Preincubation of bovine blood neutrophils with bovine herpesvirus-1 does not impair neutrophil interaction with Pasteurella haemolytica A1 in vitro

Gene expression profiling of bovine bronchial epithelial cells exposed in vitro to bovine herpesvirus 1 and Mannheimia haemolytica

Bovine respiratory disease (BRD) often occurs when active respiratory virus infections (BHV-1, etc.) impair resistance to Mannheimia haemolytica infection in the lower respiratory tract. The interactions that occur when the respiratory epithelium encounters these viral and bacterial pathogens are poorly understood. We used Agilent bovine gene microarray chips containing 44,000 transcripts to elucidate bovine bronchial epithelial cell (BBEC) responses following in vitro exposure to BHV-1 alone, M. haemolytica alone, or both BHV-1 and M. haemolytica. Microarray analysis revealed differential regulation (>2-fold) of 978 transcripts by BHV-1 alone, 2040 transcripts by M. haemolytica alone, and 2189 genes by BHV-1 and M. haemolytica in combination. M. haemolytica treatment produced significantly greater inductions (>10-fold) of several inflammation associated genes, such as CXCL2, IL-6, IL-1α, e-selectin, and IL-8, than to BHV-1 alone. Functional analysis of the microarray data revealed a significant upregulation of genes involved in important biological processes such as inflammation (TNF-α, IL-8, Tlr-2, IL-1, CXCL2, CSF2), vascular functions (VEGF, EDN2) and leukocyte migration (ICAM1, IL-16) during a co-infection with BHV-1 and M. haemolytica compared to either pathogen alone. This study provides evidence to support that lung epithelial cells are a source of mediators that may promote inflammatory changes observed during bovine respiratory disease.

Impairment of oxidative burst in porcine neutrophils induced by pseudorabies virus

Industrial swine production is affected by several serious viral diseases, such as pseudorabies, hog cholera, porcine reproductive and respiratory syndrome, which are frequently complicated with the increased incidence of bacterial complications such as Actinobacillus pleuropneumoniae (APP). This clinical observation is suggestive of a virus-bacteria synergism on the pathogenesis. One hypothesis is that viruses induce polymorphonuclear cell (PMNs, primarily neutrophils) dysfunction resulting in defective antibacterial resistance. The purpose of this study was to use the pseudorabies virus (PrV) as a model to explore the possibility of virus-induced PMN dysfunctions in pigs. The goals were to evaluate, in ex vivo settings, the oxidative burst (OB) function of pig PMNs, and to evaluate whether PrV could affect these responses to APP. We found that PrV served as a mild OB stimulant (2-fold) to pig PMNs, which also launched a significant burst to phorbol 12-myristate 13-diacetate (PMA; 61-fold), to non-opsonized, heat-killed and formaldehyde-fixed APP (8-fold), and to normal pig serum-opsonized APP (34-fold). Interestingly, the PMA-induced OB could be reduced 50-70% by preincubating PMNs with PrV, and the critical target was not likely the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase itself. Inactivated PrV was as efficient as viable PrV at exerting the inhibitory effect. On the other hand, PrV exerted a primarily additive effect on APP-induced OB, when the cytotoxic effect of APP on PMNs was avoided. The current finding suggests the possibility that activated PMNs are susceptible to PrV-induced dysfunction, and that the PrV-APP synergism may require upstream stimuli of PMNs to be initiated.

BHV-1 infection and inflammatory cytokines amplify the interaction of Mannheimia haemolytica leukotoxin with bovine peripheral blood mononuclear cells in vitro

Bovine herpesvirus-1 (BHV-1) has been reported to increase the susceptibility of cattle to respiratory disease caused by Mannheimia (Pasteurella) haemolytica A1. The principal virulence factor of M. haemolytica is a leukotoxin (LKT) that can specifically kill ruminant leukocytes following its binding to the beta2-integrin CD11a/CD18 (lymphocyte function-associated antigen 1 (LFA-1)). In this study, we investigated the effects of experimental infection of bovine peripheral blood mononuclear cells (MNCs) with BHV-1 in vitro, on the subsequent interaction of these cells with the M. haemolytica LKT. We found that BHV-1 infection increased LFA-1 expression (as assessed by flow cytometry), and subsequently enhanced LKT binding and cytotoxicity to bovine MNCs. We also found that BHV-1 infection increased CD18, IL-1beta, and IFN-gamma mRNA expression by MNCs. As previously reported for bovine polymorphonuclear neutrophils (PMNs), MNCs increased their expression of LFA-1, and their LKT binding and cytotoxicity, following exposure to IL-1beta, TNF-alpha, and IFN-gamma. These findings suggest that BHV-1 infection, and the resulting release of inflammatory cytokines, can stimulate expression of LFA-1 in bovine MNCs, thus enhancing the binding and biological effects of LKT. If such a mechanism occurs in vivo it might explain, in part, the increased susceptibility of BHV-1 infected cattle to bovine pasteurellosis.

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.

Influence of Pasteurella haemolytica A1 crude leukotoxin on bovine neutrophil chemiluminescence

Pasteurella haemolytica A1 crude leukotoxin (25%, vol/vol) rapidly diminished the bovine neutrophil chemiluminescence response to opsonized zymosan. This inhibition was neither prevented nor reversed by 75 mM sucrose. Dilute leukotoxin did not directly stimulate neutrophil chemiluminescence nor did it alter the chemiluminescence response of the neutrophils to opsonized zymosan.

Modulation of bovine neutrophil antibacterial activities by Pasteurella haemolytica A1 purified capsular polysaccharide

Preincubation of bovine neutrophils with Pasteurella haemolytica A1 purified capsular polysaccharide markedly diminished their ability to ingest and kill P. haemolytica, but not Escherichia coli, in vitro. Ingestion and killing were impaired even when the P. haemolytica were preopsonized, thus suggesting that the inhibitory effects of the polysaccharide included a direct effect on bovine neutrophils rather than simply competition for serum opsonins. Preincubation of neutrophils with purified polysaccharide did not elicit a chemiluminescence response, nor did it alter the chemiluminescence response of neutrophils to subsequent stimulation with opsonized P. haemolytica or opsonized zymosan. In addition, purified polysaccharide alone was neither chemotactic nor did it induce a shape change in bovine neutrophils. These data suggest that the deposition of capsular polysaccharide in the lung during the onset of pulmonary pasteurellosis might impair the ability of neutrophils to ingest and kill P. haemolytica. The capsular polysaccharide of P. haemolytica, therefore, may contribute in part to the fibrinous pleuropneumonia that characterizes acute pasteurellosis.

Effects of immunization with bovine herpesvirus-1 glycoproteins on bovine herpesvirus-1-induced alteration of bovine neutrophil chemotactic and anti-Pasteurella haemolytica activities

It has been reported previously that active bovine herpesvirus-1 (BHV-1) infection greatly enhances the susceptibility of cattle to secondary bacterial pneumonia involving Pasteurella haemolytica. The present study examines the possibility that immunization of BHV-1 naive calves with purified BHV-1 glycoproteins would protect them against changes in neutrophil function that might compromise their ability to eliminate P. haemolytica during an active BHV-1 infection. The results show that circulating neutrophil chemotactic activity was generally reduced at 7-8 days after BHV-1 challenge; immunization with a 77 kilodalton BHV-1 glycoprotein (gIV) prevented impairment of neutrophil chemotaxis. BHV-1 infection did not markedly affect the ability of neutrophils to ingest and kill P. haemolytica in vitro. Immunization and challenge with BHV-1 had little effect on the chemiluminescence response of bovine neutrophils to opsonized P. haemolytica in vitro, although in one experiment a marked increase in baseline neutrophil chemiluminescence was observed which may be relevant to understanding the pathogenesis of pulmonary damage that occurs in BHV-1 infected calves.