T-Cell Antigen CD7 is a single-pass type I membrane protein that that belongs to the the immunoglobulin superfamily. Human CD7 is synthesized as a 240 amino acid precursor that contains a 25 amino acid signal sequence and a 215 amino acid mature chain with a Ig-like (immunoglobulin-like) domain. CD7 is normally expressed on all T-lymphocytes, NK-cells, pre-B lymphocytes and pleuripotent hematopoietic stem cells. CD7 plays an essential role in T-cell interactions, T-cell/B-cell interaction during early lymphoid development, T- and NK-cell activation and cytokine production. CD7 has been shown to interact with PIK3R1and SECTM1. However, the function of the CD7 protein in the immune system is still largely unknown.