Protein phosphorylation initiates signal transduction that triggers lymphocyte activation. However, other posttranslational modifications may contribute to this process. Here, we show that CD28 engagement induced protein arginine methyltransferase activity and methylation on arginine of several proteins, including Vav1. Methylation of Vav1 and IL-2 production were reduced by inhibiting S-adenosyl-L-homocysteine hydrolase, an enzyme that regulates cellular transmethylation. Methylated Vav1 was induced in human and mouse T cells and selectively localized in the nucleus, which suggested that this form marks a nuclear function of Vav1. Our findings uncover a signaling pathway that is controlled by CD28 that is likely to be important for T cell activation.

Interleukin-12 (IL-12) is a key cytokine for the development of T helper type 1 (Th1) responses; however, naïve CD4 þ T cells do not express IL-12Rb2, and are therefore unresponsive to IL-12. We have examined the mechanisms that control Th1-specific expression of the human IL12Rb2 gene at early time points after T-cell stimulation.We have identified a Th1-specific enhancer element that binds signal transducer and activator of transcription 4 (STAT4) in vivo in developing Th1 but not Th2 cells. T-cell receptor (TCR) signaling induced histone hyperacetylation and recruitment of BRG1, the ATPase subunit of the SWI/SNF-like BAF chromatin remodeling complex, to the IL-12Rb2 regulatory regions and was associated with lowlevel gene transcription at the IL-12Rb2 locus. However, high-level IL-12Rb2 expression required TCR triggering in the presence of IL-12. Our results indicate a synergistic role of TCR-induced chromatin remodeling and cytokineinduced STAT4 activation to direct IL-12Rb2 expression during Th1 cell development.

HIV-1 infection is characterized by a progressive decline in CD4 + T cells leading to a state of profound immunodeficiency. IL-2 therapy has been shown to improve CD4 + counts beyond that observed with antiretroviral therapy. Recent phase III trials revealed that despite a sustained increase in CD4 + counts, IL-2-treated patients did not experience a better clinical outcome [Abrams D, et al. (2009) N Engl J Med 361(16):1548-1559. To explain these disappointing results, we have studied phenotypic, functional, and molecular characteristics of CD4 + T cell populations in IL-2-treated patients. We found that the principal effect of long-term IL-2 therapy was the expansion of two distinct CD4 + CD25 + T cell populations (CD4 + CD25 lo CD127 lo FOXP3 + and CD4 + CD25 hi CD127 lo FOXP3 hi ) that shared phenotypic markers of Treg but could be distinguished by the levels of CD25 and FOXP3 expression. IL-2-expanded CD4 + CD25 + T cells suppressed proliferation of effector cells in vitro and had gene expression profiles similar to those of natural regulatory CD4 + CD25 hi FOXP3 + T cells (Treg) from healthy donors, an immunosuppressive T cell subset critically important for the maintenance of self-tolerance. We propose that the sustained increase of the peripheral Treg pool in IL-2-treated HIV patients may account for the unexpected clinical observation that patients with the greatest expansion of CD4 + T cells had a higher relative risk of clinical progression to AIDS. molecular profiling | immune-based therapy H IV infection is mainly associated with a progressive decrease in the number of CD4 + T lymphocytes and defective CD4-and CD8-specific T cell responses against HIV and other pathogens. Quantitative and qualitative CD4 T cell reconstitution following introduction of antiretroviral therapy (ART) in HIVinfected patients is often incomplete, leading one to evaluate the impact of immune-based therapy in combination with ART. In the past 20 years, a large set of clinical trials demonstrated that intermittent interleukin (IL)-2 therapy increased the CD4 T cell pool in HIV-infected patients and induced, in a large majority of patients, significant and sustained increases in CD4 T cell count beyond that seen in patients treated with antiviral drugs alone. In particular, recombinant IL-2 therapy raised naive and central memory CD4 + cells expressing CD25, the α-chain of the IL-2 receptor, more than antiretroviral drugs alone (1-6). This population accounted for up to 70% of the total CD4 + T cell pool of IL-2-treated patients and persisted for a long time.The clinical impact of IL-2 was evaluated in two long-run large phase III trials (SILCAAT and ESPRIT) involving almost 6,000 chronically HIV-1-infected patients. Results recently reported showed that, despite a sustained increase in CD4 + T cell counts, over a median follow-up of 7-8 years, IL-2-treated patients did not experience a better clinical outcome (7). These disappointing results have remained unexplained so far.In mice, IL-2 has been shown to be essential for the...

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