title: IL-7 and the HIV Tat protein act synergistically to down-regulate CD127 expression on CD8 T cells.
abstract: IL-7 signaling is essential for optimal CD8 T cell function, homeostasis and establishment of memory. We have previously shown decreased expression of the IL-7 receptor alpha-chain (CD127) on CD8 T cells from HIV-infected patients with active viral replication. We have also shown that soluble HIV Tat protein specifically down-regulates CD127 on the surface of CD8 T cells and impairs cell proliferation and cytolytic potential following stimulation with IL-7 in vitro. We now show that soluble HIV Tat protein and IL-7 at near physiologic concentrations act synergistically to suppress CD127 expression. While soluble HIV Tat protein and IL-7 both independently reduce CD127 expression on the surface of CD8 T cells, Tat concentrations of 10 microg ml(-1) and IL-7 concentrations of 500 pg ml(-1) are required in vitro to have an appreciable effect. However, where 0.5 microg ml(-1) of Tat has no effect on CD127 expression and 200 pg ml(-1) of IL-7 decreases CD127 by only 14%, these two together at these same concentrations induce a 35% reduction in CD127 expression after 24 h. Inhibition of Janus kinase (JAK) completely blocks IL-7's ability to down-regulate CD127 on the surface of CD8 T cells and also abolishes synergy with Tat. Interestingly, while Tat acts synergistically with IL-7 to reduce CD127 expression, it antagonizes IL-7-induced cell proliferation and Ki-67 expression and has no effect on IL-7-mediated signal transducer and activator of transcription 5 (STAT5) phosphorylation or expression of the anti-apoptotic gene Bcl-2. Thus, by affecting different IL-7 signal transduction pathways, HIV Tat protein is able to impair both CD8 T cell activation and proliferation without inducing apoptosis.
authors.affiliation: Ottawa Health Research Institute, 501 Smyth Road, Ottawa, Ontario, Canada.
authors.forename: Elliott
authors.initials: E
authors.lastname: Faller
authors.forename: Juzer
authors.initials: J
authors.lastname: Kakal
authors.forename: Ritesh
authors.initials: R
authors.lastname: Kumar
authors.forename: Paul
authors.initials: P
authors.lastname: Macpherson
mesh_terms: D017209:Apoptosis / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation; D015536:Down-Regulation; D019254:Genes, bcl-2 / Q000276:immunology; D015658:HIV Infections / Q000276:immunology* / Q000821:virology; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D018189:Immunomagnetic Separation; D053645:Interleukin-2 Receptor alpha Subunit / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D015851:Interleukin-7 / Q000276:immunology / Q000378:metabolism*; D053699:Interleukin-7 Receptor alpha Subunit / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D053612:Janus Kinases / Q000276:immunology; D019394:Ki-67 Antigen / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008213:Lymphocyte Activation / Q000276:immunology; D010766:Phosphorylation; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000276:immunology / Q000378:metabolism*
chemical_list: D053645:Interleukin-2 Receptor alpha Subunit; D015851:Interleukin-7; D053699:Interleukin-7 Receptor alpha Subunit; D019394:Ki-67 Antigen; D050799:STAT5 Transcription Factor; D054322:tat Gene Products, Human Immunodeficiency Virus; D053612:Janus Kinases