Efficient production of single-stranded DNA as long as 2 kb for sequencing of PCR-amplified DNA

A modification of the asymmetric PCR method is described, which reliably facilitates sequencing of PCR-amplified DNA. This procedure produces single-stranded DNA fragments as long as two kilobases that are suitable for dideoxy DNA sequencing. First, a PCR for double-stranded DNA is preformed under optimal conditions (double-stranded PCR). Then, a 5-10-microliters fraction of the double-stranded PCR and a single primer are used to generate single-stranded DNA in a separate PCR (single-stranded PCR). The concentration of the single primer are used to generate single-stranded DNA in a separate PCR (single-stranded PCR). The concentration of the single primer is approximately 0.4 microM. Usually 15 to 25 cycles of single-stranded PCR are optimal to produce single-stranded DNA for four to eight sequencing reactions. The single-stranded DNA is purified by centrifugal ultrafiltration and used directly in dideoxy sequencing. This method was employed to produce high-quality single-stranded DNA templates from a variety of organisms for efficient DNA sequencing of PCR-amplified DNA.

The hemagglutinin/esterase gene of human coronavirus strain OC43: phylogenetic relationships to bovine and murine coronaviruses and influenza C virus

The complete nucleotide sequences of the hemagglutinin/esterase (HE) genes of human coronavirus (HCV) strain OC43 and bovine respiratory coronavirus (BRCV) strain G95 were determined from single-stranded cDNA fragments generated by reverse transcription of virus-specific mRNAs and amplified by polymerase chain reaction. An open reading frame of 1272 nucleotides was identified as the putative HE gene by homology to the bovine coronavirus HE gene. This open reading frame encodes a protein of 424 amino acids with an estimated molecular weight of 47.7 kDa. Ten potential N-linked glycosylation sites were predicted in the HE protein of HCV-OC43 while nine of them were present in BRCV-G95. Fourteen cysteine residues were conserved in the HE proteins of both viruses. Two hydrophobic sequences at the N-terminus and the C-terminus may serve as signal peptide and transmembrane anchoring domain, respectively. The predicted HE protein of HCV-OC43 was 95% identical to the HEs of BRCV-G95 and other bovine coronaviruses, and 60% identical to the HEs of mouse hepatitis viruses. Phylogenetic analysis suggests that the HE genes of coronaviruses and influenza C virus have a common ancestral origin, and that bovine coronaviruses and HCV-OC43 are closely related.

Comparison of hemagglutinating, receptor-destroying, and acetylesterase activities of avirulent and virulent bovine coronavirus strains

Hemagglutinating and acetylesterase functions as well as the 124 kDa glycoprotein were present in the highly cell-culture adapted, avirulent bovine coronavirus strain BCV-L9, in the Norden vaccine strain derived from it, and in 5 wild-type, virulent strains that multiplied in HRT-18 cells but were restricted in several types of cultured bovine cells. The BCV-L9 and the wild-type strain BCV-LY-138 agglutinated chicken and mouse erythrocytes. The acetylesterase facilitated break-down of the BCV-erythrocyte complex with chicken but only to a minimal extent with mouse erythrocytes in the receptor-destroying enzyme test. Purified preparations of the vaccine and the wild-type strains agglutinated chicken erythrocytes at low titers and mouse erythrocytes at 128 to 256 times higher titers whereas receptor destroying enzyme activity was detectable only with chicken erythrocytes. When wild-type strains were propagated in HRT cells at low passage levels, they produced 5 x 10(5) to 4.5 x 10(6) plaque forming units per 50 microliters which agglutinated erythrocytes from mice but not from chickens. Diisopropylfluoro-phosphate moderately increased the hemagglutination titers, but completely inhibited the receptor destroying enzyme of purified virus of all strains. It had virtually no influence on the plaque-forming infectivity of the different BCV strains. The acetylesterase of strain BCV-L9 reacting in the receptor-destroying enzyme test was stable for 3 h at 37 and 42 degrees C. It was inactivated within 30 min at 56 degrees C while the hemagglutinin function of this strain was stable for 3 h at 37, 42, and 56 degrees C, but it was inactivated at 65 degrees C within 1 h.

The hemagglutinin/esterase glycoprotein of bovine coronaviruses: sequence and functional comparisons between virulent and avirulent strains

The entire nucleotide sequences of the hemagglutinin/esterase (HE) genes specified by the highly virulent strain LY138 and the avirulent strain L9 of bovine coronavirus (BCV) were determined. These sequences were compared with recently published sequences of the HE genes of the Quebec and Mebus strains. A large open reading frame of 1272 nt encoding a protein of 424 amino acid residues was predicted. The putative esterase active site was conserved in the virulent and avirulent BCV strains, indicating that this domain is probably not a determinant for BCV virulence. Four amino acid substitutions occurred between the HE proteins of BCV-L9 and BCV-LY138 (leu to Pro at 5, Leu to Val at 103, Ser to Pro at 367, and Thr to Asn at 379). Monoclonal antibodies specific for the HE glycoprotein inhibited the hemagglutination and acetylesterase activities of BCV-L9, but showed no inhibitory effect on the acetylesterase activity of BCV-LY138. These results suggest that at least one epitope is located proximal to one of the three strain-specific amino acids. Four S-specific monoclonal antibodies inhibited hemagglutination but not acetylesterase activity of BCV-L9, implying that the S glycoprotein can promote hemagglutination of chicken erythrocytes in addition to the HE glycoprotein.

Monoclonal antibodies differentiate between the haemagglutinating and the receptor-destroying activities of bovine coronavirus

A relatively simple and sensitive method is described which enables the effect of monoclonal antibodies (MAbs) on the receptor-destroying enzyme (RDE) and the haemagglutination (HA) activity of bovine coronavirus (BCV) to be analysed in one assay. A lysate of HRT-18 cells infected with the L9 strain of BCV was found to have a higher RDE:HA ratio than purified virus. At 4 degrees C the lysate induced an HA pattern which completely disappeared upon raising of the temperature to 37 degrees C. This L9-infected cell lysate was used to determine the HA inhibition (HAI) titres of MAbs directed against the surface glycoproteins S and HE of BCV. Thereafter, the test plates were incubated at 37 degrees C to enable the ability of the MAbs to prevent elution of virus from BCV-erythrocyte complexes to be assessed. No inhibition of RDE was detectable with MAbs against glycoprotein S, which had HAI titres ranging from 1:16 to 1:128. On the other hand, MAbs directed against glycoprotein HE had similar HAI titres, but they inhibited elution of 8 HA units of BCV at titres of up to 1:65,000.

Detection and strain differentiation of Chlamydia psittaci mediated by a two-step polymerase chain reaction

Specific and sensitive amplification of major outer membrane protein (MOMP) gene DNA sequences of Chlamydia psittaci was achieved in a two-step polymerase chain reaction. First, oligonucleotide primers specific for 5' and 3' nontranslated regulatory regions of the MOMP gene were used in a polymerase chain reaction to amplify a DNA fragment of approximately 1,400 bp. A portion of this DNA fragment was amplified in a second reaction using a degenerate oligonucleotide primer specific for a DNA sequence contained within the 1,400-bp DNA fragment and one of the first-step primers. This method detected 10 cognate chlamydial genomes. C. psittaci MOMP genes from two avian strains and from mammalian serovars 1, 7, and 8 were amplified and analyzed by restriction endonuclease digestion. MOMP genes from mammalian serovars 2 through 6 and 9 and from strains of C. trachomatis and C. pneumoniae could not be amplified. Restriction endonuclease analysis with HaeIII indicated a close relationship between C. psittaci strains of avian and mammalian serovar 1 lineage, while those of mammalian serovars 7 and 8 exhibited distinct restriction patterns. DNA sequences corresponding to the mammalian serovar 1-wild type parakeet MOMP genotype of C. psittaci were detected in two of seven milk samples from cases of bovine mastitis.

Comparison of bovine coronavirus (BCV) antigens: monoclonal antibodies to the spike glycoprotein distinguish between vaccine and wild-type strains

Monoclonal antibodies (MAbs) against two major structural proteins of the cell-adapted Mebus strain of bovine coronavirus (BCV-L9) were produced and characterized. Seven MAbs reacted with the peplomeric glycoprotein, gp 100/S, while three MAbs reacted with the nucleoprotein p53/N in Western blot analysis of BCV polypeptides. MAbs to gp 100/S reacted with discontinuous epitopes of gp 100/S in Westerns under mild but not under standard denaturing conditions. In contrast, MAbs to p53/N reacted in both types of Westerns, and those epitopes were thus continuous. MAbs to p53/N failed to neutralize BCV infectivity, while 4 MAbs to gp 100/S neutralized BCV effectively. Cross reactivity of MAbs to gp 100/S specified by five virulent wild-type strains and two high passage, cell-culture-adapted strains in mildly denaturing Westerns and neutralization assays indicated that two epitopes were conserved in all seven strains, while two epitopes of the avirulent strains were not detected in the wild-type strains. Non-neutralizing MAbs of gp 100/S reacted with all seven strains in Westerns with the exception of one MAb that was specific for the highly cell-adapted strain BCV-L9.

Comparison of the nucleotide and deduced amino acid sequences of the S genes specified by virulent and avirulent strains of bovine coronaviruses

The entire nucleotide sequences of the spike glycoprotein (S) genes of the highly virulent bovine coronavirus (BCV) strain BCV-LY138, the avirulent BCV-L9 and related Norden Vaccine (BCV-Vaccine) strains were determined using the polymerase chain reaction (PCR) to amplify cDNAs obtained by reverse transcription of viral RNA, and to produce single strand cDNAs for DNA sequencing. The S gene sequences of these viral strains were compared with those of recently published strains BCV-Mebus, BCV-Quebec, and BCV-F15. An open reading frame of 4092 nucleotides, encoding a protein of 1363 amino acid residues, was found in all six strains. Frameshifts and insertions or deletions were not observed except for the BCV-F15. The S gene sequences were more than 98% conserved overall inspite of different origins of the six viruses. There were 45 to 56 nt differences between the virulent and avirulent groups while there were 6 to 14 nt differences among four avirulent strains. Comparison of the deduced amino acid sequences indicated that the S proteins had typical properties of membrane glycoproteins. Nineteen N-linked glycosylation sites were predicted in five strains, and 18 of them were conserved in the avirulent strain BCV-L9. The sequence KRRSRR at the predicted proteolytic cleavage site was identified in five strains while the sequence KRRSVR was found in BCV-F15. Substitutions of few amino acids in the putative fusogenic domains and two prolines at 507 and 567 in the antigenic domains may cause altered immunogenic and other functional properties of the S proteins specified by the virulent and avirulent BCV strains. Nine amino acid substitutions between the virulent and avirulent groups may correlate with BCV virulence.

Infectious mechanisms of enteropathogenic bovine coronaviruses

The primary disease mechanism in infections of calves with enteropathogenic bovine coronaviruses (BCV) involves cytocidal interaction with differentiated enterocytes. Cytopathic expression of BCV infection of cultured cells depends on the viral strain and the cell type. BCV-induced cell fusion occurred under neutral or alkaline but not acidic conditions. Lysosomotropic bases did not significantly reduce virus yield, suggesting that productive BCV infection was not mediated by endocytosis but rather by direct fusion of the viral envelope with the plasma membrane. Trypsin cleavage of the 185 kDa S glycoprotein into 100 and 110 kDa subunits was required for cell fusion and productive infection of cultured BFS cells with the cell-adapted, avirulent strain BCV-L9. This strain has a wide host cell range in vitro while several wild-type, virulent strains were restricted to HRT-18 cells. Antigenic and genomic comparisons of the avirulent and virulent strains revealed corresponding differences. Some monoclonal antibodies against S reacted with both virulent and avirulent strains, while others reacted only with the avirulent strain BCV-L9. Nucleotide sequences of the S genes indicated that amino acid substitutions in cleavage sites, antigenic regions, and putative fusion domains occurred and differentiated BCV strains.

Bovine coronavirus antigen in the host cell plasmalemma

Expression of bovine coronavirus (BCV) antigen in the plasmalemma of epithelioid human rectal tumor (HRT-18) and fibroblastic bovine fetal spleen (BFS) cell lines was traced by immunofluorescence and immunoelectron microscopy facilitated by colloidal gold. Cytoplasmic fluorescence was first observed at 12 hr postinfection (h.p.i) in infected HRT-18 cultures. This fluorescence coincided with the appearance of cell surface antigen reacting with colloidal gold-labeled antibodies to BCV antigens. At 24 h.p.i the amount of viral antigens at the surface of HRT-18 had increased, although cytoplasmic fluorescence remained constant. Infected BFS cells but not HRT-18 cells formed polykaryons when incubated in the presence of trypsin. One viral antigen in the plasma membrane of BFS cells was thus identified as the S glycoprotein with a fusion domain. In contrast to HRT-18 cells, the overall amount of BCV antigens at the surface of BFS cells remained constant after the onset of fusion. Analysis of the labeling characteristics established that the gold-marked-sites represented de novo expression of BCV antigen in the plasma membrane of infected cells.

Scanning electron microscopic characterization of bovine coronavirus plaques in HRT cells

The ecology of cytopathic expression of bovine coronavirus (BCV) in HRT-18 cells was analyzed within virus-induced plaques by scanning electron microscopy. Virus replication was cytocidal for many HRT-18 cells, a function enhanced in the presence of trypsin. A monolayer of cells remained that imparted a characteristic turbidity to the plaque. These structurally normal, lysis-resistant cells did not stain with fluorescent antibodies specific for BCV antigens, failed to adsorb virus particles or mouse erythrocytes in contrast to the susceptible cells. The survival of cells in the plaque interior reflects a non-productively infected population with evidence of viral persistence.

Antibody response to epitopes of chlamydial major outer membrane proteins on infectious elementary bodies and of the reduced polyacrylamide gel electrophoresis-separated form

Approximately 60% of the outer membrane of chlamydial elementary bodies (EBs) consists of the major outer membrane protein (MOMP) that has structural and metabolic functions. The antigenic properties of MOMPs from mammalian strains of serovars 1 and 2 and an avian strain of Chlamydia psittaci were analyzed. Polyclonal-monospecific antisera (PMAs), one monoclonal antibody (MAb), and polyclonal antisera (PAs) were produced against reduced polyacrylamide gel electrophoresis-separated MOMPs and against infectious EBs. Three PMAs and the MAb, which were induced by reduced polyacrylamide gel electrophoresis-separated MOMPs, reacted strongly in Western blot (immunoblot) assays with MOMPs of serovar 1 and 2 strains as well as with that of the avian strain 6BC, and two of these PMAs reacted weakly (dilution, 1:20) with the MOMP of strain LGV-2. The third PMA and the MAb against the MOMP of the serovar 2 strain did not react with the MOMP of LGV-2. Four PAs were produced against infectious EBs of the serovar 1 strain. One of these PAs reacted with the homologous MOMP and that of the avian strain 6BC but did not recognize MOMPs of other chlamydial strains. Three of the PAs reacted with MOMPs of homologous strains only and failed to recognize MOMPs of avian, serovar 2, and LGV-2 strains. Five PAs induced against infectious EBs of the serovar strain 2 reacted only with the MOMPs of the homologous strains and failed to recognize MOMPs of other strains of chlamydiae. Consequently, MOMPs of C. psittaci strains possess genus-, species-, and serovar-specific epitopes whereby the immune response to serovar-specific epitopes of MOMP predominate when infectious EBs are used for immunization.

Initial events in bovine coronavirus infection: analysis through immunogold probes and lysosomotropic inhibitors

The early events in the infection of human rectal tumor cells by bovine coronavirus were investigated by colloidal gold-mediated immunoelectron microscopy and by analysis of the effect of lysosomotropic weak bases on virus yield. Electron microscopic studies revealed sites of fusion between the virus envelope and the plasmalemma but fusion events along intracellular membranes were not observed despite extensive searches. Virion-antibody-colloidal gold complexes were, in fact, endocytosed by synchronously infected cells. These complexes were apparently non-infectious, and they accumulated in vacuoles that resembled secondary lysosomes. Exposure of cells to ammonium chloride or to methylamine during the first hour of infection had little inhibitory effect on the production of infectious virus. Chloroquine treatments were inhibitory but this effect depended on relatively late events in the infectious process. The chloroquine inhibitory step blocked infection of virus absorbed to cells that were exposed to buffers in the pH range of 4.4 to 8.4. These findings indicate that BCV penetrates its host cell by direct fusion with the plasmalemma and does not require an acidic intracellular compartment for infectious entry.

Structural proteins of bovine coronavirus strain L 9: effects of the host cell and trypsin treatment

The polypeptide profile of the cell-adapted strain of bovine coronavirus (Mebus BCV-L 9) is remarkably affected by the host cell and trypsin. We compared the structural proteins of virus purified from different cell lines and found cell-dependent differences in the virus structure. BCV was purified from four clones of human rectal tumour cells (HRT-18): 3F3, D2, 3E3, and 4B3. The structural profiles of BCV propagated in clones 3E3 and 3F3 were identical, consisting of proteins with molecular weights of 185, 160, 140, 125, 110, 100, 52, 46, 37, 31-34, and 26-28 kilodaltons (kd). BCV purified from clone D2 lacked the 100 kd species, and clone 4B3 yielded virus lacking the 46 kd protein. We compared the structures of BCV propagated in HRT-18 cells [BCV(HRT-18)] and virus raised in bovine fetal spleen cells [BCV(D2 BFS)]. The concentration of the 185 kd protein was higher in BCV (D2BFS), and it also contained a 200 kd species. Protein profiles of in vitro trypsin treated and untreated BCV(HRT-18) differed only under reducing conditions, suggesting that trypsin cleavage sites are located within disulfide-linked regions of affected proteins. Propagation of BCV in D2 BFS cells in the presence of trypsin resulted in cleavage of the 185 kd protein and a concomitant increase of the 100 kd protein. Activation of the fusion function probably depends on this cleavage process because fusion of BCV-infected D2 BFS cells is trypsin dependent.

Analysis of cell fusion induced by bovine coronavirus infection

Polykaryon formation in bovine fetal spleen (BFS) cells infected with bovine coronavirus L9 occurred only in media supplemented with trypsin. A single 1 to 2 h trypsin treatment 10 h and later after infection induced formation of polykaryons. Trypsin treatment at pH 7.5 and 8.0 induced polykaryons while treatments at lower or higher pH levels did not. Cell fusion activity was partially suppressed by the presence of antibody.

Specific interaction of bovine IgG1 and IgG2 subclasses with different chlamydial antigens

Antigens of the immunotype 1 strain B-577 of Chlamydia psittaci, which were separated by SDS-PAGE and electrophoretically transferred to nitrocellulose membranes were used to probe sequential serum samples of cattle with experimentally induced or naturally occurring chlamydial infections. Applying IgG1- and IgG2-specific markers in an enzyme immunoassay procedure, a predominance of IgG2 reactions with different proteins was determined. The interaction of IgG1 with antigens such as the genus-specific lipopolysaccharide and the major outer membrane protein was usually limited to periods immediately following overt clinical disease. Some other antigens like the 60,000 and 62,000 D proteins, for example, were recognized by both subclasses over the entire period of investigation. This indicates that it may be possible to determine the phase of infection through analysis of the IgG1 and IgG2 responses with the Western blot technique. The different IgG1 and IgG2 responses of cattle infected with different strains of Chlamydia psittaci as well as the diverse reactions of cattle from different herds with naturally occurring chlamydial infections further indicate that it may be feasible to distinguish the strains causing these chlamydial infections using different antigens in the Western blot technique. The results obtained by this method may have implications for the production of a subunit vaccine as well as for serodiagnostic purposes.

Dominance of Chlamydia psittaci-specific IgG2 subclass in the humoral immune responses of naturally and experimentally infected cattle

Indirect enzyme-linked immunosorbent assays were applied to differentiate Chlamydia (C.) psittaci-specific IgG1 and IgG2 levels in 143 individual serum samples from cattle with naturally occurring chlamydial infections and in 190 sequential serum samples from 26 experimentally infected pregnant cows, calves, and a bull. The mean IgG1:IgG2 ratio of naturally infected cattle was 1:4 indicating a significant (p less than 0.001) IgG2 dominance. Similar ratios were detected in the experimentally infected cattle. The dominance of IgG2 was independent of breed, sex, and age. Twenty-nine cattle had significant immunoglobulin levels to both C. psittaci and Coxiella (C.) burnetii simultaneously. The predominance of C. psittaci-specific IgG2, in contrast to the predominance of C. burnetti-specific IgG1 detected in these same individual serum samples under identical conditions, indicates that the ability to preferentially produce either IgG1 or IgG2 was not limited in these individual cattle. A transient yet significant IgG1 response was also developed in cows following chlamydia-induced abortions (immunotype 1) or in cattle infected with the polyarthritis-serositis-encephalomyelitis agents (immunotype 2). IgG1 levels decreased faster than IgG2 levels. These findings have diagnostic implications and identify the need for determining the immunoglobulin classes and subclasses of the humoral immune responses of animals and man to chlamydial infections.

Isolation of a retrovirus from the American bison and its relation to bovine retroviruses

Tissue samples were removed at necropsy from five American bison (Bison bison) with clinical signs of a disease resembling malignant catarrhal fever (MCF). Using cell-associated virus techniques, attempts were made to isolate viruses from these tissues by culturing them directly or by co-culture with bovine fetal cells. Among the viruses isolated was one which was syncytiogenic and multiplied in bovine fetal spleen cells and remained highly cell-associated. The presence of reverse transcriptase activity indicated that it was a retrovirus. Also, it had antigenic cross activity with bovine syncytial virus, but not with bovine leukemia or bovine maedi-like retroviruses. We do not attribute a direct causative role of this retrovirus to MCF, but indirect relationships are possible.

Problems concerning the taxonomy of the 'Movar-type' bovine herpesviruses

The inconsistency in naming and labeling bovine herpesviruses (BHVs), other than BHV types 1 and 2 (BHV-1 and BHV-2), found in the literature is reviewed. To resolve the confusion and misunderstanding caused by the use of BHV-3, BHV-4 and BHV-5 for the same kind of BHVs, the most used label BHV-4 is proposed for designating Movar-type BHVs (which also were named 'orphan viruses' or 'cytomegaloviruses').

Bovine chlamydial abortion: serodiagnosis by modified complement-fixation and indirect inclusion fluorescence tests and enzyme-linked immunosorbent assay

Sequential serum samples from 11 cows experimentally inoculated with different abortigenic strains of Chlamydia psittaci were tested by a modified complement-fixation (MoCF) test, an indirect inclusion fluorescence antibody (IIFA) test, and an enzyme-linked immunosorbent assay (ELISA). One of these cows was not pregnant, another gave birth at term to a healthy calf, and all the others prematurely delivered infected dead calves or weak live calves. The results achieved with these tests on sera of 3 of the cows were compared with those from the previously used standard complement-fixation (CF) test. Six of 11 cows had detectable preinoculation titers between 1:8 and 1:16 when tested by the MoCF test, yet preinoculation titers were not detected by CF. In contrast, 9 of 11 and 10 of 11 preinoculation samples had detectable chlamydia-specific antibodies when examined by the IIFA test and the ELISA, respectively. The preinoculation IIFA titers ranged from 1:8 to 1:64, and the ELISA optical density values varied from 0.150 to 0.450. All cows responded with significant increases in antibody levels detected by the MoCF test, the IIFA test, and ELISA after they were experimentally inoculated and after they aborted or delivered infected calves. Overall, the dynamics of the antibody responses were found to be similar with the 3 different serologic techniques. When cows aborted later than 36 days after they were inoculated, the antibody response was biphasic, whereby the more pronounced responses occurred after the abortion occurred. The nonpregnant cow and the cow that delivered a healthy calf at term had only one phase of increasing and decreasing titers directly after they were inoculated.