Sera from patients with Burkitt's lymphoma (BL), infectious mononucleosis (IM), carcinoma of the postnasal space (Ca PNS), and various controls were investigated for antibodies against the Epstein-Barr virus (EBV) by immunofluorescence on acetone-fixed smears (5) and for antibodies against the distinctive antigenic sites expressed on the surface of viable lymphoblastoid cells within EBV-carrying culture lines (1). The latter were studied by the blocking of direct membrane staining with FITC-conjugated Mutua serum. This serum has been derived from a Burkitt's lymphoma patient in long-term regression after chemotherapy and is free from detectable isoantibodies. It has been used previously as a standard of reference to demonstrate the presence of the membrane antigen(s) on all lines derived from BL biopsies and leukocytes from IM patients. It was found that 102 of 279 (37%) of the sera tested had high anti-EBV titers (≧80) and high membrane-blocking (Bl > 0.5) activity, 124 of 279 (44%) of the sera were low in both tests, 22 of 279 (8%) had low EBV titers (≦80), in spite of a high blocking index, and 31 of 279 (11%) of the sera were low in blocking activity (<0.5), in spite of a high EBV titer. The two tests thus gave concordant results with 81% and discordant with 19% of the sera.

The majority of sera from BL patients were high in both tests. IM sera also showed a relationship between the two antibody activities but, in general, both activities were lower than in BL cases. Ca PNS sera seemed to fall into two main groups: (a) high anti-EBV, high blocking or (b) low anti-EBV, low blocking. Control sera, including four isoantisera, showed predominantly low reactivities in both tests.

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