What is the generic function of leukocytes? What are leukocytosis and leukopenia?

The generic function of leukocytes is to contribute in the defense of the body against strange agents that penetrate it or are made inside the body.

Leukocytosis and leukopenia are clinical conditions in which the count of leukocytes in a blood sample is abnormal. When the leukocyte count in a blood sample is above the normal level for the individual leukocytosis is explained. When the leukocyte count is lower than the expected normal level leukopenia is explained. The multiplication of these defense cells, leukocytosis, generally takes place when the body is suffering infections or in cancers of these cells. The lowering of these defense cells, or leukopenia, occurs when some diseases attack the cells, as AIDS, or when immunosuppressor drugs are used.

In general the body makes leukocytosis as a defense reaction when it is facing infectious or pathogenic agents. The clinical condition of leukocytosis is there is a sign of infection. Leukopenia happens when there is a deficiency in the production (for instance, in bone marrow diseases) or excessive destruction of leukocytes (for instance, in case of HIV infection).