Cytotoxic effect of Pasteurella haemolytica on ovine bronchoalveolar macrophages in vitro

The effect of Pasteurella haemolytica A2 infection on phagocytosis efficiency of caprine broncho-alveolar macrophages

An experiment was designed to study the in vivo effect of Pasteurella haemolytica A2 infection on the phagocytosis activity of caprine broncho-alveolar macrophages and the extent of pneumonic lesions. Twelve healthy local Kacang goats, about 7 months of age, were divided into two groups of six. Goats in group 1 were inoculated intratracheally with 4 ml inoculum containing 2.8 x 10(9) colony-forming units (CFU)/ml of Staphylococcus aureus. Goats in group 2 were inoculated intratracheally with 4 ml of inoculum containing 9.5 x 10(8) CFU/ml of Pasteurella haemolytica A2 isolated earlier from pneumonic lungs of goat. At intervals of 3 and 7 days post-challenge five goats from each group were killed and the lungs were washed with sterile phosphate-buffered saline. Smears were prepared from the lung washing fluid and the number of macrophages with phagocytic activity was determined. At day 3 post-infection, goats of both groups showed a similar pattern of pneumonic lesion. The lung washing fluid of goats in group 2 was found to contain numerous neutrophils and macrophages. Goats in group 2 showed significantly (P < 0.05) higher extent of lung lesions than group 1. Similarly, the average extent of lung lesions was significantly (P < 0.05) more severe in group 2 at day 7 post-infection. The lung washing fluid contained mostly macrophages. The phagocytic activity following S. aureus infection was more efficient and significantly (P < 0.01) higher compared with infection by P. haemolytica A2. There were weak correlations between the extent of pneumonic lesion and the phagocytic activity. Thus, goats with poor phagocytic activity were likely to develop more extensive lung lesions.

The inhibitory effect of ovine recombinant interferon-gamma on intracellular replication of Toxoplasma gondii

A model for the in vitro infection of ovine cells with Toxoplasma gondii tachyzoites has been developed and used to investigate the effect of treatment with ovine recombinant interferon-gamma (ov.rIFN gamma) on parasite replication. Treatment of both alveolar macrophages and fibroblast cells either 24 h pre-infection or 2 h post-infection with ov.rIFN gamma inhibited replication of T. gondii and was quantified by suppression of 3H uracil uptake by the parasite. Replication of T. gondii in the fibroblast cells was significantly inhibited by treatment with 200-300 U/ml ov.rIFN gamma, whereas concentrations as low as 1 U/ml suppressed parasite replication in the alveolar macrophages.

Pasteurella haemolytica A1 and bovine respiratory disease: pathogenesis

The severe fibrinonecrotic pneumonia associated with pneumonic pasteurellosis usually results from colonization of the lower respiratory tract by Pasteurella haemolytica biotype A, serotype 1(A1). Despite recent research efforts, the authors lack a detailed understanding of the interactions and host response to P. haemolytica in the respiratory tract. The authors hypothesize that management and environmental stress factors or viral infection alters the upper respiratory tract (URT) epithelium allowing P. haemolytica to colonize the epithelium. Once the URT is colonized, large numbers of organisms enter the lung where they interact with alveolar macrophages. Endotoxin, released from the bacteria, crosses the alveolar wall where it activates pulmonary intravascular macrophages, endothelium, neutrophils, lymphocytes, platelets, complement, and Hageman factor leading to complex interactions of cells and mediators. It is the progression of this inflammatory response with neutrophil influx that is ultimately responsible for the pulmonary injury. Leukotoxin is a major virulence factor of P. haemolytica that allows it to survive by destroying phagocytic cells. At subcytolytic concentrations it may also enhance the inflammatory response by activating cells to produce mediators and release reactive oxygen metabolites and proteases.

Experimental pneumonia in mice produced by combined administration of Bordetella parapertussis and Pasteurella haemolytica isolated from sheep

One-hundred-and-thirty-seven, 3-week-old, Swiss mice were inoculated intranasally with Bordetella parapertussis and Pasteurella haemolytica which had been isolated from naturally occurring cases of chronic non-progressive pneumonia in sheep. The combined administration produced a significantly more severe bronchopneumonia which occurred earlier, persisted for a longer period and involved a higher percentage of mice than that which was produced with B. parapertussis or P. haemolytica alone. These findings demonstrate an additive or synergic action between the two agents or their metabolic products, and provide indirect evidence that such interaction may occur in ovine chronic non-progressive pneumonia.

Lymphocyte subpopulations in peripheral blood of lambs experimentally infected with Pasteurella haemolytica

The lymphocyte subpopulations in peripheral blood obtained from eleven lambs experimentally infected with Pasteurella haemolytica were compared with those obtained from eight control lambs by flow cytometry, using a panel of monoclonal antibodies against specific lymphocyte epitopes. Experimental infection with P. haemolytica was characterized by a transient but significant reduction in SBU-T1+ (CD5+) T cells and SBU-T4+ (CD4+ or helper) T lymphocytes (P less than 0.05) and a significant rise in lymphocytes which did not express the LCA p220 epitope and the pan T cell surface marker (CD5-LCA p220-) ("null"). The reductions in CD5+ and CD4+ lymphocytes occurred 24 h after experimental infection, returning to preinoculation levels 5 days post inoculation (DPI). Five to 9 days after experimental infection, there was a significant increase in the number of lymphocytes, which expresses the pan T cell surface marker (CD5+) but which were CD4-CD8-. Lymphocyte transformation responses to the mitogen phytohaemagglutinin (PHA) were significantly reduced 24 h after experimental infection with P. haemolytica (P less than 0.05).

Morphological and morphometrical analysis of the acute response of the bovine alveolar wall to Pasteurella haemolytica A1-derived endotoxin and leucotoxin

Endotoxin or leucotoxin derived from Pasteurella haemolytica biotype A serotype 1 or saline was deposited by fibreoptic bronchoscopy into the caudal segment of the right anterior lung lobe of calves, and the lesions were characterized by light and transmission electron microscopy. Morphometric techniques were used to determine if changes in the arithmetic mean thickness of the alveolar wall occurred. Group 1 calves (n = 2) were inoculated with 6 ml saline, groups 2 calves (n = 3) received 6 ml of a partially purified leucotoxin preparation, group 3 calves (n = 3) received 96 micrograms of endotoxin in 6 ml of saline and group 4 calves (n = 3) received 2.5 mg of endotoxin in 6 ml of saline. Calves were killed 4 h after inoculation. Lesions in groups 2, 3 and 4 were similar and we found that (a) endotoxin alone is capable of initiating an inflammatory response in the bovine lung, (b) leucotoxin causes cytotoxic changes in alveolar macrophages but not in parenchymal cells of the lung, (c) neutrophil sequestration and platelet aggregation occur in alveolar capillaries in association with pulmonary intravascular macrophages, (d) neutrophils and fibrin were found in the alveolus in close association with alveolar macrophages, (e) disruption of the alveolar epithelial layer occurred in association with neutrophils and (f) there were no significant increases in the arithmetic mean thickness of the alveolar wall.

A colourimetric, microplate assay for the leucotoxin of Pasteurella haemolytica

Culture supernates of Pasteurella haemolytica, which contain leucotoxin, inhibited the reduction of nitroblue tetrazolium (NBT) by bovine and ovine but not rabbit leucocytes in response to phorbol 12-myristate 13-acetate (PMA). Culture supernates of P. multocida, which contain no leucotoxin, had no inhibitory effect on the response of leucocytes from any species. The inhibition of NBT reduction was assessed visually or spectrophotometrically in the wells of microplates and used as a simple assay for leucotoxin. It was as sensitive as the trypan blue dye-exclusion method and did not require the use of radioisotopes. In addition, sera from P. haemolytica-infected calves inhibited leucotoxin activity in the microplate assay. Thus, inhibition of NBT reduction after stimulation of ruminant leucocytes with PMA can be used as a simple, specific assay for leucotoxin and for anti-leucotoxin antibodies.

A crude cytotoxin vaccine protects sheep against experimental Pasteurella haemolytica serotype A2 infection

Three vaccines containing Pasteurella haemolytica serotype A2 antigens were tested for their ability to protect sheep against a homologous challenge. A crude cytotoxin preparation in combination with a sodium salicylate extract (SSE) or crude cytotoxin alone were highly protective (98 and 86%, respectively), whereas SSE alone was poorly (47%) protective. These findings indicated that the crude cytotoxin was an essential component of a protective vaccine. Protection correlated with serum cytotoxin-neutralising (CN) titres and bactericidal activity, which were stimulated by antigens in the crude cytotoxin preparation.

Pneumonia in lambs inoculated with Bordetella parapertussis: bronchoalveolar lavage and ultrastructural studies

Eight colostrum-deprived lambs were inoculated intratracheally with ovine isolates of Bordetella parapertussis. Fluids obtained by bronchoalveolar lavage had a large increase in total cell counts 24 hours after inoculation; up to 93% of cells were neutrophils. From 3 days after inoculation, the number of alveolar macrophages in lavage samples was markedly increased. From 5 days onwards, many alveolar macrophages had moderate to severe cytoplasmic vacuolation. Topographically, tracheal and bronchial epithelium was covered by a large amount of inflammatory exudate 24 hours after inoculation. Later, the tracheobronchial epithelium showed focal extrusions from ciliated cells, which were occasionally associated with B. parapertussis organisms. Ultrastructurally, cytopathological changes associated with B. parapertussis infection were mild focal degeneration of airway epithelium with slight loss of cilia, moderate to severe degeneration of type I and type II alveolar epithelial cells, and focal inflammation in the lungs. These results suggest that the primary targets of B. parapertussis infection are alveolar macrophages and the epithelial cells of bronchioles and alveoli.

The effect of parainfluenza virus type 3 and Pasteurella haemolytica on oxygen-dependent and oxygen-independent bactericidal mechanisms of ovine pulmonary phagocytic cells

Groups of caesarean-derived, colostrum-deprived lambs were inoculated by the intratracheal route with Pasteurella haemolytica, either alone or 4 or 6 days after the inoculation of parainfluenza virus type 3 (PI3). Other groups were inoculated with PI3 followed by veal infusion broth, or with uninfected cell culture fluid followed by veal infusion broth (controls). All lambs were killed 24 h after the second inoculation. Pulmonary phagocytic cells were recovered by lavage and separated into alveolar macrophage (AM) and neutrophil fractions by density gradient centrifugation. Bacterial proliferation was detected in the lungs of all five lambs inoculated with P. haemolytica 6 days after PI3 but in only one of five inoculated with P. haemolytica 4 days after PI3 and one of five inoculated with P. haemolytica alone. The number of phagocytic cells recovered from the lungs was highest in animals inoculated with P. haemolytica 6 days after PI3 and, overall, a greater number of both AM and neutrophils was recovered from the lungs of animals where bacterial proliferation occurred (greater than 10(5.0) P. haemolytica 100 g-1 lung) than from those that controlled the bacterial infection. Oxygen-dependent bactericidal activity of AM and neutrophils was measured by chemiluminescence. Infection with PI3 and P. haemolytica increased the chemiluminescence responses. The highest responses were recorded from lambs inoculated with P. haemolytica 6 days after PI3, the group where pulmonary clearance was poorest. Overall, responses were higher in lambs in which bacterial proliferation occurred than in those that controlled the infection. On the other hand, oxygen-independent bactericidal activity, measured by the direct effects of neutrophil lysates on Escherichia coli, was lowest in lambs inoculated with P. haemolytica 6 days after PI3 and was lower in lambs where bacterial proliferation occurred.

Cytotoxin from an ovine strain of Pasteurella haemolytica: characterisation studies and partial purification

A cell-free, water-soluble cytotoxin from an ovine strain of Pasteurella haemolytica biotype A serotype 1 killed sheep bronchoalveolar macrophages at 37 degrees C, but not at 4 degrees C or 22 degrees C. The cytotoxin was stable over the pH range 2-12, resistant to heat at 60 degrees C but inactivated at 100 degrees C or by autoclaving. Trypsin also destroyed the cytotoxin, which is therefore thought to contain a protein component essential for biological activity. A preliminary purification of the crude cytotoxin using gel-filtration column chromatography resulted in the isolation of a biologically active fraction which resolved as a single protein band and one carbohydrate band on non-dissociating polyacrylamide gels. However, this fraction resolved into approximately 16 component bands on a sodium dodecyl sulphate polyacrylamide gel.

Cytotoxic effect of serotypes of Pasteurella haemolytica on sheep bronchoalveolar macrophages

Ovine isolates of the 15 known serotypes found within the A and T biotypes of Pasteurella haemolytica were cytotoxic for sheep bronchoalveolar macrophages (BAM). Weaker toxicity for the same target cells was also expressed by non-serotypable ovine isolates of P. haemolytica. The results suggest that cytotoxicity for sheep BAM is a virulence factor common to both A and T biotypes of P. haemolytica.

Morphological study of the in vitro cytotoxic effect of alpha-hemolytic E. coli bacteria and culture supernatants on human blood granulocytes and monocytes

The morphological changes of human blood granulocytes and monocytes caused in vitro by alpha-hemolytic strains of E. coli and bacteria-free culture supernatants of these bacteria were studied by light- and transmission electron microscopy. The following sequence of cellular alterations were observed: Cessation of intracellular cytoplasmic streaming and cellular movements succeeded by extension of cytoplasmic pseudopodia, degranulation and development of cytoplasmic and nuclear edema. Within two hours the leukocytes appeared as empty sacks. Finally, long straight filaments were formed between the cells. The changes induced by alpha-hemolytic bacteria and culture supernatants containing free alpha-hemolysin appeared to be identical. The cytotoxic effect became more pronounced as the numbers of bacteria, the hemolytic activity of growth supernatants or the period of incubation were increased. A beta-hemolytic and a nonhemolytic E. coli strain were not cytotoxic.

Immunity of specific pathogen-free lambs to challenge with an aerosol of Pasteurella haemolytica biotype A serotype 2. Pulmonary antibody and cell responses to primary and secondary infections

Specific pathogen-free (SPF) lambs previously exposed to an aerosol of P. haemolytica biotype A serotype 2 (A2) were immune to subsequent challenge with an aerosol of P. haemolytica A2. Untreated control lambs were not immune to this challenge. The local immune responses of the lung to these challenges were examined. High IgG and IgA titres to P. haemolytica and high levels of opsonizing antibody against P. haemolytica were present in the lung washings from previously infected immune lambs at autopsy, seven days after the second infection. Lung washings from control lambs, 7 days after challenge with P13 virus and P. haemolytica A2, had no IgG titres, very little opsonizing activity but did have IgA titres which were significantly higher than in unchallenged control lambs. The cellular response of animals challenged with P13 virus and P. haemolytica was significantly greater than that of unchallenged controls or of lambs exposed only to P. haemolytica. However, this finding was complicated by the response to P13 virus. Lymphocytes from lung washings of all lambs failed to respond in a lymphocyte stimulation test to phytohaemagglutinin while blood lymphocytes did respond. There was little specific response to P. haemolytica antigen in the test.

Effects of Pasteurella haemolytica cytotoxin on ovine peripheral blood leucocytes and lymphocytes obtained from gastric lymph

Ovine peripheral blood leucocytes were separated on discontinuous Percoll density gradients into fractions rich in lymphocytes (PBLy) and polymorphonuclear leucocytes. Supernatant fluid from a dialysis sac culture of Pasteurella haemolytica biotype A serotype 1 (A1) was cytotoxic to these leucocytes in vitro. PBLy retained viability after storage in liquid nitrogen and could be employed in cytotoxicity assays. However, sheep cannulated via the common gastric lymph duct were an excellent source of large numbers of homogeneous lymphoid cells (GLy) which also stored well in liquid nitrogen. As both freshly collected and stored GLy were killed by culture supernatant fluid GLy offer advantages as target cells for further characterisation of the extracellular cytotoxin produced by P. haemolytica. From the results obtained, it is considered that all ovine leucocytes are susceptible to P. haemolytica cytotoxin.

Biochemical and functional properties of a leucocidin produced by several strains of Fusobacterium necrophorum

A soluble exotoxin (a leucocidin) which was lethal to peripheral blood leucocytes from cattle, sheep, rabbits and man (in order of decreasing sensitivity) was elaborated by a variety of isolates of Fusobacterium necrophorum when the majority of organisms were present as filaments in liquid culture. Maximum production of the leucocidin was achieved by concentrations of bacteria equivalent to between 4 X 10(7) and 4 X 10(8) short cells per ml of culture above which no further increase in titre was observed. The ability of different batches of medium to support production of leucocidin was reflected in their capacity to enable F. necrophorum to grow to this range of concentration. Prolonged culture of the organism, resulting in a decline to below 6 in the pH of the medium was associated with a depression in the titre of leucocidin, presumably due to its inactivation under these conditions. The leucocidin was stable at 4 degrees C for at least 30 days, to extremes of pH (4 to 9) for 1 h at room temperature, and showed maximum activity in assays conducted at 37 degrees C at pH 7 to 8. The exotoxin was inactivated by heating at 56 degrees C for 30 min and possessed a molecular weight around 250,000 to 300,000 as determined by gel filtration and membrane partition chromatography.