Moving out: mobilizing activated T cells from lymphoid tissues

Suppression of Foxo1 activity and down-modulation of CD62L (L-selectin) in HIV-1 infected resting CD4 T cells

HIV-1 hijacks and disrupts many processes in the cells it infects in order to suppress antiviral immunity and to facilitate its replication. Resting CD4 T cells are important early targets of HIV-1 infection in which HIV-1 must overcome intrinsic barriers to viral replication. Although resting CD4 T cells are refractory to infection in vitro, local environmental factors within lymphoid and mucosal tissues such as cytokines facilitate viral replication while maintaining the resting state. These factors can be utilized in vitro to study HIV-1 replication in resting CD4 T cells. In vivo, the migration of resting naïve and central memory T cells into lymphoid tissues is dependent upon expression of CD62L (L-selectin), a receptor that is subsequently down-modulated following T cell activation. CD62L gene transcription is maintained in resting T cells by Foxo1 and KLF2, transcription factors that maintain T cell quiescence and which regulate additional cellular processes including survival, migration, and differentiation. Here we report that HIV-1 down-modulates CD62L in productively infected naïve and memory resting CD4 T cells while suppressing Foxo1 activity and the expression of KLF2 mRNA. Partial T cell activation was further evident as an increase in CD69 expression. Several other Foxo1- and KLF2-regulated mRNA were increased or decreased in productively infected CD4 T cells, including IL-7rα, Myc, CCR5, Fam65b, S1P₁ (EDG1), CD52, Cyclin D2 and p21^CIP1, indicating a profound reprogramming of these cells. The Foxo1 inhibitor AS1842856 accelerated de novo viral gene expression and the sequella of infection, supporting the notion that HIV-1 suppression of Foxo1 activity may be a strategy to promote replication in resting CD4 T cells. As Foxo1 is an investigative cancer therapy target, the development of Foxo1 interventions may assist the quest to specifically suppress or activate HIV-1 replication in vivo.

Chronic exposure to staphylococcal superantigen elicits a systemic inflammatory disease mimicking lupus

Chronic nasal and skin colonization with superantigen (SAg)-producing Staphylococcus aureus is well documented in humans. Given that trans-mucosal and trans-cutaneous absorption of SAgs can occur, we determined whether chronic exposure to small amounts of SAg per se could activate autoreactive CD4(+) and CD8(+) T cells and precipitate any autoimmune disease without further external autoantigenic stimulation. Because HLA class II molecules present SAg more efficiently than do mouse MHC class II molecules, HLA-DQ8 transgenic mice were implanted s.c. with mini-osmotic pumps capable of continuously delivering the SAg, staphylococcal enterotoxin B (total of 10 μg/mouse), or PBS over 4 wk. Chronic exposure to staphylococcal enterotoxin B resulted in a multisystem autoimmune inflammatory disease with features similar to systemic lupus erythematosus. The disease was characterized by mononuclear cell infiltration of lungs, liver, and kidneys, accompanied by the production of anti-nuclear Abs and deposition of immune complexes in the renal glomeruli. The inflammatory infiltrates in various organs predominantly consisted of CD4(+) T cells bearing TCR Vβ8. The extent of immunopathology was markedly reduced in mice lacking CD4(+) T cells and CD28, indicating that the disease is CD4(+) T cell mediated and CD28 dependent. The absence of disease in STAT4-deficient, as well as IFN-γ-deficient, HLA-DQ8 mice suggested the pathogenic role of Th1-type cytokines, IL-12 and IFN-γ. In conclusion, our study suggests that chronic exposure to extremely small amounts of bacterial SAg could be an etiological factor for systemic lupus erythematosus.

Temporal regulation of rapamycin on memory CTL programming by IL-12

Mammalian target of rapamycin (mTOR) is a master regulator of cell growth. Recent reports have defined its important role in memory cytotoxic T lymphocyte (CTL) differentiation in infections and memory programming. We report that rapamycin regulated memory CTL programming by IL-12 to a similar level in a wide range of concentrations, and the enhanced memory CTLs by rapamycin were functional and provided similar protection against Listeria Monocytogenes challenge compared to the control. In addition, rapamycin-experienced CTLs went through substantially enhanced proliferation after transfer into recipients. Furthermore, the regulatory function of rapamycin on CD62L expression in memory CTLs was mainly contributed by the presence of rapamycin in the first 24-hr of stimulation in vitro, whereas the effective window of rapamycin on the size of memory CTLs was determined between 24 to 72 hrs. In conclusion, rapamycin regulates IL-12-driven programming of CTLs to a similar level in a wide range of concentrations, and regulates the phenotype and the size of memory CTLs in different temporal windows.