Coronavirus-associated antibodies in nasopharyngeal carcinoma and infectious mononucleosis

Coronavirus-like particles are found within the cytoplasm of NPC tumor cells, within the cytoplasm of the tumor cells of the regional metastases, and within tumor cells grown on nude mice. For the immunologic identification of the coronaviruses, the cultures of human tracheal epithelium (MRC-C) were used and inoculated with a known coronavirus strain. Whereas blood sera from NPC patients (n = 73) contain significantly elevated antibody titers against corona viruses, unselected sera from patients without NPC showed a low antibody titer (n = 83). Only patients suffering from infectious mononucleosis (n = 40) showed a titer pattern similar to that of NPC patients. For demonstration of antigen-antibody reaction within the NPC tumor cell cytoplasm, sera with a high antibody content against coronaviruses deriving from other than NPC patients or anticoronavirus sera from rabbits were used. By indirect immunofluorescence, the NPC tumor cells showed a bright cytoplasmic fluorescence. No fluorescence was seen when tumor cells were exposed to human sera with known low or absent corona antibody titer or to normal rabbit sera. The results indicate that next to a DNA virus infection (EBV), an RNA virus infection (coronavirus) may play a role in NPC as well as in infectious mononucleosis.