Apoptosis regulators Fas and Bim synergistically control T-lymphocyte homeostatic proliferation.
The size of the peripheral T-lymphocyte compartment is governed by complex homeostatic mechanisms that balance T-cell proliferation and death. Proliferation and survival signals are mediated in part by recurrent self-peptide/MHC-TCR interactions and signaling by the common γ chain-containing cytokine receptors, including those for IL-7 and IL-15. We have previously shown that the death receptor Fas (CD95/APO-1) regulates apoptosis in response to repeated TCR stimulation, whereas the Bcl-2 homology domain 3-only protein Bim mediates cytokine withdrawal-induced apoptosis. We therefore reasoned that these two molecules might cooperate in the regulation of homeostatic proliferation. In this study, we observe that the combined loss of Fas and Bim synergistically enhances the accumulation of T cells in lymphopenic host mice, and this is particularly pronounced for the unusual CD4(-) CD8(-) TCRαβ(+) T cells that are characteristic of Fas-deficient (Fas(lpr/lpr) ) mice. Our findings demonstrate that these CD4(-) CD8(-) TCRαβ(+) T cells arise from homeostatic proliferation of CD8(+) T cells. These studies also underscore the profound rate of baseline T-cell proliferation that likely occurs in wild-type mice even in the absence of foreign antigen, and the consequent need for its coordinated regulation by multiple death-signaling pathways.
Vermont Center for Immunology and Infectious Disease, The University of Vermont College of Medicine, Burlington, VT 05405-0068, USA. karen.fortner@uvm.edu
Karen A
KA
Fortner
Philippe
P
Bouillet
Andreas
A
Strasser
Ralph C
RC
Budd
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000276:immunology*; D051017:Apoptosis Regulatory Proteins / Q000819:agonists / Q000235:genetics / Q000276:immunology*; D000072224:Bcl-2-Like Protein 11; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D049109:Cell Proliferation; D006649:Histocompatibility Antigens / Q000276:immunology; D006706:Homeostasis / Q000235:genetics / Q000276:immunology*; D019409:Interleukin-15 / Q000235:genetics / Q000276:immunology; D015851:Interleukin-7 / Q000235:genetics / Q000276:immunology; D008565:Membrane Proteins / Q000819:agonists / Q000235:genetics / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D010455:Peptides / Q000276:immunology; D011518:Proto-Oncogene Proteins / Q000819:agonists / Q000235:genetics / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D019014:fas Receptor / Q000819:agonists / Q000235:genetics / Q000276:immunology*
D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C491899:Fas protein, mouse; D006649:Histocompatibility Antigens; D019409:Interleukin-15; D015851:Interleukin-7; D008565:Membrane Proteins; D010455:Peptides; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D019014:fas Receptor