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.

Increased leukocyte elastase activity in mice lacking secretory leukocyte protease inhibitor (SLPI) leads to impaired wound healing due to enhanced activity of TGFbeta and perhaps additional mechanisms. Proepithelin (PEPI), an epithelial growth factor, can be converted to epithelins (EPIs) in vivo by unknown mechanisms with unknown consequences. We found that PEPI and EPIs exert opposing activities. EPIs inhibit the growth of epithelial cells but induce them to secrete the neutrophil attractant IL-8, while PEPI blocks neutrophil activation by tumor necrosis factor, preventing release of oxidants and proteases. SLPI and PEPI form complexes, preventing elastase from converting PEPI to EPIs. Supplying PEPI corrects the wound-healing defect in SLPI null mice. Thus, SLPI/elastase act via PEPI/EPIs to operate a switch at the interface between innate immunity and wound healing.

Secretory leukocyte protease inhibitor (SLPI) is a serine protease inhibitor with anti-microbial properties found in mucosal fluids. It is expressed during cutaneous wound healing. Impaired healing states are characterized by excessive proteolysis and often bacterial infection, leading to the hypothesis that SLPI may have a role in this process. We have generated mice null for the gene encoding SLPI (Slpi), which show impaired cutaneous wound healing with increased inflammation and elastase activity. The altered inflammatory profile involves enhanced activation of local TGF-beta in Slpi-null mice. We propose that SLPI is a pivotal endogenous factor necessary for optimal wound healing.

T cell apoptosis is critical to development and homeostasis of the immune system. The most salient feature of apoptosis is the lack of an attendant inflammatory response or tissue damage. Here, we present evidence that apoptotic T cells release TGF-beta, thereby contributing to an immunosuppressive milieu. Apoptotic T cells released not only latent but also bio-active TGF-beta. Nonetheless, TGF-beta transcription was not upregulated, suggesting release of existing rather than synthesis of new TGF-beta. Localized within the intracellular membrane-bound compartment, which includes mitochondria, TGF-beta was redistributed into the cytosol following loss of mitochondrial membrane potential. TGF-beta secreted from apoptotic T cells inhibited proinflammatory cytokine production by activated macrophages to foster immune suppression. These findings broaden the potential mechanisms whereby induction of immune tolerance or deficiency occurs through T cell deletion.

Evidence indicates that cytotoxic T lymphocyte–associated antigen 4 (CTLA-4) may negatively regulate T cell activation, but the basis for the inhibitory effect remains unknown. We report here that cross-linking of CTLA-4 induces transforming growth factor β (TGF-β) production by murine CD4+ T cells. CD4+ T helper type 1 (Th1), Th2, and Th0 clones all secrete TGF-β after antibody cross-linking of CTLA-4, indicating that induction of TGF-β by CTLA-4 signaling represents a ubiquitous feature of murine CD4+ T cells. Stimulation of the CD3–T cell antigen receptor complex does not independently induce TGF-β, but is required for optimal CTLA-4–mediated TGF-β production. The consequences of cross-linking of CTLA-4, together with CD3 and CD28, include inhibition of T cell proliferation and interleukin (IL)-2 secretion, as well as suppression of both interferon γ (Th1) and IL-4 (Th2). Moreover, addition of anti–TGF-β partially reverses this T cell suppression. When CTLA-4 was cross-linked in T cell populations from TGF-β1 gene–deleted (TGF-β1−/−) mice, the T cell responses were only suppressed 38% compared with 95% in wild-type mice. Our data demonstrate that engagement of CTLA-4 leads to CD4+ T cell production of TGF-β, which, in part, contributes to the downregulation of T cell activation. CTLA-4, through TGF-β, may serve as a counterbalance for CD28 costimulation of IL-2 and CD4+ T cell activation.

The distribution of secretory leukocyte protease inhibitor (SLPI) at entry portals indicates its involvement in defending the host from pathogens, consistent with the ability of SLPI to inhibit human immunodeficiency virus (HIV)-1 infection by an unknown mechanism. We now demonstrate that SLPI binds to the membrane of human macrophages through the phospholipid-binding protein, annexin II. Based on the recent identification of human cell membrane phosphatidylserine (PS) in the outer coat of HIV-1, we define a novel role for annexin II, a PS-binding moiety, as a cellular cofactor supporting macrophage HIV-1 infection. Moreover, this HIV-1 PS interaction with annexin II can be disrupted by SLPI or other annexin II–specific inhibitors. The PS–annexin II connection may represent a new target to prevent HIV-1 infection.

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...

D-mannose, a C-2 epimer of glucose, exists naturally in many plants and fruits, and is found in human blood at concentrations less than one-fiftieth of that of glucose. However, although the roles of glucose in T cell metabolism, diabetes and obesity are well characterized, the function of D-mannose in T cell immune responses remains unknown. Here we show that supraphysiological levels of D-mannose safely achievable by drinking-water supplementation suppressed immunopathology in mouse models of autoimmune diabetes and airway inflammation, and increased the proportion of Foxp3 regulatory T cells (T cells) in mice. In vitro, D-mannose stimulated T cell differentiation in human and mouse cells by promoting TGF-β activation, which in turn was mediated by upregulation of integrin αβ and reactive oxygen species generated by increased fatty acid oxidation. This previously unrecognized immunoregulatory function of D-mannose may have clinical applications for immunopathology.