Chicken interferon type I inhibits infectious bronchitis virus replication and associated respiratory illness

Infectious bronchitis virus (IBV) causes an economically important respiratory disease in poultry worldwide. Previous studies have shown that CD8(+) cytotoxic T lymphocytes (CTL) are critical in controlling acute IBV infection, but the role of innate immunity is unknown. This study describes the in vitro and in vivo anti-IBV activity of natural spleen cell-derived and recombinant chicken interferon type I (rChIFN-alpha). Both natural and rChIFN-alpha inhibited replication of the Beaudette strain of IBV in chicken kidney cells (CKC) in a dose-dependent manner, with the antiviral activity of the former accounted for entirely by its content of type I IFN. IFN at 100 U/ml reduced viral replication by 50% as measured by syncytia formation. In addition, the spleen cell-derived supernatants (natural IFN) inhibited tracheal ring ciliostasis mediated by the Gray strain of IBV. Optimal protection against IBV-induced respiratory disease was obtained after intravenous or oral administration of ChIFN given 1 day before virus challenge and each of 5 days thereafter. ChIFN-I protected chicks from clinical illness by delaying the onset of the disease and decreasing the severity of illness, demonstrating its potential as an immune enhancer.

Evaluation of expression patterns of feline CD28 and CTLA-4 in feline immunodeficiency virus (FIV)-infected and FIV antigen-induced PBMC

It is known that CD28, a positive costimulatory receptor, plays a very important role in inducing the optimal stimulation of T lymphocytes. CTLA-4 (CD152), however, acts as a negative regulator in T lymphocyte activation. The effect of an feline immunodeficiency virus (FIV) infection on the expression of feline CD28 and CTLA-4 was studied with FIV-infected and uninfected peripheral blood mononuclear cells (PBMC) using a competitive PCR assay. The nature of CD28 and CTLA-4 expression was also examined with fresh and antigen-stimulated PBMC. FIV infection induced a lower expression of CD28, but a higher expression of CTLA-4 in the infected PBMC than in the uninfected PBMC. Relatively high levels of CD28 expression were demonstrated in both the fresh and the antigen-stimulated PBMC. The expression level of CTLA-4 in the freshly isolated PBMC was rather low, however, FIV antigen stimulation induced a relatively high expression of CTLA-4 in feline PBMC.

Dose response studies of acute feline immunodeficiency virus PPR strain infection in cats

The effects of virus dose on host response were evaluated for the PPR strain of feline immunodeficiency virus (FIV-PPR). Specific pathogen-free cats were inoculated intravenously with 50, 250 or 1250 TCID(50) of FIV-PPR. Two weeks after inoculation, virus was detected in 10(6) peripheral blood mononuclear cells (PBMCs) of all infected animals, and the CD4(+):CD8(+) T lymphocyte ratios fell from greater than 2 to approximately 1 in all infected animals within the first 8 weeks after infection. Provirus detected in all groups using PCR and 10(3) PBMC was biphasic. Nine of 15 animals were positive between weeks 2 and 4 p.i. and 14 of 15 were positive by week 8 p.i. Transient lymphadenopathy was detected in most cats receiving 1250 TCID(50) and the 250 TCID(50) of virus, whereas no lymphadenopathy was detected in the 50 TCID(50) group or the five uninfected cats. Animals that had received the largest dose seroconverted earliest (on average at week 4.0) and those receiving the least seroconverted last (on average at week 5.6). Neither neutropenia nor lymphopenia were detected. FIV-specific CTL responses of memory effector cells could be detected in animals receiving all three doses but was highly variable among individual animals. Neurological manifestations determined after 15 weeks p.i. were observed in most infected cats, including two of the three that had received 50 TCID(50) of virus. However, the observed neurologic abnormalities were markedly less severe in the animals receiving the least amount of virus. Therefore, lymphadenopathy and neurologic signs of illness were less severe and seroconversion was slower in the animals that received the lowest dose compared with those receiving the 250 and 1250 TCID(50) doses of the FIV-PPR strain.

Molecular cloning and expression of feline CD28 and CTLA-4 cDNA

Feline CD28 and CTLA-4 (CD152) cDNA were cloned from Con-A stimulated feline peripheral blood mononuclear cells (PBMC) by rapid amplification of cDNA end-PCR (RACE-PCR). Both CD28 and CTLA-4 proteins belong to the immunoglobulin superfamily (Ig SF) and are composed of a signal sequence, an extracellular domain, a transmembrane domain and a cytoplasmic domain. The open reading frame (ORF) of CD28 cDNA encoded a predicted protein of 221 amino acids and that of CTLA-4 cDNA encoded a predicted protein of 223 amino acids. The B7 ligands binding motif MYPPPY hexamer was found on the extracellular Ig V-like domains of both receptors and phosphatidylinositol 3-kinase (PI 3-kinase) binding motifs pYMNM for CD28 and pYVKM for CTLA-4 were identified in the cytoplasmic domains. Comparisons of amino acid sequences of feline proteins with known sequences of other species indicated that rabbit CD28 and CTLA-4 were most closely related and mouse molecules were the least conserved with feline molecules. Comparison of each domain of both molecules with that of other animals showed that the cytoplasmic domain of CTLA-4 was 100% conserved and that of CD28 was the most conserved domain. The cloned CD28 and CTLA-4 cDNA could be expressed in transfected mammalian cells. Expression of feline CD28 and CTLA-4 mRNA in freshly isolated feline PBMC was demonstrated by RT-PCR. Stimulation of PBMC with Con-A similarly increased the expression of both CD28 and CTLA-4 mRNA.

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.

Sequence analyses of feline B7 costimulatory molecules

Using RT-PCR amplifications with mRNA from mitogen-stimulated feline peripheral blood mononuclear cells, cDNA of feline B7-1 (CD80) and B7-2 (CD86) were cloned. The cDNA were sequenced and putative translated protein sequences compared with known counterpart sequences. Hydrophilicity patterns of the feline CD80 and CD86 which were only 26.8% identical at the amino acid sequence were very distinct from each other, but similar to the putative human CD80 and CD86 proteins, respectively. The feline CD80 gene encoded a protein of 292 amino acids and the CD86 gene encoded a protein of 329 amino acids. Amino-terminal signal sequences, extracellular Ig V- and Ig C-like domains, transmembrane domains, and carboxyl cytoplasmic domains were identified in both molecules. Although the most conserved domain among the CD80 sequences was the Ig C-like domain, the most conserved domain among the CD86 sequences was the Ig V-like domain. Among the known sequences, the bovine CD80 and the porcine CD86 sequences available for comparisons were identified as most closely related to the feline CD80 (63.3%) and CD86 (67.5%), respectively. The mouse molecules were the least identical (43.6 and 43.6%, respectively) with the feline CD80 and CD86 proteins. The human CD80 and CD86 molecules were 56.3 and 57.0% identical with the feline molecules.

Cytotoxic T lymphocytes are critical in the control of infectious bronchitis virus in poultry

Various strains of infectious bronchitis virus (IBV) cause respiratory, kidney, enteric and reproductive illnesses in chickens, especially in newly hatched chicks. Assays have been developed to identify Gray strain IBV-specific cytotoxic T lymphocyte (CTL) responses using viral infected antigen presenting cells (APC) and using the Semliki Forest virus vector infected APC expressing individual viral polypeptides. It was shown that major histocompatibility complex restricted CTL are responsible for early control of IBV infection. The kinetics of viral load observed in the lungs and kidneys correlated with the level of IBV-specific CTL activity of effector cells prepared from spleens of infected chicks. Adoptive transfer of immune T cells to chicks prior to infection demonstrated that IBV primed CD8(+), alphabeta T lymphocytes could protect chicks from acute infection. CTL determinants in the viral particle can be mapped to the spike and nucleocapsid proteins but not to the membrane protein. The carboxyl terminus of the nucleocapsid protein houses an epitope(s) responsible for induction of CTL responses to IBV N protein. Inoculation of DNA plasmid expressing the carboxyl terminus of Gray strain N resulted in induction of CTL that cross-react with two distinct IBV strains. In addition, this potential DNA vaccine resulted in protection of chicks against acute infection.

The amino and carboxyl domains of the infectious bronchitis virus nucleocapsid protein interact with 3' genomic RNA

Previous studies indicated that the nucleocapsid (N) protein of infectious bronchitis virus (IBV) interacted with specific sequences in the 3' non-coding region of IBV RNA. In order to identify domains in the N protein that bind to RNA, the whole protein (409 amino acids) and six overlapping fragments were expressed as fusion polypeptides with six histidine-tags. Using gel shift assays, the intact N protein and amino polypeptides, from residues 1 to 171 and residues 1 to 274, and carboxyl polypeptides, extending from residues 203 to 409 and residues 268 to 407, were found to interact with positive-stranded IBV RNA representing the 3' end of the genome. The two 32P-labeled probes that interacted with N and the amino and carboxyl fragments of N were RNA consisting of the IBV N gene and adjacent 3' non-coding terminus, and RNA consisting of the 155-nucleotide sequences at the 3' end of the 504-nt 3' untranslated region. In contrast, the polypeptide fragment from the middle region, residues 101-283, did not interact with these 3' IBV RNAs. The binding site in the amino region of N was either not present or only partially present in the first 91 residues because no interaction with RNA was observed with the polypeptide incorporating these residues. Cache Valley virus N expressed with a histidine tag, bovine serum albumin, and the basic lysozyme protein did not shift the IBV RNA. The lower molarities of the carboxyl fragment compared with residue 1-274 fragment needed for equivalent shifts suggested that the binding avidity for RNA at the carboxyl domain was greater than the amino domain.

Anti-feline immunodeficiency virus (FIV) soluble factor(s) produced from antigen-stimulated feline CD8(+) T lymphocytes suppresses FIV replication

Feline immunodeficiency virus (FIV) causes AIDS-like symptoms in infected cats. Concanavalin A (ConA)-stimulated peripheral blood mononuclear cells (PBMC) from chronically FIV strain PPR-infected cats readily expressed FIV. In contrast, when PBMC from these animals were stimulated with irradiated, autologous antigen-presenting cells (APC), at least a 10-fold drop in viral production was observed. In addition to FIV-specific cytotoxic T lymphocytes, anti-FIV activity was demonstrated in the cell-free supernatants of effector T lymphocytes stimulated with APC. The FIV-suppressive activity was induced from APC-stimulated PBMC of either FIV-infected or uninfected cats but not from ConA-stimulated PBMC. Suppression of FIV strain PPR replication was observed for both autologous and heterologous feline PBMC, was dose dependent, and demonstrated cross-reactivity and cell specificity. It was also demonstrated that the anti-FIV activity originated from CD8(+) T lymphocytes and was mediated by a noncytolytic mechanism.

Cytotoxic T lymphocyte responses to infectious bronchitis virus infection

Cytotoxic T lymphocyte (CTL) activity to infectious bronchitis virus (IBV) was examined at regular intervals between 3 and 30 days post infection (p.i.). The maximal CTL lysis of target cells infected with IBV with 82% was detected at 10 days p.i. The specific CTL activity began to decrease only after viral loads, which peaked at day 8 p.i. in both kidneys and lungs, started to decline. Therefore, the CTL response correlated with elimination of acute infection. IgM antibody did not appear until day 10 and levels peaked at day 12 p.i. whereas IgG antibody titers were detectable only by day 15 p.i., but continued to increase exponentially until day 30 p.i., the last day examined. IBV specific CTL epitope(s) were mapped within the carboxyl terminal 120 amino acids of nucleocapsid protein. In vivo inoculation of this fragment, as cDNA, induced protection against acute infection. The absence of viral neutralizing epitopes on the nucleocapsid protein would suggest that protection with known CTL eptiope(s) can be induced in the absence of neutralizing antibody.

Recombinant nucleocapsid protein is potentially an inexpensive, effective serodiagnostic reagent for infectious bronchitis virus

The nucleocapsid protein of the Gray strain of infectious bronchitis virus (IBV) is highly immunogenic and cross-reactive among various distinct serotypes. Recombinant nucleocapsid polypeptide expressed in bacteria with a histidine tag at the amino terminus has been used as antigen for developing an assay to detect IBV-specific antibody. This fusion protein was produced readily in bacteria and easily purified with a nickel column which bound to the histidine tag. Conditions were optimized for using these preparations for an IBV-specific ELISA. Although differences in optical densities could be detected between pre-immune and positive sera for the Ark, Mass, and Gray strains with antigen concentrations between 50 and 0.1 microg per well, the greatest differences could be detected with 3 and 1.5 microg of protein per well. Maximum differences in optical densities between pre-immune and positive sera were obtained using 2.4 microg per well of protein and sera diluted between 1:80 and 1:160. In addition, as little as 30 ng/dot of recombinant nucleocapsid consistently detected IBV-specific sera in immunoblot assays which have convenient field applications.

Cellular mechanisms of feline immunodeficiency virus (FIV)-induced neuropathogenesis

The high incidence of neurologic dysfunction from human immunodeficiency virus (HIV) infection has heightened interest in neuropathogenesis of other lentiviruses, including that associated with feline immunodeficiency virus (FIV). Both HIV and FIV efficiently enter the central nervous system and cause primary neurological disease that is not attributable to opportunistic infections or systemic disease. Cells in the brain infected by FIV are similar to those observed in HIV infection, both viruses infect macrophages, microglia, and astrocytes. Although substantial neuronal loss can occur in the cortex of HIV- or FIV-infected patients, most studies agree that neurons are not infected and indirect mechanisms of neurotoxicity are postulated. This review describes recent information on the neuropathogenesis of FIV and how this information correlates with what is known about the neuropathogenesis of HIV. Although the pathogenesis of neurological dysfunction in HIV- and FIV-infected patients is far from clear, it is becoming increasingly evident that the relationship between lentivirus presence in the brain and neurological signs is not straightforward and cannot be explained by simple cytolytic infection. The observed neurologic dysfunction is likely multifactorial and complex involving an intricate web of subcellular pathways and neurotoxic factors interacting with multiple cell types.

The carboxyl-terminal 120-residue polypeptide of infectious bronchitis virus nucleocapsid induces cytotoxic T lymphocytes and protects chickens from acute infection

Specific cytotoxic T-lymphocyte (CTL) responses to nucleocapsid of infectious bronchitis virus (IBV) were identified by using target cells infected with a Semliki Forest virus (SFV) vector. Effector cells for CTL assays were collected from chickens infected with the Gray strain of IBV or inoculated with a DNA plasmid encoding nucleocapsid proteins. IBV-specific CTL epitopes were mapped within the carboxyl-terminal 120 amino acids of the nucleocapsid protein. CTL lysis of target cells infected with SFV encoding nucleocapsid was major histocompatibility complex restricted and mediated by CD8+ T cells. In addition, splenic T cells collected from chickens inoculated in the breast muscle with a DNA plasmid encoding this CTL epitope(s) recognized target cells infected with wild-type virus or an SFV vector encoding nucleocapsid proteins. CTL activity of splenic T cells collected from chicks immunized with a DNA plasmid encoding CTL epitopes was cross-reactive, in that lysis of target cells infected with serologically distinct strains of IBV was dose responsive in a manner similar to that for lysis of target cells infected with the homologous strain of IBV. Furthermore, chickens immunized with a DNA plasmid encoding a CTL epitope(s) were protected from acute viral infection.

Specific cytotoxic T lymphocytes are involved in in vivo clearance of infectious bronchitis virus

Cytotoxic T-lymphocyte (CTL) responses to infectious bronchitis virus (IBV) were determined at regular intervals between 3 and 30 days postinfection (p.i.). The maximum response with 82% lysis of labeled target cells was detected at 10 days p.i. The specific CTL response did not begin to decline until the amount of virus, which peaked at day 8 p.i. in both the kidneys and lungs, started to decrease. Clinical respiratory signs of illness also correlated with amount of virus. CTL activity was shown to be major histocompatibility complex (MHC) class restricted because the lysis of MHC-mismatched targets was negligible, and lysis was mediated by CD8+ CD4- T cells, as the CTL response could be abolished with removal of CD8+ CD4- but not CD4+ CD8- lymphocytes. In contrast, immunoglobulin M (IgM) antibody was not detected until day 10 p.i., and levels peaked at day 12 p.i.; IgG antibody levels were minimal until day 15 p.i. but continued to increase exponentially until day 30 p.i., the last day examined. In summary, CTL responses correlated with initial decreases in infection and illness.

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.

Ovine fetal malformations induced by in utero inoculation with Main Drain, San Angelo, and LaCrosse viruses

The teratogenic potential of three bunyaviruses, two California serogroup bunyaviruses, LaCrosse virus and San Angelo virus, and a Bunyamwera serogroup member, Main Drain virus, in sheep was studied following in utero inoculation of ewes in early gestation. Although Main Drain virus appeared to be most teratogenic, all three viruses induced a range of lesions including arthrogryposis, hydrocephalus, fetal death, axial skeletal deviations, anasarca, and oligohydramnios. The teratogenic effects of these viruses are identical to those described in ovine infections by Cache Valley and Akabane viruses. Demonstration of a common bunyaviral tropism for fetal tissue infection that results in congenital brain and musculoskeletal malformations provides evidence that human in utero infection by bunyaviruses could result in similar malformations in human infants.

The infectious bronchitis virus nucleocapsid protein binds RNA sequences in the 3' terminus of the genome

The infectious bronchitis virus (IBV) nucleocapsid protein was expressed as a bacterial fusion protein which differed from the native protein only in the addition of six amino terminus histidine residues. Using RNA overlay protein blot assays, the recombinant protein was shown to bind to RNA fragments specific for the positive sense 3' noncoding end of the IBV genome. At greater concentrations of sodium chloride, the native and fusion nucleocapsid proteins similarly bound to G RNA, representing the terminal 1805 3' nt of the genome, whereas bovine serum albumin and allantoic fluid protein did not bind to labeled G RNA. Competitive gel shift assays with labeled G RNA indicated that the protein interacted with several unlabeled RNA representing sequences at the 3' noncoding end of the IBV genome. Cache Valley virus (a bunyavirus) mRNA transcribed from the small segment cDNA also inhibited the interaction with IBV G RNA to approximately the same extent as homologous unlabeled G RNA, whereas reactions with bovine liver RNA and yeast tRNA were considerably weaker. Whereas yeast tRNA did not inhibit the interaction with the labeled large G RNA, interactions of the fusion protein with EF, a region from 78 to 217 nt from the 3' terminus of the IBV genome, were also apparently weaker than interactions with fragment CD which consisted of the 3' terminal 155 nt. On a molar basis, the latter interacted in an identical nature to a RNA consisting of CD and an additional 1053 nt of plasmid sequences. Compared to bovine liver RNA, unlabeled G specifically inhibited binding to the two smaller labeled IBV fragments in gel shift assays. The binding of IBV nucleocapsid protein with RNA probably requires specific sequences and/or structures that are present on the genome, and may represent a common mechanism used by similar viral nucleoproteins whose functions depend on binding to RNA.

Retroviral vector-transduced cells expressing the core polyprotein induce feline immunodeficiency virus-specific cytotoxic T-lymphocytes from infected cats

The core polyprotein of feline immunodeficiency virus (FIV) was expressed in primary feline T-lymphocytes using a retroviral vector. These cells were used as antigen-presenting stimulator cells (APSC) for the in vitro induction of cytotoxic T-lymphocytes (CTL) from feline peripheral blood mononuclear cells (PBMC). CTL from 4 cats chronically infected with the Petaluma strain of FIV specifically lysed autologous FIV-infected targets in an MHC-restricted manner. The CD8 phenotype of more than 70% of the induced effector cells (97% for cells from one cat) was consistent with MHC class I-restricted cytotoxicity. In addition, it was possible to detect low levels of core polyprotein-specific lysis from effector cells of two of the FIV-infected cats. When observed, the level of lysis, measured as a percentage of specific 111In release, was lower for the transgenic gag-expressing targets than for FIV-infected targets. The difference in killing may reflect the low level of core CTL were not detected in either PBMC stimulated with cells transduced by a retroviral vector without the FIV gag sequence or PBMC from an uninfected cat stimulated with autologous transgenic APSC. The detection of FIV-specific CTL from infected cats following stimulation with transgenic APSC suggests a role for retroviral vectors in determining CTL specific for individual lentiviral proteins in protective immunity.

Feline immunodeficiency virus (FIV)-specific cytotoxic T lymphocytes from chronically infected cats are induced in vitro by retroviral vector-transduced feline T cells expressing the FIV capsid protein

We have previously reported the presence of feline immunodeficiency virus (FIV)-specific, major histocompatibility complex (MHC)-restricted cytolytic T lymphocytes (CTL) in experimentally FIV-infected cats. However, the fine specificity of the CTL and the role of individual FIV proteins in inducing FIV-specific CTL responses remain unknown. In this study, we examined the in vitro induction and activity of FIV p24 capsid-specific CTL obtained from cats that had been experimentally infected with FIV Petaluma for 30 to 56 months. An amphotropic murine retroviral vector was used to generate transgenic primary feline T lymphoblasts that expressed the FIV capsid protein. When the autologous capsid-transduced T cells were used in vitro to stimulate CTL responses from peripheral blood mononuclear cells of chronically infected cats, MHC-restricted lysis of virus-infected target cells was observed. The majority of the CTL expressed CD8, and depletion of this population, but not CD4+ cells, effectively diminished the CTL activity. When the autologous capsid-transduced T cells were used as target cells, lysis by capsid-induced effectors was not observed. Analysis of capsid-transduced T cell clones revealed a variable and low level of capsid expression among the clones. This study demonstrates the potential for using retroviral vectors as a means of inducing CTL effector cells that will specifically kill lentivirus-infected cells during lentiviral infection.

Molecular mimicry between Fc receptor and S peplomer protein of mouse hepatitis virus, bovine corona virus, and transmissible gastroenteritis virus

We have previously demonstrated molecular mimicry between the S peplomer protein of mouse hepatitis virus (MHV) and Fc gamma R (Fc gamma R). A monoclonal antibody (MAb) to mouse Fc gamma R (2.4G2 anti-Fc gamma R MAb), purified rabbit immunoglobulin, but not their F(ab')2 fragments, as well as mouse and rat IgG, immunoprecipitated (1) recombinant S peplomer protein expressed by a vaccinia virus recombinant in human, rabbit, and mouse cells, and (2) natural S peplomer protein from cells infected with several strains of MHV and MHV escaped mutants. We report here results of studies documenting molecular mimicry between Fc gamma R and S peplomer protein of viruses representing three distinct antigenic subgroups of the Coronaviridae. We have shown a molecular mimicry between the S peplomer protein of bovine corona virus (BCV) and Fc gamma R. The 2.4G2 anti-Fc gamma R MAb, rabbit IgG, but not its F(ab')2 fragments, as well as homologous bovine serum, free of anti-BCV antibodies, immunoprecipitated S peplomer protein of BCV (Mebus strain). In contrast, we did not find molecular mimicry between S peplomer protein of human corona virus (HCV-OC43) and Fc gamma R. Although the OC43 virus belongs to the same antigenic group as MHV and BCV, MAb specific for human Fc gamma RI or Fc gamma RII and purified human IgG1, IgG2, and IgG3 myeloma proteins did not immunoprecipitate the S peplomer protein from HCV-OC43-infected RD cells. In addition, we did demonstrate molecular mimicry between the S peplomer protein of porcine transmissible gastroenteritis virus (TGEV) and Fc gamma R. TGEV belongs to the second antigenic subgroup of coronaviridae.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser cytometric analysis of FIV-induced injury in astroglia

Glia are the predominant brain cells infected by the lentiviruses human immunodeficiency virus (HIV) and feline immunodeficiency virus (FIV). The importance of astrocytes in maintenance of central nervous system homeostasis suggests that astrocytes are likely to play a strategic role in the progression of neurological disease in lentiviral-infected patients. In consideration of this postulate, the ability of FIV to cause injury by infection of cultured feline astroglia was examined via vital fluorescence assays. Intracellular Ca2+ homeostasis, plasma membrane permeability and fluidity, and cytosolic glutathione (GSH) levels were evaluated. Although basal intracellular Ca2+ was not significantly different between groups, FIV-infected astroglia displayed both a significant delay in development of peak Ca2+ levels following ionophore application and a decrease in the amount of Ca2+ released from intracellular stores. Plasma membrane lipid mobility was increased in FIV-infected cells within 24 h of infection. Glutathione levels were affected in a dose dependent fashion. With a standard viral inoculum there was a decrease in GSH which became significant after 8 days postinfection. With a high inoculum dose there was rapid loss of cell viability with an increase in GSH in surviving cells. We have identified several cellular processes altered in FIV-infected astroglia and our findings suggest that FIV-infection of feline astroglia affects cellular membranes, both structurally and functionally.

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.

Interactions between the IBV nucleocapsid protein and RNA sequences specific for the 3' end of the genome

The infectious bronchitis virus (IBV) nucleocapsid protein was expressed as a fusion protein in bacteria. The coding sequence differed from the native protein only in the addition of six histidine residues at the amino terminus which were used for enrichment with a nickel affinity column. In gel shift assays, the mobility of labelled G RNA was decreased with increasing concentrations of the fusion protein. Competitive gel shift assays with labelled G RNA indicated that the protein interacted with relatively high avidities to several unlabelled RNAs representing sequences at the 3' noncoding end of the IBV genome. Cache Valley virus (a bunyavirus) mRNA transcribed from the smaller segment cDNA also inhibited the interaction with IBV G RNA to the same extent as homologous unlabelled G RNA. In contrast, interactions of the fusion proteins with a region from 99 to 249 bases from the 3' terminus of the IBV genome and bovine liver RNA were relatively weak. The binding of IBV nucleocapsid protein with RNA probably requires specific sequences and/or structures that are present at a number of sites on the genome, and may represent a common mechanism used by similar viral proteins whose functions depend on binding to RNA.

Evolutionary implications of genetic variations in the S1 gene of infectious bronchitis virus

The large number of phenotypically distinct strains of infectious bronchitis virus (IBV) provide a broad genetic background for examining naturally occurring coronavirus variation. Comparisons of the published nucleotide sequence of S1 genes of strains isolated in Europe, Japan and the USA and four additional American strains described in this report identified 4 genetically distinct groups. The Dutch group was the most divergent sharing only about 60% identity with the American, Mass and European groups which were about 80% homologous with each other. Whereas the strains within the Mass, European and Dutch strains were at least 95% homologous, the strains within the American group were most variable, sharing about 80% identity. The hypervariable region (HVR) which tended to correlate with serotype extended from amino acid residue 53 to 148. In addition to the previously described putative recombination events in the S1 gene of PP14 and SE17, we have now described similar shifts in homology in the corresponding gene of the Gray, Holte, 6/82 (European strain), and Iowa strains. Although minor cross-over sites were identified in the more conserved 3' end at approximately nt 1000 and 1400, a frequently used hot-spot for recombination extended from nt 25 to a region immediately upstream of, but not including, the hypervariable region (HVR). In addition to point mutations, deletions, and insertions, recombination often involving Mass-like and Ark-like sequences, is a commonly used mechanism responsible for the evolution of IBV.

Feline immunodeficiency virus decreases cell-cell communication and mitochondrial membrane potential

The in vitro effects of viral replication on mitochondrial membrane potential (MMP) and gap junctional intercellular communication (GJIC) were evaluated as two parameters of potential cellular injury. Two distinct cell types were infected with the Petaluma strain of feline immunodeficiency virus (FIV). Primary astroglia supported acute FIV infection, resulting in syncytia within 3 days of infection, whereas immortalized Crandell feline kidney (CRFK) cells of epithelial origin supported persistent FIV infection in the absence of an obvious cytopathic effect. An examination of cells under conditions that included an infection rate of more than 90% for either population revealed that the astroglia produced about four times more virus than the CRFK cells. The mitochondrial uptake of the cationic fluorescent dye rhodamine 123 in infected astroglia was less than 45% of that of normal control cells, whereas the MMP of the CRFK cells, which produced about one-fourth as much virus, was 80.8% of that of the normal cells. Cell-cell communication between adjacent cells was determined by the recovery of fluorescence following photobleaching of a single cell. In spite of the lower level of innate cell-cell communication among cultured CRFK cells than among astroglia, viral replication resulted in a 30% decrease in the GJIC of both astroglia and CRFK cells. These studies indicate that cell injury, as defined by an inhibition of MMP and GJIC, can occur as a result of persistent and acute infection with the Petaluma strain of FIV.

Molecular mimicry between S peplomer proteins of coronaviruses (MHV, BCV, TGEV and IBV) and Fc receptor

In previous studies we have demonstrated molecular mimicry between the S peplomer protein of Mouse Hepatitis Virus (MHV) and Fc gamma Receptor (Fc gamma R) of IgG. Rabbit IgG, but not its F(ab')2 fragments, monoclonal rat and mouse IgG and the rat 2.4G2 anti-mouse Fc gamma R monoclonal antibody (mab) immunoprecipitated natural and recombinant MHV S protein. On the basis of a number of criteria, MHV S peplomer protein exhibits Fc IgG binding ability. We report here a molecular mimicry between the S peplomer protein of Bovine Coronavirus (BCV) and Fc gamma R. BCV S peplomer protein which belongs to the same antigenic subgroup as MHV also binds Fc portion of rabbit IgG and is immunoprecipitated by the 2.4G2 anti-Fc gamma R mab. In contrast, Transmissible Gastroenteritis Coronavirus (TGEV) and Infectious Bronchitis Virus (IBV) S peplomer proteins which represent two distinct antigenic subgroups of Coronaviridae do not bind rabbit IgG and do not react with anti-Fc gamma R mab. However, homologous swine IgG, but not its F(ab')2 fragments, immunoprecipitated from TGEV-infected cells a polypeptide chain with molecular mass of 195 kDa, identical to that immunoprecipitated by the T36 mab anti-TGEV S peplomer protein.

Evaluation of cofactor effect of feline syncytium-forming virus on feline immunodeficiency virus infection

Although feline immunodeficiency virus (FIV) and the unrelated retrovirus feline leukemia virus (FeLV) are associated with acquired immune deficiency in cats, experimental and field evidence indicates that coinfection with both viruses may lead to more serious disease syndrome. A third feline retrovirus, feline syncytium-forming virus (FeSFV), which is far more prevalent than either FIV or FeLV and is considered nonpathogenic in nature, is consistently coisolated from sick, FIV-infected cats. To determine the potential role of FeSFV in enhancement of FIV-mediated disease, persistent FeSFV infection was established in 14 of 24 nine-month-old cats. Four months later, half the FeSFV-infected and half the noninfected cats were inoculated with blood obtained from a cat persistently infected with the Petaluma strain of FIV. At postinoculation week 17, 1 male cat infected with only FIV died of bacterial bronchopneumonia that could have been attributed to FIV-induced acquired immune deficiency-like syndrome. However, none of the remaining cats had clinical illness, whether infected with either virus alone or coinfected with both viruses. As early as postinoculation week 6, decreases were observed in the CD4+ to CD8+ T-lymphocyte ratio of both groups of cats inoculated with FIV. Infection with FeSFV had no effect on the CD4+ to CD8+ T-cell ratio. Mitogen stimulation assays and total WBC count were unaffected by FeSFV infection, although an increase in numbers of neutrophils from FeSFV-infected cats was consistent, especially when compared with the decrease observed after FIV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of a hypervariable region in the 3' non-coding end of the infectious bronchitis virus genome

Previous studies on infectious bronchitis virus (IBV) cDNA have identified a region of about 184 bases in the 3' non-coding terminus of both the U.S. prototype strain (Beaudette) and a Japanese strain (KB8523), that was not present in an antigenically closely related U.S. strain, Massachusetts (Mass) 41 (Boursnell et al., 1985; Sutou et al., 1988). In order to investigate the origin and function of this region and its occurrence in nature, the cDNA sequences of the 3' non-coding regions of three additional strains of IBV, Gray, Arkansas (Ark) 99 and Holland (Holl) 52, were determined and compared to the sequences of the Beaudette, KB8523 and Mass41 strains. Not only was this Urich sequence absent from the 3' non-coding region of the Mass41 strain, it was also highly variable, especially in comparison to the highly conserved 3' non coding region downstream of this sequence. Computer analyses of the sequences adjacent to this hypervariable region (HVR) showed that the 3' end of the IBV genome was highly conserved downstream of this region, with 94.3 to 97.8% similarity. However, the similarities for the HVR ranged from 53.2% between Holl52 and Ark99, to 92.8% between Beaudette and Gray. The flanking sequences were not only conserved but these sequences upstream and downstream of the HVR also formed mirrored images.

Evidence of natural recombination within the S1 gene of infectious bronchitis virus

During an outbreak of severe respiratory disease, a field strain of infectious bronchitis virus (IBV), PP14, was isolated from a bird in a Texas flock that had been previously vaccinated with an attenuated Mass serotype virus. After cloning and sequencing the S1 gene from several IBV strains, it was found that the 5' end of the cDNA was 96% identical to the published sequences of Mass41 and 77% identical with Ark99. The following 402 bases which included the hypervariable regions (HVR) of the S1 gene were 94% homologous with Ark99 and only 69% with Mass41. In addition, the HVR in the 3' noncoding region of the genome, which is totally absent in Mass41, was 99% homologous with the Ark99 strain. This abrupt shift in identity of PP14 in the S1 strongly indicated that a recombination event had occurred about 98 bases from the beginning of the S1 gene between an Ark-like and a Mass-like virus. Downstream, 33 bases from the PP14 recombination junction, a second putative "cross-over" site was identified in the S1 of the SE17 strain where the 5'131 bases of the S1 gene of the Ark99 and SE17 were found to be 95% identical and the following 368 base sequence was only 78% homologous. In addition, a second shift in homology in the S1 of SE17 was identified between nucleotide 1112 and 1460 which shared 95% identity with Mass41. The putative recombination junctions which were downstream of the signal sequence and upstream of the S1 HVR may represent a "hot spot," but not an exclusive region, for exchanging genetic material between IBV strains. Genetic shifts are apparently not only common mechanisms for variation in nature, but vaccine strains may actually play a critical role in these events in the evolution of virulent strains of IBV.

Comparative analyses of the nucleocapsid genes of several strains of infectious bronchitis virus and other coronaviruses

The natural sequence variations of the nucleocapsid genes of the Gray, Arkansas99 (Ark99), and Holland52 (Holl52) strains of infectious bronchitis virus (IBV) were determined. These were compared with previously published sequencing data of other IBV strains, as well as other coronaviruses, in order to correlate the serological and evolutionary relationship of coronaviruses. IBV nucleotide sequence alignment shows that overall the sequences are highly conserved, with homologies from 91.1 to 96.5%. However, there are also two regions (730 to 800 and 1138 to 1166) that appear to be even more highly conserved. Overall, the nucleocapsid protein is highly variable both in size and composition between coronavirus major antigenic groups but is conserved within these groups. A phylogenetic tree of the nucleocapsid protein of various coronaviruses indicates that the coronaviruses fall into distinct groups that correspond to the three major antigenic groups; however, a phylogenetic tree of the IBV nucleocapsid shows that this does not hold true for the type specific antigenic groups of IBV.

Induction of feline immunodeficiency virus-specific cytolytic T-cell responses from experimentally infected cats

We have examined the in vitro induction and activity of feline immunodeficiency virus (FIV)-specific cytolytic T cells obtained from cats experimentally infected for 7 to 17 weeks or 20 to 22 months with the Petaluma isolate of FIV. Normal or FIV-infected autologous and allogeneic T lymphoblastoid cells were used as target cells in chromium-51 or indium-111 release assays. When effector cells consisted of either fresh peripheral blood mononuclear cells or concanavalin A- and interleukin-2-stimulated cells, only low levels of cytotoxicity were observed. However, the levels of FIV-specific cytotoxicity were consistently higher in both groups of cats following in vitro stimulation of the effector cells with irradiated, FIV-infected autologous T lymphoblastoid cells and interleukin-2. The effector cells lysed autologous but not allogeneic FIV-infected target cells and were composed predominantly of CD8+ T cells, indicating that the FIV-specific cytotoxicity measured in this system is mediated by CD8+, major histocompatibility complex class I-restricted T cells. These studies show that FIV-specific cytolytic T cells can be detected as early as 7 to 9 weeks postinfection, and they define a system to identify virus-encoded epitopes important in the induction of protective immunity against lentiviruses.

Cache Valley virus infection in Texas sheep flocks

Cache Valley virus (CVV), an arbovirus indigenous to the United States, has been implicated as an important teratogenic agent in sheep. The prevalence and distribution of Texas sheep with CVV-specific antibody were investigated. In 1981, 19.1% of 366 sheep located in 22 counties of Texas had antibodies specific for CVV. Of 50 flocks examined in the major sheep-producing counties in Texas, 34 had sheep with antibodies that reacted with CVV, including all sheep tested in 6 flocks that were seropositive. Sera obtained from sheep at the Texas Agricultural Experiment Station at San Angelo between 1986 and 1989 were also examined for CVV-specific antibody because this flock was the subject of the episode of CVV-associated congenital malformations during the 1986 and 1987 lambing season. Approximately 8.6% of 104 sheep in 1986, 63.4% of 164 in 1987, 11.3% of 44 in 1988, and 71.9% of 89 in 1989 from the Texas Agricultural Experiment Station at San Angelo tested were seropositive. The data indicate that CVV infections in sheep were widespread in Texas in 1981 and that the virus is enzootic in sheep at the Texas Agricultural Experiment Station in San Angelo, where the episode of congenital malformations had initially been reported in 1987.

Isolation and identification of a variant of bluetongue virus serotype 11 from a ram in a bluetongue outbreak in western Texas

A field strain of bluetongue virus was isolated from a blood sample of a ram during an outbreak of bluetongue in November 1985 in western Texas. In this bluetongue outbreak at least 25 of the 2,000 sheep were infected. Isolation was made by intravenous inoculation of 11-day-old embryonated chicken eggs. The serotype was identified as serotype 11 by serum neutralization tests. The genomic pattern on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) of the new isolate is similar to that of bluetongue virus prototype 11. Comparisons were also made with proteins labeled in vivo with [3H]leucine and separated by SDS-PAGE. We conclude that this virus belongs to serotype 11, with slight differences in both genome and protein electrophoretic patterns.

Feline immunodeficiency virus infects both CD4+ and CD8+ T lymphocytes

Monoclonal populations of feline T cells, derived from a specific-pathogen-free cat and expressing either the CD4 or CD8 surface antigen, were infected in vitro with two geographically distinct isolates of feline immunodeficiency virus (FIV). Both infected T-cell subsets exhibited decreased cell viability, expressed FIV-encoded proteins, and generated reverse transcriptase activity. All clones examined retained their original surface phenotype after infection. It appears, therefore, that both CD4+ and CD8+ T cells may be productively infected by FIV in vivo.

Comparison of cytopathic and noncytopathic isolates of bovine viral diarrhea virus by oligonucleotide fingerprinting

The molecular technique of RNA fingerprinting was used to characterize the genomes of 5 isolates of bovine viral diarrhea virus (BVDV): 2 viral pairs from the same animal, BVD-ILN/BVD-ILC and BVD-TGAN/BVD-TGAC, and the cytopathic viral prototype, BVD-NADL. Oligonucleotide patterns from the viruses were compared, and unique and overlapping oligonucleotides were identified. A comparison of the fingerprints indicated that the genome of each virus was distinguishable by the T1 RNase oligonucleotide fingerprinting technique. The greatest similarity observed was between oligonucleotides from BVD-ILC and BVD-ILN. Eighteen large oligonucleotides were conserved in all 5 BVDV isolates studied. We found that within a pair of BVDV, the cytopathic fingerprint was different from the noncytopathic fingerprint, indicating that cytopathic and noncytopathic BVDV may be distinct viruses.

Congenital malformations in sheep resulting from in utero inoculation of Cache Valley virus

Serologic evidence indicated that an episode of congenital abnormalities in sheep was caused by Cache Valley virus (CVV), a bunyavirus indigenous to the United States. To determine the teratogenic potential of CVV in sheep, fetuses were infected in utero between 27 and 54 days of gestation with an isolate (CK-102) obtained in 1987 from a sentinel sheep in San Angelo, Texas. The dams of these fetuses were euthanatized between 28 and 75 days after inoculation, and the fetuses were examined for malformations. Twenty-eight of 34 fetuses had congenital abnormalities, including arthrogryposis, hydranencephaly, mummification, reabsorption, and oligohydroamnion. Virus was isolated from the allantoic fluid of 11 of 17 fetuses euthanatized at less than 70 days of gestation. The virus-positive fetuses, which were all negative for CVV-neutralizing antibody, had lesions ranging from none to severe arthrogryposis and hydranencephaly. Virus was not recovered from the allantoic fluid of fetuses after 76 days' gestation when CVV-specific antibody could be detected in 5 of 8 fetuses examined. The 2 fetuses infected on days 50 and 54 of gestation appeared normal and 1 had antibody to CVV.

Detection of avian infectious bronchitis viral infection using in situ hybridization and recombinant DNA

A recombinant DNA probe with specificity for the 3' end of genomic RNA from the Ark 99 strain of infectious bronchitis virus (IBV) was found to hybridize with extracted RNA of three strains with the Ark serotype, as well as the Mass41, Holl52, Gray, JMK, Conn, Fla and SE17 strains of IBV. Viral infection was detected in the cytoplasm of chicken embryo kidney cells inoculated with Mass41, Ark99, SE17 or two recent field isolates of IBV using in situ cytohybridization and a biotinylated probe. In vivo infections were detected in individual cells of tracheas and lungs 2,4, and 6 days after inoculation of chicks with Mass41 and Ark99. In situ hybridization of Ark99 infected tissue sections using 32P-dATP labelled probe indicated that more viral replication was present in the trachea on day 4 than either days 2 or 6; whereas more viral RNA was found in the lungs on day 6 than days 2 or 4 after inoculation.

Characterization of avian reovirus strain-specific polymorphisms

Avian reoviruses have been associated with several pathologic conditions, but correlative relationships between genotypes and specific diseases have not been demonstrated. Six avian reoviruses (883, 176, 81-5, S1133, FC, and TX) were selected for this study, and a comparative study of the pathogenic properties of the viruses in chickens, following peroral and footpad inoculation, was carried out, along with a comparison of the electrophoretic mobility of viral genomic segments and viral proteins encoded by the gene segments. The pathogenic properties of the viruses were shown to be diverse, with three distinct pathotypes being defined: Pathotype I (883) caused only a syndrome that we have termed "transient digestive system disorder" (TDSD); Pathotype II (FC, TX, and S1133) caused only "viral arthritis syndrome" (VAS), whereas Pathotype III (176 and 81-5) caused both TDSD and VAS. Likewise, the genomes of the viruses were shown to be extremely polymorphic, with a maximum of five segments co-migrating between any two strains. Considerable variation in the electrophoretic mobility of the encoded proteins also was demonstrated with pronounced variation in the molecular size of the sigma 4 protein, the purported viral attachment protein, being evident. These results show that the genomes of avian reoviruses were extremely polymorphic, preventing correlation between genotypes and pathotypes. But these studies have provided us with the genetic elements needed to characterize the gene functions involved in viral pathogenesis.

Comparisons of the genomic RNA of Arkansas DPI embryonic passages 10 and 100, Australian T, and Massachusetts 41 strains of infectious bronchitis virus

The genomic ribonucleic acid (RNA) of Arkansas DPI at embryonic passages 10 and 100, Australian T, and Massachusetts 41 strains of infectious bronchitis virus (IBV) were compared using two-dimensional, 32PpCp-labeled oligonucleotide fingerprinting. The Arkansas DPI strain embryonic passage 10 was pathogenic for chickens and had one oligonucleotide not present in the attenuated passage 100. The remaining Arkansas DPI oligonucleotides had identical electrophoretic mobility. The fingerprint patterns of the Australian T, Massachusetts 41, and Arkansas DPI IBV genomes were dissimilar, thus indicating they were genetically distinct. The distinctive fingerprint patterns of these virus strains, all identified as IBV by other criteria, indicate considerable genomic variation. Fingerprinting is reliable and sensitive, and should be used in combination with other characterization methods for identifying and differentiating IBV strains.

Evidence that Cache Valley virus induces congenital malformations in sheep

An outbreak of congenital abnormalities occurred in sheep at San Angelo, Texas, between December 1986 and February 1987. Of 360 lambs born, 19.2% had arthrogryposis or other musculo-skeletal problems and hydranencephaly (AGH), and the total neonatal loss was 25.6%. In 1987, all ewes that were tested with AGH lambs had antibody to Cache Valley virus (CVV), whereas 62% of the ewes with normal lambs had CVV-specific antibody. Pre-colostral serum samples from AGH lambs had neutralizing antibody to CVV. An increase in prevalence of CVV-specific antibody, from 5% during the spring of 1986 to 63.4% during the winter of 1987, occurred during a time that included the gestation of these affected lambs, as well as a period of increased rainfall. The isolation of a CVV-related strain from a sentinel sheep in October 1987 confirmed the continued presence of this virus in the pasture where this outbreak occurred and provided a recent field strain for future studies.

Oligonucleotide fingerprint analysis of the genomes of two variants of bluetongue virus serotype 2 isolated in the U.S.A

The genome segments of two electrophoretically distinct variants of bluetongue virus (BTV) Serotype 2 (Ona A and Ona B) from the U.S.A. were analyzed by double-dimension gel electrophoresis of RNase T1 produced oligonucleotides. Segments 1, 4, 5, 6, 7 and 10 were examined individually after separation by SDS-PAGE; and Segments 2 and 3, and 8 and 9, which were difficult to resolve, were fingerprinted as pairs. The Ona A and Ona B strains appeared to be closely related since corresponding segments were comparable, sharing 53-89% of the large oligonucleotides counted. Since the strains with the Ona A electropherotype preceded Ona B infection in Florida, U.S.A. and since Ona A was indistinguishable from the early African isolate of Serotype 2, Ona B was thought to be a variant of an Ona A strain. These data tend to support the hypothesis that Ona B could have evolved from Ona A as the result of point mutations or genetic drift.

Genotypic transitions among bluetongue viral isolates from domestic ruminants in Colorado during 1981-1984

Two predominant electropherotypes of bluetongue virus (BTV) serotype 11 isolates from cattle during a 1981-1984 field study in eastern Colorado were characterized. The genomes of strains isolated from the first 2 years of the study had 1 predominant electropherotype (CO81), with the exception of 1 isolate that differed only in the migration of segment 3. A second electropherotype (CO83), with differences in the migration of 4 segments, coexisted in the same region during 1983 and 1984 with strains having the CO81 RNA profile. The genomes of CO81 and CO83 were also distinguishable from those of the US prototype of BTV 11. Analysis of the polypeptides of representative strains of each electropherotype by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the proteins were very similar. The occurrence of the CO81 electropherotype was apparently the result of multiple viral infections since the positions of 7 segments had faint second bands and single-banded variants were isolated after serial plaque purifications. In addition, protein 7 of 1 of the CO81 isolates and protein 7 of the single-banded variant differed as shown by reverse phase-high performance liquid chromatography of 35S-methionine-labeled tryptic peptides.

Comparisons of the structural proteins of avian infectious bronchitis virus as determined by western blot analysis

The antigenic diversity of ten strains of avian infectious bronchitis virus (IBV) was examined by Western blot analyses using polyclonal antisera specific for the Massachusetts 41 (M41), Gray, Arkansas DPI (Ark DPI), Connecticut (Conn) and Australian T (Aust T) serotypes. Although antigenic variation was found in all three structural viral proteins, the matrix protein appeared to be antigenically the most highly variable. Four distinct antigenic groups, which did not correspond to virulence or pathotype, could be defined according to the variations observed in the matrix protein. Somewhat less variation was seen in the spike polypeptide. The only variation in the nucleocapsid protein was indicated by the lack of a detectable reaction between the Aust T antiserum and the Ark DPI nucleocapsid protein. Antisera made against M41 had the broadest reactivity while antisera against Aust T, the only strain tested which was exotic to the U.S.A., had the greatest specificity.

Tissue tropism and target cells of bluetongue virus in the chicken embryo

In situ cytohybridization was used to determine the tissue tropism and target cells for replication of bluetongue virus (BTV) in the developing chicken embryo. Hybridization with a biotinylated probe specific for segment 3 of BTV serotype 17 detected viral replication in embryos inoculated with U.S. serotypes 2, 10, 11, 13, and 17 or sheep blood containing a BTV field strain. At the final stages of infection, when the embryos were hemorrhagic, viral infection could consistently be detected in the brain, kidney, spinal cord, heart, lung, and liver, with the brain and kidney most severely affected. Other tissues, such as the retina, skin, tongue, and intestinal villi, also supported viral replication in some embryos. Greater concentrations of virus tended to be localized within epithelial cells, such as those lining the kidney tubules and tertiary bronchi of the lungs. Kinetics studies with BTV serotypes 11 and 17 and a field strain indicated that within 24 h after inoculation, viral replication occurred initially in the brain and kidney. By 48 h, viral replication was also detected in the lungs, heart, and spinal cord, with the liver being severely infected by 72 h. Low levels of hybridization could be detected in embryos infected with epizootic hemorrhagic disease virus, which is antigenically related to BTV.

Two electropherotypes of bluetongue virus serotype 2 from naturally infected calves

The first isolation of bluetongue virus (BTV) serotype 2 in the U.S.A. was in 1982 from a sentinel herd of cattle at Ona, Florida. Electrophoretic analysis of genome RNA revealed that all 16 serotype 2 isolates obtained from this focus of infection had one of two electropherotypes (designated Ona A and Ona B). All genome segments of Ona A and Ona B had detectable differences in electrophoretic mobility, with major differences noted for segments 1, 4, 5, 7, 8, 9 and 10. Electrophoretic comparison revealed that Ona A was indistinguishable from the African serotype 2 prototype isolated 23 years earlier. In 1983, Ona B, in the apparent absence of Ona A, was isolated from two additional cattle herds in Florida. These results suggest that Ona B may be a variant of Ona A that evolved as a result of mutation or reassortment with another BTV strain, and may be better adapted to the selective pressures found in southern Florida. Comparison of the electropherotypes of Ona B with two Florida isolates of serotype 13 and 17 and the prototypes of BTV 10, 11, 13 or 17 produced no evidence for reassortment between Ona A and any of these strains as the possible origin of Ona B.

Potentiation of antibody responses by specific IgM: specificity and thymus dependency

Modulation of antibody responses induced by IgM directed against the immunogen was investigated. When IgM directed against ox erythrocytes (ORBC) was given together with trinitrophenyl (TNP)-ORBC, the subsequent antibody response to the carrier, ORBC, as well as the response to the hapten, TNP, was potentiated. In contrast, IgG with carrier specificity inhibited both responses. The hapten-specific potentiation was found in both direct and indirect plaques, and was antigen-dose dependent, i.e., no potentiation was found with the lowest antigen doses. The response to 2,4-dinitrophenyl (DNP)-labeled proteins was potentiated by a monoclonal IgM with specificity for the hapten. The effects were observed both in primary and secondary responses. One strict requirement for IgM potentiation to occur was observed. The determinant against which potentiation was achieved had to be physically linked to the determinant against which the IgM was directed, be it hapten or carrier determinants. Thus, irrelevant IgM-antigen complexes were incapable of potentiating the responses. Similar specificity requirements were found for IgG induced suppression of antibody responses. Experiments with nude mice and their euthymic littermates showed that IgM potentiation of antibody production is T-cell dependent. Furthermore, passive transfer of carrier-primed spleen cells together with antigen challenge suggests that IgM potentiation of secondary antibody responses is dependent on specific carrier-primed immune T cells.