Antigenic analysis of the major outer membrane protein of Haemophilus somnus with monoclonal antibodies

Monitoring ventral tail base surface temperature for fever detection in calves

In this study, we investigated whether monitoring the ventral tail base surface temperature (ST) using a wearable wireless sensor could be effective for fever detection in calves with experimentally induced pneumonia after inoculation with Histophilus somni strain 2336. We found a significant difference in the changes in ST values between the control and H. somni-inoculated groups after 24 h of inoculation and detected fever; however, the rectal temperature showed a significant difference between the groups after 12 h of inoculation. When a significant difference in the ST between the two groups was observed, serum haptoglobin concentration and exacerbation of clinical score increased in the H. somni-inoculated group compared with those in the control group. Pneumonia was observed in the H. somni-inoculated group at necropsy, indicating that the changes in ST may reflect fever with inflammation caused by H. somni infection. Our results demonstrated that monitoring ST using a sensor attached to the ventral tail base can detect fever in calves and may be a useful and labor-saving tool for the health management of calves.

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.

The role of uspE in virulence and biofilm formation by Histophilus somni

UspE is a global regulator in Escherichia coli. To study the function of Histophilus somni uspE, strain 2336::TnuspE was identified from a bank of mutants generated with EZ::Tn5™<KAN-2> Tnp Transposome™ that were biofilm deficient. The 2336::TnuspE mutant was highly attenuated in mice, the electrophoretic profile of its lipooligosaccharide (LOS) indicated the LOS was truncated, and the mutant was significantly more serum-sensitive compared to the wildtype strain. In addition to forming a deficient biofilm, exopolysaccharide (EPS) production was also compromised, but the electrophoretic profile of outer membrane proteins was not altered. RNA sequence analysis revealed that the transcription levels of some stress response chaperones, transport proteins, and a large number of ribosomal protein genes in 2336::TnuspE were significantly differentially regulated compared to strain 2336. Therefore, uspE may differentially function in direct and indirect expression of H. somni genes, but its attenuation may be linked to poor biofilm formation and rapid clearance of the bacteria resulting from a compromised LOS structure. Our results support that uspE is a global stress regulatory gene in H. somni.

The Role of luxS in Histophilus somni Virulence and Biofilm Formation

S-Ribosylhomocysteinase (LuxS) is required for the synthesis of the autoinducer-2 (AI-2) quorum-sensing signaling molecule in many Gram-negative bacteria. The bovine (and ovine) opportunistic pathogen Histophilus somni contains luxS and forms a biofilm containing an exopolysaccharide (EPS) in the matrix. Since biofilm formation is regulated by quorum sensing in many bacteria, the roles of luxS in H. somni virulence and biofilm formation were investigated. Although culture supernatants from H. somni were ineffective at inducing bioluminescence in the Vibrio harveyi reporter strain BB170, H. somni luxS complemented the biosynthesis of AI-2 in the luxS-deficient Escherichia coli strain DH5α. H. somni strain 2336 luxS was inactivated by transposon mutagenesis. RNA expression profiles revealed that many genes were significantly differentially expressed in the luxS mutant compared to that in the wild-type, whether the bacteria were grown planktonically or in a biofilm. Furthermore, the luxS mutant had a truncated and asialylated lipooligosaccharide (LOS) and was substantially more serum sensitive than the wild-type. Not surprisingly, the luxS mutant was attenuated in a mouse model for H. somni virulence, and some of the altered phenotypes were partially restored after the mutation was complemented with a functional luxS However, no major differences were observed between the wild-type and the luxS mutant in regard to outer membrane protein profiles, biofilm formation, EPS production, or intracellular survival. These results indicate that luxS plays a role in H. somni virulence in the context of LOS biosynthesis but not biofilm formation or other phenotypic properties examined.

A Predominant Clonal Thromboembolic Meningoencephalitis Group of Histophilus somni Assigned by Major Outer Membrane Protein Gene Sequencing and Pulsed-Field Gel Electrophoresis

Histophilus somni, a member of the family Pasteurellaceae, causes a variety of diseases, including thromboembolic meningoencephalitis (TEME) and respiratory diseases, which result in considerable economic losses to the cattle and sheep industries. In this study, 132 chronologically diverse isolates from cattle in Japan and 68 isolates from other countries comprising 49 from cattle and 19 from sheep were characterized using major outer membrane protein (MOMP) gene sequence and pulsed-field gel electrophoresis (PFGE) analyses. The H. somni isolates formed nine MOMP genetic clades (clade Ia, Ib, and II-VIII) and 10 PFGE clusters (HS1-HS10). Except for two (1.0%), all isolates fell into one of the nine MOMP genetic clades, while 62 (31.0%) isolates belonged to no PFGE cluster. MOMP genetic clade Ia and PFGE cluster HS1 were the major groups, and all HS1 isolates possessed the clade Ia MOMP gene. Isolates from TEME cases were significantly associated with these major groups (chi-square test, p < 0.0001), as 88.2% of the TEME isolates belonged to MOMP genetic clade Ia and PFGE cluster HS1, which formed the most predominant clonal group. After an inactivated vaccine using an HS1 strain with the clade Ia MOMP gene was introduced in Japan in late 1989, the number of TEME cases and isolates assigned into the clonal group decreased simultaneously. However, the proportions of clade Ia and cluster HS1 isolates from TEME cases remained high after 1990. These results suggest a close association of TEME with PFGE cluster HS1 and MOMP genetic clade Ia, and imply the presence of factors or characteristics commonly possessed by those strains that contribute to the development of TEME.

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.

Molecular characterization of the major outer membrane protein of Haemophilus somnus

The major outer membrane protein (MOMP) of Haemophilus somnus shows antigenic and molecular mass diversity that forms the basis of a preliminary grouping system for H. somnus strains. In this study, the gene encoding MOMP of H. somnus strain 8025 was cloned in three overlapping fragments by PCR techniques, and then sequenced. The gene consists of a 1164-bp open reading frame encoding a deduced 380-amino acid protein with a 19-amino acid signal sequence, giving a mature protein with a calculated molecular mass of 39,913 Da. Significant homology was found between MOMP and porin protein sequences of bacteria in Pasteurellaceae species. When expressed in Escherichia coli, the protein from the MOMP gene directed by the T7 promoter was identical in size (approximately 40 kDa) to native MOMP and reacted with MOMP-specific antibodies. Comparisons of the MOMP gene sequences from six unrelated strains of H. somnus to that of strain 8025 revealed that the genes of three MOMP type 1 strains were highly conserved with that of strain 8025 in length and sequence. However, two MOMP type 3c strains and one MOMP type 3a strain differed markedly from the MOMP of strain 8025 in their 3'-terminal halves. Their deduced MOMP amino acid sequences differed in sequence (3c, 80.5 and 82.7% identity; 3a, 62.4% identity) and in length (3c, 384 and 376; 3a, 316), indicating that the molecular differences are the basis of antigenicity and molecular mass differences of H. somnus MOMP. In the predicted MOMP secondary structure, the variable sequences primarily mapped to putative surface-exposed loops, and a variable and surface-exposed epitope of MOMP-specific antibody was identified in the seventh-largest loop. These findings are useful for understanding the structural and immunological characteristics of H. somnus.

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.

Characterization of an outer membrane protein of Pasteurella multocida belonging to the OmpA family

The outer membrane vesicle and N-lauroylsarcosine-insoluble protein preparations of Pasteurella multocida 656 were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A major outer membrane protein (OMP) was found to be heat-modifiable, having a molecular mass of 28 kDa when the OMP preparation was solubilized at 60 degrees C and a molecular mass of 37 kDa when it was solubilized at 100 degrees C. A monoclonal antibody, designated mAb MT4.1, was generated against heat-modifiable OMP of P. multocida. This mAb reacted with the heat-modifiable OMP irrespective of the temperature at which it was solubilized, as demonstrated by immunoblot results. The heat-modifiable OMP of P. multocida showed a significant N-terminal amino acid sequence homology with OmpA family. Immunoelectron microscopic study revealed that the mAb Mt4.1 epitope was not surface exposed on the intact bacterium. The mAb MT4.1 reacted with all the reference strains of 5 capsular and 16 somatic serotypes, as well as with 75 field strains of P. multocida in immunoblot assay. This mAb MT4.1 also reacted with strains of various other Pasteurella species such as P. stomatis, P. aerogenes P. gallinarum, P. betti, P. sp, B, P. SP-g and P. canis, but not with strains of 12 other Gram-negative bacteria. These results indicated that this protein carried a genus-specific epitope and mAb MT4.1 may be useful for identification of Pasteurella species. This is the first report in which a major heat-modifiable OMP has been identified and characterized using a mAb, and has been shown belonging to the OmpA family.

An immunodominant epitope on 40 kilodalton outer membrane protein is conserved among different strains of Haemophilus (Histophilus) somnus

Four murine monoclonal antibodies (mAb) were constructed against Haemophilus (Histophilus) somnus, an important bovine pathogen, and used to analyze immunologically significant antigenic determinants on these organisms. These mAbs specifically recognized immunodominant epitopes present on the 40 kilodalton (kD) fraction of the major outer membrane protein (OMP) of H. somnus. The 9D3 IgG1 kappa mAb recognized an immunodominant epitope on the 40 kD major outer membrane protein that is conserved or shared among all the three strains (septicemic, respiratory and uro-genital) of H. somnus. Two IgM kappa mAbs (4D6 and 10C2) recognized epitope(s) on the 40 kD OMP from septicemic and respiratory strains of H. somnus but none from the whole bacterial cell preparations. Another IgM kappa mAb 9D2 recognized an antigenic determinant on the 40 kD protein from the OMP as well as a whole bacterial cell preparation of a septicemic strain of H. somnus. These data demonstrate that, at least, three immunologically significant antigenic determinants on H. somnus are defined by mAbs against this bovine pathogen. Importantly, these studies suggest that the epitope present on the 40 kD major OMP, recognized by the 9D3 mAb, is immunodominant and conserved among septicemic, respiratory and urogenital strains, and is, therefore, suitable for further investigating its use in the development of an immunodiagnostic assay and also as a recombinant vaccine.

Characterization of an immunoreactive 17.5-kilodalton outer membrane protein of Haemophilus somnus by using a monoclonal antibody

A single outer membrane protein (OMP) of Haemophilus somnus, with an apparent molecular mass of 17.5 kDa, was identified in the sodium dodecyl sulfate (SDS)-insoluble fraction after extraction with 1% SDS-0.5 M NaCl-0.1% beta-mercaptoethanol. A hybridoma derived from mice immunized with H. somnus OMP fractions produced a monoclonal antibody (MAb), designated 20-3-5, that bound to the 17.5-kDa OMP of H. somnus. The MAb 20-3-5 epitope was present on 45 of 45 strains of H. somnus tested. MAb 20-3-5 cross-reacted with Haemophilus agni, Histophilus ovis, and Haemophilus haemoglobinophilus but not with 13 other species and subspecies of gram-negative bacteria. Immunoelectron-microscopic and antibody absorption studies revealed that the MAb 20-3-5 epitope is exposed on the surface of bacteria. In an immunoblot analysis, convalescent-phase sera obtained from calves with experimental H. somnus pneumonia contained antibodies to the 17.5-kDa OMP of H. somnus. Future studies will be directed toward examining the role of the 17.5-kDa OMP in immunity to H. somnus infections.