title: Role of Bim in regulating CD8+ T-cell responses during chronic viral infection.
abstract: Apoptosis is critical for the development and maintenance of the immune system. The proapoptotic Bcl-2 family member Bim is important for normal immune system homeostasis. Although previous experiments have shown that Bim is critical for the apoptosis of antigen-specific CD8(+) T cells during acute viral infection, the role of Bim during chronic viral infection is unclear. Using lymphocytic choriomeningitis virus clone 13 infection of mice, we demonstrate a role for Bim in CD8(+) T-cell apoptosis during chronic viral infection. Enumeration of antigen-specific CD8(+) T cells by major histocompatibility complex class I tetramer staining revealed that CD8(+) D(b)NP396-404(+) T cells, which undergo extensive deletion in wild-type mice, exhibited almost no decrease in Bim mutant mice. This contrasts with CD8(+) D(b)GP33-41(+) and CD8(+) D(b)GP276-286(+) T cells that underwent similar decreases in numbers in both Bim mutant and wild-type mice. Increased numbers of CD8(+) D(b)NP396-404(+) T cells in Bim mutant mice were due to lack of apoptosis and could not be explained by altered proliferation, differential homing to tissues, or increased help from CD4(+) T cells. When viral titers were examined, high levels were initially observed in both groups, but in Bim mutant mice, clearance from the spleen and sera was slightly accelerated. These experiments demonstrate the critical role of Bim during chronic viral infection to down-regulate CD8(+) T-cell responses and have implications for designing strategies for optimizing immunotherapies during situations where antigen persists, such as chronic infection, autoimmune syndromes, and cancer.
authors.affiliation: Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. jgrayson@wfubmc.edu
authors.forename: Jason M
authors.initials: JM
authors.lastname: Grayson
authors.forename: Ashley E
authors.initials: AE
authors.lastname: Weant
authors.forename: Beth C
authors.initials: BC
authors.lastname: Holbrook
authors.forename: David
authors.initials: D
authors.lastname: Hildeman
mesh_terms: D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002908:Chronic Disease; D015536:Down-Regulation; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D008216:Lymphocytic Choriomeningitis / Q000276:immunology* / Q000821:virology; D008217:Lymphocytic choriomeningitis virus / Q000276:immunology / Q000472:pathogenicity; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins