The exact function of the basophil is not known. Increased numbers are often associated with chronic, long tern illnesses. They also appear to play a role in the early stages of inflammation. Lymphocytes and heterophils are the most numerous WBCs seen in psittacine birds. Some species, such as cockatiels and Amazon parrots, are naturally lymphocytic, which means more lymphs than hets are seen normally.
Lymphocytes are a very important part of the bird s immune system.
They decrease in numbers in acute viral infections. In a disease state, lymphocytes will become reactive. A few reactive lymphs on a blood smear is normal but if many are reactive then this is a significant finding that the body is responding to an infection of some sort. Reactive lymphs synthesize antibodies and other agents involved in the host immune system. Birds with a marked lymphocytosis in which most or all of the lymphocytes appear abnormal or immature is consistent with leukemia.