Objective: The importance of cold‐shock Y‐box binding protein 1 (YB‐1) for cell homeostasis is well‐documented based on prior observations of its association with certain cancer entities. This study was undertaken to explore the role of YB‐1 in T cell homeostasis and survival and the potential contribution of YB‐1 to the pathogenesis of systemic lupus erythematosus (SLE). Methods: In the peripheral blood from 25 SLE patients and 25 healthy donors, the expression of YB‐1 and frequency of T cell apoptosis was analyzed by quantitative polymerase chain reaction (qPCR) and fluorescence‐activated cell sorting of CD4+ T cells ex vivo and also analyzed in T cells in vitro after 6 days of stimulation with anti‐CD3–coupled or anti‐CD3/anti‐CD28–coupled microspheres. YB‐1 was overexpressed using lentiviral transduction with wild‐type green fluorescent protein (wtGFP) YB‐1, and knockdown of YB‐1 was achieved using specific short hairpin RNA (shRNA) (3‐fold reduction; P < 0.0001). Results: YB‐1 expression was significantly lower in apoptosis‐prone T cells and in activated T cells from SLE patients compared to YB‐1 expression in nonapoptotic T cells and activated T cells from healthy donors (P = 0.001). Knockdown of YB‐1 in T cells consequently led to expression of proapoptotic molecules and caspase 3 activation (1.6‐fold), and subsequently, to apoptosis. Furthermore, YB‐1 promoted survival pathways involving enhanced protein expression of the kinase Akt (2‐fold) and Bcl‐2 (3‐fold), even when Fas/CD95 was triggered. YB‐1–mediated T cell survival was reversed by Akt and phosphatidylinositol 3‐kinase (PI3K) inactivation. In SLE patients, rescue of YB‐1 expression strongly promoted survival of T cells and even prevented cell death in T cells that were extremely apoptosis‐prone. Conclusion: Our data show that failure of YB‐1 up‐regulation in T cells from SLE patients led to enhanced apoptosis. These findings imply that YB‐1 plays a crucial role in the disturbed homeostasis of activated T cells leading to hematopoietic alterations in SLE. These insights may help facilitate the development of new treatment strategies for SLE. [ABSTRACT FROM AUTHOR]