Induction of inflammatory cytokines in bovine alveolar macrophages following stimulation with Pasteurella haemolytica lipopolysaccharide

Identification, Biochemical Characterization, and In Vivo Detection of a Zn-Metalloprotease with Collagenase Activity from Mannheimia haemolytica A2

Respiratory diseases in ruminants are a main cause of economic losses to farmers worldwide. Approximately 25% of ruminants experience at least one episode of respiratory disease during the first year of life. Mannheimia haemolytica is the main etiological bacterial agent in the ruminant respiratory disease complex. M. haemolytica can secrete several virulence factors, such as leukotoxin, lipopolysaccharide, and proteases, that can be targeted to treat infections. At present, little information has been reported on the secretion of M. haemolytica A2 proteases and their host protein targets. Here, we obtained evidence that M. haemolytica A2 proteases promote the degradation of hemoglobin, holo-lactoferrin, albumin, and fibrinogen. Additionally, we performed biochemical characterization for a specific 110 kDa Zn-dependent metalloprotease (110-Mh metalloprotease). This metalloprotease was purified through ion exchange chromatography and characterized using denaturing and chaotropic agents and through zymography assays. Furthermore, mass spectrometry identification and 3D modeling were performed. Then, antibodies against the 110 kDa-Mh metalloprotease were produced, which achieved great inhibition of proteolytic activity. Finally, the antibodies were used to perform immunohistochemical tests on postmortem lung samples from sheep with suggestive histology data of pneumonic mannheimiosis. Taken together, our results strongly suggest that the 110-Mh metalloprotease participates as a virulence mechanism that promotes damage to host tissues.

Enhanced phagocytosis and complement-mediated killing of Mannheimia haemolytica serotype 1 following in-frame CMP-sialic acid synthetase (neuA) gene deletion

IMPORTANCE

The Gram-negative coccobacillus Mannheimia haemolytica is a natural inhabitant of the upper respiratory tract in ruminants and the most common bacterial agent involved in bovine respiratory disease complex development. Key virulence factors harbored by M. haemolytica are leukotoxin, lipopolysaccharide, capsule, adhesins, and neuraminidase which are involved in evading innate and adaptive immune responses. In this study, we have shown that CMP-sialic acid synthetase (neuA) is necessary for the incorporation of sialic acid onto the membrane, and inactivation of neuA results in increased phagocytosis and complement-mediated killing of M. haemolytica, thus demonstrating that sialylation contributes to the virulence of M. haemolytica.

Hematological and immunological responses to naturally occurring bovine respiratory disease in newly received beef calves in a commercial stocker farm

The objective was to determine temporal changes in hematological and immune parameters in response to naturally occurring bovine respiratory disease (BRD) in commercially managed stocker calves. Forty newly weaned beef steers purchased from auction markets were housed at a commercial stocker operation in Crossville, TN. Blood samples, rectal temperature, and thoracic ultrasonography (TUS; 1: normal to 3: severe) were collected on days 0, 7, 14, and 21. Castration status (FC: freshly castrated; PC: previously castrated) was determined on arrival based on presence of a fresh castration site at the scrotum. Calves received antibiotics for BRD based on clinical severity scoring (CSS; 0: moribund, 4: moribund) and rectal temperature. Complete blood counts (CBC) were performed. Calves were categorized based on the number of treatments (NumTrt) received (0x, 1x, and 2x). Temporal variations in CBC and immune parameters were analyzed using mixed model repeated measure ANOVA (Proc GLIMMIX; SAS 9.4). Variation of CBCs and immune parameters based on TUS was determined using mixed model ANOVA. There was a NumTrt by day interaction effect on the responses of white blood cells (WBC) (P = 0.04) and haptoglobin (HPT) (P = 0.04). On day 21, WBC were greater in the 2x NumTrt group than other groups, but there were no differences in WBC between NumTrt levels on other days. Haptoglobin was greater in the 2x group on days 14 and 21 than 0x or 1x. Red blood cells (RBC) (P = 0.02) and WBC (P = 0.04) differed between FC and PC groups, and lower RBC and WBC were observed in the FC group. A castration status × day effect for mean corpuscular volume (MCV; P = 0.04) was observed where FC group had higher MCV at days 14 and 21 than the PC group. Tumor necrosis factor-α differed based on NumTrt (P = 0.03) and higher concentrations were found in 2x group. We observed a day effect for IL-1β (P = 0.009) and TNF-α (P = 0.001). Significant effect of TUS on HPT at day 14 (P = 0.0004) and day 21 (P = 0.002) was observed. Combining HPT and platelet explained 15% of the variability in treatment status on a given day, whereas HPT and hemoglobin explained 10% of the variability in lung consolidation status. Although hematological and immunological parameters varied largely in our study, the potential of combining HPT with hematological variables should be studied further. Results from this study would help in understanding temporal changes in CBC and immune parameters in newly received stocker cattle.

Cytokine and Haptoglobin Profiles From Shipping Through Sickness and Recovery in Metaphylaxis- or Un-Treated Cattle

Fifty-six head of cattle, 28 animals with bovine respiratory disease complex (BRDC), and 28 healthy animals that were matched by treatment, sale barn of origin, day, and interactions among these variables, were identified from a population of 180 animals (60 each purchased at three sale barns located in Missouri, Tennessee, and Kentucky) enrolled in a study comparing animals receiving metaphylaxis to saline-treated controls. Cattle were transported to a feedlot in KS and assigned to treatment group. Blood samples were collected at Day 0 (at sale barn), Day 1, Day 9, and Day 28 (at KS feedlot), and transported to the US Meat Animal Research Center in Clay Center, NE where plasma was harvested and stored at −80°C until assayed for the cytokines IFN-γ, IL-1β, IL-6, and TNF-α, and the acute stress protein haptoglobin (HPT). Our objectives were to determine if cytokine and haptoglobin profiles differed between control and metaphylaxis treatment groups over time, and if profiles differed between animals presenting with BRDC and those that remained healthy. There was no difference between the treated animals and their non-treated counterparts for any of the analytes measured. Sale barn of origin tended to affect TNF-α concentration. Differences for all analytes changed over days, and on specific days was associated with state of origin and treatment. The Treatment by Day by Case interaction was significant for HPT. The analyte most associated with BRDC was HPT on D9, possibly indicating that many of the cattle were not exposed to respiratory pathogens prior to entering the feedlot.

Comparative Pathogenesis of Bovine and Porcine Respiratory Coronaviruses in the Animal Host Species and SARS-CoV-2 in Humans

Discovery of bats with severe acute respiratory syndrome (SARS)-related coronaviruses (CoVs) raised the specter of potential future outbreaks of zoonotic SARS-CoV-like disease in humans, which largely went unheeded. Nevertheless, the novel SARS-CoV-2 of bat ancestral origin emerged to infect humans in Wuhan, China, in late 2019 and then became a global pandemic. Less than 5 months after its emergence, millions of people worldwide have been infected asymptomatically or symptomatically and at least 360,000 have died. Coronavirus disease 2019 (COVID-19) in severely affected patients includes atypical pneumonia characterized by a dry cough, persistent fever, and progressive dyspnea and hypoxia, sometimes accompanied by diarrhea and often followed by multiple organ failure, especially of the respiratory and cardiovascular systems. In this minireview, we focus on two endemic respiratory CoV infections of livestock: bovine coronavirus (BCoV) and porcine respiratory coronavirus (PRCV). Both animal respiratory CoVs share some common features with SARS-CoV and SARS-CoV-2. BCoV has a broad host range including wild ruminants and a zoonotic potential. BCoV also has a dual tropism for the respiratory and gastrointestinal tracts. These aspects, their interspecies transmission, and certain factors that impact disease severity in cattle parallel related facets of SARS-CoV or SARS-CoV-2 in humans. PRCV has a tissue tropism for the upper and lower respiratory tracts and a cellular tropism for type 1 and 2 pneumocytes in lung but is generally a mild infection unless complicated by other exacerbating factors, such as bacterial or viral coinfections and immunosuppression (corticosteroids).

Pulmonary Expression of Tumor Necrosis Factor Alpha, Interleukin-1 Beta, and Interleukin-8 in the Acute Phase of Bovine Pneumonic Pasteurellosis

Inflammatory cytokines are suspected to contribute to the pathogenesis of bovine pneumonic pasteurellosis (BPP) through neutrophil recruitment, leukocyte activation, and the induction of a broad array of soluble inflammatory mediators. An in vivo experimental model of BPP was used to characterize the pulmonary expression kinetics of tumor necrosis factor alpha (TNFα), interleukin-1 beta (IL-1β), and interleukin-8 (IL-8) genes and proteins during the acute phase of disease development. Cytokine expression in bronchoalveolar lavage (BAL) fluid, BAL cells, and pneumonic lung parenchyma was quantitated by northern blot analysis, enzyme-linked immunosorbent assay (ELISA), and in situ hybridization at 2, 4, 8, 16, and 24 hours after endobronchial inoculation of Pasteurella (Mannheimia) haemolytica. Expression of TNFα, IL-1β, and IL-8 was significantly increased in the airways and lung lesions of infected calves as compared with mock-infected controls. Although kinetic patterns varied, peak levels of cytokine mRNA occurred within 8 hours postinfection (PI), and peak cytokine concentrations occurred within 16 hours PI. In all samples, IL-8 was expressed to the greatest extent and TNFα was least expressed. Expression of TNFα was restricted to alveolar macrophages. Alveolar and interstitial macrophages produced IL-1β and IL-8 in the first 4 hours; bronchial and bronchiolar epithelial cells were also significant sources of IL-8 during this period. By 8 hours PI, neutrophils were the dominant source of both IL-1β and IL-8. These findings demonstrate a spatial and temporal association between pulmonary expression of inflammatory cytokines and acute lung pathology, supporting the hypothesis that cytokines contribute to inflammatory lung injury in BPP.

MicroRNA-26b Modulates the NF-κB Pathway in Alveolar Macrophages by Regulating PTEN

NF-κB is one of the best-characterized transcription factors, providing the link between early membrane-proximal signaling events and changes in many inflammatory genes. MicroRNAs are small noncoding RNAs that regulate gene expression at the posttranscriptional level. In this study, we evaluated the role of miR-26b in the LPS-induced inflammatory response in bovine alveolar macrophages (bAMs). LPS stimulation of bAMs upregulated miR-26b at 1 h and downregulated it at 6 and 36 h. Overexpression of miR-26b in bAMs enhanced the LPS-induced mRNA expression of proinflammatory cytokines and chemokines, including TNF-α, IL-1β, IL-8, and IL-10, but it directly inhibited that of IL-6. A similar trend was observed for the release of these cytokines and chemokines from bAMs. miR-26b directly bound the 3'-untranslated region of PTEN, leading to the reduction of PTEN protein in bAMs. miR-26b also enhanced the LPS-induced NF-κB signaling pathway, as revealed by increased NF-κB transcriptional activity and phosphorylation of p65, IκBα, IκB kinase, and Akt. Moreover, PTEN silencing increased the LPS-induced mRNA expression of TNF-α, IL-1β, IL-6, IL-8, and IL-10 and upregulated the NF-κB pathway. Taken together, we conclude that miR-26b participates in the inflammatory response of LPS-stimulated bAMs by modulating the NF-κB pathway through targeting PTEN.

Age-related changes in phagocytic activity and production of pro-inflammatory cytokines by lipopolysaccharide stimulated porcine alveolar macrophages

The aim of the present study was to determine the age-related changes of phagocytic capacity and the kinetic production of cytokines in lipopolysaccharide-stimulated porcine alveolar macrophages. For this purpose, AMs were isolated from 5 (newborn), 40 (post-weaned) and 120 (young) day old pigs. Results of phagocytosis assay showed that AMs from newborn piglets had less phagocytic capacity than those of young pigs (P<0.05). For the kinetics study, cells and supernatant were collected at 1, 6, 12, 24, 36 and 48 h after LPS stimulation for quantification of cytokine mRNA and protein by quantitative real-time PCR and ELISA, respectively. The kinetics results showed that AMs from newborn piglets were significantly less capable of producing IL1β, IL6, IL12β, TNFα and IL8 than post-weaned piglets or young pigs. IL18 mRNA did not show significant differences between ages. MIP2 and MCP1 mRNA was higher in young pigs. Hence, higher production of cytokines by AMs may be the surfactant factors in the pulmonary host defense system. These results indicate that AMs from newborn piglets might be functionally immature, which may lead to increased susceptibility to lung infections. Future studies of cytokine kinetics in more animals are clearly needed to confirm these results across a wider age range.

A three-way comparative genomic analysis of Mannheimia haemolytica isolates

BACKGROUND

Mannhemia haemolytica is a Gram-negative bacterium and the principal etiological agent associated with bovine respiratory disease complex. They transform from a benign commensal to a deadly pathogen, during stress such as viral infection and transportation to feedlots and cause acute pleuropneumonia commonly known as shipping fever. The U.S beef industry alone loses more than one billion dollars annually due to shipping fever. Despite its enormous economic importance there are no specific and accurate genetic markers, which will aid in understanding the pathogenesis and epidemiology of M. haemolytica at molecular level and assist in devising an effective control strategy.

DESCRIPTION

During our comparative genomic sequence analysis of three Mannheimia haemolytica isolates, we identified a number of genes that are unique to each strain. These genes are "high value targets" for future studies that attempt to correlate the variable gene pool with phenotype. We also identified a number of high confidence single nucleotide polymorphisms (hcSNPs) spread throughout the genome and focused on non-synonymous SNPs in known virulence genes. These SNPs will be used to design new hcSNP arrays to study variation across strains, and will potentially aid in understanding gene regulation and the mode of action of various virulence factors.

CONCLUSIONS

During our analysis we identified previously unknown possible type III secretion effector proteins, clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated sequences (Cas). The presence of CRISPR regions is indicative of likely co-evolution with an associated phage. If proven functional, the presence of a type III secretion system in M. haemolytica will help us re-evaluate our approach to study host-pathogen interactions. We also identified various adhesins containing immuno-dominant domains, which may interfere with host-innate immunity and which could potentially serve as effective vaccine candidates.

Mannheimia haemolytica: bacterial-host interactions in bovine pneumonia

Mannheimia haemolytica serotype S1 is considered the predominant cause of bovine pneumonic pasteurellosis, or shipping fever. Various virulence factors allow M haemolytica to colonize the lungs and establish infection. These virulence factors include leukotoxin (LKT), lipopolysaccharide, adhesins, capsule, outer membrane proteins, and various proteases. The effects of LKT are species specific for ruminants, which stem from its unique interaction with the bovine β2 integrin receptor present on leukocytes. At low concentration, LKT can activate bovine leukocytes to undergo respiratory burst and degranulation and stimulate cytokine release from macrophages and histamine release from mast cells. At higher concentration, LKT induces formation of transmembrane pores and subsequent oncotic cell necrosis. The interaction of LKT with leukocytes is followed by activation of these leukocytes to undergo oxidative burst and release proinflammatory cytokines such as interleukins 1, 6, and 8 and tumor necrosis factor α. Tumor necrosis factor α and other proinflammatory cytokines contribute to the accumulation of leukocytes in the lung. Formation of transmembrane pores and subsequent cytolysis of activated leukocytes possibly cause leakage of products of respiratory burst and other inflammatory mediators into the surrounding pulmonary parenchyma and so give rise to fibrinous and necrotizing lobar pneumonia. The effects of LKT are enhanced by lipopolysaccharide, which is associated with the release of proinflammatory cytokines from the leukocytes, activation of complement and coagulation cascade, and cell cytolysis. Similarly, adhesins, capsule, outer membrane proteins, and proteases assist in pulmonary colonization, evasion of immune response, and establishment of the infection. This review focuses on the roles of these virulence factors in the pathogenesis of shipping fever.

Molecular cloning of interleukin-1β, interleukin-8, and tumor necrosis factor-α of bighorn sheep (Ovis canadensis) and comparison with those of other species

The susceptibility to, and pathology induced by, Mannheimia haemolytica infection in bighorn sheep (BHS) and domestic sheep (DS) are distinctly different. Bighorn sheep are particularly susceptible to pneumonia caused by M. haemolytica, and the pneumonic lesions in infected BHS are more severe than those in DS. The molecular basis for this disparity has not been elucidated. Proinflammatory cytokines have been implicated in the pathogenesis of multiple lung diseases of humans and animals. It is possible that the enhanced pathology observed in the pneumonic lungs of M. haemolytica-infected BHS, in comparison to that of DS, is due to comparatively higher levels of proinflammatory cytokine expression in BHS. As the first step towards elucidating this concept, we have cloned and sequenced the cDNA encoding the cytokines interleukin-1β (IL-1β), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α) of BHS. The cDNA of BHS IL-1β, IL-8, and TNF-α consists of 801, 306, and 705 base pairs encoding 266, 101, and 234 amino acids, respectively. The availability of cDNA encoding IL-1β, IL-8, and TNF-α of BHS should facilitate the elucidation of the role of these cytokines in the differential pathology induced by M. haemolytica infection in BHS and DS.

Differential expression of interleukin-8 by polymorphonuclear leukocytes of two closely related species, Ovis canadensis and Ovis aries, in response to Mannheimia haemolytica infection

The pneumonic lesions and mortality caused by Mannheimia haemolytica in bighorn sheep (BHS; Ovis canadensis) are more severe than those in the related species, domestic sheep (DS; Ovis aries), under both natural and experimental conditions. Leukotoxin (Lkt) and lipopolysaccharide (LPS) are the most important virulence factors of this organism. One hallmark of pathogenesis of pneumonia is the influx of polymorphonuclear leukocytes (PMNs) into the lungs. Lkt-induced cytolysis of PMNs results in the release of cytotoxic compounds capable of damaging lung tissue. Interleukin-8 (IL-8) is a potent PMN chemoattractant. The objective of the present study was to determine if there is differential expression of IL-8 by the macrophages and PMNs of BHS and DS in response to M. haemolytica. Macrophages and PMNs of BHS and DS were stimulated with heat-killed M. haemolytica or LPS. IL-8 expression by the cells was measured by enzyme-linked immunosorbent assays and real-time reverse transcription-PCR (RT-PCR). The PMNs of BHS expressed severalfold higher levels of IL-8 than those of DS upon stimulation. Lesional lung tissue of M. haemolytica-infected BHS contained significantly higher levels of IL-8 than nonlesional tissue. The bronchoalveolar lavage (BAL) fluid of infected BHS also contained higher levels of IL-8 than that of infected DS. Depletion of IL-8 reduced migration of PMNs toward BAL fluid by approximately 50%, indicating that IL-8 is integral to PMN recruitment to the lung during M. haemolytica infection. Excessive production of IL-8, enhanced recruitment of PMNs, and PMN lysis by Lkt are likely responsible for the severity of the lung lesions in M. haemolytica-infected BHS.

Immuno-modulation and anti-inflammatory benefits of antibiotics: the example of tilmicosin

Exaggerated immune responses, such as those implicated in severe inflammatory reactions, are costly to the metabolism. Inflammation and pro-inflammatory mediators negatively affect production in the food animal industry by reducing growth, feed intake, reproduction, milk production, and metabolic health. An ever-increasing number of findings have established that antibiotics, macrolides in particular, may generate anti-inflammatory effects, including the modulation of pro-inflammatory cytokines and the alteration of neutrophil function. The effects are time- and dose-dependent, and the mechanisms responsible for these phenomena remain incompletely understood. Recent studies, mostly using the veterinary macrolide tilmicosin, may have shed new light on the mode of action of some macrolides and their anti-inflammatory properties. Indeed, research findings demonstrate that this compound, amongst others, induces neutrophil apoptosis, which in turn provides anti-inflammatory benefits. Studies using tilmicosin model systems in vitro and in vivo demonstrate that this antibiotic has potent immunomodulatory effects that may explain why at least parts of its clinical benefits are independent of anti-microbial effects. More research is needed, using this antibiotic and others that may have similar properties, to clarify the biological mechanisms responsible for antibiotic-induced neutrophil apoptosis, and how this, in turn, may provide enhanced clinical benefits. Such studies may help establish a rational basis for the development of novel, efficacious, anti-microbial compounds that generate anti-inflammatory properties in addition to their antibacterial effects.

Tumor-inhibitory effect and immunomodulatory activity of fullerol C60(OH)x

The tumor-inhibitory effect of C60(OH)x was tested on the murine H22 hepatocarcinoma model. Doses of 0.2 and 1.0 mg kg(-1) body weight both showed significant antitumor activity with tumor inhibition rates of 31.9 and 38.4%, respectively, when mice were treated for 17 consecutive days. The damnification of liver was prominently reduced. Furthermore, histological examination indicated that an envelope of fibroblasts and lymphocytes was formed surrounding tumor tissues in the C60(OH)x-treated group, which inhibited the infiltration of tumor to the neighboring normal skeleton muscle tissues. To understand the antitumor mechanism, the immunomodulatory activity of C60(OH)x was investigated. The results indicate that C60(OH)x enhances the phagocytosis of peritoneal macrophages and elevates the activity of arginase and acid phosphatase in vivo. The tumor necrosis factor alpha production of C60(OH)x-treated macrophages also increases in vitro. These results suggest that C60(OH)x can enhance the innate immunity of tumor-bearing mice, and therefore inhibits growth of the tumor.

Immune evasion by pathogens of bovine respiratory disease complex

Bovine respiratory tract disease is a multi-factorial disease complex involving several viruses and bacteria. Viruses that play prominent roles in causing the bovine respiratory disease complex include bovine herpesvirus-1, bovine respiratory syncytial virus, bovine viral diarrhea virus and parinfluenza-3 virus. Bacteria that play prominent roles in this disease complex are Mannheimia haemolytica and Mycoplasma bovis. Other bacteria that infect the bovine respiratory tract of cattle are Histophilus (Haemophilus) somni and Pasteurella multocida. Frequently, severe respiratory tract disease in cattle is associated with concurrent infections of these pathogens. Like other pathogens, the viral and bacterial pathogens of this disease complex have co-evolved with their hosts over millions of years. As much as the hosts have diversified and fine-tuned the components of their immune system, the pathogens have also evolved diverse and sophisticated strategies to evade the host immune responses. These pathogens have developed intricate mechanisms to thwart both the innate and adaptive arms of the immune responses of their hosts. This review presents an overview of the strategies by which the pathogens suppress host immune responses, as well as the strategies by which the pathogens modify themselves or their locations in the host to evade host immune responses. These immune evasion strategies likely contribute to the failure of currently-available vaccines to provide complete protection to cattle against these pathogens.

Effects of melengestrol acetate on the inflammatory response in heifers challenged with Mannheimia haemolytica1

Previous research from our laboratory has indicated that melengestrol acetate (MGA) added to the diet during the first 35 d after arrival in the feedlot improves growth rates and tends to reduce chronic respiratory disease in heifers naturally challenged with bovine respiratory disease. The current study was conducted to provide further insight into the possible immunomodulatory effects of MGA. Crossbred heifers (n = 48; 232 +/- 5.5 kg of BW) were used in a randomized complete block design to determine the effects of MGA on lung pathology and markers of inflammation after Mannheimia haemolytica challenge. On d 0, cattle were blocked by BW and randomly assigned, within block, to diets (54% concentrate) that provided 0 or 0.5 mg of MGA per heifer daily for the duration of the experiment. Inoculum containing from 1.3 x 10(9) to 1.7 x 10(9) cfu of M. haemolytica (20 mL) was instilled at the bifurcation of the trachea on d 14. Blood samples were collected, clinical observations were made, and rectal temperatures were recorded for each animal at 0, 12, 24, 48, 72, 96, 120, and 138 h after inoculation. Heifers fed MGA had greater circulating concentrations of eosinophils and postchallenge concentrations of segmented neutrophils and white blood cells (P < 0.01) than controls, as well as elevated plasma protein, serum haptoglobin, and fibrinogen after M. haemolytica challenge (P < 0.01). Heifers fed MGA had lower plasma glucose (P < 0.01), greater plasma urea N (P = 0.02), and elevated respiratory indices (P < 0.01) compared with controls. Necropsies performed on d 6 after inoculation suggested that M. haemolytica challenge was relatively mild, because lesions were confined to a small portion of the lungs. On a 0 to 100 scale, average lung lesion scores were 3 and 1 for MGA-fed and control groups, respectively (P < 0.06). Heifers fed MGA before mild M. haemolytica challenge were more susceptible to infection, as evidenced by a greater number of heifers fed MGA exhibiting pulmonary lesions 138 h after inoculation than controls (14 out of 23 vs. 6 out of 24 for MGA and controls, respectively; P < 0.02).

Endotoxin-neutralizing activity of polymyxin B in blood after IV administration in horses

OBJECTIVES

To measure serum polymyxin B concentration after single and repeated IV infusions in horses.

ANIMALS

5 healthy horses.

PROCEDURES

In study 1, 1 mg (6,000 U) of polymyxin B/kg was given IV and blood samples were collected for 24 hours. In study 2, 1 mg of polymyxin B/kg was given IV every 8 hours for 5 treatments and blood samples were collected until 24 hours after the last dose. Polymyxin B concentration was measured as the ability to suppress nitrite production by murine macrophages stimulated with lipopolysaccharide and interferon-alpha. Urine was collected prior to the first drug infusion and 24 hours after the fifth drug infusion for determination of urinary gamma-glutamyl transferase (GGT)-to-creatinine ratios.

RESULTS

In study 1, mean +/- SEM maximal serum polymyxin B concentration was 2.93 +/- 0.38 microg/mL. Polymyxin B was undetectable 18 hours after infusion. In study 2, maximal polymyxin B concentrations after the first and fifth doses were 2.98 +/- 0.81 microg/mL and 1.91 +/- 0.50 microg/mL, respectively. Mean trough concentration for all doses was 0.22 +/- 0.01 microg/mL. A significant effect of repeated administration on peak and trough serum concentration was not detected. Urine GGT-to-creatinine ratios were not affected by polymyxin B administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Polymyxin B given as multiple infusions to healthy horses by use of this protocol did not accumulate in the vascular compartment and appeared safe. Results support repeated IV use of 1 mg of polymyxin B/kg at 8-hour intervals as treatment for endotoxemia.

Potential involvement of gelatinases and their inhibitors in Mannheimia haemolytica pneumonia in cattle

Mannheimia haemolytica infection of the lower respiratory tract of cattle results in a bronchofibrinous pneumonia characterized by massive cellular influx and lung tissue remodeling and scarring. Since altered levels of gelatinases and their inhibitors have been detected in a variety of inflammatory conditions and are associated with tissue remodeling, we examined the presence of gelatinases in lesional and nonlesional lung tissue obtained from calves experimentally infected with M. haemolytica. Lesional tissue had elevated levels of progelatinase A and B and active gelatinase A and B when compared with nonlesional tissue obtained from the same lung lobe. In vitro, M. haemolytica products stimulated production of gelatinase B, but not its activation, by bovine monocytes. Alveolar macrophages showed constitutive production of gelatinase B but no change in response to M. haemolytica products. Bovine neutrophils exposed to M. haemolytica products also released gelatinase B, and there was a significant increase in the activated form of this enzyme. These effects were virtually identical when recombinant O-sialoglycoprotease was used to stimulate these cells. M. haemolytica products also enhanced the expression by bovine monocytes and alveolar macrophages of the tissue inhibitor of metalloproteinase 1. Our results provide evidence that matrix metalloproteinases are activated in lung lesions from cattle with shipping fever and that M. haemolytica virulence products induce production, release, and especially activation of gelatinase B by bovine inflammatory cells in vitro.

Pharmacological inhibition of Mannheimia haemolytica lipopolysaccharide and leukotoxin-induced cytokine expression in bovine alveolar macrophages

The inflammatory cytokines tumor necrosis factor-alpha (TNFalpha), interleukin-1 beta (IL-1beta), and interleukin-8 (IL-8) are believed to contribute to the pathogenesis of lung injury in bovine pneumonic mannheimiosis (BPM) caused by Mannheimia (Pasteurella) haemolytica. Inflammatory cytokines may, therefore, represent therapeutic targets to be modulated for the purpose of treating or preventing this important disease of cattle. The purpose of this study was to evaluate the ability of six pharmacological agents to suppress the expression of TNFalpha, IL-1beta, and IL-8 genes and proteins in bovine alveolar macrophages (AM) exposed to M. haemolytica lipopolysaccharide (LPS) and leukotoxin (LktA) in vitro. The compounds tested included dexamethasone (DEX), tetrahydropapaveroline (THP), pentoxifylline (PTX), rolipram (ROL), SB203580 (SB), and thalidomide (THL). Cytokine expression was induced by the addition of purified M. haemolytica LPS and LktA to AM cell cultures following pretreatment with inhibitor compounds. Secretion of TNFalpha, IL-1beta, and IL-8 proteins into the cell culture supernatant was measured using enzyme-linked immunosorbent assays, and steady-state accumulation of cytokine-specific mRNA was measured by northern blot analysis. Dose-dependent inhibition of cytokine secretion occurred in response to pretreatment of AM with DEX (TNFalpha, IL-1beta, IL-8), THP (TNFalpha, IL-1beta, IL-8), PTX (TNFalpha, IL-1beta, IL-8), ROL (TNFalpha, IL-1beta), and SB (TNFalpha, IL-8). Significant dose-dependent inhibition of cytokine mRNA expression occurred in response to pretreatment with DEX (TNFalpha, IL-1beta, IL-8), THP (TNFalpha, IL-1beta, IL-8), and PTX (TNFalpha). DEX was the most effective inhibitor by far; pretreatment with this compound yielded greater than 95% inhibition of cytokine gene and protein expression over a broad range of concentrations. These findings demonstrate that DEX, THP, PTX, ROL, and SB are capable of suppressing inflammatory cytokine secretion by bovine AM in vitro. If pulmonary cytokine secretion may be similarly inhibited in vivo, anti-cytokine therapy may represent a novel strategy for the management of BPM.

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.

Prior exposure to Mannheimia haemolytica leukotoxin or LPS enhances beta(2)-integrin expression by bovine neutrophils and augments LKT cytotoxicity

Mannheimia (Pasteurella) haemolytica serotype1 produces a variety of virulence factors that play an important role during the pathogenesis of bovine pneumonic pasteurellosis. Among these, a leukotoxin (LKT) and lipopolysaccharide (LPS) are thought to be the primary virulence factors that contribute to the characteristic pathology of pasteurellosis. Recent evidence suggests that M. haemolytica LKT binding to bovine leukocytes is mediated by the beta(2)-integrin CD11a/CD18 (LFA-1), which subsequently induces activation and death of these cells. Exposure of bovine peripheral blood neutrophils (PMNs) to LKT or LPS induces expression of inflammatory cytokines, which in turn can increase LFA-1 expression and conformational activation. In this study we demonstrated, by flow cytometry and Western blot, that bovine PMNs increased their LFA-1 expression following in vitro exposure to M. haemolytica LKT and LPS. Increased LFA-1 expression by PMNs exposed to LKT and LPS was associated with increased LKT binding and cell death. The results of this study suggest that M. haemolytica LKT and LPS might cooperatively increase LFA-1 expression, and by so doing amplify the lung inflammation that characterizes bovine pasteurellosis.

Serum-mediated release of leukotoxin from the cell surface of the periodontal pathogen Actinobacillus actinomycetemcomitans

The leukotoxin of the periodontopathogen Actinobacillus actinomycetemcomitans is an important virulence factor that lyses human neutrophils and monocytes and thus, it may enable the bacterium to evade the local host defense. The toxin also induces degranulation of neutrophils and cytokine release in monocytes. To trigger these biological activities, leukotoxin has to be released from the bacterium and diffuse into the periodontal tissues. To date, the conditions found to cause toxin release have been artificial and have included high ion concentration and alkaline conditions. To study the release of the toxin under conditions mimicking the natural environment of the periodontium the ability of human serum to enable leukotoxin release from the bacterial surface was examined. Suspensions of leukotoxic A. actinomycetemcomitans strains were incubated with various concentrations of human serum or serum albumin. The suspensions were centrifuged and the leukotoxin in the supernatants or the cell pellets was detected by gel electrophoresis and immunoblotting. Serum was found to cause the rapid release of leukotoxin from the bacteria in a concentration-dependent manner. Pure albumin exhibited a similar effect. The leukotoxin released was active against human neutrophils. Only a minor proportion of it was associated with membranous vesicles produced by the bacteria. The results indicate that serum, a fluid closely related to the exudate in inflamed periodontal pockets, releases leukotoxin from the cell surface of A. actinomycetemcomitans. The process may enable the diffusion of the toxin from the bacterial biofilm into the surrounding tissues, where it can exert its biological effect.

Role of Mannheimia haemolytica leukotoxin in the pathogenesis of bovine pneumonic pasteurellosis

Bovine pneumonic pasteurellosis continues to be a major respiratory disease in feedlot cattle despite the recent advances in our understanding of the underlying complexities of causation. The etiological agent, Mannheimia haemolytica, possesses several virulence factors, including capsule, outer membrane proteins, adhesins, neuraminidase, endotoxin and exotoxic leukotoxin. Accumulating scientific evidence implicates leukotoxin as the primary factor contributing to clinical presentation and lung injury associated with this disease. Unlike other virulence factors, leukotoxin shows cell-type- and species-specific effects on bovine leukocytes. Recent investigations have delineated the mechanisms underlying the target-cell-specificity of leukotoxin and how this contributes to the pathogenesis of lung damage. This review summarizes current understanding of the secretion, regulation, mechanisms of action and evolutionary diversity of leukotoxin of M. haemolytica. Understanding the precise molecular mechanisms of leukotoxin is critical for the development of more effective prophylactic and therapeutic strategies to control this complex disease.

Evaluation of cytokine gene expression in porcine spleen cells, peripheral blood mononuclear cells, and alveolar macrophages by competitive RT-PCR

Cytokines act as an important regulator of immune responses. Since cytokine expression levels are generally very low, more accurate and reliable methods of measuring their expression are needed. In this study, a modified competitive reverse transcription-polymerase chain reaction assay was developed to determine the expression levels and patterns of porcine IFN-gamma, IL-2, IL-4, IL-10, IL-12 p 35, and IL-12 p40 in spleen cells, peripheral blood mononuclear cells (PBMC), and alveolar macrophages that were stimulated for 4 h by lipopolysaccharide or phytohemagglutinin. Of these cytokines, the expression level of IFN-gamma was the highest in all examined cells. Constitutive expression of IL-2 and IL-4 was demonstrated in spleen cells and PBMC stimulated with phytohemagglutinin. However, their expression extent was not determinable or extremely low in the lipopolysaccharide-stimulated spleen cells and alveolar macrophages. Moderately high IL-10 expression was observed in all examined cells. IL-12 p 35 expression in alveolar macrophages was always higher than in spleen cells and PBMC. IL-12 p40 expression in alveolar macrophages was higher than in PBMC, but was lower than in spleen cells. In spleen cells, the expression of IL-12 p40 was higher than that of IL-12 p 35. In alveolar macrophages and PBMC, however, IL-12 p 35 showed a higher expression than IL-12 p40. These results indicate that each cytokine has its own characteristic expression profile in different immune cells.

Inflammatory cytokines enhance the interaction of Mannheimia haemolytica leukotoxin with bovine peripheral blood neutrophils in vitro

Mannheimia (Pasteurella) haemolytica A1 produces several virulence factors that play an important role in the pathogenesis of bovine pneumonic pasteurellosis. Foremost among these is a leukotoxin (LKT) that specifically kills ruminant leukocytes. Recent evidence suggests that M. haemolytica LKT binding to bovine leukocytes is mediated by the beta(2)-integrin CD11a/CD18 (lymphocyte function-associated antigen 1 [LFA-1]), which subsequently induces activation and cytolysis of these cells. Inflammatory cytokines, which are released during viral and bacterial infection, are reported to increase LFA-1 expression and conformational activation. We investigated the effects of the inflammatory cytokines interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and gamma interferon (IFN-gamma) on the interaction of M. haemolytica LKT with bovine peripheral blood neutrophils (PMNs). In this study we demonstrated, by flow cytometry, that bovine PMNs increased their binding to an anti-bovine LFA-1 monoclonal antibody (BAT75A) following in vitro incubation with IL-1beta, TNF-alpha, or IFN-gamma. Incubation with cytokines also increased CD18 expression, as assessed by real-time PCR and by Western blotting. Increased LFA-1 expression by PMNs exposed to cytokines was associated with increased LKT binding and cytotoxicity. The latter represented, at least in part, enhanced PMN apoptosis, as assessed by propidium iodine staining and caspase-3 activation. The results of this study suggest that inflammatory cytokines may play an important role in enhancing the biological response of bovine PMNs to M. haemolytica LKT.

In vitro evaluation of the role of platelet-activating factor and interleukin-8 in Mannheimia haemolytica-induced bovine pulmonary endothelial cell injury

OBJECTIVE

To develop an in vitro model of the bovine alveolar-capillary interface and to evaluate the roles of interleukin-8 (IL-8) and platelet-activating factor (PAF) in neutrophil-mediated endothelial injury induced by infection with Mannheimia haemolytica.

SAMPLE POPULATION

Cultured bovine pulmonary microvascular endothelial cells, freshly isolated bovine neutrophils, and monocyte-derived bovine macrophages.

PROCEDURE

A coculture system was developed in which endothelial cells were grown to confluence in tissue culture inserts, neutrophils were added to the inserts, and macrophages were added to tissue culture wells. Mannheimia haemolytica-derived lipopolysaccharide (LPS) or supernatant was added to activate macrophages, and inhibitors of PAF or IL-8 were added to the insert. Endothelial cell cytotoxicity and permeability (ie, albumin leakage) and neutrophil activation (ie, adhesion, degranulation [lactoferrin expression], and superoxide production) were assessed.

RESULTS

The addition of M haemolytica-derived LPS to bovine macrophages in the coculture system resulted in significant increases in endothelial cell cytotoxicity and permeability and neutrophil degranulation and adhesion. Inhibition of IL-8 reduced endothelial cell permeability and neutrophil degranulation induced by exposure to M haemolytica-derived supernatant, whereas inhibition of PAF decreased superoxide release by neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro activation of bovine macrophages by M haemolytica-derived LPS resulted in neutrophil activation and neutrophil-mediated endothelial damage. Neutrophil-mediated endothelial injury and neutrophil degranulation were, at least in part, mediated by IL8, whereas PAF promoted superoxide release by neutrophils in this in vitro system designed to mimic the in vivo events that occur during the early stages of bovine pneumonic pasteurellosis.

Lipopolysaccharide enhances cytolysis and inflammatory cytokine induction in bovine alveolar macrophages exposed to Pasteurella (Mannheimia) haemolytica leukotoxin

Pasteurella (Mannheimia) haemolytica leukotoxin (Lkt) and lipopolysaccharide (LPS) are the primary virulence factors contributing to the pathogenesis of lung injury in bovine pneumonic pasteurellosis. Previous studies have characterized in vitro responses of bovine alveolar macrophages (AMs) to Lkt and LPS. Activation of AMs with Lkt or LPS causes induction of proinflammatory cytokines, and Lkt causes cytolysis of AMs at higher concentrations. Since AMs are exposed to both of these bacterial virulence factors during disease, previous studies may have underestimated the possibility of functional interactions between Lkt and LPS. The purpose of this study was to characterize the effect of simultaneous exposure to both Lkt and LPS on AM cytolysis and proinflammatory cytokine expression. Using cellular leakage of lactate dehydrogenase as an indirect measure of cytolysis, we studied AM responses to Lkt alone, LPS alone and Lkt+LPS. We found that 80-200 pg/ml LPS, which does not itself cause cytolysis, synergistically enhanced the cytolysis induced by 2-5 Lkt units (LU)/ml Lkt. Northern blot analysis demonstrated that synergism between Lkt and LPS resulted in increased levels of IL-8 mRNA, and that the kinetic patterns of TNF-alpha and IL-8 mRNA expression induced by Lkt+LPS differed from those induced by each agent separately. Finally, the WEHI 164 (clone 13) bioassay was used to show that Lkt/LPS synergism resulted in enhanced secretion of biologically active TNF-alpha. These results provide direct evidence of synergism between Lkt and LPS in AM cytolysis and inflammatory cytokine expression. Additional studies to characterize the molecular basis of this phenomenon are indicated.

Differential regulation of protein tyrosine kinase on free radical production, granule enzyme release, and cytokine synthesis by activated murine peritoneal macrophages

The present study examined the regulatory effect of tyrosine kinase inhibitors (genistein, tyrphostin, and 2,5-dihydroxycinnamate) on the free radical production, granule enzyme release, and synthesis of interleukin (IL)-8 and granulocyte macrophage-colony stimulating factor (GM-CSF) in murine peritoneal macrophages exposed to different stimulators [10 ng/mL of IL-1, 1 microgram/mL of lipopolysaccharide (LPS), and 1 microM N-formyl-methionyl-leucyl-phenylalanine (fMLP)]. Protein tyrosine kinase (PTK) inhibitors attenuated the stimulated superoxide, hydrogen peroxide, and nitric oxide production in macrophages stimulated with IL-1, LPS, or fMLP. N,N-Dimethylsphingosine (DMS) alone stimulated superoxide and hydrogen peroxide production by intact macrophages, but at 45 microM the stimulatory effect on superoxide production was not found. In contrast, DMS attenuated nitric oxide production by macrophages. High concentrations of DMS, tyrphostin, and 2,5-dihydroxycinnamate showed cytotoxic effects. PTK inhibitors did not exhibit a significant effect on granule enzyme release induced by IL-1, whereas they attenuated the effect of LPS and fMLP on degranulation. Genistein and tyrphostin decreased the production of IL-8 and GM-CSF in macrophages activated by IL-1, whereas 2,5-dihydroxycinnamate did not affect it. The results suggest that tyrosine kinases exposed to IL-1, LPS, and fMLP may exert different modulatory actions on macrophage responses. The IL-1-activated macrophage responses, particularly degranulation, appear to be differently regulated by tyrosine kinases compared with the responses activated by LPS and fMLP.

Tilmicosin induces apoptosis in bovine peripheral neutrophils in the presence or in the absence of Pasteurella haemolytica and promotes neutrophil phagocytosis by macrophages

Pathogen virulence factors and inflammation are responsible for tissue injury associated with respiratory failure in bacterial pneumonia, as seen in the bovine lung infected with Pasteurella haemolytica. Tilmicosin is a macrolide antibiotic used for the treatment of bovine bacterial pneumonia. Recent evidence suggests that tilmicosin-induced neutrophil apoptosis may have anti-inflammatory effects. Using bovine leukocytes, we sought to define whether live P. haemolytica affected tilmicosin-induced neutrophil apoptosis, assessed the proapoptotic effects of tilmicosin in comparison with other drugs, and characterized its impact on phagocytic uptake of neutrophils by macrophages. Induction of apoptosis in the presence or absence of P. haemolytica was assessed by using an enzyme-linked immunosorbent assay for apoptotic nucleosomes. In addition, fluorescent annexin-V staining identified externalized phosphatidylserine in neutrophils treated with tilmicosin, penicillin, ceftiofur, oxytetracycline, or dexamethasone. Neutrophil membrane integrity was assessed by using propidium iodide and trypan blue exclusion. As phagocytic clearance of apoptotic neutrophils by macrophages contributes to the resolution of inflammation, phagocytosis of tilmicosin-treated neutrophils by esterase-positive cultured bovine macrophages was assessed with light microscopy and transmission electron microscopy. Unlike bovine neutrophils treated with penicillin, ceftiofur, oxytetracycline, or dexamethasone, neutrophils exposed to tilmicosin became apoptotic, regardless of the presence or absence of P. haemolytica. Tilmicosin-treated apoptotic neutrophils were phagocytosed at a significantly greater rate by bovine macrophages than were control neutrophils. In conclusion, tilmicosin-induced neutrophil apoptosis occurs regardless of the presence or absence of live P. haemolytica, exhibits at least some degree of drug specificity, and promotes phagocytic clearance of the dying inflammatory cells.

Influence of beta(2)-integrin adhesion molecule expression and pulmonary infection with Pasteurella haemolytica on cytokine gene expression in cattle

beta(2)-Integrins are leukocyte adhesion molecules composed of alpha (CD11a, -b, -c, or -d) and beta (CD18) subunit heterodimers. Genetic CD18 deficiency results in impaired neutrophil egress into tissues that varies between conducting airways and alveoli of the lung. In this study, we investigated whether CD18 deficiency in cattle affects proinflammatory cytokine (PIC) expression in pulmonary tissue after respiratory infection with Pasteurella haemolytica. Cattle were infected with P. haemolytica via fiberoptic deposition of organisms into the posterior part of the right cranial lung lobe. Animals were euthanized at 2 or 4 h postinoculation (p.i.), and tissues were collected to assess PIC gene expression using antisense RNA probes specific for bovine interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) along with the beta-actin (beta-Act) housekeeping gene. Expression of PIC was induced at 2 h p.i. in P. haemolytica-infected cattle and continued to 4 h p.i. At 2 h p.i., induction of gene expression and increase of cells that expressed PIC were observed both in CD18(+) and CD18(-) cattle after inoculation of P. haemolytica. The induction of gene expression with P. haemolytica inoculation was more prominent in CD18(-) cattle than in CD18(+) cattle by comparison to pyrogen-free saline (PFS)-inoculated control animals. At 4 h p.i., however, the induction of PIC, especially IL-1alpha, IL-6, and IFN-gamma, in the lungs of CD18(+) cattle inoculated with P. haemolytica was greater than that in lungs of the CD18(-) cattle. IFN-gamma and TNF-alpha genes were not increased in P. haemolytica-inoculated CD18(-) cattle lungs compared to the PFS-inoculated control lungs at 4 h p.i. In PFS-inoculated lungs, we generally observed a higher percentage of cells and higher level of gene expression in the lungs of CD18(-) cattle than in the lungs of CD18(+) cattle, especially at 4 h p.i. The rate of neutrophil infiltration into the lungs of CD18(-) cattle at 2 h p.i. was significantly higher than that of CD18(+) cattle; at 4 h p.i., there was no difference between the two groups. These data suggest that beta(2)-integrins may contribute to the induction of expression of some PIC genes, as a consequence of P. haemolytica infection.

Role of inflammatory mediators in priming, activation, and deformability of bovine neutrophils

OBJECTIVE

To determine the capacity of inflammatory mediators tumor necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), platelet-activating factor (PAF), lipopolysaccharide (LPS), and leukotoxin to prime, activate, or alter deformability of adult bovine neutrophils.

SAMPLE POPULATION

Blood collected from 5 healthy adult Holstein cows.

PROCEDURE

Isolated neutrophils or whole blood was incubated with TNF-alpha, IL-8, PAF, LPS, or leukotoxin, and neutrophil chemiluminescence, degranulation, deformability, shape change, CD11b expression, and size distribution was measured.

RESULTS

Incubation with TNF-alpha, IL-8, PAF, and LPS primed neutrophils for oxygen radical release but caused minimal oxygen radical release by themselves. None of the inflammatory mediators induced degranulation. Incubation with TNF-alpha and PAF resulted in a decrease in neutrophil deformability and induced shape change in neutrophils. Incubation with PAF consistently resulted in an increase in neutrophil size as measured by use of flow cytometry. Only IL-8 caused an increase in expression of CD11b by neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

Inflammatory mediators tested had minimal effects on neutrophil oxygen radical production or degranulation but did prime neutrophils for oxygen radical production. Incubation with PAF and TNF-alpha caused a decrease in neutrophil deformability and altered neutrophil shape and size. Results of our study indicate that PAF- and TNF-alpha-induced changes in neutrophil deformability and size may cause integrin- and selectin-independent trapping of neutrophils in the lungs of cattle with pneumonic pasteurellosis.

Evidence for paracrine signaling between macrophages and bovine adrenal chromaffin cell Ca(2+) channels

The adrenal gland contains resident macrophages, some of which lie adjacent to the catecholamine producing chromaffin cells. Because macrophages release a variety of secretory products, it is possible that paracrine signaling between these two cell types exists. Of particular interest is the potential paracrine modulation of voltage-gated calcium channels (I(Ca)), which are the main calcium influx pathway triggering catecholamine release from chromaffin cells. We report that prostaglandin E(2) (PGE(2)), one of the main signals produced by macrophages, inhibited I(Ca) in cultured bovine adrenal chromaffin cells. The inhibition is rapid, robust, and voltage dependent; the activation kinetics are slowed and inhibition is largely reversed by a large depolarizing prepulse, suggesting that the inhibition is mediated by a direct G-protein betagamma subunit interaction with the calcium channels. About half of the response to PGE(2) was sensitive to pertussis toxin (PTX) incubation, suggesting both PTX-sensitive and -insensitive G proteins were involved. We show that activation of macrophages by endotoxin rapidly (within minutes) releases a signal that inhibits I(Ca) in chromaffin cells. The inhibition is voltage dependent and partially PTX sensitive. PGE(2) is not responsible for this inhibition as blocking cyclooxygenase with ibuprofen did not prevent the production of the inhibitory signal by the macrophages. Nor did blocking the lipoxygenase pathway with nordihydroguaiaretic acid alter production of the inhibitory signal. Our results suggest that macrophages may modulate I(Ca) and catecholamine secretion by releasing PGE(2) and other chemical signal(s).

Depressant effects of ambroxol on lipopolysaccharide- or fMLP-stimulated free radical production and granule enzyme release by alveolar macrophages

In order to explore the depressant action of ambroxol, a bronchial expectorant, on the activated alveolar macrophage responses, its effect on lipopolysaccharide (LPS)- or N-formyl-methionyl-leucyl-phenylalanine (fMLP)- stimulated free radical production and granule enzyme release by rat lung alveolar macrophages was investigated. Ambroxol attenuated the 100 ng/ml LPS- or 1 microM fMLP-stimulated superoxide, H(2)O(2)and nitric oxide production and releases of acid phosphatase and lysozyme by alveolar macrophages. Ambroxol attenuated phorbol myristate acetate-stimulated superoxide and nitric oxide production that was inhibited by 100 nM staurosporine. N,N-dimethylsphingosine (DMS, 4.5 and 9 microM) alone stimulated superoxide production by macrophages, while 45 microM of the compound did not show a stimulatory effect. However, DMS decreased nitric oxide production in a dose-dependent manner. Ambroxol did not alter the DMS effect on free radical production that was affected by 10 microM genistein. A preincubation of macrophages with ambroxol (10 and 100 microM), staurosporine and genistein attenuated the elevation of [Ca(2+)](i)caused by LPS. The results suggest that ambroxol exerts a depressant effect on LPS- or fMLP-stimulated free radical production and granule enzyme release by rat alveolar macrophages, which may be attributed to its inhibitory action on the activation process, protein kinase C, but its action on protein tyrosine kinase is not suggested.

The effect of steroidal and non-steroidal anti-inflammatory drugs on the cellular immunity of calves with experimentally-induced local lung inflammation

We examined the effect of a single intravenous dose of flumetasone (SAID) and meloxicam (NSAID) treatment of calves with experimentally-induced localized lung inflammation on immunological and hematological variables such as total protein, gamma globulin, hemoglobin (Hb) concentrations, alkaline phosphatase activity, packed red cell volume (PCV), red blood cell (RBC) and white blood cell (WBC) counts. The influence of drug treatment on the phagocytic activity of WBC and bronchoalveolar lavage (BAL) cells and their ex vivo ability to produce interferon (IFN) and tumor necrosis factor (TNF) after induction with Newcastle disease virus (NDV), as well as on the development of PHA-induced skin delayed hypersensitivity reaction was also determined. Two days after the treatment of calves with experimentally-induced local lung inflammation with flumetasone (5 mg per calf), we observed a significant increase in WBC count, especially neutrophils, and a decrease in gamma globulin concentration, in the percent of blood phagocytic cells and their random migration. Flumetasone treatment also inhibited the development of skin delayed hypersensitivity reaction. In contrast, the treatment of calves with meloxicam (50 mg per calf) did not influence any hematological parameters or skin reactivity. Both drugs, flumetasone and meloxicam, influenced TNF production in ex vivo cultures of blood and BAL cells, inhibiting excessive TNF production induced by local lung inflammation. Contrary to TNF, the treatment of calves with meloxicam and flumetasone enhanced ex vivo IFN production in blood and BAL cells. Histological examination of lung tissue revealed that in control calves (those not treated with anti-inflammatory drugs) and in calves treated with flumetasone, symptoms of stromo-purulent inflammation of pulmonary tissue developed. However, in calves treated with meloxicam, only interstitial inflammation with a slight thickening of interalveolar septa and infiltration of lymphoid cells was observed. These results suggest that in this model of pneumonia, it is more appropriate to use a single dose of meloxicam, rather than flumetasone, to modulate lung inflammation.

Secretion of TNF-alpha, IL-8 and nitric oxide by macrophages activated with polyanions, and involvement of interferon-gamma in the regulation of cytokine secretion

When macrophages derived from rat bone marrow were cultured in the presence of polyanions such as acetyl lignin (EP3), sulfonyl lignin (LS) or dextran sulfate (DS), the cells secreted TNF-alpha, IL-8 and nitric oxide (NO). EP3 had a dose-dependent effect on the secretion of TNF-alpha, IL-8 and NO. EP3 significantly affected secretion at concentrations greater than 5 microg/ml. The EP3 effect was at its maximum between concentrations of 50 and 100 microg/ml. LS and DS induced a slight increase in the secretion of cytokines and NO at a concentration of 100 microg/ml. The use of the reverse-transcription polymerase chain reaction (RT-PCR) showed that the increases in cytokine and NO secretion were due to an increase in cytokine mRNAs or NO synthase mRNA. Anti-TNF-alpha antibodies partially inhibited NO secretion by EP3-activated macrophages, although IL-8 secretion was independent of antibody treatment. The secretion of TNF-alpha and NO was also unaffected by the addition of anti-IL-8 antibodies. The addition of interferon-gamma (IFN-gamma) to the culture medium did not alter TNF-alpha and NO secretion by the EP3-activated macrophages, however, IL-8 secretion was increased when a low concentration of IFN-gamma (0.2 U/ml) was added, but was reduced in the presence of a high concentration of IFN-gamma (2000 U/ml). IFN-gamma produced similar effects on cytokine and NO secretion in macrophages activated with lipopolysaccharide (LPS). Therefore, it is concluded that macrophages treated with polyanions secrete cytokines and NO, and that INF-gamma is involved in the regulatory mechanism of cytokine and NO secretion.

Mast cells of the bovine trachea: staining characteristics, dispersion techniques and response to secretagogues

Sections of the lower trachea of cattle, fixed in either Carnoy's or formalin, were stained with toluidine blue, alcian blue, or alcian blue and safranin O to study the mast cell population. After toluidine blue staining, about twice as many cells in tissue fixed in Carnoy's contained dark blue granules compared with tissue fixed in formalin. In addition, for the first time in cattle, a population of cells containing red granules was identified after staining with alcian blue and safranin O. Most of these red granules were formalin sensitive. An enzymatic dispersal technique for mast cells is described that yielded 9.4+/-0.4% mast cells (percentage of nucleated cells) with a viability of 92.3+/-0.6%. Spontaneous histamine release was 3.3+/-0.8%. Dispersed mast cells were challenged with various immunological and nonimmunological secretagogues. The calcium ionophores, A23187, ionomyocin, and BrX537A, were effective in releasing up to 94% of histamine in mast cells in a dose-response relationship. Pasteurella haemolytica culture supernate caused about 10% histamine release at a dose of 0.5 mg/mL after correction for spontaneous release. The average histamine content of the mast cells was 6.6+/-1.0 pg/cell. Cytospins of dispersed cells fixed in Carnoy's and stained with alcian blue and safranin O contained mast cells with blue and red granules, and a few cells with a mixture of both granule types. Based on the effects of type of fixation, staining characteristics and histamine content, a mix of subtypes of mast cells is present in the bovine trachea. However, functionally they respond to secretagogues differently than rodent mast cells. Without an immunological secretagogue, studies to determine compounds that will be effective in blocking mast cell degranulation will be limited.

Induction of endogenous tumor necrosis factor-alpha: suppression of centrally stimulated gastric motility

Gastric stasis is frequently seen in conjunction with critical infectious illness, chronic inflammatory disorders, radiation sickness, and carcinogenesis. These conditions are associated with elevated circulating levels of the cytokine tumor necrosis factor-alpha (TNF-alpha). The present studies examined the relationship between endogenously produced TNF-alpha and the central neural mechanisms that augment gastric motility. Systemic lipopolysaccharide (LPS) was employed to induce TNF-alpha production in thiobutabarbital-anesthetized rats. Sixty minutes after intravenous LPS injection, gastric motility could not be stimulated by a potent centrally acting gastrokinetic stimulant, thyrotropin-releasing hormone (TRH). This failure to elicit gastric motility via central mechanisms coincided with high circulating levels of TNF-alpha. However, intravenous injections of bethanecol, a peripherally acting cholinergic agonist with direct gastrokinetic effects, were still able to elicit normal increases in gastric motility in the presence of TNF-alpha and LPS. Therefore, the inability to stimulate gastric motility via central TRH could not be attributed to the direct inhibitory effects of either LPS or TNF-alpha on the stomach. If the production of endogenous TNF-alpha was suppressed via the use of urethan as the anesthetic agent, then intravenous injections of LPS were no longer effective in suppressing gastric motility. Thus these effects on gastric motility are not directly attributable to LPS nor are they due to direct effects on the gastric smooth muscle. Our previous study demonstrated that microinjection of femtomole quantities of TNF-alpha in the brain stem dorsal vagal complex (DVC) can modulate gastric motility. This central TNF-alpha effect on gastric motility was dose dependent and required an intact vagal efferent pathway. The results from these two studies suggest that systemically produced TNF-alpha may gain access to the DVC to modulate gastric function.

The release of tumor necrosis factor-alpha, interleukin-1, interleukin-6 and prostaglandin E2 in bovine Kupffer cells stimulated with bacterial lipopolysaccharide

Kupffer cells, in response to gut-derived bacteria, viruses and endogenous endotoxins, are thought to be a major source of proinflammatory cytokines and other mediators. In the present study, we investigated the mode of tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1), interleukin-6 (IL-6) and prostaglandin E2 (PGE2) production by bovine Kupffer cells in response to LPS in vitro. By semi-quantitative reverse transcription-polymerase chain reaction, both TNF-alpha and IL-1beta mRNAs were expressed between 3 and 12 h after stimulation with 1 microg/ml of LPS. The IL-1alpha transcript also increased at 3 h, and then disappeared at 6 h. Although IL-6 mRNA was slightly expressed without stimulation, it increased and reached a peak after 6 h, and then decreased to normal levels by 24 h. The secretion of TNF-alpha and IL-1 was detected after 3 h and increased until 12 and 24 h, respectively, as detected by bioassay. IL-6 was secreted at a low level without stimulation, peaked 6 h after stimulation and remained elevated until 24 h. The secretion of prostaglandin E2 continued to increase for 24 h. These results suggest that several inflammatory cytokines released from bovine Kupffer cells are regulated in different modes.

The biphasic mRNA expression pattern of bovine interleukin-8 in Pasteurella haemolytica lipopolysaccharide-stimulated alveolar macrophages is primarily due to tumor necrosis factor alpha

Pasteurella haemolytica serotype 1 is the bacterial agent responsible for the pathophysiological events associated with bovine pneumonic pasteurellosis. Our previous studies support a role for the lipopolysaccharide (LPS) from P. haemolytica in the induction of proinflammatory cytokines. One of the pathological hallmarks of bovine pneumonic pasteurellosis is an influx of neutrophils into the alveolar spaces. This pronounced influx suggests the local production of a chemotactic factor(s) such as interleukin-8 (IL-8). In the context of the lung, the alveolar macrophage appears to be the major producer of IL-8, a proinflammatory cytokine with potent neutrophil chemotactic activity. By using Northern blot analysis, we have examined the kinetics of IL-8 mRNA expression in P. haemolytica LPS-stimulated bovine alveolar macrophages and found that 1 ng of LPS per ml induces maximal expression of IL-8 mRNA. The results also indicate a biphasic time course expression pattern in which IL-8 mRNA levels peak between 1 and 2 h in the first phase and between 16 and 24 h in the second phase (P < 0.01). In addition, monospecific polyclonal antibodies were used to demonstrate the role of tumor necrosis factor alpha (TNF-alpha) in the second phase of IL-8 mRNA expression. Our findings support a role for P. haemolytica LPS and TNF-alpha in the induction of IL-8 from bovine alveolar macrophages.

The sepsis-coagulant axis: a review

Activation of coagulation is a normal component of the acute inflammatory response. Inflammatory cytokines initiate coagulation events locally at sites of inflammation by converting endothelium from an antithrombotic surface to a prothrombotic surface; by stimulating tissue factor production, which activates both the extrinsic and intrinsic coagulation systems; and by stimulating production of platelet-activating factors. The fibrinolytic system is initially activated but is subsequently inhibited. This results in a marked imbalance in coagulation and fibrinolysis resulting in a net procoagulant state. When thrombin generation and platelet activation exceed the body's capacity to inactivate or remove these factors, disseminated intravascular coagulation (DIC) results. DIC directly contributes to multiple organ failure and death associated with sepsis. Presently available treatments (i.e., heparin and aspirin) are relatively ineffective in treating DIC; however, newer, more potent drugs may soon be available for clinical use.

Pasteurella haemolytica A1-derived leukotoxin and endotoxin induce intracellular calcium elevation in bovine alveolar macrophages by different signaling pathways

Leukotoxin and endotoxin derived from Pasteurella haemolytica serotype 1 are the primary virulence factors contributing to the pathogenesis of lung injury in bovine pneumonic pasteurellosis. Activation of bovine alveolar macrophages with endotoxin or leukotoxin results in the induction of cytokine gene expression, with different kinetics (H. S. Yoo, S. K. Maheswaran, G. Lin, E. L. Townsend, and T. R. Ames, Infect. Immun. 63:381-388, 1995; H. S. Yoo, B. S. Rajagopal, S. K. Maheswaran, and T. R. Ames, Microb. Pathog. 18:237-252, 1995). Furthermore, extracellular Ca2+ is required for leukotoxin-induced cytokine gene expression. However, the involvement of Ca2+ in endotoxin effects and the precise signaling mechanisms in the regulation of intracellular Ca2+ by leukotoxin and endotoxin are not known. In fura-2-acetoxymethyl ester-loaded alveolar macrophages, intracellular Ca2+ regulation by leukotoxin and endotoxin was studied by video fluorescence microscopy. Leukotoxin induced a sustained elevation of intracellular Ca2+ in a concentration-dependent fashion by influx of extracellular Ca2+ through voltage-gated channels. In the presence of fetal bovine serum, endotoxin elevated intracellular Ca2+ even in the absence of extracellular Ca2+. Leukotoxin-induced intracellular Ca2+ elevation was inhibited by pertussis toxin, inhibitors of phospholipases A2 and C, and the arachidonic acid analog 5,8,11,14-eicosatetraynoic acid. Intracellular Ca2+ elevation by endotoxin was inhibited by inhibitors of phospholipase C and protein tyrosine kinase, but not by pertussis toxin, or the arachidonic acid analog. To the best of our knowledge, this is the first report of Ca2+ signaling by leukotoxin through a G-protein-coupled mechanism involving activation of phospholipases A2 and C and release of arachidonic acid in bovine alveolar macrophages. Ca2+ signaling by endotoxin, on the other hand, involves activation of phospholipase C and requires tyrosine phosphorylation. The differences in the Ca2+ signaling mechanisms may underlie the reported temporal differences in gene expression during leukotoxin and endotoxin activation.

Expression of beta-defensin genes in bovine alveolar macrophages

Bovine alveolar macrophages (BAM) were examined for the expression of beta-defensins and to determine whether their expression could be upregulated by bacterial lipopolysaccharide (LPS), as observed with beta-defensins expressed in bovine tracheal epithelial cells. Four beta-defensins were expressed constitutively in BAM, with bovine neutrophil beta-defensin (BNBD)-4 and BNBD-5 being the most predominant. This is the first evidence of beta-defensin gene expression in a mature myeloid cell. LPS had no effect on beta-defensin expression in BAM, even though tumor necrosis factor alpha (TNF-alpha) production was induced. Nonbacterial inflammatory particles had little effect on beta-defensin gene expression or TNF-alpha production in BAM. We hypothesize that constitutively expressed beta-defensins of alveolar macrophages may have a role in lung host defense.

Primary culture and expression of cytokine mRNAs by lipopolysaccharide in bovine Kupffer cells

Kupffer cells are sessile tissue macrophages that have a role in liver defense against endogenous endotoxins. Because little information is available on the role of bovine Kupffer cells, we developed a primary culture method to investigate the function of bovine Kupffer cells. Kupffer cells were isolated from the caudate lobe of calf liver by perfusion with collagenase and pronase. Then, the cells were purified by gradient centrifugation followed by counterflow centrifugal elutriation. With the methods, a mean number of 1.5 x 10(6) Kupffer cells with a final viability of over 98% was obtained from 1 g of the liver. Over 95% of the isolated cells were positive for non-specific esterase activity and had surface molecule of CD68. The cultured Kupffer cells expressed mRNAs of tumor necrosis factor-alpha, interleukin (IL)-1 alpha, IL-1 beta and IL-6 by stimulation for 3 h with lipopolysaccharide. The primary culture of bovine Kupffer cells could be useful to investigate the systemic inflammatory response in bovine liver.

Epithelial antibiotic induced in states of disease

Epithelial defensins provide an active defense against the external microbial environment. We investigated the distribution and expression of this class of antimicrobial peptides in normal cattle and in animals in varying states of disease. beta-defensin mRNA was found to be widely expressed in numerous exposed epithelia but was found at higher levels in tissues that are constantly exposed to and colonized by microorganisms. We observed induction in ileal mucosa during chronic infection with Mycobacterium paratuberculosis and in bronchial epithelium after acute infection with Pasteurella haemolytica. It has been proposed that expression of antimicrobial peptides is an integral component of the inflammatory response. The results reported here support this hypothesis and suggest that epithelial defensins provide a rapidly mobilized local defense against infectious organisms.

Molecular cloning of bovine CD14 gene

Genomic DNA encoding bovine CD14 was isolated from a bovine (Holstein) genomic library. Utilizing PCR fragment of mouse CD14 gene as a probe, we screened 9 x 10(5) plaques and obtained 3 clones containing the bovine CD14 gene. DNA sequencing showed that bovine CD14 gene encodes 373 amino acids, and the coding sequence was separated by a 90 nt intron. The identity of the deduced amino acid sequence of bovine CD14 was 61-73% to those of mouse, rabbit and human. Northern blot analysis revealed that CD14 mRNA (1.5 kb) was expressed in the lung. Expression of CD14 mRNA was stimulated about 2-fold in bovine peripheral blood macrophage activated with LPS in vitro.

Nitric oxide production following in vitro stimulation of ovine pulmonary alveolar macrophages

Production of inducible nitric oxide (NO) as measured by nitrite in supernatant from ovine pulmonary alveolar macrophage (PAM) cultures was assessed following stimulation of PAM with live cells and supernatants from Corynebacterium pseudotuberculosis and Pasteurella haemolytica cultures; purified bacterial lipopolysaccharide derived from both Escherichia coli and Pasteurella haemolytica alone and in combination with interferon-gamma or lymphocyte conditioned medium; or ovine lentivirus. PAM cultured ex vivo with no further stimulation for 24 h, 48 h or 72 h, produced low concentrations of NO that was not substantially increased following co-culture by the various additives. Assessment of NO production in PAM cultures containing P. haemolytica or supernatant from P. haemolytica cultures was complicated by production of high levels of nitrite in the bacterial cultures. Species differences in inducible NO production may affect the efficacy of clearance of bacterial infections and be responsible for inter-host differences in disease expression following infection by intracellular pathogens.