Interaction between the Extracellular Domain of CD7 and Concanavalin A: A Clue to the Identity of the Ligand for CD7

• Published in: Cellular immunology 1996-10, Vol.173 (1), p.15-21
• Main Authors: Leta, Eric, Hou, Zhongcheng, Lederman, Lynne, Jung, Lawrence K.
• Format: Article
• Language: English
• Subjects: Adult; Antigens, CD7 - genetics; Antigens, CD7 - immunology; Cell Division; Cell Line; Concanavalin A - immunology; Female; Humans; Jurkat Cells; Ligands; Male; Mannose; Middle Aged; Receptors, Antigen, T-Cell - immunology; Receptors, Concanavalin A - immunology; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - immunology; Structure-Activity Relationship; T-Lymphocytes - immunology
• ISSN: 0008-8749; 1090-2163
• DOI: 10.1006/cimm.1996.0247

During the process of lymphocyte activation, cell surface molecules interact with their respective ligands, leading to the transduction of activation signals intracellularly. Well-known examples of this process include the interaction of the Ti/CD3 complex with the antigenic peptide, between CD28 and CD80, between CD40 and its ligand, and between cytokines and their receptors. These observations have confirmed the importance of ligand-receptor interactions in biological functions and prompted investigators to search for ligands of surface molecules with yet-unknown functions. One such molecule is the T cell differentiation antigen, CD7. CD7, a 40-kDa glycoprotein, is the earliest T cell differentiation antigen to appear during ontogeny. Its possible role in the process of T cell development is suggested by the observation that T cells of a patient with severe combined immunodeficiency (SCID) did not express CD7. In mature T cells, CD7 has been shown to have a costimulatory role in Ti/CD3-mediated T cell activation. Anti-CD7 antibodies induced the activation of gamma / delta T cells and NK cells. Recent data indicated that ligation of CD7 led to tyrosine phosphorylation of cellular substrates in NK and T cells. Thus, it appears likely that CD7 is an important molecule which regulates the function and development of T cells and NK cells. The ligand which interacts with CD7 has not been identified. Some investigators have suggested that CD7 may act as an adhesion molecule. There is no evidence for this hypothesis, although the crosslinking of CD7 modulated T cell adhesion. Similarly, crosslinking CD7 leads to increased NK adhesion to fibronectin via the integrin receptor alpha 4 beta 1 and alpha 5 beta 1. As a first step in identifying the ligand for CD7, we have expressed the extracellular domain of CD7 in the baculovirus gene expression system. The effect of this recombinant product on T cell activation was studied. The recombinant product blocked the ability of Con A to bind to T cells and to activate them whereas it had no effect on T cell proliferation induced by PHA or superantigens SEA and SEB. These findings suggest that CD7 may interact with lectin-like molecules in vivo, and provide a clue which may help to identify the CD7 ligand.