Janet Lord

Persistent induction of the chemokine receptor CXCR4 by TGF-beta 1 on synovial T cells contributes to their accumulation within the rheumatoid synovium.

Chemokines and their receptors determine the distribution of leukocytes within tissues in health and disease. We have studied the role of the constitutive chemokine receptor CXCR4 and its ligand, stromal-derived factor-1 (SDF-1) in the perivascular accumulation of T cells in rheumatoid arthritis. We show that synovial T cells, which are primed CD45RO+CD45RBdull cells and consequently not expected to express constitutive chemokine receptors, have high levels of the chemokine receptor CXCR4. Sustained expression of CXCR4 was maintained on synovial T cells by specific factors present within the synovial microenvironment. Extensive screening revealed that TGF-β isoforms induce the expression of CXCR4 on CD4 T cells in vitro. Depletion studies using synovial fluid confirmed an important role for TGF-β1 in the induction of CXCR4 expression in vivo. The only known ligand for CXCR4 is SDF-1. We found SDF-1 on synovial endothelial cells and showed that SDF-1 was able to induce strong integrin-mediated adhesion of synovial fluid T cells to fibronectin and ICAM-1, confirming that CXCR4 expressed on synovial T cells was functional. These results suggest that the persistent induction of CXCR4 on synovial T cells by TGF-β1 leads to their active, SDF-1-mediated retention in a perivascular distribution within the rheumatoid synovium.

Spontaneous Neutrophil Apoptosis Involves Caspase 3-mediated Activation of Protein Kinase C-δ

Neutrophils are short-lived leukocytes that die by apoptosis. Whereas stress-induced apoptosis is mediated by the p38 mitogen-activated protein (MAP) kinase pathway (Frasch, S. C., Nick, J. A., Fadok, V. A., Bratton, D. L., Worthen, G. S., and Henson, P. M. (1998) J. Biol. Chem. 273, 8389–8397), signals regulating spontaneous neutrophil apoptosis have not been fully determined. In this study we found increased activation of protein kinase C (PKC)-β and -δ in neutrophils undergoing spontaneous apoptosis, but we show that only activation of PKC-δ was directly involved in the induction of apoptosis. PKC-δ can be proteolytically activated by caspase 3. We detected the 40-kDa caspase-generated fragment of PKC-δ in apoptotic neutrophils and showed that the caspase 3 inhibitor Asp-Glu-Val-Asp-fluoromethylketone prevented generation of the 40-kDa PKC-δ fragment and delayed neutrophil apoptosis. In a cell-free system, removal of PKC-δ by immunoprecipitation reduced DNA fragmentation, whereas loss of PKC-α, -β, or -ζ had no significant effect. Rottlerin and LY379196 inhibit PKC-δ and PKC-β, respectively. Only Rottlerin was able to delay neutrophil apoptosis. Inhibitors of MAP-ERK kinase 1 (PD98059) or p38 MAP kinase (SB202190) had no effect on neutrophil apoptosis, and activation of p42/44 and p38 MAP kinase did not increase in apoptotic neutrophils. We conclude that spontaneous neutrophil apoptosis involves activation of PKC-δ but is MAP kinase-independent.

Neutrophils are a key component of the antitumor efficacy of topical chemotherapy with ingenol-3-angelate.

Harnessing neutrophils for the eradication of cancer cells remains an attractive but still controversial notion. In this study, we provide evidence that neutrophils are required to prevent relapse of skin tumors following topical treatment with a new anticancer agent, ingenol-3-angelate (PEP005). Topical PEP005 treatment induces primary necrosis of tumor cells, potently activates protein kinase C, and was associated with an acute T cell-independent inflammatory response characterized by a pronounced neutrophil infiltrate. In Foxn1nu mice depleted of neutrophils and in CD18-deficient mice (in which neutrophil extravasation is severely impaired) PEP005 treatment was associated with a >70% increase in tumor relapse rates. NK cell or monocyte/macrophage deficiency had no effect on relapse rates. Both in vitro and in mice, PEP005 induced MIP-2/IL-8, TNF-α, and IL-1β, all mediators of neutrophil recruitment and activation. In vitro, PEP005 activated human endothelial cells resulting in neutrophil adhesion and also induced human neutrophils to generate tumoricidal-reactive oxygen intermediates. Treatment of tumors with PEP005 significantly elevated the level of anticancer Abs, which were able to promote neutrophil-mediated Ab-dependent cellular cytotoxicity (ADCC) in vitro. PEP005 treatment of tumors grown in SCID mice was also associated with >70% increase in tumor relapse rates. Taken together, these data suggest a central role for neutrophil-mediated ADCC in preventing relapse. PEP005-mediated cure of tumors therefore appears to involve initial chemoablation followed by a neutrophil-dependent ADCC-mediated eradication of residual disease, illustrating that neutrophils can be induced to mediate important anticancer activity with specific chemotherapeutic agents.

Inhibition of Neutrophil Apoptosis by Type 1 IFN Depends on Cross-Talk Between Phosphoinositol 3-Kinase, Protein Kinase C-δ, and NF-κB Signaling Pathways

Neutrophils are abundant, short-lived leukocytes with a key role in the defense against rapidly dividing bacteria. They enter apoptosis spontaneously within 24–48 h of leaving the bone marrow. However, their life span can be extended during inflammatory responses by several proinflammatory cytokines. Inappropriate survival of neutrophils contributes to chronic inflammation and tissue damage associated with diseases such as rheumatoid arthritis. We have previously reported that type I IFNs can inhibit both cytokine deprivation and Fas-induced apoptosis in activated T cells. IFN-β locally produced by hyperplastic fibroblasts within the pannus tissue of patients with rheumatoid arthritis contributes to the inappropriately extended life span of infiltrating T cells. Type I IFNs are equally effective at delaying spontaneous apoptosis in human neutrophils. In the work presented here we investigated the signaling pathways involved in mediating this effect. The antiapoptotic actions of IFN-β were targeted at an early stage of neutrophil apoptosis, occurring upstream of mitochondrial permeability transition, and were phosphatidylinositol 3-kinase (PI3K) dependent, as they were blocked by the PI3K inhibitor LY294002. Analysis of signaling pathways downstream of PI3K revealed that the antiapoptotic effect of type 1 IFN was inhibited by rottlerin, SN50, and cycloheximide, indicating requirements for activation of protein kinase C-δ, NF-κB, and de novo protein synthesis, respectively. Moreover, EMSA was used to show that the activation of NF-κB occurred downstream of PI3K and protein kinase C-δ activation. We conclude that type I IFNs inhibit neutrophil apoptosis in a PI3K-dependent manner, which requires activation of protein kinase C-δ and induction of NF-κB-regulated genes.

Dehdyroepiandrosterone sulfate directly activates protein kinase C-β to increase human neutrophil superoxide generation

Dehydroepiandrosterone sulfate (DHEAS) is the most abundant steroid in the human circulation and is secreted by the adrenals in an age-dependent fashion, with maximum levels during the third decade and very low levels in old age. DHEAS is considered an inactive metabolite, whereas cleavage of the sulfate group generates dehydroepiandrosterone (DHEA), a crucial sex steroid precursor. However, here we show that DHEAS, but not DHEA, increases superoxide generation in primed human neutrophils in a dose-dependent fashion, thereby impacting on a key bactericidal mechanism. This effect was not prevented by coincubation with androgen and estrogen receptor antagonists but was reversed by the protein kinase C inhibitor Bisindolylmaleimide 1. Moreover, we found that neutrophils are unique among leukocytes in expressing an organic anion-transporting polypeptide D, able to mediate active DHEAS influx transport whereas they did not express steroid sulfatase that activates DHEAS to DHEA. A specific receptor for DHEAS has not yet been identified, but we show that DHEAS directly activated recombinant protein kinase C-beta (PKC-beta) in a cell-free assay. Enhanced PKC-beta activation by DHEAS resulted in increased phosphorylation of p47(phox), a crucial component of the active reduced nicotinamide adenine dinucleotide phosphate complex responsible for neutrophil superoxide generation. Our results demonstrate that PKC-beta acts as an intracellular receptor for DHEAS in human neutrophils, a signaling mechanism entirely distinct from the role of DHEA as sex steroid precursor and with important implications for immunesenescence, which includes reduced neutrophil superoxide generation in response to pathogens.

Topical Glucocorticoid Therapy Directly Induces Up-Regulation of Functional CXCR4 on Primed T Lymphocytes in the Aqueous Humor of Patients with Uveitis

Overexpression of the constitutive chemokine receptor CXCR4 has been shown to contribute to the accumulation of leukocytes at sites of chronic inflammation. Glucocorticoids are widely used to treat inflammatory disorders such as uveitis to considerable effect, yet paradoxically have been reported to increase CXCR4 expression in vitro. We show here that ocular lymphocytes isolated from patients with uveitis who had been treated with topical glucocorticoids expressed highly elevated levels of CXCR4. The up-regulation of CXCR4 could be reproduced in vitro by culture of CD4+ T cells with aqueous humor (AqH), indicating a role for the ocular microenvironment rather than preferential recruitment of CXCR4+ cells. Untreated uveitis and noninflammatory AqH up-regulated CXCR4 to a limited extent; this was dependent on TGF-β2. However, the highest levels of CXCR4 both in vivo and in vitro were found in the glucocorticoid-treated patients. Glucocorticoids appeared to be directly responsible for the induction of CXCR4 in treated patients, as the glucocorticoid receptor antagonist RU38486 inhibited the in vitro up-regulation by AqH from these patients. Dexamethasone selectively up-regulated CXCR4 in vitro, but not any of a wide range of other chemokine receptors. CXCL12, the ligand for CXCR4, was present in AqH under noninflammatory conditions, but the levels were low in untreated uveitis and undetectable in treated uveitis AqH. The importance of these results for the treatment of HIV patients with glucocorticoids is discussed as well as a role for glucocorticoid-induced CXCR4 up-regulation and CXCL12 down-regulation in controlling the migration of lymphocyte populations, resulting in resolution of inflammation.

Adiponectin inhibits neutrophil phagocytosis of Escherichia coli by inhibition of PKB and ERK 1/2 MAPK signalling and Mac-1 activation.

Full length adiponectin is a potent immune modulatory adipokine, impacting upon the actions of several immune cells. Neutrophil oxidative burst has been shown to decrease in response to adiponectin, and we speculated that it could have other effects on neutrophil function. Here we report that adiponectin reduces the phagocytic ability of human neutrophils, decreasing significantly the ingestion of opsonised E. coli by these cells in whole blood (p<0.05) and as isolated neutrophils (p<0.05). We then determined the mechanisms involved. We observed that the activation of Mac-1, the receptor engaged in complement-mediated phagocytosis, was decreased by adiponectin in response to E. coli stimulation. Moreover, treatment of neutrophils with adiponectin prior to incubation with E. coli significantly inhibited signalling through the PI3K/PKB and ERK 1/2 pathways, with a parallel reduction of F-actin content. Studies with pharmacological inhibitors showed that inhibition of PI3K/PKB, but not ERK 1/2 signalling was able to prevent the activation of Mac-1. In conclusion, we propose that adiponectin negatively affects neutrophil phagocytosis, reducing the uptake of E. coli and inhibiting Mac-1 activation, the latter by blockade of the PI3K/PKB signal pathway.

Primary adrenal insufficiency is associated with impaired natural killer cell function: A potential link to increased mortality

Objective Mortality in patients with primary adrenal insufficiency (PAI) is significantly increased, with respiratory infections as a major cause of death. Moreover, patients with PAI report an increased rate of non-fatal infections. Neutrophils and natural killer (NK) cells are innate immune cells that provide frontline protection against invading pathogens. Thus, we compared the function and phenotype of NK cells and neutrophils isolated from PAI patients and healthy controls to ascertain whether altered innate immune responses could be a contributory factor for the increased susceptibility of PAI patients to infection. Design and methods We undertook a cross-sectional study of 42 patients with PAI due to autoimmune adrenalitis (nu2009=u200937) or bilateral adrenalectomy (nu2009=u20095) and 58 sex- and age-matched controls. A comprehensive screen of innate immune function, consisting of measurements of neutrophil phagocytosis, reactive oxygen species production, NK cell cytotoxicity (NKCC) and NK cell surface receptor expression, was performed on all subjects. Results Neutrophil function did not differ between PAI and controls. However, NKCC was significantly reduced in PAI (12.0u2009±u20091.5% vs 21.1u2009±u20092.6%, Pu2009<u20090.0001). Phenotypically, the percentage of NK cells expressing the activating receptors NKG2D and NKp46 was significantly lower in PAI, as was the surface density of NKG2D (all Pu2009<u20090.0001). Intracellular granzyme B expression was significantly increased in NK cells from PAI patients (Pu2009<u20090.01). Conclusions Adrenal insufficiency is associated with significantly decreased NKCC, thereby potentially compromising early recognition and elimination of virally infected cells. This potential impairment in anti-viral immune defense may contribute to the increased rate of respiratory infections and ultimately mortality in PAI.

An aged T cell phenotype: A prognostic indicator in liver transplant recipients?

There is now little doubt that aging has a profound effect on both the innate and adaptive arms of the immune system that results in a decline in immunity termed immunosenescence. This is evidenced by increased susceptibility to bacterial and viral infections, reactivation of latent infections (herpes zoster leading to shingles), increased production of autoantibodies, and decreased response to vaccination in older adults. Two key drivers for senescence in the adaptive immune system are thymic involution, which reduces the output of naive T cells, and consequent homeostatic expansion of the peripheral T cell pool. Moreover, with repeated antigen exposure and proliferation of memory T cells throughout life, there is also shortening of telomeres, which limits the proliferative capacity of T cells and eventually results in replicative senescence. With repeated stimulation, T cells also become highly differentiated: they lose costimulatory receptors such as CD28, CD27, cytotoxic T lymphocyte antigen 4, and inducible T cell costimulator, up-regulate inhibitory receptors such as killer cell lectin-like receptor subfamily G member 1, and acquire expression of immune effector molecules, including killer cell immunoglobulin-like receptors, chemokines, and chemokine receptors. Each of these factors contributes to the agerelated loss of T cell responsiveness and can be considered a biomarker for the biological age of an individual’s immune system. Importantly, longitudinal studies have revealed that T cell immunosenescence is associated with increased morbidity and mortality, and specific age-related changes in the T cell phenotype have been proposed to represent an immune risk phenotype. Shortened leukocyte telomeres are associated with several agerelated pathologies, including cardiovascular disease and cancer, and the number of CD4þCD28 T cells is increased in patients with autoimmune inflammatory diseases such as rheumatoid arthritis. In this issue of Liver Transplantation, Gelson et al. report on their investigation of whether the chronic immune stress of organ transplantation accelerates aging of the immune system. It has already been well documented in the literature that transplant recipients have an increased incidence of cancer, cardiovascular disease, and infections, but this has been largely ascribed to the effects of the long-term use of immunosuppressants. However, the authors show clearly that another possible factor contributing to excess morbidity and mortality in established organ graft recipients is senescence of the immune system as liver graft recipients had shorter T cell telomeres and more cells of a mature phenotype than healthy age-matched controls. Interestingly, multiple linear regression analyses of case and control data have allowed Gelson et al. to estimate the impact of organ grafts and comorbidities on T cell telomere length, and this has allowed them to gauge the effect in terms of relative T cell aging. Thus, those patients with established liver grafts had 1 year added to their T cells’ biological clock, whereas patients with hepatocellular carcinoma at transplantation or skin malignancy subsequent to transplantation had 6.2 and 3.7 additional years, respectively. Crucially, the use of immunosuppressive drugs was not independently associated with shortened telomeres or an increase in cells with a mature