Detection of IgA against Epstein-Barr virus BZLF-1 replication activator (ZEBRA) in sera of nasopharyngeal carcinoma patients with a recombinant ZEBRA protein

BACKGROUND

Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC). An EBV-encoded immediate-early antigen, BZLF-1 replication activator (ZEBRA) initiates EBV replication and expression in all NPC tumors. In this study, we investigated whether immunoglobulin A (IgA) against ZEBRA is present in the sera of patients with NPC, and whether it was able to be determined by enzyme-linked immunosorbent assay (ELISA) using a recombinant ZEBRA prepared from Escherichia coli.

METHODS

A polymerase chain reaction-amplified cDNA fragment of the ZEBRA gene was inserted into the expression vector of E coli under the control of an IpL promoter. E coli bacteria containing the CI857 gene served as host to overexpress the ZEBRA protein by heat induction. Recombinant ZEBRA was collected by mechanical disruption of the bacteria, purified by column chromatography, and analyzed by SDS-PAGE and Western blot assay using sera from NPC patients. The recombinant ZEBRA was used to develop the ELISA to detect IgA against ZEBRA.

RESULTS

The amount of ZEBRA produced comprised 30% of total E coli protein. Western blot assay confirmed that affinity of the recombinant ZEBRA to IgA antibody was preserved. IgA against ZEBRA was shown to be positive by ELISA in 36 of 40 NPC sera, but in only nine of 55 patients with other head and neck malignancies, and two of 35 normal individuals. For serologic diagnosis of NPC, the sensitivity of IgA/ZEBRA detected by ELISA was 90% and the specificity was 87.4%.

CONCLUSIONS

A recombinant ZEBRA was produced at high levels in E coli and retained affinity to IgA against ZEBRA. The recombinant ZEBRA was successfully used to develop an ELISA for the detection of IgA against ZEBRA. The high sensitivity and specificity of IgA against ZEBRA show that the ELISA is feasible for serologic diagnosis of NPC.

Molecular cloning and analysis of a HSP (heat shock protein)-like 42 kDa antigen gene of Mycoplasma hyopneumoniae

The recombinant clone expressing the 42 kDa protein (P42) of Mycoplasma hyopneumoniae in Escherichia coli was analyzed. The 4.4 kb HindIII-Xmal DNA fragment expressing the p42 gene product encodes three ORFs: p42 and p16 in the forwarding strand, p24 in the reverse strand. Sequence comparisons revealed that p42 could be part of a p65 gene, and has 62% identities with Mycoplasma genitalium HSP70 gene and 56% identities with Bacillus subtilis dnaK gene; p16 and p24 genes share 73% and 47% identities with Erysipelothrix rhusiopathiae dnaJ gene and Pseudomonas fluorescens uvrC gene, respectively. Further analysis demonstrated that P42 is indeed a heat shock protein and the monospecific antibodies against P42 can block the growth of Mycoplasma hyopneumoniae.

Cloning and expression of an antigenic domain of glycoprotein gE of pseudorabies virus in Escherichia coli and its use as antigen in diagnostic assays

Use of a combination of an effective gE gene-deleted pseudorabies virus (PRV) vaccine with a companion diagnostic kit for PRV glycoprotein gE has proven successful in several pseudorabies-eradication programs. To produce a large quantity of functional gE protein for development of a PRV-gE diagnostic kit, an Escherichia coli expression system containing the distal region of the PRV-gE gene of a PRV strain CF was constructed. The expressed protein contained 134 amino acids of gE protein (amino acids 77-210) fused to a 19-amino acids tag containing 6 histidine residues. After induction, a truncated PRV-gE polypeptide of 18-kd was expressed to about 20% of the total E coli proteins. Results of immunoblot analysis indicated that this E coli-produced PRV-gE protein reacted specifically with serum from PRV-hyperimmunized pigs and from field PRV-infected pigs, but not with serum samples from specific-pathogen-free pigs or pigs inoculated with gE-deleted PRV vaccine. These data indicate that, although the recombinant gE protein is produced in E coli, it still retains the antigenicity of the viral gE glycoprotein. Comparison between the recombinant gE protein, using immunoblot analysis with a commercial gE ELISA containing natural PRV-gE protein, revealed comparable test performance. This finding indicated that recombinant gE protein produced by E coli can be used for development of a companion serologic assay for a PRV-gE gene-deleted vaccine.

Molecular cloning of cDNA coding for the 68 kDa allergen of Penicillium notatum using MoAbs

To characterize the 68 kDa allergen of Penicillium notatum (also known as P. chrysogenum), a molecular antibody (MoAb) (P40) was previously generated. For cDNA cloning, three more MoAbs (3F, 5A3, 5G2) were generated in the present study. A mixture of all the four MoAbs was used in cloning of the gene coding for the 68 kDa allergen from a lambda gt11 cDNA library of P. chrysogenum. A cDNA clone (A6) with DNA insert of about 0.5 kb which encodes for the 3'-terminal nucleotide sequence of the 68 kDa allergen was obtained. The cloned sequence contained two putative N-glycosylation sites. The reduction in molecular weight from 68 to 62 kDa in immunoblotting after treatment of the crude extract of P. notatum with N-glycosidase F indicates that the 68 kDa allergen is a glycoprotein. Nucleotide sequence determination showed that 188 (54%) of the 348 nucleotides of the cDNA sequence obtained were identical to the same region of the nucleotide sequence of the beta-N-acetylglucosaminidase gene of Candida albicans. Although the cDNA clone obtained did not encode the full-length gene of the 68 kDa allergen, polypeptide expressed from the A6 cDNA showed positive immunological reactivities to all four MoAbs used in the cloning experiment and to IgE antibodies in sera of asthmatic patients. There was a loss of immunoblotting activity to the 68 kDa component after absorption of MoAb P40-containing culture supernatant with filters blotted on plaque lawns of cDNA clone A6. Moreover, the immunoblotting activity remained when the MoAbs affinity-purified with filters containing polypeptides encoded by the cDNA insert of clone A6 were used.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the Epstein-Barr virus DNA polymerase in Escherichia coli for use as antigen for the diagnosis of nasopharyngeal carcinoma

Epstein-Barr virus (EBV) encoded DNA polymerase (POL) was cloned and over-expressed in Escherichia coli. Western blot analysis confirmed the presence of antibody to this POL protein in sera from nasopharyngeal carcinoma (NPC) patients. By Western blot analysis, moderate to high concentration of IgG POL-specific antibodies were present in 43 of 48 NPC sera and only 4 of 48 healthy, seropositive controls. The POL-specific IgG antibodies appear as early as stage I of NPC, suggesting that the recombinant POL protein can be a useful diagnostic marker for early diagnosis of the disease. It was also found that human sera containing high titer of cytomegalovirus (CMV) antibodies or herpes simplex virus type 1 (HSV-1) antibodies did not cross-react with the recombinant EBV POL, despite the homology shared by DNA polymerase proteins of these viruses.

Rapid purification of antiserum against Mycoplasma hyopneumoniae by an efficient absorption method

A simple and efficient method for the removal of unwanted cross-reactive antibodies has been developed. The antiserum purification method was based on treatment of the antiserum with both sonicated extracts and boiling extracts of the Escherichia coli host cells used in immunoscreening the lambda EMBL3 library. We have demonstrated unambiguously that through this simple treatment, the rabbit anti-Mycoplasma hyopneumoniae antiserum can be effectively purified so that the amount of antibodies cross-reacted with Escherichia coli lysate proteins is drastically reduced. Compared with the traditional absorption methods, which require the chemical coupling of an absorbing agent to an insoluble support, and affinity purification methods, which have harsh denaturing condition, this method should greatly facilitate a successful immunoscreening experiment.

Comparison of Mycoplasma hyopneumoniae strains by serologic methods

Six field strains of Mycoplasma hyopneumoniae isolated from pneumonic lungs of pigs, reference strains 11 and J of M hyopneumoniae, Ms 42 strain of Mycoplasma flocculare, and BTS 7 strain of Mycoplasma hyorhinis were compared serologically, using hyperimmune antisera produced in rabbits. All strains of M hyopneumoniae were closely related as determined with the disk growth-inhibition test; however, differences in zone sizes indicated that some antigenic heterogeneity existed. Cross-reactions were not detected between M hyopneumoniae, M flocculare, and M hyorhinis with the growth-inhibition test. The metabolic-inhibition test was more useful for detection of intraspecies antigenic difference than was the growth-inhibition test, since antigenic diversity was clearly detected among M hyopneumoniae strains. Slight cross-reactions were observed between M hyopneumoniae and M flocculare. Using 2-dimensional immunoelectrophoresis, antigenic differences were observed among M hyopneumoniae strains, although many common components also were detected in electropherograms. Mycoplasma flocculare possessed a close antigenic relationship to M hyopneumoniae, as determined by two-dimensional immunoelectrophoresis, whereas both organisms were less related to M hyorhinis. Evidence obtained in this study indicated that strains of mycoplasmas tentatively identified as M hyopneumoniae were similar antigenically, but evidence was obtained also of some diversity in antigenic structure among these strains.