The leukocyte response of Japanese quail to Rous sarcoma virus-induced tumors

In male Japanese quail, different circulating leukocyte responses were observed for progressors (birds developing a massive tumor that persisted throughout the experiment) and regressors (birds developing a tumor that gradually disappeared) after initial challenge with Rous sarcoma virus (RSV). Blood was sampled before and at weekly intervals postinoculation. Blood smears were prepared and stained with Diff Quik, and a light microscope (1000 x) was used in a direct count of 50 fields. Leukocytes were classified as heterophils, lymphocytes, monocytes, or eosinophils. The significant increase (P < 0.05) in total leukocytes at 14 days in regressors and progressors was consistent with the increase in tumor growth. The regressors' individual percentage of leukocytes did not deviate from control values, whereas the progressors' percentages of heterophils and monocytes were significantly higher (P < 0.05) and of lymphocytes significantly lower (P < 0.05) than those of controls by 14 days postinoculation. Indicative of this was the progressors' heterophil to lymphocyte ratio, which was significantly higher (P < 0.05) than that of controls 14 days post RSV challenge and remained elevated throughout the experiment. These findings suggest that the progressors' immune response is suppressed by proliferation of malignant cells. Therefore, the heterophil to lymphocyte ratio may be used in addition to tumor size to identify those birds that will regress RSV-induced tumors.