Distribution of Epstein-Barr virus antigenic sites on the carboxyl terminal end of ribonucleotide reductase against nasopharyngeal carcinoma serum antibodies using an immunoabsorption method

In an attempt to clone and express proteins from the Epstein-Barr virus (EB V) cDNA library to be used as antigens in an enzyme-linked immuno-sorbent a ssay (ELISA) format to test against the antibodies found in the sera of nas opharyngeal carcinoma (NPC) patients, we have isolated and characterized th ree clones. All three clones ex pressed the same polypeptides of different lengths, which belong to the carboxyl terminal end of the large subunit of ribonucleotide reductase (RR) of the EBV genome. All three clones were foun d to be immunogenic and could be used in an IgA and IgG ELISA against the N PC sera with various degrees of sensitivity and specificity. Because the cl ones varied in length, this difference provides a simple system to determin e where most of the antibody epitopes lies on the protein. We designed an i mmunoabsorption assay and a mathematical model to help map the segment of t he polypeptide most immunogenic to 43 NPC patients. Results were unexpected : 77% of the patients were most immunogenic to region z, which was the smal lest fragment among the three fragments studied. Fragment z was only 33 ami no acids in length. Only 14% and 19% of patients showed the most immunogeni c region in segment x and y, respectively. This variation could be due to m ajor histocompatibility complex antigens. The patients could be divided int o three groups based on the immunoabsorption assays, in which each group re sponded to a different immunodominant segment in the RR antigen. The larges t group responded to an immunodominant segment, which was only 33 amino aci ds long. This domain was coded for by the gene fragment from nucleotide 78, 129 to nucleotide 78,227 of the EBV genome, This segment of the protein wou ld be suitable for further epitope mapping studies. (C) 1999 Wiley-Liss, In c.