High interferon titer and defective NK-cell activity in the circulation of nasopharyngeal carcinoma patients.

The interferon (IFN) activity of sera from 19 patients with nasopharyngeal carcinoma (NPC) was determined by the plaque-reduction assay with vesicular stomatitis virus (VSV) in HeLa cells and compared to that of sera from matched healthy controls. High titers of interferon were detected in the sera of the NPC patients with a geometric mean titer (GMT) of 43 +/- 25 U/ml. The interferon activity of the patients' sera was acid- and heat-labile (pH = 2 and 56 degrees C for 1 hr) and could be neutralized by a goat antiserum to human IFN-gamma. Interferon titers of the patients, in contrast, to normal controls, were not correlated with natural killer (NK) activity which was abnormally low in the NPC patients. On the other hand, a high percentage of circulating cells co-expressing the LGL marker (HNK-I) and the OKT8 antigen was detected in parallel with high IFN levels in NPC patients.