Danielle Burger

High-density lipoprotein-associated apolipoprotein A-I: the missing link between infection and chronic inflammation?

The etiology of chronic immuno-inflammatory diseases including rheumatoid arthritis (RA), multiple sclerosis (MS), systemic lupus erythematosus (SLE), and atherosclerosis is far from being elucidated. It is generally accepted that multiple factors are involved in the development of such pathologies, including factors of genetic susceptibility that interact in complex ways with diverse environmental factors, i.e. gender, nutrition, environment, etc. Furthermore, infection has often been pinpointed as playing a causal role. However, no distinctive pattern has yet emerged from the tremendous number of compiled results that would provide a generally acceptable hypothesis of the etiology of immuno-inflammatory diseases, and the possibility of a persistent antigenic stimulus arising from an infection cannot be confirmed or refuted. At the cellular level, chronic inflammation is characterized by the infiltration of immuno-inflammatory cells into the target tissue, which mostly precedes tissue damage. At the inflammatory site, monocytes and T lymphocytes are in close proximity. We have demonstrated that contact-mediated activation of monocytes by stimulated T lymphocytes is a major stimulus triggering the production of large amounts of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) whose importance in chronic inflammation is well known. We recently established that high-density lipolipoprotein (HDL)-associated apolipoprotein (apo) A-I is a specific inhibitor of cytokine production in monocyte-macrophages upon contact with stimulated T cells. HDL-associated apo A-I is a negative acute-phase protein, i.e. a protein whose level is lowered by more than 25% during the acute phase. This review aims at highlighting the fact that HDL-associated apo A-I might play the role of a constitutive anti-inflammatory factor. The decrease of plasma levels of HDL-associated apo A-I upon acute inflammation may be a sign of the possible development of chronic inflammation, i.e. individuals presenting with risk factors might develop chronic inflammatory diseases after infection. We thus hypothesize that HDL-associated apo A-I might be the missing link between infection and chronic inflammation.

Imbalance between interstitial collagenase and tissue inhibitor of metalloproteinases 1 in synoviocytes and fibroblasts upon direct contact with stimulated T lymphocytes involvement of membrane-associated cytokines

OBJECTIVE To determine whether direct cell-cell contact with stimulated T lymphocytes (a) differentially modulates the production of interstitial collagenase (matrix metalloproteinase 1 [MMP-1]) and tissue inhibitor of metalloproteinases 1 (TIMP-1) on human synoviocytes and dermal fibroblasts, and (b) induces the production of prostaglandin E2 (PGE2); and to identify the membrane-associated factors on T cell surfaces involved in these mechanisms. METHODS Dermal fibroblasts and fibroblast-like synovial cells (synoviocytes) were cultured with fixed T cells, isolated plasma membranes from T cells, interleukin-1beta (IL-1beta; 250 pg/ml), or transforming growth factor beta (TGFbeta; 5 ng/ml). Culture supernatants were assayed for the production of MMP-1, TIMP-1, and PGE2. The expression of MMP-1 and TIMP-1 messenger RNA was analyzed by Northern blot of total fibroblast RNA. RESULTS Membranes of stimulated T cells, i.e., human peripheral blood T lymphocytes (PBTL) and the human T cell line HUT-78, induced the production of PGE2 and MMP-1 on both synoviocytes and dermal fibroblasts. TIMP-1 production was enhanced upon contact with PBTL stimulated for short periods of time (2-4 hours) but not for longer periods. Similar results were obtained with CD4+ and CD8+ synovial tissue T cell clones (TCCs), which induced the production of TIMP-1 by fibroblasts when stimulated for short (2-4 hours), but not long, periods of time. This time dependency was not observed with HUT-78 cells. The production of MMP-1 by fibroblasts and synoviocytes upon cellular contact with stimulated T cells was higher than that induced by an optimum concentration of IL-1beta, whereas the production of PGE2 was equivalent or slightly lower. Cell membrane-associated IL-1alpha and tumor necrosis factor a, but not CD69, CD40 ligand, or CD11b, were involved in the induction of MMP-1 and PGE2 production, as shown by blockade experiments using monoclonal antibodies and cytokine antagonists. CONCLUSION Synovial tissue TCCs and PBTL stimulated for long periods of time trigger the production of PGE2 and MMP-1, but not TIMP-1, in synoviocytes and dermal fibroblasts, thus inducing an imbalance between the metalloenzyme and its inhibitor. These results demonstrate that T cells may affect fibroblast and synoviocyte functions directly (i.e., by contact activation) and indirectly (i.e., by activation of cytokine production in monocyte/macrophages, which in turn, trigger stromal cell functions). Since the production of MMPs in monocyte/macrophages is also induced upon contact with stimulated T cells, our results strongly suggest that contact of synovial cells with chronically stimulated T lymphocytes favors matrix catabolism. By analogy, this mechanism may trigger tissue destruction in vivo and, thus, may potentiate tissue destruction in chronic inflammatory diseases such as RA.

Cytokines, Acute‐Phase Proteins, and Hormones

Abstract: The cytokine network is a homeostatic system that has to be perceived in an analogous fashion to the acid/base equilibrium. The level of any cytokine in biological fluids can be interpreted correctly only by taking into account the levels of other synergistic cytokines, of their respective inhibitors, and of each cytokine receptor. Due to their potent activities in many different processes (including cell growth and differentiation, development, and repair processes leading to the restoration of homeostasis), the cytokine activities have to be tightly controlled by natural inhibitory mechanisms. Since one of the main functions of cytokines is to mediate interactions between the immune and inflammatory system, it is thought that chronic immuno‐inflammatory diseases might be caused in part by the uncontrolled production of cytokines. Depending on the stage of inflammation or the biological effect determined, the same cytokine might be pro‐ or anti‐inflammatory. This applies, for instance, to IL‐4, IL‐10, and TGFβ. An important mechanism that triggers the production of pro‐inflammatory cytokines in chronic inflammatory diseases is the direct cellular contact between stimulated T cells and monocyte‐macrophages. This mechanism is blocked at the systemic level by the “negative” acute‐phase protein apolipoprotein A‐I (apo A‐I). The levels of expression of cytokines and cytokine inhibitors and acute‐phase proteins are ruled by hormones. Estrogens as well as androgens inhibit the production of IL‐1β and TNF‐α on monocyte‐macrophages. However, androgens antagonize estrogen stimulatory effects on apo A‐I synthesis by the liver. Other studies suggest that estradiol is more inhibitory to Thl cytokines (e.g., IFNγ, IL‐2), while testosterone is inhibitory to Th2 cytokines (e.g., IL‐4). Cytokines also control the axis of the hypothalamic‐hypophyseal‐adrenal glands as well as the sexual hormones. The discrepancy between studies would suggest that the mechanisms are different in physiological and pathophysiological conditions.

Glatiramer acetate increases IL-1 receptor antagonist but decreases T cell-induced IL-1β in human monocytes and multiple sclerosis

Mechanisms of action as well as cellular targets of glatiramer acetate (GA) in multiple sclerosis (MS) are still not entirely understood. IL-1β is present in CNS-infiltrating macrophages and microglial cells and is an important mediator of inflammation in experimental autoimmune encephalitis (EAE), the MS animal model. A natural inhibitor of IL-1β, the secreted form of IL-1 receptor antagonist (sIL-1Ra) improves EAE disease course. In this study we examined the effects of GA on the IL-1 system. In vivo, GA treatment enhanced sIL-1Ra blood levels in both EAE mice and patients with MS, whereas IL-1β levels remained undetectable. In vitro, GA per se induced the transcription and production of sIL-1Ra in isolated human monocytes. Furthermore, in T cell contact-activated monocytes, a mechanism relevant to chronic inflammation, GA strongly diminished the expression of IL-1β and enhanced that of sIL-1Ra. This contrasts with the effect of GA in monocytes activated upon acute inflammatory conditions. Indeed, in LPS-activated monocytes, IL-1β and sIL-1Ra production were increased in the presence of GA. These results demonstrate that, in chronic inflammatory conditions, GA enhances circulating sIL-1Ra levels and directly affects monocytes by triggering a bias toward a less inflammatory profile, increasing sIL-1Ra while diminishing IL-1β production. This study sheds light on a mechanism that is likely to participate in the therapeutic effects of GA in MS.

The role of human T-lymphocyte-monocyte contact in inflammation and tissue destruction

Chapter summary Contact-mediated signaling of monocytes by human stimulated T lymphocytes (TL) is a potent proinflammatory mechanism that triggers massive upregulation of the proinflammatory cytokines IL-1 and tumor necrosis factor-α. These two cytokines play an important part in chronic destructive diseases, including rheumatoid arthritis. To date this cell–cell contact appears to be a major endogenous mechanism to display such an activity in monocyte-macrophages. Since TL and monocyte-macrophages play a pivotal part in the pathogenesis of chronic inflammatory diseases, we investigated the possible ligands and counter-ligands involved in this cell–cell interaction. We also characterized an inhibitory molecule interfering in this process, apolipoprotein A-I. This review aims to summarize the state of the art and importance of contact-mediated monocyte activation by stimulated TL in cytokine production in rheumatoid arthritis and mechanisms that might control it.

Glatiramer acetate in the treatment of multiple sclerosis: emerging concepts regarding its mechanism of action.

Glatiramer acetate is a synthetic, random copolymer widely used as a first-line agent for the treatment of relapsing-remitting multiple sclerosis (MS). While earlier studies primarily attributed its clinical effect to a shift in the cytokine secretion of CD4+ T helper (Th) cells, growing evidence in MS and its animal model, experimental autoimmune encephalomyelitis (EAE), suggests that glatiramer acetate treatment is associated with a broader immunomodulatory effect on cells of both the innate and adaptive immune system. To date, glatiramer acetate-mediated modulation of antigen-presenting cells (APC) such as monocytes and dendritic cells, CD4+ Th cells, CD8+ T cells, Foxp3+ regulatory T cells and antibody production by plasma cells have been reported; in addition, most recent investigations indicate that glatiramer acetate treatment may also promote regulatory B-cell properties. Experimental evidence suggests that, among these diverse effects, a fostering interplay between anti-inflammatory T-cell populations and regulatory type II APC may be the central axis in glatiramer acetate-mediated immune modulation of CNS autoimmune disease. Besides altering inflammatory processes, glatiramer acetate could exert direct neuroprotective and/or neuroregenerative properties, which could be of relevance for the treatment of MS, but even more so for primarily neurodegenerative disorders, such as Alzheimer’s or Parkinson’s disease. In this review, we provide a comprehensive and critical overview of established and recent findings aiming to elucidate the complex mechanism of action of glatiramer acetate.

Th2 Cell Membrane Factors in Association with IL-4 Enhance Matrix Metalloproteinase-1 (MMP-1) While Decreasing MMP-9 Production by Granulocyte-Macrophage Colony-Stimulating Factor-Differentiated Human Monocytes

Monocytes/macrophages are directly involved in tissue remodeling and tissue destruction through the release of matrix metalloproteinases (MMP). In the present study, we examined the effect mediated by contact of polarized Th cells with mononuclear phagocytes on the production of MMP-1, MMP-9, and their inhibitor. Plasma cell membranes from Ag-activated Th1 and Th2 cells were potent inducers of MMP-1 production by THP-1 cells. Cell membrane-associated TNF was found to be only partially involved in MMP-1 induction by both Th1 and Th2 cells. In Th2 cells exclusively, membrane-associated IL-4 induced MMP-1 production by THP-1 cells. This membrane-associated IL-4 effect was additive to that of TNF and was specifically observed on MMP-1 as MMP-9 production was concomitantly inhibited. Similarly, soluble IL-4 induced THP-1 cells to produce MMP-1, its effect proving additive to that of soluble TNF and to that of cell membranes of mitogen-activated HUT-78 cells. Its activity was blocked by IL-4 neutralization, and was unaffected by the presence of indomethacin. These effects on THP-1 cells were observed at protein and mRNA levels. Although inhibitory on freshly isolated peripheral blood monocytes, soluble IL-4 enhanced T cell-induced MMP-1 and inhibited MMP-9 production both at protein and mRNA levels in monocytes cultured for 7 days in the presence of GM-CSF. Thus, in contrast with previously reported effects, Th2 and IL-4 specifically induce MMP-1 production by mononuclear phagocytes at various stages of differentiation. This IL-4 activity may be relevant to pathological conditions dominated by Th2 inflammatory responses, resulting in tissue remodeling and destruction.

Anti-interleukin-1 therapy in rheumatic diseases.

Recent research has shown that in the processes of rheumatoid arthritis (RA), interleukin (IL)-1 is one of the pivotal cytokines in initiating disease, and the body’s natural response, IL-1 receptor antagonist (IL-1Ra), has been shown conclusively to block its effects. In laboratory and animal studies inhibition of IL-1 by either antibodies to IL-1 or IL-1Ra proved beneficial to the outcome. To date, two large well-controlled studies in patients with RA led to the conclusion that IL-1Ra is clinically effective and that it slows progression of bone damage as measured radiographically. Being a specific, selective inhibitor of the IL-1 pathway, IL-1Ra could constitute an important new approach to treating patients with RA that significantly reduces the signs and symptoms of the disease, reduces joint destruction and up to now has proved safe and well tolerated.

Stimulated T cells generate microparticles, which mimic cellular contact activation of human monocytes: differential regulation of pro- and anti-inflammatory cytokine production by high-density lipoproteins.

Imbalance in cytokine homeostasis plays an important part in the pathogenesis of chronic inflammatory diseases such as multiple sclerosis and rheumatoid arthritis. We demonstrated that T cells might exert a pathological effect through direct cellular contact with human monocytes/macrophages, inducing a massive up‐regulation of the prototypical proinflammatory cytokines IL‐1β and TNF. This mechanism that might be implicated in chronic inflammation is specifically inhibited by high‐density lipoproteins (HDL). Like many other stimuli, besides proinflammatory cytokines, the contact‐mediated activation of monocytes induces the production of cytokine inhibitors such as the secreted form of the IL‐1 receptor antagonist (sIL‐1Ra). The present study demonstrates that stimulated T cells generate microparticles (MP) that induce the production of TNF, IL‐1β, and sIL‐1Ra in human monocytes; the production of TNF and IL‐1β but not that of sIL‐1Ra is inhibited in the presence of HDL. The results were similar when monocytes were stimulated by whole membranes of T cells or soluble extracts of the latter. This suggests that MP carry similar monocyte‐activating factors to cells from which they originate. Thus, by releasing MP, T cells might convey surface molecules similar to those involved in the activation of monocytes by cellular contact. By extension, MP might affect the activity of cells, which are usually not in direct contact with T cells at the inflammatory site. Furthermore, this study demonstrates that HDL exert an anti‐inflammatory effect in nonseptic activation of human monocytes, not only by inhibiting the production of IL‐1β and TNF but also, by leaving sIL‐1Ra production unchanged.

Direct Contact between T Lymphocytes and Human Dermal Fibroblasts or Synoviocytes Down-regulates Types I and III Collagen Production via Cell-associated Cytokines

In many inflammatory diseases where tissue remodeling occurs, T cells are in close contact with mesenchymal cells. We investigated the effect of direct cell-cell contact between peripheral blood T lymphocytes or HUT-78 lymphoma cells and dermal fibroblasts or synoviocytes on the deposition of the major extracellular matrix components: types I and III collagen. Incubation of dermal fibroblasts and synoviocytes with plasma membrane preparations from resting T cells slightly increased the production of collagen I but did not significantly affect that of collagen III. Conversely, direct contact with either plasma membranes or fixed phytohemagglutinin/phorbol myristate acetate-activated T cells markedly inhibited the synthesis of types I and III collagen by 60–70% in untreated dermal fibroblasts and synoviocytes and by 85% in transforming growth factor β-stimulated fibroblasts. This decrease of collagen synthesis was abrogated when fixed T cells were separated physically from fibroblasts, demonstrating that direct contact between the two cell types was necessary. This inhibition was associated with a marked decrease in steady-state levels of pro-α1(I) and pro-α1(III) collagen mRNAs. T cell contact decreased the transcription rate but did not significantly alter the stability of the α1(I) and α1(III) transcripts. Finally, using neutralizing antibodies or cytokine inhibitors we provide evidence that this inhibition of extracellular matrix production mediated by T cell contact was partially due to additive effects of T cell membrane-associated interferon γ, tumor necrosis factor α, and interleukin-1α.