title: Signal 3 tolerant CD8 T cells degranulate in response to antigen but lack granzyme B to mediate cytolysis.
abstract: Naive CD8 T cells that respond in vivo to Ag and costimulation in the absence of a third signal, such as IL-12, fail to develop cytolytic function and become tolerized. We show in this study that CD8 T cells purified from TCR transgenic mice and stimulated in vitro in the presence or absence of IL-12 form conjugates with specific target cells, increase intracellular Ca2+, and undergo degranulation to comparable extents. Perforin is also expressed at comparable levels in the absence or presence of a third signal, but expression of granzyme B depends upon IL-12. Levels of granzyme B also correlate strongly with the cytolytic activity of cells responding in vivo. In contrast, an increase in CD107a (lysosomal-associated membrane protein 1) expression resulting from degranulation cannot distinguish in vivo generated lytic effector cells from tolerized, noncytolytic cells. Thus, it appears that cells rendered tolerant as a result of stimulation in the absence of a third signal fail to lyse target cells because they are "shooting blanks."
authors.affiliation: Center for Immunology, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA. curts001@umn.edu
authors.forename: Julie M
authors.initials: JM
authors.lastname: Curtsinger
authors.forename: Debra C
authors.initials: DC
authors.lastname: Lins
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Johnson
authors.forename: Matthew F
authors.initials: MF
authors.lastname: Mescher
mesh_terms: D000818:Animals; D000941:Antigens / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000201:enzymology / Q000276:immunology*; D015550:Cell Degranulation / Q000276:immunology*; D045744:Cell Line, Tumor; D003602:Cytotoxicity, Immunologic / Q000235:genetics*; D053804:Granzymes; D018664:Interleukin-12 / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000276:immunology; D012697:Serine Endopeptidases / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*
chemical_list: D000941:Antigens; D011948:Receptors, Antigen, T-Cell; D018664:Interleukin-12; D053804:Granzymes; C509214:Gzmb protein, mouse; D012697:Serine Endopeptidases