The S1 glycoprotein but not the N or M proteins of avian infectious bronchitis virus induces protection in vaccinated chickens

Development of attenuated vaccines from Taiwanese infectious bronchitis virus strains

Due to variations in serotypes among different strains of avian infectious bronchitis viruses (IBV), vaccination of chicks with imported vaccines fails to protect them from IBV infections in Taiwan. Therefore, we develop attenuated vaccines from local strains in Taiwan. A Taiwan Group I (TW I) strain was passaged 74 times through specific pathogen-free (SPF) chicken embryonated eggs, and then tested in SPF chickens. The attenuated vaccine was not pathogenic in 1-week-old chicks, had a neutralization index (NI) of greater than 4.4 and efficacy of 90% when inoculated birds were challenged with a field IBV strain. Similar results were obtained for a vaccine made from a Taiwan Group II IBV strain. Additionally, the TW I attenuated vaccine strain had no reversion to virulence after five back passages in chicks. In conclusion, these attenuated vaccines have potential for controlling local Taiwanese IBV infections in chickens.

BRONQUITE INFECCIOSA DAS GALINHAS

RESUMO A bronquite infecciosa das galinhas (BIG) é uma doença respiratória altamente contagiosa causada por um Coronavírus, o vírus da bronquite infecciosa das galinhas (VBIG). Embora o VBIG seja um patógeno primário do trato respiratório, ele é também uma causa comum de redução da produção e qualidade dos ovos em galinhas. Certos tipos de VBIG causam lesões renais, com significativa mortalidade. Há também mortalidade por conseqüências respiratórias. A doença possui grande importância econômica devida às perdas na produção, sendo estas maiores que as perdas por mortalidade. A ocorrência de múltiplos sorotipos e as características mutantes de seu agente etiológico tem complicado e aumentado os custos de produção e dificultado sua prevenção através da imunização. Recentemente, uma variante do VBIG tem sido descrita associado com a miopatia dos músculos peitorais em muitas partes do mundo, inclusive no Brasil.

Identification of previously unknown antigenic epitopes on the S and N proteins of avian infectious bronchitis virus

This paper describes mapping of antigenic and host-protective epitopes of infectious bronchitis virus proteins by assessing the ability of defined peptide regions within the S1, S2 and N proteins to elicit humoral, cell-mediated and protective immune responses. Peptides corresponding to six regions in the S1 (Sp1–Sp6), one in the S2 (Sp7) and four in the N protein (Np1–Np4) were synthesized and coupled to either diphtheria toxoid (dt) or biotin (bt). Bt-peptides were used to assess if selected regions were antigenic and contained B- or T-cell epitopes and dt-peptides if regions induced an antibody response and protection against virulent challenge. All S1 and S2 peptides were antigenic, being recognised by IBV immune sera and also induced an antibody response following inoculation into chicks. Three S1-and one S2-bt peptides also induced a delayed type hypersensitivity response indicating the presence of T-cell epitopes. The S2 peptide Sp7 (amino acid position 566–584) previously identified as an immundominant region, was the most antigenic of all peptides used in this study. Two S1 (Sp4 and Sp6) and one S2 peptide (Sp7), protected kidney tissue against virulent challenge. From four N peptides located in the amino-terminal part of the N protein, only one, Np2 (amino acid position 72–86), was antigenic and also induced a delayed type hypersensitivity response. None of the N peptides induced protection against virulent challenge. The results suggest that the S1 glycoprotein carries additional antigenic regions to those previously identified and that two regions located in the S1 and one in the S2 at amino acid positions 294–316 (Sp4), 532–537 (Sp6) and 566–584 (Sp7) may have a role in protection.

Recombinant infectious bronchitis coronavirus Beaudette with the spike protein gene of the pathogenic M41 strain remains attenuated but induces protective immunity

We have replaced the ectodomain of the spike (S) protein of the Beaudette strain (Beau-R; apathogenic for Gallus domesticus chickens) of avian infectious bronchitis coronavirus (IBV) with that from the pathogenic M41 strain to produce recombinant IBV BeauR-M41(S). We have previously shown that this changed the tropism of the virus in vitro (R. Casais, B. Dove, D. Cavanagh, and P. Britton, J. Virol. 77:9084-9089, 2003). Herein we have assessed the pathogenicity and immunogenicity of BeauR-M41(S). There were no consistent differences in pathogenicity between the recombinant BeauR-M41(S) and its apathogenic parent Beau-R (based on snicking, nasal discharge, wheezing, watery eyes, rales, and ciliostasis in trachea), and both replicated poorly in trachea and nose compared to M41; the S protein from the pathogenic M41 had not altered the apathogenic nature of Beau-R. Both Beau-R and BeauR-M41(S) induced protection against challenge with M41 as assessed by absence of recovery of challenge virus and nasal exudate. With regard to snicking and ciliostasis, BeauR-M41(S) induced greater protection (seven out of nine chicks [77%]; assessed by ciliostasis) than Beau-R (one out of nine; 11%) but less than M41 (100%). The greater protection induced by BeauR-M41(S) against M41 may be related to the ectodomain of the spike protein of Beau-R differing from that of M41 by 4.1%; a small number of epitopes on the S protein may play a disproportionate role in the induction of immunity. The results are promising for the prospects of S-gene exchange for IBV vaccine development.

Generation of the transgenic potato expressing full-length spike protein of infectious bronchitis virus

To seek a new delivery system of vaccine for infectious bronchitis virus (IBV), transgenic potato expressing full-length spike (S) protein of IBV was produced and its immunogenicity in chickens was investigated. One to three copies of S gene of IBV were randomly and stably inserted into potato (Solanum tuberrosum cv. Dongnong 303) genome by Agrobacterium tumefaciens-mediated transformation. Transcription and translation of S gene for IBV were confirmed by Northern blot and Western blot analyses in transgenic plantlets. Chickens immunized orally and intramuscularly with transgenic potato tubers expressing S protein generated the detectable levels of serum neutralizing antibodies and were protected against the challenge with the virulent IBV. In vitro secretion of interleukin 2 and T lymphocyte proliferation of spleen cells from the immunized chickens varied with the dose and the manner of vaccination with S protein derived from transgenic plants. The results indicated that S protein expressed in transgenic plants might be a new source for the production of Coronaviridae IBV vaccine.

Severe acute respiratory syndrome vaccine development: experiences of vaccination against avian infectious bronchitis coronavirus

Vaccines against infectious bronchitis of chickens (Gallus gallus domesticus) have arguably been the most successful, and certainly the most widely used, of vaccines for diseases caused by coronaviruses, the others being against bovine, canine, feline and porcine coronaviruses. Infectious bronchitis virus (IBV), together with the genetically related coronaviruses of turkey (Meleagris gallopovo) and ring-necked pheasant (Phasianus colchicus), is a group 3 coronavirus, severe acute respiratory syndrome (SARS) coronavirus being tentatively in group 4, the other known mammalian coronaviruses being in groups 1 and 2. IBV replicates not only in respiratory tissues (including the nose, trachea, lungs and airsacs, causing respiratory disease), but also in the kidney (associated with minor or major nephritis), oviduct, and in many parts of the alimentary tract--the oesophagus, proventriculus, duodenum, jejunum, bursa of Fabricius, caecal tonsils (near the distal end of the tract), rectum and cloaca (the common opening for release of eggs and faeces), usually without clinical effects. The virus can persist, being re-excreted at the onset of egg laying (4 to 5 months of age), believed to be a consequence of the stress of coming into lay. Genetic lines of chickens differ in the extent to which IBV causes mortality in chicks, and in respect of clearance of the virus after the acute phase. Live attenuated (by passage in chicken embryonated eggs) IBV strains were introduced as vaccines in the 1950s, followed a couple of decades later by inactivated vaccines for boosting protection in egg-laying birds. Live vaccines are usually applied to meat-type chickens at 1 day of age. In experimental situations this can result in sterile immunity when challenged by virulent homologous virus. Although 100% of chickens may be protected (against clinical signs and loss of ciliary activity in trachea), sometimes 10% of vaccinated chicks do not respond with a protective immune response. Protection is short lived, the start of the decline being apparent 9 weeks after vaccination with vaccines based on highly attenuated strains. IBV exists as scores of serotypes (defined by the neutralization test), cross-protection often being poor. Consequently, chickens may be re-vaccinated, with the same or another serotype, two or three weeks later. Single applications of inactivated virus has generally led to protection of <50% of chickens. Two applications have led to 90 to 100% protection in some reports, but remaining below 50% in others. In practice in the field, inactivated vaccines are used in laying birds that have previously been primed with two or three live attenuated virus vaccinations. This increases protection of the laying birds against egg production losses and induces a sustained level of serum antibody, which is passed to progeny. The large spike glycoprotein (S) comprises a carboxy-terminal S2 subunit (approximately 625 amino acid residues), which anchors S in the virus envelope, and an amino-terminal S1 subunit (approximately 520 residues), believed to largely form the distal bulbous part of S. The S1 subunit (purified from IBV virus, expressed using baculovirus or expressed in birds from a fowlpoxvirus vector) induced virus neutralizing antibody. Although protective immune responses were induced, multiple inoculations were required and the percentage of protected chickens was too low (<50%) for commercial application. Remarkably, expression of S1 in birds using a non-pathogenic fowl adenovirus vector induced protection in 90% and 100% of chickens in two experiments. Differences of as little as 5% between the S1 sequences can result in poor cross-protection. Differences in S1 of 2 to 3% (10 to 15 amino acids) can change serotype, suggesting that a small number of epitopes are immunodominant with respect to neutralizing antibody. Initial studies of the role of the IBV nucleocapsid protein (N) in immunity suggested that immunization with bacterially expressed N, while not inducing protection directly, improved the induction of protection by a subsequent inoculation with inactivated IBV. In another study, two intramuscular immunizations of a plasmid expressing N induced protective immunity. The basis of immunity to IBV is not well understood. Serum antibody levels do not correlate with protection, although local antibody is believed to play a role. Adoptive transfer of IBV-infection-induced alphabeta T cells bearing CD8 antigen protected chicks from challenge infection. In conclusion, live attenuated IBV vaccines induce good, although short-lived, protection against homologous challenge, although a minority of individuals may respond poorly. Inactivated IBV vaccines are insufficiently efficacious when applied only once and in the absence of priming by live vaccine. Two applications of inactivated IBV are much more efficacious, although this is not a commercially viable proposition in the poultry industry. However, the cost and logistics of multiple application of a SARS inactivated vaccine would be more acceptable for the protection of human populations, especially if limited to targeted groups (e.g. health care workers and high-risk contacts). Application of a SARS vaccine is perhaps best limited to a minimal number of targeted individuals who can be monitored, as some vaccinated persons might, if infected by SARS coronavirus, become asymptomatic excretors of virus, thereby posing a risk to non-vaccinated people. Looking further into the future, the high efficacy of the fowl adenovirus vector expressing the IBV S1 subunit provides optimism for a live SARS vaccine, if that were deemed to be necessary, with the possibility of including the N protein gene.

Evaluation of the protection conferred by commercial vaccines against the California 99 isolate of infectious bronchitis virus

An infectious bronchitis virus (IBV) was isolated from commercial broilers from the state of California exhibiting respiratory distress, inflamed tracheas, airsaculitis, and edematous lungs. After reverse transcriptase-polymerase chain reaction (RT-PCR), the California isolate exhibited an identical restriction fragment length polymorphism (RFLP) pattern to some isolates obtained from California, known as California 99 isolates. Commercial Mass-Conn and Mass-Ark vaccines were used to vaccinate commercial broiler chickens via eye drop once at 1 or 10 days of age or twice at 1 and 10 days of age. At 27 days of age the birds were challenged via eye drop with the isolated IBV California 99 strain. Protection was measured by failure to reisolate the challenge virus from tracheas 5 days postchallenge and complemented withthe tracheal and epithelium thickness scores. When the Mass-Ark vaccine was included in the vaccination programs, there was protection against challenge with the IBV California 99 isolate. The Mass-Conn vaccine conferred protection when used once at 1 day of age and twice at 1 and 10 days of age. However, no total protection was achieved when used as the only vaccine at 10 days of age, since one of the replicates was positive for virus isolation. Significant differences (P < 0.05) in the epithelium thickness and tracheal scores were observed between the unvaccinated-unchallenged group and the groups vaccinated once or twice with the Mass-Conn vaccine. Based on these results, all chickens were protected against the California 99 isolate when the IBV Arkansas type was used as a vaccine.

A Recombination Event, Induced In Ovo, Between a Low Passage Infectious Bronchitis Virus Field Isolate and a Highly Embryo Adapted Vaccine Strain

The possibility of genomic recombination among different strains of infectious bronchitis virus (IBV) was examined in eve by coinfecting specific pathogen free embryonating chicken eggs with commonly used, embryo-adapted vaccine strains of IBV (Arkansas, Massachusetts, and Connecticut), and a Delaware-072-like field virus isolated from a layer farm in Minnesota. Recombination was observed between th e Massachusetts and the Delaware-072-like strains of the virus. The recombination event was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR) using a combination of specific primers designed to flank a known recombination hot spot of the viral genomic sequence that codes for the S1 subunit of the spike envelope protein. The use of these primers allowed the detection of viruses that have undergone recombination around this hot spot. Cloning and sequencing of the RT-PCR product obtained was performed to confirm these results.

A recombinant fowl adenovirus expressing the S1 gene of infectious bronchitis virus protects against challenge with infectious bronchitis virus

The spike peplomer S1 subunit sequence from avian infectious bronchitis virus (IBV) Vic S strain was expressed in a plasmid under the control of the fowl adenovirus (FAV) major late promoter (MLP). Two recombinants were constructed in FAV serotype 8 (FAV 8) by inserting the expression cassette between the SnaBI and XbaI restriction enzyme sites (clone DA3) or between the SpeI sites (clone CA6-20). Expression of the S1 gene in the recombinants was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) by 20h post-infection. Commercial broiler chickens were orally vaccinated at day 0 or day 6 post-hatch and challenged at day 35 post-hatch. FAV antibody ELISA confirmed that maternal antibody directed against inclusion body hepatitis (serotype 8) had decayed in control birds and that FAV specific serum IgG responses were produced in vaccinated birds at the time of challenge. Further, an S1 specific antibody response was detected prior to challenge. Birds were challenged with either Vic S (serotype B) or N1/62 (serotype C) strains of IBV. The tracheas of challenged birds were analyzed by RT-PCR and re-isolation of virus. In birds vaccinated at day 6, 90-100% protection at the trachea was induced against either homologous or heterologous challenge. The construction of a recombinant FAV expressing S1 of IBV demonstrates the potential of an alternative vaccination strategy against IBV.

Protection of chickens after live and inactivated virus vaccination against challenge with nephropathogenic infectious bronchitis virus PA/Wolgemuth/98

Protection provided by live and inactivated virus vaccination against challenge with the virulent nephropathogenic infectious bronchitis virus (NIBV) strain PA/Wolgemuth/98 was assessed. Vaccinations with combinations of live attenuated strains Massachusetts (Mass) + Connecticut (Conn) or Mass + Arkansas (Ark) were given by eyedrop to 2-wk-old specific-pathogen-free leghorn chickens. After live infectious bronchitis virus (IBV) vaccination, some chickens at 6 wk of age received an injection of either an oil emulsion vaccine containing inactivated IBV strains Mass + Ark or an autogenous vaccine prepared from NIBV PA/Wolgemuth/98. Challenge with PA/Wolgemuth/98 was given via eyedrop at 10 wk of age. Serum IBV enzyme-linked immunosorbent assay antibody geometric mean titers (GMTs) after vaccination with the combinations of live attenuated strains were low, ranging from 184 to 1,354, prior to NIBV challenge at 10 wk of age. Both inactivated vaccines induced an anamnestic response of similar magnitudes with serum GMTs of 6,232-12,241. Assessment of protection following NIBV challenge was based on several criteria virus reisolation from trachea and kidney and renal microscopic pathology and IBV-specific antigen immunohistochemistry (IHC). Live attenuated virus vaccination alone with combinations of strains Mass + Conn or Mass + Ark did not protect the respiratory tract and kidney of chickens after PA/Wolgemuth/98 challenge. Chickens given a live combination vaccination of Mass + Conn and boosted with an inactivated Mass + Ark vaccine were also susceptible to NIBV challenge on the basis of virus isolation from trachea and kidney butshowed protection on the basis of renal microscopic pathology and IHC. Live IBV-primed chickens vaccinated with an autogenous inactivated PA/Wolgemuth/98 vaccine had the highest protection against homologous virulent NIBV challenge on the basis of virus isolation.

Construction and immunogenicity studies of recombinant fowl poxvirus containing the S1 gene of Massachusetts 41 strain of infectious bronchitis virus

The spike 1 (S1) surface glycoprotein of infectious bronchitis virus (IBV) is the major inducer of the generation of virus neutralizing antibodies, and the administration of purified S1 has been shown to elicit a protective immune response against virulent virus challenge. On the basis of these observations, recombinant fowl poxvirus (rFPV) containing a cDNA copy of the S1 gene of IBV Mass 41 (rFPV-S1) was constructed and its immunogenicity and vaccine potential were evaluated. Initially, rFPV-S1 was shown to express the S1 in vito by indirect immunofluorescence staining and western blot analyses. Later, in vivo expression was demonstrated by the detection of IBV-specific serum immunoglobulin G and neutralization antibodies in the sera of chickens immunized with rFPV-S1. That the recombinant virus elicited anti-IBV protective immunity was indicated by the manifested, relatively mild clinical signs of disease, decreased titers of recovered challenge virus, and less severe histologic changes of the tracheas in virulent IBV Mass 41-challenged chickens previously receiving rFPV-S1 as compared with parental fowl poxvirus (FPV)-vaccinated control birds. In contrast, chickens immunized with either recombinant or parental FPV were resistant to a subsequent virulent FPV challenge. As to a preferred method of immunization, wing web administration appeared to be superior to the subcutaneous route because a greater percentage of birds vaccinated by the former protocol exhibited an anti-IBV humoral immune response. Thus, rFPV-S1 has potential as a poultry vaccine against both fowl pox and infectious bronchitis.

An ELISA for antibodies against infectious bronchitis virus using an S1 spike polypeptide

Using the whole infectious bronchitis virus (IBV) for detecting the antibody against IBV by enzyme-linked immunosorbent assay (ELISA) is a routine work in poultry industry. To prepare virus is time consuming and tedious. Furthermore, the whole viral antigen detects all antibodies against the viral structural proteins, including spike (S), nucleocapsid, matrix, and other proteins. Among those, S protein is related to neutralization. Thus, to develop and express protein fragment from S gene and to use the protein as a coating antigen for antibody detection against IBV are the purposes of this experiment. A partial S gene fragment (n.t. 1143-1665) was cloned into pRSET vectors and transformed into competent Escherichia coli (E. coli) BL21 (DE3). A 27.5 kDa fusion protein (S-fg, containing S1-F and partial S2-G antigenic sites) was successfully expressed, affinity-purified and detected specifically with chicken anti-IBV serum by Western blot. The expressed S-fg protein was used as a coating antigen for developing an ELISA (S-fg ELISA) for serum antibody detection in anti-IBV antisera from different IBV serotypes and in field sera. The results show that the S-fg fusion protein is highly cross-reactive among different IBV serotypes, and the S-fg ELISA is found to be a convenient, economical, and efficient method for antibody detection against IBV.

Genetic and antigenic diversity in avian infectious bronchitis virus isolates of the 1940s

In order to verify a commonly held assumption that only Massachusetts (Mass) serotype of infectious bronchitis virus (IBV) was prevalent in the United States between the 1930s (when IBV was first isolated) and the 1950s (when the use of commercial IBV vaccines began), we examined 40 IBV field isolates from the 1940s. Thirty-eight of those isolates were recognized as Mass serotype viruses based on their reactivity to Mass-specific monoclonal antibody (Mab) and neutralization by Mass-specific chicken serum. The remaining two isolates, N-M24 and N-M39, that did not react with Mass-specific Mab, resisted neutralization by Mass-specific chicken serum, and were neutralized only by homologous chicken antibody were identified as non-Mass IBV. When the first 900 nucleotides (nt) from the 5'-end of the spike (S1) glycoprotein gene and their deduced amino acid (aa) sequences were compared, the two non-Mass isolates differed from each other by 24% and 28%, respectively. In a similar comparison, the non-Mass viruses N-M24 and N-M39 differed from M28, a Mass-type isolate from the 1940s, by 21% and 22% (nt) and 28% and 27% (aa), respectively. These data indicate that antigenic and genetic diversity among IBV isolates existed even in the 1940s. Interestingly, when the N-terminal region of the S1 of M28 was compared to that of M41, a prototype Mass virus that has undergone countless number of in vivo and in vitro host passages, the two viruses differed by only 2% (nt) and 4% (aa). This finding suggests that frequent genetic changes are not inherent in all IBV genomes.

Molecular characterization of three new avian infectious bronchitis virus (IBV) strains isolated in Quebec

Three unrecognized field isolates of Infectious Bronchitis Virus (IBV) were recovered from commercial broiler chickens vaccinated with live Mass viral strain (H120). These isolates were identified by immunofluorescence using monoclonal antibodies produced against reference serotypes: Mass, Conn, and Ark. RT-PCRs were performed on viral RNAs to amplify S1 gene using a specific set of primers S1OLIGO3' and S1OLIGO5'. Restriction polymorphism (RFLP) of PCR products was determined by the use of HaeIII restriction enzyme. As expected, patterns of PCR products were different from common pattern of strains assigned to Mass serotype M41, Beaudette, H120, and Florida. Molecular analysis showed a nucleotide insertion in hypervariable region one (HVR-1) of S1 gene of only Quebec isolates (Qu16, Qu_mv and Q_37zm). However, New Brunswick IBV isolate (NB_cp) did not display these insertions. Major amino acid changes involved insertion of two stretches (aa118-119: Arg-Ser and aa141-145: Sys-Ser-Asn-Ala-Ser-Cys) located at N-terrminal and C-terminal regions of HVR-2. It is speculated that cysteine residue located upstream and downstream of Cys-Ser-Asn-Ala-Ser-Cys segment might be involved in the formation of loop structure and disulfide bond that could trigger important epitope changes. Insertion of new NXT and NXS (X not equal to P) glycosylation motifs scattered along S1 region and insertion of cysteine residues in HVR are contributing to the antigenic shifting of Quebec isolates. Fragment insertions were thought to be induced by inter-serotype recombination between vaccine strain (H120) that belongs to Mass serotype and another strain belonging to Ark serotype. Phylogenetic tree based on amino acid sequences showed that Quebec isolates formed a new phylogenetic cluster.

Adoptive transfer of infectious bronchitis virus primed alphabeta T cells bearing CD8 antigen protects chicks from acute infection

Infectious bronchitis virus (IBV) infection and associated illness may be dramatically modified by passive transfer of immune T lymphocytes. Lymphocytes collected 10 days postinfection were transferred to naive chicks before challenge with virus. As determined by respiratory illness and viral load, transfer of syngeneic immune T lymphocytes protected chicks from challenge infection, whereas no protection was observed in the chicks receiving the MHC compatible lymphocytes from uninfected chicks. Protection following administration of T lymphocytes could be observed in chicks with three distinct MHC haplotypes: B(8)/B(8), B(12)/B(12), and B(19)/B(19). Nearly complete elimination of viral infection and illness was observed in chicks receiving cells enriched in alphabeta lymphocytes. In contrast, removal of gammadelta T lymphocytes had only a small effect on their potential to protect chicks. The adoptive transfer of enriched CD8(+) or CD4(+) T lymphocytes indicated that protection was also a function primarily of CD8-bearing cells. These results indicated that alphabeta T lymphocytes bearing CD8(+) antigens are critical in protecting chicks from IBV infection.

The molecular biology of coronaviruses

This chapter discusses the manipulation of clones of coronavirus and of complementary DNAs (cDNAs) of defective-interfering (DI) RNAs to study coronavirus RNA replication, transcription, recombination, processing and transport of proteins, virion assembly, identification of cell receptors for coronaviruses, and processing of the polymerase. The nature of the coronavirus genome is nonsegmented, single-stranded, and positive-sense RNA. Its size ranges from 27 to 32 kb, which is significantly larger when compared with other RNA viruses. The gene encoding the large surface glycoprotein is up to 4.4 kb, encoding an imposing trimeric, highly glycosylated protein. This soars some 20 nm above the virion envelope, giving the virus the appearance-with a little imagination-of a crown or coronet. Coronavirus research has contributed to the understanding of many aspects of molecular biology in general, such as the mechanism of RNA synthesis, translational control, and protein transport and processing. It remains a treasure capable of generating unexpected insights.

Experimental confirmation of recombination upstream of the S1 hypervariable region of infectious bronchitis virus

Chimeric infectious bronchitis virus (IBV) genomes with cross-over sites in the S1 gene were generated by co-infection with two distinct IBV strains. Recombinant viruses were collected from chicken embryos, embryonic cultured cells and chickens co-infected with Ark99 and Mass41 strains and purified by differential centrifugation. The recombinant S1 genes were identified by reverse transcription polymerase chain reaction (RTPCR) using heterologous primers and confirmed by nucleotide sequencing. The recombinants with Ark99 5' and Mass41 3' sequences were identified following the in vitro, in ovo and in vivo co-infections. Mixed RNA extracted from Ark99 and Mass41 did not produce RTPCR products with these primers at the PCR conditions used. Cross-over sites within the amplified 580 (Mass41) or 604 (Ark99) bases of the 5' S1 gene could only be detected between nucleotides 50 and 155. While this region, lying upstream of the S1 hypervariable region, corresponded with sites commonly identified in naturally occurring isolates, recombination sites identified in these studies could not be detected within the HVR of S1 of the genomes of chimeric viruses.

Infectious bronchitis virus: Immunopathogenesis of infection in the chicken

The immunopathogenesis of infectious bronchitis virus (IBV) infection in the chicken is reviewed. While infectious bronchitis (IB) is considered primarily a disease of the respiratory system, different IBV strains may show variable tissue tropisms and also affect the oviduct and the kidneys, with serious consequences. Some strains replicate in the intestine but apparently without pathological changes. Pectoral myopathy has been associated with an important recent variant. Several factors can influence the course of infection with IBV, including the age, breed and nutrition of the chicken, the environment and intercurrent infection with other infectious agents. Immunogenic components of the virus include the S (spike) proteins and the N nucleoprotein. The humoral, local and cellular responses of the chicken to IBV are reviewed, together with genetic resistance of the chicken. In long-term persistence of IBV, the caecal tonsil or kidney have been proposed as the sites of persistence. Antigenic variation among IBV strains is related to relatively small differences in amino acid sequences in the S1 spike protein. However, antigenic studies alone do not adequately define immunological relationships between strains and cross-immunisation studies have been used to classify IBV isolates into 'protectotypes'. It has been speculated that changes in the S1 protein may be related to differences in tissue tropisms shown by different strains. Perhaps in the future, new strains of IBV may arise which affect organs or systems not normally associated with IB.

The molecular biology of coronaviruses

This chapter discusses the manipulation of clones of coronavirus and of complementary DNAs (cDNAs) of defective-interfering (DI) RNAs to study coronavirus RNA replication, transcription, recombination, processing and transport of proteins, virion assembly, identification of cell receptors for coronaviruses, and processing of the polymerase. The nature of the coronavirus genome is nonsegmented, single-stranded, and positive-sense RNA. Its size ranges from 27 to 32 kb, which is significantly larger when compared with other RNA viruses. The gene encoding the large surface glycoprotein is up to 4.4 kb, encoding an imposing trimeric, highly glycosylated protein. This soars some 20 nm above the virion envelope, giving the virus the appearance-with a little imagination-of a crown or coronet. Coronavirus research has contributed to the understanding of many aspects of molecular biology in general, such as the mechanism of RNA synthesis, translational control, and protein transport and processing. It remains a treasure capable of generating unexpected insights.

A highly conserved epitope on the spike protein of infectious bronchitis virus

The predicted amino acid sequence and secondary structures of S1 of the spike protein (S) of infectious bronchitis viral (IBV) strains from Europe, the U.S.A., and Japan were compared. An antigenic determinant that was highly conserved in both the primary amino acid sequence and secondary structure of all strains was identified between amino acid positions 240 to 255. A synthesized peptide corresponding to this region was found to react with all polyclonal antisera examined from various IBV strains and with one monoclonal antibody (MAb), 9B1B6, out of nine known to react with the S of Gray. The specificity of the interaction with MAb 9B1B6 was confirmed by competitive ELISA using bound and unbound peptide. Interestingly, the previously described epitope for 9B1B6 had been characterized as cross-reactive with several strains of IBV, as conformation-independent but reacting only with intact whole S, and as associated with the functional integrity of other epitopes, including neutralizing epitopes on the S protein. The apparent critical functional and structural nature of this highly immunogenic determinant suggests a potential contribution in developing protective, cross-reactive subunit vaccines to IBV.