Gene Symbol: Stat5b
Description: signal transducer and activator of transcription 5B
Alias: signal transducer and activator of transcription 5B, mammary gland factor STAT5B
Species: mouse
Products:     Stat5b

Top Publications

  1. Abraham N, Ma M, Snow J, Miners M, Herndier B, Goldsmith M. Haploinsufficiency identifies STAT5 as a modifier of IL-7-induced lymphomas. Oncogene. 2005;24:5252-7 pubmed
    ..In addition, STAT5A/5B+/- compound heterozygous mice with one targeted allele each of STAT5A and STAT5B showed striking amelioration of IL-7-induced mortality and disease development...
  2. Liu X, Robinson G, Gouilleux F, Groner B, Hennighausen L. Cloning and expression of Stat5 and an additional homologue (Stat5b) involved in prolactin signal transduction in mouse mammary tissue. Proc Natl Acad Sci U S A. 1995;92:8831-5 pubmed
    ..We isolated and sequenced from mouse mammary tissue Stat5 mRNA and a previously unreported member, which we named Stat5b (Stat5 is renamed to Stat5a). On the protein level Stat5a and Stat5b show a 96% sequence similarity...
  3. Barnstein B, Li G, Wang Z, Kennedy S, Chalfant C, Nakajima H, et al. Stat5 expression is required for IgE-mediated mast cell function. J Immunol. 2006;177:3421-6 pubmed
    ..These data have a direct impact on MC-associated inflammatory and autoimmune diseases. ..
  4. Moucadel V, Constantinescu S. Differential STAT5 signaling by ligand-dependent and constitutively active cytokine receptors. J Biol Chem. 2005;280:13364-73 pubmed
    ..In transformed cells it was mainly STAT5B that was constitutively activated. In contrast, Epo stimulation activated both STAT5A and STAT5B...
  5. Sexl V, Piekorz R, Moriggl R, Rohrer J, Brown M, Bunting K, et al. Stat5a/b contribute to interleukin 7-induced B-cell precursor expansion, but abl- and bcr/abl-induced transformation are independent of stat5. Blood. 2000;96:2277-83 pubmed
    ..Using mice deficient for the 2 highly related transcription factors, Stat5a and Stat5b (Stat5a/b(-/-)), we investigated the role of Stat5 for B-cell differentiation, expansion, and function...
  6. Park S, Liu X, Hennighausen L, Davey H, Waxman D. Distinctive roles of STAT5a and STAT5b in sexual dimorphism of hepatic P450 gene expression. Impact of STAT5a gene disruption. J Biol Chem. 1999;274:7421-30 pubmed
    b>Stat5b gene disruption leads to an apparent growth hormone (GH) pulse insensitivity associated with loss of male-characteristic body growth rates and male-specific liver gene expression (Udy, G. B., Towers, R. P., Snell, R. G., Wilkins, R...
  7. Nurieva R, Podd A, Chen Y, Alekseev A, Yu M, Qi X, et al. STAT5 protein negatively regulates T follicular helper (Tfh) cell generation and function. J Biol Chem. 2012;287:11234-9 pubmed publisher
    ..Taken together, this study demonstrates that STAT5 controls Tfh differentiation. ..
  8. Udy G, Towers R, Snell R, Wilkins R, Park S, Ram P, et al. Requirement of STAT5b for sexual dimorphism of body growth rates and liver gene expression. Proc Natl Acad Sci U S A. 1997;94:7239-44 pubmed
    The signal transducer and activator of transcription, STAT5b, has been implicated in signal transduction pathways for a number of cytokines and growth factors, including growth hormone (GH)...
  9. Tripathi P, Kurtulus S, Wojciechowski S, Sholl A, Hoebe K, Morris S, et al. STAT5 is critical to maintain effector CD8+ T cell responses. J Immunol. 2010;185:2116-24 pubmed publisher
    ..Finally, IL-7 and IL-15 required STAT5 to induce Bcl-2 expression and to maintain effector CD8(+) T cells. Together, these data demonstrate that IL-7 and IL-15 signaling converge on STAT5 to maintain effector CD8(+) T cell responses. ..

More Information


  1. Moriggl R, Sexl V, Piekorz R, Topham D, Ihle J. Stat5 activation is uniquely associated with cytokine signaling in peripheral T cells. Immunity. 1999;11:225-30 pubmed
    ..Mice deficient in Stat5a and Stat5b have demonstrated the essential role that these highly related proteins play in cell cycle progression following ..
  2. Yang X, Ghoreschi K, Steward Tharp S, Rodriguez Canales J, Zhu J, Grainger J, et al. Opposing regulation of the locus encoding IL-17 through direct, reciprocal actions of STAT3 and STAT5. Nat Immunol. 2011;12:247-54 pubmed publisher
    ..Thus, the balance rather than the absolute magnitude of these signals determined the propensity of cells to make a key inflammatory cytokine. ..
  3. Azam M, Erdjument Bromage H, Kreider B, Xia M, Quelle F, Basu R, et al. Interleukin-3 signals through multiple isoforms of Stat5. EMBO J. 1995;14:1402-11 pubmed
    ..These studies indicate that the IL-3 family of ligands is able to activate multiple isoforms of the signal transducing protein Stat5. ..
  4. Burchill M, Yang J, Vogtenhuber C, Blazar B, Farrar M. IL-2 receptor beta-dependent STAT5 activation is required for the development of Foxp3+ regulatory T cells. J Immunol. 2007;178:280-90 pubmed
    ..Finally, STAT5 binds to the promoter of the foxp3 gene suggesting that IL-2Rbeta-dependent STAT5 activation promotes Treg differentiation by regulating expression of foxp3. ..
  5. Kimura A, Martin C, Robinson G, Simone J, Chen W, Wickre M, et al. The gene encoding the hematopoietic stem cell regulator CCN3/NOV is under direct cytokine control through the transcription factors STAT5A/B. J Biol Chem. 2010;285:32704-9 pubmed publisher
    ..ChIP assays using 32D cells revealed IL-3-induced binding of STAT5A/B to a γ-interferon-activated sequences site in the Ccn3/Nov gene promoter. This is the first report that Ccn3/Nov is directly induced by cytokines through STAT5A/B. ..
  6. Hoelbl A, Kovacic B, Kerenyi M, Simma O, Warsch W, Cui Y, et al. Clarifying the role of Stat5 in lymphoid development and Abelson-induced transformation. Blood. 2006;107:4898-906 pubmed
    The Stat5 transcription factors Stat5a and Stat5b have been implicated in lymphoid development and transformation...
  7. Kelly J, Spolski R, Kovanen P, Suzuki T, Bollenbacher J, Pise Masison C, et al. Stat5 synergizes with T cell receptor/antigen stimulation in the development of lymphoblastic lymphoma. J Exp Med. 2003;198:79-89 pubmed
    ..We now report the development of thymic T cell lymphoblastic lymphomas in transgenic mice in which Stat5a or Stat5b is overexpressed within the lymphoid compartment...
  8. Schwaller J, Parganas E, Wang D, Cain D, Aster J, Williams I, et al. Stat5 is essential for the myelo- and lymphoproliferative disease induced by TEL/JAK2. Mol Cell. 2000;6:693-704 pubmed
    ..These data define a critical role for Stat5a/b and mOSM in the pathogenesis of TEL/JAK2 disease. ..
  9. Li G, Wang Z, Zhang Y, Kang Z, Haviernikova E, Cui Y, et al. STAT5 requires the N-domain to maintain hematopoietic stem cell repopulating function and appropriate lymphoid-myeloid lineage output. Exp Hematol. 2007;35:1684-94 pubmed
    ..mice with potential to express STAT5ab deltaN (STAT5ab(deltaN/deltaN)) with mice completely lacking STAT5a and STAT5b (STAT5abnull/null)...
  10. Yao Z, Kanno Y, Kerenyi M, Stephens G, Durant L, Watford W, et al. Nonredundant roles for Stat5a/b in directly regulating Foxp3. Blood. 2007;109:4368-75 pubmed
    ..Therefore, we conclude that Stat5a/b have an essential, nonredundant role in regulating Treg cells, and that Stat3 and Stat5a/b appear to have opposing roles in the regulation of Foxp3. ..
  11. Moriggl R, Topham D, Teglund S, Sexl V, McKay C, Wang D, et al. Stat5 is required for IL-2-induced cell cycle progression of peripheral T cells. Immunity. 1999;10:249-59 pubmed
    ..These phenotypes are not seen in mice lacking Stat5a or Stat5b alone...
  12. Cui Y, Riedlinger G, Miyoshi K, Tang W, Li C, Deng C, et al. Inactivation of Stat5 in mouse mammary epithelium during pregnancy reveals distinct functions in cell proliferation, survival, and differentiation. Mol Cell Biol. 2004;24:8037-47 pubmed
  13. Shillingford J, Miyoshi K, Robinson G, Bierie B, Cao Y, Karin M, et al. Proteotyping of mammary tissue from transgenic and gene knockout mice with immunohistochemical markers: a tool to define developmental lesions. J Histochem Cytochem. 2003;51:555-65 pubmed
    ..We propose that the technique of proteotyping will have wide applications in the analyses of defects in other mouse models. ..
  14. Clodfelter K, Holloway M, Hodor P, Park S, Ray W, Waxman D. Sex-dependent liver gene expression is extensive and largely dependent upon signal transducer and activator of transcription 5b (STAT5b): STAT5b-dependent activation of male genes and repression of female genes revealed by microarray analysis. Mol Endocrinol. 2006;20:1333-51 pubmed pituitary GH secretion, with the transcription factor, signal transducer and activator of transcription (STAT5b), proposed to mediate signaling by the pulsatile, male plasma GH profile...
  15. Bradley H, Hawley T, Bunting K. Cell intrinsic defects in cytokine responsiveness of STAT5-deficient hematopoietic stem cells. Blood. 2002;100:3983-9 pubmed
    ..we have analyzed mice lacking expression of both signal transducer and activator of transcription 5a (STAT5a) and STAT5b (STAT5ab(-/-))...
  16. Duy C, Hurtz C, Shojaee S, Cerchietti L, Geng H, Swaminathan S, et al. BCL6 enables Ph+ acute lymphoblastic leukaemia cells to survive BCR-ABL1 kinase inhibition. Nature. 2011;473:384-8 pubmed publisher
    ..We identify BCL6 as a central component of this drug-resistance pathway and demonstrate that targeted inhibition of BCL6 leads to eradication of drug-resistant and leukaemia-initiating subclones. ..
  17. Yamaji D, Kang K, Robinson G, Hennighausen L. Sequential activation of genetic programs in mouse mammary epithelium during pregnancy depends on STAT5A/B concentration. Nucleic Acids Res. 2013;41:1622-36 pubmed publisher
    ..We have used mouse genetics and genome-wide analyses to determine how altering concentrations of STAT5A and STAT5B impacts mammary epithelial development during pregnancy and the regulation of target genes...
  18. Johnston R, Choi Y, Diamond J, Yang J, Crotty S. STAT5 is a potent negative regulator of TFH cell differentiation. J Exp Med. 2012;209:243-50 pubmed publisher
    ..These results demonstrate that IL-2, STAT5, and Blimp-1 collaborate to negatively regulate T(FH) cell differentiation. ..
  19. Couldrey C, Bradley H, Bunting K. A STAT5 modifier locus on murine chromosome 7 modulates engraftment of hematopoietic stem cells during steady-state hematopoiesis. Blood. 2005;105:1476-83 pubmed
    Homologous disruption of expression of signal transducer and activator of transcription 5a (STAT5a) and STAT5b (STAT5ab(-/-)) in mice results in hematopoietic stem cells (HSCs) that can engraft irradiated hosts alone but are ..
  20. Kovanen P, Young L, Al Shami A, Rovella V, Pise Masison C, Radonovich M, et al. Global analysis of IL-2 target genes: identification of chromosomal clusters of expressed genes. Int Immunol. 2005;17:1009-21 pubmed
    ..3, a region that contains genes encoding the tumor necrosis factor (TNF) superfamily members TNF, LT-alpha and LT-beta. ..
  21. Davoodi Semiromi A, Laloraya M, Kumar G, Purohit S, Jha R, She J. A mutant Stat5b with weaker DNA binding affinity defines a key defective pathway in nonobese diabetic mice. J Biol Chem. 2004;279:11553-61 pubmed
    ..We report here a defective gene (Stat5b) located on chromosome 11 within a previously mapped T1D susceptibility interval (Idd4) in the nonobese diabetic (..
  22. Kelly J, Spolski R, Imada K, Bollenbacher J, Lee S, Leonard W. A role for Stat5 in CD8+ T cell homeostasis. J Immunol. 2003;170:210-7 pubmed
    ..We have now investigated the role of Stat5 proteins in this process. Whereas Stat5a and Stat5b KO mice have decreased numbers of CD8+ T cells, Stat5-transgenic mice have an increased number of these cells...
  23. Fievez L, Desmet C, Henry E, Pajak B, Hegenbarth S, Garze V, et al. STAT5 is an ambivalent regulator of neutrophil homeostasis. PLoS ONE. 2007;2:e727 pubmed
    ..In LECs, STAT5 negatively regulates granulopoiesis by directly or indirectly repressing G-CSF expression. Removal of this STAT5-imposed brake contributes to induction of emergency granulopoiesis. ..
  24. Moriggl R, Gouilleux Gruart V, Jähne R, Berchtold S, Gartmann C, Liu X, et al. Deletion of the carboxyl-terminal transactivation domain of MGF-Stat5 results in sustained DNA binding and a dominant negative phenotype. Mol Cell Biol. 1996;16:5691-700 pubmed
    ..Two closely related variants of Stat5, Stat5a and Stat5b, are encoded by distinct genes. We examined the functional properties of the carboxyl termini of these molecules...
  25. Yamaji D, Na R, Feuermann Y, Pechhold S, Chen W, Robinson G, et al. Development of mammary luminal progenitor cells is controlled by the transcription factor STAT5A. Genes Dev. 2009;23:2382-7 pubmed publisher
    ..Thus, STAT5A is necessary and sufficient for the establishment of luminal progenitor cells...
  26. Shelburne C, McCoy M, Piekorz R, Sexl V, Roh K, Jacobs Helber S, et al. Stat5 expression is critical for mast cell development and survival. Blood. 2003;102:1290-7 pubmed
    ..These results indicate that Stat5A and Stat5B are critical regulators of in vitro and in vivo mast cell development and survival.
  27. Liu F, Kunter G, Krem M, Eades W, Cain J, Tomasson M, et al. Csf3r mutations in mice confer a strong clonal HSC advantage via activation of Stat5. J Clin Invest. 2008;118:946-55 pubmed publisher
    ..proliferative advantage conferred by the mutant Csf3r was abrogated in myeloid progenitors lacking both Stat5A and Stat5B, and HSC function was reduced in mice expressing a truncated mutant Csf3r engineered to have impaired Stat5 ..
  28. Lin J, Li P, Liu D, Jin H, He J, Ata Ur Rasheed M, et al. Critical Role of STAT5 transcription factor tetramerization for cytokine responses and normal immune function. Immunity. 2012;36:586-99 pubmed publisher
    ..We generated Stat5a-Stat5b double knockin (DKI) N-domain mutant mice in which STAT5 proteins form dimers but not tetramers, identified ..
  29. Bradley H, Couldrey C, Bunting K. Hematopoietic-repopulating defects from STAT5-deficient bone marrow are not fully accounted for by loss of thrombopoietin responsiveness. Blood. 2004;103:2965-72 pubmed
    ..We have directly compared bone marrow (BM) from mice mutant for STAT5a and STAT5b (STAT5ab(-/-)) with that from mice lacking c-Mpl (c-Mpl(-/-)), the thrombopoietin receptor...
  30. Dai X, Chen Y, Di L, Podd A, Li G, Bunting K, et al. Stat5 is essential for early B cell development but not for B cell maturation and function. J Immunol. 2007;179:1068-79 pubmed
    The two closely related Stat5 (Stat5A and Stat5B) proteins are activated by a broad spectrum of cytokines...
  31. Malin S, McManus S, Cobaleda C, Novatchkova M, Delogu A, Bouillet P, et al. Role of STAT5 in controlling cell survival and immunoglobulin gene recombination during pro-B cell development. Nat Immunol. 2010;11:171-9 pubmed publisher
    ..Hence, STAT5 and IL-7 signaling control cell survival and the developmental ordering of immunoglobulin gene rearrangements by suppressing premature Igk recombination in pro-B cells. ..
  32. Lin J, Leonard W. The role of Stat5a and Stat5b in signaling by IL-2 family cytokines. Oncogene. 2000;19:2566-76 pubmed
    The activation of Stat5 proteins (Stat5a and Stat5b) is one of the earliest signaling events mediated by IL-2 family cytokines, allowing the rapid delivery of signals from the membrane to the nucleus...
  33. Kieslinger M, Woldman I, Moriggl R, Hofmann J, Marine J, Ihle J, et al. Antiapoptotic activity of Stat5 required during terminal stages of myeloid differentiation. Genes Dev. 2000;14:232-44 pubmed
    ..findings with dnStat5-expressing chicken myeloblasts were confirmed with primary hematopoietic cells from Stat5a/Stat5b-deficient mice...
  34. Miyoshi K, Shillingford J, Smith G, Grimm S, Wagner K, Oka T, et al. Signal transducer and activator of transcription (Stat) 5 controls the proliferation and differentiation of mammary alveolar epithelium. J Cell Biol. 2001;155:531-42 pubmed
    ..These data demonstrate that signaling via the PrlR and Stat5 is critical for the proliferation and differentiation of mammary alveoli during pregnancy. ..
  35. Laloraya M, Davoodi Semiromi A, Kumar G, McDuffie M, She J. Impaired Crkl expression contributes to the defective DNA binding of Stat5b in nonobese diabetic mice. Diabetes. 2006;55:734-41 pubmed
    A point mutation in the Stat5b DNA binding domain in the nonobese diabetic (NOD) mouse was shown to have weaker DNA binding compared with the B6 Stat5b...
  36. Teglund S, McKay C, Schuetz E, van Deursen J, Stravopodis D, Wang D, et al. Stat5a and Stat5b proteins have essential and nonessential, or redundant, roles in cytokine responses. Cell. 1998;93:841-50 pubmed
    ..Among the Stats, the two highly related proteins, Stat5a and Stat5b, are activated by a variety of cytokines...
  37. Yan D, Hutchison R, Mohi G. Critical requirement for Stat5 in a mouse model of polycythemia vera. Blood. 2012;119:3539-49 pubmed publisher
    ..These findings also provide strong support for the development of Stat5 inhibitors as targeted therapies for the treatment of PV and other JAK2V617F-positive MPNs. ..
  38. Zhu B, Kang K, Yu J, Chen W, Smith H, Lee D, et al. Genome-wide analyses reveal the extent of opportunistic STAT5 binding that does not yield transcriptional activation of neighboring genes. Nucleic Acids Res. 2012;40:4461-72 pubmed publisher
    ..Up to 40% of STAT5-bound genes were not expressed. For the first time we demonstrate the magnitude of opportunistic genomic STAT5 binding that does not translate into transcriptional activation of neighboring genes. ..
  39. Wang Z, Li G, Tse W, Bunting K. Conditional deletion of STAT5 in adult mouse hematopoietic stem cells causes loss of quiescence and permits efficient nonablative stem cell replacement. Blood. 2009;113:4856-65 pubmed publisher
  40. Bennett E, McGuinness L, Gevers E, Thomas G, Robinson I, Davey H, et al. Hypothalamic STAT proteins: regulation of somatostatin neurones by growth hormone via STAT5b. J Neuroendocrinol. 2005;17:186-94 pubmed
    ..We demonstrate that STAT5b protein expression, similar to somatostatin mRNA, is sexually dimorphic in the periventricular nucleus of rats and ..
  41. Grimley P, Dong F, Rui H. Stat5a and Stat5b: fraternal twins of signal transduction and transcriptional activation. Cytokine Growth Factor Rev. 1999;10:131-57 pubmed
    Stat5a and Stat5b are discretely encoded transcription factors that mediate signals for a broad spectrum of cytokines...
  42. Socolovsky M, Fallon A, Wang S, Brugnara C, Lodish H. Fetal anemia and apoptosis of red cell progenitors in Stat5a-/-5b-/- mice: a direct role for Stat5 in Bcl-X(L) induction. Cell. 1999;98:181-91 pubmed
    ..These findings are explained by a crucial role for Stat5 in EpoR's antiapoptotic signaling: it mediates the immediate-early induction of Bcl-X(L) in erythroid cells through direct binding to the Bcl-X promoter. ..
  43. Lin J, Mietz J, Modi W, John S, Leonard W. Cloning of human Stat5B. Reconstitution of interleukin-2-induced Stat5A and Stat5B DNA binding activity in COS-7 cells. J Biol Chem. 1996;271:10738-44 pubmed
    We have isolated a second human Stat5 cDNA, Stat5B, and demonstrated that the genes encoding both Stat5A and Stat5B are located at chromosome 17q11.2. Both genes were constitutively transcribed in peripheral blood lymphocytes...
  44. Lockyer H, Tran E, Nelson B. STAT5 is essential for Akt/p70S6 kinase activity during IL-2-induced lymphocyte proliferation. J Immunol. 2007;179:5301-8 pubmed
    ..Our results not only explain the severe proliferative defect in STAT5-deficient T cells but also provide mechanistic insight into the oncogenic properties of STAT5 in various leukemias and lymphomas. ..
  45. Snow J, Abraham N, Ma M, Abbey N, Herndier B, Goldsmith M. STAT5 promotes multilineage hematolymphoid development in vivo through effects on early hematopoietic progenitor cells. Blood. 2002;99:95-101 pubmed
    ..Multilineage peripheral blood cytopenias were observed in adult mice lacking both isoforms of STAT5 (STAT5A and STAT5B) as well as accelerated rates of apoptosis in the bone marrow...
  46. Jin Y, Purohit S, Chen X, Yi B, She J. Over-expression of Stat5b confers protection against diabetes in the non-obese diabetic (NOD) mice via up-regulation of CD4(+)CD25(+) regulatory T cells. Biochem Biophys Res Commun. 2012;424:669-74 pubmed publisher
    ..Previous reports showed that a mutation (L327M) in the Stat5b protein leads to aberrant cytokine signaling in the NOD mice...
  47. Boucheron C, Dumon S, Santos S, Moriggl R, Hennighausen L, Gisselbrecht S, et al. A single amino acid in the DNA binding regions of STAT5A and STAT5B confers distinct DNA binding specificities. J Biol Chem. 1998;273:33936-41 pubmed
    STAT5A and STAT5B are two highly related transcription factors encoded by two distinct genes. STAT5A and STAT5B are activated by a broad range of cytokines and growth factors...
  48. Imada K, Bloom E, Nakajima H, Horvath Arcidiacono J, Udy G, Davey H, et al. Stat5b is essential for natural killer cell-mediated proliferation and cytolytic activity. J Exp Med. 1998;188:2067-74 pubmed
    ..that can be overcome by high dose interleukin (IL)-2, we now demonstrate that defective proliferation in Stat5b-/- splenocytes cannot be corrected by this treatment...
  49. Meyer R, Laz E, Su T, Waxman D. Male-specific hepatic Bcl6: growth hormone-induced block of transcription elongation in females and binding to target genes inversely coordinated with STAT5. Mol Endocrinol. 2009;23:1914-26 pubmed publisher
    ..induced in female mice deficient in hepatic signal transducer and activator of transcription (STAT)5a/STAT5b, suggesting that these STAT transcriptional mediators of GH signaling repress Bcl6...
  50. Mui A, Wakao H, O Farrell A, Harada N, Miyajima A. Interleukin-3, granulocyte-macrophage colony stimulating factor and interleukin-5 transduce signals through two STAT5 homologs. EMBO J. 1995;14:1166-75 pubmed
    ..In IL-3-dependent hemopoietic cells, both forms of STAT5 are expressed and activated in response to IL-3. ..
  51. Kagami S, Nakajima H, Suto A, Hirose K, Suzuki K, Morita S, et al. Stat5a regulates T helper cell differentiation by several distinct mechanisms. Blood. 2001;97:2358-65 pubmed
  52. Davoodi Semiromi A, McDuffie M, Litherland S, Clare Salzler M. Truncated pStat5B is associated with the Idd4 locus in NOD mice. Biochem Biophys Res Commun. 2007;356:655-61 pubmed
    We investigate JAK-STAT5 activation and its relationship to full-length Stat5B (FL-Stat5) and constitutive phosphorylated carboxy-truncated Stat5B (ct-pStat5) in four different strains of mouse...
  53. Burchill M, Goetz C, Prlic M, O Neil J, Harmon I, Bensinger S, et al. Distinct effects of STAT5 activation on CD4+ and CD8+ T cell homeostasis: development of CD4+CD25+ regulatory T cells versus CD8+ memory T cells. J Immunol. 2003;171:5853-64 pubmed
    Using transgenic mice that express a constitutively active version of STAT5b, we demonstrate that STAT5 plays a key role in governing B cell development and T cell homeostasis...