Aiolos, an Ikaros family member, is also known as Izkf3. It has a molecular weight of 58 kD and shows 70% homology to the Ikaros isoform, Ik-1, particularly in the DNA binding and C-terminal domains. Aiolos can form a heteromer with Ikaros or exist as a homodimer. The homomeric complex is a potent transcriptional activator. Unlike Ikaros, Aiolos is expressed in late fetal thymus and adult lymphoid organs. Among the adult hematopoietic progenitors, Aiolos is expressed at low levels in mulitpotent but not in pluripotent stem cells. When these multipotent progenitors become more restricted to T and B lymphoid pathways there is an upregulation in Aiolos expression. The highest expression of Aiolos is detected in the spleen (especially in B-cells) followed by thymus and bone marrow, and cannot be detected in the non-lymphoid organs. Aiolos plays an important role in lymphocyte proliferation and differentiation.