A role for CD5 in cognate interactions between T cells and B cells, and identification of a novel ligand for CD5.
CD5 is a glycoprotein expressed at a high level on the surface of mature T lymphocytes. Studies with CD5 mAb and CD5-deficient mice have shown that the CD5 molecules have a significant role in T cell growth response. However, the precise role of CD5 in immune cell interactions is still unclear. The present study provides evidence that CD5 plays a direct role in providing growth signals during the contact-dependent activation and proliferation of splenic B cells. An anti-CD5 mAb inhibited Th1- and Th2-type cell-induced B cell proliferation. CD5-Ig, a chimeric fusion protein, induced proliferation of resting B cells. Flow cytometric analyses using CD5-Ig and mAb to CD72 demonstrated that CD5 bound to a ligand (CD5L), and this binding was not blocked by a variety of anti-CD72 mAb. Also, CD5-Ig did not bind to CD72+-transfected cells. Immunoprecipitation of surface labeled B cell molecules with CD5-Ig showed that CD5L was composed of 77-80 and 38-40 kDa polypeptide chains, distinct from CD72. CD5L was expressed on activated splenic B cells, but not T cells, whereas its expression was constitutive on peritoneal B cells and on B lymphoma cell lines.
Bikah
G
G
Department of Microbiology and Immunology and The Sanders Brown Center on Aging, University of Kentucky, Lexington 40536, USA.
Lynd
F M
FM
Aruffo
A A
AA
Ledbetter
J A
JA
Bondada
S
S
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000917:Antibody Formation; D015703:Antigens, CD / Q000276:immunology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D018956:CD5 Antigens / Q000276:immunology* / Q000378:metabolism / Q000494:pharmacology; D002455:Cell Division; D002460:Cell Line; D005260:Female; D005434:Flow Cytometry; D007136:Immunoglobulins; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology*; D008211:Lymphocyte Cooperation / Q000276:immunology*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D011233:Precipitin Tests; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017421:Sequence Analysis; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D018956:CD5 Antigens; C064228:CD72 protein, human; D007136:Immunoglobulins; D008024:Ligands; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins