Alternatively activated macrophages actively inhibit proliferation of peripheral blood lymphocytes and CD4+ T cells in vitro

Engineered Strategies to Interfere with Macrophage Fate in Myocardial Infarction

Myocardial infarction (MI), a severe cardiovascular condition, is typically triggered by coronary artery disease, resulting in ischemic damage and the subsequent necrosis of the myocardium. Macrophages, known for their remarkable plasticity, are capable of exhibiting a range of phenotypes and functions as they react to diverse stimuli within their local microenvironment. In recent years, there has been an increasing number of studies on the regulation of macrophage behavior based on tissue engineering strategies, and its regulatory mechanisms deserve further investigation. This review first summarizes the effects of key regulatory factors of engineered biomaterials (including bioactive molecules, conductivity, and some microenvironmental factors) on macrophage behavior, then explores specific methods for inducing macrophage behavior through tissue engineering materials to promote myocardial repair, and summarizes the role of macrophage-host cell crosstalk in regulating inflammation, vascularization, and tissue remodeling. Finally, we propose some future challenges in regulating macrophage-material interactions and tailoring personalized biomaterials to guide macrophage phenotypes.

Microfluidic models of the neurovascular unit: a translational view

The vasculature of the brain consists of specialized endothelial cells that form a blood-brain barrier (BBB). This barrier, in conjunction with supporting cell types, forms the neurovascular unit (NVU). The NVU restricts the passage of certain substances from the bloodstream while selectively permitting essential nutrients and molecules to enter the brain. This protective role is crucial for optimal brain function, but presents a significant obstacle in treating neurological conditions, necessitating chemical modifications or advanced drug delivery methods for most drugs to cross the NVU. A deeper understanding of NVU in health and disease will aid in the identification of new therapeutic targets and drug delivery strategies for improved treatment of neurological disorders.To achieve this goal, we need models that reflect the human BBB and NVU in health and disease. Although animal models of the brain's vasculature have proven valuable, they are often of limited translational relevance due to interspecies differences or inability to faithfully mimic human disease conditions. For this reason, human in vitro models are essential to improve our understanding of the brain's vasculature under healthy and diseased conditions. This review delves into the advancements in in vitro modeling of the BBB and NVU, with a particular focus on microfluidic models. After providing a historical overview of the field, we shift our focus to recent developments, offering insights into the latest achievements and their associated constraints. We briefly examine the importance of chip materials and methods to facilitate fluid flow, emphasizing their critical roles in achieving the necessary throughput for the integration of microfluidic models into routine experimentation. Subsequently, we highlight the recent strides made in enhancing the biological complexity of microfluidic NVU models and propose recommendations for elevating the biological relevance of future iterations.Importantly, the NVU is an intricate structure and it is improbable that any model will fully encompass all its aspects. Fit-for-purpose models offer a valuable compromise between physiological relevance and ease-of-use and hold the future of NVU modeling: as simple as possible, as complex as needed.

Association of the Circulating Supar Levels with Inflammation, Fibrinolysis, and Outcome in Severe Burn Patients

BACKGROUND

Hyperfibrinolysis and pro/anti-inflammatory imbalance usually occur in the early stage of severe burns. Soluble urokinase-type plasminogen activator receptor (suPAR) is involved in fibrinolysis and inflammation. To date, the levels of circulating suPAR in non-survivors with severe burns remain unknown. This study aimed to investigate the early association between circulating suPAR levels and biomarkers of fibrinolysis, pro/anti-inflammatory, and prognosis.

METHODS

Sixty-four consecutive Chinese patients with severe burns and 26 healthy volunteers were enrolled in a prospective observational cohort. Clinical characteristics and laboratory data were collected prospectively. Blood samples were collected at 48 h post-burn, and suPAR and biomarkers of pro/anti-inflammatory and fibrinolysis were detected by enzyme-linked immunosorbent assays. Important indicators between non-survivors and survivors were compared. Linear regression analysis was performed to screen variables associated with suPAR. Logistic regression analysis and receiver operating characteristic curve (ROC) analysis were performed to evaluate the prognostic value of suPAR.

RESULT

Compared with the control group, the circulating suPAR levels in the survivors (P < 0.001) and non-survivors (P = 0.017) were higher. Compared with survivors, non-survivors had lower circulating suPAR levels at 48 h post-burn, and they showed a higher degree of fibrinolysis (higher D-dimer) and a lower TNF-α/IL-10 ratio. According to linear regression analysis, the variables independently associated with a lower suPAR level were lower platelet factor 4 (PF-4), urokinase-type plasminogen activator (uPA), and TNF-α/IL-10 levels and a higher D-dimer level. Logistic regression and ROC analyses indicated that a suPAR level ≤ 4.70 μg/L was independently associated with 30-day mortality.

CONCLUSION

Low circulating suPAR levels at 48 h post-burn in severe burn patients may reflect decreased TNF-α/IL-10 ratio and increased hyperfibrinolysis. suPAR can predict 30-day mortality in patients with severe burn.

Involvement of increased expression of chemokine C-C motif chemokine 22 (CCL22)/CC chemokine receptor 4 (CCR4) in the inflammatory injury and cartilage degradation of chondrocytes

CCL22, which could induce chondrocyte apoptosis, was identified to be overexpressed in damaged cartilage. This study was conducted with the aim of investigating the effects of CCL22 interference on chondrocyte injury. The osteoarthritis model was established by stimulating chondrocytes with LPS. The expressions of CCL22, CCR4, matrix metallopeptidase (MMP) 3, MMP9, MMP13, (a disintegrin and metalloproteinase with thrombospondin-like motifs) ADAMTS-4, collagen II and inflammatory cytokines were measured using quantitative reverse transcription PCR (RT-qPCR) and western blot. Besides, immunoprecipitation (IP) was employed to verify the binding of CCL22 and CCR4. After CCR4 was overexpressed, cell viability was observed using Cell Counting Kit-8 (CCK-8). Additionally, cell apoptosis as well as its related proteins was detected by TUNEL and western blot, respectively. ng What's more, glycosaminoglycan (GAG) level was detected using GAG kits. CCL22 and CCR4 expression increased noticeably in LPS-stimulated ATDC5 chondrocytes. CCL22 inhibition could suppress the expression of CCR4 in LPS-induced ATDC5 cells. Likewise, CCL22 inhibition could revive the activation of LPS-induced ATDC5 cells by regulating CCR4. In addition, CCL22 knockdown alleviated inflammatory response and cell apoptosis through CCR4. Furthermore, the cartilage degradation of ADTC5 cells could be relieved by CCL22 silence via regulating CCR4. CCL22/CCR4 expression was increased in osteoarthritic cartilage injury and participated in the inflammation and cartilage degradation of chondrocytes.

Macrophages in bovine term placenta: An ultrastructural and molecular study

Retention of foetal membranes (RFM) is a major reproductive disorder in dairy cows. An appropriate immune response is important for a physiological expulsion of the foetal membranes at parturition. Our study aims to provide a deeper insight into characteristics of foetal and maternal macrophages in bovine term placenta. We used transmission electron microscopy (TEM), immunohistochemistry and semi-quantitative RT-PCR to provide a deeper insight into characteristics of foetal and maternal macrophages in bovine term placenta. Semi-quantitative RT-PCR was used to define macrophage polarization in foetal and maternal compartments of normal term placenta. Gene expression of factors involved in M1 polarization [interferon regulatory factor-5 (IRF5), interleukin (IL)-12A, IL12B] and in M2 polarization (IL10) were studied. Ultrastructurally, foetal macrophages showed an irregular shape and large vacuoles, whereas the maternal macrophages were spindle shaped. By immunohistochemistry, macrophages were identified by a strong staining with the lysosomal marker Lysosome-associated membrane glycoprotein 1 (LAMP-1), while myofibroblast in the maternal stroma was positive for alpha-smooth muscle actin. We used the LAMP-1 marker to compare the density of foetal stromal macrophages in placentas of cows with RFM and in controls, but no statistically significant difference was observed. RT-PCR showed a higher expression of all studied genes in the maternal compartment of the placenta and generally a higher expression of M1-, compared to M2-associated genes. Our results indicated that at parturition placental macrophages predominantly show the pro-inflammatory M1 polarization. The higher expression of all the target genes in the maternal compartment may denote that maternal macrophages in bovine term placenta are more frequent than foetal macrophages.

Tumor-Derived Lactic Acid Contributes to the Paucity of Intratumoral ILC2s

Group 2 innate lymphoid cells (ILC2s) are abundant in non-lymphoid tissues and increase following infectious and inflammatory insults. In solid tumors, however, ILC2s constitute a relatively small proportion of immune cells. Here, we show, using melanoma as a model, that while the IL-33/IL C2/eosinophil axis suppresses tumor growth, tumor-derived lactate attenuates the function and survival of ILC2s. Melanomas with reduced lactate production (LDHA^low) are growth delayed and typified by an increased number of ILC2s compared with control tumors. Upon IL-33 stimulation, ILC2s accompanied by eosinophils more effectively restrain the growth of LDHA^low tumors than control melanomas. Furthermore, database analysis reveals a negative correlation between the expression of LDHA and markers associated with ILC2s and the association of high expression of IL33 and an eosinophil marker SIGLEC8 with better overall survival in human cutaneous melanoma patients. This work demonstrates that the balance between the IL-33/ILC2/eosinophil axis and lactate production by tumor cells regulates melanoma growth.

More Than Suppression: Glucocorticoid Action on Monocytes and Macrophages

Uncontrolled inflammation is a leading cause of many clinically relevant diseases. Current therapeutic strategies focus mainly on immunosuppression rather than on the mechanisms of inflammatory resolution. Glucocorticoids (GCs) are still the most widely used anti-inflammatory drugs. GCs affect most immune cells but there is growing evidence for cell type specific mechanisms. Different subtypes of monocytes and macrophages play a pivotal role both in generation as well as resolution of inflammation. Activation of these cells by microbial products or endogenous danger signals results in production of pro-inflammatory mediators and initiation of an inflammatory response. GCs efficiently inhibit these processes by down-regulating pro-inflammatory mediators from macrophages and monocytes. On the other hand, GCs act on “naïve” monocytes and macrophages and induce anti-inflammatory mediators and differentiation of anti-inflammatory phenotypes. GC-induced anti-inflammatory monocytes have an increased ability to migrate toward inflammatory stimuli. They remove endo- and exogenous danger signals by an increased phagocytic capacity, produce anti-inflammatory mediators and limit T-cell activation. Thus, GCs limit amplification of inflammation by repressing pro-inflammatory macrophage activation and additionally induce anti-inflammatory monocyte and macrophage populations actively promoting resolution of inflammation. Further investigation of these mechanisms should lead to the development of novel therapeutic strategies to modulate undesirable inflammation with fewer side effects via induction of inflammatory resolution rather than non-specific immunosuppression.

Thymoquinone Potently Enhances the Activities of Classically Activated Macrophages Pulsed with Necrotic Jurkat Cell Lysates and the Production of Antitumor Th1-/M1-Related Cytokines

Antitumor activity of classically activated macrophage (Mϕ) may be impaired within the tumors, spleen, and bone marrow. Thus, it is possible to boost its antitumor activity after its pulsing with necrotic tumor cell lysates combined with an adjuvant. We set out to determine the potential adjuvant effects of thymoquinone (TQ; 2-isopropyl-5-methyl-1,4-benzoquinone, C₁₀H₁₂O₂) on both functional activities of classically activated Mϕs, pulsed or not with necrotic Jurkat T cell line lysates (NecrJCL), and the balance of antitumor cytokines (ATCs) versus immunosuppressive cytokines (ISCs) during crosstalk with autologous human CD4⁺ T cells. We found that TQ treatment resulted in a significant upregulation of phagocytic activity, respiratory burst, the production of interleukin-2 (IL-2), IL-6, and IL-17 in NecrJCL-pulsed Mϕ co-culture system, and, conversely, in downregulation of the production of IL-6, IL-17, nitric oxide (NO), and arginase activity in nonpulsed TQ-treated Mϕs co-culture system. In addition, TQ has also shown low upregulation effect on the production of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and IL-1β, pathogen killing capacity and H₂O₂ in NecrJCL-pulsed Mϕs co-cultures. Moreover, TQ significantly downregulated arginase activity, and significantly upregulated inducible NO synthase (iNOS) activity-to-arginase activity ratio in NecrJCL-pulsed Mϕ co-cultures. Furthermore, TQ downregulated IL-10-to-IL-17 ratio and total cellular cholesterol content (_ttcCHOL), but upregulated the ratios of IL-1β-to-IL-4, IL-1β-to-IL-10, IFN-γ-to-IL-4, IFN-γ-to-IL-10, TNF-α-to-IL-4, TNF-α-to-IL-10, and combined proinflammatory cytokines (PICs)-to-anti-inflammatory cytokines (AICs) in NecrJCL-pulsed Mϕs co-culture system, whereas significant differences were highlighted only for IL-10-to-IL-17, IFN-γ-to-IL-10, and PICs-to-AICs ratios. Our outcomes demonstrated that TQ can act as potent adjuvant for enhancing both the functional activities of NecrJCL-pulsed Mϕ and the production of ATCs during their interplay with CD4⁺ T cells.

Multifaceted Roles for Macrophages in Prostate Cancer Skeletal Metastasis

Bone-metastatic prostate cancer is common in men with recurrent castrate-resistant disease. To date, therapeutic focus has largely revolved around androgen deprivation therapy (ADT) and chemotherapy. While second-generation ADTs and combination ADT/chemotherapy approaches have been successful in extending overall survival, the disease remains incurable. It is clear that molecular and cellular components of the cancer-bone microenvironment contribute to the disease progression and potentially to the emergence of therapy resistance. In bone, metastatic prostate cancer cells manipulate bone-forming osteoblasts and bone-resorbing osteoclasts to produce growth and survival factors. While osteoclast-targeted therapies such as bisphosphonates have improved quality of life, emerging data have defined important roles for additional cells of the bone microenvironment, including macrophages and T cells. Disappointingly, early clinical trials with checkpoint blockade inhibitors geared at promoting cytotoxic T cell response have not proved as promising for prostate cancer compared to other solid malignancies. Macrophages, including bone-resident osteomacs, are a major component of the bone marrow and play key roles in coordinating normal bone remodeling and injury repair. The role for anti-inflammatory macrophages in the progression of primary prostate cancer is well established yet relatively little is known about macrophages in the context of bone-metastatic prostate cancer. The focus of the current review is to summarize our knowledge of macrophage contribution to normal bone remodeling and prostate-to-bone metastasis, while also considering the impact of standard of care and targeted therapies on macrophage behavior in the tumor-bone microenvironment.

Extracellular Purine Metabolism Is the Switchboard of Immunosuppressive Macrophages and a Novel Target to Treat Diseases With Macrophage Imbalances

If misregulated, macrophage (Mϕ)-T cell interactions can drive chronic inflammation thereby causing diseases, such as rheumatoid arthritis (RA). We report that in a proinflammatory environment, granulocyte-Mϕ (GM-CSF)- and Mϕ colony-stimulating factor (M-CSF)-dependent Mϕs have dichotomous effects on T cell activity. While GM-CSF-dependent Mϕs show a highly stimulatory activity typical for M1 Mϕs, M-CSF-dependent Mϕs, marked by folate receptor β (FRβ), adopt an immunosuppressive M2 phenotype. We find the latter to be caused by the purinergic pathway that directs release of extracellular ATP and its conversion to immunosuppressive adenosine by co-expressed CD39 and CD73. Since we observed a misbalance between immunosuppressive and immunostimulatory Mϕs in human and murine arthritic joints, we devised a new strategy for RA treatment based on targeted delivery of a novel methotrexate (MTX) formulation to the immunosuppressive FRβ⁺CD39⁺CD73⁺ Mϕs, which boosts adenosine production and curtails the dominance of proinflammatory Mϕs. In contrast to untargeted MTX, this approach leads to potent alleviation of inflammation in the murine arthritis model. In conclusion, we define the Mϕ extracellular purine metabolism as a novel checkpoint in Mϕ cell fate decision-making and an attractive target to control pathological Mϕs in immune-mediated diseases.

New insights into the multidimensional concept of macrophage ontogeny, activation and function

Macrophages have protective roles in immunity to pathogens, tissue development, homeostasis and repair following damage. Maladaptive immunity and inflammation provoke changes in macrophage function that are causative of disease. Despite a historical wealth of knowledge about macrophages, recent advances have revealed unknown aspects of their development and function. Following development, macrophages are activated by diverse signals. Such tissue microenvironmental signals together with epigenetic changes influence macrophage development, activation and functional diversity, with consequences in disease and homeostasis. We discuss here how recent discoveries in these areas have led to a multidimensional concept of macrophage ontogeny, activation and function. In connection with this, we also discuss how technical advances facilitate a new roadmap for the isolation and analysis of macrophages at high resolution.

Macrophages: Regulators of the Inflammatory Microenvironment during Mammary Gland Development and Breast Cancer

Macrophages are critical mediators of inflammation and important regulators of developmental processes. As a key phagocytic cell type, macrophages evolved as part of the innate immune system to engulf and process cell debris and pathogens. Macrophages produce factors that act directly on their microenvironment and also bridge innate immune responses to the adaptive immune system. Resident macrophages are important for acting as sensors for tissue damage and maintaining tissue homeostasis. It is now well-established that macrophages are an integral component of the breast tumor microenvironment, where they contribute to tumor growth and progression, likely through many of the mechanisms that are utilized during normal wound healing responses. Because macrophages contribute to normal mammary gland development and breast cancer growth and progression, this review will discuss both resident mammary gland macrophages and tumor-associated macrophages with an emphasis on describing how macrophages interact with their surrounding environment during normal development and in the context of cancer.

Interaction studies reveal specific recognition of an anti-inflammatory polyphosphorhydrazone dendrimer by human monocytes

Dendrimers are nano-materials with perfectly defined structure and size, and multivalency properties that confer substantial advantages for biomedical applications. Previous work has shown that phosphorus-based polyphosphorhydrazone (PPH) dendrimers capped with azabisphosphonate (ABP) end groups have immuno-modulatory and anti-inflammatory properties leading to efficient therapeutic control of inflammatory diseases in animal models. These properties are mainly prompted through activation of monocytes. Here, we disclose new insights into the molecular mechanisms underlying the anti-inflammatory activation of human monocytes by ABP-capped PPH dendrimers. Following an interdisciplinary approach, we have characterized the physicochemical and biological behavior of the lead ABP dendrimer with model and cell membranes, and compared this experimental set of data to predictive computational modelling studies. The behavior of the ABP dendrimer was compared to the one of an isosteric analog dendrimer capped with twelve azabiscarboxylate (ABC) end groups instead of twelve ABP end groups. The ABC dendrimer displayed no biological activity on human monocytes, therefore it was considered as a negative control. In detail, we show that the ABP dendrimer can bind both non-specifically and specifically to the membrane of human monocytes. The specific binding leads to the internalization of the ABP dendrimer by human monocytes. On the contrary, the ABC dendrimer only interacts non-specifically with human monocytes and is not internalized. These data indicate that the bioactive ABP dendrimer is recognized by specific receptor(s) at the surface of human monocytes.

The current 'state of play' of regenerative medicine in horses: what the horse can tell the human

The horse is an attractive model for many human age-related degenerative diseases of the musculoskeletal system because it is a large animal species that both ages and exercises, and develops naturally occurring injuries with many similarities to the human counterpart. It therefore represents an ideal species to use as a 'proving ground' for new therapies, most notably regenerative medicine. Regenerative techniques using cell-based therapies for the treatment of equine musculoskeletal disease have been in use for over a decade. This review article provides a summary overview of the sources, current challenges and problems surrounding the use of stem cell and non-cell-based therapy in regenerative medicine in horses and is based on presentations from a recent Havemeyer symposium on equine regenerative medicine where speakers are selected from leading authorities in both equine and human regenerative medicine fields from 10 different countries.

Alternatively activated microglia and macrophages in the central nervous system

Macrophages are important players in the fight against viral, bacterial, fungal and parasitic infections. From a resting state they may undertake two activation pathways, the classical known as M1, or the alternative known as M2. M1 markers are mostly mediators of pro-inflammatory responses whereas M2 markers emerge for resolution and cleanup. Microglia exerts in the central nervous system (CNS) a function similar to that of macrophages in the periphery. Microglia activation and proliferation occurs in almost any single pathology affecting the CNS. Often microglia activation has been considered detrimental and drugs able to stop microglia activation were considered for the treatment of a variety of diseases. Cumulative evidence shows that microglia may undergo the alternative activation pathway, express M2-type markers and contribute to neuroprotection. This review focuses on details about the role of M2 microglia and in the approaches available for its identification. Approaches to drive the M2 phenotype and data on its potential in CNS diseases are also reviewed.

Innate immune regulation by STAT-mediated transcriptional mechanisms

The term innate immunity typically refers to a quick but non-specific host defense response against invading pathogens. The innate immune system comprises particular immune cell populations, epithelial barriers, and numerous secretory mediators including cytokines, chemokines, and defense peptides. Innate immune cells are also now recognized to play important contributing roles in cancer and pathological inflammatory conditions. Innate immunity relies on rapid signal transduction elicited upon pathogen recognition via pattern recognition receptors (PRRs) and cell:cell communication conducted by soluble mediators, including cytokines. A majority of cytokines involved in innate immune signaling use a molecular cascade encompassing receptor-associated Jak protein tyrosine kinases and STAT (signal transducer and activator of transcription) transcriptional regulators. Here, we focus on roles for STAT proteins in three major innate immune subsets: neutrophils, macrophages, and dendritic cells (DCs). While knowledge in this area is only now emerging, understanding the molecular regulation of these cell types is necessary for developing new approaches to treat human disorders such as inflammatory conditions, autoimmunity, and cancer.

Role for cFMS in maintaining alternative macrophage polarization in SIV infection: implications for HIV neuropathogenesis

BACKGROUND

Macrophage-colony stimulating factor (M-CSF) has been implicated in HIV neuropathogenesis through its ability to modulate activation of macrophages (MΦs) and microglia, as well as enhance the susceptibility of these cells to infection and promote virus production. We have recently reported that MΦs accumulating perivascularly and within nodular lesions in archival brain tissue of simian immunodeficiency virus (SIV)-infected rhesus macaques with encephalitis (SIVE) express M-CSF. In contrast, IL-34, which shares the same receptor, cFMS, was observed more often in parenchymal cells.

METHODS

Frontal white and grey matter from non-infected and SIV-infected rhesus macaques with and without SIVE were examined by single- and double-label immunohistochemistry for M-CSF, IL-34, and CD163 expression. Primary rhesus macaque and human peripheral blood mononuclear cells were cultured with and without 2.5 ng/ml M-CSF or IL-34 alone and with 470 nM or 4.7 μM of GW2580, a receptor tyrosine kinase inhibitor with high specificity for cFMS. After 24 h, cells were analyzed by flow cytometry to examine the effect of these cytokines on promoting an M2 monocyte/MΦ phenotype.

RESULTS

Here, we demonstrate that in SIVE brain, accumulating M-CSF(+) MΦs are also CD163(+), while IL-34 does not appear to co-localize significantly with CD163 in the parenchyma. We further demonstrate that M-CSF and IL-34 are expressed by neurons in normal brain but are altered in SIV and SIVE. Through in vitro studies, we show that M-CSF and IL-34 upregulate CD163, a marker for type 2 activation of MΦs (M2), by primary monocytes, which is attenuated by the addition of GW2580.

CONCLUSIONS

Together, these data suggest that both cFMS ligands may promote and/or prolong M2 activation of MΦs and microglia in brains of SIV-infected animals with encephalitis. As such, cFMS signaling may be an attractive target for eliminating long-lived MΦ reservoirs of HIV infection in brain, as well as other tissues.

Secreted proteins from the helminth Fasciola hepatica inhibit the initiation of autoreactive T cell responses and prevent diabetes in the NOD mouse

Infections with helminth parasites prevent/attenuate auto-inflammatory disease. Here we show that molecules secreted by a helminth parasite could prevent Type 1 Diabetes (T1D) in nonobese diabetic (NOD) mice. When delivered at 4 weeks of age (coincident with the initiation of autoimmunity), the excretory/secretory products of Fasciola hepatica (FhES) prevented the onset of T1D, with 84% of mice remaining normoglycaemic and insulitis-free at 30 weeks of age. Disease protection was associated with suppression of IFN-γ secretion from autoreactive T cells and a switch to the production of a regulatory isotype (from IgG2a to IgG1) of autoantibody. Following FhES injection, peritoneal macrophages converted to a regulatory M2 phenotype, characterised by increased expression levels of Ym1, Arg-1, TGFβ and PD-L1. Expression of these M2 genetic markers increased in the pancreatic lymph nodes and the pancreas of FhES-treated mice. In vitro, FhES-stimulated M2 macrophages induced the differentiation of Tregs from splenocytes isolated from naïve NOD mice. Collectively, our data shows that FhES contains immune-modulatory molecules that mediate protection from autoimmune diabetes via the induction and maintenance of a regulatory immune environment.

Endothelial outgrowth cells shift macrophage phenotype and improve kidney viability in swine renal artery stenosis

OBJECTIVE

Endothelial outgrowth cells (EOC) decrease inflammation and improve endothelial repair. Inflammation aggravates kidney injury in renal artery stenosis (RAS), and may account for its persistence upon revascularization. We hypothesized that EOC would decrease inflammatory (M1) macrophages and improve renal recovery in RAS.

APPROACH AND RESULTS

Pigs with 10 weeks of RAS were studied 4 weeks after percutaneous transluminal renal angioplasty (PTRA+stenting) or sham, with or without adjunct intrarenal delivery of autologous EOC (10×10(6)), and compared with similarly treated normal controls (n=7 each). Single-kidney function, microvascular and tissue remodeling, inflammation, oxidative stress, and fibrosis were evaluated. Four weeks after PTRA, EOC were engrafted in injected RAS-kidneys. Stenotic-kidney glomerular filtration rate was restored in RAS+EOC, RAS+PTRA, and RAS+PTRA+EOC pigs, whereas stenotic-kidney blood flow and angiogenesis were improved and fibrosis attenuated only in EOC-treated pigs. Furthermore, EOC increased cell proliferation and decreased the ratio of M1 (inflammatory)/M2 (reparative) macrophages, as well as circulating levels and stenotic-kidney release of inflammatory cytokines. Cultured-EOC released microvesicles in vitro and induced phenotypic switch (M1-to-M2) in cultured monocytes, which was inhibited by vascular endothelial growth factor blockade. Finally, a single intrarenal injection of rh-vascular endothelial growth factor (0.05 μg/kg) in 7 additional RAS pigs also restored M1/M2 ratio 4 weeks later.

CONCLUSIONS

Intrarenal infusion of EOC after PTRA induced a vascular endothelial growth factor-mediated attenuation in macrophages inflammatory phenotype, preserved microvascular architecture and function, and decreased inflammation and fibrosis in the stenotic kidney, suggesting a novel mechanism and therapeutic potential for adjunctive EOC delivery in experimental RAS to improve PTRA outcomes.

Emerging trends in the formation and function of tuberculosis granulomas

The granuloma is an elaborated aggregate of immune cells found in non-infectious as well as infectious diseases. It is a hallmark of tuberculosis (TB). Predominantly thought as a host-driven strategy to constrain the bacilli and prevent dissemination, recent discoveries indicate the granuloma can also be modulated into an efficient tool to promote microbial pathogenesis. The aim of future studies will certainly focus on better characterization of the mechanisms driving the modulation of the granuloma functions. Here, we provide unique perspectives from both the innate and adaptive immune system in the formation and the role of the TB granuloma. As macrophages (Mϕs) comprise the bulk of granulomas, we highlight the emerging concept of Mϕ polarization and its potential impact in the microbicide response, and other activities, that may ultimately shape the fate of granulomas. Alternatively, we shed light on the ability of B-cells to influence inflammatory status within the granuloma.

Comparative analysis of the interaction of Helicobacter pylori with human dendritic cells, macrophages, and monocytes

Helicobacter pylori may cause chronic gastritis, gastric cancer, or lymphoma. Myeloid antigen-presenting cells (APCs) are most likely involved in the induction and expression of the underlying inflammatory responses. To study the interaction of human APC subsets with H. pylori, we infected monocytes, monocyte-derived dendritic cells (DCs), and monocyte-derived (classically activated; M1) macrophages with H. pylori and analyzed phenotypic alterations, cytokine secretion, phagocytosis, and immunostimulation. Since we detected CD163(+) (alternatively activated; M2) macrophages in gastric biopsy specimens from H. pylori-positive patients, we also included monocyte-derived M2 macrophages in the study. Upon H. pylori infection, monocytes secreted interleukin-1β (IL-1β), IL-6, IL-10, and IL-12p40 (partially secreted as IL-23) but not IL-12p70. Infected DCs became activated, as shown by the enhanced expression of CD25, CD80, CD83, PDL-1, and CCR7, and secreted IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, and IL-23. However, infection led to significantly downregulated CD209 and suppressed the constitutive secretion of macrophage migration inhibitory factor (MIF). H. pylori-infected M1 macrophages upregulated CD14 and CD32, downregulated CD11b and HLA-DR, and secreted mainly IL-1β, IL-6, IL-10, IL-12p40, and IL-23. Activation of DCs and M1 macrophages correlated with increased capacity to induce T-cell proliferation and decreased phagocytosis of dextran. M2 macrophages upregulated CD14 and CD206 and secreted IL-10 but produced less of the proinflammatory cytokines than M1 macrophages. Thus, H. pylori affects the functions of human APC subsets differently, which may influence the course and the outcome of H. pylori infection. The suppression of MIF in DCs constitutes a novel immune evasion mechanism exploited by H. pylori.

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

Collective action of hematopoietic cell subsets mediates anti-IL10R1 and CpG tumor immunity

Based on the specificity of antigen recognition and the ability to generate long-lived memory responses, cancer immunotherapies primarily target tumor-associated T cells. Systemic administration of anti-IL-10R1 antibody in combination with local CpG administration has been shown to induce tumor regression in a T-cell-dependent manner. Here, we confirmed the anti-tumor efficacy of anti-IL-10R1 and CpG therapy in the highly aggressive B16F10 melanoma model. However, T cells were not required for tumor growth inhibition. Through cellular depletions and genetic models of leukocyte deficiency, we demonstrated that T, B, and NK cells, and neutrophils are not essential for anti-tumor efficacy. Nevertheless, hematopoietic cells as a whole are required for anti-IL-10R1- and CpG-induced tumor growth inhibition, suggesting that the collective action of multiple subsets of hematopoietic-derived cells is required for anti-tumor efficacy.

Diabetes-impaired wound healing and altered macrophage activation: a possible pathophysiologic correlation

Macrophages play a critical role in wound healing and can be activated to two distinctive phenotypes in vitro: classical macrophage activation (caM) and alternative macrophage activation (aaM). This study investigated whether the impaired cutaneous repair observed in streptozotocin-induced diabetic rats was associated with altered macrophage activation. Our results show that macrophage activation phenotypes could be observed in wound healing through double immunostaining. The caM macrophages appeared in the initial stage of wound healing, followed by aaM macrophages, which predominated in normal wounds. However, through examining markers associated with activation by immunoblotting and real-time polymerase chain reaction (PCR), diabetic wounds demonstrated insufficient caM in the early stage but excessive aaM in the later proliferative phase. Moreover, the macrophage activation markers were correlated with the instructive T helper cell type 1 (Th1)/Th2 cytokines in both groups. It was indicated that changed macrophage activation might contribute to impaired healing in diabetes wounds, and that strategies for reverting this abnormal activation could be useful for enhancing the wound healing process.

Toll-like receptor 3 ligand polyinosinic:polycytidylic acid promotes wound healing in human and murine skin

Toll-like receptors (TLRs) are pattern-recognition receptors and have a critical role in both innate and adaptive responses to tissue injury. Our previous study showed that wound healing was impaired in TLR3-deficient mice. In this study, we investigated the capacity of the TLR3 agonist polyriboinosinic-polyribocytidylic acid (poly(I:C)) to promote the healing of skin wounds in humans and mice. We found that topical application with poly(I:C) accelerated the closure of wounds in patients with laser plastic surgery. In a mouse model, topical application of poly(I:C) markedly enhanced re-epithelialization, granulation, and neovascularization required for wound closure. Further studies revealed that poly(I:C) treatment resulted in enhanced recruitment of neutrophils and macrophages in association with upregulation of a chemokine, macrophage inflammatory protein-2 (MIP-2/CXCL2), in the wounds. The effect of poly(I:C) was abolished in TLR3-deficient mice or by treatment with MIP-2/CXCL2-neutralizing antibodies. These results suggest a potential therapeutic value of the TLR3 activator poly(I:C) for wound healing.

Allergic airway disease is unaffected by the absence of IL-4Rα-dependent alternatively activated macrophages

BACKGROUND

Markers of alternatively activated macrophages (AAMs) are upregulated in the lungs of asthmatic patients and in mice with allergic airway disease. AAMs are thought to contribute to the pathogenesis of allergic airway disease by virtue of their decreased NO production and increased production of proline and polyamines, which are important in the synthesis of connective tissues such as collagen.

OBJECTIVE

We aimed to define the role of AAMs in the pathogenesis of allergic airway disease.

METHODS

The IL-4 receptor alpha (IL-4Rα) gene is genetically abrogated in macrophages in LysM(cre)IL-4Rα(-/lox) mice, which therefore have impaired IL-4/IL-13 activation of AAMs through IL-4R types 1 and 2. Responses of LysM(cre)IL-4Rα(-/lox) mice and IL-4Rα(-/lox) littermate controls were examined in ovalbumin- and house dust mite-induced allergic airway disease.

RESULTS

IL-4Rα expression was shown to be efficiently depleted from alveolar macrophages, interstitial macrophages, and CD11b(+)MHCII(+) inflammatory macrophages. Although the expression of markers of AAMs such as Ym-1, arginase and found in inflammatory zone 1 was decreased in macrophages of LysM(cre)IL-4Rα(-/lox) mice in chronic ovalbumin-induced allergic airway disease, airway hyperreactivity, T(H)2 responses, mucus hypersecretion, eosinophil infiltration, and collagen deposition were not significantly reduced. LysM(cre)IL-4Rα(-/lox) mice and littermate controls also developed similar responses in acute ovalbumin- and house dust mite-induced allergic airway disease.

CONCLUSION

Our results suggest that the presence of AAMs in allergic airway disease may be only an association, as a result of the increased T(H)2 responses present during disease, and that IL-4Rα-dependent AAMs do not play an important role in the pathology of disease.

Differential macrophage activation alters the expression profile of NTPDase and ecto-5'-nucleotidase

Macrophages are key elements in the inflammatory process, whereas depending on the micro-environmental stimulation they exhibit a pro-inflammatory (classical/M1) or an anti-inflammatory/reparatory (alternative/M2) phenotype. Extracellular ATP can act as a danger signal whereas adenosine generally serves as a negative feedback mechanism to limit inflammation. The local increase in nucleotides communication is controlled by ectonucleotidases, such as members of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family and ecto-5′-nucleotidase/CD73 (ecto-5′-NT). In the present work we evaluated the presence of these enzymes in resident mice M1 (macrophages stimulated with LPS), and M2 (macrophages stimulated with IL-4) macrophages. Macrophages were collected by a lavage of the mice (6–8 weeks) peritoneal cavity and treated for 24 h with IL-4 (10 ng/mL) or LPS (10 ng/mL). Nitrite concentrations were measured using the Greiss reaction. Supernatants were harvested to determine cytokines and the ATPase, ADPase and AMPase activities were determined by the malachite green method and HPLC analysis. The expression of selected surface proteins was evaluated by flow cytometry. The results reveal that M1 macrophages presented a decreased ATP and AMP hydrolysis in agreement with a decrease in NTPDase1, -3 and ecto-5′-nucleotidase expression compared to M2. In contrast, M2 macrophages showed a higher ATP and AMP hydrolysis and increased NTPDase1, -3 and ecto-5′-nucleotidase expression compared to M1 macrophages. Therefore, macrophages of the M1 phenotype lead to an accumulation of ATP while macrophages of the M2 phenotype may rapidly convert ATP to adenosine. The results also showed that P1 and P2 purinoreceptors present the same mRNA profile in both phenotypes. In addition, M2 macrophages, which have a higher ATPase activity, were less sensitive to cell death. In conclusion, these changes in ectoenzyme activities might allow macrophages to adjust the outcome of the extracellular purinergic cascade in order to fine-tune their functions during the inflammatory set.

[Molecular mechanisms regulating the activity of macrophages]

This article reviews modern concepts of the most common types of macrophage activation: classical, alternative, and type II. Molecular mechanisms of induction and regulation of these three types of activation are discussed. Any population of macrophages was shown to change its properties depending on its microenvironment and concrete biological situation (the "functional plasticity of macrophages"). Many intermediate states of macrophages were described along with the most pronounced and well-known activation types (classical activation, alternative activation, and type II activation). These intermediate states are characterized by a variety of combinations of their biological properties, including elements of the three afore mentioned types of activation. Macrophage activity is regulated by a complex network of interrelated cascade mechanisms.

Systematic validation of specific phenotypic markers for in vitro polarized human macrophages

BACKGROUND

Polarization of macrophages by specific micro-environmental conditions impacts upon their function following subsequent activation. This study aimed to systematically validate robust phenotypic markers for in vitro polarized human macrophages in order to facilitate the study of macrophage subsets in vivo.

METHODS

Human peripheral blood monocytes were polarized in vitro with IFN-γ, IL-4, or IL-10. Similar experiments were performed with TNF, IL-13, dexamethasone, M-CSF and GM-CSF as polarizing stimuli. Phenotypic markers were assessed by flow cytometry and qPCR.

RESULTS

IFN-γ polarized macrophages (MΦ(IFN-γ)) specifically enhanced membrane expression of CD80 and CD64, IL-4 polarized macrophages (MΦ(IL-4)) mainly upregulated CD200R and CD206, and downregulated CD14 levels, and IL-10 polarized macrophages (MΦ(IL-10)) selectively induced CD163, CD16, and CD32. The expression profiles of the most specific markers were confirmed by qPCR, dose-response experiments, and the use of alternative polarizing factors for each macrophage subset (TNF, IL-13, and dexamethasone, respectively). GM-CSF polarized macrophages (MΦ(GM-CSF)) upregulated CD80 but not CD64 expression, showing a partial phenotypic similarity with MΦ(IFN-γ), and also upregulated the expression of the alternative activation marker CD206. M-CSF polarized macrophages (MΦ(M-CSF)) not only expressed increased levels of CD163 and CD16, resembling MΦ(IL-10,) but also displayed high levels of CD64. The phenotype of MΦ(M-CSF) could be further modulated by additional polarization with IFN-γ, IL-4, or IL-10, whereas MΦ(GM-CSF) showed less phenotypic plasticity.

CONCLUSION

This study validated CD80 as the most robust phenotypic marker for human MΦ(IFN-γ), whereas CD200R was upregulated and CD14 was specifically downregulated on MΦ(IL-4). CD163 and CD16 were found to be specific markers for MΦ(IL-10). The GM-CSF/M-CSF differentiation model showed only a partial phenotypic similarity with the IFN-γ/IL-4/IL-10 induced polarization.

Induction of an anti-inflammatory human monocyte subtype is a unique property of glucocorticoids, but can be modified by IL-6 and IL-10

Glucocorticoids (GC) are the most widely used immunosuppressive agents in clinical medicine. Recently we showed that GC enhance survival of human monocytes and induce a specific anti-inflammatory monocyte subtype which actively induces resolution of inflammation. We now investigated if cytokines IL-4, IL-6 and IL-10, which, like GC, have mostly anti-inflammatory effects on macrophages, would have GC-like effects also on monocytes. Human monocytes were stimulated with either cytokine, GC or combination thereof, and resulting effects on apoptosis, adherence, migration, phagocytosis, ROS production and cell surface phenotype were determined. We found that IL-4, IL-6, and IL-10 had either less or different effects on various anti-inflammatory functions of monocytes compared to GC. As such, IL-4 and IL-6 alone did not delay apoptosis while IL-10 even enhanced it. However, IL-6 or IL-10 increased GC-mediated protection from apoptosis when applied together with GC. Thus, the potential of GC to induce anti-inflammatory human monocytes is unique and not mimicked by the investigated cytokines. However, IL-6 and IL-10 amplify GC-induced anti-inflammatory and pro-resolution mechanisms by enhancing survival of GC-induced monocytes and thus sustaining their function. This combined effect of GC and cytokines could be important for the physiological switch from amplification towards resolution phase of inflammation.

Macrophages at the fetal-maternal interface express markers of alternative activation and are induced by M-CSF and IL-10

During pregnancy, the maternal immune system is challenged by the presence of the fetus, which must be tolerated despite being semiallogeneic. Uterine mucosal (or decidual) macrophages (M), one of the major leukocyte populations at the fetal-maternal interface, have been implicated in fetal tolerance, but information regarding their regulation is scarce. In this study, we investigated the role of several factors potentially involved in the differentiation and polarization of decidual M with an in vitro M differentiation model. By using flow cytometry, we showed that M-CSF and IL-10 were potent inducers of M2 (immunoregulatory) M markers expressed on human decidual M (CD14, CD163, CD206, CD209). In contrast, proinflammatory stimuli, and unexpectedly also the Th2-associated IL-4 and IL-13, induced different patterns of expression, indicating that a Th2-dominated environment is not required for decidual M polarization. M-CSF/IL-10-stimulated and decidual M also showed similar cytokine secretion patterns, with production of IL-10 as well as IL-6, TNF, and CCL4. Conversely, the proinflammatory, LPS/IFN-γ-stimulated M produced significantly higher levels of TNF and no IL-10. We also used a gene array with 420 M-related genes, of which 100 were previously reported to be regulated in a global gene expression profiling of decidual M, confirming that M-CSF/IL-10-induced M are closely related to decidual M. Taken together, our results consistently point to a central role for M-CSF and in particular IL-10 in the shaping of decidual M with regulatory properties. These cytokines may therefore play an important role in supporting the homeostatic and tolerant immune milieu required for a successful pregnancy.

Umbilical cord-derived mesenchymal stromal cells modulate monocyte function to suppress T cell proliferation

Mesenchymal stromal cells (MSCs) may be derived from a variety of tissues, with human umbilical cord (UC) providing an abundant and noninvasive source. Human UC-MSCs share similar in vitro immunosuppressive properties as MSCs obtained from bone marrow and cord blood. However, the mechanisms and cellular interactions used by MSCs to control immune responses remain to be fully elucidated. In this paper, we report that suppression of mitogen-induced T cell proliferation by human UC-, bone marrow-, and cord blood-MSCs required monocytes. Removal of monocytes but not B cells from human adult PBMCs (PBMNCs) reduced the immunosuppressive effects of MSCs on T cell proliferation. There was rapid modulation of a number of cell surface molecules on monocytes when PBMCs or alloantigen-activated PBMNCs were cultured with UC-MSCs. Indomethacin treatment significantly inhibited the ability of UC-MSCs to suppress T cell proliferation, indicating an important role for PGE(2). Monocytes purified from UC-MSC coculture had significantly reduced accessory cell and allostimulatory function when tested in subsequent T cell proliferation assays, an effect mediated in part by UC-MSC PGE(2) production and enhanced by PBMNC alloactivation. Therefore, we identify monocytes as an essential intermediary through which UC-MSCs mediate their suppressive effects on T cell proliferation.

Histiocytic sarcoma with two immunohistopathologically distinct populations

This report is a case of histiocytic sarcoma (HS), in which tumor cells consist of two immunohistopathologically distinct populations (A) oval CD68+lysozyme+CD163- cells and (B) abundant cytoplasm or spindle-shaped CD68+lysozyme-CD163+ cells. Cervical lymph node was infiltrated mainly by population (A), where chemotherapy was quite effective. On the other hand, vast majority of infiltrated tumor cells in the hilar lymph node belonged to population (B), in which the cells were resistant to chemo-radiotherapy. Considering the poor prognosis of HS, the expression of CD163 could be a marker for resistance to chemo-radiotherapy. It is also notable that CD163-negative stage of HS may exist and still be reactive for the treatment.

Macrophages: master regulators of inflammation and fibrosis

Macrophages are found in close proximity with collagen-producing myofibroblasts and indisputably play a key role in fibrosis. They produce profibrotic mediators that directly activate fibroblasts, including transforming growth factor-beta1 and platelet-derived growth factor, and control extracellular matrix turnover by regulating the balance of various matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases. Macrophages also regulate fibrogenesis by secreting chemokines that recruit fibroblasts and other inflammatory cells. With their potential to act in both a pro- and antifibrotic capacity, as well as their ability to regulate the activation of resident and recruited myofibroblasts, macrophages and the factors they express are integrated into all stages of the fibrotic process. These various, and sometimes opposing, functions may be performed by distinct macrophage subpopulations, the identification of which is a growing focus of fibrosis research. Although collagen-secreting myofibroblasts once were thought of as the master "producers" of fibrosis, this review will illustrate how macrophages function as the master "regulators" of fibrosis.

Recurrent respiratory papillomatosis: a complex defect in immune responsiveness to human papillomavirus-6 and -11

Recurrent respiratory papillomatosis (RRP) is a rare disease of the larynx caused by infection with human papillomaviruses (HPV) -6 or -11, associated with significant morbidity and on occasion mortality. Here we summarize our current understanding of the permissive adaptive and innate responses made by patients with RRP that support chronic HPV infection and prevent immune clearance of these viruses. Furthermore, we provide new evidence of T(H)2-like polarization in papillomas and blood of patients with RRP, restricted CD4 and CD8 Vbeta repertoires, the effect of HPV-11 early protein E6 on T-cell alloreactivity, enriched Langerhans cell presence in papillomas, and evidence that natural killer cells are dysfunctional in RRP. We review the immunogenetic mechanisms that regulate the dysfunctional responses made by patients with RRP in response to HPV infection of the upper airway. In addition, we are identifying T-cell epitopes on HPV-11 early proteins, in the context of human leukocyte antigen (HLA) class II alleles enriched in RRP that should help generate a therapeutic vaccine. Taken together, RRP is a complex, multigene disease manifesting as a tissue and HPV-specific, immune deficiency that prevents effective clearance and/or control of HPV-6 and -11 infection.

Notch signaling determines the M1 versus M2 polarization of macrophages in antitumor immune responses

Macrophages are important tumor-infiltrating cells and play pivotal roles in tumor growth and metastasis. Macrophages participate in immune responses to tumors in a polarized manner: classic M1 macrophages produce interleukin (IL) 12 to promote tumoricidal responses, whereas M2 macrophages produce IL10 and help tumor progression. The mechanisms governing macrophage polarization are unclear. Here, we show that the M2-like tumor-associated macrophages (TAM) have a lower level of Notch pathway activation in mouse tumor models. Forced activation of Notch signaling increased M1 macrophages which produce IL12, no matter whether M1 or M2 inducers were applied. When Notch signaling was blocked, the M1 inducers induced M2 response in the expense of M1. Macrophages deficient in canonical Notch signaling showed TAM phenotypes. Forced activation of Notch signaling in macrophages enhanced their antitumor capacity. We further show that RBP-J-mediated Notch signaling regulates the M1 versus M2 polarization through SOCS3. Therefore, Notch signaling plays critical roles in the determination of M1 versus M2 polarization of macrophages, and compromised Notch pathway activation will lead to the M2-like TAMs. These results provide new insights into the molecular mechanisms of macrophage polarization and shed light on new therapies for cancers through the modulation of macrophage polarization through the Notch signaling.

Impaired immune functions of monocytes and macrophages in Whipple's disease

BACKGROUND & AIMS

Whipple's disease is a chronic multisystemic infection caused by Tropheryma whipplei. Host factors likely predispose for the establishment of an infection, and macrophages seem to be involved in the pathogenesis of Whipple's disease. However, macrophage activation in Whipple's disease has not been studied systematically so far.

METHODS

Samples from 145 Whipple's disease patients and 166 control subjects were investigated. We characterized duodenal macrophages and lymphocytes immunohistochemically and peripheral monocytes by flow cytometry and quantified mucosal and systemic cytokines and chemokines indicative for macrophage activation. In addition, we determined duodenal nitrite production and oxidative burst induced by T whipplei and by other bacteria.

RESULTS

Reduced numbers of duodenal lymphocytes, increased numbers of CD163(+) and stabilin-1(+), reduced numbers of inducible nitric synthase+ duodenal macrophages, and increased percentages of CD163(+) peripheral monocytes indicated a lack of inflammation and a M2/alternatively activated macrophage phenotype in Whipple's disease. Incubation with T whipplei in vitro enhanced the expression of CD163 on monocytes from Whipple's disease patients but not from control subjects. Chemokines and cytokines associated with M2/alternative macrophage activation were elevated in the duodenum and the peripheral blood from Whipple's disease patients. Functionally, Whipple's disease patients showed a reduced duodenal nitrite production and reduced oxidative burst upon incubation with T whipplei compared with healthy subjects.

CONCLUSIONS

The lack of excessive local inflammation and alternative activation of macrophages, triggered in part by the agent T whipplei itself, may explain the hallmark of Whipple's disease: invasion of the intestinal mucosa with macrophages incompetent to degrade T whipplei.

Modeling the immune rheostat of macrophages in the lung in response to infection

In the lung, alternatively activated macrophages (AAM) form the first line of defense against microbial infection. Due to the highly regulated nature of AAM, the lung can be considered as an immunosuppressive organ for respiratory pathogens. However, as infection progresses in the lung, another population of macrophages, known as classically activated macrophages (CAM) enters; these cells are typically activated by IFN-gamma. CAM are far more effective than AAM in clearing the microbial load, producing proinflammatory cytokines and antimicrobial defense mechanisms necessary to mount an adequate immune response. Here, we are concerned with determining the first time when the population of CAM becomes more dominant than the population of AAM. This proposed "switching time" is explored in the context of Mycobacterium tuberculosis (MTb) infection. We have developed a mathematical model that describes the interactions among cells, bacteria, and cytokines involved in the activation of both AAM and CAM. The model, based on a system of differential equations, represents a useful tool to analyze strategies for reducing the switching time, and to generate hypotheses for experimental testing.

Immune regulation by non-lymphoid cells in transplantation

Regulatory cells play a crucial role in the induction and maintenance of tolerance by controlling T cell as well as B and natural killer (NK) cell-mediated immunity. In transplantation, CD4+CD25+forkhead box P3+ T regulatory cells are instrumental in the maintenance of immunological tolerance, as are several other T cell subsets such as NK T cells, double negative CD3+ T cells, gammadelta T cells, interleukin-10-producing regulatory type 1 cells, transforming growth factor-beta-producing T helper type 3 cells and CD8+CD28(-) cells. However, not only T cells have immunosuppressive properties, as it is becoming increasingly clear that both T and non-T regulatory cells co-operate and form a network of cellular interactions controlling immune responses. Non-T regulatory cells include tolerogenic dendritic cells, plasmacytoid dendritic cells, mesenchymal stem cells, different types of stem cells, various types of alternatively activated macrophages and myeloid-derived suppressor cells. Here, we review the mechanism of action of these non-lymphoid regulatory cells as they relate to the induction or maintenance of tolerance in organ transplantation.

Pathologic correlates of primary central nervous system lymphoma defined in an orthotopic xenograft model

PURPOSE

The prospect for advances in the treatment of patients with primary central nervous system lymphoma (PCNSL) is likely dependent on the systematic evaluation of its pathobiology. Animal models of PCNSL are needed to facilitate the analysis of its molecular pathogenesis and for the efficient evaluation of novel therapeutics.

EXPERIMENTAL DESIGN

We characterized the molecular pathology of CNS lymphoma tumors generated by the intracerebral implantation of Raji B lymphoma cells in athymic mice. Lymphoma cells were modified for bioluminescence imaging to facilitate monitoring of tumor growth and response to therapy. In parallel, we identified molecular features of lymphoma xenograft histopathology that are evident in human PCNSL specimens.

RESULTS

Intracerebral Raji tumors were determined to faithfully reflect the molecular pathogenesis of PCNSL, including the predominant immunophenotypic state of differentiation of lymphoma cells and their reactive microenvironment. We show the expression of interleukin-4 by Raji and other B lymphoma cell lines in vitro and by Raji tumors in vivo and provide evidence for a role of this cytokine in the M2 polarization of lymphoma macrophages both in the murine model and in diagnostic specimens of human PCNSL.

CONCLUSION

Intracerebral implantation of Raji cells results in a reproducible and invasive xenograft model, which recapitulates the histopathology and molecular features of PCNSL, and is suitable for preclinical testing of novel agents. We also show for the first time the feasibility and accuracy of tumor bioluminescence in the monitoring of a highly infiltrative brain tumor.

Alternative activation of macrophages: immune function and cellular biology

Macrophages are the first line of defense of the organism against pathogens and, in response to the microenvironment, become differentially activated. In the presence of IL-4 and IL-13, cytokines that are produced in a Th-2 type response, particularly during allergy and parasitic infections, macrophages become differentially activated. Alternative activated macrophages play an important role in the protection of the host by decreasing inflammation and promoting tissues repair. However, alternative activation of macrophages also downregulates host protection against selected pathogens. This defect is associated with an altered receptor expression pattern and extensive modulation of intracellular membrane trafficking. This review shows how alternative activation of macrophages induces extensive cellular remodelling of phagocytic, endocytic, signaling and secretory pathways which play an important, but unclear role in the pathogenesis of different disease.

Ca2+/calmodulin-dependent kinase kinase alpha is expressed by monocytic cells and regulates the activation profile

Macrophages are capable of assuming numerous phenotypes in order to adapt to endogenous and exogenous challenges but many of the factors that regulate this process are still unknown. We report that Ca²⁺/calmodulin-dependent kinase kinase α (CaMKKα) is expressed in human monocytic cells and demonstrate that its inhibition blocks type-II monocytic cell activation and promotes classical activation. Affinity chromatography with paramagnetic beads isolated an approximately 50 kDa protein from nuclear lysates of U937 human monocytic cells activated with phorbol-12-myristate-13-acetate (PMA). This protein was identified as CaMKKα by mass spectrometry and Western analysis. The function of CaMKKα in monocyte activation was examined using the CaMKKα inhibitors (STO-609 and forskolin) and siRNA knockdown. Inhibition of CaMKKα, enhanced PMA-dependent CD86 expression and reduced CD11b expression. In addition, inhibition was associated with decreased translocation of CaMKKα to the nucleus. Finally, to further examine monocyte activation profiles, TNFα and IL-10 secretion were studied. CaMKKα inhibition attenuated PMA-dependent IL-10 production and enhanced TNFα production indicating a shift from type-II to classical monocyte activation. Taken together, these findings indicate an important new role for CaMKKα in the differentiation of monocytic cells.

Long-term interleukin-10 presence induces the development of a novel, monocyte-derived cell type

Interleukin (IL)-10 is one of the most crucial immunoregulatory cytokines. Its short-term effects have been analysed extensively, but little is known about its long-term effects. This is of considerable importance, as high systemic IL-10 levels are present for long periods in patients with persistent viral infections, certain cancers and in critical care patients. Our study investigated the effects of the long-term presence of IL-10 on human peripheral blood monocytes. In vitro, IL-10 treatment of these cells for 7 days induced the development of a novel cell type characterized by unique phenotypical and functional characteristics. These cells showed high HLA-DR expression and low expression of CD86 and other co-stimulatory molecules on their surface. The mRNA levels of both HLA-DR and CD86 were high, but no intracellular accumulation of CD86 protein was observed. With respect to its function, these cells showed strongly diminished tumour necrosis factor-alpha production following lipopolysaccharide stimulation, strongly diminished allogenic CD4(+) T cell stimulatory capacity, and even induced a hyporesponsive state in CD4(+) T cells. The phenotype remained stable despite the removal of IL-10. In vivo, we found monocytic cells from patients exhibiting this phenotype after long-term IL-10 exposure. These results complement our knowledge further about the biological effects of IL-10 and may provide an explanation for the sustained immunodeficiency in cases of the persistent presence of systemic IL-10.

Neurotrophins modulate monocyte chemotaxis without affecting macrophage function

Neurotrophins nerve growth factor (NGF), brain-derived growth factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) and their high-affinity tyrosine protein kinase receptor (Trk) family, TrkA, TrkB, TrkC, and low-affinity p75(NTR) receptor, are key molecules implicated in the development of the central nervous system. Increasing evidence suggests that they also have physiological and pathological roles outside the nervous system. In this study we examined the expression of neurotrophins and their receptors in human activated macrophages and to what extent neurotrophins themselves modulate macrophage activation, in a model of primary adult monocyte-derived macrophage. Our data indicate that macrophages express neurotrophin and neurotrophin receptor genes differentially, and respond to cell stimulation by specific inductions. Neurotrophins did not modify the antigen-presenting capacities of macrophages or their production of proinflammatory cytokines, but somehow skewed their activation phenotype. In contrast, NGF clearly increased CXCR-4 expression in macrophage and their chemotactic response to low CXCL-12 concentration. The differential effect of specific macrophage stimuli on neurotrophin expression, in particular NGF and NT-3, and the specific enhancement of CXCR-4 expression suggest that neurotrophins might participate in tissue-healing mechanisms that should be investigated further in vivo.