CD4+CD25+ regulatory T cells (Treg) are instrumental in the maintenance of immunological tolerance. One critical question is whether Treg can only be generated in the thymus or can differentiate from peripheral CD4+CD25− naive T cells. In this paper, we present novel evidence that conversion of naive peripheral CD4+CD25− T cells into anergic/suppressor cells that are CD25+, CD45RB−/low and intracellular CTLA-4+ can be achieved through costimulation with T cell receptors (TCRs) and transforming growth factor β (TGF-β). Although transcription factor Foxp3 has been shown recently to be associated with the development of Treg, the physiological inducers for Foxp3 gene expression remain a mystery. TGF-β induced Foxp3 gene expression in TCR-challenged CD4+CD25− naive T cells, which mediated their transition toward a regulatory T cell phenotype with potent immunosuppressive potential. These converted anergic/suppressor cells are not only unresponsive to TCR stimulation and produce neither T helper cell 1 nor T helper cell 2 cytokines but they also express TGF-β and inhibit normal T cell proliferation in vitro. More importantly, in an ovalbumin peptide TCR transgenic adoptive transfer model, TGF-β–converted transgenic CD4+CD25+ suppressor cells proliferated in response to immunization and inhibited antigen-specific naive CD4+ T cell expansion in vivo. Finally, in a murine asthma model, coadministration of these TGF-β–induced suppressor T cells prevented house dust mite–induced allergic pathogenesis in lungs.

IntroductionThe complex life cycle of HIV-1 involves critical functional interactions with CD4 ϩ host-cell factors. In addition to CD4 ϩ T cells, CD4 ϩ CCR5 ϩ macrophages represent a primary target and host of HIV-1. Infected macrophages replicate copious amounts of virus at their surface and at intracellular membranes where the virions accumulate in vesicles. 1 Macrophages are not typically subject to viral-induced death and may persist as reservoirs of virus in tissues for long periods of time. 2,3 In addition, infected macrophages may be resistant to antiviral agents, 3-6 and the unique attributes and factors that are enabling for this persistent viral host remain elusive. Critically, all monocytic cells are neither equally permissive to HIV-1 nor supportive of the viral life cycle. In vitro or in vivo, dendritic cells (DCs) may or may not become infected, depending on maturational status 7 ; peripheral-blood monocytes are nearly impervious (Ͻ 1% HIV-1 DNA ϩ ) 8,9 ; and of longstanding interest is the enhanced susceptibility of macrophages to HIV-1 compared with immature monocytes, the basis of which remains a mystery. The fact that macrophages, in culture and in tissues, are more susceptible to infection than monocytes cannot be attributed to levels of membrane CD4 or HIV-1 coreceptor expression 10 or multiple other criteria that have been considered. 11 This fundamental question has obvious significance in that if the monocyte-resistance factor(s) can be identified, opportunities may emerge for manipulating susceptible myeloid populations to impose a restrictive barrier to HIV-1. Limited evidence supports an early postentry block that occurs in association with or shortly after reverse transcription (RT). 8 Beyond the well-established CD4 and CCR5/CXCR4 entry requirements, recent evidence implicates additional membrane and intracellular factors that influence early host-cell responsiveness to productive infection. [11][12][13][14][15][16][17] Among the potential innate intracellular viral antagonists, initially characterized in T cells 18 and more recently in monocytes, 19,20 are cytidine deaminases that edit viral RNA and mutate DNA. These cytoplasmic apolipoprotein B mRNA-editing enzyme catalytic polypeptidelike (APOBEC) subunits, particularly APOBEC3G (hA3G), become incorporated into virions, leading to mutation of nascent HIV-1 DNA formed during reverse transcription and its subsequent degradation. 18,21,22 HIV-1, in turn, inhibits hA3G via HIV-1-encoded viral infectivity factor (Vif)-dependent and -independent pathways to thwart this antiviral defense within the target cell. Vif not only facilitates 26S proteasome-mediated degradation of hA3G but also diminishes its synthesis to collectively exclude hA3G incorporation into the budding virions. [23][24][25] Nonetheless, whether differential HIV-1 susceptibility in myeloid populations could be attributed to constitutively expressed hA3G or any other components of this defensive superfamily had not been addressed.In this study, by oligonucleotide microarr...

Apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G), a cytidine deaminase, is a recently recognized innate intracellular protein with lethal activity against human immunodeficiency virus (HIV). Packaged into progeny virions, APOBEC3G enzymatic activity leads to HIV DNA degradation. As a counterattack, HIV virion infectivity factor (Vif) targets APOBEC3G for proteasomal proteolysis to exclude it from budding virions. Based on the ability of APOBEC3G to antagonize HIV infection, considerable interest hinges on elucidating its mechanism(s) of regulation. In this study, we provide the first evidence that an innate, endogenous host defense factor has the potential to promote APOBEC3G and rebuke the virus-mediated attempt to control its cellular host. We identify interferon (IFN)-α as a potent inducer of APOBEC3G to override HIV Vif neutralization of APOBEC3 proteins that pose a threat to efficient macrophage HIV replication. Our data provide a new dimension by which IFN-α mediates its antiviral activity and suggest a means to render the host nonpermissive for viral replication.