The F18 fimbrial adhesin FedF is highly conserved among F18+Escherichia coli isolates

F18+Escherichia coli cause postweaning diarrhoea and oedema disease in newly weaned piglets. Protection against these diseases can be established by preventing the fimbrial adhesion of these bacteria to the enterocytes of the porcine intestine. To test a vaccine against F18+E. coli consisting of the adhesin of F18 fimbriae, FedF, the conservation of the FedF subunit had to be examined. Therefore, the fedF sequence of 37 F18+E. coli isolates from different countries was determined and compared to the fedF gene of the F18ab reference strain F107/86. The amino acid sequence of the mature FedF from the individual F18+E. coli isolates was 96-100% identical to that from E. coli F107/86, but the overall homology was 90.4%. Hyper variable regions were not found in the FedF sequence. The FedF sequence was conserved over the different countries and between the two antigenic variants, F18ab and F18ac, suggesting that F18ab and F18ac strains have the same receptor. Furthermore, the conserved C-terminal region in the FedF adhesin suggests that the F18 fimbriae, in analogy with type 1 and P pili, are assembled by a donor strand mechanism. In conclusion, the reported conservation of FedF supports the usefulness of the fimbrial adhesin as a subunit vaccine against F18+E. coli infection.

F4 (K88) fimbrial adhesin FaeG expressed in alfalfa reduces F4+ enterotoxigenic Escherichia coli excretion in weaned piglets

Transgenic plants are attractive bioreactors to large-scale production of recombinant proteins because of their relatively low cost. This study reports for the first time the use of transgenic plants to reduce enterotoxigenic Escherichia coli (ETEC) excretion in its natural host species. The DNA sequence encoding the major subunit and adhesin FaeG of F4+ ETEC was transformed into edible alfalfa plants. Targeting of FaeG production to chloroplasts led to FaeG levels of up to 1% of the total soluble protein fraction of the transgenic alfalfa. Recombinant plant-produced FaeG (pFaeG) remained stable for 2 years when the plant material was dried and stored at room temperature. Intragastric immunization of piglets with pFaeG induced a weak F4-specific humoral response. Co-administration of pFaeG and the mucosal adjuvant cholera toxin (CT) enhanced the immune response against FaeG, reflected a better induction of an F4-specific immune response. In addition, the intragastric co-administration of CT with pFaeG significantly reduced F4+ E. coli excretion following F4+ ETEC challenge as compared with pigs that had received nontransgenic plant material. In conclusion, transgenic plants producing the FaeG subunit protein could be used for production and delivery of oral vaccines against F4+ ETEC infections.

The Effect of Different Isolation Procedures on Canine Leucocyte Populations and on Lectin-induced Lymphocyte Proliferation

Proliferation assays performed on peripheral blood mononuclear cells (PBMC) are commonly used in experimental and clinical immunology. A prerequisite for an in vitro assay is the ability to obtain relatively pure populations of mononuclear cells from whole blood, as contaminating polymorphonuclear cells may affect the proliferation of lymphocytes. Purification of canine leucocytes from whole blood is associated with difficulties in obtaining pure lymphocytes in high yields. The aim of this study was to optimize the lymphocyte purification from canine whole blood in terms of total cell recovery and purity, while not influencing the proliferation capacity of the isolated cells. To acquire optimal isolation of canine lymphocytes several density gradient media of different densities and osmolalities were examined. For optimal phagocyte removal, pre-treatment of whole blood with carbonyl iron/arabic gum and/or adherence to fibrinogen pre-coated polystyrene tissue flasks were examined. Lectin-induced proliferation was used as measurement of cell activity of the obtained cell fractions after the different separation procedures. Canine blood pre-treated with carbonyl iron/arabic gum followed by density gradient centrifugation with medium 'G' (density: 1.079 g/cm(3), osmolality: 256 mOsm) and adherence to pre-coated polystyrene tissue flask obtained the best PBMC cultures with a median lymphocyte purity of 88% and a median yield of recovered lymphocytes of 54%. This culture also resulted in the highest proliferation and subsequently the highest stimulation index upon lectin stimulation.

Interleukin-8 mRNA expression in synovial fluid of canine stifle joints with osteoarthritis

The objective of this study was to examine and compare the presence of interleukin (IL)-8 mRNA in canine stifle osteoarthritis (OA) differing in etiopathogenesis. Synovial fluid (SF) samples were collected from 24 clinically normal stifle joints and 46 diseased stifle joints (32 stifle joints with cranial cruciate ligament rupture (CCLR), 2 joints with CCLR and patella luxation (PL), 7 joints with medial PL and 5 joints with primary OA). The samples were centrifuged to collect synovial fluid cells for RNA extraction. Reverse transcription polymerase chain reaction (RT-PCR) was performed to obtain cDNA from all samples. Canine IL-8 mRNA expression was determined using real time PCR. Synovial fluid glass smears were made of all samples and coloured with H&E for differential cell counts. All stifle joints were radiographed and graded for the severity of OA. Sixty-one percent (28/46) of the samples from canine stifle OA had IL-8 mRNA expression in contrast to 4% (1/24) in the control stifle joints. This difference in prevalence is highly significant. There were no statistically significant pairwise differences among the mean ranks of the various OA groups for the absolute amount of IL-8 mRNA expression. Neither was there a link between the severity of OA (determined by radiographic evaluation) and the presence of IL-8 in the SF nor any significant difference in the absolute amount of IL-8 between the different OA grades. No statistical difference was found in differential cell counts between IL-8-positive and -negative SF samples. IL-8 cannot be used as a specific joint disease marker since IL-8 expression is found in OA differing in etiopathogenesis. It might, however, relate to the ongoing inflammation within the joint.

Protection of turkeys against Chlamydophila psittaci challenge by DNA and rMOMP vaccination and evaluation of the immunomodulating effect of 1α,25-dihydroxyvitamin D3

Plasmid DNA expressing the major outer membrane protein (MOMP) of an avian Chlamydophila psittaci serovar D strain and recombinant MOMP (rMOMP) with or without the immunomodulating adjuvant 1 alpha,25-dihydroxyvitamin D(3) have been tested for their ability to elicit an immune response and induce protection in turkeys against challenge with the same serovar. Three vaccination strategies were compared: priming and boosting with either pcDNA1::MOMP or rMOMP and priming with pcDNA1::MOMP followed by rMOMP boosting. Turkeys primed with pcDNA1::MOMP showed significant protection against Cp. psittaci challenge, turkeys primed with rMOMP did not. The steroid hormone 1 alpha,25-dihydroxyvitamin D(3) augmented serum and mucosal antibody titres. However, higher antibody titres were not related to better protection and even had a negative effect on especially bacterial excretion.

Development of an enteric-coated pellet formulation of F4 fimbriae for oral vaccination of suckling piglets against enterotoxigenic Escherichia coli infections

A multi-particulate formulation of F4 fimbriae was developed for oral vaccination of suckling piglets against enterotoxigenic Escherichia coli infections. A feasibility test showed that incorporation of F4 fimbriae in a disintegrating pellet formulation consisting of 87.5% Pharmatose 200 M, 2.5% Avicel CL 611 and 10% Explotab by extrusion/spheronisation and subsequent fluid bed drying resulted in the maintenance of 69+/-12% of the biological activity. But subsequent coating resulted in pellets with poor enteric properties, although good in vivo immunising results were obtained after administration to piglets. From the economical point of view, a pellet formulation was optimised to decrease vaccine dose and dosing frequency. After disintegration testing, pellets consisting of lactose (alpha-lactose monohydrate 90 mesh/beta-lactose 75/25 (w/w)) and microcrystalline cellulose in a ratio of 80/20 (w/w) showed a sponge-like structure from which F4 fimbriae could be released. Coating of these pellets resulted in good enteric properties. To improve disintegrating properties of the pellets, the lactose concentration was increased or sodium carboxymethyl starch was added. But this resulted in poor enteric properties after coating. Dissolution test showed that F4 fimbriae were released from the optimised enteric-coated pellets but interaction between F4 fimbriae and the coating polymer was seen. This incompatibility leads to unpredictable in vitro quantification of F4 biological activity.

Correlation Between Type of Adaptive Immune Response Against Porcine Circovirus Type 2 and Level of Virus Replication

Porcine circovirus 2 (PCV2) replication is characterized by high variation among infected pigs. This study investigated the role of immunologic responses in causing this variation. Twelve gnotobiotic pigs were inoculated with PCV2. Four of these pigs were treated with cyclosporin A (CysA) to monitor the effect of the adaptive immunity on the development of the PCV2 infection. Through lymph node biopsies at 10, 15, and 21 days postinoculation (DPI), PCV2 replication in lymphoid tissues was monitored. The production of total PCV2-specific and PCV2-neutralizing antibodies was followed, together with interferon-gamma (IFN-gamma) mRNA expression levels in peripheral blood monocytes as a marker for cellular immunity. In general, the CysA-treated pigs showed the highest PCV2 titers, indicating that the adaptive immunity is necessary to restrain PCV2 replication. Three different PCV2 replication patterns were observed in non-CysA-treated pigs. Pattern 1: In two pigs, PCV2 was not detected. They had the highest neutralizing antibody titers, appearing from 15 DPI. In these pigs a good cellular response was indicated by a peak in IFN-gamma mRNA at 15 DPI. Pattern 2: Five pigs contained low to moderate PCV2 titers at 15 DPI, remaining constant or decreasing towards 21 DPI. Lower neutralizing antibody titers were observed and no rise in IFN-gamma was detected. Pattern 3: In one pig, a low PCV2 titer at 15 DPI dramatically increased toward 21 DPI. Although an antibody response against PCV2 was mounted, no PCV2-neutralizing antibodies were detected. This pig also showed no rise in IFN-gamma. The study findings indicate that variation in the onset of the adaptive immunity may account for variation in PCV2 replication among pigs. Absence of PCV2-neutralizing antibodies may be an important factor in the development of an increased virus replication.

Porcine-specific CpG-oligodeoxynucleotide activates B-cells and increases the expression of MHC-II molecules on lymphocytes

Two CpG-oligodeoxynucleotide motifs, a mouse-specific one (CpG(mouse)) 5'-GCTAGACGTTAGCGT-3' and a porcine-specific one (CpG(pig)), 5'-TGCATCGATGCAG-3' were synthesized by two different companies and tested in vitro for their capacity to stimulate porcine peripheral blood monomorphonuclear cells (PBMC). The porcine-specific motif, consisting of a nuclease-resistant phosphorothioate guanosines at the 5' and at the 3'-end (CpG(pig)-S), enhanced significantly the proliferation of porcine PBMC in comparison with CpG(mouse). The latter motif did not induce any proliferation. Methylation of CpG(pig) diminished the proliferation. Four days of culture with CpG(pig)-S increased the percentage of B-cells as well as B-cell blasting. Moreover, CpG(pig)-S also enhanced the expression of class II MHC in most cultures while there were no changes in percentage of macrophages or in the degree of expression of the macrophage marker (monoclonal 74-22-15). In conclusion, in this study, it was confirmed that 5'-ggTGCATCGATGCAGggggg-3' is a swine-specific CpG-ODN, that activates porcine B-cells and deserves further evaluation in vivo as a potential immunostimulating adjuvant.

Immunocompetence of fattening pigs fed organic versus conventional diets in organic versus conventional housing

The effect of organic or conventional feeding on the immune response of pigs was determined using organic or conventional housing in a pig fattening unit. The experimental design involved four pens of four animals per housing and diet combination (organic housing and organic nutrition; organic housing and conventional nutrition; conventional housing and organic nutrition and conventional housing and conventional nutrition). The IgM, IgA and IgG responses against intramuscularly injected bovine thyroglobulin were determined as indicators of the antigen-specific immune responsiveness. Some general health and welfare related parameters were evaluated by measuring haptoglobin concentrations at selected times; blood lactate concentration was measured at slaughter. Conventional housing led to a higher IgG response three weeks after the first immunisation. Organic housing led to lower haptoglobin and lactate concentrations at slaughter, indicating a higher stress resistance in these pigs. No major differences between the two feeding types were found. We conclude that the immune responses following either a conventional or an organic diet are comparable, whereas organic housing can increase stress resistance at slaughter compared to conventional housing.

Fimbriae of enterotoxigenic Escherichia coli function as a mucosal carrier for a coupled heterologous antigen

Receptor-mediated uptake of orally administered antigen can lead to an antigen-specific immune response, whereas oral administration of most other non-replicating soluble antigens results in the induction of oral tolerance. In the present study, it is shown that fimbriae purified from an F4(K88)(+) enterotoxigenic Escherichia coli strain can function as a mucosal carrier molecule for the model antigen human serum albumin (HSA). Glutaraldehyde-coupled F4/HSA conjugates were able to bind F4 receptor positive (F4R(+)) enterocytes, but not to F4R(-) enterocytes. Moreover, oral immunization of F4R(+) pigs with F4/HSA conjugates induced a HSA-specific immune response, whereas oral immunization with HSA/HSA conjugates did not. This mucosal carrier function of F4 fimbriae was improved following oral co-administration of the F4/HSA conjugates with the mucosal adjuvant cholera toxin (CT) to F4R(+) pigs, since both humoral and cellular HSA-specific responses were significantly increased. In comparison with F4R(+) pigs, the HSA-specific response was reduced following oral F4/HSA+CT immunization of F4R(-) pigs. This indicates that F4 fimbriae as mucosal carrier and CT as adjuvant synergistically improve the induction of a HSA-specific immune response following oral immunization of pigs. These results could open new perspectives in the development of vaccines against enteropathogens.

Immunostimulatory capacity of DNA vaccine vectors in porcine PBMC: a specific role for CpG-motifs?

With the development of DNA vaccines in pigs, the possibility was investigated that the nature and the amount of certain CpG-motifs present on plasmid DNA might have an effect on their immunostimulatory capacity. A panel of three CpG-oligodeoxynucleotides (ODN) and three eukaryotic expression vectors currently used in experimental DNA vaccines in pigs (pcDNA1, pcDNA3.1 and pCI) were screened for their immunostimulatory activity on porcine PBMC by evaluating in vitro the lymphocyte proliferative responses and cytokine profiles (IL-1alpha, IL-2, IL-4, IL-6, IL-10, IFN-gamma, TGF-beta, TNF-alpha). The vectors were chosen so that they differed in number and nature of certain CpG-motifs present on their backbone. CpG-ODN A (5'ATCGAT3') and to a lesser extend CpG-ODN C (5'AACGTT3') significantly enhanced the proliferation of porcine PBMC in contrast to CpG-ODN B (5'GACGTT3') where no effect was observed. Furthermore, CpG-ODN A significantly induced IL-6 and TNF-alpha together with elevated levels of IFN-gamma and IL-2 mRNA expression even though considerable heterogeneity was observed in the response of individual pigs. Comparison of the three vectors showed significantly increased proliferative responses for both pcDNA3.1 and pCI combined with a significant increase in IL-6 mRNA levels for pCI. For pcDNA1, proliferation was absent together with significantly decreased levels of IL-6 and IFN-gamma. CpG-ODN and plasmids both suppressed the TGF-beta and IL-1alpha mRNA expression. Taken together, these data confirm the identity of an optimal immunostimulating CpG-motif in pigs (5'-ggTGCATCGATGCAG-3') and demonstrates that the choice of the vector or the insertion of immunostimulatory motifs can be important in the future design of DNA vaccines in pigs, although further research is necessary to explore the possible link between certain CpG-motifs and the immunogenicity of DNA vaccines.

Immunocompetence in organically fed finishing pigs: effect of corn cob mix

Two consecutive experiments were performed to evaluate the effects on the immune response of corn cob mix (CCM) in an organic pig diet. The immunoglobulin (Ig) M, IgA and IgG responses against an intramuscularly injected model antigen, bovine thyroglobulin, were used as indicator. The experiments were performed in an organic barn with nine pens of four crossbred pigs (two barrows and two sows) from 45 kg to slaughter. In the first experiment, the organic concentrate was mixed with organic CCM-silage to obtain three concentrate: CCM ratios of 100:0, 80:20 and 60:40 (w:w). In the second experiment, three concentrates were produced to obtain diets with equal nutrient levels on a dry matter basis after 0%, 20% and 40% CCM inclusion. Higher inclusion rates of CCM in the ration were accompanied by lower thyroglobulin-specific IgG responses. These effects could not be attributed to one specific component of the CCM, such as fatty acid composition, although there was a degree of correlation with lower vitamin A concentrations. Mycotoxin concentrations were absent or minimal. The study indicated that dietary ingredient composition may affect immunocompetence.

Cholera toxin improves the F4(K88)-specific immune response following oral immunization of pigs with recombinant FaeG

Oral immunization of both humans and animals with non-replicating soluble antigens often results in the induction of oral tolerance. However, receptor-dependent uptake of orally administered soluble antigens can lead to the induction of an antigen-specific immune response. Indeed, oral immunization of pigs with recombinant FaeG (rFaeG), the adhesin of the F4(K88) fimbriae of enterotoxigenic Escherichia coli (ETEC), induces an F4-specific humoral and cellular immune response. This response is accompanied with a reduction in the excretion of F4(+)E. coli following challenge. To improve the immune response against F4, rFaeG was orally co-administered with the mucosal adjuvant cholera toxin (CT). Oral immunization of pigs with rFaeG and CT significantly improved the induction of an F4-specific humoral and cellular immune response and also significantly reduced the faecal F4(+)E. coli excretion following F4(+) ETEC challenge as compared to rFaeG-immunized pigs. Therefore, the present study demonstrates that CT can act in pigs as a mucosal adjuvant for antigens that bind to the intestinal epithelium by a CT-receptor-independent mechanism.

Oral immunization of piglets with recombinant F4 fimbrial adhesin FaeG monomers induces a mucosal and systemic F4-specific immune response

The importance of adhesins in the pathogenicity of several bacteria resulted in studies on their usefulness in vaccines. In this study, the gene of the F4(K88)-fimbrial adhesin FaeG of the pathogenic enterotoxigenic Escherichia coli (ETEC) strain GIS26 was cloned in the pET30Ek-LIC vector and expressed with an N-terminal His- and S-tag in the cytoplasm of BL21(DE3). Recombinant FaeG (rFaeG) subunits were isolated from insoluble cytoplasmic aggregates and refolded into a native-like F4 receptor (F4R)-binding conformation. Indeed, the presence of conformational epitopes was shown by ELISA and the ability to bind the F4R was observed by inhibiting the adhesion of F4+ ETEC to F4R+ villi with increasing concentrations of native-like refolded rFaeG subunits. The rFaeG subunits appear as monomers, whereas the purified F4 fimbriae are multimers. Oral immunization of newly weaned piglets with native-like rFaeG induced a mucosal and systemic F4-specific immune response, significantly reducing F4+ E. coli excretion from 2 till 5 days following challenge infection. However, improvement of stability and immunogenicity of rFaeG is necessary since a higher F4-specific response was obtained following immunization with purified F4 fimbriae. Furthermore, the N-terminal fusion of a His- and S-tag was not detrimental for binding the F4R, supporting the use of FaeG as mucosal carrier. In conclusion, oral immunization with a recombinant fimbrial adhesin subunit of Escherichia coli induces a mucosal and systemic fimbriae-specific immune response.

F4 fimbriae expressed by porcine enterotoxigenic Escherichia coli, an example of an eccentric fimbrial system?

An overwhelming number of infectious diseases in both humans and animals are initiated by bacterial adhesion to carbohydrate structures on a mucosal surface. Most bacterial pathogens mediate this adhesion by fimbriae or pili which contain an adhesive lectin subunit. The importance of fimbriae as virulence factors led to research elucidating the regulation of fimbrial expression and their molecular assembly process. This review provides an overview of the current knowledge of induction, expression and assembly of F4 (K88) fimbriae and discusses its unique as well as its identical characteristics compared to other intensively studied fimbriae or pili expressed by Escherichia coli.

Binding of a monoclonal antibody positively correlates with bioactivity of the F4 fimbrial adhesin FaeG associated with post-weaning diarrhoea in piglets

Piglets are susceptible to F4 (K88)+ enterotoxigenic Escherichia coli (ETEC)-induced neonatal and post-weaning diarrhoea. The F4 fimbriae are composed of some minor subunits and the major subunit FaeG that also constitutes the adhesin. Parenteral vaccination of sows with an F4-containing vaccine protects the suckling piglets against neonatal F4+ ETEC-induced diarrhoea, but no commercial (mucosal) vaccine exists against F4+ ETEC-induced weaning diarrhoea. To develop a vaccine, a bioactive F4-receptor (F4R) binding FaeG molecule is required that binds to the F4R following oral immunization and induces a FaeG-specific immune response. The present study reports the altered binding of the FaeG-specific monoclonal antibody IMM01 with bioactive versus non-bioactive F4 fimbrial adhesin FaeG. The correlation of altered IMM01 binding with altered FaeG bioactivity permits the use of an IMM01-based ELISA as a fast, specific and sensitive in vitro selection for potent F4 or (recombinant) FaeG antigen formulations, useful in an F4+ ETEC vaccine.

Gastrointestinal transit time of nondisintegrating radio-opaque pellets in suckling and recently weaned piglets

The objective was to determine the gastrointestinal (GI) transit times of pellets in piglets at different time points around weaning, as transit times are essential criteria to develop oral drug delivery systems. Nondisintegrating radio-opaque pellets were given orally in order to define the transit times by radiography. The radiographs were analysed with a software programme to calculate the number of pellets present in the different parts of the GI tract. In suckling piglets, the gastric emptying was faster (75% in 1.5 to 3.5 h), and the colonic accumulation (to 73%) was greater than in weaned piglets (3 days, 2 and 3 weeks postweaning, 65% gastric emptying in 18 h, 75% in 17 h, and 75% in 7 h, respectively; maximal colonic accumulations of 48%). Immediately after weaning, the transit was markedly prolonged but shortened with increased postweaning time (3 days, 2 and 3 weeks postweaning, 85% excretion in 175.5, 77, and 50.5 h, respectively). Three weeks postweaning, the transit was no longer affected by weaning as transit times were similar to values reported in growing and adult pigs, and retention appeared to be restricted to the stomach and the colon. These data are of crucial importance in the design of enteric-coated formulations for oral administration of vaccines and therapeutics to young piglets and for human research using the pig model.

Conserved regions in the sequence of the F4 (K88) fimbrial adhesin FaeG suggest a donor strand mechanism in F4 assembly

Oral immunization of newly weaned piglets with recombinant F4 (K88) fimbrial adhesin FaeG induces a F4-specific immune response, significantly reducing F4+ Escherichia coli excretion following challenge. In order to use FaeG subunits in an oral vaccine against F4+ enterotoxigenic E. coli, it is necessary to determine the conservation of the adhesin subunit. Hereto, the faeG sequence was determined of 21 F4ac+ E. coli field isolates from piglets with diarrhoea and subsequently compared with these of the reference strain GIS26 and previously reported FaeG sequences from F4ab, F4ac and F4ad antigenic variant strains. The FaeG amino acid sequence was 96-100% homologous within each F4 serotype, but only 92 and 88% when the F4ab and F4ad antigenic variants were compared with the F4ac antigenic variant. Furthermore, the conserved regions of the adhesin suggest a donor strand mechanism in F4 fimbriae assembly as reported for type 1 and P pili. In conclusion, the results of the reported experiments support the usefulness FaeG in an oral subunit vaccine against F4+ E. coli infections or as a mucosal carrier since the adhesin is conserved among F4+ E. coli field isolates.

Inhibition of adhesion of F18+ Escherichia coli to piglet intestinal villous enterocytes by monoclonal antibody against blood group H-2 antigen

Enterotoxigenic and verotoxigenic F18+ Escherichia coli colonising the pig small intestine, adhere to receptors on intestinal villous enterocytes by F18 fimbriae. The aim of the present study was to define the F18R nature. The knowledge on the nature of this receptor could be important for the development of receptor-based treatments against F18+ E. coli-induced disease. The adhesion of F18+ E. coli to pig intestinal villous enterocytes was analysed in an in vitro assay. The adhesion of F18+ E. coli but not of F4ac+ E. coli was strongly inhibited by monoclonal antibodies (mAb) with blood group H-2 specificity. Conversely, blood group H-1 specific mAb could not inhibit the adhesion of F18+ E. coli nor F4ac+ E. coli. Moreover, the blood group H-2 trisaccharide strongly inhibited the adhesion of F18+ E. coli, but only partially the adhesion of F4ac+ E. coli. These data demonstrate that the F18 receptor contains the blood group antigen H-2 (alpha-fuc-(1-2)-beta-Gal-(1-4)-GlcNAc) as major carbohydrate.

1alpha,25-dihydroxyvitamin D3 increases IgA serum antibody responses and IgA antibody-secreting cell numbers in the Peyer's patches of pigs after intramuscular immunization

Pigs were injected intramuscularly (i.m.) twice with human serum albumin (HSA) with or without 1alpha,25-dihydroxyvitamin D3[1alpha,25(OH)2D3] with a 5-week interval. The supplementation of 1alpha,25(OH)2D3 enhanced the HSA-specific IgA serum antibody response but decreased the IgM, IgG, IgG1 and IgG2 responses. Furthermore, higher numbers of HSA-specific IgA antibody-secreting cells were obtained in systemic lymphoid tissues (local draining lymph node, spleen and bone marrow) as well as in Peyer's patches and lamina propria of the gut (GALT). In addition, the in vivo mRNA expression for Th1 [interferon (IFN)-gamma, interleukin (IL-2)], Th2 (IL-4, IL-6 and IL-10) and Th3 [transforming growth factor (TGF)-beta] cytokines as well as the percentage of different cell subsets (CD2+, CD4+, CD8+, IgM+, MHC II+, CD25+) of monomorphonuclear cells from the local draining lymph node were determined at different time-points after the i.m. immunizations. Cytokine profiles did not resemble a typical Th-cytokine profile using 1alpha,25(OH)2D3: higher levels of IL-10 and significantly lower levels of IL-2 were observed the first day after the primary immunization. However, significantly higher levels of IL-2 and significantly lower levels of IFN-gamma were observed the first day after the second immunization. Furthermore, after the second immunization TGF-beta mRNA expression decreased more quickly in the 1alpha,25(OH)2D3 group. This difference became significant 7 days after the second immunization. One week later a significantly higher percentage of CD25+ cells was observed in this group, indicating more activated T and B cells using the steroid hormone. These results suggest that in pigs the addition of 1alpha,25(OH)2D3 to an intramuscularly injected antigen can enhance the antigen-specific IgA-response and prime GALT tissues, but the relation with cytokines and cell phenotype in the local draining lymph node needs further clarification.

Priming of piglets against enterotoxigenic E. coli F4 fimbriae by immunisation with FAEG DNA

Early vaccination is necessary to protect pigs against postweaning diarrhoea caused by enterotoxigenic Escherichia coli (ETEC). However, at present no commercial vaccine allows successful vaccination. This is partly due to the presence of maternally derived antibodies. Since DNA vaccines are suggested to be superior to protein vaccines in young animals with maternal antibodies, we determined whether the fimbrial adhesin (FaeG) of F4ac(+) ETEC could be used as a plasmid DNA vaccine to prime piglets in a heterologous prime-boost approach. Hereto, pcDNA1/faeG19 was constructed and expression of rFaeG in Cos-7 cells was demonstrated. Thereafter, pigs were immunised (days 0, 21 and 42) intramuscularly by injection or intradermally by gene gun and humoral and cellular immune responses were analysed. Even though responses were low, results demonstrated that intramuscular injection was superior to gene gun delivery for priming the humoral immune response since higher antibody titres were raised, whereas gene gun delivery better induced a cellular response, evaluated by a lymphocyte proliferation assay. Effective priming of the humoral immune response was evidenced by high IgG titres 1 week after a protein boost with purified F4. The low responses to the pcDNA1/faeG19 DNA vaccination suggest that delivery of the DNA and/or the expression of the faeG gene should be improved.

Enteric-coated pellets of F4 fimbriae for oral vaccination of suckling piglets against enterotoxigenic Escherichia coli infections

To prevent enterotoxigenic Escherichia coli (ETEC) induced postweaning diarrhoea, the piglet needs an active mucosal immunity at the moment of weaning. In the present study, the feasibility of oral vaccination of suckling piglets against F4+ETEC infection with F4 fimbriae was studied. Furthermore, oral vaccination with enteric-coated pellets of F4 fimbriae was compared to vaccination with F4 fimbriae in solution. Therefore, piglets were orally administered 1mg F4 fimbriae in pellets or in solution during three successive days at the age of 7 and 21 days, whereas control piglets were not vaccinated. Five days postweaning (33 days of age), all animals were orally challenged with F4+ETEC. Despite the induction of an immune response upon oral administration of both F4 fimbriae in pellets as in solution, the colonisation of the small intestine by F4+ETEC upon oral challenge could not be prevented. However, a marginal but significant reduction in F4+ E. coli faecal excretion was found in the piglets vaccinated with F4 fimbriae in pellets, indicating that the use of an enteric-coat which protects the F4 fimbriae against inactivation by milk factors and degradation by enzymes and bile improves vaccination.

Open status of pig-breeding farms is associated with slightly higher seroprevalence of F18+ Escherichia coli in northern Belgium

F18+ enterotoxigenic and verotoxigenic Escherichia coli (E. coli) are widespread and induce post-weaning diarrhoea and oedema disease, respectively. No commercial vaccine exists. Therefore, the F18 herd seroprevalence of 178 randomly selected pig-breeding farms in northern Belgium was evaluated by determining F18-specific IgG antibody titres in pooled sera of sows per breeding farm. This survey reported the first data concerning F18 herd seroprevalence and showed that F18+ E. coli seroprevalence was common in northern Belgium. Significantly more open pig-breeding farms were F18 seropositive (96.4%) compared to closed (88.8%). Furthermore, no clear association was determined between the F18 herd seroprevalence and the number of sows per breeding farm (rsp = 0.19), or with the number of fattening pigs per breeding farm (rsp = 0.17).