Oral immunization of mice with attenuated Salmonella typhimurium aroA expressing a recombinant Mycoplasma hyopneumoniae antigen (NrdF)

Mycoplasma hyopneumoniae is the etiological agent of porcine enzootic pneumonia, a commercially expensive respiratory disease of swine. Salmonella typhimurium SL3261 was used as a live carrier of plasmid pKF1, which encodes a 15-kDa recombinant M. hyopneumoniae protein. This expressed recombinant protein consists of the carboxy-terminal 11 kDa of a 42-kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Rabbit anti-15-kDa serum was able to inhibit the growth of viable M. hyopneumoniae J in vitro. When used as a live oral vaccine, S. typhimurium SL3261(pKF1) induced a significant secretory immunoglobulin A immune response in the lungs of mice orally immunized against the M. hyopneumoniae antigen. Utilization of live oral vaccines expressing potentially protective M. hyopneumoniae proteins, such as the NrdF antigen, which can stimulate a lung mucosal response against surface-accessible proteins may provide a cost-effective alternative to the present control strategies used for porcine enzootic pneumonia.     

Oral immunization with recombinant vaccina expressing cell-surface-anchored beta hCG induces anti-hCG antibodies and T-cell proliferative response in rats

A vaccinia recombinant, VSS2, expressing cell-surface-anchored beta-subunit of human chorionic gonadotropin (beta hCG) has earlier been found to induce high titered anti-hCG antibodies in rats immunized by tail scarification. The immunogenicity of this recombinant was compared in rats which received the virus through different routes of inoculation: intradermal, intragastric, intrajejunal or by tail scarification. The recombinant virus induced high titers of anti-hCG antibodies in all instances although the titers were about one log lower when the recombinant virus was delivered orally. The recombinant was found to induce T-cell proliferative response in rats of all immunization groups.     

Oral immunization of macaques with attenuated vaccine virus induces protection against vaginally transmitted AIDS

The chimeric simian-human immunodeficiency virus SHIVKU-1, bearing the envelope of human immunodeficiency virus type 1 (HIV-1), causes fulminant infection with subtotal loss of CD4(+) T cells followed by development of AIDS in intravaginally inoculated macaques and thus provides a highly relevant model of sexually transmitted disease caused by HIV-1 in human beings. Previous studies using this SHIV model had shown that the vpu and nef genes were important in pathogenesis of the infection, and so we deleted portions of these genes to create two vaccines, DeltavpuDeltanefSHIV-4 (vaccine 1) and DeltavpuSHIVPPc (vaccine 2). Six adult macaques were immunized subcutaneously with vaccine 1, and six were immunized orally with vaccine 2. Both viruses caused infection in all inoculated animals, but whereas vaccine 1 virus caused only a nonproductive type of infection, vaccine 2 virus replicated productively but transiently for a 6- to 10-week period. Both groups were challenged 6 to 7 months later with pathogenic SHIVKU-1 by the intravaginal route. All four unvaccinated controls developed low CD4(+) T-cell counts (<200/microliter) and AIDS. The 12 vaccinated animals all became infected with SHIVKU-1, and two in group 1 developed a persistent productive infection followed by development of AIDS in one. The other 10 have maintained almost complete control over virus replication even though spliced viral RNA was detected in lymph nodes. This suppression of virus replication correlated with robust antiviral cell-mediated immune responses. This is the first demonstration of protection against virulent SHIV administered by the intravaginal route. This study supports the concept that sexually transmitted HIV disease can be prevented by parenteral or oral immunization.     

Antineuraminidase serum antibodies in natural influenza A and immunization with influenza vaccines

Parallel HI and virus-elution-from-erythrocytes-inhibition (a simplified method for titration of neuraminidase antibody) tests were used for examinations of 1117 blood serum specimens from 440 adults and children under study, 5250 single serum specimens from healthy subjects from birth to 65 years of age, 38 paired serum specimens from children who experienced influenza A/Texas/1/77 disease in the epidemic of 1979-1980, and 590 paired serum specimens from subjects immunized with influenza vaccines. In 7%-23% of influenza patients and immunized subjects antibody rise was observed to only one of the influenza A virus surface antigens, hemagglutinin or neuraminidase. The protective activity of antibody to influenza A virus neuraminidase was as good as that of antihemagglutinins. Both kinds of antibody interacted in protection against the disease. Antineuraminidase antibody was found to affect the decrease in severity of the infectious process in natural infection with influenza A. The formation of immunological memory in the system of synthesis of antihemagglutinins and antineuraminidase antibodies was shown to have features in common. The pattern of heterologous immune responses in immunized subjects and patients with influenza showed all antigenic varieties of neuraminidase N2 as well as neuraminidases N1 and N2 to share common cross-reacting determinants.     

Oral immunization with a Salmonella typhimurium vaccine vector expressing recombinant enterotoxigenic Escherichia coli K99 fimbriae elicits elevated antibody titers for protective immunity

Bovine enterotoxigenic Escherichia coli (ETEC) continues to cause mortality in piglets and newborn calves. In an effort to develop a safe and effective vaccine for the prevention of F5(+) ETEC infections, a balanced lethal asd+ plasmid carrying the complete K99 operon was constructed and designated pMAK99-asd+. Introduction of this plasmid into an attenuated Salmonella typhimurium Deltaaro Deltaasd strain, H683, resulted in strain AP112, which stably expresses E. coli K99 fimbriae. A single oral immunization of BALB/c and CD-1 mice with strain AP112 elicited significant mucosal immunoglobulin A (IgA) titers that remained elevated for >11 weeks. IgA and IgG responses in serum specific for K99 fimbriae were also induced, with a prominent IgG1, as well as IgG2a and IgG2b, titer. To assess the derivation of these antibodies, a K99 isotype-specific B-cell ELISPOT analysis was conducted by using mononuclear cells from the lamina propria of the small intestines (LP), Peyer's patches (PP), and spleens of vaccinated and control BALB/c mice. This analysis revealed elevated numbers of K99 fimbria-specific IgA-producing cells in the LP, PP, and spleen, whereas elevated K99 fimbria-specific IgG-producing cells were detected only in the PP and spleen. These antibodies were important for protective immunity. One-day-old neonates from dams orally immunized with AP112 were provided passive protection against oral challenge with wild-type ETEC, in contrast to challenged neonates from unvaccinated dams or from dams vaccinated with a control Salmonella vector. These results confirm that oral Salmonella vaccine vectors effectively deliver K99 fimbriae to mucosal inductive sites for sustained elevation of IgA and IgG antibodies and for eliciting protective immunity.     

Oral immunization with recombinant Norwalk virus-like particles induces a systemic and mucosal immune response in mice

Recombinant Norwalk virus-like particles (rNV VLPs) produced in insect cells were evaluated as an oral immunogen in CD1 and BALB/c mice by monitoring rNV-specific serum total and subclass immunoglobulin G (IgG) and intestinal IgA responses. Dose and kinetics of response were evaluated in the presence and absence of the mucosal adjuvant cholera toxin (CT). rNV-specific serum IgG and intestinal IgA were detected in the absence of CT, and the number of responders was not significantly different from that of mice administered VLPs with CT at most doses. The use of CT was associated with induction of higher levels of IgG in serum; this effect was greater at higher doses of VLPs. IgG in serum was detected in the majority of animals by 9 days postimmunization (dpi), and intestinal IgA responses were detected by 24 dpi. In the absence of CT, IgG2b was the dominant IgG subclass response in both mouse strains. Thus, nonreplicating rNV VLPs are immunogenic when administered orally in the absence of any delivery system or mucosal adjuvant. These studies demonstrate that rNV VLPs are an excellent model to study the oral delivery of antigen, and they are a potential mucosal vaccine for NV infections.     

Association of human leucocyte antigen phenotype with vaccine efficacy in patients receiving vaginal mucosal immunization for recurrent urinary tract infection

CONTEXT: One or both commercial tuberculin skin test reagents (Aplisol and Tubersol) may have a high rate of false-positive reactions. OBJECTIVE: To compare the reaction size and specificity of skin testing with Aplisol, Tubersol, and the standard purified protein derivative (PPD-S1). DESIGN: Double-blind trial, conducted between May 14, 1997, and October28, 1997, in which each individual received 4 tuberculin skin reagents at sites assigned at random. SETTING: Health departments and universities in 6 US cities. PARTICIPANTS: A total of 1555 persons at low risk of latent tuberculosis infection. INTERVENTION: Simultaneous skin tests with Aplisol, Tubersol, PPD-S1, and either a second PPD-S1 or PPD-S2 (a proposed new standard). MAIN OUTCOME MEASURE: Reaction size at each injection site measured by 2 investigators blinded to type of reagent. RESULTS: Aplisol produced slightly larger reactions than Tubersol, but this difference did not significantly change skin test interpretation. The mean +/- SD reaction sizes were 3.4+/-4.2 mm with Aplisol, 2.1+/-3.2 mm with Tubersol, and 2.5+/-3.6 mm with PPD-S1. Assuming that all participants were uninfected and using a 10-mm cutoff, the specificities of the tests were high: Aplisol, 98.2%; Tubersol, 99.2%; and PPD-S1, 98.9%. Significant variability was not detected in interobserver, host, and lot-to-lot reagent comparisons. CONCLUSION: Using a cutoff of at least 10 mm, testing with 3 different PPD reagents resulted in similar numbers of uninfected persons being correctly classified.     

Protection against lethal Japanese encephalitis virus infection of mice by immunization with the highly attenuated MVA strain of vaccinia virus expressing JEV prM and E genes

Genes encoding the glycosylated precursor of the membrane (prM) and envelope (E) proteins of a Korean strain of Japanese encephalitis virus (JEV) were inserted into the genome of the host-range restricted, highly attenuated, and safety-tested MVA strain of vaccinia virus. MVA recombinants containing the JEV genes, under strong synthetic or modified H5 vaccinia virus promoters, were isolated. Synthesis of JEV prM and E proteins was detected by immunofluorescence microscopy, flow cytometry, and polyacrylamide gel electrophoresis. Mice inoculated and boosted by various routes with either of the MVA recombinants produced JEV neutralizing antibodies, that had titres comparable with those induced by an inactivated JEV vaccine, as well as haemagglutination-inhibiting antibodies. Mice immunized with 2 x 10(6) infectious units of MVA/JEV recombinants by intramuscular or intraperitoneal routes were completely protected against a 10(5) LD50 JEV challenge at 9 weeks of age.     

Systemic lupus erythematosus in women and serum interleukin-6, sperm and zona pellucida antibodies

Systemic lupus erthematosus (SLE) has been very often associated with complication in reproduction. 29 SLE women divided into two groups A (10 patients aged 18-36 years) and B (19 patients aged 42-67 years) were queried with regard to general, obstetric and SLE history by the use of a questionnaire. Serum of each patient was tested for interleukin-6 (by ELISA), sperm antibodies (by mixed antiglobulin reaction and tray agglutination test) and zona pellucida antibodies (passive haemagglutination test and ELISA methods). Neuropathic, cutaneous and nephrotic symptoms prevailed in the SLE women. The group of younger women showed significant problems in fertility (only one woman became a happy mother) while 15 women in the elderly group were successfully pregnant before SLE diagnosis. Low serum II-6 levels were detectable only in 3 cases as a possible consequence of corticoid treatment. Levels of zona pellucida antibodies were higher in the elderly group B, levels of sperm antibodies were higher in contrast to younger SLE women (group A). The laboratory findings may be related to the severity of autoimmune disease and to menopause onset (group B) or good sexual activity (group A).     

The xenoestrogen bisphenol A induces growth, differentiation, and c-fos gene expression in the female reproductive tract

The xenoestrogen bisphenol A (BPA) has been shown to mimic estrogen both in vivo and in vitro. BPA stimulates PRL secretion and the expression of a PRL regulating factor from the posterior pituitary in the estrogen-sensitive Fischer 344 rat (F344), but not in Sprague-Dawley (SD) rats. The goal of the present studies was to examine the in vivo actions of BPA on the reproductive tract. The specific objectives were 1) to characterize the short term effects of BPA on cell proliferation and c-fos expression in the uterus and vagina, and 2) to compare the effects of prolonged exposure to low doses of BPA on the reproductive tract of F344 and SD rats. Treatment with single high doses of BPA induced cell proliferation in the uterus and vagina of ovariectomized F344 rats, as determined by bromodeoxyuridine immunostaining. This proliferation was dose dependent (from 37.5-150 mg/kg) and followed a time course similar to that of estradiol (E2). Quantitative RT-PCR revealed that both BPA and E2 increased c-fos messenger RNA levels in the uterus 14- to 16-fold within 2 h, which returned to basal levels after 6 h. In the vagina, BPA-induced c-fos expression remained elevated for up to 6 h, compared with the transient increase caused by E2. Treatment of F344 rats for 3 days with continuous release capsules that supplied a much lower dose of BPA (approximately 0.3 mg/kg x day) resulted in hypertrophy, hyperplasia, and mucus secretion in the uterus and hyperplasia and cornification of the vaginal epithelium. The reproductive tract of SD rats did not respond to this treatment paradigm with BPA. These studies demonstrate that 1) the molecular and morphological alterations induced by BPA in the uterus and vagina are nearly identical to those induced by estradiol; 2) the vagina appears to be especially sensitive to the estrogenic actions of BPA; 3) the reproductive tract of the inbred F344 rat appears more sensitive to BPA than that of the outbred SD rat; and 4) continuous exposure to microgram levels of BPA is sufficient for exerting estrogenic actions.     

Protection of mice against gastric colonization by Helicobacter pylori by single oral dose immunization with attenuated Salmonella typhimurium producing urease subunits A and B

Helicobacter pylori is a Gram-negative bacterial pathogen associated with gastritis, peptic ulceration, and gastric carcinoma. The bacteria express a strong urease activity which is known to be essential for colonization of gnotobiotic pigs and nude mice. UreA and UreB, two structural subunits of the active enzyme, were expressed in the attenuated Salmonella typhimurium live vaccine SL3261 strain. Evaluation of protection against H. pylori was performed in Balb/c mice by oral immunization with a single dose of the vaccine strain. Five weeks after immunization, mice were challenged orally three times with a mouse-adapted H. pylori wild type strain and, six weeks later, mice were sacrificed to determine H. pylori infection by detection of urease activity from the antral region of the mouse stomachs. In several independent experiments, we observed 100% infection with H. pylori in the non-immunized mice and no infection (100% protection) in the mice immunized with S. typhimurium expressing recombinant UreA and UreB. Specific humoral and mucosal antibody responses against UreA and UreB were observed in mice immunized as indicated by western blots and ELISA assays. These data shows that oral immunization of mice with urease subunits delivered by an attenuated Salmonella strain induced a specific immune response and protected mice against H. pylori colonization. Single oral dose immunization with UreA and UreB delivered by a live Salmonella vaccine vector appears to be an attractive candidate for human vaccination against H. pylori infection. In addition, this model will aid to elucidate the effective protection mechanisms against H. pylori in the gastric mucosa.     

Oral vaccination against tetanus: comparison of the immunogenicities of Salmonella strains expressing fragment C from the nirB and htrA promoters

We have found the in vivo-regulated nirB promoter (PnirB) to be effective for directing expression of a number of antigens in salmonella in vivo. We wished to determine if other in vivo-regulated promoters have utility for antigen expression in salmonella and to compare the effectiveness of these promoters with that of PnirB. To this end, we have devised a scheme that allows the promoter element of the PnirB-fragment C plasmid pTETnir15 to be swapped with other promoters of interest. We demonstrate the usefulness of this system by replacing PnirB with PhtrA to create plasmid pTEThtrA1. htrA is a stress response gene that is required for virulence of salmonella in mice and survival within macrophages. Expression of fragment C in Salmonella typhimurium BRD509 (aroA aroD) harboring pTEThtrA1 (strain BRD937) correlated with growth temperature in vitro. A comparison was made of the immune responses to fragment C elicited in mice immunized orally with BRD937 or BRD847 (BRD509/pTETnir15) or subcutaneously with purified fragment C plus alhydrogel. High levels of anti-fragment C antibodies that persisted for at least 12 weeks were present in all groups of mice. Vaccination with BRD937 was the most effective means of immunization: the serum immunoglobulin G (IgG), IgA, and IgM anti-fragment C titers were higher in the BRD937-immunized mice throughout the duration of the study than in mice in the other groups. The kinetics of the serum anti-fragment C responses were different in different groups. The response was most rapid in the BRD937 group, with the titers almost at peak levels at 2 weeks postimmunization. Only the mice immunized with BRD937 or BRD847 developed an intestinal IgA response to fragment C. Again, the response was superior in the BRD937 group. The peak of the intestinal response was delayed with respect to the serum response. Analysis of the IgG subtype response to fragment C revealed a dominant IgG2a response in the salmonella-immunized mice, indicating a type 1 helper T-cell response to fragment C, whereas the major subtype in the group parenterally immunized with fragment C plus alhydrogel was IgG1. The IgG1/IgG2a ratio was much higher in sera of BRD937-immunized mice than in sera of BRD847-immunized mice. At 15 to 20 weeks after immunization, the mice immunized with BRD937 or BRD847 were solidly immune to tetanus toxin and salmonella. The immune responses to fragment C seen in mice immunized with BRD937 are the strongest we have observed and indicate that the htrA promoter may be very useful for expressing foreign antigens in salmonella vaccine strains.     

Safety and immunogenicity in humans of an attenuated Salmonella typhi vaccine vector strain expressing plasmid-encoded hepatitis B antigens stabilized by the Asd-balanced lethal vector system

Attenuated Salmonella typhi organisms which express genes encoding protective antigens of other pathogens have been developed for use as experimental oral vaccines. A delta asd S. typhi strain attenuated by deletions in cya, crp, and cdt which contains hepatitis B core (HBc) and pre-S genes encoded on an Asd+ pBR-based plasmid vector was constructed. Healthy adult volunteers ingested a single dose of 5 x 10(5) to 5 x 10(8) CFU of strain chi4073 (delta cya delta crp delta cdt S. typhi Ty2), 6 x 10(7) or 1 x 10(9) CFU of strain chi4632(pYA3149), a further derivative of chi4073 deleted in asd and containing the Asd+ vector without the HBc-pre-S fusion, or 3 x 10(7) or 7 x 10(8) CFU of strain X4632(pYA3167), a derivative containing the vector with the HBc-pre-S fusion. Chi4073 was generally well tolerated by 22 volunteers. No volunteer had fever or positive blood cultures; 4 of 22 volunteers shed vaccine organisms in the stool in the first 48 h only. Two of 18 volunteers who received one of the plasmid-containing derivatives of chi4073 developed low-grade fevers on day 10 or 12 after ingestion. One of these volunteers had positive blood cultures on days 7 and 8. Seven of these 18 volunteers had vaccine organisms detected in their stools in the first 48 h only. Most volunteers developed S. typhi-specific serum responses and developed S. typhi-specific antibody-secreting cells. However, no volunteer developed serum antibody to hepatitis pre-S or pre-S-specific antibody-secreting cells. Although the parent strain chi4073 was well tolerated, induced immunoglobulin G seroconversion to S. typhi lipopolysaccharide in 80 to 100% of vaccinees and stimulated specific IgA-secreting lymphocytes in 80 to 100% of vaccinees given a single oral dose of 2 x 10(7) and 5 x 10(8) CFU, chi4073 derivatives containing the Asd+ vector with and without sequences encoding the HBc-pre-S fusion caused occasional febrile reactions at high doses and did not stimulate detectable immune responses to hepatitis B antigens.     

NGF induces apoptosis in a human neuroblastoma cell line expressing the neurotrophin receptor p75NTR

Galactocerebroside (GalC) and sulfatide are major constituent lipids in vertebrate myelin. Their precise immunolocalization in electron microscopy so far has been hampered by the fact that lipids are not immobilized by chemical fixation and thus get extracted during dehydration with organic solvents. Here, we examined the suitability of cryotechniques for the preservation and immunohistochemical localization of myelin glycolipids in rat brain at the ultrastructural level. Native cerebral cortex tissue, obtained by fine-needle biopsy, was cryoimmobilized by high-pressure freezing and dehydrated by freeze-substitution before embedding in Epon. This procedure resulted in an excellent preservation of brain ultrastructure. Concomitantly, immunogold labeling of ultrathin sections with the well-defined monoclonal antibodies (mAbs) O1, O4, and R-mAb, which were shown to react with GalC and/or sulfatide and some structurally related glycolipids, revealed a good conservation of relevant epitopes. These data suggest that in adult rat cerebral cortex, the most relevant antigens recognized by R-mAb, O1, and O4, namely GalC and sulfatide, are exclusively expressed in myelin structures. Because these mAbs are common markers for the identification of developing oligodendrocytes, this "postembedding glycolipid-labeling technique" holds great potential for studying oligodendroglial differentiation in normal and pathological conditions at the ultrastructural level.     

Lesions in the reproductive tract of boars experimentally infected with porcine rubulavirus

"Blue eye" disease of pigs in Mexico is caused by porcine rubulavirus and characterized by infertility in sows and boars, nervous signs in young pigs, and corneal opacity in pigs of all ages. The pathogenesis of reproductive tract lesions in rubulavirus-infected boars has not previously been investigated. In a first experiment, four 9-month-old boars were inoculated with porcine rubulavirus and killed 5, 15, 30 or 45 days post-inoculation (pi). In a second experiment, four similar boars were inoculated with the same virus and two animals were killed on each of days 70 and 80 pi. Swelling of the head of the epididymis developed in all inoculated boars at approximately day 15 pi. Reduced spermatozoan motility and concentration were detected in semen samples collected from one boar from day 21 pi. At post-mortem examination, nodules were seen in the head of the epididymis of the boars killed 15, 30 or 45 days pi and the right testis of the pig killed 30 days pi was atrophic. Corresponding histopathological epididymal alterations included formation of spermatic granulomas and vacuolar degeneration of ductular epithelium. These lesions were associated with mononuclear cell infiltration and interstitial fibroplasia. Degeneration of seminiferous tubules and interstitial mononuclear cell infiltration were seen in the atrophic testis of the pig killed 30 days pi. There was fibrosis of the head of the epididymis in all boars killed 70 or 80 days pi and one of these animals also had right testicular atrophy associated with degeneration of seminiferous tubules, lymphocytic infiltration and giant cell formation. Porcine rubulavirus antigen was detected by immunofluorescence labelling in the head of the epididymis of the pigs killed 15, 30 or 45 days pi and in one animal killed on day 70 pi. These results indicate that porcine rubulavirus can cause severe epididymo-orchitis and reduced semen quality in sexually mature boars.     

Indirect ultramicroELISA for the detection of total adenovirus antibodies in human serum

An indirect ultramicroELISA method was normalized for the detection of total antibodies to Adenovirus (AD) (UMELISA AD). The optimum concentration of surface antigen determined was 30 micrograms/mL; serum dilution was of 1:40; and conjugate dilution, of 1:1,000. The UMELISA AD was compared with the complement fixing and indirect immunofluorescence techniques. Results showed accordance by 88% and 96.6%, respectively. The method is valid for the screening of antibodies in seroepidemiological studies as well as for the diagnosis of the infection by paired serum samples.     

Comparison of the oral, rectal, and vaginal immunization routes for induction of antibodies in rectal and genital tract secretions of women

To determine which mucosal immunization routes may be optimal for induction of antibodies in the rectum and female genital tract, groups of women were immunized a total of three times either orally, rectally, or vaginally with a cholera vaccine containing killed Vibrio cholerae cells and the recombinant cholera toxin B (CTB) subunit. Systemic and mucosal antibody responses were assessed at 2-week intervals by quantitation of CTB-specific antibodies in serum and in secretions collected directly from mucosal surfaces of the oral cavity, rectum, cervix, and vagina with absorbent wicks. The three immunization routes increased levels of specific immunoglobulin G (IgG) in serum and specific IgA in saliva to similar extents. Rectal immunization was superior to other routes for inducing high levels of specific IgA and IgG in rectal secretions but was least effective for generating antibodies in female genital tract secretions. Only vaginal immunization significantly increased both specific IgA and specific IgG in both the cervix and the vagina. In addition, local production of CTB-specific IgG in the genital tract could be demonstrated only in vaginally immunized women. Vaginal immunization did not generate antibodies in the rectum, however. Thus, generation of optimal immune responses to sexually transmitted organisms in both the rectal and the genital mucosae of women may require local immunization at both of these sites.     

Oral administration of human T-cell leukemia virus type 1 induces immune unresponsiveness with persistent infection in adult rats

The major route of human T-cell leukemia virus type 1 (HTLV-1) infection is mother-to-child transmission caused by breast-feeding. We investigated the host immune responses to orally established persistent HTLV-1 infection in adult rats. HTLV-1-producing MT-2 cells were inoculated into immunocompetent adult rats either orally, intravenously, or intraperitoneally. HTLV-1 proviruses were detected in the peripheral blood and several organs for at least 12 weeks. Transmission of HTLV-1 to these animals was confirmed by analysis of HTLV-1 flanking regions. Despite persistent HTLV-1 presence, none of the orally inoculated rats produced detectable levels of anti-HTLV-1 antibodies, whereas all intravenously or intraperitoneally inoculated rats showed significant anti-HTLV-1 antibody responses. T-cell proliferative responses against HTLV-1 were also absent in orally inoculated rats. Our findings suggest that gastrointestinal exposure of adult rats to HTLV-1-infected cells induces persistent HTLV-1 infection in the absence of both humoral and cellular immune responses against HTLV-1. This immune unresponsiveness at primary infection may subsequently affect the host defense ability against HTLV-1.