Macrophages block insulin action in adipocytes by altering expression of signaling and glucose transport proteins

Obesity leads to a proinflammatory state with immune responses that include infiltration of adipose tissue with macrophages. These macrophages are believed to alter insulin sensitivity in adipocytes, but the mechanisms that underlie this effect have not been characterized. We have explored the interaction between macrophages and adipocytes in the context of both indirect and direct coculture. Macrophage-secreted factors blocked insulin action in adipocytes via downregulation of GLUT4 and IRS-1, leading to a decrease in Akt phosphorylation and impaired insulin-stimulated GLUT4 translocation to the plasma membrane. GLUT1 was upregulated with a concomitant increase in basal glucose uptake. These changes recapitulate those seen in adipose tissue from insulin-resistant humans and animal models. TNF-alpha-neutralizing antibodies partially reversed the insulin resistance produced by macrophage-conditioned media. Peritoneal macrophages and macrophage-enriched stromal vascular cells from adipose tissue also attenuated responsiveness to insulin in a manner correlating with inflammatory cytokine secretion. Adipose tissue macrophages from obese mice have an F4/80(+)CD11b(+)CD68(+)CD14(-) phenotype and form long cellular extensions in culture. Peritoneal macrophages take on similar characteristics in direct coculture with adipocytes and induce proinflammatory cytokines, suggesting that macrophage activation state is influenced by contact with adipocytes. Thus both indirect/secreted and direct/cell contact-mediated factors derived from macrophages influence insulin sensitivity in adipocytes.     

Preadipocyte conversion to macrophage. Evidence of plasticity

Preadipocytes are present throughout adult life in adipose tissues and can proliferate and differentiate into mature adipocytes according to the energy balance. An increasing number of reports demonstrate that cells from adipose lineages (preadipocytes and adipocytes) and macrophages share numerous functional or antigenic properties. No large scale comparison reflecting the phenotype complexity has been performed between these different cell types until now. We used profiling analysis to define the common features shared by preadipocyte, adipocyte, and macrophage populations. Our analysis showed that the preadipocyte profile is surprisingly closer to the macrophage than to the adipocyte profile. From these data, we hypothesized that in a macrophage environment preadipocytes could effectively be converted into macrophages. We injected labeled stroma-vascular cells isolated from mouse white adipose tissue or 3T3-L1 preadipocyte cell line into the peritoneal cavity of nude mice and investigated changes in their phenotype. Preadipocytes rapidly and massively acquired high phagocytic activity and index. 60-70% of preadipocytes also expressed five macrophage-specific antigens: F4/80, Mac-1, CD80, CD86, and CD45. These values were similar to those observed for peritoneal macrophages. In vitro experiments showed that cell-to-cell contact between preadipocytes and peritoneal macrophages partially induced this preadipocyte phenotype conversion. Overall, these results suggest that preadipocyte and macrophage phenotypes are very similar and that preadipocytes have the potential to be very efficiently and rapidly converted into macrophages. This work emphasizes the great cellular plasticity of adipose precursors and reinforces the link between adipose tissue and innate immunity processes.     

A subpopulation of macrophages infiltrates hypertrophic adipose tissue and is activated by free fatty acids via Toll-like receptors 2 and 4 and JNK-dependent pathways

Obesity and type 2 diabetes are characterized by decreased insulin sensitivity, elevated concentrations of free fatty acids (FFAs), and increased macrophage infiltration in adipose tissue (AT). Here, we show that FFAs can cause activation of RAW264.7 cells primarily via the JNK signaling cascade and that TLR2 and TLR4 are upstream of JNK and help transduce FFA proinflammatory signals. We also demonstrate that F4/80(+)CD11b(+)CD11c(+) bone marrow-derived dendritic cells (BMDCs) have heightened proinflammatory activity compared with F4/80(+)CD11b(+)CD11c(-) bone marrow-derived macrophages and that the proinflammatory activity and JNK phosphorylation of BMDCs, but not bone marrow-derived macrophages, was further increased by FFA treatment. F4/80(+)CD11b(+)CD11c(+) cells were found in AT, and the proportion and number of these cells in AT is increased in ob/ob mice and by feeding wild type mice a high fat diet for 1 and 12 weeks. AT F4/80(+)CD11b(+)CD11c(+) cells express increased inflammatory markers compared with F4/80(+)CD11b(+)CD11c(-) cells, and FFA treatment increased inflammatory responses in these cells. In addition, we found that CD11c expression is increased in skeletal muscle of high fat diet-fed mice and that conditioned medium from FFA-treated wild type BMDCs, but not TLR2/4 DKO BMDCs, can induce insulin resistance in L6 myotubes. Together our results show that FFAs can activate CD11c(+) myeloid proinflammatory cells via TLR2/4 and JNK signaling pathways, thereby promoting inflammation and subsequent cellular insulin resistance.     

Obesity-associated mouse adipose stem cell secretion of monocyte chemotactic protein-1

Studies showed that monocyte chemotactic protein-1 (MCP-1) concentrations are increased in obesity. In our current study, we demonstrate that plasma MCP-1 level in leptin-deficient ob/ob mice is significantly higher than in lean mice. Furthermore, we determined that basal adipose tissue MCP-1 mRNA levels are significantly higher in ob/ob mice compared with lean mice. To determine the mechanisms underlying obesity-associated increases in plasma and adipose tissue MCP-1 levels, we determined adipose tissue cell type sources of MCP-1 production. Our data show that adipose tissue stem cells (CD34(+)), macrophages (F4/80(+)), and stromal vascular fraction (SVF) cells express significantly higher levels of MCP-1 compared with adipocytes under both basal and lipopolysaccharide (LPS)-stimulated conditions. Furthermore, basal and LPS-induced MCP-1 secretion levels were the same for both adipose F4/80(+) and CD34(+) cells, whereas adipose CD34(+) cells have twofold higher cell numbers (30% of total SVF cells) compared with F4/80(+) macrophages (15%). Our data also show that CD34(+) cells from visceral adipose tissue depots secrete significantly higher levels of MCP-1 ex vivo when compared with CD34(+) cells from subcutaneous adipose tissue depots. Taken together, our data suggest that adipose CD34(+) stem cells may play an important role in obesity-associated increases in plasma MCP-1 levels.     

Human primary adipocytes exhibit immune cell function: adipocytes prime inflammation independent of macrophages

Background

Obesity promotes inflammation in adipose tissue (AT) and this is implicated in pathophysiological complications such as insulin resistance, type 2 diabetes and cardiovascular disease. Although based on the classical hypothesis, necrotic AT adipocytes (ATA) in obese state activate AT macrophages (ATM) that then lead to a sustained chronic inflammation in AT, the link between human adipocytes and the source of inflammation in AT has not been in-depth and systematically studied. So we decided as a new hypothesis to investigate human primary adipocytes alone to see whether they are able to prime inflammation in AT.

Methods and Results

Using mRNA expression, human preadipocytes and adipocytes express the cytokines/chemokines and their receptors, MHC II molecule genes and 14 acute phase reactants including C-reactive protein. Using multiplex ELISA revealed the expression of 50 cytokine/chemokine proteins by human adipocytes. Upon lipopolysaccharide stimulation, most of these adipocyte-associated cytokines/chemokines and immune cell modulating receptors were up-regulated and a few down-regulated such as (ICAM-1, VCAM-1, MCP-1, IP-10, IL-6, IL-8, TNF-α and TNF-β highly up-regulated and IL-2, IL-7, IL-10, IL-13 and VEGF down-regulated. In migration assay, human adipocyte-derived chemokines attracted significantly more CD4+ T cells than controls and the number of migrated CD4+ cells was doubled after treating the adipocytes with LPS. Neutralizing MCP-1 effect produced by adipocytes reduced CD4+ migration by approximately 30%.

Conclusion

Human adipocytes express many cytokines/chemokines that are biologically functional. They are able to induce inflammation and activate CD4+ cells independent of macrophages. This suggests that the primary event in the sequence leading to chronic inflammation in AT is metabolic dysfunction in adipocytes, followed by production of immunological mediators by these adipocytes, which is then exacerbated by activated ATM, activation and recruitment of immune cells. This study provides novel knowledge about the prime of inflammation in human obese adipose tissue, opening a new avenue of investigations towards obesity-associated type 2 diabetes.     

PRSS14/Epithin is induced in macrophages by the IFN-γ/JAK/STAT pathway and mediates transendothelial migration

PRSS14/Epithin (also known as matriptase and ST14), a member of the type II transmembrane serine proteases, is primarily found in a subpopulation of normal epithelial cells and in epithelial cancers. Its known functions include maintaining the epithelial barrier, thymic development, and cancer progression. In this study, we show that several macrophage cell lines and activated bone marrow-derived macrophages also express PRSS14/Epithin. Surface expression, as well as cytoplasmic expression, was detectable upon activation by IFN-γ, but not TNF-α or TGF-β. Induction of the protein appeared to be restricted to macrophages. IFN-γ showed a biphasic regulation in RAW264.7 cells, and upregulated expression was sustained for several days. This induction by IFN-γ was partially through the increase of PRSS14/Epithin mRNA production, which is downstream of the JAK pathway, shown by the inhibition by tyrphostin AG490. Using chromatin immunoprecipitation, we verified that two sites among six putative STAT1 binding sites in the PRSS14/Epithin promoter were occupied by STAT1 upon activation. Treatment with IFN-γ enhanced the serum-triggered transendothelial migration of RAW264.7 cells, but not that of PRSS14/Epithin knock-down RAW264.7 cells, although they express multiple markers such as ICAM1, CD80, and CD40 at normal levels. These data strongly suggest that PRSS14/Epithin plays an important role in the transendothelial migration of activated macrophages in the inflammatory microenvironment, and the mode of action is similar to the events in cancer metastasis.     

Augmentation of 11beta-hydroxysteroid dehydrogenase type 1 in LPS-activated J774.1 macrophages--role of 11beta-HSD1 in pro-inflammatory properties in macrophages

Macrophage infiltration in obese adipose tissue provokes local inflammation and insulin resistance. Evidence has accumulated that activation of 11beta-HSD1 in adipocytes is critically involved in dysfunction of adipose tissue. However, the potential role of 11beta-HSD1 in macrophages still remains unclear. We here demonstrate that a murine macrophage cell line, J774.1 cells expressed 11beta-HSD1 mRNA and reductase activity, both of which were augmented by lipopolysaccharide (LPS)-induced cell activation. Three kinds of pharmacological inhibition of 11beta-HSD1 in LPS-treated macrophages significantly suppressed the expression and secretion of interleukin 1beta, tumor necrosis factor alpha or monocyte chemoattractant protein 1, thereby highlighting a novel role of 11beta-HSD1 in pro-inflammatory properties of activated macrophages.     

Pregravid obesity associates with increased maternal endotoxemia and metabolic inflammation

Obese pregnant women develop severe insulin resistance and enhanced systemic and placental inflammation, suggesting associated modifications of endocrine and immune functions. Activation of innate immunity by endotoxins/lipopolysaccharides (LPS) has been proposed as a mechanism for enhancing metabolic alterations in disorders with insulin resistance. The aim of this study was to characterize the immune responses developed by the adipose tissue (AT) and their potential links to maternal endotoxemia in pregnancy with obesity. Blood and subcutaneous abdominal AT were obtained from 120 lean and obese women (term pregnancy) recruited at delivery. Gene expression was assessed in AT and stromal vascular cells isolated from a subset of 24 subjects from the same cohort. Doubling of plasma endotoxin concentrations indicated subclinical endotoxemia in obese compared with lean women. This was associated with significant increase in systemic C-reactive protein and interleukin-6 (IL-6) but not tumor necrosis factor-α (TNF-α) concentrations. AT inflammation was characterized by accumulation of CD68(+) macrophages with a threefold increased gene expression of the macrophage markers CD68, EMR1, and CD14. Gene expression for cytokines IL-6, TNF-α, IL-8, and monocyte chemotactic protein-1 (MCP1) and for LPS-sensing CD14, toll-like receptor 4 (TLR4), translocating chain-associated membrane protein 2 was 2.5-5-fold higher in stromal cells of obese compared to lean. LPS-treated cultured stromal cells of obese women expressed a 5-16-fold stimulation of the same cytokines upregulated in vivo. Our data demonstrate that subclinical endotoxemia is associated with systemic and AT inflammation in obese pregnant women. Recognition of bacterial pathogens may contribute to the combined dysfunction of innate immunity and the metabolic systems in AT.     

TPA-induced differentiation and adhesion of U937 cells: changes in ultrastructure, cytoskeletal organization and expression of cell surface antigens

Incubation of the human promonocytic cell line U937 with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 72 h resulted in differentiation into immature macrophage-like cells and was accompanied by marked morphological and functional changes. U937 cells which normally grow in suspension and show a smooth surface, extended pseudopodia and became adherent to each other and to the surface of the culture vessel. Concomitant with the TPA-induced adherence U937 cells ceased to proliferate. Our results show that phorbol ester-treated U937 cells exhibited markedly increased levels of fibronectin and of the cytoskeletal proteins actin, myosin and vimentin including a reorganization of actin and vimentin filaments. The induction of both cellular adherence and growth inhibition were accompanied by a significantly reduced level of cells expressing transferrin receptors and changes in cell surface antigen expression. Here, the expression of the leukocytefunction antigens (LFA-1), including CD11 and CD18 was markedly enhanced during phorbol ester-induced differentiation. TPA-treatment, however, failed to enhance the small amount of U937 cells expressing the monocyte/macrophage-specific CD14 antigen or expressing MHC class-II antigens. A detailed analysis of the CD14 cluster by 7 differential antibodies resulted in an induction of TM1, UCHM1, MEM15, My4, and 3C10, whereas the epitopes recognized by TM2 and Mo2 remained unaltered. Neither indomethacin nor interferon-gamma were capable of inducing a marked expression of these antigen epitopes in TPA-treated cells. Although these data demonstrate that during phorbol ester-induced differentiation U937 cells acquire many properties typically associated with macrophages, the failure to express marked levels of macrophage-specific cell surface antigens suggests a transition of U937 cells from a promonocytic to an immature macrophage intermediate state rather than into mature macrophage-like cells.     

T cell-activated macrophages are capable of both recognition and rejection of pancreatic islet xenografts

Macrophages have been proposed as the major effector cell in T cell-mediated xenograft rejection. To determine their role in this response, NOD-SCID mice were transplanted with fetal pig pancreas (FPP) before reconstitution with CD4(+) T cells from BALB/c mice. Twelve days after CD4(+) T cell reconstitution, purified macrophages (depleted of T cells) were isolated from CD4(+) T cell-reconstituted FPP recipient mice and adoptively transferred to their nonreconstituted counterparts. After adoptive macrophage transfer, FPP recipient mice transferred with macrophages from CD4(+) T cell-reconstituted mice demonstrated xenograft destruction along with massive macrophage infiltration at day 4 and complete graft destruction at day 8 postmacrophage transfer. By contrast, FPP recipients that received macrophages from nonreconstituted mice showed intact FPP xenografts with few infiltrating macrophages at both days 4 and 8 after macrophage transfer. The graft-infiltrating macrophages showed increased expression of their activation markers. Depletion of endogenous macrophages or any remaining CD4(+) T cells did not delay graft rejection in the macrophage-transferred FPP recipients, whereas depletion of transferred macrophages with clodronate liposomes prevented graft rejection. Our results show that macrophages primed by FPP and activated by CD4(+) T cells were attracted from the peripheral circulation and were capable of specific targeting and destruction of FPP xenografts. This suggests that in xenograft rejection, there are macrophage-specific recognition and targeting signals that are independent of those received by T cells.     

Resolvin D1 and its precursor docosahexaenoic acid promote resolution of adipose tissue inflammation by eliciting macrophage polarization toward an M2-like phenotype

We recently demonstrated that ω-3-polyunsaturated fatty acids ameliorate obesity-induced adipose tissue inflammation and insulin resistance. In this study, we report novel mechanisms underlying ω-3-polyunsaturated fatty acid actions on adipose tissue, adipocytes, and stromal vascular cells (SVC). Inflamed adipose tissue from high-fat diet-induced obese mice showed increased F4/80 and CD11b double-positive macrophage staining and elevated IL-6 and MCP-1 levels. Docosahexaenoic acid (DHA; 4 μg/g) did not change the total number of macrophages but significantly reduced the percentage of high CD11b/high F4/80-expressing cells in parallel with the emergence of low-expressing CD11b/F4/80 macrophages in the adipose tissue. This effect was associated with downregulation of proinflammatory adipokines in parallel with increased expression of IL-10, CD206, arginase 1, resistin-like molecule α, and chitinase-3 like protein, indicating a phenotypic switch in macrophage polarization toward an M2-like phenotype. This shift was confined to the SVC fraction, in which secretion of Th1 cytokines (IL-6, MCP-1, and TNF-α) was blocked by DHA. Notably, resolvin D1, an anti-inflammatory and proresolving mediator biosynthesized from DHA, markedly attenuated IFN-γ/LPS-induced Th1 cytokines while upregulating arginase 1 expression in a concentration-dependent manner. Resolvin D1 also stimulated nonphlogistic phagocytosis in adipose SVC macrophages by increasing both the number of macrophages containing ingested particles and the number of phagocytosed particles and by reducing macrophage reactive oxygen species production. No changes in adipocyte area and the phosphorylation of hormone-sensitive lipase, a rate-limiting enzyme regulating adipocyte lipolysis, were observed. These findings illustrate novel mechanisms through which resolvin D1 and its precursor DHA confer anti-inflammatory and proresolving actions in inflamed adipose tissue.     

Functional and structural regression of the rabbit corpus luteum is associated with altered luteal immune cell phenotypes and cytokine expression patterns

Following attenuation of progesterone production corpora lutea are selectively cleared, a process associated with recruitment of macrophages. In the rabbit little is known about luteal immune cell phenotypes and expression of cytokines, which influence immune cells and resident luteal cells, during luteolysis. Consequently, we studied luteal immune cells by immunohistochemistry as well as luteal IL-10, TNFalpha, MCP-1, IFN-gamma, and IL-1beta mRNA expression by semiquantitative RT-PCR from day 8 to day 20 in pseudopregnant rabbits (d8-d20 p.hCG). Luteal function was assayed by serum progesterone levels. Functional luteolysis commenced by d14 p.hCG as indicated by attenuation of serum progesterone levels. X4(+) tissue macrophage levels increased transiently on d12 and d14 p.hCG, whereas CD5(+) T-cell levels transiently declined on these two days. CD68(+) macrophages increased progressively after d16 p.hCG. The luteal mRNA level of the anti-inflammatory cytokine IL-10 as well as the mRNA levels of the pro-inflammatory cytokines TNFalpha and MCP-1 increased after d16 p.hCG and remained elevated up to d20 p.hCG. IFN-gamma and IL-1beta mRNA expression did not vary systematically. In summary, luteolysis was associated with an initial transient increase of X4(+) macrophages and decrease of CD5(+) T-cells, and later recruitment of CD68(+) macrophages. During structural regression pro- and anti-inflammatory cytokines are upregulated possibly to control immune cell function.     

Allograft inflammatory factor-1/Ionized calcium-binding adapter molecule 1 is specifically expressed by most subpopulations of macrophages and spermatids in testis

Ionized calcium-binding adapter molecule 1 (Iba1) is a 147-amino-acid calcium-binding protein widely in use as a marker for microglia. It has actin-crosslinking activity and is involved in aspects of motility-associated rearrangement of the actin cytoskeleton. The Iba1 gene and protein are identical to allograft inflammatory factor-1 (AIF-1), a protein involved in various aspects of inflammation, which was investigated independently from Iba1. Although regarded to be monocyte/macrophage-specific, expression by germ cells in testis showed that AIF-1/Iba1 is not exclusively expressed by cells of the monocyte/macrophage lineage. Furthermore, AIF-1 was found in cells not belonging to the monocyte/macrophage lineage under pathological conditions. Here, the distribution of AIF-1/Iba1 in the normal mouse has been examined, by immunohistochemistry, to determine whether AIF-1/Iba1 expression is confined to macrophages and spermatids. Spermatids are the only cells not belonging to the monocyte/macrophage lineage found to express AIF-1/Iba1 in the normal mouse, by this method. This study has not demonstrated AIF-1/Iba1 expression in dendritic cells, although this protein might be expressed by subsets of dendritic cells. AIF-1/Iba1 can be regarded a “pan-macrophage marker” because, except for alveolar macrophages, all subpopulations of macrophages examined express AIF-1/Iba1.     

Macrophage precursors as natural killer cells against tumor cells and microorganisms

Macrophage precursors cells have been isolated from spleen and liver of mice and have characterized using F4/80 antibody, their proliferative response to CSF-1 and their maturation to macrophages. These nonadherent and nonphagocytic cells exert strong killing of Yac-1 tumor cells and of various microorganisms. Transplantation of these macrophage precursors into lethally irradiated allogenic hosts restores natural killer (NK) activity within 14 days. Macrophage precursors show enhanced NK activity when activated with interleukin 2. FACS analysis of F 4/80 presorted macrophage precursors reveals about 30% of the cells coexpressing NK 1.1. and F 4/80. These data support the assumption that at least a part of the NK cell compartment is derived from the myeloid lineage.     

Recruitment and activation of macrophages by pathogenic CD4 T cells in type 1 diabetes: evidence for involvement of CCR8 and CCL1

Adoptive transfer of diabetogenic CD4 Th1 T cell clones into young NOD or NOD.scid recipients rapidly induces onset of diabetes and also provides a system for analysis of the pancreatic infiltrate. Although many reports have suggested a role for macrophages in the inflammatory response, there has been little direct characterization of macrophage activity in the pancreas. We showed previously that after migration to the pancreas, diabetogenic CD4 T cell clones produce a variety of inflammatory cytokines and chemokines, resulting in the recruitment of macrophages. In this study, we investigated mechanisms by which macrophages are recruited and activated by T cells. Analysis of infiltrating cells after adoptive transfer by the diabetogenic T cell clone BDC-2.5 indicates that large numbers of cells staining for both F4/80 and CD11b are recruited into the pancreas where they are activated to make IL-1beta, TNF-alpha, and NO, and express the chemokine receptors CCR5, CXCR3, and CCR8. Diabetogenic CD4 T cell clones produce several inflammatory chemokines in vitro, but after adoptive transfer we found that the only chemokine that could be detected ex vivo was CCL1. These results provide the first evidence that CCR8/CCL1 interaction may play a role in type 1 diabetes through macrophage recruitment and activation.     

A unique hybrid renal mononuclear phagocyte activation phenotype in murine systemic lupus erythematosus nephritis

Renal infiltration with mononuclear cells is associated with poor prognosis in systemic lupus erythematosus. A renal macrophage/dendritic cell signature is associated with the onset of nephritis in NZB/W mice, and immune-modulating therapies can reverse this signature and the associated renal damage despite ongoing immune complex deposition. In nephritic NZB/W mice, renal F4/80(hi)/CD11c(int) macrophages are located throughout the interstitium, whereas F4/80(lo)/CD11c(hi) dendritic cells accumulate in perivascular lymphoid aggregates. We show here that F4/80(hi)/CD11c(int) renal macrophages have a Gr1(lo)/Ly6C(lo)/VLA4(lo)/MHCII(hi)/CD43(lo)/CD62L(lo) phenotype different from that described for inflammatory macrophages. At nephritis onset, F4/80(hi)/CD11c(int) cells upregulate cell surface CD11b, acquire cathepsin and matrix metalloproteinase activity, and accumulate large numbers of autophagocytic vacuoles; these changes reverse after the induction of remission. Latex bead labeling of peripheral blood Gr1(lo) monocytes indicates that these are the source of F4/80(hi)/CD11c(int) macrophages. CD11c(hi)/MHCII(lo) dendritic cells are found in the kidneys only after proteinuria onset, turnover rapidly, and disappear rapidly after remission induction. Gene expression profiling of the F4/80(hi)/CD11c(int) population displays increased expression of proinflammatory, regulatory, and tissue repair/degradation-associated genes at nephritis onset that reverses with remission induction. Our findings suggest that mononuclear phagocytes with an aberrant activation profile contribute to tissue damage in lupus nephritis by mediating both local inflammation and excessive tissue remodeling.     

The role of LAIR-1 (CD305) in T cells and monocytes/macrophages in patients with rheumatoid arthritis

The LAIR-1 receptor is expressed on a majority of mononuclear leukocytes. It is used as a biomarker when testing synovial fluid for evidence of rheumatoid arthritis (RA). The primary objective of this study was to measure T cell- and monocyte/macrophage-specific LAIR-1 expression in RA patients and compare this to LAIR-1 expression in osteoarthritis (OA) patients and healthy individuals. LAIR-1 expression was significantly decreased in circulating CD4⁺ T cells in RA patients compared to both OA patients and healthy individuals. In contrast, LAIR-1 is high in CD14⁺ monocytes and local CD68⁺ macrophages in synovial tissues from RA patients. Upon stimulation with TNF-α, LAIR-1 expression decreased in T-helper (Th)1 and Th2 CD4⁺ T cells from healthy donors. These results indicate that LAIR-1 may exert different functions on T cells and monocytes/macrophages and suggest that LAIR-1 may be a novel therapeutic target for the treatment of RA.     

Functional heterogeneity of murine macrophage precursor cells from spleen and bone marrow

We previously reported that highly purified bone marrow-derived macrophage precursors can exert strong spontaneous cytotoxicity against YAC-1 tumor cells, Candida albicans, and protozoa of the genus Leishmania. In the present paper, evidence is shown that macrophage precursors in normal untreated mice are not confined to the bone marrow compartment but can also be found in the spleen. These organ-associated cells, which have the same buoyant density as large granular lymphocytes, have been positively sorted by means of an indirect rosetting technique employing the macrophage-specific monoclonal antibodies F4/80 and M143. The rosetting fractions represented an extremely homogeneous population of macrophage precursors characterized by high candidacidal and natural killer activity and by a strong proliferative response to the macrophage-specific colony-stimulating factor CSF-1. Spleen- and bone marrow-derived macrophage precursors differed in their target selectivity. In addition, the mature macrophages derived in vitro from these two precursor populations displayed striking differences in their candidacidal activity. The implications of these findings in relationship to heterogeneity in the macrophage differentiation line are discussed.