Journal
JOURNAL OF IMMUNOLOGY
Volume 176, Issue 4, Pages 2299-2306Publisher
AMER ASSOC IMMUNOLOGISTS
DOI: 10.4049/jimmunol.176.4.2299
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- NIAID NIH HHS [1-R01-AI-60037-01] Funding Source: Medline
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The processes of positive and negative selection in the thymus both determine the population of T cells that will enter the peripheral immune system and eliminate self-reactive T cells by apoptosis. Substantial evidence indicates that TCR signal intensity mediates this cell fate choice: low-intensity signals lead to survival and differentiation, whereas high-intensity signals generated by self-Ag lead to cell death. The molecular mechanism by which these graded signals are converted to discrete outcomes is not understood. Positive selection requires the Ca2(+)-dependent phosphatase calcineurin, whereas negative selection requires the proapoptotic Bcl-2 family member Bcl-2-interacting mediator of cell death (Bim). In this study, we investigated the regulation of Bim expression and the role of Ca2+ in mediating negative selection. Our results show that transcription is necessary for both negative selection and Bim induction. Surprisingly, we also found that Ca2+ is necessary for Bim induction. Induction of bim transcription appears to involve protein kinase C, but not calcineurin, JNK, p38 MAPK, or MEK. These results localize the decision point in positive vs negative selection to a step downstream of Ca2+ signaling and suggest that negative selection signals induce Ca2+-dependent bim transcription through PKC. The Journal of Immunology, 2006, 176: 2299-2306.
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