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IL-17F and IL-17A are members of the IL-17 pro-inflammatory cytokine family. IL-17A has been implicated in the pathogenesis of autoimmune diseases. IL-17F is a disulfide-linked dimer that contains a cysteine-knot motif. We hypothesized that IL-17F and IL-17A could form a heterodimer due to their sequence homology and overlapping pattern of expression. We evaluated the structure of recombinant IL-17F and IL-17A proteins,as well as that of natural IL-17F and IL-17A derived from activated human CD4+ T cells,by enzyme-linked immunosorbent assay,immunoprecipitation followed by Western blotting,and mass spectrometry. We find that both IL-17F and IL-17A can form both homodimeric and heterodimeric proteins when expressed in a recombinant system,and that all forms of the recombinant proteins have in vitro functional activity. Furthermore,we find that in addition to the homodimers of IL-17F and IL-17A,activated human CD4+ T cells also produce the IL-17F/IL-17A heterodimer. These data suggest that the IL-17F/IL-17A heterodimer may contribute to the T cell-mediated immune responses. View Publication

IL-12 is an immunoregulatory cytokine,which promotes Th1 cell differentiation and is a major inducer of IFN-gamma. IFN-beta,a Type I IFN used in the treatment of multiple sclerosis,has been shown to significantly increase the expression of the anti-inflammatory cytokine IL-10,a major suppressor of Th1 cytokines. The beneficial immunomodulatory effects of IFN-beta may in part be a result of its ability to suppress IL-12. However,IL-12 and IFN-beta signal via the STAT4 pathway. Our aim was to investigate the relationship between IL-12 and IFN-beta by observing the effect of prior exposure to IL-12 or IFN-beta on the ability of T cells to subsequently respond to the other cytokine. We report that IFN-beta increases IL-12-induced STAT4 phosphorylation and up-regulates IL-12 receptor beta1 and beta2 expression. However,despite this up-regulation,IFN-beta suppressed IL-12-induced IFN-gamma expression. Our results suggest that this may be a result of the parallel induction of IL-10 by IFN-beta. View Publication

T cell activation is predicated on the interaction between the T cell receptor and peptide-major histocompatibility (pMHC) ligands. The factors that determine the stimulatory potency of a pMHC molecule remain unclear. We describe results showing that a peptide exhibiting many hallmarks of a weak agonist stimulates T cells to proliferate more than the wild-type agonist ligand. An in silico approach suggested that the inability to form the central supramolecular activation cluster (cSMAC) could underlie the increased proliferation. This conclusion was supported by experiments that showed that enhancing cSMAC formation reduced stimulatory capacity of the weak peptide. Our studies highlight the fact that a complex interplay of factors determines the quality of a T cell antigen. View Publication

Microbial products serving as superantigens (SAgs) have been implicated in triggering various T cell-mediated chronic inflammatory disorders,including severe asthma. Given earlier evidence demonstrating that airway smooth muscle (ASM) cells express MHC class II molecules,we investigated whether ASM can present SAg to resting CD4(+) T cells,and further examined whether this action reciprocally elicits proasthmatic changes in ASM responsiveness. Coincubation of CD4(+) T cells with human ASM cells pulsed with the SAg,staphylococcal enterotoxin A (SEA),elicited adherence and clustering of class II and CD3 molecules at the ASM/T cell interface,indicative of immunological synapse formation,in association with T cell activation. This ASM/T cell interaction evoked up-regulated mRNA expression and pronounced release of the Th2-type cytokine,IL-13,into the coculture medium,which was MHC class II dependent. Moreover,when administering the conditioned medium from the SEA-stimulated ASM/T cell cocultures to isolated naive rabbit ASM tissues,the latter exhibited proasthmatic-like changes in their constrictor and relaxation responsiveness that were prevented by pretreating the tissues with an anti-IL-13 neutralizing Ab. Collectively,these observations are the first to demonstrate that ASM can present SAg to CD4(+) T cells,and that this MHC class II-mediated cooperative ASM/T cell interaction elicits release of IL-13 that,in turn,evokes proasthmatic changes in ASM constrictor and relaxant responsiveness. Thus,a new immuno-regulatory role for ASM is identified that potentially contributes to the pathogenesis of nonallergic (intrinsic) asthma and,accordingly,may underlie the reported association between microbial SAg exposure,T cell activation,and severe asthma. View Publication

NK and T cells are important for combating CMV infection. Some NK and T cells express leukocyte Ig-like receptor-1 (LIR-1),an inhibitory receptor recognizing MHC class I and the CMV-encoded homolog UL18. We previously demonstrated an early increase in LIR-1-expressing blood lymphocytes in lung-transplanted patients later developing CMV disease. We now show that NK and T cells account for the observed LIR-1 augmentation. Coincubation of PBMC from CMV-seropositive donors with virus-infected lung fibroblasts led to a T cell-dependent secretion of IFN-gamma,produced mainly by LIR-1(+) T cells and by NK cells. Cytokine production during coculture with fibroblasts infected with virus containing the UL18 gene was augmented compared with the UL18 deletion virus,suggesting a stimulatory role for UL18. However,purified UL18Fc proteins inhibited IFN-gamma production of LIR-1(+) T cells. We propose that cytokine production in the transplant induces NK and T cells to express LIR-1,which may predispose to CMV disease by MHC/LIR-1-mediated suppression. Although the UL18/LIR-1 interaction could inhibit T cell responses,this unlikely plays a role in response to infected cells. Instead,our data point to an activating role for viral UL18 during infection,where indirect intracellular effects cannot be excluded. View Publication

RATIONALE: Excessive recruitment of polymorphonuclear leukocytes (PMNs) to the lung promotes acute lung injury (ALI). Chemokine receptors and adhesion molecules initiate leukocyte-endothelial interactions,but mediators of PMN migration through the alveolo-capillary membrane remain to be identified. p21-Activated kinase (PAK) is an effector of small GTPases and has been implicated in cell migration. OBJECTIVES: To test the role of PAK in ALI. METHODS: An inhibitory PAK peptide was used to determine the role of PAK in cytoskeletal actin polymerization,cell adhesion,and oxidative burst. PMN migration was investigated in vitro and in a murine model of lipopolysaccharide-induced lung injury. MEASUREMENTS AND MAIN RESULTS: PMN migration into lung interstitium and alveolar space was suppressed by an inhibitory PAK peptide. Neutrophils that had taken up the inhibitory PAK peptide were unable to enter the alveolar space. CXCL2/3,an important PMN chemoattractant in murine lung injury,induced PAK phosphorylation in PMNs. Blocking PAK function inhibited chemotaxis,chemokine-induced cytoskeletal actin polymerization,and adhesion-induced oxidative burst. CONCLUSIONS: We conclude that neutrophil PAK is a critical mediator of PMN migration and may be an attractive target in ALI. View Publication

Differences in clinical outcome of simian immunodeficiency virus (SIV) infection in disease-resistant African sooty mangabeys (SM) and disease-susceptible Asian rhesus macaques (RM) prompted us to examine the role of regulatory T cells (Tregs) in these two animal models. Results from a cross-sectional study revealed maintenance of the frequency and absolute number of peripheral Tregs in chronically SIV-infected SM while a significant loss occurred in chronically SIV-infected RM compared to uninfected animals. A longitudinal study of experimentally SIV-infected animals revealed a transient increase in the frequency of Tregs from baseline values following acute infection in RM,but no change in the frequency of Tregs occurred in SM during this period. Further examination revealed a strong correlation between plasma viral load (VL) and the level of Tregs in SIV-infected RM but not SM. A correlation was also noted in SIV-infected RM that control VL spontaneously or in response to antiretroviral chemotherapy. In addition,immunofluorescent cell count assays showed that while Treg-depleted peripheral blood mononuclear cells from RM led to a significant enhancement of CD4+ and CD8+ T-cell responses to select pools of SIV peptides,there was no detectable T-cell response to the same pool of SIV peptides in Treg-depleted cells from SIV-infected SM. Our data collectively suggest that while Tregs do appear to play a role in the control of viremia and the magnitude of the SIV-specific immune response in RM,their role in disease resistance in SM remains unclear. View Publication

Ras activation is crucial for lymphocyte development and effector function. Both T and B lymphocytes contain two types of Ras activators: ubiquitously expressed SOS and specifically expressed Ras guanyl nucleotide-releasing protein (RasGRP). The need for two activators is enigmatic since both are activated following antigen receptor stimulation. In addition,RasGRP1 appears to be dominant over SOS in an unknown manner. The crystal structure of SOS provides a clue: an unusual allosteric Ras-GTP binding pocket. Here,we demonstrate that RasGRP orchestrates Ras signaling in two ways: (i) by activating Ras directly and (ii) by facilitating priming of SOS with RasGTP that binds the allosteric pocket. Priming enhances SOS' in vivo activity and creates a positive RasGTP-SOS feedback loop that functions as a rheostat for Ras activity. Without RasGRP1,initiation of this loop is impaired because SOS' catalyst is its own product (RasGTP)-hence the dominance of RasGRP1. Introduction of an active Ras-like molecule (RasV12C40) in T- and B-cell lines can substitute for RasGRP function and enhance SOS' activity via its allosteric pocket. The unusual RasGRP-SOS interplay results in sensitive and robust Ras activation that cannot be achieved with either activator alone. We hypothesize that this mechanism enables lymphocytes to maximally respond to physiologically low levels of stimulation. View Publication

In this study,we analyzed IL-2-activated polyclonal natural killer (NK) cells derived from 2 patients affected by leukocyte adhesion deficiency type I (LAD1),an immunodeficiency characterized by mutations of the gene coding for CD18,the beta subunit shared by major leukocyte integrins. We show that LAD1 NK cells express normal levels of various triggering NK receptors (and coreceptors) and that mAb-mediated engagement of these receptors results in the enhancement of both NK cytolytic activity and cytokine production. Moreover,these activating NK receptors were capable of recognizing their specific ligands on target cells. Thus,LAD1 NK cells,similarly to normal NK cells,were capable of killing most human tumor cells analyzed and produced high amounts of IFN-gamma when cocultured in presence of target cells. Murine target cells represented a common exception,as they were poorly susceptible to LAD1 NK cells. Finally,LAD1 NK cells could efficiently kill or induce maturation of monocyte-derived immature dendritic cells (DCs). Altogether our present study indicates that in LAD1 patients,3 important functions of NK cells (eg,cytotoxicity,IFN-gamma production,and DC editing) are only marginally affected and provides new insight on the cooperation between activating receptors and LFA-1 in the induction of NK cell activation and function. View Publication

Systemic lupus erythematosus (SLE) is an autoimmune/inflammatory disease characterized by autoantibody production and abnormal T cells that infiltrate tissues through not well-known mechanisms. We report that SLE T lymphocytes display increased levels of CD44,ezrin,radixin,and moesin (ERM) phosphorylation,stronger actin polymerization,higher polar cap formation,and enhanced adhesion and chemotactic migration compared with T cells from patients with rheumatoid arthritis and normal individuals. Silencing of CD44 by CD44 small interfering RNA in SLE T cells inhibited significantly their ability to adhere and migrate as did treatment with Rho kinase and actin polymerization inhibitors. Forced expression of T567D-ezrin,a phosphorylation-mimic form,enhanced remarkably the adhesion and migration rate of normal T cells. Anti-CD3/TCR autoantibodies present in SLE sera caused increased ERM phosphorylation,adhesion,and migration in normal T cells. pERM and CD44 are highly expressed in T cells infiltrating in the kidneys of patients with lupus nephritis. These data prove that increased ERM phosphorylation represents a key molecular abnormality that guides T cell adhesion and migration in SLE patients. View Publication