CD103, or αE, functions as an integrin subunit and is created from the ITGAE gene positioned on chromosome 17. Its presence is noted in practically all instances of hairy cell leukemia (HCL), but it’s generally not present in most other B-cell cancers, except for some uncommon instances of splenic marginal zone lymphoma that exhibit CD103. Research has identified CD103 within mononuclear cells located in the spaces between follicles of lymph nodes, as well as in intraepithelial cells within the top layer of the inner lining mainly close to the bottom layer of the tonsil. Because anti-CD103 is very sensitive in detecting hairy cell leukemia, it serves as a helpful marker for telling it apart from other B-cell cancers.