Ian Dransfield

A blast from the past: clearance of apoptotic cells regulates immune responses

Apoptosis, which is a programmed and physiological form of cell death, is known to shape the immune system by regulating populations of effector lymphocytes. However, the binding and ingestion of dying cells by monocytes/macrophages and dendritic cells can also influence immune responses markedly by enhancing or suppressing inflammation. Therefore, dead cells, which are a reflection of an organisms immediate past, can control its immunological future.

Extracellular matrix proteins protect small cell lung cancer cells against apoptosis: a mechanism for small cell lung cancer growth and drug resistance in vivo.

Resistance to chemotherapy is a principal problem in the treatment of small cell lung cancer (SCLC). We show here that SCLC is surrounded by an extensive stroma of extracellular matrix (ECM) at both primary and metastatic sites. Adhesion of SCLC cells to ECM enhances tumorigenicity and confers resistance to chemotherapeutic agents as a result of β1 integrin-stimulated tyrosine kinase activation suppressing chemotherapy-induced apoptosis. SCLC may create a specialized microenvironment, and the survival of cells bound to ECM could explain the partial responses and local recurrence of SCLC often seen clinically after chemotherapy. Strategies based on blocking β1 integrin-mediated survival signals may represent a new therapeutic approach to improve the response to chemotherapy in SCLC.

Increased Platelet Binding to Circulating Monocytes in Acute Coronary Syndromes

Background—Present therapies for acute coronary syndromes aim toward limiting platelet–platelet adhesion and aggregation processes. However, platelet–leukocyte interactions may contribute importantly to disease progression in the arterial wall. Recent studies suggest that prevention of platelet–leukocyte binding via P-selectin glycoprotein ligand-1 (PSGL-1) may be beneficial in animal models of vascular injury. Methods and Results—P-selectin–PSGL-1 interactions were found to account for most platelet–monocyte binding observed in peripheral blood samples from healthy donors. However, a significant component of observed adhesion was calcium independent, involving neither PSGL-1 nor P-selectin. Platelet–monocyte interactions were examined in 52 patients admitted within 14 hours of symptom onset, with acute coronary syndromes defined as unstable angina (n=12) and acute myocardial infarction (n=13) or noncardiac chest pain (n=27). When compared with patients with noncardiac chest pain, significantly elevated levels of platelet–monocyte binding were found in patients with acute myocardial infarction (70.1±15.4% versus 45.4±23.3%;P <0.01) and unstable angina (67.4±12.9% versus 45.4±23.3%;P >0.01). Calcium-independent platelet–monocyte binding was significantly elevated in myocardial infarction patients alone (14.7±7.7% versus 6.1±5.96%;P <0.001). Conclusions—There is evidence for a significant P-selectin–independent molecular component to the platelet–monocyte conjugation observed in peripheral blood. Patients with myocardial infarction and unstable angina demonstrate increased total binding of platelets to monocytes. Additionally, calcium-independent adhesion was significantly elevated in patients with evidence of myocardial infarction. These findings demonstrate that novel cation-independent adhesion mechanisms may mediate platelet–monocyte binding, representing a new therapeutic target after vascular injury associated with myocardial infarction.

Pharmacological manipulation of granulocyte apoptosis: potential therapeutic targets

Resolution of inflammation involves the clearance of excess or effete inflammatory cells by a process of physiological programmed cell death (apoptosis) and the subsequent recognition and removal of apoptotic cells by phagocytes. The therapeutic induction of apoptosis for the resolution of chronic inflammation and the general pharmacology of apoptosis have become subjects of increasing interest. In this article, some of the unique and important differences in the control of apoptosis of various inflammatory cells (particularly neutrophil and eosinophil granulocytes) are highlighted. It is suggested that apoptosis can be specifically regulated pharmacologically and could be exploited to develop new drug therapies.

Glucocorticoid augmentation of macrophage capacity for phagocytosis of apoptotic cells is associated with reduced p130Cas expression, loss of paxillin/pyk2 phosphorylation, and high levels of active Rac

Phagocytic clearance of apoptotic granulocytes has a pivotal role in determining an inflammatory outcome, resolution or progression to a chronic state associated with development of fibrotic repair mechanisms, and/or autoimmune responses. In this study, we describe reprogramming of monocyte to macrophage differentiation by glucocorticoids, resulting in a marked augmentation of their capacity for phagocytosis of apoptotic neutrophils. This monocyte/macrophage phenotype was characterized by decreased phosphorylation, and therefore recruitment of paxillin and pyk2 to focal contacts and a down-regulation of p130Cas, a key adaptor molecule in integrin adhesion signaling. Glucocorticoid-treated cells also displayed higher levels of active Rac and cytoskeletal activity, which were mirrored by increases in phagocytic capability for apoptotic neutrophils. We propose that changes in the capacity for reorganization of cytoskeletal elements induced by glucocorticoids are essential for efficient phagocytic uptake of apoptotic cells.

Macrophage phagocytosis of apoptotic neutrophils is critically regulated by the opposing actions of pro-inflammatory and anti-inflammatory agents: key role for TNF-α

Apoptosis of inflammatory cells and their subsequent clearance (efferocytosis) by macrophages (M

Prostaglandin D2 and Its Metabolites Induce Caspase-Dependent Granulocyte Apoptosis That Is Mediated Via Inhibition of IκBα Degradation Using a Peroxisome Proliferator-Activated Receptor-γ-Independent Mechanism

Many inflammatory mediators retard granulocyte apoptosis. Most natural PGs studied herein (e.g., PGE2, PGA2, PGA1, PGF2α) either delayed apoptosis or had no effect, whereas PGD2 and its metabolite PGJ2 selectively induced eosinophil, but not neutrophil apoptosis. This novel proapoptotic effect does not appear to be mediated via classical PG receptor ligation or by elevation of intracellular cAMP or Ca2+. Intriguingly, the sequential metabolites Δ12PGJ2 and 15-deoxy-Δ12, Δ14-PGJ2 (15dPGJ2) induced caspase-dependent apoptosis in both granulocytes, an effect that did not involve de novo protein synthesis. Despite the fact that Δ12PGJ2 and 15dPGJ2 are peroxisome proliferator-activated receptor-γ (PPAR-γ) activators, apoptosis was not mimicked by synthetic PPAR-γ and PPAR-α ligands or blocked by an irreversible PPAR-γ antagonist. Furthermore, Δ12PGJ2 and 15dPGJ2 inhibited LPS-induced IκBα degradation and subsequent inhibition of neutrophil apoptosis, suggesting that apoptosis is mediated via PPAR-γ-independent inhibition of NF-κB activation. In addition, we show that TNF-α-mediated loss of cytoplasmic IκBα in eosinophils is inhibited by 15dPGJ2 in a concentration-dependent manner. The selective induction of eosinophil apoptosis by PGD2 and PGJ2 may help define novel therapeutic pathways in diseases in which it would be desirable to specifically remove eosinophils but retain neutrophils for antibacterial host defense. The powerful proapoptotic effects of Δ12PGJ2 and 15dPGJ2 in both granulocyte types suggest that these natural products control the longevity of key inflammatory cells and may be relevant to understanding the control and resolution of inflammation.

Phagocytosis of opsonized apoptotic cells: roles for 'old-fashioned' receptors for antibody and complement

Efficient phagocytic clearance of apoptotic cells is crucial in many biological processes. A bewildering array of phagocyte receptors have been implicated in apoptotic cell clearance, but there is little convincing evidence that they act directly as apoptotic cell receptors. Alternatively, apoptotic cells may become opsonized, whereby naturally occurring soluble factors (opsonins) bind to the cell surface and initiate phagocytosis. Evidence is accumulating that antibodies and complement proteins opsonize apoptotic cells, leading to phagocytosis mediated by well‐defined ‘old‐fashioned’ receptors for immunoglobulin‐Fc and complement. In this review we summarize the evidence that opsonization is necessary for high capacity clearance of apoptotic cells, which would render putative direct apoptotic cell receptors redundant.

Priming differentially regulates neutrophil adhesion molecule expression/function.

Lung injury in a variety of disease states is critically dependent on neutrophil‐mediated inflammatory responses. Neutrophil recruitment to sites of infection or tissue damage requires co‐ordinated regulation of neutrophil adhesion and activation status. We have examined the effects of treatment of human peripheral blood neutrophils with priming agents [lipopolysaccharide (LPS), tumour necrosis factor‐α (TNF‐α) and platelet‐activating factor (PAF)] upon expression of CD11a, CD11b, CD11c, CD35 and CD62‐L and CD11b function to assess whether subtle regulation of neutrophil adhesion potential accompanies augmented formyl‐methionyl‐leucyl‐phenylalanine‐stimulated superoxide production. We have found that there are differential effects of ‘priming’ concentrations of these agents. For LPS, CD62L loss occurs in the absence of changes in CD11b, whereas for PAF, CD11b up‐regulation occurs in the absence of detectable loss of CD62‐L. However, for TNF‐α, decreased expression of CD62‐L occurs concomitantly with increased expression of CD11b. In addition, we have shown that priming agents augment CD11b functional activity in a manner that parallels the priming of the respiratory burst. Thus, priming agents may differentially regulate neutrophil adhesive capacity and data presented in this manuscript suggest that the increased effector cell function observed in primed cells may be associated with a distinct repertoire of potential adhesive interactions.

Functional and clinical consequences of Fc receptor polymorphic and copy number variants

Receptors for immunoglobulins (Fc receptors) play a central role during an immune response, as they mediate the specific recognition of antigens of almost infinite diversity by leucocytes, thereby linking the humoral and cellular components of immunity. Indeed, engagement of Fc receptors by immunoglobulins initiates a range of immunoregulatory processes that might also play a role in disease pathogenesis. In the circulation, five main types of immunoglobulins (Ig) exist – namely IgG, IgA, IgE, IgM and IgD and receptors with the ability to recognize and bind to IgG (Fcγ receptor family), IgE (FcεRI and CD23), IgA (CD89; Fcα/µR) and IgM (Fcα/µR) have been identified and characterized. However, it is astonishing that nearly all the known human Fc receptors display extensive genetic variation with clear implications for their function, thus representing a substantial genetic risk factor for the pathogenesis of a range of chronic inflammatory disorders.