Metabolic Alterations in Aging Macrophages: Ingredients for Inflammaging?

Aging is a complex process with an impact on essentially all organs. Declined cellular repair causes increased damage at genomic and proteomic levels upon aging. This can lead to systemic changes in metabolism and pro-inflammatory cytokine production, resulting in low-grade inflammation, or 'inflammaging'. Tissue macrophages, gatekeepers of parenchymal homeostasis and integrity, are prime inflammatory cytokine producers, as well as initiators and regulators of inflammation. In this opinion piece, we summarize intrinsic alterations in macrophage phenotype and function with age. We propose that alternatively activated macrophages (M2-like), which are yet pro-inflammatory, can accumulate in tissues and promote inflammaging. Age-related increases in endoplasmic reticulum stress and mitochondrial dysfunction might be cell-intrinsic forces driving this unusual phenotype.

Systemic Listeria monocytogenes infection in aged mice induces long-term neuroinflammation: the role of miR-155.

BACKGROUND: Understanding mechanisms of pathologic neuroinflammation is essential for improving outcomes after central nervous system infections. Brain tissue-resident memory T cells (bTRM) are recruited during central nervous system infection and promote pathogen control as well as noxious inflammation. Our prior studies in young mice showed optimal recruitment of CD8+ bTRM during neuroinvasive Listeria monocytogenes (Lm) infection required miR-155, and was significantly inhibited by anti-miR-155 oligonucleotides. Since Lm is an important pathogen in the elderly, we hypothesized anti-miR-155 would also inhibit accumulation of CD8+ bTRM in aged mice infected with Lm. METHODS: Young (2 mo) and aged (> 18 mo) male C57BL/6 mice were infected intra-peritoneally with wild-type Lm, or avirulent Lm mutants lacking the genes required for intracellular motility (ΔactA) or phagosomal escape (Δhly), then were given antibiotics. Brain leukocytes and their intracellular cytokine production were quantified by flow cytometry >28d post-infection (p.i.). The role of miR-155 was tested by injecting mice with anti-miR-155 or control oligonucleotides along with antibiotics. RESULTS: Aged mice had significantly more homeostatic CD8+ bTRM than did young mice, which did not increase after infection with wild-type Lm despite 50% mortality, whereas young mice suffered no mortality after a larger inoculum. For direct comparison of post-infectious neuroinflammation after the same inoculum, young and aged mice were infected with 107 CFU ΔactA Lm. This mutant caused no mortality and significantly increased CD8+ bTRM 28d p.i. in both groups, whereas bone marrow-derived myeloid cells, particularly neutrophils, increased only in aged mice. Notably, anti-miR-155 reduced accumulation of brain myeloid cells in aged mice after infection, whereas CD8+ bTRM were unaffected. CONCLUSIONS: Systemic infection with Lm ΔactA is a novel model for studying infection-induced brain inflammation in aged mice without excessive mortality. CD8+ bTRM increase in both young and aged mice after infection, whereas only in aged mice bone marrow-derived myeloid cells increase long-term. In aged mice, anti-miR-155 inhibits brain accumulation of myeloid cells, but not CD8+ bTRM. These results suggest young and aged mice differ in manifestations and mechanisms of infection-induced neuroinflammation and give insight for developing therapies to ameliorate brain inflammation following severe infection in the elderly.

Immunotherapy Added to Antibiotic Treatment Reduces Relapse of Disease in a Mouse Model of Tuberculosis.

Immune-modulating drugs that target myeloid-derived suppressor cells or stimulate natural killer T cells have been shown to reduce mycobacterial loads in tuberculosis (TB). We aimed to determine if a combination of these drugs as adjunct immunotherapy to conventional antibiotic treatment could also increase therapeutic efficacy against TB. In our model of pulmonary TB in mice, we applied treatment with isoniazid, rifampicin, and pyrazinamide for 13 weeks alone or combined with immunotherapy consisting of all-trans retinoic acid, 1,25(OH)2-vitamin D3, and α-galactosylceramide. Outcome parameters were mycobacterial load during treatment (therapeutic activity) and 13 weeks after termination of treatment (therapeutic efficacy). Moreover, cellular changes were analyzed using flow cytometry and cytokine expression was assessed at the mRNA and protein levels. Addition of immunotherapy was associated with lower mycobacterial loads after 5 weeks of treatment and significantly reduced relapse of disease after a shortened 13-week treatment course compared with antibiotic treatment alone. This was accompanied by reduced accumulation of immature myeloid cells in the lungs at the end of treatment and increased TNF-α protein levels throughout the treatment period. We demonstrate, in a mouse model of pulmonary TB, that immunotherapy consisting of three clinically approved drugs can improve the therapeutic efficacy of standard antibiotic treatment.

Pharmacodynamic Monitoring of Tacrolimus-Based Immunosuppression in CD14+ Monocytes After Kidney Transplantation.

BACKGROUND: Monocytes significantly contribute to ischemia-reperfusion injury and allograft rejection after kidney transplantation. However, the knowledge about the effects of immunosuppressive drugs on monocyte activation is limited. Conventional pharmacokinetic methods for immunosuppressive drug monitoring are not cell type-specific. In this study, phosphorylation of 3 signaling proteins was measured to determine the pharmacodynamic effects of immunosuppression on monocyte activation in kidney transplant patients. METHODS: Blood samples from 20 kidney transplant recipients were monitored before and during the first year after transplantation. All patients received induction therapy with basiliximab, followed by tacrolimus (TAC), mycophenolate mofetil, and prednisolone maintenance therapy. TAC whole-blood predose concentrations were determined using an antibody-conjugated magnetic immunoassay. Samples were stimulated with phorbol 12-myristate 13-acetate (PMA)/ionomycin, and phosphorylation of p38MAPK, ERK, and Akt in CD14 monocytes was quantified by phospho-specific flow cytometry. RESULTS: Phosphorylation of p38MAPK and Akt in monocytes of immunosuppressed recipients was lower after 360 days compared with before transplantation in the unstimulated samples [mean reduction in median fluorescence intensity 36%; range -28% to 77% for p-p38MAPK and 20%; range -22% to 53% for p-Akt; P < 0.05]. P-ERK was only decreased at day 4 after transplantation (mean inhibition 23%; range -52% to 73%; P < 0.05). At day 4, when the highest whole-blood predose TAC concentrations were measured, p-p38MAPK and p-Akt, but not p-ERK, correlated inversely with TAC (rs = -0.65; P = 0.01 and rs = -0.58; P = 0.03, respectively). CONCLUSIONS: Immunosuppressive drug combination therapy partially inhibits monocyte activation pathways after kidney transplantation. This inhibition can be determined by phospho-specific flow cytometry, which enables the assessment of the pharmacodynamic effects of immunosuppressive drugs in a cell type-specific manner.

Langerhans cell histiocytosis is a neoplasm and consequently its recurrence is a relapse: In memory of Bob Arceci.

Langerhans cell histiocytosis (LCH) remains a poorly understood disorder with heterogeneous clinical presentations characterized by focal or disseminated lesions that contain excessive CD1a+ langerin+ cells with dendritic cell features known as "LCH cells." Two of the major questions investigated over the past century have been (i) the origin of LCH cells and (ii) whether LCH is primarily an immune dysregulatory disorder or a neoplasm. Current opinion is that LCH cells are likely to arise from hematopoietic precursor cells, although the stage of derailment and site of transformation remain unclear and may vary in patients with different extent of disease. Over the years, evidence has provided the view that LCH is a neoplasm. The demonstration of clonality of LCH cells, insufficient evidence alone for neoplasia, is now bolstered by finding driver somatic mutations in BRAF in up to 55% of patients with LCH, and activation of the RAS-RAF-MEK-ERK (where MEK and ERK are mitogen-activated protein kinase and extracellular signal-regulated kinase, respectively) pathway in nearly 100% of patients with LCH. Herein, we review the evidence that recurrent genetic abnormalities characterized by activating oncogenic mutations should satisfy prerequisites for LCH to be called a neoplasm. As a consequence, recurrent episodes of LCH should be considered relapsed disease rather than disease reactivation. Mapping the complete genetic landscape of this intriguing disease will provide additional support for the conclusion that LCH is a neoplasm and is likely to provide more potential opportunities for molecularly targeted therapies.

Immune suppression via glucocorticoid-stimulated monocytes: a novel mechanism to cope with inflammation.

Glucocorticoids (GCs) are used as first-line therapies for generalized suppression of inflammation (e.g., allergies or autoimmune diseases), but their long-term use is limited by severe side effects. Our previous work revealed that GCs induced a stable anti-inflammatory phenotype in monocytes, the GC-stimulated monocytes (GCsMs) that we exploited for targeted GC-mediated therapeutic effects. We demonstrate that GCsMs interact with T cells in suppressing proliferation, as well as cytokine release of CD8(+) and, especially, CD4(+) T cells in vitro, and that they support generation of Foxp3(+) cells. Therefore, we tested their immunosuppressive potential in CD4(+) T cell-induced colitis in vivo. We found that injection of GCsMs into mice with severe colitis abolished the inflammation and resulted in significant clinical improvement within a few days. T cells recovered from GCsM-treated mice exhibited reduced secretion of proinflammatory cytokines IFN-γ and IL-17. Furthermore, clusters of Foxp3(+) CD4(+) T cells were detectable at local sites of inflammation in the colon. Thus, GCsMs are able to modify T cell responses in vitro and in vivo, as well as to downregulate and clinically cure severe T cell-mediated colitis.

M-CSF priming of osteoclast precursors can cause osteoclastogenesis-insensitivity, which can be prevented and overcome on bone.

Osteoclasts and macrophages share progenitors that must receive decisive lineage signals driving them into their respective differentiation routes. Macrophage colony stimulation factor M-CSF is a common factor; bone is likely the stimulus for osteoclast differentiation. To elucidate the effect of both, shared mouse bone marrow precursor myeloid blast was pre-cultured with M-CSF on plastic and on bone. M-CSF priming prior to stimulation with M-CSF and osteoclast differentiation factor RANKL resulted in a complete loss of osteoclastogenic potential without bone. Such M-CSF primed cells expressed the receptor RANK, but lacked the crucial osteoclastogenic transcription factor NFATc1. This coincided with a steeply decreased expression of osteoclast genes TRACP and DC-STAMP, but an increased expression of the macrophage markers F4/80 and CD11b. Compellingly, M-CSF priming on bone accelerated the osteoclastogenic potential: M-CSF primed cells that had received only one day M-CSF and RANKL and were grown on bone already expressed an array of genes that are associated with osteoclast differentiation and these cells differentiated into osteoclasts within 2 days. Osteoclastogenesis-insensitive precursors grown in the absence of bone regained their osteoclastogenic potential when transferred to bone. This implies that adhesion to bone dictates the fate of osteoclast precursors. Common macrophage-osteoclast precursors may become insensitive to differentiate into osteoclasts and regain osteoclastogenesis when bound to bone or when in the vicinity of bone.

Human monocytes produce interferon-gamma upon stimulation with LPS.

Representing a crucial T-helper 1 cytokine, IFN-γ acts as an important bridge between innate and adaptive immunity and is involved in many acute and chronic pathologic states, such as autoimmune diseases and solid organ transplant rejection. At present, debate still prevails about the ability of human monocytes to produce IFN-γ. We aimed to investigate whether human monocytes possess the capacity to produce IFN-γ at mRNA and protein level. Using real time PCR, flow cytometric analysis and ELISA, we investigated the capacity of freshly isolated CD14+ monocytes of healthy individuals and kidney transplant recipients to produce IFN-γ after stimulation with IFN-γ and LPS or LPS alone. We observed increased IFN-γ mRNA levels in CD14+ monocytes after stimulation as compared to the unstimulated controls in both populations. In addition, stimulation with IFN-γ and LPS or LPS alone led to a significant increase in the percentage of CD14+ monocytes producing TNF-α and IFN-γ at protein level (p<0.05). A trend towards increased secreted IFN-γ production in supernatants was also observed after LPS stimulation using ELISA. We conclude that human monocytes from healthy individuals and kidney transplant recipients possess the capacity to produce IFN-γ.

Des-acyl ghrelin analogs prevent high-fat-diet-induced dysregulation of glucose homeostasis.

There is clinical evidence that des-acyl ghrelin (DAG) favorably modulates glucose and lipid metabolism, although its mode of action is unknown. A murine model of prediabetes was used to assess possible mechanisms of action for DAG and a newly developed bioactive analog, AZP531. C57BL/6J mice were infused with saline, DAG, or AZP531 continuously for 4 wk, and fed either normal diet (ND) or normal diet for 2 wk followed by a high-fat diet (HFD) for 2 wk. Compared with mice in the ND group, HFD increased body and fat mass, caused glucose intolerance and insulin resistance, had proinflammatory effects in white adipose tissue, and caused lipid accumulation in brown adipose tissue. DAG and AZP531 treatment prevented HFD-induced proinflammatory effects, stimulated expression of mitochondrial function markers in brown adipose tissue, and prevented development of a prediabetic metabolic state. AZP531 also prevented a HFD-induced increase in acyl ghrelin levels. Our data indicate DAG analogs as potential treatment for the prevention of metabolic syndrome.

Langerhans cell histiocytosis: fascinating dynamics of the dendritic cell-macrophage lineage.

In its rare occurrence, Langerhans cell histiocytosis (LCH) is a dangerous but intriguing deviation of mononuclear phagocytes, especially dendritic cells (DCs). Clinically, the disease ranges from self-resolving or well manageable to severe and even fatal. LCH lesions in skin, bone, and other sites contain high numbers of cells with phenotypic features resembling LCs admixed with macrophages, T cells, eosinophils, and multinucleated giant cells. Here we review current progress in the LCH field based on two central questions: (i) are LCH cells intrinsically aberrant, and (ii) how does the lesion drive pathogenesis? We argue that LCH cells may originate from different sources, including epidermal LCs, tissue Langerin(+) DCs, or mononuclear phagocyte precursors. Current and prospective in vitro and in vivo models are discussed. Finally, we discuss recent insights into plasticity of T-helper cell subsets in light of the lesion microenvironment. LCH continues to provide urgent clinical questions thereby inspiring innovative DC lineage research.

Long-term glucocorticoid exposure and incident cardiovascular diseases - the Lifelines cohort.

CONTEXT: Long-term glucocorticoid levels in scalp hair (HairGCs), including cortisol and the inactive form cortisone, represent the cumulative systemic exposure to glucocorticoids over months. HairGCs have repeatedly shown associations with cardiometabolic and immune parameters, but longitudinal data are lacking. DESIGN: We investigated 6341 hair samples of participants from the Lifelines cohort study for cortisol and cortisone levels, and associated these to incident cardiovascular diseases (CVD) during 5-7 years of follow-up. We computed the odds ratio (OR) of HairGC levels for incident CVD via logistic regression, adjusting for classical cardiovascular risk factors, and performed a sensitivity analysis in subcohorts of participants <60 years and >= 60 years. Also, we associated HairGC levels to immune parameters (total leukocytes and subtypes). RESULTS: Hair cortisone levels (available in n = 4701) were independently associated with incident CVD (p < 0.001), particularly in younger individuals (multivariate-adjusted OR 4.21, 95% confidence interval (CI) 1.91-9.07 per point increase in 10-log cortisone concentration (pg/mg), p < 0.001). All immune parameters except eosinophils were associated with hair cortisone (all multivariate-adjusted p < 0.05). CONCLUSIONS: In this large, prospective cohort study, we found that long-term cortisone levels, measured in scalp hair, represent a relevant and significant predictor for future cardiovascular diseases in younger individuals. These results highlight glucocorticoid action as possible treatment target for CVD prevention, where hair glucocorticoid measurements could help identify individuals that may benefit from such treatments.

Arginase activity is associated with fibrosis in experimental infection with Taenia crassiceps, but does not play a major role in resistance to infection.

Murine infection with Taenia crassiceps cysticerci is used as an experimental model for human and animal cysticercosis. In this infection parasites can be found associated with an inflammatory infiltrate enriched with macrophages. Experimental evidence exists supporting a role for either NO-producing classically activated (CAMΦ) or arginase- and CD301-expressing alternatively activated macrophages (AAMΦ) in T. crassiceps resistance. In both cell types, arginine is utilized as an important mediator in macrophage effector functions. To investigate whether there is an association between arginine availability, susceptibility to T. crassiceps and other parameters such as fibrosis, BALB/c mice were infected intraperitoneally with cysticerci and treated daily with the arginase inhibitor nor-NOHA or supplemented with l-arginine and followed for eight weeks. The numbers and developmental stages of parasites were evaluated as well as the presence of CD301+ AAMΦ, arginase activity and collagen deposition in the peritoneal membrane. Treatment with the arginase inhibitor or supplementation with l-arginine did not change the parasitic load or profile of the infection. However, the arginase inhibitor significantly decreased the deposition of collagen. These results suggest that arginase activity does not interfere with parasite control during experimental infection with T. crassiceps, but it is important for fibrosis in cysticercosis.

Psychological, behavioural, and physical aspects of caregiver strain in autism-caregivers: a cohort study.

Background: People who give care to autistic individuals (autism-caregivers) experience higher levels of caregiver strain than people who provide care for individuals with other chronic conditions (non-autism-caregivers). This places them at higher risk for psychological, behavioural and physical health concerns. The aim of this study is to delineate psychological, behavioural, and physical aspects of caregiver strain in autism-caregivers compared to non-autism-caregivers. Methods: We included 3354 adult caregivers from the general population in the Netherlands participating in the second assessment (January, 1, 2014-December, 31, 2017) of the Lifelines Cohort. In this cohort study, using multivariable regression adjusted for age, sex, and socioeconomic status, we analysed psychological (anxiety and depression based on a Mini International Neuropsychiatric Interview, and self-reported stress and perceived health), behavioural (questionnaire-assessed physical activity, alcohol use, and smoking), and physical aspects (body mass index, waist circumference, and leukocyte-counts) of caregiver strain in autism-caregivers (n = 722) compared with non-autism-caregivers (n = 2632). Findings: Autism-caregivers reported more stress (OR 3.61, 95% CI 2.60-4.99). Both anxiety (OR 1.85, 95% CI 1.37-2.49) and depressive disorders (OR 1.83, 95% CI 1.17-2.86) were more common in autism-caregivers than in non-autism-caregivers. Perceived health, physical activity, alcohol use, and smoking were not different between autism- and non-autism-caregivers. In autism-caregivers, lymphocyte- and monocyte-counts were lower than in non-autism-caregivers. Interpretation: In this large cohort, autism-caregivers had worse psychological health than non-autism-caregivers. Moreover, autism-caregiving might be associated with an altered immune balance. These findings underline the higher caregiver strain in autism-caregivers compared to other caregivers. This calls for increased support to autism-caregivers. Funding: Lifelines has been funded by the Dutch government.

Altered Functionality of Lipoprotein(a) Impacts on Angiogenesis in Diabetic Retinopathy.

Purpose: Diabetic retinopathy (DR) is a complication of type 2 diabetes mellitus (T2DM). Lipoprotein(a) (Lp(a)) contributes to the progression of DR, but how is unclear. In homeostasis of the retinal microvasculature, myeloid-derived pro-angiogenic cells (PACs) also play a pivotal role, and fail to function properly in diabetic conditions. Here, we explored the putative contribution of Lp(a) from patients with T2DM with/without DR and healthy controls on inflammation and angiogenesis of retinal endothelial cells (RECs), and on PAC differentiation. Subsequently, we compared the lipid composition of Lp(a) from patients to that from healthy controls. Methods: Lp(a)/LDL obtained from patients and healthy controls were added to TNF-alpha-activated RECs. Expression of VCAM-1/ICAM-1 was measured using flowcytometry. Angiogenesis was determined in REC-pericyte co-cultures stimulated by pro-angiogenic growth factors. PAC differentiation from peripheral blood mononuclear cells was determined by measuring expression of PAC markers. The lipoprotein lipid composition was quantified using detailed lipidomics analysis. Results: Lp(a) from patients with DR (DR-Lp(a)) failed to block TNF-alpha-induced expression of VCAM-1/ICAM-1 in REC whereas Lp(a) from healthy controls (healthy control [HC]-Lp(a)) did. DR-Lp(a) increased REC angiogenesis more than HC-Lp(a) did. Lp(a) from patients without DR showed intermediate profiles. HC-Lp(a) reduced the expression of CD16 and CD105 in PAC, but T2DM-Lp(a) did not. Phosphatidylethanolamine content was lower in T2DM-Lp(a) than in HC-Lp(a). Conclusions: DR-Lp(a) does not show the anti-inflammatory capacity seen with HC-Lp(a), but increases REC angiogenesis, and affects PAC differentiation less than HC-Lp(a). These functional differences in Lp(a) in T2DM-related retinopathy are associated with alterations in the lipid composition as compared to healthy conditions.

Improved Physical and Mental Health After a Combined Lifestyle Intervention with Cognitive Behavioural Therapy for Obesity.

Background: Obesity is a multifactorial, chronic, progressive disease associated with decreased health-related quality of life, comorbidities, and increased mortality risk. Lifestyle interventions, focusing on dietetics, physical exercise, and behavioral therapy, are a cornerstone of therapy. Despite this very multidisciplinary treatment approach, the definition of treatment success is often based only on a weight loss of ≥ 5%. However, the heterogeneous nature of obesity may necessitate a more comprehensive approach to assessing treatment effects. Objectives: Here, we describe changes in physiological, psychological, and behavioral health after a multidisciplinary combined lifestyle intervention (CLI). Additionally, we investigated whether these changes were related to weight loss. Methods: This prospective observational longitudinal study comprised 96 adults with obesity (73 women, 81 Caucasian) participating in a CLI at the Obesity Center CGG, Erasmus University Medical Center, Rotterdam, the Netherlands. The 1.5-year intervention comprised multidisciplinary professional guidance towards a healthy diet, increased physical activity, and included cognitive behavioral therapy. Physiological health outcomes, psychological well-being, eating behavior, and physical activity were assessed after ten weeks and 1.5 years and compared to baseline. Results: An average of 5.2% weight loss (-6.0 kg) was accompanied by a mean 9.8% decrease in fat mass (-5.9 kg; both P < 0.001) and significant improvements in metabolism, hormonal status, and immune parameters (all P < 0.05). Moreover, we observed decreased psychopathology, increased quality of life, and decreased disordered eating (all P < 0.05). Weight loss correlated with most metabolic changes (all P < 0.05) but not with most psychological/behavioral changes. Conclusions: Combined lifestyle intervention in patients with obesity was accompanied by significant improvements in body weight and body composition along with cardiometabolic, endocrine, immunological, psychological, and behavioral improvements. Interestingly, most changes in psychological and behavioral health occurred independently of weight loss. Obesity treatment success should be evaluated based on a combination of physical and patient-reported outcomes rather than weight loss alone.

Nomenclature of monocytes and dendritic cells in blood.

Monocytes and cells of the dendritic cell lineage circulate in blood and eventually migrate into tissue where they further mature and serve various functions, most notably in immune defense. Over recent years these cells have been characterized in detail with the use of cell surface markers and flow cytometry, and subpopulations have been described. The present document proposes a nomenclature for these cells and defines 3 types of monocytes (classical, intermediate, and nonclassical monocytes) and 3 types of dendritic cells (plasmacytoid and 2 types of myeloid dendritic cells) in human and in mouse blood. This classification has been approved by the Nomenclature Committee of the International Union of Immunological Societies, and we are convinced that it will facilitate communication among experts and in the wider scientific community.

S100A8 enhances osteoclastic bone resorption in vitro through activation of Toll-like receptor 4: implications for bone destruction in murine antigen-induced arthritis.

OBJECTIVE: Rheumatoid arthritis, which is associated with elevated levels of S100A8 and S100A9, is characterized by severe bone erosions caused by enhanced osteoclast formation and activity. The aim of the present study was to investigate the role of S100A8 and S100A9 in osteoclastic bone destruction in murine antigen-induced arthritis (AIA). METHODS: Bone destruction was analyzed in the arthritic knee joints of S100A9-deficient mice in which S100A8 protein expression was also lacking, and in wild-type (WT) controls. Osteoclast precursors from S100A9-deficient and WT mice were differentiated into osteoclasts in vitro. Additionally, precursors were stimulated with S100A8, S100A9, or S100A8/A9 during osteoclastogenesis. Receptor involvement was investigated using an anti-receptor for advanced glycation end products (anti-RAGE)-blocking antibody, soluble RAGE, or Toll-like receptor 4 (TLR-4)-deficient osteoclast precursors. The formation of osteoclasts and actin rings, the regulation of osteoclast markers, and bone resorption were analyzed. RESULTS: Bone erosions and cathepsin K staining were significantly suppressed in S100A9-deficient mice after AIA induction. However, osteoclast precursors from S100A9-deficient mice developed normally into functional osteoclasts, which excludes a role for intrinsic S100A8/A9. In contrast to the results observed with S100A9 and S100A8/A9, the addition of S100A8 during osteoclastogenesis resulted in stimulation of osteoclast formation in conjunction with enhanced actin ring formation and increased bone resorption. Analysis of the putative receptor for S100A8 in osteoclastogenesis revealed that osteoclast differentiation and function could not be inhibited by blocking RAGE, whereas the increase in osteoclast numbers and enhanced bone resorption were completely abrogated using TLR-4-deficient osteoclast precursors. CONCLUSION: These results demonstrate that S100A8 stimulated osteoclast formation and activity and suggest that both S100A8 and TLR-4 are important factors in mediating osteoclastic bone destruction in experimental arthritis.

Severe Listeria monocytogenes infection induces development of monocytes with distinct phenotypic and functional features.

Monocytes perform diverse roles during infection with the facultative intracellular bacterium Listeria monocytogenes. They are essential as bactericidal cells in host defense but can also become Trojan horses transporting bacteria into the brain. To explain these contrasting roles, we characterized bone marrow (BM) monocytes in steady state and generated during lethal and sublethal L. monocytogenes infection. Ly-6C(high)CD11b(+) BM monocytes expressed high amounts of M-CSFR/CD115 in steady state and 72 h following sublethal infection. However, infection with increasing numbers of bacteria resulted in progressive loss of CD115 and strongly decreased CD115-encoding c-fms mRNA expression. Conversely, analysis of regulatory molecules showed de novo expression of the nonsignaling IL-1RII, CD121b, under the same conditions. Ly-6C(high)CD11b(+) monocytes in circulation also acquired a CD115(neg/low)CD121b(high) phenotype during lethal infection. These BM monocytes showed upregulation of suppressor of cytokine signaling 1 and 3 and IL-1R-"associated kinase-M to a greater extent and/or earlier compared with cells from sublethal infection and showed decreased LPS-induced IL-6 production despite similar levels of surface TLR4 expression. BM monocytes from uninfected or sublethally infected mice bound and internalized very few L. monocytogenes in vitro. However, both functions were significantly increased in monocytes developing during lethal infection. Nonetheless, these cells did not produce reactive oxygen intermediates, suggesting an inability to kill L. monocytogenes. Together, these data show that systemic infections with lethal and sublethal amounts of bacteria differentially shape developing BM monocytes. This results in distinct phenotypic and functional properties consistent with being Trojan horses rather than bactericidal effector cells.

Intra-articular injection of triamcinolone acetonide sustains macrophage levels and aggravates osteophytosis during degenerative joint disease in mice.

BACKGROUND AND PURPOSE: Corticosteroids such as triamcinolone acetonide (TAA) are potent drugs administered intra-articularly as an anti-inflammatory therapy to relieve pain associated with osteoarthritis (OA). However, the ability of early TAA intervention to mitigate OA progression and modulate immune cell subsets remains unclear. Here, we sought to understand the effect of early intra-articular injection of TAA on OA progression, local macrophages, and peripheral blood monocytes. EXPERIMENTAL APPROACH: Degenerative joint disease was induced by intra-articular injection of collagenase into the knee joint of male C57BL/6 mice. After 1 week, TAA or saline was injected intra-articularly. Blood was taken throughout the study to analyse monocyte subsets. Mice were killed at days 14 and 56 post-induction of collagenase-induced OA (CiOA) to examine synovial macrophages and structural OA features. KEY RESULTS: The percentage of macrophages relative to total live cells present within knee joints was increased in collagenase- compared with saline-injected knees at day 14 and was not altered by TAA treatment. However, at day 56, post-induction of CiOA, TAA-treated knees had increased levels of macrophages compared with the knees of untreated CiOA-mice. The distribution of monocyte subsets present in peripheral blood was not altered by TAA treatment during the development of CiOA. Osteophyte maturation was increased in TAA-injected knees at day 56. CONCLUSION AND IMPLICATIONS: Intra-articular injection of TAA increases long-term synovial macrophage numbers and osteophytosis. Our findings suggest that TAA accentuates the progression of osteoarthritis-associated features when applied to an acutely inflamed knee.

Monocyte adaptations in patients with obesity during a 1.5 year lifestyle intervention.

Background: Obesity is associated with chronic, low-grade inflammation, which is reflected in altered peripheral blood monocyte characteristics. The aim of this study was to analyze the monocyte subset composition (classical (CM), intermediate (IM) and non-classical monocytes (NCM)), and their inflammatory marker profile (CD14, CD16, CD36, CD45, CD64, CD300e, HLA-DR) in individuals with obesity during a 1.5 year combined lifestyle intervention (CLI), comprising healthy nutrition, increased exercise and behavioral changes. Methods: We analyzed monocyte subset counts and immunophenotypes in 73 individuals with obesity, and associated these to baseline body mass index (BMI) and waist circumference (WC). The measurements were repeated after 10 weeks and at the end of the intervention (1.5 years). Results: Generally, monocyte subset counts were not associated to BMI or WC at baseline, neither did monocyte counts change during the 1.5 year CLI. Immunophenotypically, higher baseline BMI and WC were associated to lower CD14 and higher CD300e expression by all subsets. During CLI there were remarkable changes in marker profiles: expression of CD14, CD36, CD45 and CD64 significantly decreased in CM and IM, as did CD16 (IM and NCM) (p<0.05). CD300e initially decreased after 10 weeks, but increased sharply at 1.5 years (all subsets). We observed no consistent associations between changes in monocyte characteristics and anthropometric changes. Conclusion: A 1.5 year CLI in individuals with obesity mediates persistent immunophenotypic adaptations related to cellular activation in blood monocytes, whereas changes in subset distribution are limited. Lifestyle-induced changes in the inflammatory profile of monocytes differ from the 'less-severe-obesity'-phenotype, suggesting a novel, 'post-weight-loss' monocyte setpoint.