This article is a more specific discussion of CLL. Please be sure to read Leukemia: The Basics first, so you have a basic understanding of leukemia. What is CLL? CLL is a chronic blood cancer that affects the lymphocytes, of which there are two types, B and T lymphocytes. These white blood cells are an important component of the immune system, helping to fight infection. More than 90% of CLL cases affect the B cells. In acute leukemia, one cell begins rapidly reproducing, leaving little room for healthy cells, eventually causing symptoms. In CLL, the abnormal B cells accumulate over time, but the rate they are reproducing is not abnormal. Rather than overgrowth, CLL is caused by a loss of apoptosis, or programmed cell death. The B cells should die once they reach a certain number, but cancerous B cells have lost the ability to self destruct in this situation. CLL accounts for a little ... read more on Chronic Lymphocytic Leukemia (CLL)