Alymphoblast is a modified naivelymphocyte with altered cell morphology. It occurs when the lymphocyte is activated by an antigen and increased in volume by nucleus and cytoplasm growth as well as new mRNA and protein synthesis. The lymphoblast then starts dividing two to four times every 24 hours for three to five days, with a single lymphoblast making approximately 1000 clones of its original naive lymphocyte, with each clone sharing the originally unique antigen specificity. Finally the dividing cells differentiate into effector cells, known asplasma cells (for B cells),cytotoxic T cells, andhelper T cells.[1]
Lymphoblasts can also refer to immature cells which typicallydifferentiate to form maturelymphocytes.[2] Normally, lymphoblasts are found in the bone marrow, but inacute lymphoblastic leukemia (ALL), lymphoblasts proliferate uncontrollably and are found in large numbers in the peripheral blood.
The size is between 10 and 20 μm.[3]
Although commonly lymphoblast refers to a precursor cell in the maturation ofleukocytes, the usage of this term is sometimes inconsistent. The Chronic Lymphocytic Leukemia Research Consortium defines a lymphoblast as "A lymphocyte that has become larger after being stimulated by an antigen. Lymphoblasts look like immature lymphocytes, and were once thought to be precursor cells."[4] Commonly, when speaking about leukemia, "blast" is used as an abbreviation for lymphoblasts.
Lymphoblasts can be distinguished microscopically frommyeloblasts by having less distinctnucleoli, more condensedchromatin, and an absence ofcytoplasmic granules. However these morphologic distinctions are not absolute and a definitive diagnosis relies on antibodyimmunostaining for the presence of uniquecluster of differentiationreceptors.[5]
