The 94- to 97-kDa mouse macrophage membrane protein that recognizes oxidized low density lipoprotein and phosphatidylserine-rich liposomes is identical to macrosialin, the mouse homologue of human CD68

Oxidized Low-Density Lipoprotein and Its Role in Immunometabolism

Modified cholesterols such as oxidized low-density lipoprotein (OxLDL) contribute to atherosclerosis and other disorders through the promotion of foam cell formation and inflammation. In recent years, it has become evident that immune cell responses to inflammatory molecules such as OxLDLs depend on cellular metabolic functions. This review examines the known effects of OxLDL on immunometabolism and immune cell responses in atherosclerosis and several other diseases. We additionally provide context on the relationship between OxLDL and aging/senescence and identify gaps in the literature and our current understanding in these areas.

Surface property and in vitro toxicity effect of insoluble particles given by protein corona: Implication for PM cytotoxicity assessment

In vitro toxicological assessment helps explore key fractions of particulate matter (PM) in association with the toxic mechanism. Previous studies mainly discussed the toxicity effects of the water-soluble and organic-soluble fractions of PM. However, the toxicity of insoluble fractions is relatively poorly understood, and the adsorption of proteins is rarely considered. In this work, the formation of protein corona on the surface of insoluble particles during incubation in a culture medium was investigated. It was found that highly abundant proteins in fetal bovine serum were the main components of the protein corona. The adsorbed proteins increased the dispersion stability of insoluble particles. Meanwhile, the leaching concentrations of some metal elements (e.g., Cu, Zn, and Pb) from PM increased in the presence of proteins. The toxicity effects and potential mechanisms of the PM insoluble particle-protein corona complex on macrophage cells RAW264.7 were discussed. The results revealed that the PM insoluble particle-protein corona complex could influence the phagosome pathway in RAW264.7 cells. Thus, it promoted the intracellular reactive oxygen species generation and induced a greater degree of cell differentiation, significantly altering cell morphology. Consequently, this work sheds new light on the combination of insoluble particles and protein corona in terms of PM cytotoxicity assessment.

Azithromycin with scaling and root planing versus scaling and root planing alone in the treatment of periodontitis: A randomized controlled trial

Background

The growing interest in the possibilities of macrophages modulation with therapeutic purposes promotes new approaches for periodontitis treatment.

Aim

The aim of this randomized controlled open clinical study was to evaluate the early clinical and immunological effects of the long-course azithromycin as an adjunct to scaling and root planing in periodontitis.

Methods

50 patients (with stage I-III, grade A/B periodontitis) and 22 periodontally healthy volunteers as the reference group were recruited. Following scaling and root planing (SRP), the patients were randomly assigned to one of two treatment modalities: SRP only (n = 25) and adjunct azithromycin (Az) treatment (n = 25). The patients were monitored at baseline, and 30 ± 5 days after therapy. Clinical attachment loss (CAL), periodontal probing depth (PPD) and bleeding on probing (BoP) were evaluated. Secondary outcome measures included mean changes in single-positive CD68 + and CD163 + macrophages (Mφs) density and ratio, evaluated by immunohistochemistry, and IL1-β, IL-6, IL-10, TGF-β levels, detected by ELISA.

Results

At 1 month both groups showed significant improvements of CAL, PPD and BoP, without significant added benefit in terms of CAL, PPD and BoP of Az. But Az increased the density of CD68 + and CD163 + Mφs (P < 0.0001), decreased the CD68+/CD163 + ratio (P = 0.043), decreased IL-1β (P < 0.01), IL-6 (P < 0.001) levels, and increased IL-10 (P < 0.0001) and TGF-β (P < 0.001) levels compared to SRP and periodontitis at baseline.

Conclusion

The long course of Az demonstrated modulation of CD68 + and CD163 + Mφs towards M2 polarization, which may play a significant role in achieving favorable long-term treatment outcomes. ClinicalTrials.gov.

The markers to delineate different phenotypes of macrophages related to metabolic disorders

Macrophages have a wide variety of roles in physiological and pathological conditions, making them promising diagnostic and therapeutic targets in diseases, especially metabolic disorders, which have attracted considerable attention in recent years. Owing to their heterogeneity and polarization, the phenotypes and functions of macrophages related to metabolic disorders are diverse and complicated. In the past three decades, the rapid progress of macrophage research has benefited from the emergence of specific molecular markers to delineate different phenotypes of macrophages and elucidate their role in metabolic disorders. In this review, we analyze the functions and applications of commonly used and novel markers of macrophages related to metabolic disorders, facilitating the better use of these macrophage markers in metabolic disorder research.

Molecular feature of neutrophils in immune microenvironment of muscle atrophy

Homeostasis in skeletal muscle is sustained by the balance of functional and physical interactions between muscle and myofibre microenvironment. Various factors, such as ageing, disuse and denervation, tip the balance and induce skeletal muscle atrophy. Skeletal muscle atrophy, which involves complex physiological and biochemical changes, is accompanied by adverse outcomes and even increased mortality. Multiple studies have investigated the role of neutrophils in atrophied skeletal muscles; however, neutrophil intrusion in muscle is still a polemical knot. As technical obstacles have been overcome, people have gradually discovered new functions of neutrophils. The classical view of neutrophils is no longer applicable to their biological characteristics. To date, no clear association between the hidden injurious effect of neutrophil intrusion and muscle atrophy has been convincingly proven. Throughout this review, we have discussed the neutrophil activities that mediate muscle atrophy for distinct disease occurrences. Hopefully, this review will help both clinicians and researchers of skeletal muscle atrophy with relevant targets to further explore efficient medical interventions and treatments.

Voices from the dead: The complex vocabulary and intricate grammar of dead cells

Of the roughly one million cells per second dying throughout the body, the vast majority dies by apoptosis, the predominant form of regulated cell death in higher organisms. Long regarded as mere waste, apoptotic cells are now recognized as playing a prominent and active role in homeostatic maintenance, especially resolution of inflammation, and in the sculpting of tissues during development. The activities associated with apoptotic cells are continually expanding, with more recent studies demonstrating their ability to modulate such vital functions as proliferation, survival, differentiation, metabolism, migration, and angiogenesis. In each case, the role of apoptotic cells is active, exerting their effects via new activities acquired during the apoptotic program. Moreover, the capacity to recognize and respond to apoptotic cells is not limited to professional phagocytes. Most, if not all, cells receive and integrate an array of signals from cells dying in their vicinity. These signals comprise a form of biochemical communication. As reviewed in this chapter, this communication is remarkably sophisticated; each of its three critical steps-encoding, transmission, and decoding of the apoptotic cell's "message"-is endowed with exquisite robustness. Together, the abundance and intricacy of the variables at each step comprise the vocabulary and grammar of the language by which dead cells achieve their post-mortem voice. The combinatorial complexity of the resulting communication network permits dying cells, through the signals they emit and the responses those signals elicit, to partake of an expanded role in homeostasis, acting as both sentinels of environmental change and agents of adaptation.

Signals from the Niche: Insights into the Role of IGF-1 and IL-6 in Modulating Skeletal Muscle Fibrosis

Muscle regeneration, characterized by the activation and proliferation of satellite cells and other precursors, is accompanied by an inflammatory response and the remodeling of the extracellular matrix (ECM), necessary to remove cellular debris and to mechanically support newly generated myofibers and activated satellite cells. Muscle repair can be considered concluded when the tissue architecture, vascularization, and innervation have been restored. Alterations in these connected mechanisms can impair muscle regeneration, leading to the replacement of functional muscle tissue with a fibrotic scar. In the present review, we will discuss the cellular mediators of fibrosis and how the altered expression and secretion of soluble mediators, such as IL-6 and IGF-1, can modulate regulatory networks involved in the altered regeneration and fibrosis during aging and diseases.

Inactivation of Venom PLA₂ Alleviates Myonecrosis and Facilitates Muscle Regeneration in Envenomed Mice: A Time Course Observation

Snake venom is a complex cocktail of toxins which induces a series of clinical and pathophysiological manifestations in victims, including severe local tissue damage and systemic alterations. Deinagkistrodon acutus (D. acutus) ranks among the “big four” life-threatening venomous species in China, whose venom possesses strong myotoxicity and hematotoxicity that often lead to permanent disability or muscle atrophy. Varespladib, an inhibitor of mammalian phospholipase A₂ (PLA₂), has been recently reproposed as an effective antidote against snakebite envenomation. The present study aimed at evaluating the protective role of varespladib on muscle regeneration in envenomed mice. Mice were grouped and subjected to inoculation with D. acutus venom or a mixture of venom and varespladib or control vehicle in the gastrocnemius muscle. Local injuries including hemorrhage, myonecrosis, ulceration, and systemic damages including general dysfunction, visceral failure, and inflammatory responses were observed at 1, 3, 7, 14, and 21 days. The results indicated that most of the muscle myonecrosis and hemorrhage were alleviated by varespladib. Besides, the pretreated mice recovered rapidly with lesser atrophy and muscle fibrosis. In conclusion, the findings of the present study suggested that varespladib is an effective antidote that could neutralize D. acutus venom and allow for earlier and improved rehabilitation outcome.

Carcinogenesis-relevant biological events in the pathophysiology of the efferocytosis phenomenon

The effective removal of cells undergoing programmed cell death, which is referred to as efferocytosis, prevents the leakage of intracellular contents into the surrounding tissue, which could lead to tissue damage and inflammation. Efferocytosis involves a coordinated orchestration of multiple steps that lead to a swift, coherent and immunologically silent removal of dying cells. The release of wound healing cytokines, which resolve inflammation and enhance tissue repair, is an important feature of efferocytosis. However, in addition to the healing cytokines released during efferocytosis, the immunosuppressive action of cytokines promotes the tumor microenvironment, enhances the motility of cancer cells and promotes the evasion of antitumor immunity. The aim of the present review was to comprehensively discuss the efferocytosis phenomenon, the important players associated with this process and their role in cancer-related biological events.

LAMPs: Shedding light on cancer biology

Lysosomes are important cytoplasmic organelles whose critical functions in cells are increasingly being understood. In particular, despite the long-standing accepted concept about the role of lysosomes as cellular machineries solely assigned to degradation, it has been demonstrated that they play active roles in homeostasis and even in cancer biology. Indeed, it is now well documented that during the process of cellular transformation and cancer progression lysosomes are changing localization, composition, and volume and, through the release of their enzymes, lysosomes can also enhance cancer aggressiveness. LAMPs (lysosome associated membrane proteins) represent a family of glycosylated proteins present predominantly on the membrane of lysosomes whose expression can vary among different tissues, suggesting a separation of functions. In this review we focus on the functions and roles of the different LAMP family members, with a particular emphasis on cancer progression and metastatic spread. LAMP proteins are involved in many different aspects of cell biology and can influence cellular processes such as phagocytosis, autophagy, lipid transport, and aging. Interestingly, for all the five members identified so far (LAMP1, LAMP2, LAMP3, CD68/Macrosialin/LAMP4, and BAD-LAMP/LAMP5), a role in cancer has been suggested. While this is well documented for LAMP1 and LAMP2, the involvement of the other three proteins in cancer progression and aggressiveness has recently been proposed and remains to be elucidated. Here we present different examples about how LAMP proteins can influence and support tumor growth and metastatic spread, emphasizing the impact of each single member of the family.

Skeletal muscle regeneration and impact of aging and nutrition

After skeletal muscle injury a regeneration process takes place to repair muscle. Skeletal muscle recovery is a highly coordinated process involving cross-talk between immune and muscle cells. It is well known that the physiological activities of both immune cells and muscle stem cells decline with advancing age, thereby blunting the capacity of skeletal muscle to regenerate. The age-related reduction in muscle repair efficiency contributes to the development of sarcopenia, one of the most important factors of disability in elderly people. Preserving muscle regeneration capacity may slow the development of this syndrome. In this context, nutrition has drawn much attention: studies have demonstrated that nutrients such as amino acids, n-3 polyunsaturated fatty acids, polyphenols and vitamin D can improve skeletal muscle regeneration by targeting key functions of immune cells, muscle cells or both. Here we review the process of skeletal muscle regeneration with a special focus on the cross-talk between immune and muscle cells. We address the effect of aging on immune and skeletal muscle cells involved in muscle regeneration. Finally, the mechanisms of nutrient action on muscle regeneration are described, showing that quality of nutrition may help to preserve the capacity for skeletal muscle regeneration with age.

Atherogenesis: hyperhomocysteinemia interactions with LDL, macrophage function, paraoxonase 1, and exercise

Despite great strides in understanding the atherogenesis process, the mechanisms are not entirely known. In addition to diet, cigarette smoking, genetic predisposition, and hypertension, hyperhomocysteinemia (HHcy), an accumulation of the noncoding sulfur-containing amino acid homocysteine (Hcy), is a significant contributor to atherogenesis. Although exercise decreases HHcy and increases longevity, the complete mechanism is unclear. In light of recent evidence, in this review, we focus on the effects of HHcy on macrophage function, differentiation, and polarization. Though there is need for further evidence, it is most likely that HHcy-mediated alterations in macrophage function are important contributors to atherogenesis, and HHcy-countering strategies, such as nutrition and exercise, should be included in the combinatorial regimens for effective prevention and regression of atherosclerotic plaques. Therefore, we also included a discussion on the effects of exercise on the HHcy-mediated atherogenic process.

Clearance of primary necrotic cells by non-professional phagocytes

BACKGROUND INFORMATION

Homotypic internalisation of tumour cells has frequently been observed in tumour tissue sections. Events of non-professional phagocytosis, however, may also occur in normal tissue if the number of dying cells exceeds the phagocytic capacity of professional phagocytes such as macrophages and dendritic cells. The aim of this study was to investigate the molecular background of non-professional phagocytosis of primary necrotic cells by neighbouring tumour cells and normal skin fibroblasts.

RESULTS

We demonstrate that homotypic and heterotypic uptake of necrotic cells is a feature common to various cell types. Investigating critical stimuli of necrotic cell clearance we found that non-professional phagocytes require cytoskeleton rearrangement, recognition of phosphatidylserine and GTPase activity of dynamin II, which is normally engaged in endocytosis. Additionally, we have observed an accumulation of adhesion molecule E-cadherin, phosphorylated actin-linker protein ezrin, lysosomal-associated membrane protein 1 and microtubule-associated protein 1 light chain 3 at the site of engulfment. Loss of membrane integrity and an increase in the intracellular level of heat-shock protein 70 in the necrotic cells have also been observed.

CONCLUSIONS

Our results shed light on the mechanism of necrotic cell removal by tumour cells and normal skin fibroblasts in vitro. It is reasonable to assume that this process has a physiological relevance in inflammation and autoimmune disease in normal tissue as well as in tumours regarding immune cell infiltration. We conclude that necrotic cell clearance by non-professional phagocytes contributes to the phagocytic activity by macrophages and that this process may prevent release of proinflammatory damage-associated molecular pattern molecules.

IFN-γ ameliorates autoimmune encephalomyelitis by limiting myelin lipid peroxidation

Evidence has suggested both a pathogenic and a protective role for the proinflammatory cytokine IFN-γ in experimental autoimmune encephalomyelitis (EAE). However, the mechanisms underlying the protective role of IFN-γ in EAE have not been fully resolved, particularly in the context of CNS antigen-presenting cells (APCs). In this study we examined the role of IFN-γ in myelin antigen uptake by CNS APCs during EAE. We found that myelin antigen colocalization with APCs was decreased substantially and that EAE was significantly more severe and showed a chronic-progressive course in IFN-γ knockout (IFN-γ-/-) or IFN-γ receptor knockout (IFN-γR-/-) mice as compared with WT animals. IFN-γ was a critical regulator of phagocytic/activating receptors on CNS APCs. Importantly, "free" myelin debris and lipid peroxidation activity at CNS lesions was increased in mice lacking IFN-γ signaling. Treatment with N-acetyl-l-cysteine, a potent antioxidant, abolished lipid peroxidation activity and ameliorated EAE in IFN-γ-signaling-deficient mice. Taken together the data suggest a protective role for IFN-γ in EAE by regulating the removal of myelin debris by CNS APCs and thereby limiting the substrate available for the generation of neurotoxic lipid peroxidation products.

Scavenger Receptors: Emerging Roles in Cancer Biology and Immunology

Scavenger receptors constitute a large family of evolutionally conserved protein molecules that are structurally and functionally diverse. Although scavenger receptors were originally identified based on their capacity to scavenge modified lipoproteins, these molecules have been shown to recognize and bind to a broad spectrum of ligands, including modified and unmodified host-derived molecules or microbial components. As a major subset of innate pattern recognition receptors, scavenger receptors are mainly expressed on myeloid cells and function in a wide range of biological processes, such as endocytosis, adhesion, lipid transport, antigen presentation, and pathogen clearance. In addition to playing a crucial role in maintenance of host homeostasis, scavenger receptors have been implicated in the pathogenesis of a number of diseases, e.g., atherosclerosis, neurodegeneration, or metabolic disorders. Emerging evidence has begun to reveal these receptor molecules as important regulators of tumor behavior and host immune responses to cancer. This review summarizes our current understanding on the newly identified, distinct functions of scavenger receptors in cancer biology and immunology. The potential of scavenger receptors as diagnostic biomarkers and novel targets for therapeutic interventions to treat malignancies is also highlighted.

Transient activation of microglia following acute alcohol exposure in developing mouse neocortex is primarily driven by BAX-dependent neurodegeneration

Fetal alcohol exposure is the most common known cause of preventable mental retardation, yet we know little about how microglia respond to, or are affected by, alcohol in the developing brain in vivo. Using an acute (single day) model of moderate (3 g/kg) to severe (5 g/kg) alcohol exposure in postnatal day (P) 7 or P8 mice, we found that alcohol-induced neuroapoptosis in the neocortex is closely correlated in space and time with the appearance of activated microglia near dead cells. The timing and molecular pattern of microglial activation varied with the level of cell death. Although microglia rapidly mobilized to contact and engulf late-stage apoptotic neurons, apoptotic bodies temporarily accumulated in neocortex, suggesting that in severe cases of alcohol toxicity the neurodegeneration rate exceeds the clearance capacity of endogenous microglia. Nevertheless, most dead cells were cleared and microglia began to deactivate within 1-2 days of the initial insult. Coincident with microglial activation and deactivation, there was a transient increase in expression of pro-inflammatory factors, TNFα and IL-1β, after severe (5 g/kg) but not moderate (3 g/kg) EtOH levels. Alcohol-induced microglial activation and pro-inflammatory factor expression were largely abolished in BAX null mice lacking neuroapoptosis, indicating that microglial activation is primarily triggered by apoptosis rather than the alcohol. Therefore, acute alcohol exposure in the developing neocortex causes transient microglial activation and mobilization, promoting clearance of dead cells and tissue recovery. Moreover, cortical microglia show a remarkable capacity to rapidly deactivate following even severe neurodegenerative insults in the developing brain.

Molecular imaging of inflammation in the ApoE -/- mouse model of atherosclerosis with IodoDPA

BACKGROUND

Atherosclerosis is a common and serious vascular disease predisposing individuals to myocardial infarction and stroke. Intravascular plaques, the pathologic lesions of atherosclerosis, are largely composed of cholesterol-laden luminal macrophage-rich infiltrates within a fibrous cap. The ability to detect those macrophages non-invasively within the aorta, carotid artery and other vessels would allow physicians to determine plaque burden, aiding management of patients with atherosclerosis.

METHODS AND RESULTS

We previously developed a low-molecular-weight imaging agent, [(125)I]iodo-DPA-713 (iodoDPA), which selectively targets macrophages. Here we use it to detect both intravascular macrophages and macrophage infiltrates within the myocardium in the ApoE -/- mouse model of atherosclerosis using single photon emission computed tomography (SPECT). SPECT data were confirmed by echocardiography, near-infrared fluorescence imaging and histology. SPECT images showed focal uptake of radiotracer at the aortic root in all ApoE -/- mice, while the age-matched controls were nearly devoid of radiotracer uptake. Focal radiotracer uptake along the descending aorta and within the myocardium was also observed in affected animals.

CONCLUSIONS

IodoDPA is a promising new imaging agent for atherosclerosis, with specificity for the macrophage component of the lesions involved.

The Basis of Muscle Regeneration

Muscle regeneration recapitulates many aspects of embryonic myogenesis and is an important homeostatic process of the adult skeletal muscle, which, after development, retains the capacity to regenerate in response to appropriate stimuli, activating the muscle compartment of stem cells, namely, satellite cells, as well as other precursor cells. Moreover, significant evidence suggests that while stem cells represent an important determinant for tissue regeneration, a “qualified” environment is necessary to guarantee and achieve functional results. It is therefore plausible that the loss of control over these cell fate decisions could lead to a pathological transdifferentiation, leading to pathologic defects in the regenerative process. This review provides an overview about the general aspects of muscle development and discusses the cellular and molecular aspects that characterize the five interrelated and time-dependent phases of muscle regeneration, namely, degeneration, inflammation, regeneration, remodeling, and maturation/functional repair.

P53, Bcl-2 and CD68 expression in response to amethopterin-induced lung injury and ameliorating role of L-carnitine

Amethopterin (methotrexate, MTX) is an antimetabolite and antifolate drug with antiflammatory properities and is used to treat autoimmune diseases, such as psoriasis, rheumatoid arthritis and certain types of cancer, such as breast, lymphoma and lung. The present study aimed to study the changes in P53, Bcl-2 and CD68 expression in response to amethopterin-induced lung injury and ameliorating the role of l-carnitine. A total of 36 male albino rats were equally divided into six groups: the first and second groups were the control and l-carnitine groups respectively while the 3rd group was amethopterin rat group; the 4th and 5th groups were co- and post-treated amethopterin rat with l-carnitine respectively and the 6th group was self treated amethopterin rat group. Our results shows that lung in amethopterin-treated rats showed many of histopathological alterations as severe to strong alveolar damage in the form of collapsed alveoli and strong thickened interalveolar septa with heavy infiltration of inflammatory cells. This damage was increased or remaining in self-amethopterin-treated group. Treatment (co- and post) with l-carnitine were improved in the lung structure that was treated with amethopterin. A significant increase in p53 and CD68 and decrease in Bc1-2 immunoreactivity in the lung in amethopterin group is observed when compared with the control group. However, treatment of rats with l-carnitine decreased the intensity of P53-ir and CD68-ir and increased the intensity of Bcl-2 in lung when compared with amethopterin rat group. Co-treatment with l-carnitine improved lung damage induced with amethopterin.

Mechanisms of muscle injury, repair, and regeneration

Skeletal muscle continuously adapts to changes in its mechanical environment through modifications in gene expression and protein stability that affect its physiological function and mass. However, mechanical stresses commonly exceed the parameters that induce adaptations, producing instead acute injury. Furthermore, the relatively superficial location of many muscles in the body leaves them further vulnerable to acute injuries by exposure to extreme temperatures, contusions, lacerations or toxins. In this article, the molecular, cellular, and mechanical factors that underlie muscle injury and the capacity of muscle to repair and regenerate are presented. Evidence shows that muscle injuries that are caused by eccentric contractions result from direct mechanical damage to myofibrils. However, muscle pathology following other acute injuries is largely attributable to damage to the muscle cell membrane. Many feaures in the injury-repair-regeneration cascade relate to the unregulated influx of calcium through membrane lesions, including: (i) activation of proteases and hydrolases that contribute muscle damage, (ii) activation of enzymes that drive the production of mitogens and motogens for muscle and immune cells involved in injury and repair, and (iii) enabling protein-protein interactions that promote membrane repair. Evidence is also presented to show that the myogenic program that is activated by acute muscle injury and the inflammatory process that follows are highly coordinated, with myeloid cells playing a central role in modulating repair and regeneration. The early-invading, proinflammatory M1 macrophages remove debris caused by injury and express Th1 cytokines that play key roles in regulating the proliferation, migration, and differentiation of satellite cells. The subsequent invasion by anti-inflammatory, M2 macrophages promotes tissue repair and attenuates inflammation. Although this system provides an effective mechanism for muscle repair and regeneration following acute injury, it is dysregulated in chronic injuries. In this article, the process of muscle injury, repair and regeneration that occurs in muscular dystrophy is used as an example of chronic muscle injury, to highlight similarities and differences between the injury and repair processes that occur in acutely and chronically injured muscle.

Current understanding of the mechanisms for clearance of apoptotic cells-a fine balance

Apoptosis is an important cell death mechanism by which multicellular organisms remove unwanted cells. It culminates in a rapid, controlled removal of cell corpses by neighboring or recruited viable cells. Whilst many of the molecular mechanisms that mediate corpse clearance are components of the innate immune system, clearance of apoptotic cells is an anti-inflammatory process. Control of cell death is dependent on competing pro-apoptotic and anti-apoptotic signals. Evidence now suggests a similar balance of competing signals is central to the effective removal of cells, through so called 'eat me' and 'don't eat me' signals. Competing signals are also important for the controlled recruitment of phagocytes to sites of cell death. Consequently recruitment of phagocytes to and from sites of cell death can underlie the resolution or inappropriate propagation of cell death and inflammation. This article highlights our understanding of mechanisms mediating clearance of dying cells and discusses those mechanisms controlling phagocyte migration and how inappropriate control may promote important pathologies.

Eosinophil apoptosis and clearance in asthma

Asthma is an increasingly common respiratory condition characterized by reversible airway obstruction, bronchial hyper-responsiveness and airway inflammation with a clear unmet need for more effective therapy. Eosinophilic asthma is a phenotype of the condition that features increased blood or sputum eosinophils whose numbers correlate with disease severity. Several lines of evidence are now emerging, which implicate increased persistence of eosinophils in the lungs of patients with asthma as a consequence of inhibition of and defects in the apoptotic process, together with impaired apoptotic cell removal mechanisms. This article will update our knowledge of the mechanisms controlling eosinophil apoptosis and clearance, together with evidence implicating defects in apoptosis and pro-inflammatory cell removal in asthma. Recent developments in novel therapies for asthma that target eosinophil apoptotic and/or clearance pathways will also be discussed.

Laser capture microdissection for analysis of macrophage gene expression from atherosclerotic lesions

Coronary artery disease, resulting from atherosclerosis, is the leading cause of death in the Western world. Most previous studies have subjected atherosclerotic arteries, a tissue of mixed cellular composition, to homogenization in order to identify the factors in plaque development, thereby obscuring information relevant to specific cell types. Because macrophage foam cells are critical mediators in atherosclerotic plaque advancement, we reasoned that performing gene analysis on those cells would provide specific insight in novel regulatory factors and potential therapeutic targets. We demonstrated for the first time in vascular biology that foam cell-specific RNA can be isolated by laser capture microdissection (LCM) of plaques. As expected, compared to whole tissue, a significant enrichment in foam cell-specific RNA transcripts was observed. Furthermore, because regression of atherosclerosis is a tantalizing clinical goal, we developed and reported a transplantation-based mouse model. This involved allowing plaques to form in apoE-/- mice and then changing the plaque's plasma environment from hyperlipidemia to normolipidemia. Under those conditions, rapid regression ensued in a process involving emigration of plaque foam cells to regional and systemic lymph nodes. Using LCM, we were able to show that under regression conditions, there was decreased expression in foam cells of inflammatory genes, but an up-regulation of cholesterol efflux genes. Interestingly, we also found that increased expression of chemokine receptor CCR7, a known factor in dendritic cell migration, was required for regression. In conclusion, the LCM methods described in this chapter, which have already lead to a number of striking findings, will likely further facilitate the study of cell type-specific gene expression in animal and human plaques during various stages of atherosclerosis, and after genetic, pharmacologic, and environmental perturbations.

Macrophage recognition of thiol-group oxidized cells: recognition of carbohydrate chains by macrophage surface nucleolin as apoptotic cells

The mechanism was investigated for macrophage recognition of cells oxidized by diamide, a thiol group-specific oxidizing reagent. Jurkat cells exposed to various concentrations of diamide were recognized by macrophages, the cells exposed to 25 µM diamide being best recognized. CD43, a major glycoprotein on the Jurkat cell surface, tended to form clusters upon diamide oxidization, and pretreating Jurkat cells with the anti-CD43 antibody inhibited macrophage binding. This indicates that macrophages appeared to recognize CD43. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and a Western blot analysis of CD43 of the diamide-oxidized cells showed no increase in the amount of cross-linked CD43 compared with control cells, indicating that cross-linking of CD43 by a disulphide bond was not involved in the clustering. Both CD43 clustering and binding of the oxidized cells to macrophages was prevented by the caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD-fmk), suggesting that the oxidized and macrophage-bound cells were undergoing apoptosis. A closer examination revealed that the caspase-3 activity, chromatin condensation, and DNA fragmentation in Jurkat cells were all increased by oxidation. The macrophage receptor involved in the binding appeared to be the cell-surface protein, nucleolin; an anti-nucleolin antibody treatment inhibited the binding. These results suggest that thiol group-oxidized cells underwent early apoptosis and were recognized by nucleolin on macrophages as early apoptotic cells.

Lipopolysaccharide-induced fever depends on prostaglandin E2 production specifically in brain endothelial cells

Immune-induced prostaglandin E2 (PGE2) synthesis is critical for fever and other centrally elicited disease symptoms. The production of PGE2 depends on cyclooxygenase-2 and microsomal prostaglandin E synthase-1 (mPGES-1), but the identity of the cells involved has been a matter of controversy. We generated mice expressing mPGES-1 either in cells of hematopoietic or nonhematopoietic origin. Mice lacking mPGES-1 in hematopoietic cells displayed an intact febrile response to lipopolysaccharide, associated with elevated levels of PGE2 in the cerebrospinal fluid. In contrast, mice that expressed mPGES-1 only in hematopoietic cells, although displaying elevated PGE2 levels in plasma but not in the cerebrospinal fluid, showed no febrile response to lipopolysaccharide, thus pointing to the critical role of brain-derived PGE2 for fever. Immunohistochemical stainings showed that induced cyclooxygenase-2 expression in the brain exclusively occurred in endothelial cells, and quantitative PCR analysis on brain cells isolated by flow cytometry demonstrated that mPGES-1 is induced in endothelial cells and not in vascular wall macrophages. Similar analysis on liver cells showed induced expression in macrophages and not in endothelial cells, pointing at the distinct role for brain endothelial cells in PGE2 synthesis. These results identify the brain endothelial cells as the PGE2-producing cells critical for immune-induced fever.

Source and characterization of hepatic macrophages in acetaminophen-induced acute liver failure in humans

Acetaminophen-induced acute liver failure (AALF) is associated with innate immunity activation, which contributes to the severity of hepatic injury and clinical outcome. A marked increase in hepatic macrophages (h-mφ) is observed in experimental models of AALF, but controversy exists regarding their role, implicating h-mφ in both aggravation and resolution of liver injury. The role of h-mφ in human AALF is virtually unexplored. We sought to investigate the role of chemokine (C-C motif) ligand 2 (CCL2) in the recruitment of circulating monocytes to the inflamed liver and to determine how the h-mφ infiltrate and liver microenvironment may contribute to tissue repair versus inflammation in AALF. We evaluated circulating monocytes, their chemokine (C-C motif) receptor 2 (CCR2) expression, and serum CCL2 levels in patients with AALF. Cell subsets and numbers of circulation-derived (MAC387+) or resident proliferating (CD68/Ki67+) h-mφ in hepatic immune infiltrates were determined by immunohistochemistry. Inflammatory cytokine levels were determined in whole and laser microdissected liver tissue by proteome array. In AALF, circulating monocytes were depleted, with the lowest levels observed in patients with adverse outcomes. CCL2 levels were high in AALF serum and hepatic tissue, and circulating monocyte subsets expressed CCR2, suggesting CCL2-dependent hepatic monocyte recruitment. Significant numbers of both MAC387+ and CD68+ h-mφ were found in AALF compared with control liver tissue with a high proportion expressing the proliferation marker Ki67. Levels of CCL2, CCL3, interleukin (IL)-6, IL-10, and transforming growth factor-β1 were significantly elevated in AALF liver tissue relative to chronic liver disease controls.

CONCLUSION

In AALF, the h-mφ population is expanded in areas of necrosis, both through proliferation of resident cells and CCL2-dependent recruitment of circulating monocytes. The presence of h-mφ within an anti-inflammatory/regenerative microenvironment indicates that they are implicated in resolution of inflammation/tissue repair processes during AALF.

Contribution of monocyte-derived macrophages and smooth muscle cells to arterial foam cell formation

Smooth muscle cells (SMCs) are the main cell type in intimal thickenings and some stages of human atherosclerosis. Like monocyte-derived macrophages, SMCs accumulate excess lipids and contribute to the total intimal foam cell population. In contrast, apolipoprotein (Apo)E-deficient and LDL receptor-deficient mice develop atherosclerotic lesions that are macrophage- as opposed to SMC-rich. The lesser contribution of SMCs to lesion development in these mouse models has distracted attention away from the importance of SMC cholesterol homeostasis in the artery wall. Intimal SMCs accumulate excess amounts of cholesteryl esters when compared with medial layer SMCs, possibly explained by reduced ATP-binding cassette transporter A1 expression and ApoA-I binding to intimal-type SMCs. The aim of this review is to compare the relative contribution of monocyte-derived macrophages and SMCs to human vs. mouse atherosclerosis, and describe what is known about lipid uptake and removal mechanisms contributing to arterial macrophage and SMC foam cell formation. An increased understanding of the contribution of these cell types to lesion development will help to delineate their relative importance in atherogenesis and as potential therapeutic targets.

Genetic ablation of CD68 results in mice with increased bone and dysfunctional osteoclasts

CD68 is a member of the lysosome associated membrane protein (LAMP) family that is restricted in its expression to cells of the monocyte/macrophage lineage. This lineage restriction includes osteoclasts, and, while previous studies of CD68 in macrophages and dendritic cells have proposed roles in lipid metabolism, phagocytosis, and antigen presentation, the expression and function of CD68 in osteoclasts have not been explored. In this study, we investigated the expression and localization of CD68 in macrophages and osteoclasts in response to the monocyte/macrophage-colony stimulating factor (M-CSF) and the receptor activator of NF-κB ligand (RANKL). We found that M-CSF stimulates CD68 expression and RANKL alters the apparent molecular weight of CD68 as measured by Western immunoblotting. In addition, we explored the significance of CD68 expression in osteoclasts by generating mice that lack expression of CD68. These mice have increased trabecular bone, and in vitro assessment of CD68^−/− osteoclasts revealed that, in the absence of CD68, osteoclasts demonstrate an accumulation of intracellular vesicle-like structures, and do not efficiently resorb bone. These findings demonstrate a role for CD68 in the function of osteoclasts, and future studies will determine the mechanistic nature of the defects seen in CD68^−/− osteoclasts.

Biodistribution of small interfering RNA at the organ and cellular levels after lipid nanoparticle-mediated delivery

Chemically stabilized small interfering RNA (siRNA) can be delivered systemically by intravenous injection of lipid nanoparticles (LNPs) in rodents and primates. The biodistribution and kinetics of LNP-siRNA delivery in mice at organ and cellular resolution have been studied using immunofluorescence (IF) staining and quantitative polymerase chain reaction (qPCR). At 0.5 and 2 hr post tail vein injection of Cy5-labeled siRNA encapsulated in LNP, the organ rank-order of siRNA levels is liver > spleen > kidney, with only negligible accumulation in duodenum, lung, heart, and brain. Similar conclusions were drawn by using qPCR to measure tissue siRNA levels as a secondary end point. siRNA levels in these tissues decreased by more than 10-fold after 24 hr. Within the liver, LNPs delivered siRNA to hepatocytes, Kupffer cells, and sinusoids in a time-dependent manner, as revealed by IF staining and signal quantitation methods established using OPERA/Columbus software. siRNA first accumulated in liver sinusoids and trafficked to hepatocytes by 2 hr post dose, corresponding to the onset of target mRNA silencing. Fluorescence in situ hybridization methods were used to detect both strands of siRNA in fixed tissues. Collectively, the authors have implemented a platform to evaluate biodistribution of siRNA across cell types and across tissues in vivo, with the objective of elucidating the pharmacokinetic and pharmacodynamic relationship to guide optimization of delivery vehicles.

Deletion of the murine scavenger receptor CD68

Scavenger receptors (ScRs) are a structurally unrelated family of receptors with the ability to bind modified low density lipoprotein (LDL) as well as a broad range of polyanionic ligands. CD68, whose expression is restricted to mononuclear phagocytes, is a unique ScR family member, owing to its lysosome associated membrane protein (LAMP)-like domain and predominant endosomal distribution. Knockout (ko) mice were generated to directly evaluate the role murine CD68 may play in oxidized LDL (Ox-LDL) uptake. However, CD68⁻/⁻ macrophages took up Ox-LDL robustly. Likewise, no defects were observed in the ability of CD68⁻/⁻ mononuclear phagocytes to take up or mount an effective innate response against a number of microbes. Curiously, CD68⁻/⁻ mononuclear phagocytes exhibited a trend toward enhanced antigen presentation to CD4⁺ T-cells, raising the possibility that CD68 may function either to negatively regulate antigen uptake, loading, or major histocompatibility complex class II (MHC-II) trafficking.

Effect of the oxLDL binding protein Fc-CD68 on plaque extension and vulnerability in atherosclerosis

RATIONALE

There is strong evidence that oxidative modification of low-density lipoprotein (oxLDL) plays a critical role in atherogenesis and that oxLDL may profoundly influence the mechanical stability of atherosclerotic plaques.

OBJECTIVE

To block oxLDL, we designed, expressed, and tested Fc-CD68, a soluble oxLDL binding protein consisting of human Fc and the extracellular domain of the human oxLDL-binding receptor CD68.

METHODS AND RESULTS

Fc-CD68 bound with high specific affinity to oxLDL and strongly bound and colocalized with oxLDL in plaques. To study the effects of repeated administrations of Fc-CD68 on the progression of atherosclerosis and plaque vulnerability, 12- and 16-week old cholesterol-fed ApoE(-/-) mice received either Fc-CD68 (n = 6) or Fc control protein (n = 6 to 8) thrice weekly for 4 weeks. Macroscopic and histological analysis of Sudan red lipid staining showed strong and significant reduction of plaque extension in the aorta and in the aortic root, respectively. Histological analysis of pentachrome- and Sirius-stained sections of the brachiocephalic arteries of 20 week-old ApoE(-/-) mice revealed that Fc-CD68 significantly reduced the occurrence of spontaneous ruptures of established plaques by ≈20%, compared with Fc and drastically increased the collagen content of plaques. Furthermore, in immunostained sections of the brachiocephalic artery and the aortic root, Fc-CD68 reduced the infiltration of plaques with T lymphocytes, and macrophages by ≈50% and 30%, respectively.

CONCLUSIONS

The oxLDL binding protein Fc-CD68 attenuates atherosclerosis and strengthens the stability of atherosclerotic plaques.

Identification and characterization of class B scavenger receptor CD36 from the hard tick, Haemaphysalis longicornis

Scavenger receptors (SRs) are cell-surface proteins and exhibit distinctive ligand-binding properties, recognizing a wide range of ligands that include microbial surface constituents and intact microbes. The class B scavenger receptor CD36 (SRB) is predominantly expressed by macrophages and is considered important in innate immunity. We here show the identification and characterization of SRB from the hard ixodid tick, Haemaphysalis longicornis (HlSRB). The full-length cDNA was 2,908 bp, including an ORF encoding of 1,518 amino acids with a pI value of 5.83. H. longicornis SRB contains a hydrophobic SRB domain and four centrally clustered cysteine residues for arrangement of disulfide bridges. Deduced amino acid sequence has an identity of 30-38% with the SRB of other organisms. RT-PCR analysis showed that mRNA transcripts were expressed in multiple organs of adult ticks but with a different transcript level in the developmental stages of H. longicornis ticks. His-tagged recombinant HlSRB was expressed in Escherichia coli with an expected molecular mass of 50 kDa. In Western blot analysis, mouse anti-rHlSRB serum recognized a strong reaction with a 50 kDa protein band in lysates prepared from egg and adult tick but showed a weak reaction with lysates of larva and nymph. In an indirect immunofluorescent antibody test, HlSRB antiserum recognized the protein located on the midgut, salivary glands, and ovary of partially fed H. longicornis females. Silencing of the HlSRB gene by RNAi led to a significant reduction in the engorged female body weight. It is noteworthy that more than a dozen SRB orthologs have been identified in the genomes of insect species with functions related to pheromone signaling, innate immunity, phagocytic clearance of apoptotic cells, and various aspects of the fatty acid metabolism. This is the first report of the identification and characterization of the SRB homologue in Chelicerata, including ticks, horseshoe crabs, scorpions, spiders, and mites.

Nonmyogenic cells in skeletal muscle regeneration

Although classical dogma dictates that satellite cells are the primary cell type involved in skeletal muscle regeneration, alternative cell types such as a variety of inflammatory and stromal cells are also actively involved in this process. A model describing myogenic cells as direct contributors to regeneration and nonmyogenic cells from other developmental sources as important accessories has emerged, with similar systems having been described in numerous other tissues in the body. Increasing evidence supports the notion that inflammatory cells function as supportive accessory cells, and are not merely involved in clearing damage following skeletal muscle injury. Additionally, recent studies have highlighted the role of tissue resident mesenchymal cell populations as playing a central role in regulating regeneration. These "accessory" cell populations are proposed to influence myogenesis via direct cell contact and secretion of paracrine trophic factors. The basic foundations of accessory cell understanding should be recognized as a crucial component to all prospects of regenerative medicine, and this chapter intends to provide a comprehensive background on the current literature describing immune and tissue-resident mesenchymal cells' role in skeletal muscle regeneration.

Impact of ageing on muscle cell regeneration

Skeletal muscle regeneration is a coordinate process in which several factors are sequentially activated to maintain and preserve muscle structure and function. The major role in the growth, remodeling and regeneration is played by satellite cells, a quiescent population of myogenic cells that reside between the basal lamina and plasmalemma and are rapidly activated in response to appropriate stimuli. However, in several muscle conditions, including aging, the capacity of skeletal muscle to sustain an efficient regenerative pathway is severely compromised. Nevertheless, if skeletal muscle possesses a stem cell compartment it is not clear why the muscle fails to regenerate under pathological conditions. Either the resident muscle stem cells are too rare or intrinsically incapable of repairing major damage, or perhaps the injured/pathological muscle is a prohibitive environment for stem cell activation and function. Although we lack definitive answers, recent experimental evidences suggest that the mere presence of endogenous stem cells may not be sufficient to guarantee muscle regeneration, and that the presence of appropriate stimuli and factors are necessary to provide a permissive environment that permits stem cell mediated muscle regeneration and repair. In this review we discuss the molecular basis of muscle regeneration and how aging impacts stem cell mediated muscle regeneration and repair.

Phagocytosis of dying cells: influence of smoking and static magnetic fields

It is becoming evident that failure in the removal of dying cells causes and/or promotes the onset of chronic diseases. Impairment of phagocytosis of apoptotic cells can be due not only to genetic or molecular malfunctioning but also to external/environmental factors. Two of these environmental factors have been recently reported to down regulate the clearance of apoptotic cells: cigarette smoke and static magnetic fields. Cigarette smoke contains highly reactive carbonyls that modify proteins which directly/indirectly affects cellular function. Human macrophages interacting with carbonyl or cigarette smoke modified extracellular matrix (ECM) proteins dramatically down regulated their ability to phagocytose apoptotic neutrophils. It was postulated that changes in the ECM environment as a result of cigarette smoke affect the ability of macrophages to remove apoptotic cells. This decreased phagocytic activity was as a result of sequestration of receptors involved in the uptake of apoptotic cells towards that of recognition of carbonyl adducts on the modified ECM proteins leading to increased macrophage adhesion. Downregulation of the phagocytosis of apoptotic cells was also described when performed in presence of static magnetic fields (SMFs) of moderate intensity. SMFs have been reported to perturb distribution of membrane proteins and glycoproteins, receptors, cytoskeleton and trans-membrane fluxes of different ions, especially calcium [Ca(2+)]i, that in turn, interfere with many different physiological activities, including phagocytosis. The effects of cigarette smoke and SMF on the phagocytosis of dying cells will be here discussed.

Regulation of interleukin-10 gene expression in macrophages engulfing apoptotic cells

Apoptosis and the rapid clearance of apoptotic cells (ACs) by professional or nonprofessional phagocytes are normal and coordinated processes that ensure controlled cell growth and stress response with nonpathological outcomes. Uptake of ACs by phagocytes is thought to suppress autoimmune responses through the release of anti-inflammatory cytokines such as interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), and inhibition of proinflammatory cytokines. The production of pro- and anti-inflammatory cytokines by phagocytes is highly regulated as part of an intrinsic mechanism to prevent inflammatory and autoimmune reactions in a physiological state. Production of IL-10 by phagocytes during clearance of ACs is critical to ensuring cellular homeostasis and suppression of autoimmunity. The molecular mechanism whereby IL-10 production is induced by ACs is only beginning to be understood. This review summarizes our recent work in this aspect of an essential physiological and homeostatic process.

Scavenger receptors and their potential as therapeutic targets in the treatment of cardiovascular disease

Scavenger receptors act as membrane-bound and soluble proteins that bind to macromolecular complexes and pathogens. This diverse supergroup of proteins mediates binding to modified lipoprotein particles which regulate the initiation and progression of atherosclerotic plaques. In vascular tissues, scavenger receptors are implicated in regulating intracellular signaling, lipid accumulation, foam cell development, and cellular apoptosis or necrosis linked to the pathophysiology of atherosclerosis. One approach is using gene therapy to modulate scavenger receptor function in atherosclerosis. Ectopic expression of membrane-bound scavenger receptors using viral vectors can modify lipid profiles and reduce the incidence of atherosclerosis. Alternatively, expression of soluble scavenger receptors can also block plaque initiation and progression. Inhibition of scavenger receptor expression using a combined gene therapy and RNA interference strategy also holds promise for long-term therapy. Here we review our current understanding of the gene delivery by viral vectors to cells and tissues in gene therapy strategies and its application to the modulation of scavenger receptor function in atherosclerosis.

Atherosclerosis in primary antiphospholipid syndrome

Antiphospholipid syndrome (APS) is the most common cause of acquired thrombophilia, but experimental and clinical evidence accumulated over the years suggest that the clinical manifestations of APS go beyond those of a simple hypercoagulable state. Although still a controversial topic, the elevated risk of atherosclerosis in systemic lupus erythematosus seems little accounted for by the presence of antiphospholipid antibodies, whereas premature atherosclerosis has been addressed in few series of patients with primary APS. The available data in primary APS suggest that traditional risk factors for atherosclerosis are less involved in arterial disease, rather antiphospholipid antibodies appear as major players. Their effect on the coagulation system, the vessel wall and on the antioxidant/oxidant balance impairs vascular homeostasis, leading to premature arterial thickening.

Regulatory interactions between muscle and the immune system during muscle regeneration

Recent discoveries reveal complex interactions between skeletal muscle and the immune system that regulate muscle regeneration. In this review, we evaluate evidence that indicates that the response of myeloid cells to muscle injury promotes muscle regeneration and growth. Acute perturbations of muscle activate a sequence of interactions between muscle and inflammatory cells. The initial inflammatory response is a characteristic Th1 inflammatory response, first dominated by neutrophils and subsequently by CD68(+) M1 macrophages. M1 macrophages can propagate the Th1 response by releasing proinflammatory cytokines and cause further tissue damage through the release of nitric oxide. Myeloid cells in the early Th1 response stimulate the proliferative phase of myogenesis through mechanisms mediated by TNF-alpha and IL-6; experimental prolongation of their presence is associated with delayed transition to the early differentiation stage of myogenesis. Subsequent invasion by CD163(+)/CD206(+) M2 macrophages attenuates M1 populations through the release of anti-inflammatory cytokines, including IL-10. M2 macrophages play a major role in promoting growth and regeneration; their absence greatly slows muscle growth following injury or modified use and inhibits muscle differentiation and regeneration. Chronic muscle injury leads to profiles of macrophage invasion and function that differ from acute injuries. For example, mdx muscular dystrophy yields invasion of muscle by M1 macrophages, but their early invasion is accompanied by a subpopulation of M2a macrophages. M2a macrophages are IL-4 receptor(+)/CD206(+) cells that reduce cytotoxicity of M1 macrophages. Subsequent invasion of dystrophic muscle by M2c macrophages is associated with progression of the regenerative phase in pathophysiology. Together, these findings show that transitions in macrophage phenotype are an essential component of muscle regeneration in vivo following acute or chronic muscle damage.

Thymosin beta 4 mRNA and peptide expression in phagocytic cells of different mouse tissues

Thymosin beta 4 (Tbeta4) is a peptide of 43 amino acids, mainly recognized as a regulator of actin polymerization by sequestering G-actin. Meanwhile, the peptide has been implicated in lymphocyte maturation, carcinogenesis, apoptosis, angiogenesis, blood coagulation and wound healing. The peptide is also involved in lesion-induced neuroplasticity through microglia upregulation and it participates in the growth of neuronal processes. However, its precise cellular localization throughout the entire body of the mouse has not been documented. We therefore initiated a detailed investigation of the tissue distribution and cellular expression of the Tbeta4 peptide and its precursor mRNA by immunocytochemistry and in situ hybridization, respectively. In the brain, Tbeta4 was clearly present in neurons of the olfactory bulb, neocortex, hippocampus, striatum, amygdala, piriform cortex and cerebellum, and in microglia across the entire brain. We further localized Tbeta4 in cells, typically with many processes, inside thymus, spleen, lung, kidney, liver, adrenal gland, stomach and intestine. Remarkably, Tbeta4 was thus associated with microglia and macrophages, the differentiated phagocytic cells residing in every tissue. Motility and phagocytosis, two important activities of macrophages, depend on actin, which can explain the presence of Tbeta4 in these cells.

Characterization of RAGE, HMGB1, and S100beta in inflammation-induced preterm birth and fetal tissue injury

Immune activation represents an adaptive reaction triggered by both noxious exogenous (microbes) and endogenous [high mobility group box-1 protein (HMGB1), S100 calcium binding proteins] inducers of inflammation. Cell stress or necrosis lead the release of HMGB1 and S100 proteins in the extracellular compartment where they act as damage-associated molecular pattern molecules (or alarmins) by engaging the receptor for advanced glycation end-products (RAGE). Although the biology of RAGE is dictated by the accumulation of damage-associated molecular pattern molecules at sites of tissue injury, the role of RAGE in mediating antenatal fetal injury remains unknown. First, we studied the relationships at birth between the intensity of human fetal inflammation and sRAGE (an endogenous RAGE antagonist), HMGB1, and S100beta protein. We found significantly lower sRAGE in human fetuses that mounted robust inflammatory responses. HMGB1 levels correlated significantly with levels of interleukin-6 and S100beta in fetal circulation. We then evaluated the levels and areas of tissue expression of RAGE, HMGB1, and S100beta in specific organs of mouse fetuses on E16. Using an animal model of endotoxin-induced fetal damage and preterm birth, we determined that inflammation induces a significant change in expression of RAGE and HMGB1, but not S100beta, at sites of tissue damage. Our findings indicate that RAGE and HMGB1 may be important mediators of cellular injury in fetuses delivered in the setting of inflammation-induced preterm birth.

Para-inflammation in the aging retina

Para-inflammation is a tissue adaptive response to noxious stress or malfunction and has characteristics that are intermediate between basal and inflammatory states (Medzhitov, 2008). The physiological purpose of para-inflammation is to restore tissue functionality and homeostasis. Para-inflammation may become chronic or turn into inflammation if tissue stress or malfunction persists for a sustained period. Chronic para-inflammation contributes to the initiation and progression of many human diseases including obesity, type 2 diabetes, atherosclerosis, and age-related neurodegenerative diseases. Evidence from our studies and the studies of some others suggests that para-inflammation also exists in the aging retina in physiological conditions and might contribute to age-related retinal pathologies. The purpose of this review is to introduce the notion of "para-inflammation" as a state between frank, overt destructive inflammation and the non-inflammatory removal of dead or dying cells by apoptosis, to the retinal community. In diabetes and atherosclerosis, leukocytes particularly monocytes and vascular endothelial cells are constantly under noxious stress due to glycaemic and/or lipidaemic dysregulation. These blood-borne stresses trigger para-inflammatory responses in leukocytes and endothelial cells by up-regulating the expression of adhesion molecules or releasing cytokines/chemokines, which in turn cause abnormal leukocyte-endothelial interactions and ultimately vascular damage. In the aging retina, on the other hand, oxidized lipoproteins and free radicals are considered to be major causes of tissue stress and serve as local triggers for retinal para-inflammation. Microarray analysis has revealed the up-regulation of a large number of inflammatory genes, including genes involved in complement activation and inflammatory cytokine/chemokine production, in the aging retina. Para-inflammatory responses in the neuroretina of aged mice are characterized by microglial activation and subretinal migration, and breakdown of blood-retinal barrier. At the retinal/choroidal interface para-inflammation is manifested by complement activation in Bruch's membrane and RPE cells, and microglia accumulation in subretinal space. With age, para-inflammatory changes have also been observed in the choroidal tissue, evidenced by 1) increased thickness of choroid; 2) increased number of CD45(+)CRIg(+) macrophages; 3) morphological abnormalities in choroidal melanocytes; and 4) fibrosis in choroidal tissue. An increased knowledge of contribution of retinal para-inflammation to various pathological conditions is essential for the better understanding of the pathogenesis of various age-related retinal diseases including diabetic retinopathy, glaucoma and age-related macular degeneration.

Identification of macrosialin (CD68) on the surface of host macrophages as the receptor for the intercellular adhesive molecule (ICAM-L) of Leishmania amazonensis

The intercellular adhesive molecule, ICAM-L, of Leishmania amazonensis is known to block the attachment as well as internalisation of Leishmania for infection in host macrophages. We employed monoclonal antibodies (mAb) to the surface molecules of a macrophage to block the attachment of ICAM-L to the macrophage surface and identified that CD68 macrosialin is likely the receptor molecule on the macrophage for ICAM-L. We then demonstrated physical interaction between ICAM-L and macrosialin by co-immunoprecipitation of macrosialin with ICAM-L or vice versa. Finally, macrosialin is expressed in macrosialin-negative murine fibroblast cell line NCTC clone 2555 and demonstrates that both ICAM-L and promastigotes of L. amazonensis can bind to the CD68 transfectant. We thus conclude that CD68 macrosialin is the receptor on host macrophages for ICAM-L. Also, involvement of ICAM-L-macrosialin interaction in other Leishmania species and other mammalian macrophages were demonstrated, indicating the biological relevance of this ligand-receptor interaction.

Atherosclerosis in autoimmune diseases

Lipid peroxidation occurs frequently in patients with systemic autoimmune diseases and contributes to autoimmune vascular inflammation. Oxidized low-density lipoprotein (oxLDL) interacts with beta2-glycoprotein I (beta2GPI), forming oxLDL/beta2GPI complexes. Circulating oxLDL/beta2GPI complexes and autoantibodies to these complexes have been demonstrated in patients with systemic lupus erythematosus and antiphospholipid syndrome. These findings suggest an immunogenic nature of the complexes and an active proatherogenic role in autoimmunity. Biochemical characterization of the complexes and immunohistochemical studies of atherosclerotic lesions suggest that most of the complexes originate in the arterial wall and are released into circulation. The in vitro macrophage uptake of oxLDL/beta2GPI complexes increased significantly in the presence of antiphospholipid antibodies (anti-beta2GPI), suggesting that macrophage Fcgamma receptors are involved in the lipid intracellular influx that leads to foam cell formation. These findings provide an immunologic explanation for the accelerated development of atherosclerosis seen in systemic lupus erythematosus and antiphospholipid syndrome.

Clearance of oxidatively damaged cells by macrophages: recognition of glycoprotein clusters by macrophage-surface nucleolin as early apoptotic cells

The mechanism of macrophage recognition of oxidatively damaged cells was investigated. Jurkat T cells exposed to various concentrations of H(2)O(2) were bound and phagocytosed by macrophages. The cells exposed to 0.1 mM H(2)O(2) were best bound. The cell-surface ligands recognized by macrophages were suggested to be sialylpolylactosaminyl sugar chains of a major sialoglycoprotein CD43 because 1) the cell binding was inhibited by oligosaccharides containing sialylpolylactosaminyl chains, and their inhibitory activity was destroyed by a polylactosamine-cleaving enzyme endo-beta-galactosidase, and by neuraminidase; 2) the oxidized Jurkat cells pretreated with either glycosidase or with anti-CD43 antibody were not bound. The macrophage receptor involved in the binding was suggested to be cell-surface nucleolin because 1) anti-nucleolin antibody inhibited the binding; 2) nucleolin-transfected HEK293 cells bound the oxidized cells; and 3) this binding was inhibited by anti-nucleolin antibody and by anti-CD43 antibody. CD43 on oxidized Jurkat cells tended to form clusters in good accordance with their susceptibility to the macrophage binding. CD43 clustering and the oxidized-cell binding to macrophages were prevented by a caspase inhibitor Z-VAD-fmk, suggesting that the oxidized and bound cells were undergoing apoptosis. Indeed, caspase-3 activity of Jurkat cells increased by the oxidation. These results suggest that moderately oxidized cells undergo apoptosis and are recognized by macrophages as early apoptotic cells.

Autoimmune-mediated atherothrombosis

Autoimmune vascular inflammation and oxidative stress (lipid peroxidation) are common in systemic autoimmune diseases and contribute to the oxidative modification of low-density lipoprotein (oxLDL) and oxLDL/beta2GPI complex formation. Circulating oxLDL/beta2GPI complexes have been detected in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). The presence of antibodies to oxLDL/beta2GPI complexes indicates that these complexes are immunogenic, and the coexistence of complexes and antibodies has pointed to an active proatherogenic role in the development of autoimmune vascular complications. Immunohistochemical staining of atherosclerotic lesions suggest that these complexes are formed in the arterial wall and released into circulation. The in vitro macrophage uptake of oxLDL/beta2GPI complexes was significantly increased in the presence of antiphospholipid antibodies, either beta2GPI-dependent anticardiolipin or anti-beta2GPI antibodies, suggesting that macrophage Fcgamma receptors are involved in lipid intracellular influx and foam cell formation. These findings provide an explanation for the accelerated development of atherosclerosis seen in SLE and APS. The presence of circulating oxLDL/beta2GPI complexes and IgG antibodies to these complexes indicate significant vascular injury and oxidative stress as well as an active role in autoimmune-mediated atherothrombosis.

Phagocytic clearance of apoptotic cells: role in lung disease

Apoptosis and apoptotic clearance are matched processes that are centered in the maintenance of homeostasis. Similar to apoptosis, apoptotic cell clearance is a conserved mechanism that is highly efficient and redundant, highlighting its overall functional importance in homeostasis. Increasing evidence suggests that the mismatch between apoptosis and apoptotic cell clearance underlies pathologic conditions including inflammatory lung diseases, such as chronic obstructive pulmonary disease, cystic fibrosis, asthma, acute lung injury/acute respiratory distress syndrome and cancer immunity. Although direct causality has yet to be established, this paradigm opens novel approaches towards the understanding and treatment of lung diseases. Glucocorticoids, statins and macrolide antibiotics, which are already in use for treating lung conditions, have a positive effect on apoptotic clearance and are among novel agents that are potential candidates for treatment of these disorders.