Role of Marek's disease herpesvirus in the induction of tumours in Japanese quail (Coturnix coturnix japonica) by methylcholanthrene.

The QT35 cell line, established from 20-methylcholanthrene (MCA)-induced tumours in Japanese quail, is positive for Marek's disease virus (MDV), and therefore we examined whether MDV is important for the development of MCA-induced tumours. Japanese quail were inoculated with the JM16 strain of MDV at 1 or 3 days of age or left uninoculated. At 3 weeks of age, quail were injected in the breast muscle with 4 mg MCA in corn oil or corn oil alone. Quail were observed for tumours three times/week and at post mortem at 11 to 12 weeks of age. MDV DNA was detected by polymerase chain reaction (PCR) in spleens of 14/20 birds inoculated with JM16+corn oil and of 53/71 birds inoculated with JM16+MCA. Interestingly, 1/74 quail was positive in the MCA group alone for MDV DNA. Tumours were collected for histopathology, cell line development, and PCR and reverse transcriptase-PCR for the presence of MDV. Tumours developed in 38/83 MCA-treated and 32/85 JM16+MCA-treated quail. Fibrosarcomas without metastasis were the only tumours observed in the MCA-treated quail, while quail treated with JM16 and MCA developed undifferentiated tumours, fibrosarcomas, lymphosarcomas or combinations with or without metastasis. One out of 20 quail receiving JM16 alone developed a lymphosarcoma. Cell line development was not influenced by JM16. Tumours from MCA-treated quail were negative for MDV, while 19/29 were positive in the JM16+MCA group. MDV transcripts were present in 13/18 tumours examined in the JM16+MCA group. In conclusion, MDV did not affect tumour development but did influence tumour aggression and histological type.