The B-cell surface protein CD72/Lyb-2 is the ligand for CD5.
The glycoprotein CD5 is expressed on the surface membrane of all mature T cells and a small proportion of B lymphocytes. Its exact role in immune interactions is still unknown. Studies indicate that CD5 functions both in mice and humans as a receptor, delivering co-stimulatory signals to T cells in a manner similar to CD2 (ref. 11) and CD28 (ref. 12). Anti-CD5 antibodies stimulate both T-cell proliferation mediated by CD3 in association with the T-cell receptor and secretion of interleukin-2 and expression of its receptor, as well as inducing an increase in intracellular Ca2+ concentration (refs 5-10). To identify the ligand for CD5 we purified the human CD5 protein, labelled it with biotin and used it as a probe. Here we report that CD5 specifically interacts with the cell-surface protein CD72 exclusive to B cells. This interaction is blocked by anti-CD72 antibodies, but not by any other anti-B-cell antibodies. Moreover, non-B cells (mouse L-cell fibroblasts and human Jurkat T cells) expressing a transfected human CD72 complementary DNA could bind to the CD5-biotin conjugate. The results demonstrate that the B-cell surface protein CD72 (Lyb-2 in mice) is the ligand for CD5.
Van de Velde
H
H
Division of Haematology-Immunology, Medical School of the Vrije Universiteit Brussel, Belgium.
von Hoegen
I
I
Luo
W
W
Parnes
J R
JR
Thielemans
K
K
D015703:Antigens, CD / Q000276:immunology; D000943:Antigens, Differentiation / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D018956:CD5 Antigens; D002450:Cell Communication; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D008024:Ligands; D013601:T-Lymphocytes / Q000276:immunology*
D015703:Antigens, CD; D000943:Antigens, Differentiation; D000944:Antigens, Differentiation, B-Lymphocyte; D018956:CD5 Antigens; C064228:CD72 protein, human; D008024:Ligands