Current Medicinal Chemistry - Anti-Inflammatory & Anti-Allergy Agents - Volume 4, Issue 2, 2005

Human natural killer (NK) cells are effectors of innate immunity, capable of killing transformed or virusinfected cells and producing pro-inflammatory cytokines, once activated in a non-HLA-dependent fashion. NK cells express receptors for HLA-I molecules, including CD8, or members of the Inhibitory Receptor Superfamily (IRS), such as the Killer Ig-like receptor (KIR) or C-Lectin type Inhibitory Receptor (CLIR). Soluble molecules of HLA-I (sHLA-I) are significantly increased in the serum of patients affected by auto-immune or infectious diseases. We reported that upon interaction of sHLA-I with either CD8 or IRS activating isoforms (AR), NK cells produced and released FasL which elicited NK cell apoptosis by interacting with Fas at the NK cell surface. CD94/NKG2A or KIR2DL, both inhibiting isoforms of IRS, exerted an inhibitory effect on sHLA-I-mediated apoptosis and secretion of FasL induced via CD8, suggesting that IRS can function as survival receptors. Moreover, large amounts of IFN-γ were detectable in culture supernatant of either CD8+ or AR+ NK cells incubated with the appropriate sHLA-I ligand. In chronic diseases, sHLA could amplify inflammation and, at the same time, eliminate effectors of innate immunity, thus favouring infections. On the other hand, this could represent a mechanism of down-regulation of NK-mediated functions as well, which ultimately contributes to limit self-reaction. Importantly, cyclosporin A (CsA) blocks both AR- or CD8-mediated apoptosis and IFN-γ production, without affecting AR-mediated activation of cytolysis. This would indicate that CsA, although being an immunosuppressive drug, can downregulate inflammation maintaining NK cell-dependent innate immunity, further supporting CsA treatment in autoimmune diseases.

Interferon g (IFN-γ) is a regulatory cytokine with a broad spectrum of biologic activities and considerable clinical importance. It is considered to be a master regulator of the immune system. Many human diseases, including infections, cancer and autoimmunity, are associated with aberrant production of IFN-γ. Detection and regulation of IFN-γ production is an important clinical objective. Today, levels of IFN-γ in body fluids and tissues can be reproducibly measured by a variety of assays, including single-cell assays, that are discussed below. Strategies for inhibition of IFN-γ secretion depend on immunologic, pharmacologic or genetic interventions. Increasingly, molecular approaches based on inhibition of IFN-γ signaling pathways are considered for down-regulation of excessive IFN-γ production in various pathologic conditions.

Intercellular communications are fundamental for a correct progression of immuno inflammatory responses. Major messengers in this network of information are cytokines, secretory proteins produced by immune and inflammatory cells. Blocking the function of pro-inflammatory cytokines has entered the clinical arena of treating autoimmune diseases. However, many cytokines including Interleukin (IL)-1, IL-18, HMGB1, belong to the family of “leaderless secretory proteins”, that leave the cells through pathways independent from the classical Endoplasmic Reticulum (ER)-Golgi route. Thus, a successful outcome of an approach aimed at inhibiting cytokine activity requires a clear definition of the mechanisms controlling their release. In this article we will review current hypotheses on the mechanisms underlying non classical secretion and discuss their implications in the regulation of the inflammatory and immune response. In particular, we will dissect the sequence of events required for IL-1β secretion and describe some members of the molecular machinery involved, which could provide novel targets whereby control of IL-1β production may be achieved.

The novel “induced self” recognition mode mediated by the immunoreceptor NKG2D allows NK cells to eliminate dangerous and dysfunctional cells. Long-puzzling, complex NK cell reactivity patterns can now be explained - at least in part - by the combined action of the molecular players of the “missing self” and “induced self” hypotheses. Accordingly, MHC class I down-regulation in concert with an upregulated expression of self-ligands of activating NK receptors renders cells susceptible for NK cytotoxicity. The C-type lectin-like, activating NK receptor NKG2D detects a variety of inducibly expressed MHC class I-related molecules on stressed, infected, or malignant cells, and subsequently triggers effector functions of NK cells. Recent experiments also underline an important function of NKG2D on CD8 αβ T cells in tumor immunosurveillance and in the pathogenesis of autoimmune diseases. Here, we review the current knowledge on NKG2D and its ligands (NKG2DL) with regard to their structure, expression, and function, refer to recent data on the involvement of NKG2D in anti-viral immune defence, tumor surveillance, and autoimmune phenomena, and outline emerging evidence on the modulation of NKG2D by cytokines and soluble NKG2DL.

A minority of peripheral blood T lymphocytes used heterodimeric T cell receptor (TCR) composed of a Vγ9 chain associated with Vδ2. These circulating Vγ9Vδ2 γδ T cells mainly recognize low-molecular-mass non-peptide antigens derived from microbes and plants in a MHC-unrestricted manner. Furthermore, they produce rapidly after antigen contact cytotoxic molecules and cytokines, thereby activating innate immune cells, facilitating adaptive immune responses of αβ T cells, protecting the host against infections with certain microbial pathogens, and playing a role in tumor defense. Another γδ T cell subset underrepresented in the peripheral blood expresses Vd1 chain associated with variable Vg elements and comprises the major γδ T cell population in epithelial tissues such as the small intestine. Homologous γδ T cells are found in the mouse in vagina, uterus, lung and skin. Vδ1 γδ T cells mainly recognize antigens restricted to certain cell types of epithelial origin, which are induced upon stress, infection, inflammation and tumor growth, and thus play a role in immunosurveillance against malignancy, pathogen eradication, and wound healing. Several reports suggest that γδ T cells are immunregulatory cells, interacting and modulating the activity of other immune cells directly or by cytokine production. Here we summarize the current knowledge on the role of cytokines produced by γδ T cells and their ability to influence and regulate other cells of the immune system.

Human Vγ9 / Vδ2 are a subset of γδ T cells present only in non human primates and humans that have potent in vitro activities both on mycobacteria infected cells and on different cancer cell types. Their hallmark is that they are selectively activated by non peptidic ligands that are in most instances phosphorylated. These phosphorylated compounds (also referred to as phosphoantigens) directly trigger Vγ9 / Vδ2 T cell receptor-expressing cells, without need for MHCrestricted presentation molecules. Most of the known natural phosphoantigens are of microbial origin, and have been determined as low molecular weight components of a metabolic pathway (DOXP, or non mevalonate) specific for some microorganisms and parasites. This pathway leads to the synthesis of farnesyl and genranyl disphosphate, precursors of sterols. Although the nature of tumor antigens recognized by Vγ9 / Vδ2 T cells is still debated, recent data suggest that these are derived from the mevalonate pathway, which leads in most eukaryotic cells to the same geranyl and farnesyl diphosphate, also precursors of sterols, but also used for the farnesylation of proteins such as ras. The physiological significance of recognition of these metabolites by gd T cells will be discussed. Finally we will review several recent immunotherapeutic approaches targeting Vγ9 / Vδ2 T cells, which rely on the use of several synthetic agonists or pharmacological inhibitors of the mevalonate pathway.

Dendritic cells (DC) represent a sentinel-like system with the capacity to capture and process antigens, to migrate into secondary lymphoid organs, and to activate naive T lymphocytes. DCs are considered as important elements in the induction of specific immune responses. The potency of DCs for induction of immune responses can be affected by a number of aspects related to their maturation stage and state of activation. For a long time, the critical role of DCs in many clinical situations was underscored. DCs in vivo might represent a favored target for immune tolerance (cancer) or immune activation (auto-immune diseases and allergic hypersensitivity). For immunotherapeutic applications, it is crucial to identify factors and agents that might affect the differentiation, maturation and function of DCs. This review will focus on the impact of the most widely used immunomodulatory drugs in the clinical setting on the properties and functions of DCs. The modulation and manipulation of DC functions through exposure of DCs to immunomodulatory agents both in vitro and in vivo is an approach that could result in therapeutic benefit in many clinical situations.

The innate immune system represents the fastest defense to microbial invasion although many pathogens can modulate the host response either in favor of or against their survival and propagation. In this regard, some bacterial toxins possess immunostimulating properties that have been exploited in terms of vaccine adjuvancy and induction of specific cytotoxic T lymphocytes. Among these, Bordetella pertussis toxin (PTX) possesses the ability of modulating the immune responses in in vivo, ex-vivo and in vitro experimental systems. In addition, PTX, as well its nontoxic B-oligomer PTX-B and the genetically inactivated PT-9K/129G molecule, have been recently shown to inhibit infection of CD4+ T lymphocytes and macrophages by the human immunodeficiency virus, the etiological agent of the acquired immunodeficiency syndrome. This article focuses on the regulation of the immune response and on the anti-viral properties of PTX and of its nontoxic related molecules and as an example of exploitation of a natural bacterial product to combat viral infections.

The review covers basic recent discoveries on the mechanism of action of adjuvants, which have been developed in the last decade. In particular, it focuses on the activation of TOLL like receptors and subsequent release of pro-inflammatory lymphokines (innate immunity), which, in turn, are thought to activate antigen specific responses (adaptive immunity). Given the number of novel adjuvants available to researchers, we limited the scope of the review to those adjuvants which are routinely used in our laboratories and of which we have first hand information.

We developed new immunotherapies (peptide and DNA vaccines) for treatment of Japanese cedar pollinosis. In the first place, oral administration of a dominant T cell epitope of a major Japanese cedar allergen (Cry j 2) in mice induced immunologic tolerance in both T-helper (Th) 1 and Th2 cell responses against the whole protein allergen. We found that peptide-based oral immunotherapy has a potential efficacy for treatment of the allergic immune response. Further, we developed a hybrid peptide comprising 7 T cell epitopes for human patients. It is expected that the hybrid peptide will downregulate allergen-specific T cells. We are planning a clinical study with the hybrid peptide in the near future. In the second place, we evaluated the use of DNA immunization by inoculating mice with plasmid DNA encoding a major Japanese cedar allergen (Cry j 1) gene. This DNA vaccination suppressed the IgE and IgG1 responses to subsequent alum-precipitated Cry j 1 injections. These results suggest that the DNA vaccination effectively induced Cry j 1-specific Th1-type immune responses, resulting in inhibition of the IgE responses to Cry j 1. Further, we developed DNA vaccine encoding both T cell epitope in Cry j 2 and invariant chain for the delivery of the epitope peptide into major histocompatibility complex (MHC) class II loading pathway. This DNA vaccination also suppressed the IgE responses to subsequent alum-precipitated Cry j 2 injections. DNA vaccine encoding T cell epitope and invariant chain induced epitope-specific T cell responses without allergic side effects.

Hepatitis, liver cirrhosis and liver cancer are major liver diseases particularly in Asia. Liver cancer is also one of the leading cancers causing death in the world. Cyclooxygenase 2 (COX-2) is a highly inducible and key rate-limiting enzyme involved in the production of prostaglandins (PGs), prostacyclin, and thromboxanes. COX-2 is expressed in response to a variety of proinflammatory agents and cytokines. COX-2 is associated with liver pathogenesis, including fibrosis and cancer. It has been shown that COX-2 is up-regulated in cirrhotic tissues adjacent to hepatocellular carcinoma (HCC) and well-differentiated HCC. We and others also observed the up-regulation of COX-2 in liver fibrosis. The chemopreventive efficacy of COX-2 inhibitors in liver fibrosis and hepato-carcinogenesis has been observed in animal experimental models. COX-2 inhibitors have also exhibited significant anti-proliferative effects on HCC cell lines by inducing apoptosis and cell cycle arrest and blocking growth signaling pathways. These results raise the possibility that COX-2 may be a target for the prevention or treatment of liver fibrosis, hepato-carcinogenesis and liver cancer, as it is for colon cancer. In this article, we review recent studies on the role of COX-2 in liver fibrosis and liver cancer, and discuss rationale and feasibility of COX-2 inhibitors in chemoprevention and treatment of liver fibrosis and liver cancer.