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NLM AIDSLINE
Death by neglect as a deletional mechanism of peripheral tolerance.
Bertolino P; Trescol-Biemont MC; Thomas J; de St Groth BF; Pihlgren M;
December 30, 1999
Int Immunol. 1999 Aug;11(8):1225-38. Unique Identifier : AIDSLINE

In contrast to most organs, the anatomy of the liver may allow naive CD8(+) T cells to make direct contact with liver parenchymal cells. We have previously shown, using a combination of TCR transgenic T cells specific for H-2 K(b) and hepatocytes expressing a transgenic H-2 K(b) molecule, that hepatocytes can induce antigen-specific activation and proliferation of naive CD8(+) T cells independently of CD28 co-stimulation. However, T cell activation by hepatocytes leads to premature T cell death and tolerance, both in vivo and in vitro. In this study, we investigated the mechanisms of T cell death induced by hepatocytes in vitro using primary hepatocytes to activate purified CD8(+) T cells. Neither Fas nor tumor necrosis factor receptor were involved, indicating that hepatocyte- induced death was distinct from activation-induced cell death. Before they started to divide, T cells activated by hepatocytes expressed lower levels of the bcl-x(L) survival gene and 30 times less IL-2 mRNA than CD8(+) cells activated by splenic antigen-presenting cells. Since CD28 co-stimulation increases both IL-2 and bcl-x(L) expression, this suggests that hepatocyte-activated T cells die by neglect because they fail to receive effective co-stimulatory signals. In agreement with this model, premature death promoted by hepatocytes could be prevented by cross-linking CD28. Survival after CD28 cross-linking correlated with increased IL-2 and bcl-x(L) expression, and sustained T cell proliferation, while cytotoxic T lymphocyte activity was prolonged as compared with cells stimulated without CD28 co-stimulation. This study confirms that high- affinity TCR transgenic antigen-specific CD8(+) T cells can be activated to proliferate and differentiate into cytotoxic effector cells. However, prolonged T cell survival and cytotoxicity required CD28 co-stimulation as well. To our knowledge, this is the first report suggesting that tolerance in the context of lack of CD28 co-stimulation can result from Fas-independent peripheral deletion rather than from anergy.

JOURNAL ARTICLE Animal Antigens, CD28/IMMUNOLOGY/METABOLISM Apoptosis *Clonal Deletion Coculture Cytokines/BIOSYNTHESIS CD8-Positive T-Lymphocytes/IMMUNOLOGY/*PHYSIOLOGY Dendritic Cells/IMMUNOLOGY Interleukin-2/GENETICS/METABOLISM Liver/CYTOLOGY/*IMMUNOLOGY Lymphocyte Transformation Mice Mice, Inbred C57BL Mice, Transgenic Proto-Oncogene Proteins c-bcl-2/GENETICS/METABOLISM Receptors, Antigen, T-Cell, alpha-beta/GENETICS *Self Tolerance Support, Non-U.S. Gov't T-Lymphocytes, Cytotoxic/IMMUNOLOGY

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