A lymphoblast is a different form of a naive lymphocyte that occurs when the lymphocyte is activated by an antigen (from antigen-presenting cells) and increased in volume by nucleus and cytoplasm growth as well as new mRNA and protein synthesis. The lymphoblast then starts dividing and making clones of its original naive cells. Finally the dividing cells differentiate into effector cells, known as Plasma Cells (for B cells), Cytotoxic T cells, and Helper T cells.