The Epstein-Barr virus nuclear antigen I (EBNA I) is the only latent EBV antigen consistently expressed in malignant tissues of the nasopharynx. A 20-amino-acid synthetic peptide, p107 contains a major epitope of EBNA I. We tested sera from 210 patients with nasopharyngeal carcinoma (NPC) and from 128 normal individuals (NHS) for IgA antibodies to p107 using an enzyme-linked immunosorbent assay (ELISA). Whereas 191/210 (91%) of NPC patients had IgA antibodies to p107, only 17/128 (13.3%) of NHS had such antibodies and only 6/57 (10.5%) of sera from patients with malignancies other than NPC had IgA-p107 reactivity. Thirty-nine salivary samples from 46 NPC patients (84.8%) also contained IgA-p107 antibodies whereas only 3/42 (7.1%) of normal saliva samples were IgA-p107 positive. The results suggest that IgA antibodies to EBNA I may become a useful, easily measurable, marker for NPC.
The entire amino acid sequence of the unique region of the EBNA 1 protein was synthesized as a set of 41 20-residue peptides with an overlap of 10 amino acids. The peptides were tested in the enzyme-linked immunosorbent assay for reactivity with immunoglobulin A (IgA) and IgG in sera from 50 patients with nasopharyngeal carcinoma (NPC) as compared with 36 serum samples from healthy Epstein-Barr virus (EBV)-seropositive donors and 5 serum samples from EBV-negative donors. The most immunoreactive peptide for both IgA and IgG binding was localized to the glycine-alanine repeat domain of the antigen. In the unique regions, 16 immunoreactive peptides were found. Of these, four were reactive with IgG but not IgA and three peptides were reactive with IgA but not IgG in NPC sera. In addition, several IgA and IgG epitopes on the carboxy-terminal region were specifically reactive with NPC sera, but unreactive with sera from healthy EBV-positive donors. The results suggest that EBV serology specific for individual epitopes may provide additional useful information not available by conventional serology with whole antigens or the EBNA complex.
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