Signal 3 tolerant CD8 T cells degranulate in response to antigen but lack granzyme B to mediate cytolysis

J Immunol. 2005 Oct 1;175(7):4392-9. doi: 10.4049/jimmunol.175.7.4392.


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."

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens / immunology*
  • CD8-Positive T-Lymphocytes / enzymology
  • CD8-Positive T-Lymphocytes / immunology*
  • Cell Degranulation / immunology*
  • Cell Line, Tumor
  • Cytotoxicity, Immunologic / genetics*
  • Granzymes
  • Interleukin-12 / metabolism
  • Interleukin-12 / physiology*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Receptors, Antigen, T-Cell / genetics
  • Receptors, Antigen, T-Cell / immunology
  • Serine Endopeptidases / deficiency*
  • Serine Endopeptidases / genetics*
  • Serine Endopeptidases / physiology
  • Signal Transduction / genetics
  • Signal Transduction / immunology*


  • Antigens
  • Receptors, Antigen, T-Cell
  • Interleukin-12
  • Granzymes
  • Gzmb protein, mouse
  • Serine Endopeptidases