In male Japanese quail, different circulating leukocyte responses were
observed for progressors (birds developing a massive tumor that persi
sted throughout the experiment) and regressors (birds developing a tum
or that gradually disappeared) after initial challenge with Rous sarco
ma virus (RSV). Blood was sampled before and at weekly intervals posti
noculation. Blood smears were prepared and stained with Diff Quik, and
a light microscope (1000x) was used in a direct count of 50 fields. L
eukocytes were classified as heterophils, lymphocytes, monocytes, or e
osinophils. The significant increase (P < 0.05) in total leukocytes at
14 days in regressors and progressors was consistent with the increas
e in tumor growth. The regressors' individual percentage of leukocytes
did not deviate from control values, whereas the progressors' percent
ages of heterophils and monocytes were significantly higher (P < 0.05)
and of lymphocytes significantly lower (P < 0.05) than those of contr
ols 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 el
evated throughout the experiment. These findings suggest that the prog
ressors' immune response is suppressed by proliferation of malignant c
ells. Therefore, the heterophil to lymphocyte ratio may be used in add
ition to tumor size to identify those birds that will regress RSV-indu
ced tumors.