Analysis and significance of anti-latent membrane protein-1 antibodies in the sera of patients with EBV-associated diseases

Anti-latent membrane protein-1 (LMP-1) is an EBV-encoded type III integral membrane protein with oncogenic potential that is expressed most consistent ly in various EBV-associated malignancies. Unlike many other EBV proteins, LMP-1 Abs have rarely been demonstrated in EBV-associated disease condition s. We established a high level LMP-1-expressing cell clone and used it for the detection, quantitation, and characterization of these Abs in various h uman sera in immunoblots and ELISA, Our results demonstrate that, in contra st to the commonly held notion, LMP-1 induces significant humoral immune re sponses in EBV-associated malignant conditions especially in nasopharyngeal carcinoma (NPC) patients in whom >70% sera are positive for these Abs, and their titers correlate with the clinical condition of the tumors, Interest ingly, anti-LMP-1 Abs of IgA isotype were found only in NPC patients. These Abs were absent from the sera of infectious mononucleosis and chronic EBV infection patients, whereas a small fraction (similar to 5%) of the healthy , EBV-seropositive individuals were positive for them; however, their OD va lues were much lower than those of NPC patients. These studies demonstrate, for the first time, the potential significance of LMP-1-specific Abs for t he diagnosis and prognosis of EBV-associated malignancies, especially of NP C.