The CD7 antigen is a membrane-embedded glycoprotein with a molecular weight of 37-40 kDa and a member of the immunoglobulin supergene family. It plays an important role in T-cell and T-cell/B-cell interactions during early lymphoid development. CD7 is the earliest T-cell-associated molecule to appear in stem cells and prethymic stages and extends its expression all the way to the mature T cells. This molecule is also present on NK cells. In addition, the pluripotent bone marrow stem cells may express CD7. A subpopulation of AML, particularly those with monocytic or megakaryocytic differentiation, may express CD7. Lack of CD7 expression can be used for the detection of T-cell lymphoproliferative disorders, such as mycosis fungoides/Sezary syndrome and adult T-cell leukemia/lymphoma. However, normal and reactive T cells often demonstrate variable degree of CD7 loss.
