Actinobacillus Pleuropneumonia Research Articles

Immune Response to the Dual Antigen Vaccine of Actinobacillus pleuropneumoniae in a Mouse Model

Actinobacillus pleuropneuminiae is the major cause of invasive respiratory disease in swine. To develop an efficient subunit vaccine against pathogens, we designed a dual antigen in a single vaccine that increased the potential for an immune response. We present a dual antigen vaccine (pore-forming domain and nutritional immunity) that induces humoral and cell-mediated T-cell responses, antibodies and TH1 and TH2 cells. Mice were immunized with the dual antigen and individual antigen and then subjected to immune response analysis. A significant antibody response was observed for the dual antigen group. For the cellular immune response, CD4+ and CD8+ T-cell expansion, proinflammatory cytokine (IL-1b, IL-6) and TH2-type cytokine (IL-4, IL-10) gene expression was observed for the dual antigen. Finally, in a challenge test with A. pleuropneumoniae serotype1, the dual antigen, individual antigen and PBS vaccine conferred 100, 40 and 0 % protection. In conclusion, the dual antigen presents critical antigens and increases the efficacy of the vaccine. HIGHLIGHTS The dual antigen vaccine of Actinobacillus pleuropneumonia (ApxII pore - forming domain and TonB2-the nutritional immunity antigen) were formulated as vaccines Mice were vaccinated, immune response analysis and challenge test were performed significant antibody response was observed and improved by approximately 2.5-fold for the dual antigen groups CD4 + and CD8 + T cell expansion was observed for the dual antigen group Protection rate of 100 %, 40 %, and 0 % was observed for the dual antigen, single antigen and negative control groups, respectively GRAPHICAL ABSTRACT

Influence of Probiotic Microorganisms on Microbial Biofilms in Feeds

At different stages of feed production and storage, it is possible to contaminate both feed and their components with various pathogenic and opportunistic microorganisms that can cause infectious diseases not only among animals but also have epidemiological significance. The aim of the study was to isolate biofilm-forming strains of microorganisms from feed, as well as to study the inhibitory activity of the probiotic complex of bacteria of the genus Bacillus against microbial biofilms. Identification and species affiliation of isolated bacterial field isolates were performed by cultural-morphological and biochemical properties. The formation of biofilms was studied by determining the ability of isolates of microbial associations and individual species of microorganisms to adhere to the surface of a 96-well polystyrene tablet according to the method of O'Toole & Kolter, 1998. Determination of microbial contamination of 50 industrial batches of feed from 4 pig farms in two regions of Ukraine (barley, compound feed SK-31 for rearing, SK-51 for fattening pigs, EXCELL starter for pigs 15%, shop prestarter, compound feed for lactating sows). In 11 experimental batches of barley (68.8%) and 13 batches of 3 types of feed (SK-31, SK-51, feed for lactating sows) identified associations with different microorganisms Pasteurella multocida, Corynebacterium striatum, Bacillus subtilis, Leptothrix ochracea, Haemophilus parasuis and yeast Candida albicans. The association of Actinobacillus pleuropneumonia bacteria with B. subtilis was identified in 2 batches (50%) of the shop prestarter. Moderate, by optical density, biofilm formation for associations of microorganisms P. multocida + C. striatum + C. albicans (D620=3.59) and P. multocida + L. ochracea + C. albicans (D620=3.62). Planktonic forms of C. striatum and P. multocida showed low film-forming activity at the level (D620<1.51). Inhibitory activity of the probiotic complex of bacteria of the genus Bacillus (B. subtilis, B. licheniformis, B. amyloliquefaciens) was determined by isolated variations of microbial biofilms in 5 feed species, which displaced all biofilm-forming microorganisms except H. parasuis

Microbial biofilms and microbial contamination of feed for livestock animals: Challenges and ways to overcome them

The article describes the problem of microbial contamination of feed in animal husbandry and the microflora that causes mastitis in lactating cows. The microbial contamination of 52 commercial batches of fodder from 5 farms of 3 regions of Ukraine (barley, corn silage, oat haylage, alfalfa hay, sunflower meal) has been determined. Pasteurella multocida in association with Neisseria lactamica, Actinobacillus pleuropneumonia, Clostridium perfringens was isolated from 61.5% of barley, 66.7% of corn silage, 60.0% of alfalfa hay, and 50.0% of sunflower meal. 262 samples of milk from cows with mastitis have been studied. Aspergillus candidus, Aspergillus niger were most often isolated in association with Mycoplasma bovis, Streptococcus agalactiae, Candida albicans, Neisseria sicca, Clostridium perfringens. High film-forming activity of microorganisms in feed was determined, by optical density: Pasteurella multocida + Actinobacillus pleuropneumonia D620 = 3.76 and Pasteurella multocida, Actinobacillus pleuropneumonia, Neisseria lactamica D620 = 3.62. While from the milk of cows with mastitis we isolated associations of microorganisms that were strong producers of biofilms by the optical densities D620 = 4.02 and 4.23

Методичні підходи щодо бактеріологічної діагностики актинобацилярної плевропневмонії свиней

Методичні підходи щодо бактеріологічної діагностики актинобацилярної плевропневмонії свиней

Therapeutic efficacy of a complex drug based on interferons for Actinobacillus pleuropneumonia in piglets

The article presents the results of studying the therapeutic efficacy of the complex drug tsipropig based on recombinant porcine interferons for Actinobacillus pleuropneumonia of piglets at an industrial pig-breeding complex and its effect on nonspecific immunity. It has been found that the drug has pronounced therapeutic properties and an immunomodulatory effect due to the presence of the fluoroquinolone antibiotic ciprofloxacin in the composition of tsipropig, the immunocorrective activity of its constituent recombinant porcine interferons alpha and gamma and vitamins E and A possessing antioxidant properties.

Associations between animal and herd management factors, serological response to three respiratory pathogens and pluck lesions in finisher pigs on a farrow-to-finish farm

BackgroundSerological screening is a common method to monitor antibody response to pathogen exposure, but results could vary due to several factors. This study aimed to quantify animal and management related factors associated with variation in antibody levels in finisher pigs at slaughter, in an Irish farrow-to-finish farm endemically infected with Actinobacillus pleuropneumonia (App), Mycoplasma hyopneumoniae (Mhyo) and swine influenza virus (SIV). A second objective was to estimate differences in antibody levels in pigs presenting pluck lesions. This was an observational study whereby pigs were managed as per routine farm practice. Data on sow parity, number of born alive (NBA) pigs per litter, cross-fostering status, birth and weaning body weight were recorded from 1016 pigs born from one farrowing batch. At slaughter, blood samples were collected for serological analysis and pigs were inspected for presence of enzootic pneumonia (EP)-like lesions, pleurisy, pericarditis and heart condemnations. Pigs were retrospectively classified into three production flows, depending on time spent in each production stage: flow 1 (F1; pigs followed the normal production flow); flow 2 (F2; pigs which were delayed by 1 week from advancing forward); and flow 3 (F3; pigs delayed by > 1 week from advancing forward). A nested case-control design was applied by matching pigs from each flow by sow parity, birth weight and NBA.ResultsPigs born from primiparous sows had higher antibody levels for App than those born to parity ≥5 sows (P < 0.05) and there was no association between any of the pathogens investigated and other early life indicators (P > 0.05). Pigs in F1 had lower antibody levels for App but higher antibody levels for SIV than F2 and F3 pigs (P < 0.05). There was no association between pluck lesions and respiratory pathogens (P > 0.05), except for increased antibody levels for Mhyo when EP-like lesions were present (P = 0.006).ConclusionResults indicate that offspring from primiparous sows develop higher antibody levels for App IV toxin when exposed to this disease and that enforcement of a strict all-in/all-out production system would reduce on-farm disease circulation. A high percentage of pigs were affected with EP-like lesions which were associated with higher antibody levels for Mhyo.

Actinobacillus pleuropneumoniae Interaction With Swine Endothelial Cells.

Actinobacillus pleuropneumonia is a swine (host) specific respiratory pathogen and the etiological agent of swine pleuropneumonia which affects pigs of all ages, many being asymptomatic carriers. This pathogen has high morbidity and mortality rates which generates large economic losses for the pig industry. Actinobacillus pleuropneumoniae is a widely studied bacterium, however its pathogenesis is not yet fully understood. The prevalence of the 18 serotypes of A. pleuropneumoniae varies by geographic region, in North American area, more specifically in Mexico, serotypes 1, 3, 5b, and 7 show higher prevalence. Actinobacillus pleuropneumoniae is described as a strict extracellular pathogen with tropism for lower respiratory tract. However, this study depicts the ability of these serotypes to adhere to non-phagocytic cells, using an endothelial cell model, as well as their ability to internalize them, proposing it could be considered as an intracellular pathogen.

Herd-level risk factors for chronic pleurisy in finishing pigs: a case-control study

BackgroundChronic pleurisy is a common finding in slaughtered pigs in post-mortem meat inspection. The prevalence of pleurisy has been increasing during the last decade also in Finland. The aim of this prospective case-control study was to search for environmental, infectious and management-related herd-level risk factors for pleurisy in the slaughterhouse. Altogether 46 Finnish pig herds, including 25 control (low pleurisy prevalence in meat inspection) and 21 case (high pleurisy) herds, were enrolled in the study and visited during the tenth week of the rearing period of finishing pigs. Herd personnel were asked about basic herd information, management and environmental factors. Selected pigs were examined clinically, environmental parameters were measured and 15 blood samples per herd were taken during herd visits. Antibodies against Actinobacillus pleuropneumonia serotype 2 (APP2) and ApxIV toxin and swine influenza virus were measured. After the slaughter of study pigs, meat inspection results of the batch were gathered from slaughterhouses. Multivariate logistic regression model was built to identify possible risk factors for a herd to be a case herd (i.e. having high pleurisy values).ResultsFinishing herd type and herd size were observed to act as risk factors. None of clinical signs of pigs, management-related factors or environmental measurements were associated with herd status.ConclusionsAs previously known, in endemic and subclinical infections such as APP, herd factors are important, but detailed risk factors seem to be difficult to identify.

Biofilms of pathogenic bacteria in pig industry

In the industrial pig farm for 26 thousand heads, the analysis of the influence of a forage factor on bacteria carriers of a uterine pig population in connection with mass morbidity of dairy piglets on anaerobic enterotoxemia is carried out. Actinobacillus pleuropneumonia, Pasteurella multocida, Clostridium perfringens, Neisseria spp., Candida albicans, Aspergillus niger which are able to form biofilms, were isolated from five samples of “SK-1” compound feed for pregnant sows and from the blood of animals (n=20) fed with this compound feed. The structural basis of the most stable biofilms in vitro were the aerobic fungi Aspergillus niger and Candida albicans. Biofilm-forming variants of these bacteria showed multidrug resistance to 30 antimicrobial drugs (synthetic penicillins, cephalosporins, fluoroquinolones, aminoglycosides, tetracyclines, combination drugs). Isolates of associative microflora isolated from the blood of sows were pathogenic for 30% of laboratory mice. It was found that probiotic agent No1 (composition based on Bischofite with probiotics) showed the universal bactericidal activity against the bacteria Actinobacillus pleuropneumonia, Pasteurella multocida, Clostridium perfringens, Neisseria spp.

Efficacy of bacterial vaccines to prevent respiratory disease in swine: a systematic review and network meta-analysis.

A systematic review and network meta-analysis (MA) was conducted to address the question, 'What is the efficacy of bacterial vaccines to prevent respiratory disease in swine?' Four electronic databases and the grey literature were searched to identify clinical trials in healthy swine where at least one intervention arm was a commercially available vaccine for one or more bacterial pathogens associated with respiratory disease in swine, including Mycoplasma hyopneumoniae, Actinobacillus pleuropneumonia, Actinobacillus suis, Bordetella bronchiseptica, Pasteurella multocida, Stretococcus suis, Haemophils parasuis, and Mycoplasma hyorhinis. To be eligible, trials had to measure at least one of the following outcomes: incidence of clinical morbidity, mortality, lung lesions, or total antibiotic use. There were 179 eligible trials identified in 146 publications. Network MA was undertaken for morbidity, mortality, and the presence or absence of non-specific lung lesions. However, there was not a sufficient body of research evaluating the same interventions and outcomes to allow a meaningful synthesis of the comparative efficacy of the vaccines. To build this body of research, additional rigor in trial design and analysis, and detailed reporting of trial methods and results are warranted.

Application of PCR technique in diagnosis of four respiratory pathogenic bacteria in pigs at the slaughterhouse

The polymerase chain reaction (PCR) for Actinobacillus pleuropneumonia (App), Haemophilus parasuis (Hps), Pasteurella multocida (Pm) and Bordetella bronchiseptica (Bb) were performed in pure colonies isolated from 114 lung specimens with lesions collected from the Vissan slaughterhouse in Ho Chi Minh City from July 2018 to May 2019. The aim of the experiment was to identify the four respiratory pathogenic bacteria in pigs at slaughterhouse by using PCR technique. The criteria for evaluating the results included the proportion of positive samples with multiplex PCR and percentage of samples co-infected with 2, 3, and 4 bacteria. Among a total of 114 injured lung samples, 21% of the samples was positive to at least one of the four bacteria, 3 samples (2.63%) were positive for App, 2 samples (1.75%) were positive for Hps, 7 samples (6.14%) were for Pm, and 12 lungs (10.53%) were positive for Bb. One sample (0.88%) was found co-infected with Pm and Hps.

Етіологія ензоотичної пневмонії свиней та стратегії боротьби з нею в фермерських господарствах Запорізької та Полтавської областей

Porcine enzootic pneumonia is a multifactorial disease, it leads to large and significant economic losses in pig farms and it remains a relevant veterinary problem. The involvement of new etiological agents in the association of pathogens and the constantly changing conditions on the farms lead to the fact that previously developed control schemes and methods of disease lost their effectiveness. Therefore, the identification of all the infectious agents that make up the association, as well as the concomitant factors that led to the occurrence of the disease in each case is the only correct way to control measures. When we studied the situation in pig farms in the south and in the central region of Ukraine, we found that mycoplasmas were the main etiological agent for Porcine enzootic pneumonia. We noted that mycoplasmosis as a monoinfection was recorded only in 9-12 % of cases. In most outbreaks Mycoplasmas were only members of associations along with Porcine reproductive and respiratory syndrome infection (6%), Type 2 Circovirus infection (6%), enterbacterias (19%) and pasterellas (59%). The course of the disease was also aggravated by the stress of early weaning of piglets and violations of the conditions of feeding and animal welfare. The most difficult enzootic pneumonia occurred in those farms where mycoplasmosis and pasteurellosis were exacerbated by the presence of pathogens of actinobacillus pleuropneumonia. In such farms the average daily weight gain decreased in piglets by a third and feed consumption increased to 28 %. Piglets on affected farms were ill with obvious respiratory clinical signs. And 82% of dead or killed piglets had signs of fibrinous pleuropneumonia or catarrhal pneumonia. In those farms where we recorded associated respiratory infections, we also found reproductive-neonatal infections of pigs. In such farms treatment and prophylactic measures using traditional antimicrobial special remedies and monovaccines, did not give the expected effect. We proposed the use of autovaccines for associated enzootic pneumonia.

Transcript profiling of the immunological interactions between Actinobacillus pleuropneumoniae serotype 7 and the host by dual RNA-seq

BackgroundThe complexity of the pathogenic mechanism underlying the host immune response to Actinobacillus pleuropneumonia (App) makes the use of preventive measures difficult, and a more global view of the host-pathogen interactions and new insights into this process are urgently needed to reveal the pathogenic and immune mechanisms underlying App infection. Here, we infected specific pathogen-free Mus musculus with App serotype 7 by intranasal inoculation to construct an acute hemorrhagic pneumonia infection model and isolated the infected lungs for analysis of the interactions by dual RNA-seq.ResultsFour cDNA libraries were constructed, and 2428 differentially expressed genes (DEGs) of the host and 333 DEGs of App were detected. The host DEGs were mainly enriched in inflammatory signaling pathways, such as the TLR, NLR, RLR, BCR and TCR signaling pathways, resulting in large-scale cytokine up-regulation and thereby yielding a cytokine cascade for anti-infection and lung damage. The majority of the up-regulated cytokines are involved in the IL-23/IL-17 cytokine-regulated network, which is crucial for host defense against bacterial infection. The DEGs of App were mainly related to the transport and metabolism of energy and materials. Most of these genes are metabolic genes involved in anaerobic metabolism and important for challenging the host and adapting to the anaerobic stress conditions observed in acute hemorrhagic pneumonia. Some of these genes, such as adhE, dmsA, and aspA, might be potential virulence genes. In addition, the up-regulation of genes associated with peptidoglycan and urease synthesis and the restriction of major virulence genes might be immune evasion strategies of App. The regulation of metabolic genes and major virulence genes indicate that the dominant antigens might differ during the infection process and that vaccines based on these antigens might allow establishment of a precise and targeted immune response during the early phase of infection.ConclusionThrough an analysis of transcriptional data by dual RNA-seq, our study presents a novel global view of the interactions of App with its host and provides a basis for further study.

Clinical Efficacy and Residue Depletion of 10% Enrofloxacin Enteric-Coated Granules in Pigs.

A new, more palatable formulation of 10% enrofloxacin enteric-coated granules was investigated to evaluate the pharmacokinetic effect in plasma, the residue elimination in tissues and the clinical efficacy against Actinobacillus pleuropneumonia (APP) and Mycoplasam suis (MS) in pigs. In this study, the enrofloxacin concentrations in plasma and tissues were detected using high-performance liquid chromatography with phosphate buffer (pH = 3) and acetonitrile. The pharmacokinetics and elimination of enrofloxacin enteric-coated granules were performed after oral administration at a single dose of 10 mg/kg body weight (bw) and 5 mg/kg twice per day for 5 consecutive days, respectively. The in vivo antibacterial efficacy and clinical effectiveness of enrofloxacin enteric-coated granules against APP and MS were assayed at 2.5, 5, 10 mg/kg, compared with tiamulin (8 mg/kg) based on establishment of APP and MS infection models. 56 APP strains were selected and tested for in vitro antibacterial activity of enrofloxacin enteric-coated granules. The main parameters of elimination half-life (t1/2β), Tmax, and area under the curve (AUC) were 14.99 ± 4.19, 3.99 ± 0.10, and 38.93 ± 1.52 μg h/ml, respectively, revealing that the enrofloxacin concentration remained high and with a sustainable distribution in plasma. Moreover, the analysis on the evaluation of enrofloxacin and ciprofloxacin in muscle, fat, liver and kidney showed that the recovery were more than 84% recovery in accordance with the veterinary drug residue guidelines of United States pharmacopeia, and the withdrawal periods were 4.28, 3.81, 4.84, and 3.51 days, respectively, suggesting that the withdrawal period was 5 d after oral administration of 5 mg/kg twice per day. The optimal dosage of enrofloxacin enteric-coated granules against APP and MS was 5 mg/kg, with over 90% efficacy, which was significantly different (p < 0.05) to the 2.5 mg/kg group, but not to the 10 mg/kg group or the positive control group (tiamulin). In conclusion, 10% enrofloxacin enteric-coated granules had significant potential for treating APP and MS, and it provided an alternative enrofloxacin palatability formulation.

B cell cross-epitope of Propionibacterium acnes and Actinobacillus pleuropneumonia selected by phage display library can efficiently protect from Actinobacillus pleuropneumonia infection

Contagious porcine pleuropneumonia (CPP), caused by Actinobacillus pleuropneumoniae (APP), is a highly transmissible and fatal respiratory illness that causes tremendous economic losses for the pig breeding industry worldwide. Propionibacterium acnes (PA) has a strong cross-reaction with anti-APP1 and anti-APP5 serum and can efficiently prevent APP infection, which was fortuitously found in researching the differential gene between the different APP serotypes. There seems to be some natural cross-protection between PA and APP. To identify the common epitope, the phage display library of a PA whole genome was constructed, whose size is 105. The DNA sequence of the positive clone was determined after three rounds of biopanning, and ten common protein types were identified and the epitope was predicted by computer software. Six peptide epitopes were selected and synthesized for further analysis. Among these epitopes, Ba1, Bb5 and C1 could bind to anti-PA serum and anti-APP1 serum and vice versa. Furthermore, the IgG and IL-4 levels and CD4+/CD8+ T cell ratios in the Ba1, Bb5 and C1 groups were significantly higher than that in the control group, indicating that the epitopes could trigger an immune response, which was mainly humoral immunity. Moreover, Ba1 and Bb5 equally protected 80% of mice from a fatal dose of APP1 infection compared with the control group. Mice could resist APP1 and APP5 challenge after being treated with the combination of Ba1 and Bb5, with survival rates of 80% and 90%, respectively. These findings suggest that the PA epitope confers antigenicity and can heterologously resist to the APP infection. This finding provides a novel strategy for preventing APP infection.

Isolation and the Analysis of 16S rDNA Sequence of Swine Actinobacillus pleuropneumonia

Isolation and the Analysis of 16S rDNA Sequence of Swine Actinobacillus pleuropneumonia

In this issue - June 2012

Assay to measure success of functional parathyroid excision · Palliative radiation therapy for malignant trichoepithelioma · Idiopathic haemarthrosis in horses · Fatal snail bait poisoning in a horse · Utility of diagnostic tests for Actinobacillus pleuropneumonia in pigs · Iodine deficiency disorders in sheep · Immobilisation of estuarine crocodiles

Understanding pathophysiologic mechanisms in severe sepsis using an ensemble of neutrophil kinetic based systemic inflammation model

Objectives: Disease management is becoming increasingly important in our current society, especially considering the growing population of older and immune compromised people. The development of early warning monitors for sepsis/inflammation could be a valuable tool for supporting the clinical care of critically ill patients. Several complex biological processes are involved in sepsis and inflammation, making it a challenging task to quantify infection and inflammation processes in real time. This study aimed at exploring the usefulness of data-based modeling methods to quantify the dynamics of biomarkers (3 cytokines and 4 acute-phase proteins) before and after infection by Actinobacillus pleuropneumonia in pigs as a first step in developing an early warning monitor for sepsis and inflammation processes in the intensive care. Methods: In total, 22 pigs were infected. Blood samples were taken, with a sampling interval of 2 hours. The cytokines, tumor necrosis factor α, interleukin-6 (IL-6) and interleukin-10 (IL-10), and the acute-phase proteins, C-reactive protein, haptoglobin, major acute-phase protein, and serum-amyloid A were analyzed resulting in 7 blood biomarker time series for every pig. To obtain detailed descriptions of the response characteristics to infection, dynamic models were calculated for all biomarkers. Results: Based on the first analysis, 4 biomarkers, namely, Creactive protein, serum-amyloid A, pig–major acute-phase protein, and IL-6, were selected as being most useful for the monitoring. Especially, the response characteristics of IL-6 seem most promising. Significant differences in the dynamics of IL-6 were found between surviving and nonsurviving animals after infection (P = .009). For all biomarkers, model orders and model structures varied between the individual pigs, and thus, the model parameters seemed to be linked with the pigs as individuals stressing the need for individualized monitoring systems. Conclusions: Models as developed in our study could be the first steps toward the development of an objective individualized method for a sensor-based early detection of sepsis and inflammation and early prediction of disease outcome in pigs and later in humans.

The American dream: A quest for high health

There has been at least a decade-long march to improve the health of the US swine industry. This coincided with rapid expansion of many farms and a tremendous change in the ownership structure of the US swine industry (fewer owners having larger sow farms and owning or controlling more pigs). Prior to 1990, the industry consisted of more typical farrow-to-finish farms that would live with chronic diseases such as atrophic rhinitis, Actinobacillus Pleuropneumonia (APP), Swine Dysentery, Mycoplasma pneumonia and a host of enteric organisms. Many of these would persist on an individual farm until either the owner became frustrated, or profitability and production were so poor that depopulation/repopulations were done. This was basically the technology of the 1980s. The late 1980s and early 1990s brought a tremendous amount of new sow farm construction or farm conversion. Nearly all of these were either farrow-to-wean or occasionally farrow-to-feeder pig (25 kg) with off-site finishing. The off-site nurseries and finishers (or recently wean-to-finishers) were built in several different configurations. Some would have 1 week’s worth of pigs on a site, some would have multiple weeks of nursery, some would have multiple weeks of finishing, or some would comingle farms and have only 1 week of nursery or 1 week of finishing on a site.

In vitro migratory responses of swine neutrophils to actinobacillus pleuropneumoniae.

Swine neutrophils were quantitatively examined for the direct and indirect migratory responses to Actinobacillus pleuropneumoniae (APP) in vitro and the effects of pseudorabies virus (PrV), frequently co-infecting with APP, were also observed. About 30% of swine neutrophils responded to viable APP, while 3.2% of the neutrophils responded to 0.1% casein which served as the control. The migration of APP was not affected by preincubation of neutrophils with PrV, which inhibited the random migration. When the random migration was normalized to 1, the chemotactic indices for APP, opsonized-APP and casein were 64, 70 and 8.5, respectively. Heat-killed APP or E. coli lipopolysaccharide stimulated the production of interleukin-8 activity by adherent peripheral blood mononuclear cells (PBMC). Preincubation of PBMC with PrV inhibited the production of neutrophil attractant activity when stimulated with heat-killed APP. The results suggested that the direct chemotaxis of neutrophils to viable APP might contribute to early infiltration in Actinobacillus pleuropneumonia, and that PrV might inhibit indirect recruitment of neutrophils to infected lungs by compromising the functions of PBMC.