ROTADIAL: The first nanobody-based immunoassay to detect Group A Rotavirus

ROTADIAL is a rapid nanobody (Nb)-based ELISA assay able to identify Rotavirus group A (RVA) in feces from pediatric patients. The assay is based on a sandwich of two patented llama-derived Nbs directed to the inner capsid viral protein VP6 from RVA. Nbs are directed to conformational epitopes of VP6 and recognized all human RVA strains tested, representing ideal reagents for their use in immunodiagnostic tests for RVA detection. All the steps are carried out at room temperature, bringing results in less than two hours. This assay, named ROTADIAL, was validated with a reference panel of feces from pediatric patients from Argentina. The overall sensitivity and specificity of the ROTADIAL test, when compared to a commercial test, was 100 % (100/100) and 99 % (99/100) respectively. ROTADIAL presented optimal analytical performance, being capable of detecting RVA regardless of the presence of other common human enteric infectious agents and is the first RVA-diagnostic assay developed using Nbs, worldwide.

FMD empty capsids combined with the Immunostant Particle Adjuvant -ISPA or ISA206 induce protective immunity against foot and mouth disease virus

Foot and Mouth Disease Virus (FMDV) causes economy losses and is controlled by vaccination in many countries. Vaccine formulations based on empty capsids or Virus-Like Particles (VLPs) have the advantage of avoiding the biological hazard of using infectious FMDV, albeit are poorly immunogenic. Recently, we have described that ISPA a new Immune Stimulating Complex adjuvant, is useful to improve the response against FMD of vaccines that use inactivated virus. Now, the adjuvant effects of ISPA and ISA 206 (water/oil/water) on a VLPs-based FMD vaccine were evaluated. VLPs (strain A/Argentina/2001) were obtained in mammalian cell cultures and their elicitation of an immune response against FMDV with and without ISPA or ISA 206 was evaluated in mice as a first approach. Notably, VLPs-ISPA and VLPs-ISA 206 vaccines induced protection against viral challenge in 100 % of mice, while protection induced by VLPs alone was of 40 %. Total and neutralizing FMDV antibodies were higher in the VLPs-ISPA and VLPs-ISA 206 groups compared to the VLPs group. VLPs-ISPA induced significantly higher (p < 0.001) IgG1, IgG2a, IgG2b and IgG3 titers than the VLPs vaccine. Moreover, in comparison with non-adjuvanted VLPs, VLPs-ISPA and VLPs-ISA 206 elicited an increased virus-specific T response, including higher IFNγ+/CD8 + lymphocyte production in mice. When these vaccines were tested in calves, antibody titers reached an Expected Percentage of Protection (EPP) above 90 % in the case of the VLPs-ISPA and VLPs-ISA 206 vaccines, while, in the VLPs group, EPP reached 25 %. IFNγ levels secreted by mononuclear cells of VLP-ISPA-vaccinated cattle were significantly higher than in the VLPs group. Overall, the results demonstrate that VLPs-ISPA or VLPs-ISA 206 are promising formulations for the development of a novel FMD vaccine.

An experimental subunit vaccine based on Bluetongue virus 4 VP2 protein fused to an antigen-presenting cells single chain antibody elicits cellular and humoral immune responses in cattle, guinea pigs and IFNAR(-/-) mice

Bluetongue virus (BTV), the causative agent of bluetongue disease (BT) in domestic and wild ruminants, is worldwide distributed. A total of 27 serotypes have been described so far, and several outbreaks have been reported. Vaccination is critical for controlling the spread of BTV. In the last years, subunit vaccines, viral vector vaccines and reverse genetic-based vaccines have emerged as new alternatives to conventional ones. In this study, we developed an experimental subunit vaccine against BTV4, with the benefit of targeting the recombinant protein to antigen-presenting cells. The VP2 protein from an Argentine BTV4 isolate was expressed alone or fused to the antigen presenting cell homing (APCH) molecule, in the baculovirus insect cell expression system. The immunogenicity of both proteins was evaluated in guinea pigs and cattle. Titers of specific neutralizing antibodies in guinea pigs and cattle immunized with VP2 or APCH-VP2 were high and similar to those induced by a conventional inactivated vaccine. The immunogenicity of recombinant proteins was further studied in the IFNAR(-/-) mouse model where the fusion of VP2 to APCH enhanced the cellular immune response and the neutralizing activity induced by VP2.

Comparison of strategies for the production of FMDV empty capsids using the baculovirus vector system

Recombinant FMDV empty capsids have been produced in insect cells and larvae using the baculovirus expression system, although protein yield and efficiency of capsid assembly have been highly variable. In this work, two strategies were compared for the expression of FMDV A/Arg/01 empty capsids: infection with a dual-promoter baculovirus vector coding for the capsid precursor (P12A) and the protease 3C under the control of the polyhedrin and p10 promoters, respectively (BacP12A-3C), or a single-promoter vector coding the P12A3C cassette (BacP12A3C). Expression levels and assembly into empty capsids were analyzed in insect cells and larvae. We observed that the use of the single-promoter vector allowed higher levels of expression both in insect cells and larvae. Recombinant capsid proteins produced by both vectors were recognized by monoclonal antibodies (mAbs) directed against conformational epitopes of FMDV A/Arg/01 and proved to self-assemble into empty capsids (75S) and pentamers (12S) when analyzed by sucrose gradient centrifugation.

First finding of genetic and antigenic diversity in 1b-BVDV isolates from Argentina

Infection with Bovine Viral Diarrhea Viruses (BVDV) in cattle results in a wide range of clinical manifestations, ranging from mild respiratory disease to fetal death and mucosal disease, depending on the virulence of the virus and the immune and reproductive status of the host. In this study 30 Argentinean BVDV isolates were characterized by phylogenetic analysis. The isolates were genotyped based on comparison of the 5' untranslated region (5' UTR) and the E2 gene. In both phylogenetic trees, 76% of the viruses were assigned to BVDV 1b, whereas BVDV 1a, 2a and 2b were also found. Eight of the BVDV 1b isolates were further characterized by cross-neutralization tests using guinea pig antisera and sera from bovines vaccinated with two different commercial vaccines. The results demonstrated the presence of a marked antigenic diversity among Argentinean BVDV isolates and suggest the need to incorporate BVDV 1b isolates in diagnostic strategies.

VP8* antigen produced in tobacco transplastomic plants confers protection against bovine rotavirus infection in a suckling mouse model

Group A rotavirus is a major leading cause of diarrhea in mammalian species worldwide. In Argentina, bovine rotavirus (BRV) is the main cause of neonatal diarrhea in calves. VP4, one of the outermost capsid proteins, is involved in various virus functions. Rotavirus infectivity requires proteolytic cleavage of VP4, giving an N-terminal non-glycosilated sialic acid-recognizing domain (VP8*), and a C-terminal fragment (VP5*) that remains associated with the virion. VP8* subunit is the major determinant of the viral infectivity and one of the neutralizing antigens. In this work, the C486 BRV VP8* protein was produced in tobacco chloroplasts. Transplastomic plants were obtained and characterized by Southern blot, northern blot and western blot. VP8* was highly stable in the transplastomic leaves, and formed insoluble aggregates that were partially solubilized by sonication. The recombinant protein yield was 600 μg/g of fresh tissue (FT). Both the soluble and insoluble fractions of the VP8* plant extracts were able to induce a strong immune response in female mice as measured by ELISA and virus neutralization test. Most important, suckling mice born to immunized dams were protected against oral challenge with virulent rotavirus. Results presented here contribute to demonstrate the feasibility of using antigens expressed in transplastomic plants for the development of subunit vaccines.

Truncated E2 of bovine viral diarrhea virus (BVDV) expressed in Drosophila melanogaster cells: a candidate antigen for a BVDV ELISA

A simple and reliable indirect enzyme-linked immunosorbent assay for detection of antibodies directed against a major bovine viral diarrhea virus (BVDV) immunogen, the E2 glycoprotein (tE2-ELISA), has been developed using the recombinant C-terminal truncated E2 glycoprotein (tE2) expressed in a Drosophila melanogaster system. This strategy demonstrated that tE2 is secreted efficiently in the supernatant, no purification steps are necessary, it is easy to produce and carries out the post translational modifications necessary to preserve its native conformation. Preliminary analysis of 183 cattle serum samples using tE2-ELISA showed a 98% specificity and a 100% sensitivity compared with the standard homologous BVDV virus neutralization test. The results also showed that the tE2 is immunoreactive because the conformation and antigenicity of the original E2 are maintained to a large extent. To our knowledge this is the first study report of the recombinant tE2 of BVDV expressed in D. melanogaster system as an antigen for ELISA.

[Expression of foot and mouth disease virus antigens in transgenic plants]

Owing to its geographical distribution and its highly contagious character, the foot and mouth disease (FMD) virus is responsible for one of the most dreaded of all livestock diseases. The currently-used vaccine is polyvalent and is based on an inactivated virus. Current research on FMD vaccines focuses on the creation of vaccines that are easier and cheaper to produce, and that avoid manipulation of large quantities of virus. The use of transgenic plants to express relevant antigens has been evaluated for the purpose of vaccine production. The authors' working group has taken the FMD virus as a model to evaluate the feasibility of using transgenic plants to express viral antigens and to develop experimental vaccines. The purpose of this paper is to set forth the working group's results in the expression of FMD antigens in transgenic plants.

Passive protection to bovine rotavirus (BRV) infection induced by a BRV VP8* produced in plants using a TMV-based vector

We have previously reported on the use of a tobacco mosaic virus (TMV) vector TMV-30B to express foreign viral antigens for use as experimental immunogens. Here we describe the development of an improved TMV-30B vector that adds a sequence of 7 histidine residues to the C-terminus of recombinant proteins expressed in the vector. We used this TMV-30B-HISc vector to express the VP8* fragment of the VP4 protein from bovine rotavirus (BRV) strain C-486 in plants. Recombinant VP8* protein was purified from N. benthamiana leaves at 7 days post-inoculation by immobilized metal affinity chromatography. The plant-produced VP8* was initially detected using anti-His tag mAb and its antigenic nature was confirmed using both monoclonal and polyclonal specific antisera directed against BRV. Adult female mice, inoculated by the intraperinoteal route with an immunogen containing 4 microg of recombinant VP8*, developed a specific and sustained response to the native VP8* from the homologous BRV. Eighty five percent of suckling mice from immunized dams that were challenged with the homologous virus at the fifth day of age were protected from virus as compared to 35% of the pups from mothers immunized with a control protein. These results demonstrate that the plant-produced VP8* was able to induce passive protection in the new born through the immunization of dams. This suggests that the technology presented here provides a simple method for using plants as an inexpensive alternative source for production of recombinant anti-rotavirus antigens.

Induction of a virus-specific antibody response to foot and mouth disease virus using the structural protein VP1 expressed in transgenic potato plants

We have recently communicated the oral and parental immunogenicity of the structural protein VP1 of foot and mouth disease virus (FMDV) expressed in different transgenic plants. Those results clearly indicated the necessity of increasing the expression of the foreign genes in the transgenic plant to avoid additional steps toward the purification and/or concentration of the antigen of interest. Here, we report the production of transgenic potatoes plants containing the VP1 gene cloned under the regulatory activity of either a single (pRok2) or a double (pRok3) copy of the S35 cauliflower mosaic virus (CaMV 35S) promoter, as a strategy for increasing the level of VP1 gene expression. The presence of the VP1 gene in the plants was confirmed by polymerase chain reaction (PCR) and its specific transcription activity was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR). The results showed that, although the immunized animals presented a FMDV VP1 specific antibody response and protection against the experimental challenge, no significant differences were demonstrated in the immunizing activity of plant extracts obtained from the pRok2 or pRok3 transformed plants. These results confirm those previously obtained using other plant species allowing the possibility of using plants as antigen expression vectors, and demonstrated that at least in the potato system, the use of double CaMV 35S promoter does not cause a significant increase in the level of the VP1 expressed.

High-yield expression of a viral peptide vaccine in transgenic plants

A high-yield production of a peptide vaccine in transgenic plants is described here. A 21-mer peptide, which confers protection to dogs against challenge with virulent canine parvovirus, has been expressed in transgenic plants as an amino-terminal translational fusion with the GUS gene. Transformants were selected on the basis of their GUS activities, showing expression levels of the recombinant protein up to 3% of the total leaf soluble protein, a production yield comparable to that obtained with the same epitope expressed by chimeric plant viruses. The immunogenicity of the plant-derived peptide was demonstrated in mice immunized either intraperitoneally or orally with transgenic plant extracts, providing the suitability of the GUS fusions approach for low-cost production of peptide vaccines.

Serodiagnosis of African swine fever using the recombinant protein p30 expressed in insect larvae

African swine fever (ASF) has a substantial economic impact in many African developing countries and its eradication is based only on an efficient diagnosis program because of the absence of an available vaccine. Previous data suggested the convenience of using the highly antigenic virus protein p30 as ELISA antigen for serological diagnosis of this disease. A simple and efficient method is described for producing the recombinant protein p30 from ASF virus in Trichoplusia ni larvae (cabbage looper) in order to facilitate the large-scale production of this recombinant protein in the absence of fermentation procedures. A baculovirus encoding the virus protein p30 was used to infect insect larvae, showing that recombinant protein production had a sharp optimal peak with a time of occurrence dependent on the initial virus dose inoculated to the larvae. Crude lysates of infected larvae were used without further purification as coating antigen in ELISA to analyse a limited number of sera from natural or experimentally ASF virus infected pigs. Remarkably, the recombinant protein obtained from a single infected larva was sufficient for serological diagnosis of at least 3750 serum samples. Recombinant p30 obtained by this procedure was also used in a confirmatory immunoblotting, reacting with all positive sera tested previously by ELISA. In conclusion, production of the recombinant ASF virus protein p30 in larvae should be applicable to large-scale production of diagnostic reagents for this disease in developing countries, eliminating the need for specialised facilities for tissue culture.

Detection and characterization of functional T-cell epitopes on the structural proteins VP2, VP3, and VP4 of foot and mouth disease virus O1 campos

Foot and mouth disease virus (FMDV) is the cause of a widespread infectious disease affecting cloven-hoofed animals. It is controlled by vaccination with immune-inactivated virus grown in tissue culture. However, peptide vaccines represent a safer alternative to the current virus-inactivated immunogens. Their design requires the identification and evaluation of the sequences recognized by T- and B-lymphocytes. Four structural proteins, VP1, VP2, VP3, and VP4, comprise the viral capsid of the FMDV, but only VP1 has been extensively studied regarding the existence of relevant T-cell epitopes. Here, we utilize a murine model to present a functional T-cell epitope mapping on the complete sequences of VP2, VP3, and VP4 of FMDV O1 Campos. We used two in vitro assays to describe 13 amino acid sequences, each one of them including at least one T-cell epitope. The in vivo T-cell helper function of these sequences was studied in an adoptive cell-transfer assay in mice. Immunization experiments with a fusion peptide containing one of the sequences characterized were also done comparing the helper activity of this sequence with other T-cell epitopes included in the major immunogenic region of VP1.

A comparison of methods for measuring the antibody response in mice and cattle following vaccination against foot and mouth disease

We present a comparison of methods for evaluating the potency of foot and mouth disease vaccine in the laboratory. The anti-FMDV antibodies (Ab) in vaccinated mice were tested by liquid phase (lp) ELISA, solid phase (sp) ELISA and virus neutralization (VN), and were compared with the Ab titres detected by lpELISA, which is the official test in Argentina for testing the potency of FMD vaccines and protection against a virulent challenge in cattle. The results demonstrated that it is possible to relate the Ab levels induced in vaccinated mice with both the Ab and protective responses elicited in cattle. Furthermore, it was found that the anti-FMDV Ab titres in mice detected by lpELISA 14 days after vaccination should be an accurate parameter for predicting the results of the challenge test in cattle. Thus, this test in mice appears to be an inexpensive and rapid alternative for testing FMD vaccines in cattle.

Oral immunogenicity of the plant derived spike protein from swine-transmissible gastroenteritis coronavirus

Transgenic plants represent an inexpensive alternative to classical fermentation systems for production of recombinant subunit vaccines. Transgenic potato plants were created that express the N-terminal domain of the glycoprotein S (N-gS) from Transmissible gastroenteritis coronavirus (TGEV), containing the major antigenic sites of the protein. Extracts from potato tubers expressing N-gS were inoculated intraperitoneally to mice, and the vaccinated mice developed serum IgG specific for TGEV. Furthermore, when potato tubers expressing N-gS were fed directly to mice, they developed serum antibodies specific for gS protein, demonstrating the oral immunogenicity of the plant derived spike protein from TGEV.

Protection of mice against challenge with foot and mouth disease virus (FMDV) by immunization with foliar extracts from plants infected with recombinant tobacco mosaic virus expressing the FMDV structural protein VP1

A tobacco mosaic virus (TMV)-based vector has been used to express in plants the complete open reading frame coding for VP1, the major immunogenic protein of foot and mouth disease virus (FMDV). In vitro RNA transcripts were inoculated into Nicotiana benthamiana plants and detectable amounts of recombinant VP1 were identified by Western blot as soon as 4 days postinfection. Foliar extracts prepared from infected leaves were injected intraperitoneally into mice and all of the immunized animals developed a specific antibody response to both the complete virus particle and the major immunogenic region as determined by ELISA and Western blot analysis. Most importantly, all immunized mice developed a protective immune response against experimental challenge with virulent FMDV. To our knowledge, this is the first report showing the expression of a complete open reading frame of an antigenic foreign protein in plants, using a recombinant plant virus, in sufficient quantity to permit use of the crude plant extract as an experimental immunogen to protect animals against virus challenge.

Improvement of the immune response to foot and mouth disease virus vaccine in calves by using Avridine as adjuvant

The epidemiological analysis of the cattle population during the eradication plan of foot and mouth disease (FMD) in Argentina clearly indicated a higher incidence of the disease in animals within their first year of age. It is important to improve the efficacy of the vaccination in those animals. In a previous report, we have shown the effect of an immunomodulator, Avridine (Avr), in the enhancement of the immune response elicited by FMD virus (FMDV) vaccines in experimental hosts [Berinstein, A., Pérez Filgueira, M., Schudel, A., Zamorano, P., Borca, M., Sadir, A.M., 1993. Avridine and LPS from Brucella ovis: effect on the memory induced by foot-and-mouth disease virus vaccination in mice. Vaccine 11, 1295-1301]. In this report, we analyze the effect of Avr in the improvement of the anti-FMDV immune response elicited in young animals immunized with a tetravalent vaccine. The anti-FMDV antibody response was evaluated using a liquid-phase blocking sandwich ELISA (LPBE) [Smitsaart, E.N., Zanelli, M., Rivera, I., Fondevila, N., Compaired, D., Maradei, E., Bianchi, T., O'Donnell, V., Schudel, A.A., 1998. Assessment using ELISA of the herd immunity levels induced in cattle by foot and mouth disease oil vaccines. Prev. Vet. Med 33, 283-296] while the cellular response was detected using an antigen specific lymphoproliferative test [Zamorano, P., Wigdorovitz, A., Chaher, M., Fernández, F., Sadir, A., Borca, M., 1994. Localization of B and T cell epitopes on a synthetic peptide containing the major immunogenic site of FMDV O1 Campos. Virology 201, 383-387]. The results show that, while no differences were detected in the cellular response, the anti-FMDV antibody reaction was significantly (<0.05) higher in animals immunized with the immunogen containing Avr. At 90 days post vaccination, 89-100% of the animals immunized with Avr presented predicted protection (PP) higher than 82% while just 50-61% of the animals immunized with vaccine without immunomodulator presented that characteristic. Also, it is shown that the increase in the anti-FMDV antibody titre in animals immunized with the vaccine containing Avr was mediated by an increase in the levels of both IgG1 and IgG2 which presented a significative correlation with LPELISA antibodies titres. It is concluded that the addition of Avr in the FMDV vaccines improve the immune status of the calves, the cattle population that suffers the highest epidemiological risk.

Induction of a protective antibody response to foot and mouth disease virus in mice following oral or parenteral immunization with alfalfa transgenic plants expressing the viral structural protein VP1

The utilization of transgenic plants expressing recombinant antigens to be used in the formulation of experimental immunogens has been recently communicated. We report here the development of transgenic plants of alfalfa expressing the structural protein VP1 of foot and mouth disease virus (FMDV). The presence of the transgenes in the plants was confirmed by PCR and their specific transcription was demonstrated by RT-PCR. Mice parenterally immunized using leaf extracts or receiving in their diet freshly harvested leaves from the transgenic plants developed a virus-specific immune response. Animals immunized by either method elicited a specific antibody response to a synthetic peptide representing amino acid residues 135-160 of VP1, to the structural protein VP1, and to intact FMDV particles. Additionally, the immunized mice were protected against experimental challenge with the virus. We believe this is the first report demonstrating the induction of a protective systemic antibody response in animals fed transgenic plants expressing a viral antigen. These results support the feasibility of producing edible vaccines in transgenic forage plants, such as alfalfa, commonly used in the diet of domestic animals even for those antigens for which a systemic immune response is required.

Effect of Mycobacterium sp. wall and Avridine on the antibody response, IgG isotype profile and proliferative response induced by foot and mouth disease virus (FMDV) vaccination in cattle

Different immunomodulators have been previously tested in our laboratory as enhancers of the specific immune response to FMDV vaccines in a murine model [2-4]. Here, we present results of two of these immunomodulators, a water-soluble fraction of the cell wall of Mycobacterium sp. (WSF) and a synthetic lipoamide, Avridine (AV), which were tested in bovines included in FMDV oil vaccines. Two different concentrations of inactivated viral antigen were employed and the effect of different concentrations of the adjuvants were studied when added to the lower viral dose. It is shown that the inclusion of these adjuvants in the higher concentration in vaccines formulated with low antigen concentration induced the same antibody levels as those induced by vaccines containing twice the concentration of virus, and no adjuvants, and as a commercial formulation which performed with 100% of protection in the potency test. The IgG isotypes profiles induced in these experimental vaccines differed from those elicited by the commercial and control vaccines. Both IgG1 and IgG2 were augmented by the experimental formulations. These adjuvants, specially the WSF, also enhanced the cellular immune response against the FMDV in antigen driven proliferation assays, thus acting on a broad range of immune mechanisms.

Modulation of the antigen presentation activity in foot and mouth disease virus (FMDV) vaccines by two adjuvants: avridine and a water soluble fraction of Mycobacterium sp

We have previously demonstrated that the presence of the antigen presenting cells (APC) is critical in the induction and maintenance of the immune response in animals infected or immunized with inactivated FMDV. The use of immunological adjuvants has been repeatedly shown to be essential for the improvement of the immunogenicity in FMDV vaccines. Specifically, we have previously shown that the addition of the synthetic lipoamide Avridine (AVR) or a water soluble fraction of Mycobacterium sp. (WSF) significantly increased the immune response and protection against FMDV challenge. Here, we study the effect of these adjuvants on the induction of APC activity in mice immunized with inactivated FMDV. Both adjuvants were able to induce a long lasting antibody response which correlates with an efficient APC activity. Experiments using sequential cell transfers showed that the presence of the APC activity is not related with the efficiency of keeping free antigen in the vaccinated host. Interestingly, APC from animals immunized with AVR as adjuvant elicited virus neutralizing antibodies, while those APC obtained from donors vaccinated using WSF as adjuvant (or just an oil emulsion) induced anti-FMDV detectable only by ELISA. The analysis of the antibody response to a well studied synthetic peptide raised evidences that indicate that this difference could be explained by a differential presentation of viral B epitopes when different adjuvants were used. These results suggest that the induction of APC should be considered as one of the critical factors in the process of improving the immunogenicity of experimental FMDV vaccines.

Induction of anti foot and mouth disease virus T and B cell responses in cattle immunized with a peptide representing ten amino acids of VP1

We previously demonstrated that the immunization of cattle with a synthetic peptide representing the amino acid sequence of foot and mouth disease virus (FMDV) type O1 Campos VP1 residues 135-160 (p135-160), containing immunodominant T and B epitopes, was able to induce a strong neutralizing antibody (NA) response. The epitope mapping of p135-160 identified T and B epitopes in the area restricted to amino acid residues 135-144 (Zamorano et al. 1994, Virology 201; 1995, Virology 212). We are now reporting that, although immunization with a synthetic peptide covering amino acids 135-144 (p135-144) failed to elicit an anti-FMDV response, a synthetic peptide representing a tandem duplication of the VP1 epitope 135-144 (p135-144 x 2) was very efficient in inducing a strong NA response in cattle. Both the antibody and T cell responses elicited by p135-144 x 2 were highly specific for the VP1 135-144 sequence since no reactivity was detected against synthetic peptides representing the 140-160 sequence of VP1. Additionally, both responses to B and T epitopes were long lasting in the immunized cattle. These results constitute a good example of the improvement of the immune response by rational handling of precisely identified B and T epitopes. To our knowledge, this is the shortest native amino acid sequence to induce a significant NA response to FMDV in cattle.

Protective immune response to foot-and-mouth disease virus with VP1 expressed in transgenic plants

It has been reported recently that genes encoding antigens of bacterial and viral pathogens can be expressed in plants in a form in which they retain native immunogenic properties. The structural protein VP1 of foot-and-mouth disease virus (FMDV), which has frequently been shown to contain critical epitopes, has been expressed in different vectors and shown to induce virus-neutralizing antibodies and protection in experimental and natural hosts. Here we report the production of transformed plants (Arabidopsis thaliana) expressing VP1. Mice immunized with leaf plant extracts elicited specific antibody responses to synthetic peptides representing amino acid residues 135 to 160 of VP1, to VP1 itself, and to intact FMDV particles. Additionally, all of the immunized mice were protected against challenge with virulent FMDV. To our knowledge, this is the first study showing protection against a viral disease by immunization with an antigen expressed in a transgenic plant.

Duration of the foot-and-mouth disease virus antibody response in mice is closely related to the presence of antigen-specific presenting cells

Natural and experimental hosts infected with foot-and-mouth disease virus (FMDV) develop a long-lasting immune response that is closely related to the presence of anti-FMDV antibodies (Ab). We show here that spleen cells from animals which had been infected 3 or more months previously induced an anti-FMDV-Ab response in untreated animals which lasted more than 210 days after cell transfer. Persistence of infectious virus was excluded since virus isolation or detection of the viral genome by PCR in donor splenocytes were consistently negative. The role of antigen presentation (AP) in this phenomenon was studied in vivo by using irradiated splenocytes from virus-sensitized donor mice. Although these irradiated cells were unable to induce anti-FMDV-Ab in normal or irradiated recipient mice, they elicited a strong secondary reaction in FMDV-pre-sensitized recipients. The presence of AP cells (APC) presenting FMDV epitopes (FMDV/APC) was also analysed in mice sensitized to FMDV in different ways. A close correlation between FMDV/APC and the presence of anti-FMDV-Ab was found in infected mice as well as in mice immunized with different doses of inactivated virus, with or without adjuvants. Experiments in vivo and in vitro showed that the APC activity can be specifically blocked with either anti-MHC class II monoclonal antibody or anti-FMDV antiserum, and is dependent on the presence of T cell function. These results strongly suggest that persistent FMDV/APC are responsible for the existence and maintenance of an anti-virus immune response regardless of the immunization method used.

[Mechanisms involved in the prolonged humoral immune response: behavior of aphthous fever virus]

Foot and mouth disease (FMD) is a widespread infectious disease affecting cloven-hoofed animals with severe economic consequences. Animals infected with FMD virus (FMDV) develop an immunological status of immunity characterized by high titers of virus serotype-specific neutralizing antibodies (NAb) which persist for at least 18 months. In contrast, currently inactivated virus vaccines elicit lower antibody response for shorter periods. Protection against FMDV infection has been commonly related to the level of NAb in serum. The new generation vaccines are immunologically poor, and for this reason it is important that the immunological mechanisms are activated during the infection to potentiate the action of these vaccines. The objective of this review is to present the possible mechanisms involved in the long lasting humoral immune response after FMDV infection. The necessity of the Ag for the initiation of the response is well known, although its role in maintaining and regulating the immune response is still unclear. The continuous role of the Ag in maintaining the response was demonstrated in experiments in which Abs with different specificities for long periods of time without the administration of exogen Ag were detected. The capture and retention of Ab-Ag complex by dendritic follicular cells seems to be a important factor in the increase of the Ag production and in the generation of B memory cells. The genomic persistence is strongly related to the Ag persistence. During a persistent infection, in which the genome is maintained and able to synthesize proteins, the immune system would be continuously stimulated. The continuous liberation of soluble Ag, as a productive persistent infection, induces the B cells memory for its differentiation in Abs producing cells. The antigen presenting cells (APC) are cells which present the Ag to lymphocytes in the class II MHC context. Langerhans islets, dendritic, B and phagocytic cells form the APC group. The modulation of the function of the APC cells is very important in the self regulation of the immune system. The function on the immune response depends on the capacity of generating signals for the stimulation of T cells.

A 10-amino-acid linear sequence of VP1 of foot and mouth disease virus containing B- and T-cell epitopes induces protection in mice

The area of foot and mouth disease virus (FMDV) comprising residues 140 and 160 of capsid protein VP1 has been used extensively as an immunogen in natural and experimental hosts. A detailed epitope mapping of this region, however, has not been reported. For this purpose a synthetic peptide containing the residues 135 to 160 (p135-160) of VP1 of FMDV O1 Campos was analyzed for its T- and B-cell epitopes. The p135-160 is highly immunogenic, either by itself or coupled to a carrier protein (BSA), elicits a long-lasting neutralizing antibody response in mice, and provides solid protection against virulent challenge. By using a set of synthetic 10mer overlapping peptides, which cover the entire sequence 135-160 of VP1, we have shown that at least four discrete B epitopes are regularly distributed along the peptide. Although immunization with each of the 10mers coupled with BSA as a carrier protein induced peptide-specific antibody responses, individually none of the 10mers was able to induce neutralizing antibodies. However, anti-135-160 antibodies sorted by immunoaffinity chromatography using each of the 10mers revealed the existence of at least four discrete neutralizing sites: one spanning residues 135-144, at least two more between residues 140 and 154, and another in the region 150-160. Moreover, T-cell epitopes were identified, both by antigen-dependent proliferation assays and by adoptive cell transfer. By both methods, a T-cell epitope was located in the area comprising residues 135-144; the cell transfer experiment, which seems to be more sensitive, also identified a second T-cell epitope between residues 150 and 160. Interestingly, when the region 135-144, which contains both B- and T-cell epitopes, was in a tandem repeat configuration it induced a strong neutralizing antibody response in mice and solid protection against the challenge.

Recognition of B and T cell epitopes by cattle immunized with a synthetic peptide containing the major immunogenic site of VP1 FMDV 01 Campos

The precise location of B and T cell epitopes have been established in a peptide containing the major immunogenic site (residues 135-160) of FMDV strain 01 Campos (01C) VP1. The peptide (p135-160), administered free or conjugated to bovine serum albumin, induced complete protection in guinea pigs and a strong neutralizing antibody (NAb) response in cattle. Using a set of partially overlapping peptides it was shown that although several B cell epitopes were distributed along the p135-160, the residues responsible for the induction of NAb were restricted to the amino acids 135-144. In addition, bovines immunized with the p135-160 showed a strong proliferative response to this peptide but a very poor response against purified virus. Two T-epitopes were located in the 135-160 sequence: one on the region 135-144 and the other in the region 150-160. The immunodominance of these two T cell epitopes was confirmed in cattle immunized with inactivated virus vaccines.