What is a B lymphocyte? Esta entrada también está disponible en: Español (Spanish) B lymphocytes are a type of cell related to different diseases, including chronic lymphocytic leukemia (CLL) and mantle cell lymphoma, which will be discussed later. Blood, one of the most important fluids in the body, is made up of blood cells called white blood cells and red blood cells that move within plasma. Plasma is mainly water. Blood cells form in the bone marrow, a spongy tissue in the center of most bones. Within the bone marrow there are blood stem cells, from these all blood cells are formed: Now, within the white blood cells there is a type of cells called B lymphocytes or B cells, these are of special importance as part of the immune system and act by producing antibodies to eliminate microorganisms that enter the body. Lymphocytes travel through the lymph, a clear fluid through which proteins, fats, some cells and substances filtered from the blood circulate, to the lymph nodes or other organs of the lymphatic system. The lymphatic system is made up of the lymph nodes, the thymus, the spleen, the bone marrow, and the network of lymphatic vessels that carry lymph throughout the body. Bibliography National Comprehensive Cancer Network Guidelines for Patients: Mantle Cell Lymphoma, NCCC Non Hodgkin Lymphoma Series, 2017. National Comprehensive Cancer Network Guidelines for Patients: Chronic Lymphocytic Leukemia, 2019.