Chronic Lymphocytic Leukemia Health Article

Definition

Chronic lymphocytic leukemia (CLL) is a cancer of white blood cells. In CLL, mature white blood cells of certain types called lymphocytes function abnormally and cause disease.

Description

Chronic leukemia is a cancer that starts in the blood cells made in the bone marrow. The bone marrow is the spongy tissue found in the large bones of the body. The bone marrow makes precursor cells called "blasts" or "stem cells" that mature into different types of blood cells. Unlike acute leukemias, in which the process of maturation of the blast cells is interrupted, in chronic leukemias, most of the cells do mature and only a few remain as immature cells. However, even though the cells appear normal, they do not function as normal cells.

The different types of cells produced in the bone marrow are red blood cells (RBCs), which carry oxygen and other materials to all tissues of the body, and white blood cells (WBCs), which fight infection. Platelets play a part in the clotting of the blood. The white blood cells can be further subdivided into three main types: the granulocytes, monocytes, and the lymphocytes.

The granulocytes, as their name suggests, contain granules (particles). These granules contain special proteins (enzymes) and several other substances that can break down chemicals and destroy microorganisms such as bacteria. Monocytes are the second type of white blood cell. They also are important in defending the body against pathogens.

The lymphocytes form the third type of white blood cell. There are two main types of lymphocytes: T lymphocytes and B lymphocytes. They have different functions within the immune system. The B cells protect the body by making "antibodies." Antibodies are proteins that can attach to the surfaces of bacteria and viruses. The occurrence of this attachment sends signals to many other cell types to travel through the blood and destroy the antibody-coated organism. The T cell protects the body against viruses. When a virus enters a cell, it produces certain proteins that are projected onto the surface of the infected cell. T cells recognize these proteins and produce certain chemicals (cytokines) capable of destroying the virus-infected cells. In addition, T cells destroy some types of cancer cells.

Chronic leukemias develop very gradually. The abnormal lymphocytes multiply slowly, and in a poorly regulated manner. These lymphocytes live much longer than normal lymphocytes and, thus, their numbers build up in the body. In CLL, lymphocytes accumulate. The enlarged lymphocyte population congregates in the blood, bone marrow, lymph nodes, spleen, and liver. The two types of chronic leukemias can be easily distinguished under the microscope. Chronic lymphocytic leukemia (CLL) involves the T or B lymphocytes. B-cell abnormalities are more common than T-cell abnormalities. T cells are affected in only 5% of the patients.