Leukocyte is a type of blood cells that is made in the bone marrow and fo und in the blood and lymph tissue. Leukocytes are part of the body’s imm une system. They help the body fight infection and other diseases . Types of leukocytes are granulocytes (neutrophils, eosinophils, and baso phils), monocytes, and lymphocytes (T cells and B cells). Checking the number of leukocytes in the blood is usually part of a compl ete blood cell (CBC) test. It may be used to look for conditions such as in fection, inflammation, allergies, and leukemia. Also called WBC and w hite blood cell.