Protective ability and specificity of convalescent serum from calves with Haemophilus somnus pneumonia

Subcutaneous application of hyperimmune serum against Histophilus somni recombinant proteins affects serum antibody reactivity in beef calves

BACKGROUND

Respiratory tract diseases cause significant economic loss in beef cattle. This study aimed to determine whether the application of hyperimmune serum (HS) containing antibodies against selected antigens of Gram-negative bacteria would improve the health and growth of different breeds of beef calves kept on three farms. Two recombinant protein antigens (Histophilus somni rHsp60 and rOMP40) were used to immunize four cows to produce HS. Eighty seven beef calves (Charolaise n = 36, Limousine n = 34, and crossbreed n = 17) were included into study. One hundred milliliters of serum were administered subcutaneously to 43 beef calves (Charolaise n = 18, Limousine n = 17, and crossbreed n = 8) twice, between 1 and 5 and 21-28 days of life. Calves were examined three times, and blood samples were taken to evaluate immunoglobulin M, G1, and G2, fibrinogen, serum amyloid A, and haptoglobin concentrations and reactivity of these Ig classes of antibodies against H. somni rHsp60 and rOMP40. Average daily weight gain during the first month and until weaning was calculated.

RESULTS

HS showed higher (p ≤ 0.05) reactivity in calf sera against H. somni rHsp60 and OMP40 in IgG1 and IgG2. In experimental calves, compared to control calves, the reactivity of IgG1 against rOMP40 in the second sampling was higher in Limousine calves (p ≤ 0.001) and in the other two herds (p ≤ 0.05). Serum IgG2 antibody activity against H. somni rHsp60 in the second sampling was higher in experimental calves than in control calves in charolaise (p ≤ 0.05) and limousine (p ≤ 0.001) herds. The reactivity of IgG2 against rOMP40 in the second sampling of experimental calves was higher in herds with Charolaise and Limousine calves (p ≤ 0.001) and in crossbred calves (p ≤ 0.05). In the third sampling, serum IgG1 antibody reactivity against rOMP40 in Limousine calves was higher (p ≤ 0.05) in the experimental group. Among the other evaluated parameters, only SAA in the second sampling in the herd with Charolaise calves and heart rate in the herd with Limousine calves were significantly higher in the control calves (p ≤ 0.05).

CONCLUSION

The application of HS to calves in all herds had an impact on specific reactivity in IgG1 and IgG2 classes against H. somni rOMP40 and rHsp60, antigens which were used for serum production.

Evaluation of the immunogenic properties of the recombinant Histophilus somni outer membrane protein 40 kDa (rOMP40)

Background

Gram-negative bacterial infections are a serious problem in beef and dairy cattle. Bacterial outer membrane proteins (OMPs) play a pivotal role in cellular survival and the host-bacterium interaction. Histophilus somni OMP40 was identified as a porin with homology between its N-terminal amino acid sequence and the sequences of porins of other gram-negative bacteria The aim of this study was to produce recombinant H. somni OMP40 (rOMP40), optimize its production and evaluate its immunogenic properties in calves. The cross-reactivity of anti-rOMP40 antibodies were also checked.

Results

The highest overexpression of rOMP40 was demonstrated by Escherichia coli C41 using the autoinduction process. Double immunization of calves (20 μg rOMP40 per animal) induced a significant increase of anti-rOMP40 antibodies in the IgG1 (P ≤ 0.01) and IgG2 (P ≤ 0.01, after first immunization only) subclasses, but not IgM. ELISA revealed increased reactivity of the IgG against surface antigens of E. coli and Pasteurella multocida after the second immunization (P < 0.01). Cross reactivity of anti-rOMP40 antibodies with ~ 40 kDa antigens of most common gram-negative pathogens was shown by Western blotting.

Conclusion

Immunization with H. somni rOMP40 induced a humoral response in cattle with broad cross-reactivity with similar antigens of other species of Pasteurellaceae and Enterobacteriaceae families and the delayed-type hypersensitivity reaction. The obtained results encourage further study to evaluate the protective effect of the produced protein as a subunit vaccine in cattle.

Polymicrobial Biofilm Interaction Between Histophilus somni and Pasteurella multocida

Histophilus somni and Pasteurella multocida are two of multiple agents responsible for bovine respiratory disease (BRD) in cattle. Following respiratory infection of calves with H. somni, P. multocida may also be isolated from the lower respiratory tract. Because H. somni may form a biofilm during BRD, we sought to determine if P. multocida can co-exist with H. somni in a polymicrobial biofilm in vitro and in vivo. Interactions between the two species in the biofilm were characterized and quantified by fluorescence in situ hybridization (FISH). The biofilm matrix of each species was examined using fluorescently tagged lectins (FTL) specific for the exopolysaccharide (EPS) using confocal laser scanning microscopy. Bacterial interactions were determined by auto-aggregation and biofilm morphology. Pasteurella multocida and H. somni were evenly distributed in the in vitro biofilm, and both species contributed to the polymicrobial biofilm matrix. The average biomass and biofilm thickness, and the total carbohydrate and protein content of the biofilm, were greatest when both species were present. Polymicrobial bacterial suspensions auto-aggregated faster than single species suspensions, suggesting physical interactions between the two species. Almost 300 P. multocida genes were significantly differentially regulated when the bacteria were in a polymicrobial biofilm compared to a mono-species biofilm, as determined by RNA-sequencing. As expected, host genes associated with inflammation and immune response were significantly upregulated at the infection site following H. somni challenge. Encapsulated P. multocida isolates not capable of forming a substantial biofilm enhanced an in vitro polymicrobial biofilm with H. somni, indicating they contributed to the polymicrobial biofilm matrix. Indirect evidence indicated that encapsulated P. multocida also contributed to a polymicrobial biofilm in vivo. Only the EPS of H. somni could be detected by FTL staining of bovine tissues following challenge with H. somni. However, both species were isolated and an immune response to the biofilm matrix of both species was greater than the response to planktonic cells, suggesting encapsulated P. multocida may take advantage of the H. somni biofilm to persist in the host during chronic BRD. These results may have important implications for the management and prevention of BRD.

Histophilus somni: Antigenic and Genomic Changes Relevant to Bovine Respiratory Disease

Histophilus somni is associated with several disease syndromes in cattle and plays an important role in the bovine respiratory disease complex. H somni isolates exhibit significant differences in terms of susceptibility to inactivation by normal serum corresponding to the general ability to cause clinical disease. Isolates possess a variety of virulence factors, and variation in virulence factor expression is well recognized and associated with antigenic differences. Sequencing of genes associated with known virulence factors has identified genetic variability between isolates. The antigenic and genomic differences represent significant challenges to the host immune system and are problematic for vaccine design.

Effect of Histophilus somni on Heart and Brain Microvascular Endothelial Cells

Histophilus somni is a pathogenic gram-negative bacterium responsible for pneumonia and septicemia in cattle. Sequelae include infectious thrombotic meningoencephalitis (ITME), myocarditis, arthritis, and abortion. These syndromes are associated with widespread vasculitis and thrombosis, implicating a role for endothelium in pathogenesis. Histopathologic and immunohistochemical investigation of 10 natural cases of bovine H. somni myocarditis and 1 case of ITME revealed intravascular H. somni in large biofilm-like aggregates adherent to the luminal surface of microvascular endothelium. Ultrastructurally, bacterial communities were extracellular and closely associated with degenerating or contracted endothelial cells. Histophilus somni was identified by bacterial culture and/or immunohistochemistry. Western blots of the bacterial isolates revealed that they expressed the immunodominant protective 40 kDa OMP and immunoglobulin-binding protein A (IbpA) antigens. The latter is a large surface antigen and shed fibrillar antigen with multiple domains. The cytotoxic DR2Fic domain of IbpA was conserved as demonstrated by polymerase chain reaction. Treatment of endothelial cells in vitro with IbpA in crude culture supernatants or purified recombinant GST-IbpA DR2Fic (rDR2) cytotoxin induced retraction of cultured bovine brain microvascular endothelial cells. By contrast, no retraction of bovine endothelium was induced by mutant rDR2H/A with an inactive Fic motif or by a GST control, indicating that the cytotoxic DR2Fic motif plays an important role in endothelial cell retraction in vasculitis. The formation of biofilm-like aggregates by H. somni on bovine microvascular endothelium may be fundamental to its pathogenesis in heart and brain.

Histophilosis as a Natural Disease

Histophilus somni is responsible for sporadic disease worldwide in cattle and, to a lesser extent, in small ruminants, bighorn sheep (Ovis canadensis), and North American bison (Bison bison). The importance of H. somni diseases can be attributed to improved clinical and laboratory recognition, combined with the growth in intensive management practices for cattle. Although outbreaks of bovine histophilosis can occur year-round, in northern and southern hemispheres, it is most frequent in late fall and early winter. Weather, stress, dietary changes, and comingling of cattle are likely to be major triggers for outbreaks. The most frequent clinical expressions of histophilosis include undifferentiated fever, fibrinosuppurative pneumonia, encephalitis-leptomeningitis, necrotizing myocarditis, and diffuse pleuritis. Neurological disease occurs either as thrombotic meningoencephalitis (TME) or as suppurative meningitis with ventriculitis. Acute myocarditis is characteristically necrotizing and generally involves one or both papillary muscles in the left ventricular myocardium. Biofilm-like aggregates of bacteria occur in capillaries and veins in myocardium, in the central nervous system, and on endocardial surfaces. H. somni is a component of bovine respiratory disease (BRD) complex. In our experience, it is most commonly diagnosed in subacute-to-chronic polymicrobial pulmonary infections in combination with Mannheimia haemolytica, Trueperella pyogenes, Pasteurella multocida, or Mycoplasma bovis. Other, less common forms of H. somni disease present as polyarthritis/tenosynovitis, abortion with placentitis and fetal septicemia, epididymitis-orchitis, and ocular infections. It is likely that H. somni is under-recognized clinically and diagnostically. Most state and provincial laboratories in North America rely on bacterial isolation to confirm infection. The use of more sensitive detection methods on field cases of histophilosis will help resolve the pathogenesis of H. somni in natural outbreaks, and whether the disease is as common elsewhere as it is in Canada.

Histophilus somni Stimulates Expression of Antiviral Proteins and Inhibits BRSV Replication in Bovine Respiratory Epithelial Cells

Our previous studies showed that bovine respiratory syncytial virus (BRSV) followed by Histophilus somni causes more severe bovine respiratory disease and a more permeable alveolar barrier in vitro than either agent alone. However, microarray analysis revealed the treatment of bovine alveolar type 2 (BAT2) epithelial cells with H. somni concentrated culture supernatant (CCS) stimulated up-regulation of four antiviral protein genes as compared with BRSV infection or dual treatment. This suggested that inhibition of viral infection, rather than synergy, may occur if the bacterial infection occurred before the viral infection. Viperin (or radical S-adenosyl methionine domain containing 2—RSAD2) and ISG15 (IFN-stimulated gene 15—ubiquitin-like modifier) were most up-regulated. CCS dose and time course for up-regulation of viperin protein levels were determined in treated bovine turbinate (BT) upper respiratory cells and BAT2 lower respiratory cells by Western blotting. Treatment of BAT2 cells with H. somni culture supernatant before BRSV infection dramatically reduced viral replication as determined by qRT PCR, supporting the hypothesis that the bacterial infection may inhibit viral infection. Studies of the role of the two known H. somni cytotoxins showed that viperin protein expression was induced by endotoxin (lipooligosaccharide) but not by IbpA, which mediates alveolar permeability and H. somni invasion. A naturally occurring IbpA negative asymptomatic carrier strain of H. somni (129Pt) does not cause BAT2 cell retraction or permeability of alveolar cell monolayers, so lacks virulence in vitro. To investigate initial steps of pathogenesis, we showed that strain 129Pt attached to BT cells and induced a strong viperin response in vitro. Thus colonization of the bovine upper respiratory tract with an asymptomatic carrier strain lacking virulence may decrease viral infection and the subsequent enhancement of bacterial respiratory infection in vivo.

The bovine lung in biomedical research: visually guided bronchoscopy, intrabronchial inoculation and in vivo sampling techniques

There is an ongoing search for alternative animal models in research of respiratory medicine. Depending on the goal of the research, large animals as models of pulmonary disease often resemble the situation of the human lung much better than mice do. Working with large animals also offers the opportunity to sample the same animal repeatedly over a certain course of time, which allows long-term studies without sacrificing the animals.

The aim was to establish in vivo sampling methods for the use in a bovine model of a respiratory Chlamydia psittaci infection. Sampling should be performed at various time points in each animal during the study, and the samples should be suitable to study the host response, as well as the pathogen under experimental conditions.

Bronchoscopy is a valuable diagnostic tool in human and veterinary medicine. It is a safe and minimally invasive procedure. This article describes the intrabronchial inoculation of calves as well as sampling methods for the lower respiratory tract. Videoendoscopic, intrabronchial inoculation leads to very consistent clinical and pathological findings in all inoculated animals and is, therefore, well-suited for use in models of infectious lung disease. The sampling methods described are bronchoalveolar lavage, bronchial brushing and transbronchial lung biopsy. All of these are valuable diagnostic tools in human medicine and could be adapted for experimental purposes to calves aged 6-8 weeks. The samples obtained were suitable for both pathogen detection and characterization of the severity of lung inflammation in the host.

The role of lipooligosaccharide phosphorylcholine in colonization and pathogenesis of Histophilus somni in cattle

Histophilus somni is a Gram-negative bacterium and member of the Pasteurellaceae that is responsible for respiratory disease and other systemic infections in cattle. One of the bacterium’s virulence factors is antigenic phase variation of its lipooligosaccharide (LOS). LOS antigenic variation may occur through variation in composition or structure of glycoses or their substitutions, such as phosphorylcholine (ChoP). However, the role of ChoP in the pathogenesis of H. somni disease has not been established. In Haemophilus influenzae ChoP on the LOS binds to platelet activating factor on epithelial cells, promoting bacterial colonization of the host upper respiratory tract. However, ChoP is not expressed in the blood as it also binds C-reactive protein, resulting in complement activation and killing of the bacteria. In order to simulate the susceptibility of calves with suppressed immunity due to stress or previous infection, calves were challenged with bovine herpes virus-1 or dexamethazone 3 days prior to challenge with H. somni. Following challenge, expression of ChoP on the LOS of 2 different H. somni strains was associated with colonization of the upper respiratory tract. In contrast, lack of ChoP expression was associated with bacteria recovered from systemic sites. Histopathology of cardiac tissue from myocarditis revealed lesions containing bacterial clusters that appeared similar to a biofilm. Furthermore, some respiratory cultures contained substantial numbers of Pasteurella multocida, which were not present on preculture screens. Subsequent biofilm experiments have shown that H. somni and P. multocida grow equally well together in a biofilm, suggesting a commensal relationship may exist between the two species. Our results also showed that ChoP contributed to, but was not required for, adhesion to respiratory epithelial cells. In conclusion, expression of ChoP on H. somni LOS contributed to colonization of the bacteria to the host upper respiratory tract, but phase variable loss of ChoP expression may help the bacteria survive systemically.

Antibody responses of calves to Histophilus somni recombinant IbpA subunits

Histophilus somni causes bovine pneumonia and septicemia, but protective immune responses are not well understood and immunodiagnostic methods are not well defined. We previously showed that antibody to a new virulence factor, IbpA, neutralizes cytotoxicity and immunization with a recombinant IbpA domain protects calves against experimental H. somni pneumonia. To further define immune responses to IbpA, we determined isotypic serum antibody responses to three IbpA domains (IbpA3, an N-terminal coiled coil region; IbpA5, a central region of 200 bp repeats and IbpA DR2, a C-terminal cytotoxic domain). ELISA was used to quantitate IgG1 or IgG2 antibodies to each of the IbpA subunits as well as H. somni whole cells (WCs) or culture supernatant (SUP). Calves experimentally infected with H. somni and monitored for up to 10 weeks had the least "0 time" (background) antibody levels to IbpA5, as well as the earliest and highest responses of greatest duration to the IbpA5 subunit. Responses of these calves were high to WC or SUP antigens but with higher "0 time" (background) antibody levels. We concluded that IbpA5 may be a useful immunodiagnostic antigen. Calves immunized with H. somni WC vaccine had antibody responses to WC antigens, but not to IbpA subunits before challenge. After challenge with H. somni, vaccinated calves had slight anamnestic responses to IbpA3 and IbpA5, but not to IbpA DR2. Since IbpA DR2 is a protective antigen, the data suggest the IbpA DR2 would be a useful addition to H. somni vaccines.

IbpA DR2 subunit immunization protects calves against Histophilus somni pneumonia

Histophilus somni is a prevalent cause of pneumonia and septicemia in cattle. Yet evidence for protection against pneumonia by current vaccines is controversial. We have identified a new H. somni virulence factor, IbpA. Previous studies implicated three likely protective subunits or domains in IbpA (A3, A5, and DR2), which were expressed as recombinant GST fusion proteins and purified for systemic vaccination of calves. After two subcutaneous immunizations, calves were challenged intrabronchially with virulent H. somni strain 2336 and clinical signs were monitored for four days before necropsy. Serum samples were collected throughout. At necropsy, the area of gross pneumonia was estimated, bronchial lavage fluid was collected, lesions were cultured and tissue samples were fixed for histopathology. Results showed that calves immunized with IbpA DR2 had a statistically lower percentage of lung with gross lesions than controls, fewer histologic abnormalities in affected areas and no H. somni isolated from residual pneumonic lesions. Calves immunized with the control GST vaccine, IbpA3 or IbpA5 had larger H. somni positive pneumonic lesions. ELISA results for serum antibodies showed that calves immunized with the IbpA DR2 antigen had high IgG1 and IgG2 and lowest IgE responses to the immunizing antigen. Specific IgG responses were also high in the bronchial lavage fluid. High specific serum IgE responses were previously shown to be associated with more severe pneumonia, but high IgG specific anti-IbpA DR2 responses seem to be critically related to protection. Since the IbpA DR2 Fic motif has been shown to cause bovine alveolar cells to retract, we tested the neutralizing ability of pooled serum from the IbpA DR2 immunized group. This pooled serum reduced cytotoxicity by 75-80%, suggesting that the protection was due to antibody neutralization of IbpA cytotoxicity, at least in part. Therefore, IbpA DR2 appears to be an important protective antigen of H. somni. The study shows, for the first time, that immunization with a purified Fic protein protects against disease in a natural host.

Histophilus somni IbpA DR2/Fic in virulence and immunoprotection at the natural host alveolar epithelial barrier

Newly recognized Fic family virulence proteins may be important in many bacterial pathogens. To relate cellular mechanisms to pathogenesis and immune protection, we studied the cytotoxicity of the Histophilus somni immunoglobulin-binding protein A (IbpA) direct repeat 2 Fic domain (DR2/Fic) for natural host target cells. Live virulent IbpA-producing H. somni strain 2336, a cell-free culture supernatant (CCS) of this strain, or recombinant DR2/Fic (rDR2/Fic) caused dramatic retraction and rounding of bovine alveolar type 2 (BAT2) epithelial cells. IbpA-deficient H. somni strain 129Pt and a Fic motif His(298)Ala mutant rDR2/Fic protein were not cytotoxic. The cellular mechanism of DR2/Fic cytotoxicity was demonstrated by incubation of BAT2 cell lysates with strain 2336 CCS or rDR2/Fic in the presence of [alpha-(32)P]ATP, which resulted in adenylylation of Rho GTPases and cytoskeletal disruption. Since IbpA is not secreted by type III or type IV secretion systems, we determined whether DR2/Fic entered the host cytoplasm to access its Rho GTPase targets. Although H. somni did not invade BAT2 cells, DR2/Fic was internalized by cells treated with H. somni, CCS, or the rDR2/Fic protein, as shown by confocal immunomicroscopy. Transwell bacterial migration assays showed that large numbers of strain 2336 bacteria migrated between retracted BAT2 cells, but IbpA-deficient strain 129Pt did not cross a monolayer unless the monolayer was pretreated with strain 2336 CCS or rDR2/Fic protein. Antibody to rDR2/Fic or passively protective convalescent-phase serum blocked IbpA-mediated cytotoxicity and inhibited H. somni transmigration across BAT2 monolayers, confirming the role of DR2/Fic in pathogenesis and corresponding to the results for in vivo protection in previous animal studies.

Aerosol infection of calves with Histophilus somni

The purpose of this study was to develop and evaluate an aerosol infection method with Histophilus somni that closely resembles the natural way of infection of calves. Another aim was to compare the virulence of two H. somni strains by collecting clinical and postmortem data of experimentally infected and control animals. Seventeen conventionally reared 3-month-old calves were divided into three groups. Two groups of six animals each were exposed to suspensions containing H. somni on three consecutive days using a vaporiser mask. The third group of five animals was used as control. The data of individual clinical examination were recorded daily. All animals were exterminated, and gross pathology of all lungs was evaluated on the 15th day after the first infection. Both H. somni strains caused an increase of rectal temperature, respiratory signs, decrease of weight gain, and severe catarrhal bronchopneumonia in both infected groups. Although some chronic lesions were detected in the lungs of the control animals as well, the histopathological findings in the infected and control groups were different. H. somni was recultured from all lungs in the challenged groups but it could not be reisolated or detected by PCR examination in the control group. This is the first paper on aerosol challenge of calves with H. somni using repeated infection and verified by detailed pathological, bacteriological and histopathological examination. The infection method proved to be successful. There was no difference in the virulence of the two H. somni strains used in the trial.

The fic domain: regulation of cell signaling by adenylylation

We show that the secreted antigen, IbpA, of the respiratory pathogen Histophilus somni induces cytotoxicity in mammalian cells via its Fic domains. Fic domains are defined by a core HPFxxGNGR motif and are conserved from bacteria to humans. We demonstrate that the Fic domains of IbpA catalyze a unique reversible adenylylation event that uses ATP to add an adenosine monophosphate (AMP) moiety to a conserved tyrosine residue in the switch I region of Rho GTPases. This modification requires the conserved histidine of the Fic core motif and renders Rho GTPases inactive. We further demonstrate that the only human protein containing a Fic domain, huntingtin yeast-interacting protein E (HYPE), also adenylylates Rho GTPases in vitro. Thus, we classify Fic domain-containing proteins as a class of enzymes that mediate bacterial pathogenesis as well as a previously unrecognized eukaryotic posttranslational modification that may regulate key signaling events.

Protection of mice against H. somni septicemia by vaccination with recombinant immunoglobulin binding protein subunits

Histophilus somni causes bovine pneumonia as well as septicemia and its sequelae but mechanisms of virulence and protective immunity are poorly understood. Since surface immunoglobulin binding proteins are virulence factors, we addressed their role as protective antigens in a mouse model of H. somni septicemia. Immunoglobulin binding protein A (IbpA), has homology to Bordetella pertussis filamentous hemagglutinin and other large bacterial exoproteins. IbpA is a major surface antigen encoded by the ibpA gene with many domains that may be important in pathogenesis and immune protection. Three IbpA recombinant protein subunits, IbpA3, IbpA5 and IbpADR2 were chosen for study because of putative functional domains and motifs. These recombinant GST fusion subunit proteins were compared with GST (negative control), formalin-killed H. somni (commercial vaccine control), live H. somni (to induce convalescent immunity) and H. somni culture supernatant (containing IbpA shed from the bacterial surface). In vaccination/challenge studies, both live H. somni (convalescent immunity) and supernatant protected equally but formalin-killed H. somni and GST did not protect against septicemia. The DR2 and A3 subunits protected moderately well and induced antibody responses against supernatant antigen and the homologous subunit in ELISA but not against whole cell antigens. Supernatant immunization protected better than the IbpA subunit antigens and induced high antibody activity against both whole cells and supernatant antigens. The results indicate that culture supernatant antigens or perhaps recombinant IbpA subunits may be useful in H. somni vaccines. These studies also provide insight into the contribution of IbpA domains to pathogenesis of H. somni septicemia.

Histophilus somni host-parasite relationships

Histophilus somni (Haemophilus somnus) is one of the key bacterial pathogens involved in the multifactorial etiology of the Bovine Respiratory Disease Complex. This Gram negative pleomorphic rod also causes bovine septicemia, thrombotic meningencephalitis, myocarditis, arthritis, abortion and infertility, as well as disease in sheep, bison and bighorn sheep. Virulence factors include lipooligosaccharide, immunoglobulin binding proteins (as a surface fibrillar network), a major outer membrane protein (MOMP), other outer membrane proteins (OMPs) and exopolysaccharide. Histamine production, biofilm formation and quorum sensing may also contribute to pathogenesis. Antibodies are very important in protection as shown in passive protection studies. The lack of long-term survival of the organism in macrophages, unlike facultative intracellular bacteria, also suggests that antibodies should be critical in protection. Of the immunoglobulin classes, IgG2 antibodies are most implicated in protection and IgE antibodies in immunopathogenesis. The immunodominant antigen recognized by IgE is the MOMP and by IgG2 is a 40 kDa OMP. Pathogenetic synergy of bovine respiratory syncytial virus (BRSV) and H. somni in calves can be attributed, in part at least, to the higher IgE anti-MOMP antibody responses in dually infected calves. Other antigens are probably involved in stimulating host defense or immunopathology as well.

Bovine plasma proteins increase virulence of Haemophilus somnus in mice

The role of bovine serum or plasma proteins in Haemophilus somnus virulence was investigated in a mouse model of septicemia. An increase in virulence was detected when the organism was pre-incubated for 5 min and inoculated with fetal calf serum. When purified bovine serum or plasma proteins were pre-incubated with H. somnus before inoculating into mice, transferrin was found to increase virulence. Bovine lactoferrin was also noted to increase virulence, but to a lesser extent and had a delayed time course when compared with transferrin. Using an ELISA assay, an increased amount of H. somnus whole cells and culture supernatant bound to bovine transferrin when the organism was grown in iron-restricted media. Lactoferrin also bound to H. somnus, but binding was not affected by growth in iron-restricted media and it was eliminated with 2M NaCl, which reversed charge mediated binding. Transferrin, but not lactoferrin, supported growth of H. somnus on iron-depleted agar based media using a disk assay. Therefore, lactoferrin increased virulence by an undetermined mechanism whereas transferrin increased virulence of H. somnus by binding to iron-regulated outer-membrane proteins (IROMPs) and providing iron to the pathogen.

Specificity of IgG and IgE antibody responses to Haemophilus somnus infection of calves

Haemophilus somnus is an important cause of bovine respiratory disease and septicemia with all it's sequelae. The role of immune responses in protection and immunopathogenesis is not well understood. We showed that infection with bovine respiratory syncytial virus (BRSV) 6 days before H. somnus increased clinical scores and levels of IgE antibody to H. somnus over that of infection with H. somnus alone. To determine whether antigenic specificity of IgE responses differed from IgG responses, Western blots were done with sera from the infected calves, at 0 time and at 21 days post infection. Thus each calf was its own control. IgG antibodies recognized primarily a 40 kDa outer membrane protein (OMP) in whole cell H. somnus preparations and a 270 kDa immunoglobulin binding protein (IgBPs) in culture supernatants but generally not the 41 kDa major OMP (MOMP). IgE antibodies recognized primarily the 41 kDa MOMP in whole cell pellet preparations. Results were consistent among calves. With culture supernatants, IgE antibodies recognized both the 270 kDa IgBPs and the MOMP. Since some H. somnus strains from asymptomatic carriers (including strain 129Pt), do not have IgBPs and express a truncated MOMP (33 kDa rather than 41 kDa), reaction of strain 129Pt cells with serum from calves infected with H. somnus or BRSV and H. somnus was studied. IgE did not react with the truncated MOMP even at much lower (1:100) dilutions than in Western blots with virulent strain 2336 (serum dilution of 1:500). Reactions of IgE with the 40 and 78 kDa antigens in strain 129Pt were noted but since the major reactivities with the IgBPs and the MOMP were not detected, this strain may be useful for inducing protective rather than immunopathogenic responses.

Genetic and functional analysis of Haemophilus somnus high molecular weight-immunoglobulin binding proteins

Haemophilus somnus immunoglobulin binding proteins (IgBPs) are virulence associated but only one (p76) has been genetically defined. We determined the nucleotide sequence of the 5'-flanking region of the p76 gene. This region had been identified as the coding region for a series of high molecular weight (HMW)-IgBPs. Analysis of the nucleotide sequence indicated the gene (immunoglobulin binding protein A, ibpA) encoding the HMW and p76 IgBPs comprised a single open reading frame of 12,285 base pairs (bp). The ibpA gene is flanked by an upstream ORF of 1758bp, designated ibpB. The predicted amino acid sequences of these two genes demonstrate similarity to virulence exoproteins and their transporter proteins that comprise a two-partner secretion pathway in various Gram-negative bacteria. Motifs associated with binding to mammalian cells were also identified within the sequence. Competitive inhibition studies implicated a putative heparin-binding domain in adherence to bovine endothelial cells. Expression plasmids for glutathione S-transferase (GST)-fused recombinant fragments covered amino acid residues 972-3201. IgG2 Fc binding studies identified fragment 972-1515 (GST-IbpA3) as an Fc binding peptide. This peptide and GST-IbpA5 (aa 2071-2730) reacted strongly with convalescent phase serum. In a small preliminary study, calves immunized with the purified GST-IbpA3 peptide were protected against an intrabronchial H. somnus challenge.

Bovine platelets activated by Haemophilus somnus and its LOS induce apoptosis in bovine endothelial cells

Haemophilus somnus is a bacterial pathogen that causes respiratory disease and vasculitis in cattle. Thrombotic meningoencephalitis (TME) and other severe forms of H. somnus-mediated vascular disease are characterized histopathologically by vasculitis, thrombosis, and infiltration of polymorphonuclear cells. It has been reported previously that activated human platelets express CD40L, FasL and P-selectin (CD62P). We hypothesized that if these surface markers are up-regulated on bovine platelets after in vitro exposure to H. somnus and its lipooligosaccharide (LOS), they might contribute to endothelial cell damage. Using flow cytometry, we demonstrated low baseline expression of these molecules by bovine platelets and increased expression following in vitro stimulation with ADP, H. somnus or H. somnus LOS. H. somnus stimulated platelets were capable of causing apoptosis in endothelial cells as measured by Hoechst-33342 staining and caspase-3 activity. If these events occur in vivo, they might promote vascular damage and endothelial cell apoptosis, leading to the development of vasculitis and thrombosis that characterize bovine H. somnus infection.

Effects of sub-minimum inhibitory concentration antibiotic levels and temperature on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus

The objective of this study was to determine the effects of sub-minimum inhibitory concentrations (sub-MICs) of 2 veterinary antibiotic preparations, chlortetracycline (CTC) and chlortetracycline-sulfamethazine (CTC + SMZ), on growth kinetics and outer membrane protein expression in Mannheimia haemolytica and Haemophilus somnus at normal and febrile body temperatures. Sub-minimum inhibitory concentrations of both antibiotics reduced the growth rates of M. haemolytica and H. somnus. Growth of both species was not inhibited when grown at 41 degrees C compared to 37 degrees C. There was no detectable consistent effect of antibiotic or temperature on outer membrane protein expression for either species. Our study indicates that sub-MIC levels of CTC and CTC + SMZ markedly impair growth of clinical M. haemolytica and H. somnus isolates, potentially allowing more effective host clearance during infection.

Caspase activation during Haemophilus somnus lipooligosaccharide-mediated apoptosis of bovine endothelial cells

Vasculitis is commonly seen during systemic Haemophilus somnus infections. Although, the mechanism of vascular damage is not completely understood, in a previous report we demonstrated that H. somnus and its lipooligosaccharide (LOS) induced apoptosis in bovine pulmonary artery endothelial cells in vitro. In the present study, we investigated the role of caspase activation in LOS-mediated apoptosis of bovine endothelial cells. Exposure to H. somnus LOS induced caspase-3 activation and chromatin condensation in endothelial cells. These responses were blocked by the addition of a pan-caspase inhibitor (z-VAD-fmk) or capase-3 inhibitor (DEVD-fmk). Incubation of endothelial cells with H. somnus LOS also induced activation of the initiator caspases, caspases-8 and 9, with the activity of the former increasing more rapidly than the latter. Addition of a caspase-8 inhibitor (IETD-fmk) significantly reduced LOS-mediated apoptosis, whereas, addition of a caspase-9 inhibitor (LEHD-fmk) had little effect. These data suggest that LOS-mediated activation of caspase-3 and apoptosis of endothelial cells is caspase-8 dependent.

Antibodies as effectors

Antibodies are critical in protection against extracellular microbial pathogens. Although antibodies also play a role in transplant/tumor rejection and in autoimmune disease, this paper focuses on defense against bovine infections. Effector mechanisms of different bovine isotypes, subisotypes and allotypes are discussed. The importance of antigen specificity is also stressed.

Immunity to bovine reproductive infections

Protective immune responses in the genital tract are robust, as shown by convalescent and vaccine-induced immunity. Systemic immunity is crucial for systemic infections that result in reproductive failure (such as brucellosis, leptospirosis, and the systemic forms of C. fetus and H. somnus infection). Although IgA responses can protect against sexually transmitted or venereal infections, systemically induced IgG antibody responses also protect. IgA responses can be induced by immunization of the genital tract, where inductive sites develop after antigenic stimulation. The common mucosal immune system can also be used to induce a genital IgA response, as shown by intranasal vaccination. Lastly, it is necessary to determine which antigens of each infectious agent are protective and which types of immune responses protect best.

Haemophilus somnus induces apoptosis in bovine endothelial cells in vitro

Haemophilus somnus causes pneumonia, reproductive failure, infectious myocarditis, thrombotic meningoencephalitis, and other diseases in cattle. Although vasculitis is commonly seen as a result of systemic H. somnus infections, the pathogenesis of vascular damage is poorly characterized. In this study, we demonstrated that H. somnus (pathogenic isolates 649, 2336, and 8025 and asymptomatic carrier isolates 127P and 129Pt) induce apoptosis of bovine endothelial cells in a time- and dose-dependent manner, as determined by Hoechst 33342 staining, terminal deoxynucleotidyl transferase-mediated dUTP-FITC nick end labeling, DNA fragmentation, and transmission electron microscopy. H. somnus induced endothelial cell apoptosis in as little as 1 h of incubation and did not require extracellular growth of the bacteria. Viable H. somnus organisms induced greater endothelial cell apoptosis than heat-killed organisms. Since viable H. somnus cells release membrane fibrils and blebs, which contain lipooligosaccharide (LOS) and immunoglobulin binding proteins, we examined culture filtrates for their ability to induce endothelial cell apoptosis. Culture filtrates induced similar levels of endothelial cell apoptosis, as did viable H. somnus organisms. Heat inactivation of H. somnus culture filtrates partially reduced the apoptotic effect on endothelial cells, which suggested the presence of both heat-labile and heat-stable factors. We found that H. somnus LOS, which is heat stable, induced endothelial cell apoptosis in a time- and dose-dependent manner and was inhibited by the addition of polymyxin B. These data demonstrate that H. somnus and its LOS induce endothelial cell apoptosis, which may play a role in producing vasculitis in vivo.

Immunological characterization of the major outer membrane protein of Haemophilus somnus

Antigens and molecular mass diversity of the Haemophilus somnus major outer membrane protein (MOMP) were investigated. The molecular mass of the MOMP of 53 strains of H. somnus varied from 43 to 33 kDa and four MOMP MAb reactivity patterns were detected in immunoblot analysis and immunodot assay. The molecular mass and MAb reactivity data were used for preliminary grouping of H. somnus strains. Disease strains fell into groups 1 and 3, including two of three Group 3 subgroups, whereas strains from asymptomatic carriers were found in all the four groups and three subgroups. Immunoblot analysis with convalescent phase serum showed strain specific reactivity with MOMPs from three isolates used to reproduce disease in cattle. The reaction with the MOMP was only detectable at dilutions of 1:100 or less, whereas the same convalescent sera showed strong reactivity at dilutions of 1:1000 (or more) with other H. somnus antigens. The data suggest that the bovine immune response to the MOMP during infection is weak and is directed to antigenically variable determinants in a strain-specific manner. This may be important in evaluating the role of the antibody response to MOMPs in protective immunity.

Pasteurellaceae isolated from tonsillar samples of commercially-reared American bison (Bison bison)

As commercial producers of American bison (Bison bison) become more numerous, concerns relative to bison health management increase. Since loss due to respiratory disease associated with Pasteurella and related Pasteurellaceae is a major concern for cattle producers, a study was conducted to determine what types of Pasteurellaceae are carried by bison to evaluate the potential of pneumonic pasteurellosis in bison herds where management practices are comparable to those used for cattle. Tonsillar biopsies, collected in May (n = 29) and August (n = 25) 1997 from 24- to 30-month-old bison bulls, at the time of slaughter were cultured for Pasteurellaceae. Pasteurella spp. were isolated from all the samples collected in May. These included isolates identified as P. haemolytica, trehalosi, testudinis, and multocida subsp. multocida a and multocida b. Actinobacillus spp. and Haemophilus somnus were also isolated from some samples. Pasteurella spp., haemolytica, trehalosi, and multocida subsp. multocida a, multocida b and septica, plus 2 nonspeciated indole-positive biotypes, U2 and U16, were isolated from the second group of tonsil samples. Most of these organisms, including P. haemolytica, P. multocida subsp., and H. somnus are associated with disease in domestic livestock and should be regarded as potential pathogens for bison, particularly in animals which become stressed by management practices commonly used with cattle such as herding, crowding, and shipping.

The association of titers to Haemophilus somnus, and other putative pathogens, with the occurrence of bovine respiratory disease and weight gain in feedlot calves

Serum samples were obtained from 602 calves (from 19 groups in four feedlots: three in Ontario, and one in Alberta) upon arrival at the feedlot and 28 d later. Of these calves, 202 developed bovine respiratory disease (BRD) and 400 did not develop BRD. Based on high antibody titers noted upon arrival, we infer that most calves were exposed to Haemophilus somnus prior to arrival at the feedlot. Within a group, calves with high titers on arrival had a reduced risk of developing BRD later. Most calves did not experience titer increases after arrival; however, calves that had stable or increasing titers had a relatively low risk of contracting BRD. The calves at greatest risk of BRD were those with titers on arrival of less than 6.8 units and subsequent titer decreases of more than 1 unit. The effects of both the titer on arrival and the titer change after arrival were stable when the serologic effects of a number of viruses and Mycoplasma agents were considered. Neither antibody titer on arrival nor titer change was related to weight gain differences among calves. Calves with BRD or calves with lower weight on arrival had decreased weight gains in the first 28-day feeding period. The high titers on arrival may have protected most calves against further infection with H. somnus. However, since the calves that developed BRD had large titer increases to a number of viruses and to Pasteurella haemolytica, while having decreased antibody titers to H. somnus, we infer that the existing antibodies were "used up" in combatting the agents, including H. somnus, which may have "caused" the BRD. Calves which were able to increase their antibody levels to H. somnus tended to have a reduced risk of BRD.

Outer membrane proteins of Bartonella henselae and their interaction with human endothelial cells

Members of the genus Bartonella are unique in that they are bacteria which cause proliferation of microvascular endothelial cells and neovascularization (angiogenesis). The mechanisms by which Bartonella henselae causes these processes are unknown. Given the importance of surface-exposed determinants in the pathogenesis of many organisms, outer membrane proteins (OMPs) of B. henselae were identified. Enrichment of the outer membrane fraction of B. henselae by sarkosyl treatment of total membranes, together with radioiodination and biotinylation of intact organisms, suggest that at least nine proteins, with molecular weights of 28, 30, 35, 43, 58, 61, 79, 92 and 171 kDa, are located in the outer membrane. Triton X-100-extracted biotinylated human umbilical vein endothelial cell (HUVEC) surface proteins bound to the 43 kDa B. henselae OMP after B. henselae whole-cell lysates and sarkosyl-fractionated OMPs were separated by SDS-PAGE and transferred onto nylon. Biotinylated B. henselae surface proteins of 28, 32, 43, 52 and 58 kDa were shown to bind intact HUVEC, with the 43 kDa protein being the major adhesin. Preincubation of HUVEC with an increasing concentration (20 microg/ml to 4 mg/ml) of sarkosyl-fractionated unlabelled B. henselae outer membrane proteins inhibited the attachment of all identified HUVEC binding proteins. The identification of B. henselae OMPs, as well as adhesins, should provide a basis for further investigation of the role of adherence in the pathogenesis of B. henselae.

Apoptosis: a possible tactic of Haemophilus somnus for evasion of killing by bovine neutrophils?

Haemophilus somnus is an important veterinary pathogen that causes respiratory disease, arthritis, septicaemia and abortion in cattle and sheep. In the present study we investigated the possibility that H. somnus resists killing by bovine neutrophils, by causing the latter to undergo morphological changes consistent with apoptosis. Both serum-sensitive and serum-resistant strains of H. somnus enhanced bovine neutrophil chromatin condensation and shape change (i.e. zeiosis) in vitro, suggesting that the cells were undergoing apoptosis. Heat-killed or formalin-killed H. somnus had less effect than viable H. somnus. Chromatin margination of neutrophils was greater whenH. somnus was opsonized with adult bovine serum, which facilitates phagocytosis of the bacteria. H. somnus culture filtrates did not cause bovine neutrophil chromatin condensation. These findings suggest that direct contact with H. somnus is required for the maximal effect on bovine neutrophils. Apoptosis was confirmed by flow cytometry, using propidium iodide staining to detect DNA fragmentation. These findings suggest that H. somnus can evade killing by bovine neutrophils, in part, by inducing these cells to undergo apoptosis.

Haemophilus somnus immunoglobulin binding proteins and surface fibrils

The high-molecular-weight (HMW) immunoglobulin binding proteins (IgBPs) of Haemophilus somnus and a 76-kDa surface protein (p76) are found in serum-resistant virulent strains but not in several serum-sensitive strains from asymptomatic carriers. For the first time, p76 was shown to be an IgBP also. This was done by competitive inhibition studies with affinity-purified antidinitrophenol (anti-DNP) and DNP to ensure that binding was not antigen specific. The HMW IgBPs, but not the p76 IgBP, were partially purified from concentrated culture supernatant in detergent by fluid-phase liquid chromatography with a gel filtration column. Membrane extraction studies showed that p76 predominated in the Sarkosyl-soluble fraction of the bacterial cell pellet. Since integral outer membrane (OM) proteins are Sarkosyl insoluble, this is consistent with our previous finding that implicated p76 as a peripheral OM protein. The HMW IgBPs were found predominantly in the Sarkosyl-soluble fraction of the culture supernatant. This suggests that they were not integral membrane proteins and that their presence in the supernatant was not due to OM blebbing. We then showed that two IgBP-positive serum-resistant virulent strains have a surface fibrillar network but that two IgBP-negative serum-sensitive H. somnus strains from asymptomatic preputial carriers do not. Fibrils on the surfaces of IgBP+ strains bound gold-labelled bovine immunoglobulin G2 (IgG2) anti-DNP, indicating that these fibrils have IgG2 binding activity. Therefore, this study shows that H. somnus has two IgBPs, including a peripheral membrane protein and a fibrillar surface network.

Bovine IgG2a antibodies to Haemophilus somnus and allotype expression

Bovine IgG2a has been implicated in protection against pyogenic infections, including those caused by Haemophilus somnus. To further investigate the role of IgG2a in defense against H. somnus, IgG1 and IgG2a antibodies were purified from antiserum against an immunodominant 40 kDa outer membrane protein (p40) of H. somnus, which was previously shown to passively protect calves against H. somnus pneumonia. The passive protective capacity of anti-p40 IgG1 or IgG2a was evaluated in vivo in calves. Purified anti-p40 IgG1 or IgG2a was incubated with H. somnus for 15 min before intrabronchial inoculation of calves. Bacteria incubated with anti-p40 IgG1 or IgG2a were inoculated into one caudal lung lobe and bacteria incubated with IgG1 or IgG2a from the respective preimmunization serum were inoculated into the contralateral lobe. The volumes of pneumonia in the right and left lungs were determined 24 h later. The difference in volume of pneumonia with H. somnus preincubated in IgG1 pre- and postimmunization anti p40 was less (16 cm3, P = 0.298) than the difference in volume of pneumonia with H. somnus preincubated in IgG2a pre- and postimmunization anti p40 (30 cm3, P = 0.146). Although the differences in lesion size between pre- and postimmunization serum were not statistically significant, the trend suggests IgG2a may be more protective than IgG1. To examine this further, the peptide specificity of these IgG1 and IgG2a antibodies to p40 was examined. After limited proteolysis of p40, IgG2a antibodies reacted with 2 peptides not recognized by IgG1 antibodies. Other peptides were recognized by both isotypes. Since these studies suggested that IgG2a may be important in protection against infection, we then investigated some aspects of the role of the 2 IgG2a allotypes, A1 and A2. In retrospective studies of age differences in expression of IgG2a allotypes, no heterozygotes were detected in calves of 60 d old or less, and fewer heterozygotes were detected in calves 61-120 d old than in cattle older than 270 d (P < 0.01). In a subsequent prospective study of the time course of allotype expression, Holstein calves shown to be heterozygotes expressed the IgG2aA1 allotype early but the IgG2aA2 allotype was not usually detected until 3 to 4 mo of age. Thus, both the retrospective and the prospective studies showed age related differences in expression of the IgG2aA1 and A2 allotypes. This could have implication in protection.

A comparative study of bovine and ovine Haemophilus somnus isolates

Bacterial isolates (including 17 Haemophilus somnus isolates and an H. somnus-like isolate) from asymptomatic or diseased cattle and sheep, were evaluated for markers associated with virulence and host predilection. The isolates were separated into 6 distinct biovariants, 3 for sheep and 3 for cattle, based on reactions in a battery of 21 test media. Three bovine isolates associated with disease caused hemolysis of bovine blood. The rest of the isolates did not hemolyze either bovine or ovine erythrocytes. Protein profiles of all H. somnus isolates were similar with the exception of the major outer membrane proteins (MOMPs). The MOMPs of isolates associated with disease in cattle had a relative molecular weight of approximately 41 kDa compared with 33 kDa for the MOMPs of isolates from asymptomatic cattle. The MOMPs from sheep isolates were either slightly higher or lower than the 41 kDa MOMPs of bovine isolates. Major antigens detected by Western blotting were similar in all isolates except the H. somnus-like isolate. An immunodominant 40 kDa antigen was conserved in all H. somnus isolates. Antibodies to this antigen have previously been found to be protective in cattle and may also be protective for sheep. Marked differences between cattle and sheep isolates were revealed by use of restriction enzyme analysis, which separated the isolates into 12 ribotypes and 15 unique DNA profiles. Thus, cattle and sheep isolates in this collection had distinctive differences in biochemical reactions, MOMP profiles, and DNA analyses. Such differences have potential value for epidemiological studies and may also be used to evaluate host specificity of H. somnus isolates.

The occurrence of Haemophilus somnus in feedlot calves and its control by postarrival prophylactic mass medication

Three field trials were conducted in a large commercial feedlot in Saskatchewan to determine the prevalence of Haemophilus somnus in calves and to evaluate the efficacy of prophylactic mass medication with long-acting oxytetracycline on day 17 (1990, n = 1336), day 11 (1991, n = 4372), or day 8 (1992, n = 5632) postarrival. Hemophilosis accounted for > 40% of the mortality in feedlot calves each year. Haemophilus somnus was cultured from the blood of one febrile calf on day 1 (0.1%, n = 895), but it was not cultured from nasal swabs on day 1 or day 11 (n = 881) or from blood samples on day 11 (n = 883). Similarly, it was not cultured from nasal swabs or blood samples from sick calves first treated for bovine respiratory disease (BRD) (n = 219). Serological titers to H. somnus increased (p < 0.05) in unvaccinated calves from day 1 (Geometric mean titer = 11,846) to day 96 (Geometric mean titer = 63,712), indicating natural infection following feedlot entry. Calves that relapsed twice with BRD or died from BRD +/- hemophilosis had significantly (p < 0.06) lower titers to H. somnus on days 1 and 96 than those that did not relapse twice or die. Postarrival mass medication with long-acting oxytetracycline did not reduce (p > 0.05) the risk of hemophilosis mortality. However, it reduced (p < 0.05) the risk of BRD treatment by 14% and the risk of BRD mortality by 71%. Additional epidemiological studies of H. somnus are needed so that we can develop strategic medication and vaccination programs to reduce losses from hemophilosis.

Ovine Haemophilus somnus: experimental intracisternal infection and antigenic comparison with bovine Haemophilus somnus

Experimental infection was produced by two of four isolates of ovine Haemophilus somnus given by intracisternal inoculation into two to three-month-old lambs. Isolate 2041 (originally obtained from a septicemic lamb in Alberta) caused lethal infection in eight of nine lambs, isolate 67p from the prepuce of a normal lamb produced less acute disease in four of nine lambs, and the other two isolates (93p and 1190) caused no detectable disease. Significant lesions were limited to the brain and spinal cord. Purulent meningitis was characteristic but vasculitis or septicemia were not detected, perhaps due to the route of inoculation. Since a difference in virulence was noted among strains, we analyzed surface proteins thought to be virulence factors of bovine H. somnus. Protein profiles of bovine and ovine H. somnus done by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed similar patterns for virulent bovine isolates and ovine septicemic isolates. Preputial isolates showed a lower molecular mass major outer membrane protein than septicemic isolates. Antigenic analysis revealed that outer membrane proteins p270, p78, p76, p40, and p39 were detected in both ovine and bovine isolates except for 1190, which was probably not a true H. somnus isolate. Thus the preputial and septicemic isolates of ovine H. somnus were similar to bovine H. somnus in pathogenicity and in surface antigens.

Identification of outer membrane proteins of Bartonella bacilliformis

Purification of the outer membrane of Bartonella bacilliformis by sucrose step gradient centrifugation and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) suggest that 14 proteins, ranging from 11.2 to 75.3 kDa, are located in the outer membrane of the pathogen. On the basis of M(r)s, eleven of these proteins have counterparts which are labeled by extrinsic radioiodination of intact bartonellae, and two of the proteins are visibly sensitive to extrinsic proteinase K digestion in analysis by SDS-PAGE. While nearly all the extrinsically radioiodinated proteins could be immunoprecipitated with rabbit antibartonella hyperimmune serum, proteins of 31.5, 42, and 45 kDa were prominent immunoprecipitants. Purified lipopolysaccharide from the outer membrane of B. bacilliformis produced a diffuse band of approximately 5 kDa on SDS-PAGE and was not detectable on immunoblots developed with rabbit antibartonella hyperimmune antiserum.

Recent advances in bovine vaccine technology

A description of new commercial and experimental vaccines for viral and bacterial diseases of cattle can be broadly divided into those used for both beef and dairy cows and those used predominantly in dairy cattle. For both types of cattle, newer and experimental vaccines are directed against several of the important viral (e.g., bovine herpesvirus 1, bovine viral diarrhea virus, bovine respiratory syncytial virus, parainfluenza type 3, and foot-and-mouth disease virus) and bacterial pathogens (e.g., Pasteurella spp., Haemophilus somnus). The viral vaccines include gene-deleted, modified live, subunit, and peptide antigens. Newer bacterial vaccines, particularly those for Pasteurella spp., are composed of either modified-live vaccines or bacterins supplemented with toxoid or surface antigens. Haemophilus somnus vaccine research has concentrated mainly on defining unique surface antigens. Novel dairy cow vaccines would include the lipopolysaccharide-core (J5) antigen approach, which has been used for successful immunization against coliform mastitis. Core antigen vaccines also have reduced calf mortality from Gram-negative pathogens. Staphylococcal mastitis vaccines that contain capsular antigens, toxoids, or the staphylococcal fibronectin receptor are of active research interest. Vaccines against mastitis induced by Streptococcus agalactiae and Streptococcus uberis also are areas of intensive research. Delivery of multiple subunit antigens with optimal immune response induction has led to the investigation of attenuated heterologous viral and bacterial expression vectors such as bovine herpesvirus 1, vaccinia, and Salmonella spp. This discussion also demonstrates that molecular biology is being used to advance bovine vaccine technology.

Cloning and sequencing of the gene encoding a 31-kilodalton antigen of Haemophilus somnus

Immunoblots using bovine antibody against Haemophilus somnus as the primary antibody consistently identified 31-, 40- and 78-kDa proteins in Sarkosyl-insoluble extracts of H. somnus. A genomic library of H. somnus 8025 DNA was constructed in plasmid pUC19, and 45 recombinants expressed proteins which were recognized by bovine antiserum in Western blots (immunoblots). Ten of the recombinants expressing a 31-kDa protein caused the lysis of bovine erythrocytes. Restriction endonuclease mapping indicated that the hemolytic recombinants shared an approximately 1.7-kb BglII fragment. Southern blot analysis using the BglII fragment as a probe revealed homology among the recombinants and the presence of an identically sized BglII fragment in the chromosome of all H. somnus isolates tested. Sequence analysis indicated the presence of an 822-bp open reading frame within the 1.7-kb BglII fragment. Deletion of this open reading frame resulted in the loss of hemolytic activity and protein expression in recombinant Escherichia coli, suggesting the possible role of the 31-kDa protein as a hemolysin. An amino acid sequence deduced from the DNA sequence shared homology with outer membrane protein A of E. coli, Salmonella typhimurium, and Shigella dysenteriae, with P6 of Haemophilus influenzae, and with PIII of Neisseria gonorrhoeae. An amino acid analysis of the recombinant 31-kDa protein agreed with the amino acid composition deduced from the DNA sequence.

Characterization of a heat-modifiable outer membrane protein of Haemophilus somnus

In immunoblot analysis, a murine monoclonal antibody (MAb), 27-1, which was produced to an outer membrane protein (OMP) of Haemophilus somnus, showed that a major OMP is heat modifiable, having a molecular mass of 28 kDa when the N-lauroylsarcosine-insoluble OMP preparation was solubilized at 60 degrees C and a mass of 37 kDa when the OMP preparation was solubilized at 100 degrees C. The heat-modifiable OMP reacted intensely with convalescent sera obtained from calves with experimental H. somnus pneumonia in immunoblot analysis. Immunoelectron microscopic and antibody absorption studies revealed that the MAb 27-1 epitope was not surface exposed on the intact bacterium. However, a decrease in antibody reactivity to the heat-modifiable OMP in immunoblot analysis after absorption of convalescent serum with intact bacterial cells of H. somnus suggests that a surface-exposed portion of the heat-modifiable OMP is expressed on the intact bacterium. MAb 27-1 reacted with 45 of 45 strains of H. somnus tested in immunoblot analysis. The apparent molecular mass of the antigen varied among strains, and five reactivity patterns demonstrated by MAb 27-1 were observed. MAb 27-1 also reacted with six species in the family Pasteurellaceae, Escherichia coli, and Salmonella dublin, but not with the other eight species of gram-negative bacteria. The heat-modifiable OMP of H. somnus showed immunological cross-reactivity with the OmpA protein of E. coli K-12 and significant N-terminal amino acid sequence homology with the OmpA proteins of gram-negative bacteria. We conclude that a major, 37-kDa heat-modifiable OMP of H. somnus, which elicits an antibody response in H. somnus-infected animals, is a common antigen among H. somnus strains tested and is structurally related to the OmpA protein of E. coli.

Purification and partial characterization of the major outer membrane protein of Haemophilus somnus

We purified the major outer membrane protein (MOMP), which is the most abundant OMP (with an apparent molecular mass of 40 kDa), from Haemophilus somnus strain 8025. The method involves solubilization of the MOMP with Zwittergent 3-14 and further purification accomplished by ion-exchange and molecular-sieve chromatographies. The amino-terminal sequence of the MOMP showed considerable similarity to those of porin proteins from other gram-negative bacteria. The MOMP of H. somnus is immunogenic to rabbits and calves. Hyperimmune sera from rabbits and calves reacted with both the MOMP and lipopolysaccharides in enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis. The rabbit antiserum to the MOMP was cross-reactive with whole-cell preparations from strains 8025, D1238, NT2301, and 540 at a band with a molecular mass of 40 kDa in immunoblot analysis, although the reactivity of the rabbit antiserum with strain 540 was lower than those with the other strains tested. Two murine monoclonal antibodies (MAbs) to the MOMP were developed. ELISA with the OMP fractions as the antigens showed that one MAb was cross-reactive with the four strains but that the other MAb was reactive with the three strains other than strain 540. These results indicate that the MOMP of H. somnus possesses at least two antigenic determinants and that the MOMP of strain 540 is antigenically different from those of the other strains. The antigenic heterogeneity of the H. somnus MOMP has implications regarding the development of a serotyping system with MAbs that is based on the MOMP epitopes.

Two linked genes for outer membrane proteins are absent in four non-disease strains of Haemophilus somnus

Linked genes encoding two outer membrane proteins (p76 and a family of proteins, p120) of the bovine pathogen, Haemophilus somnus, were investigated. The p120 group was previously shown to have immunoglobulin-binding activity and to react with polyclonal antiserum specific for a 270 kDa antigen (p270) which also had immunoglobulin Fc-binding activity. By Western blotting we showed that the p76 antigen also reacted with this antiserum. The p270, p120, and p76 antigens were undetectable in four serum-sensitive isolates from asymptomatic carriers but were present in the two serum-resistant virulent strains tested. Genes for p120 and p76 were subcloned on non-overlapping pUC plasmids from a cosmid (pHS1) originally cloned from a serum-resistant strain. In Escherichia coli, plasmid pHS138 expressed p76, while the p120 antigens were produced by pHS140. Southern blots of DNA from the above six strains of H. somnus using probes derived from pHS1 subclones showed that a 13.4 kb sequence was missing from the four serum-sensitive strains, but not the two serum-resistant strains. This segment included most of the insert in pHS138 and all of the pHS140 insert. The data indicate that p76 and the p120 proteins are absent from serum-sensitive strains because the coding sequences are missing, raising the possibility of insertion of these genes into the chromosome of both serum-resistant strains, or deletion from the four serum-sensitive strains.

Phenotypic phase variation in Haemophilus somnus lipooligosaccharide during bovine pneumonia and after in vitro passage

A high rate of phenotypic variation in the lipooligosaccharide (LOS) electrophoretic profile of Haemophilus somnus occurred in most isolates obtained at approximately weekly intervals from three calves intrabronchially challenged with a cloned isolate of H. somnus 2336. Daily subculturing for 2 weeks resulted in at least one major alteration in the LOS electrophoretic profiles for strain 2336 and both additional disease isolates examined, but no change occurred in the LOS electrophoretic profiles for any of three commensal isolates examined. None of the LOSs from any of the postchallenge intrabronchial isolates reacted with rabbit antiserum to the challenge strain LOS in immunoblotting, but LOSs from two nasopharyngeal isolates did. Antigenic variation in the extracted LOSs of most of the isolates was supported by the results of an enzyme-linked immunosorbent assay. Preimmune serum from each of the calves did not react with any of the isolates or the challenge strain, whereas sera obtained 35 days after challenge reacted with the challenge strain and zero to five additional isolates and sera obtained 74 days after challenge reacted with two to six additional isolates. Recognition of LOSs from isolates obtained near the end of the 70-day experiment by day-74 sera was related to clearance of the bacteria from the lungs. Isolates demonstrating major electrophoretic changes showed variations in the composition of the oligosaccharide, but not lipid A, moiety of their LOSs. The oligosaccharide of the LOS of each isolate was composed predominantly of glucose but varied substantially in the contents of galactose, arabinose, xylose, mannose, and 3-deoxy-D-manno-octulosonic acid. Therefore, the LOS of H. somnus is capable of undergoing compositional and antigenic variations, which may act as an important virulence mechanism for evading host immune defense mechanisms.

Characterization of immunodominant surface antigens of Haemophilus somnus

An immunodominant Haemophilus somnus outer membrane protein with an apparent molecular mass of 40 kDa on Western blots (immunoblots) of gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels was characterized because a monospecific antibody against this antigen was protective. This monospecific antibody was used for immunoaffinity purification of the antigen. The immunoaffinity-purified antigen reacted with a polyclonal antibody to the 40-kDa antigen but not with a monoclonal antibody (3G9) which reacted with the 40-kDa antigen in gradient gels. On 8 or 10% gels, the approximately 40-kDa antigen was resolved as two bands, a 40-kDa band which reacted with the protective monospecific polyclonal antibody (p40) and a band of lower molecular mass which reacted with monoclonal antibody 3G9. The latter antigen was designated p39. Both antigens were conserved in all H. somnus isolates tested. The specific antibodies were also used to detect cross-reacting antigens in other gram-negative bacteria. Antibody to p40 reacted with proteins of 55 to 28 kDa, with the greatest intensity shown among proteins from other members of the family Pasteurellaceae. Antibody to p40 was reduced by absorption with live H. somnus or other members of the family Pasteurellaceae, so the antigen appears to be surface exposed. Antibody to p39 only cross-reacted with a broad band (38 to 40 kDa) in Haemophilus agni. Since H. agni is not a bovine pathogen and since convalescent-phase serum from H. somnus-infected animals did recognize p39, the latter may be a good immunodiagnostic antigen, if the lack of cross-reactivity with antigens in other gram-negative bacteria is confirmed with a polyclonal antibody to p39. The cross-reactivity of antiserum to p40 with antigens of members of the family Pasteurellaceae and the ability of this antiserum to protect against H. somnus pneumonia indicate that p40 may be a useful vaccine antigen for H. somnus disease and perhaps even diseases caused by other members of the family Pasteurellaceae.

The development of protein A-gold electron microscopy for immunological studies of Haemophilus somnus

Two separate experiments were conducted using modifications of protein A-gold immunoelectron microscopy (PAGIEM) to evaluate the ability of sera from calves vaccinated against Haemophilus somnus to bind virulent organisms (experiment I) and to detect differences in the antibody accessible antigenic sites on the outer membrane of selected strains of H. somnus having different virulence attributes using a high IgG2 titre specific bovine hyperimmune serum (experiment II). The results of experiment I demonstrated that the direct opsonisation of H. somnus by specific antisera was related to its IgG2 titre. In experiment II, strain-dependent differences in the labelling of antigenic sites by specific IgG2 antibodies were observed. The virulent strains of both septicaemic and genital isolates of H. somnus showed higher protein A-gold labelling than their non-virulent counterparts. The results from a comparison of pathogenic and non-pathogenic respiratory isolates did not reveal the same difference in labelling intensity. The studies demonstrated the PAGIEM technique to be a sensitive, versatile and a reliable laboratory method to analyse antigen-antibody interactions of H. somnus.

The protective effect of vaccination against experimental pneumonia in cattle with Haemophilus somnus outer membrane antigens and interference by lipopolysaccharide

A semi-purified outer membrane anionic antigen (AA) fraction was isolated from Haemophilus somnus by a modified procedure of anion exchange chromatography to yield a protein fraction free of lipopolysaccharides (LPS). The AA fraction (1 mg) was administered with or without the homologous lipopolysaccharide (10 micrograms/kg body weight) as vaccines to groups of cattle twice, three weeks apart. A control group which did not receive any antigen was included in the trial. Six weeks after the first vaccination, the animals were challenged intratracheally with a virulent pneumonic strain of H. somnus (70986) and observed for clinical signs of respiratory disease. The cattle were euthanized six days later and the lungs were evaluated for the severity of lesions macroscopically as well as histopathologically. Vaccination with AA alone provided the best protection against pneumonia as indicated by significantly lower clinical scores, less extensive gross lung lesions and mild histopathological lesions with immune cell infiltration. However, when AA was combined with LPS in the vaccination, this protective effect was negated and the animals showed more detrimental histopathological lesions than the controls.