Evidence obtained with monoclonal antibodies that O antigen is the major antigen responsible for the cross-reactivities between serotypes 4 and 7 of Actinobacillus (Haemophilus) pleuropneumoniae

Immunotherapeutic targeting of LIGHT/LTβR/HVEM pathway fully recapitulates the reduced cytotoxic phenotype of LIGHT-deficient T cells

Tumor necrosis factor (TNF)/TNF receptor (TNFR) superfamily members play essential roles in the development of the different phases of the immune response. Mouse LIGHT (TNFSF14) is a type II transmembrane protein with a C-terminus extracellular TNF homology domain (THD) that assembles in homotrimers and regulates the course of the immune responses by signaling through 2 receptors, the herpes virus entry mediator (HVEM, TNFRSF14) and the lymphotoxin β receptor (LTβR, TNFRSF3). LIGHT is a membrane-bound protein transiently expressed on activated T cells, natural killer (NK) cells and immature dendritic cells that can be proteolytically cleaved by a metalloprotease and released to the extracellular milieu. The immunotherapeutic potential of LIGHT blockade was evaluated in vivo. Administration of an antagonist of LIGHT interaction with its receptors attenuated the course of graft-versus-host reaction and recapitulated the reduced cytotoxic activity of LIGHT-deficient T cells adoptively transferred into non-irradiated semiallogeneic recipients. The lack of LIGHT expression on donor T cells or blockade of LIGHT interaction with its receptors slowed down the rate of T cell proliferation and decreased the frequency of precursor alloreactive T cells, retarding T cell differentiation toward effector T cells. The blockade of LIGHT/LTβR/HVEM pathway was associated with delayed downregulation of interleukin-7Rα and delayed upregulation of inducible costimulatory molecule expression on donor alloreactive CD8 T cells that are typical features of impaired T cell differentiation. These results expose the relevance of LIGHT/LTβR/HVEM interaction for the potential therapeutic control of the allogeneic immune responses mediated by alloreactive CD8 T cells that can contribute to prolong allograft survival.

Detection of protein on BTLAlow cells and in vivo antibody-mediated down-modulation of BTLA on lymphoid and myeloid cells of C57BL/6 and BALB/c BTLA allelic variants

B- and T-lymphocyte attenuator (BTLA, CD272) is a polymorphic molecule belonging to the Ig superfamily (SF) that attenuates BCR and TCR-mediated signaling, and thereby functions as a negative regulator of lymphocyte activation. Herein, we report an anti-murine BTLA mAb (clone 4G12b) that remarkably detects protein expression on BTLA(low) cells such as naïve CD4(+) cells, CD8(+) T cells, dendritic cells (DC), as well as in NKT cells and for the first time, we found BTLA expression on DX5(dim) and DX5(bright) subsets of non-T NK cells in both C57BL/6 (B6) and BALB/c BTLA allelic variants. Anti-BTLA 4G12b mAb binds to an overlapping epitope to that recognized by anti-BTLA 6A6 mAb, but in contrast to the concept widely accepted of blocking activity of 6A6 mAb, surprisingly neither 4G12b nor 6A6 mAbs impeded murine HVEM-mIgG(2a).Fc recombinant fusion protein from interacting with BTLA-expressing cells. Lastly, in vivo administration of anti-BTLA 4G12b mAb induced a profound and lasting down-modulation of BTLA expression that led to BTLA receptor internalization with the potential utility of shutting down BTLA expression at any stage during the course of the immune response in both B6 and BALB/c strains of mice.

Padronização de três ELISAs polivalentes com lipopolissacarídeos de cadeia longa dos sorotipos 1 e 5, 2, 3 e 7 ou 10 e 12 de Actinobacillus pleuropneumoniae

Três ELISAs polivalentes baseados em lipopolissacarídeos de cadeia longa (LPS-CL) foram estabelecidos para detectar anticorpos para todos os sorotipos prevalentes de Actinobacillus pleuropneumoniae. Foram testadas amostras provenientes do banco de soros de suínos experimentalmente inoculados com todos os sorotipos de A. pleuropneumoniae. Os ELISAs foram sensíveis à detecção de anticorpos contra todos os LPS-CL. Foram observadas reações cruzadas no ELISA polivalente produzido com os sorotipos 1 e 5, com anti-soros específicos para os sorotipos 9 e 11, pois os sorotipos 1, 9 e 11 apresentaram antígenos somáticos comuns. No polivalente com os sorotipos 2, 3 e 7, observaram-se reações com anti-soros dos sorotipos 4, 6 e 8, devido à presença de antígenos somáticos entre os sorotipos 3, 6 e 8 e entre os sorotipos 4 e 7. Amostras de soros de animais infectados com Mycoplasma hyopneumoniae, Mycoplasma flocculare e Haemophilus parasuis, agentes que acometem o sistema respiratório dos suínos, não apresentaram reações cruzadas com os antígenos baseados em LPS-CL.

Multiplex PCR that can distinguish between immunologically cross- reactive serovar 3, 6, and 8 Actinobacillus pleuropneumoniae strains

We describe a highly sensitive and specific multiplex PCR, based on capsular loci and the species specific apxIV gene, that unequivocally differentiates serovar 3, 6, and 8 Actinobacillus pleuropneumoniae strains that are cross-reactive in conventional immunological tests.

Structural characterization of the antigenic capsular polysaccharide and lipopolysaccharide O-chain produced by Actinobacillus pleuropneumoniae serotype 15

The specific capsular polysaccharide produced by Actinobacillus pleuropneumoniae serotype 15 was determined to be a high-molecular-mass polymer having [alpha]D + 69 degrees (water) and composed of a linear backbone of phosphate diester linked disaccharide units of 2-acetamido-2-deoxy-D-glucose (D-GlcNAc) and 2-acetamido-2-deoxy-D-galactose (D-GalNAc) residues (1:1). Thirty percent of the D-GalNAc residues were substituted at O-4 by beta-D-galactopyranose (beta-D-Galp) residues. Through the application of chemical and NMR methods, the capsule, which defines the serotype specificity of the bacterium, was found to have the structure [structure: see text]. The O-polysaccharide (O-PS) component of the A. pleuro pneumoniae serotype 15 lipopolysaccharide (LPS) was characterized as a linear unbranched polymer of repeating pentasaccharide units composed of D-glucose (2 parts) and D-galactose (3 parts), shown to have the structure [structure: see text]. The O-PS was chemically identical with the O-antigen previously identified in the LPSs produced by A. pleuro pneumoniae serotypes 3 and 8.

Antibody-mediated signaling through PD-1 costimulates T cells and enhances CD28-dependent proliferation

Programmed death-1 (PD-1, CD279) is a molecule expressed on activated T, B and myeloid cells. The role of the interaction of PD-1 ligands (PD-L1 and PD-L2) with PD-1 receptor and the type of signals (costimulatory or inhibitory) that are delivered is a subject of intense debate. Our study has characterized two monoclonal antibodies (mAb) against murine PD-1, termed clone 1H10 and clone 4F10, that recognized different epitopes from that of anti-PD-1, clone J43. We showed that neither of them inhibited anti-CD3-mediated proliferation, but 1H10 mAb induced direct T cell proliferation in the absence of any other stimulus. Moreover, PD-1 engagement with 1H10 mAb costimulated anti-CD3-mediated proliferation and enhanced anti-CD3/CD28 proliferation on both CD4+ and CD8+ T cells in the low range of anti-CD3 concentrations. Anti-PD-1-mediated proliferation induced with 1H10 mAb was also observed in vivo on CD4+ and CD8+ T cells, when CFSE-labeled splenocytes were adoptively transferred to irradiated syngeneic and allogeneic recipients. Overall, our data indicate that PD-1 might not only deliver negative signals to T cells upon interaction through one of its ligands, PD-L1 as reported, but also could costimulate T cells, suggesting a dual potential functional activity of the extracellular domains of this receptor.

Identification and characterization of the TonB region and its role in transferrin-mediated iron acquisition in Haemophilus parasuis

Haemophilus parasuis is the causative agent of Glässer's disease, which is responsible for considerable economic losses in the pig-rearing industry. The aim of the study reported here was the identification, sequencing and molecular characterization of the TonB region that includes tonB, exbBD, and tbpBA genes in H. parasuis. In addition, two fusion proteins were generated. One of them (pGEX-6P-1-GST-TbpB) contained the first 501 amino acids of H. parasuis TbpB protein, while the second (pBAD-Thio-TbpB-V5-His) included the first 102 amino acids of H. parasuis TbpB N-terminus domain. A panel of 14 hybridomas secreting monoclonal antibodies was raised against the two recombinant TbpB fusion proteins. Furthermore, to assess whether the expression of the H. parasuis ExbB, TbpB, and TbpA proteins was upregulated under conditions of restricted availability of iron, a rabbit polyclonal antibody against H. parasuis TbpB-His fusion protein was produced. A rabbit polyclonal antibody against serotype 7 of Actinobacillus pleuropneumoniae ExbB and TbpA proteins was also used for the detection of the homologous proteins in H. parasuis. Overall, the data indicate that H. parasuis, like other members of the Pasteurellaceae family, possesses the genetic elements of the TonB region for iron acquisition and the transferrin-binding proteins encoded under this region are upregulated under restricted iron availability.

Differentiation of Actinobacillus pleuropneumoniae by PCR-REA based on sequence variability of the apxIVA gene and by ribotyping

During the period of 2001-2003, a total of 591 Actinobacillus pleuropneumoniae field isolates from the Czech Republic were serotyped with a high occurrence of cross-reactions. The cross-reactions were observed in 416 isolates. Most frequently, in 401 isolates (67.9%), cross-reactions with antisera specific for serotypes 9, 11, and/or 1 were observed. Two additional molecular methods, ribotyping and restriction analysis of PCR amplified apxIVA gene (PCR-REA), were therefore used for detailed characterisation of A. pleuropneumoniae. In this subsequent analysis, reference strains representing serotypes 1-12 and 25 field isolates showing the most frequent serotype cross-reactions were examined. PCR-REA enabled all reference strains to be distinguished except for the strains of serotypes 9 and 11. Ribotyping distinguished all reference strains except two pairs of serotypes: 3 versus 6, and 9 versus 11, respectively. Field isolates with serotype cross-reactivity 9, 11, and/or 1 could not be differentiated by either of these methods.

Serologic detection of Actinobacillus pleuropneumoniae in swine by capsular polysaccharide-biotin-streptavidin enzyme-linked immunosorbent assay

Serologic detection of Actinobacillus pleuropneumoniae infections in swine have been problematic due to antigenic cross-reactivity of Apx toxins, lipopolysaccharide, and outer membrane proteins between A. pleuropneumoniae serotypes and other bacterial species. To maximize serologic specificity and sensitivity, we developed an assay that uses highly purified A. pleuropneumoniae capsular polysaccharide (CP) conjugated to biotin, which is then bound to streptavidin-coated enzyme-linked immunosorbent assay (CP-BS-ELISA) plates. This assay was used to test a panel of 240 serum samples from pigs prior to challenge, after challenge with bacterial species other than A. pleuropneumoniae, or after challenge with A. pleuropneumoniae serotype 1, 5, or 7. Overall assay results for the individual sera tested were reproducible on the same day and on separate days. The sensitivity of the assay was 100% by ELISAs with biotin-CPs of serotypes 1 and 7 and 87.5% by ELISAs with biotin-CP of serotype 5. Specificity was 100% by ELISAs with biotin-CPs of serotypes 1 and 5 and 94.5% by ELISAs with biotin-CP of serotype 7. The biotin-CPs of at least three A. pleuropneumoniae serotypes could be combined for use in a screening assay to detect antibodies to CPs from strains of different serotypes. In conclusion, the CP-BS-ELISA proved to be a serotype-specific and species-specific assay with high sensitivity for the identification of pigs exposed to A. pleuropneumoniae.

Detection and subtyping of Actinobacillus pleuropneumoniae strains by PCR-RFLP analysis of the tbpA and tbpB genes

A PCR-based procedure for detection and serotype identification of Actinobacillus pleuropneumoniae strains was developed and evaluated. The A. pleuropneumoniae tbpA and tbpB genes were used as targets for amplification of DNA fragments, with a pair of specific primers for each gene. Amplification with tbpA primers rendered a 2.8-kb PCR product from all 12 A. pleuropneumoniae reference strains as well as from Actinobacillus suis strain CCM 5586, while amplification of a 1.9-kb PCR product was observed when testing ten Haemophilus parasuis strains of different serovars. Amplification of the tbpB gene from A. pleuropneumoniae serotypes 1, 6, 8 and 12, and A. suis CCM 5586 rendered an identical 1.8-kb fragment, while from A. pleuropneumoniae serotypes 2, 3, 4, 7, 9, 10 and 11, and H. parasuis strains it produced a 1.7-kb fragment. No PCR amplification product was observed when examining strains of 19 other swine pathogens or closely related species. The minimal detection limit for whole-cell A. pleuropneumoniae templates was between 5-50 and 3 x 10(2)-3 x 10(3) CFU when tbpA and tbpB specific primers, respectively, were used. Restriction fragment length polymorphism (RFLP) analysis of the PCR-generated products rendered different patterns, easily allowing us to discriminate between A. pleuropneumoniae, H. parasuis and A. suis and, more importantly, to distinguish ten RFLP A. pleuropneumoniae groups (the highest discrimination reported so far for a PCR assay with A. pleuropneumoniae), in such a way that the only serotypes with profiles identical to each other were 4 to 11 and 7 to 9. Moreover, the PCR-RFLP analysis was assayed in 36 A. pleuropneumoniae field isolates and in porcine samples (lungs and nasal swabs from experimentally infected animals). In both cases the system proved to be very efficient in A. pleuropneumoniae identification and serotype discrimination.

Actinobacillus species and their role in animal disease

Actinobacillus species are Gram-negative bacteria responsible for several quite distinct disease conditions of animals. The natural habitat of the organisms is primarily the upper respiratory tract and oral cavity. A. lignieresii is the cause of actinomycosis (wooden tongue) in cattle: a sporadic, insidiously-developing granulomatous infection. In sharp contrast is A. pleuropneumoniae which is responsible for a rapidly spreading often fatal pneumonia, common among intensively reared pigs. Detailed investigation of this organism has provided a much clearer picture of the bacterial factors involved in causing disease. A. equuli similarly causes a potent septicaemia in the neonatal foal; growing apparently unrestricted once infection occurs. Other members of the genus induce characteristic pathogenesis in their preferred host, with one, A. actinomycetemcomitans, being a cause of human periodontal disease. This article reviews recent understanding of the taxonomy and bacteriology of the organisms, and the aetiology, pathogenicity, diagnosis and control of animal disease caused by Actinobacillus species.

Identification of Actinobacillus pleuropneumoniae strains of serotypes 7 and 4 using monoclonal antibodies: demonstration of common LPS O-chain epitopes with Actinobacillus lignieresii

Monoclonal antibodies (Mabs) against Actinobacillus pleuropneumoniae serotype 7 were produced and characterized. Three Mabs directed against surface polysaccharides were selected. One of the Mabs was directed against a capsular polysaccharide epitope (CPS) of A. pleuropneumoniae serotype 7 whereas two other Mabs reacted with different epitopes of the LPS O-chain. One of the latter reacted with the reference strain of serotype 7 and the other one with serotypes 7 and 4. These three Mabs were used to test, by Dot-ELISA, 508 field strains of A. pleuropneumoniae. None of the strains belonging to other serotypes different from serotypes 4 and 7 were positive with the Mabs. Used in combination, the CPS and one of the LPS O-chain directed Mabs were shown to be suitable for serotyping since they detected 100% of serotype 7 strains. In this study, we confirm for the first time that A. pleuropneumoniae serotype 4 is present in North America. Finally, both O-chain specific Mabs also reacted with the O-chain of Actinobacillus lignieresii. The cross-reactivity between the two species was confirmed using sera from pigs experimentally infected with A. pleuropneumoniae serotype 7 and A. lignieresii, using immunoblotting and ELISA. This is the first report of a specific cross-reactivity between the LPS of these bacterial species.

Characterization of monoclonal antibodies that recognize common epitopes located on O antigen of lipopolysaccharide of serotypes 1, 9 and 11 of Actinobacillus pleuropneumoniae

Seven murine monoclonal antibodies (mAbs) against serotype 1 of Actinobacillus (Haemophilus) pleuropneumoniae (reference strain Shope 4074) were produced and characterized. All hybridomas secreting mAbs were reactive with whole-cell antigens from reference strains of serotypes 1, 9 and 11, except for mAb 5D6 that failed to recognized serotype 9. They did not react with other taxonomically related Gram-negative organisms tested. The predominant isotype was immunoglobulin (Ig) M, although IgG2a, IgG2b, and IgG3 were also obtained. The epitopes identified by these mAbs were resistant to proteinase K treatment and boiling in the presence of sodium dodecyl sulfate and reducing conditions; however, they were sensitive to sodium periodate treatment. Enhanced chemiluminescence-immunodetection assay showed that mAbs could be divided in two groups according to the patterns of immunoreaction observed. Group 1 (mAbs 3E10, 4B7, 9H5 and 11C3) recognized a ladder-like banding profile consistent with the O antigen of lipopolysaccharide (LPS) from smooth strains. Group II (mAbs 3B10 and 9H1) recognized a long smear of high molecular weight which ranged from 60 to 200 kDa. The mAbs were tested against 96 field isolates belonging to serotypes 1, 5, 9, 11 and 12, which had previously been classified by a combination of serological techniques based on polyclonal rabbit sera (counterimmunoelectrophoresis, immunodiffusion and coagglutination). The panel of mAbs identified all isolates of serotypes 9 and 11, but only 66% of those belonging to serotype 1. This may suggest the existence of antigenic heterogeneity among isolates of A. pleuropneumoniae serotype 1. These mAbs reacted with epitopes common to serotypes 1, 9 and 11 of Actinobacillus pleuropneumoniae which were located on the O antigen of LPS.