SERUM IGA CROSS-REACTIVITY BETWEEN GLYCINE-ALANINE REPEAT SEQUENCE OFEBNA-1 AND KERATIN OR COLLAGEN IN NASOPHARYNGEAL CARCINOMA

Inhibition studies were carried out to study possible cross-reactivity between a peptide fragment of the Epstein-Barr virus nuclear antigen, EBNA-1, and keratin/collagen. The 20-amino acid peptide (pAG), derive d from a glycine-alanine repeat region of EBNA-1, uniquely makes up ab out one-third of the viral protein and is a dominant IgA antigenic epi tope in patients with nasopharyngeal carcinoma (NPC). A small percenta ge of normal human sera (NHS) also binds pAG and this reactivity is ex amined in this study. Ten percent (2/20) and 13.4% (2/15) of IgA-pAG-p ositive NPC sera and NHS, respectively, were significantly inhibited b y keratin in a competitive ELISA system. Conversely, 31.6% (6/ 19) and 30.8% (4/13) of IgA-keratin-positive NPC sera and NHS, respectively, were significantly inhibited by pAG. This indicated minimum cross-reac tivity between IgA serum antibodies to EBNA-1 and keratin. Using colla gen as inhibitor, none of 18 and only 2/13 IgA-pAG-positive NPC sera a nd NHS, respectively, were inhibited. In the collagen ELISA system, on ly 2/19 (10.5%) and 4/25 (16%) of IgA-collagen-positive NPC sera and N HS, respectively, were inhibited with pAG. Therefore, cross-reactivity with collagen was also low. IgA-pAG-positive NHS may therefore not be a false positive phenomenon, but whether it may represent an early se rological profile related to NPC carcinogenesis remains to be determin ed. (C) 1994 Academic Press, Inc.