title: Activation of human T cells through CD6: functional effects of a novel anti-CD6 monoclonal antibody and definition of four epitopes of the CD6 glycoprotein.
abstract: The CD6 glycoprotein is expressed primarily on lymphocytes and conveys co-activating signals to T cells, but its exact function and ligand(s) are unknown. A novel mAb, termed UMCD6, was demonstrated to recognize CD6 by immunoprecipitation, Western blotting, and reactivity with COS cells transfected with CD6 cDNA. UMCD6 was mitogenic for T cells and was strongly synergistic with phorbol ester in inducing T cell activation. UMCD6 enhanced the autologous mixed lymphocyte reaction as previously observed with another anti-CD6 mAb, anti-T12. The activating effects of UMCD6 were more striking than those of other anti-CD6 mAbs and encompassed all of the diverse stimulatory properties previously reported for other anti-CD6 reagents. However, neither UMCD6 nor other anti-CD6 antibodies alone or in combination with phorbol ester or IL-2 were able to induce thymocytes to proliferate. Stimulation by UMCD6 is dependent on accessory cell function in a manner not accounted for simply by antibody cross-linking. UMCD6 did not induce an increase in cytoplasmic free Ca2+, but the CD6 activation pathway appears to involve protein kinase C. UMCD6 and a panel of seven other anti-CD6 mAbs were used in a series of experiments to define four discrete epitopes of CD6 using the criteria of antibody cross-blocking, reactivity on reduced Western blots, and resistance to controlled V8 protease digestion. The functional mAbs UMCD6, 2H1, and anti-T12 each recognized a different epitope. Taken together, the results of these studies strongly reinforce the hypothesis that CD6 plays a significant and distinct role in T cell activation, and suggest that multiple regions of CD6 may be functionally active.
authors.affiliation: Rackham Arthritis Research Unit, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109.
authors.forename: C M
authors.initials: CM
authors.lastname: Bott
authors.forename: J B
authors.initials: JB
authors.lastname: Doshi
authors.forename: C
authors.initials: C
authors.lastname: Morimoto
authors.forename: P L
authors.initials: PL
authors.lastname: Romain
authors.forename: D A
authors.initials: DA
authors.lastname: Fox
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D000938:Antigen-Presenting Cells / Q000502:physiology; D015703:Antigens, CD / Q000276:immunology*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D000939:Epitopes; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D008213:Lymphocyte Activation; D011493:Protein Kinase C / Q000502:physiology; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; C062279:CD6 antigen; D000939:Epitopes; D006023:Glycoproteins; D011493:Protein Kinase C; D002118:Calcium