaned pigs following infection with the Shiga-like toxin type II variant (SLT-IIv) producing F18(+) verotoxigenic E. coli (VTEC) (strain 107/86) was compared with the response following an infection with LT producing F4(+) enterotoxigenic E. coli (ETEC) (strain GIS 26). F4(+) ETEC were able to colonize the gut very soon after infection, as peak excretion of F4(+) E. coli bacteria was seen 2 days post-infection (dpi), but had already disappeared 7dpi. On the other hand, F18(+) VTEC infection resulted in a slower colonization of the gut as the peak excretion of F18(+) E. coli was observed between 3 and 5dpi, but this colonization remained longer as F18(+) E. coli were detected till 9dpi in feces. Furthermore, this fast colonization pattern of F4(+) ETEC is accompanied with the presence of F4-specific antibodies in mucosal tissues and serum from 4dpi onward, with maximal amounts of F4-specific IgA in the jejunal lamina propria and serum 7dpi. In contrast, F18-specific IgA was only readily detected in the jejunal lamina propria 15dpi and showed a maximum serum titer 21dpi. Besides this faster induction and higher antibody response, the switch from IgM to IgA and IgG was also earlier following the F4(+) ETEC infection.