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

Phenotypic variation in myocardial macrophage populations suggests a role for macrophage activation in SIV-associated cardiac disease

Cardiac abnormalities are common in HIV-infected individuals, and have been especially well documented as contributors to mortality in HIV-infected children. Underlying pathogenetic mechanisms responsible for myocardial disease in HIV-infection remain imperfectly understood. SIV-infected rhesus monkeys develop a spectrum of cardiac lesions similar to those seen in HIV-infected people, providing an important model for pathogenesis studies. Retrospective analysis of cardiac tissue collected at necropsy from SIV-infected rhesus monkeys was performed to evaluate myocardial macrophage and dendritic cell populations as a function of previously quantitated lymphocytic inflammatory infiltrates and cardiomyocyte degeneration or necrosis. Variations in the size and phenotype of macrophage and dendritic cell populations were examined as possible contributors to the pathogenesis of SIV-associated inflammatory lesions. Macrophages labeling immunohistochemically for CD163 differed substantially from macrophages labeling for HAM56 in overall number, distribution across groups, involvement in inflammatory clusters, correlation with the DC-SIGN(+) subpopulation of macrophages, and correlation with numbers of SIV-infected cells. CD163(+) macrophages occurred in significantly higher numbers in uninflamed hearts from SIV-infected animals than in hearts from SIV-infected animals with myocarditis or uninfected controls (p < 0.01). Numbers of CD163(+) cells correlated positively with numbers of SIV-infected cells (p < 0.05) suggesting that the CD163(+) population was associated with decreased inflammatory infiltration and reduced control of virus within the heart. As CD163 has been associated with nonclassical macrophage activation and an antiinflammatory phenotype, these results suggest that a balance between classical and nonclassical activation may affect levels of inflammatory infiltration and of myocardial virus burden.

Interleukin-4 induction of the CC chemokine TARC (CCL17) in murine macrophages is mediated by multiple STAT6 sites in the TARC gene promoter

Background

Macrophages (Mθ) play a central role in the innate immune response and in the pathology of chronic inflammatory diseases. Macrophages treated with Th2-type cytokines such as Interleukin-4 (IL-4) and Interleukin-13 (IL-13) exhibit an altered phenotype and such alternatively activated macrophages are important in the pathology of diseases characterised by allergic inflammation including asthma and atopic dermatitis. The CC chemokine Thymus and Activation-Regulated Chemokine (TARC/CCL17) and its murine homologue (mTARC/ABCD-2) bind to the chemokine receptor CCR4, and direct T-cell and macrophage recruitment into areas of allergic inflammation. Delineating the molecular mechanisms responsible for the IL-4 induction of TARC expression will be important for a better understanding of the role of Th2 cytokines in allergic disease.

Results

We demonstrate that mTARC mRNA and protein are potently induced by the Th2 cytokine, Interleukin-4 (IL-4), and inhibited by Interferon-γ (IFN-γ) in primary macrophages (Mθ). IL-4 induction of mTARC occurs in the presence of PI3 kinase pathway and translation inhibitors, but not in the absence of STAT6 transcription factor, suggesting a direct-acting STAT6-mediated pathway of mTARC transcriptional activation. We have functionally characterised eleven putative STAT6 sites identified in the mTARC proximal promoter and determined that five of these contribute to the IL-4 induction of mTARC. By in vitro binding assays and transient transfection of isolated sites into the RAW 264.7 Mθ cell-line, we demonstrate that these sites have widely different capacities for binding and activation by STAT6. Site-directed mutagenesis of these sites within the context of the mTARC proximal promoter revealed that the two most proximal sites, conserved between the human and mouse genes, are important mediators of the IL-4 response.

Conclusion

The induction of mTARC by IL-4 results from cooperative interactions between STAT6 sites within the mTARC gene promoter. Significantly, we have shown that transfer of the nine most proximal mTARC STAT6 sites in their endogenous conformation confers potent (up to 130-fold) IL-4 inducibility on heterologous promoters. These promoter elements constitute important and sensitive IL-4-responsive transcriptional units that could be used to drive transgene expression in sites of Th2 inflammation in vivo.

Regulation of effector T cells by antigen-presenting cells via interaction of the C-type lectin MGL with CD45

Homeostatic control of T cells involves tight regulation of effector T cells to prevent excessive activation that can cause tissue damage and autoimmunity. Little is known, however, about whether antigen-presenting cells (APCs) are also involved in maintaining immune system homeostasis once effector T cells are stimulated. Here we found that immature APCs downregulated effector T cell function by a mechanism involving the C-type lectin MGL expressed by APCs. Glycosylation-dependent interactions of MGL with CD45 on effector T cells negatively regulated T cell receptor-mediated signaling and T cell-dependent cytokine responses, which in turn decreased T cell proliferation and increased T cell death. Thus, regulation of effector T cells by MGL expressed on APCs may provide a target for regulating chronic inflammatory and autoimmune diseases.

Biochemical and functional characterization of three activated macrophage populations

We generated three populations of macrophages (Mphi) in vitro and characterized each. Classically activated Mphi (Ca-Mphi) were primed with IFN-gamma and stimulated with LPS. Type II-activated Mphi (Mphi-II) were similarly primed but stimulated with LPS plus immune complexes. Alternatively activated Mphi (AA-Mphi) were primed overnight with IL-4. Here, we present a side-by-side comparison of the three cell types. We focus primarily on differences between Mphi-II and AA-Mphi, as both have been classified as M2 Mphi, distinct from Ca-Mphi. We show that Mphi-II more closely resemble Ca-Mphi than they are to AA-Mphi. Mphi-II and Ca-Mphi, but not AA-Mphi, produce high levels of NO and have low arginase activity. AA-Mphi express FIZZ1, whereas neither Mphi-II nor Ca-Mphi do. Mphi-II and Ca-Mphi express relatively high levels of CD86, whereas AA-Mphi are virtually devoid of this costimulatory molecule. Ca-Mphi and Mphi-II are efficient APC, whereas AA-Mphi fail to stimulate efficient T cell proliferation. The differences between Ca-Mphi and Mphi-II are more subtle. Ca-Mphi produce IL-12 and give rise to Th1 cells, whereas Mphi-II produce high levels of IL-10 and thus, give rise to Th2 cells secreting IL-4 and IL-10. Mphi-II express two markers that may be used to identify them in tissue. These are sphingosine kinase-1 and LIGHT (TNF superfamily 14). Thus, Ca-Mphi, Mphi-II, and AA-Mphi represent three populations of cells with different biological functions.

Pathogenesis of spondyloarthritis: Insights from synovial membrane studies

Here, we review histopathologic studies of the cellular and molecular pathways of spondyloarthritis (SpA) synovial inflammation. In contrast with lymphocytes, specific macrophage subsets and polymorphonuclear cells selectively increase in SpA synovitis, correlate with global disease activity, decrease rapidly upon effective treatment with tumor necrosis factor (TNF)-alpha blockers, and serve as valuable biomarkers for treatment response in SpA. Functionally, increased Toll-like receptor triggering may be responsible for the proinflammatory response of these cells. Therefore, we propose that an exaggerated response of the innate immune system in genetically susceptible patients rather than a classic, lymphocyte-mediated autoimmune process is involved in the pathogenesis of SpA.

Helminth parasites--masters of regulation

Immune regulation by parasites is a global concept that includes suppression, diversion, and conversion of the host immune response to the benefit of the pathogen. While many microparasites escape immune attack by antigenic variation or sequestration in specialized niches, helminths appear to thrive in exposed extracellular locations, such as the lymphatics, bloodstream, or gastrointestinal tract. We review here the multiple layers of immunoregulation that have now been discovered in helminth infection and discuss both the cellular and the molecular interactions involved. Key events among the host cell population are dominance of the T-helper 2 cell (Th2) phenotype and the selective loss of effector activity, against a background of regulatory T cells, alternatively activated macrophages, and Th2-inducing dendritic cells. Increasingly, there is evidence of important effects on other innate cell types, particularly mast cells and eosinophils. The sum effect of these changes to host reactivity is to create an anti-inflammatory environment, which is most favorable to parasite survival. We hypothesize therefore that parasites have evolved specific molecular strategies to induce this conducive landscape, and we review the foremost candidate immunomodulators released by helminths, including cytokine homologs, protease inhibitors, and an intriguing set of novel products implicated in immune suppression.

Transcriptional Profiling Reveals Complex Regulation of the Monocyte IL-1β System by IL-13

IL-4 and IL-13 are prototypic Th2 cytokines that generate an "alternatively activated" phenotype in macrophages. We used high-density oligonucleotide microarrays to investigate the transcriptional profile induced in human monocytes by IL-13. After 8-h stimulation with IL-13, 142 genes were regulated (85 increased and 57 decreased). The majority of these genes were related to the inflammatory response and innate immunity; a group of genes related to lipid metabolism was also identified, with clear implications for atherosclerosis. In addition to characteristic markers of alternatively activated macrophages, a number of novel IL-13-regulated genes were seen. These included various pattern recognition receptors, such as CD1b/c/e, TLR1, and C-type lectin superfamily member 6. Several components of the IL-1 system were regulated. IL-1RI, IL-1RII, and IL-1Ra were all up-regulated, whereas the IL-1beta-converting enzyme, caspase 1, and IRAK-M were down-regulated. LPS-inducible caspase 1 enzyme activity was also reduced in IL-13-stimulated monocytes, with a consequent decrease in pro-IL-1beta processing. These data reveal that IL-13 has a potent effect on the transcriptional profile in monocytes. The IL-13-induced modulation of genes related to IL-1 clearly highlights the tightly controlled and complex levels of regulation of the production and response to this potent proinflammatory cytokine.

Differential expression and response to anti-TNFα treatment of infiltrating versus resident tissue macrophage subsets in autoimmune arthritis

Synovial macrophages play a pivotal role in the pathogenesis of chronic autoimmune arthritis by contributing to local inflammation and tissue damage and are therefore a primary target for therapeutic intervention. The aim of the present study was to investigate in more detail the relative contribution of different synovial macrophage subsets with potentially different inflammatory or anti-inflammatory functions by analysing the two most frequent forms of human autoimmune arthritis, spondyloarthropathy (SpA) and rheumatoid arthritis (RA). Both infiltrating macrophages from peripheral blood expressing myeloid-related proteins (MRP) 8 and 14, and resident tissue macrophages expressing CD163 were abundant in inflamed synovium. Whereas the global number of synovial macrophages was similar in both diseases, infiltrating macrophages were increased in the RA lining layer in contrast with resident tissue macrophages, which were more frequently observed in SpA. Soluble MRP8/MRP14 complexes, which were secreted locally in the joint during the infiltration process, were increased in the serum of arthritis patients and, in contrast with soluble CD163 shed from resident tissue macrophages, correlated well with global inflammatory parameters. Treatment in vivo with anti-TNFalpha had a rapid and pronounced effect on the infiltration of MRP-positive macrophages into tissues, as evidenced by histopathological analysis and serum MRP8/MRP14 levels. Taken together, these data support an important role for infiltrating versus resident tissue macrophages in human autoimmune synovitis and indicate that macrophage products such as soluble MRP8/MRP14 complexes are valuable biomarkers for the experimental and clinical monitoring of specific disease mechanisms in vivo.

Toward an understanding of the interaction between filarial parasites and host antigen-presenting cells

Lymphatic filarial infection, from an immunologic point of view, is one of the most complex parasite infections. Not only are there different clinical manifestations that reflect differing immune responses, but the parasite's multiple stages, each with distinct anatomic tropism, add a compartmental layer of complexity to an already complicated process. Moreover, these parasites have finely tuned immune evasion strategies that enable escape from the innate immune system. As different stages of the parasite interact with different types of antigen-presenting cells that, in turn, may play a significant role in shaping the subsequent adaptive immune response, the focus of this review is to provide insight into the interaction between filarial parasites and antigen-presenting cells with an eye toward understanding how they influence parasite antigen-driven T-cell responses.

Association of CD163+ macrophages and local production of soluble CD163 with decreased lymphocyte activation in spondylarthropathy synovitis

OBJECTIVE

Since CD163+ macrophages are selectively increased in spondylarthropathy (SpA) synovitis, we investigated the role of CD163+ macrophages in synovial inflammation.

METHODS

Synovial biopsy samples from 26 SpA and 23 rheumatoid arthritis (RA) patients were analyzed for macrophage and lymphocyte subsets. Synovial fluid (SF) samples were analyzed by Western blotting and enzyme-linked immunosorbent assay for soluble CD163 (sCD163) and by flow cytometry for lymphocyte activation. We also analyzed sCD163 in sera from 100 SpA patients, 23 RA patients, 20 healthy controls, and 20 SpA patients treated with infliximab. Polymorphism of haptoglobin (Hp), the CD163 ligand, was determined in 130 SpA and 23 RA patients.

RESULTS

CD163+ macrophages, but not CD68+ macrophages, were significantly increased in SpA versus RA synovium and in HLA-B27+ versus HLA-B27- SpA. Despite similar lymphocyte numbers, activated lymphocytes (CD69+) were significantly decreased in SpA versus RA patients, with an inverse correlation between CD163 and CD69 levels. Local production of sCD163 was evidenced by a 5-7-fold higher level of sCD163 in SF than in serum and by the correlation with synovial lining CD163+ macrophages in SpA. SF sCD163 levels correlated directly with global inflammation but correlated inversely with CD69+ SF T lymphocytes in the synovium. In contrast, serum sCD163 levels were only moderately increased, did not correlate with SF sCD163 levels or parameters of inflammation, and were unaffected by infliximab therapy. The distribution of Hp polymorphism was not altered in SpA and was not related to CD163 expression.

CONCLUSION

Increased numbers of CD163+ macrophages in SpA synovium and local production of sCD163 are associated with global inflammation as well as impairment of T cell activation, suggesting a dual role for CD163+ macrophages in SpA synovitis.

CCL17 and IL-10 as effectors that enable alternatively activated macrophages to inhibit the generation of classically activated macrophages

Classically activated macrophages (CAMphi) have been described as a major effector cell on the host's innate immunities. However, CAMphi are not generated in immunocompromised hosts whose alternatively activated macrophages (AAMphi) predominate. In this study, the mechanism by which AAMphi suppress the ability of resident macrophages (RMphi) to generate CAMphi was investigated. AAMphi were isolated from peritoneal exudates of mice 2 days after third-degree thermal injuries affecting 15% total body surface area. CAMphi were generated from RMphi (peritoneal Mphi from normal mice) through stimulation with CpG DNA, a typical CAMphi inducer. RMphi did not polarize to CAMphi when they were cultured with AAMphi in a dual-chamber Transwell even when supplemented with CpG DNA. In addition, RMphi stimulated with CpG DNA did not convert to CAMphi when they were cultured with the culture fluids of AAMphi (AAMphi Culture-Sup). AAMphi Culture-Sup contained IL-6, IL-10, CCL17, PGE(2), and TGF-beta. Among these, CCL17 and IL-10 inhibited CAMphi generation. The ability of AAMphi Culture-Sup to inhibit CAMphi generation was eliminated when the Culture-Sup was treated with a mixture of mAbs directed against CCL17 and IL-10. These results indicate that CCL17 and IL-10 released from AAMphi inhibit CAMphi generation from RMphi stimulated with CpG DNA.

Nitric oxide-independent CTL suppression during tumor progression: association with arginase-producing (M2) myeloid cells

Most of the mice bearing a s.c. BW-Sp3 lymphoma tumor mount a CD8(+) T cell-mediated response resulting in tumor regression. Nonetheless, tumor progression occurs in some of the recipients and is associated with CTL inactivity. We demonstrated that T cell-activating APC were induced in regressors whereas T cell suppressive myeloid cells predominated in the spleen of progressors. Indeed, in vitro depletion of either the adherent or the CD11b(+) populations restored T cell cytotoxicity and proliferation in these mice. This CTL inhibition was cell-to-cell contact-dependent but not mediated by NO. However, the same progressor suppressive cells prevented the activity of in vitro-restimulated CTLs derived from regressors in a cell-to-cell contact and NO-dependent fashion. Thus, either the NO-dependent or -independent suppressive pathway prevailed, depending on the target CTL population. In addition, the suppressive population expressed a high arginase activity, suggesting an association of the suppressive phenotype with alternatively activated (M2) myeloid cells. However, the high arginase activity is not directly involved in the suppressive process. Our results provide new insights for myeloid cell-mediated CTL inhibition during cancer progression.

IL-4 down-regulates anaphylatoxin receptors in monocytes and dendritic cells and impairs anaphylatoxin-induced migration in vivo

Anaphylatoxins mobilize leukocytes to the sites of inflammation. In the present study we investigated the impact of GM-CSF, IL-4, and IFN-gamma on anaphylatoxin receptor expression in monocytes and dendritic cells (DC). IL-4 was identified as the strongest down-regulator of the receptors for C5a and C3a in monocytes and monocyte-derived DC (MoDC). To study the impact of IL-4 on anaphylatoxin-induced chemotaxis, an in vivo migration model was established. For this purpose, human monocytes and MoDC were injected i.v. into SCID mice that at the same time received anaphylatoxins into the peritoneal cavity. A peritoneal influx of human monocytes could be demonstrated by 4 h after injections of C5a and C3a. In line with receptor down-regulation, IL-4 treatment inhibited in vivo mobilization of human monocytes and MoDC in response to C5a and C3a. In addition to its effects on human cells, IL-4 reduced C5a receptors in murine bone marrow-derived DC and impaired recruitment of labeled bone marrow-derived DC in syngeneic BALB/c mice to i.p. injected C5a. Overall, these data suggest that inhibition of a rapid anaphylatoxin-induced mobilization of monocytes and DC to inflamed tissues represents an important anti-inflammatory activity of the Th2 cytokine IL-4.

Macrophages in chronic type 2 inflammation have a novel phenotype characterized by the abundant expression of Ym1 and Fizz1 that can be partly replicated in vitro

Using a murine model of nematode infection, we have discovered macrophages that display a novel phenotype that may be characteristic of macrophages in chronic type 2 inflammation. These nematode-elicited macrophages (NeMphi) are characterized by two unique features: the ability to actively suppress proliferation of a broad range of cell types and the high level expression of two novel macrophage genes, Ym1 and Fizz1. NeMphi also show some similarities with in vitro-derived 'alternatively activated macrophages' such as the downregulation of inflammatory cytokines. We therefore investigated how much of the phenotype discovered in vivo could be replicated by activation with Th2 cytokines in vitro. Fizz1 and Ym1 were upregulated by IL-4 and IL-13 in vitro but at a considerably lower level than in NeMphi. In vitro treatment with IL-4 could also partly replicate the ability of NeMphi to block cellular proliferation. As well as the quantitative differences in gene expression and suppressive phenotype, we also observed phenotypic differences in the cell morphology between macrophages activated in vivo and in vitro. Although this study illustrated that macrophages activated in chronic inflammation have distinct features that cannot be readily reproduced in vitro it also demonstrated that some features of the complex NeMphi phenotype can be replicated by treatment of cultured macrophages with Th2 cytokines. In future, we hope to use in vitro analysis to help define the pathways that lead to this distinctive in vivo macrophage phenotype.

Infection stage-dependent modulation of macrophage activation in Trypanosoma congolense-resistant and -susceptible mice

The contribution of cytokines and chemokines to resistance and susceptibility to African trypanosomiasis remains controversial. In the present study, the levels of type I and type II cytokines and of the MCP-1 chemokine were compared during the early and late stages of Trypanosoma congolense infection in susceptible BALB/c and resistant C57BL/6 mice. Moreover, the status of macrophage activation was compared in these animals by analyzing the inducible nitric oxide synthase-arginase balance, tumor necrosis factor secretion, and expression of the FIZZ1 and YM genes. Data show that changing from a predominant type I cytokine environment in the early stage of infection to a predominant type II cytokine environment and an enhanced MCP-1 secretion in the late stage of infection correlates with resistance to T. congolense. Concomitantly, macrophage activation evolves from a classical to a predominant alternative phenotype. We further confirmed that the simultaneous occurrence of type I/type II cytokines in the early stage of infection in susceptible BALB/c mice, reflected by the presence of macrophages exhibiting a mixed classical/alternative activation phenotype, is associated with uncontrolled parasite growth and early death. Interleukin-4 (IL-4) and IL-13 signaling did not influence the susceptibility of BALB/c mice to T. congolense infection and interestingly were not the main trigger to alternative macrophage activation. In T. congolense-resistant C57BL/6 mice, our results corroborated the induction of FIZZ1 and YM gene expressions with the alternative pathway of macrophage activation. In susceptible BALB/c mice, however, YM but not FIZZ1 induction reflected the emergence of alternatively activated macrophages. Hence, the FIZZ1 and YM genes may be useful markers to discriminate between distinct populations of alternatively activated macrophages.

CD80+Gr-1+ myeloid cells inhibit development of antifungal Th1 immunity in mice with candidiasis

To find out whether polymorphonuclear neutrophils (PMN), abundantly recruited in disseminated Candida albicans infection, could directly affect the activation of Th cells we addressed the issues as to whether murine PMN, like their human counterparts, express costimulatory molecules and the functional consequence of this expression in terms of antifungal immune resistance. To this purpose, we assessed 1) the expression of CD80 (B7-1) and CD86 (B7-2) molecules on peripheral, splenic, and inflammatory murine Gr-1+ PMN; 2) its modulation upon interaction with C. albicans in vitro, in vivo, and in human PMN; 3) the effect of Candida exposure on the ability of murine PMN to affect CD4+ Th1 cell proliferation and cytokine production; and 4) the mechanism responsible for this effect. Murine PMN constitutively expressed CD80 molecules on both the surface and intracellularly; however, in both murine and human PMN, CD80 expression was differentially modulated upon interaction with Candida yeasts or hyphae in vitro as well as in infected mice. The expression of the CD86 molecule was neither constitutive nor inducible upon exposure to the fungus. In vitro, Gr-1+ PMN were found to inhibit the activation of IFN-gamma-producing CD4+ T cells and to induce apoptosis through a CD80/CD28-dependent mechanism. A population of CD80+Gr-1+ myeloid cells was found to be expanded in conventional as well as in bone marrow-transplanted mice with disseminated candidiasis, but its depletion increased the IFN-gamma-mediated antifungal resistance. These data indicate that alternatively activated PMN expressing CD80 may adversely affect Th1-dependent resistance in fungal infections.

Only the soluble form of the scavenger receptor CD163 acts inhibitory on phorbol ester-activated T-lymphocytes, whereas membrane-bound protein has no effect

The extracellular moiety of the hemoglobin/haptoglobin scavenger receptor CD163 (RM3/1 antigen) can be shed from monocytes and is a normal plasma component. We found that in a dose-dependent manner soluble CD163 induces a decrease in CD69 expression, a reduced [(3)H]thymidine uptake and a down-regulated matrix metalloproteinase-9 RNA expression in phorbol myristate acetate-stimulated T-cells. Co-culturing T-cells on transgenic fibroblasts, expressing membrane-bound CD163, yielded no differences compared to culture on non-transfected cells. We conclude that CD163 has at least two distinct functions: the clearance of hemoglobin in its cell-bound form and participation in anti-inflammation as a soluble factor, exhibiting cytokine-like functions.

IL-4 dependent alternatively-activated macrophages have a distinctive in vivo gene expression phenotype

BACKGROUND

"Alternatively-activated" macrophages are found in Th2-mediated inflammatory settings such as nematode infection and allergic pulmonary inflammation. Due in part to a lack of markers, these cells have not been well characterized in vivo and their function remains unknown.

RESULTS

We have used murine macrophages elicited by nematode infection (NeM(phi)) as a source of in vivo derived alternatively activated macrophages. Using three distinct yet complementary molecular approaches we have established a gene expression profile of alternatively activated macrophages and identified macrophage genes that are regulated in vivo by IL-4. First, genes abundantly expressed were identified by an expressed sequence tag strategy. Second, an array of 1176 known mouse genes was screened for differential expression between NeM(phi) from wild type or IL-4 deficient mice. Third, a subtractive library was screened to identify novel IL-4 dependent macrophage genes. Differential expression was confirmed by real time RT-PCR analysis.

CONCLUSIONS

Our data demonstrate that alternatively activated macrophages generated in vivo have a gene expression profile distinct from any macrophage population described to date. Several of the genes we identified, including those most abundantly expressed, have not previously been associated with macrophages and thus this study provides unique new information regarding the phenotype of macrophages found in Th2-mediated, chronic inflammatory settings. Our data also provide additional in vivo evidence for parallels between the inflammatory processes involved in nematode infection and allergy.

Macrophage subpopulations in rheumatoid synovium: reduced CD163 expression in CD4+ T lymphocyte-rich microenvironments

OBJECTIVE

The cell surface glycoprotein CD163 is a member of the cysteine-rich scavenger receptor family, highly specific for leukocytes of the mononuclear phagocyte lineage. In vitro, it is induced by glucocorticoids, interleukin-6 (IL-6), and IL-10 and down-regulated by interferon-gamma (IFNgamma), indicating that it has a role in antiinflammatory or other immunomodulatory pathways. We assessed CD163 expression in microenvironments within rheumatoid arthritis (RA) synovium to clarify the relationships among CD4+ T lymphocytes, IFNgamma, and macrophage function in RA.

METHODS

Double immunofluorescence and serial immunoenzymatic studies were performed on normal, osteoarthritic, and RA synovium and tonsil with antibodies to CD163, CD45, CD68, CD14, CD3, CD4, CD8, CD19, and IFNgamma.

RESULTS

CD163 was observed on all CD14+ cells in synovium and tonsil with the exception of cells within larger T lymphocyte clusters in synovium and within tonsillar follicles. All brightly CD14+ cells in or around vessel walls (interpreted as immigrant monocytes) were CD163+. CD163 labeled fewer cells than did CD68 in synovial intima, but all CD45+ intimal cells were CD163+. CD4+,IFNgamma+ T lymphocytes in RA synovium were chiefly localized within clusters containing CD68+, CD163- cells.

CONCLUSION

Within RA synovium, CD163 has major advantages as a macrophage marker and does not appear to be restricted to "mature" macrophages. CD163 discriminates between synovial macrophages and synovial intimal fibroblasts, which also stain positively for CD68 in diseased tissue.

Cruzipain, a major Trypanosoma cruzi antigen, conditions the host immune response in favor of parasite

We recently demonstrated that humoral immune response to cruzipain, a major antigen of Trypanosoma cruzi parasite, is implicated in the pathogenesis of experimental Chagas' disease. In the present study, the spleen cell phenotype and the cytokine profile induced by cruzipain in immunized mice were analyzed. The results showed that cruzipain increases the number of spleen cells with large size and granularity. Splenocyte populations with CD19(+), Mac-1(+), Gr-1(+) and CD11c(+) positive surface markers significantly increased in immune mice compared to controls ones. Histological study revealed the presence of high number of megacariocyte and granulocyte-macrophage progenitors, indicating extramedullary hemopoiesis in spleens of immune mice. The finding of high levels of IL-4, IL5 and IL-10 and low levels of IFN-gamma and IL-12 in supernatants of immune cells stimulated with cruzipain indicates a preferential activation of T2 type cells in immune animals. To investigate the role of innate immunity cells, the classical and alternative metabolic pathways of spleen macrophages from immune mice stimulated by cruzipain were also studied. The results showed an increase of urea associated with a decrease of nitrite levels, suggesting that cruzipain up-regulates the arginase way. Therefore, cruzipain leads to T2 type cytokine profile which may enhance the arginase via in the macrophages promoting a susceptible mechanism to infection. Thus, we postulate that during T. cruzi infection, cruzipain could be used by the parasite to spread inside the host.

Stabilin-1 and -2 constitute a novel family of fasciclin-like hyaluronan receptor homologues

MS-1, a high-molecular-mass protein expressed by non-continuous and angiogenic endothelial cells and by alternatively activated macrophages (Mphi2), and the hepatic sinusoidal endothelial hyaluronan clearance receptor are similar with respect to tissue distribution and biochemical characteristics. In the present study we purified these proteins by immuno- and hyaluronan-affinity chromatography respectively, sequenced tryptic peptides and generated full-length cDNA sequences in both mouse and human. The novel genes, i.e. stabilin-1 and stabilin-2, code for homologous transmembrane proteins featuring seven fasciclin-like adhesion domains, 18-20 epidermal-growth-factor domains, one X-link domain and three to six B-(X(7))-B hyaluronan-binding motifs. Northern-blotting experiments revealed the presence of both stabilins in organs with predominant endothelial sinuses such as liver, spleen and lymph node: stabilin-1 mRNA was also detected in organs with predominant Mphi2 cells, such as placenta, and in interleukin-4/glucocorticoid-stimulated Mphi2 cells in vitro. A polyclonal antibody made against human recombinant stabilin-1 confirmed the expression of stabilin-1 protein in splenic sinus endothelial cells in vivo and in Mphi2 in vitro. On the basis of high similarity at the protein level and the unique domain composition, which differs from that of all other known fasciclin-like proteins and hyaluronan receptors, stabilin-1 and stabilin-2 define a novel family of fasciclin-like hyaluronan receptor homologues that might play a role in cell-cell and cell-matrix interactions in vascular function and inflammatory processes.

Blockade of B7/CD28 in mixed lymphocyte reaction cultures results in the generation of alternatively activated macrophages, which suppress T-cell responses

Blockade of B7/CD28 costimulation allows human haploidentical bone marrow transplantation without graft-versus-host disease. This study shows that blockade of B7/CD28 in anergizing mixed lymphocyte reaction (MLR) cultures of peripheral blood mononuclear cells results in the generation of alternatively activated macrophages (AAMphi). In contrast, priming MLR cultures result in generation of classically activated macrophages (CAMphi). AAMphi had enhanced expression of CD14, major histocompatibility complex class II, and CD23; produced alternative macrophage activation-associated CC-chemokine 1 (AMAC-1) chemokine; and displayed increased phagocytotic activity but decreased ability for antigen presentation. Suppression subtractive hybridization revealed that although AAMphi had undergone terminal maturation and differentiation, they entered a distinct gene expression program as compared with CAMphi and selectively expressed beta2-microglobulin, lysozyme, ferritin heavy and light chain, and the scavenger receptors macrophage mannose receptor and sortilin. Anergic T cells isolated from cultures that led to the development of AAMphi produced low amounts of interleukin-2 (IL-2), IL-4, and interferon-gamma, but high amounts of IL-10. Addition of anti-IL-10 neutralizing monoclonal antibody in anergizing cultures reversed the functional characteristics of AAMphi, indicating that at least one mechanism involved in the generation of AAMphi was mediated by IL-10. Importantly, when added in MLR cultures, AAMphi suppressed T-cell responses. Therefore, besides direct inhibition of T-cell costimulation, blockade of B7/CD28 may facilitate induction of T-cell unresponsiveness by generating AAMphi. Because in healthy individuals, AAMphi are found in the placenta and lung, where they protect from unwanted immune reactivity, the results suggest that AAMphi may play a critical role in the induction of transplantation tolerance.

CXCR4 expression on monocytes is up-regulated by dexamethasone and is modulated by autologous CD3+ T cells

Chemokines and their receptors regulate cell migration to sites of inflammation. The glucocorticoid dexamethasone has potent anti-inflammatory effects, yet paradoxically up-regulates expression of some cytokine receptors. We have examined the effects of dexamethasone on chemokine receptor expression. Using an RNase protection assay, we show that dexamethasone up-regulates human peripheral blood mononuclear cell (PBMC) expression of CXCR4 mRNA. Flow cytometric analysis demonstrated that increased expression of CXCR4, but not CXCR1 and CXCR2, occurred on both monocytes and CD3+ T cells in PBMC mixed cultures. A stromal-derived factor (SDF)-1alpha-mediated calcium influx was detected on monocytes. Basal levels of CXCR4 expression on purified monocytes were lower when compared with monocytes in mixed PBMC cultures. Co-culture of monocytes with purified CD3+ T cells led to enhanced basal expression of CXCR4 on monocytes. The use of transwells to partition CD3+ T cells resulted in increased CXCR4 expression on monocytes, suggesting that CD3+ T-cell derived soluble factors regulate CXCR4 expression.

Activation of the stem cell-derived tyrosine kinase/RON receptor tyrosine kinase by macrophage-stimulating protein results in the induction of arginase activity in murine peritoneal macrophages

Regulation of macrophage activities in response to inflammatory stimuli must be finely tuned to promote an effective immune response while, at the same time, preventing damage to the host. Our lab and others have previously shown that macrophage-stimulating protein (MSP), through activation of its receptor RON, negatively regulates NO production in response to IFN-gamma and LPS by inhibiting the expression of inducible NO synthase (iNOS). Furthermore, activated macrophages from mice harboring targeted mutations in RON produce increased levels of NO both in vitro and in vivo, rendering them more susceptible to LPS-induced endotoxic shock. In this study, we demonstrate that stimulation of murine peritoneal macrophages with MSP results in the RON-dependent up-regulation of arginase, an enzyme associated with alternative activation that competes with iNOS for the substrate L-arginine, the products of which are involved in cell proliferation and matrix synthesis. Expression of other genes associated with alternative activation, including scavenger receptor A and IL-1R antagonist, is also up-regulated in MSP-stimulated murine macrophages. Stimulation of cells with IFN-gamma and LPS blocks the ability of MSP to induce arginase activity. However, pretreatment of cells with MSP results in the up-regulation of arginase and inhibits their ability to produce NO in response to IFN-gamma and LPS, even in the presence of excess substrate, suggesting that the inhibition of NO by MSP occurs primarily through its ability to regulate iNOS expression.

Late effects of radiotherapy on oral mucosa in humans

In order to gain further understanding of the late effects of radiotherapy on oral mucosa, we analysed the histomorphological alterations, the cell populations in the subepithelial tissue, and the endothelial expression pattern of different adhesion molecules. Biopsies were taken from patients before irradiation, directly after 60 Gy, and 6-12 months after radiotherapy. Besides the histomorphological evaluation of the vessels, the endothelial expression of ICAM-1, VCAM-1 and E-selectin was determined as well as the distribution of LFA-1-, Mac-1-, VLA-4-, RM3/1-, 27E10- and 25F9-bearing cells in the subepithelial tissue. The expression of ICAM-1 was downregulated after radiotherapy, whereas the percentage of LFA-1- and VLA-4-bearing cells increased. VCAM-1 remained at low levels. The subepithelial infiltration was still dominated by RM3/1-positive macrophages. The number of vessels decreased, while the lumen of the remaining vessels increased. In conclusion, the late effects of radiotherapy are characterized by a decreased number of blood vessels and by significantly different expression patterns of the adhesion molecules studied, and of integrins and macrophage subpopulations, compared to the conditions before irradiation and directly after irradiation with 60 Gy.

Soluble CD163 inhibits phorbol ester-induced lymphocyte proliferation

CD163 is a member of the scavenger receptor cysteine-rich family which is expressed exclusively on human monocytes and macrophages. Upon an inflammatory stimulus the protein is shed rapidly from the membranes' surface. CD163 expression is significantly upregulated by glucocorticoids and IL-10. While the membrane-bound form of CD163 was recently identified as scavenger receptor for hemoglobin-haptoglobin complexes, there is no information about a possible role of the shed soluble CD163. It has been suggested earlier that CD163 plays a pivotal role in the downregulatory phase of inflammation. However, it has remained elusive so far as to how this protein might influence the inflammatory process. We have now identified a potential direct anti-inflammatory effect mediated by soluble CD163. The highly purified protein statistically significantly inhibits phorbol ester-induced human T-lymphocyte activation, thus attenuating the immune response to the inflammatory mediator.

Tumor-induced immune dysfunctions caused by myeloid suppressor cells

In the late 1970s, several findings suggested that accessory cells distinct from lymphocytes might suppress immune reactivity in tumor-bearing hosts. Studies in animal models and patients later confirmed that cells driven to act as dominant immune suppressors by growing cancers could subvert the immune system. These cells have also been termed natural suppressors, a functional definition connoting their ability to hamper various T- and B-lymphocyte responses without prior activation and independently from antigen and MHC restriction. These properties were attributed to distinct cell populations. The phenotypic discrepancies, together with the lack of antigen specificity, have generated serious restraints to research on tumor-induced suppression. Recent evidence indicates that suppressor cells are closely related to immature myeloid precursors and can be found in several situations that can exert adverse effects on the immunotherapy of cancer. The present review is an attempt to address the nature and properties of immature myeloid suppressors and their relationship to dendritic cells and macrophages, with the aim of clarifying the complex network of tumor-induced, negative regulators of the immune system.

IFN-gamma overproduction and high level apoptosis are associated with high but not low virulence Toxoplasma gondii infection

Toxoplasma gondii is an opportunistic intracellular parasite which induces a highly strong type 1 cytokine response. The present study focuses on defining the factors influencing the outcome of infection with tachyzoites of the type I, highly lethal RH strain, relative to the type II, low virulence strain ME49. Infection with the RH strain led to widespread parasite dissemination and rapid death of mice; in contrast, mice survived low virulence strain ME49 infection, and tachyzoite dissemination was much less extensive. Furthermore, massive apoptosis and disintegration of the splenic architecture was characteristic of RH, but not ME49, infection. In addition, hyperinduction of IFN-gamma and lack of NO production were found during RH, in contrast to ME49 infection. These data demonstrate that Toxoplasma strain characteristics exert a profound effect on the host immune response and that the latter itself is a crucial determinant in parasite virulence.

Divergent roles for macrophages in lymphatic filariasis

Macrophages have long been recognized as important cells associated with filarial infection but their function as effectors and/or suppressors has not been elucidated. Recent advances in our understanding of the role that macrophages may play in lymphatic filariasis have come from in vitro studies and mouse models of filarial infection. Based on these new findings, we hypothesize that while dead or dying worms induce the 'classical' activation of macrophages and a subsequent pro-inflammatory response, live and healthy worms secrete products that induce type 2 cytokines and the differentiation of 'alternatively' activated macrophages that downregulate an inflammatory response. Thus, the balance between the 'classical' and 'alternative' activation pathways of macrophages could be an important factor in inflammatory pathology associated with filariasis.

Increase of RM3/1-positive macrophages in radiation-induced oral mucositis

The purpose of this study was to describe the distribution patterns of various leukocyte subpopulations in the oral mucosa during the course of radiotherapy and to determine whether there are dose-dependent alterations, or any correlation between the clinical stages and the population density of specific leukocytes. The distribution and density of various leukocytes in oral mucosa in 13 head and neck cancer patients were immunohistochemically analysed before radiotherapy at 30 and 60 Gy and compared with the clinical degree of oral mucositis. Antibodies were used which characterized different subtypes of macrophages (27E10, 25F9, RM3/1) and recognized epitopes of granulocytes (CD15) and T cells (CD3, CD4, CD8). The study showed that whereas macrophages reactive with RM3/1 increased significantly at 30 Gy (p<0.01) and showed a further increase at 60 Gy (p<0.01), no significant alterations could be detected in the density of macrophages which stained positively for 27E10 or 25F9. Moreover, the percentage of macrophages reactive with RM3/1 showed a non-linear correlation with the clinical mucositis score (p<0.05). No significant alterations were detected in the percentage of T cells and granulocytes, compared with the values before radiotherapy. In conclusion, radiation-induced mucositis is characterized by features of an intermediate stage of an inflammatory response, suggesting active involvement of down-regulatory macrophages in its pathogenesis.

Immortalized myeloid suppressor cells trigger apoptosis in antigen-activated T lymphocytes

We described a generalized suppression of CTL anamnestic responses that occurred in mice bearing large tumor nodules or immunized with powerful recombinant viral immunogens. Immune suppression entirely depended on GM-CSF-driven accumulation of CD11b(+)/Gr-1(+) myeloid suppressor cells (MSC) in secondary lymphoid organs. To further investigate the nature and properties of MSC, we immortalized CD11b(+)/Gr-1(+) cells isolated from the spleens of immunosuppressed mice, using a retrovirus encoding the v-myc and v-raf oncogenes. Immortalized cells expressed monocyte/macrophage markers (CD11b, F4/80, CD86, CD11c), but they differed from previously characterized macrophage lines in their capacities to inhibit T lymphocyte activation. Two MSC lines, MSC-1 and MSC-2, were selected based upon their abilities to inhibit Ag-specific proliferative and functional CTL responses. MSC-1 line was constitutively inhibitory, while suppressive functions of MSC-2 line were stimulated by exposure to the cytokine IL-4. Both MSC lines triggered the apoptotic cascade in Ag-activated T lymphocytes by a mechanism requiring cell-cell contact. Some well-known membrane molecules involved in the activation of apoptotic pathways (e.g., TNF-related apoptosis-inducing ligand, Fas ligand, TNF-alpha) were ruled out as candidate effectors for the suppression mechanism. The immortalized myeloid lines represent a novel, useful tool to shed light on the molecules involved in the differentiation of myeloid-related suppressors as well as in the inhibitory pathway they use to control T lymphocyte activation.

Can cord blood cells support the cytokine storm in GvHD?

Cord blood has a high number of proliferating hematopoietic progenitors and is therefore used as an alternative source of hematopoietic cells for allogeneic transplantation. In addition there is a wider availability of cord blood and a lower cost of procurement compared to bone marrow. However one of the most interesting immunological benefits of a cord blood transplant that has been proposed is the low severity of Graft versus Host Disease (GvHD). This review aims to address some of the immunological reasons why this may be the case by assessing the role of cord blood cytokines in the cytokine storm of GvHD.

Influence of alternatively and classically activated macrophages on fibrogenic activities of human fibroblasts

Activated macrophages regulate fibrogenesis by providing cytokines and growth factors that modulate the proliferation and collagen synthesis of fibroblasts. However, macrophages can be activated in a classical pathway induced by LPS or IFN-gamma and an alternative pathway induced by IL-4 or glucocorticoid. Differently activated macrophages display distinct biological features. To clarify the difference between these two subsets of macrophages in the regulatory mechanisms controlling fibrogenesis, human peripheral blood monocytes were used as the source of macrophages and cocultivation of differently activated macrophages and a fibroblast cell line, WI-38, was performed. Alternatively activated macrophages increased the proliferation index and collagen synthesis of cocultivated WI-38 cells in comparison to untreated monocytes, while classically activated macrophages markedly reduced collagen production of cocultivated WI-38 cells. Additionally, mRNA expression and protein production of TGF-beta(1), PDGF-AA, and PDGF-BB were elevated in alternatively activated macrophages in parallel to their profibrogenic effects. In contrast, expression and production of TNF-alpha, as well as MMP-7, were enhanced in classically activated macrophages. These findings suggested that alternatively activated macrophages enhance fibrogenesis of fibroblasts by providing profibrogenic factors, while classically activated macrophages inhibit fibrogenesis of fibroblasts by releasing antifibrogenic or fibrolytic factors.

Pseudoexons and regulatory elements in the genomic sequence of the beta-chemokine, alternative macrophage activation-associated CC-chemokine (AMAC)-1

Recently, the authors reported the cloning of a novel human CC chemokine of alternatively activated macrophages (AMAC-1), whose expression is induced by Th2-associated cytokines such as interleukin 4 (IL-4), IL-13 and IL-10; vice versa, AMAC-1 expression is inhibited by Th1-associated cytokines such as interferon gamma (IFN-gamma). In order to study the genomic organization and transcriptional regulation of the AMAC-1 gene, genomic clones were isolated by screening a human lambda genomic library. Sequencing of a clone with a 1.7-kb insert gave a partial genomic sequence for the AMAC-1 gene. The complete AMAC-1 genomic sequence was obtained by bioinformational methods and the whole region spanning the AMAC-1 gene was verified by PCR amplification of subfragments and sequencing. The AMAC-1 gene consists of three exons. Whereas exons 2 and 3 were separated by a small intron of 411 bp, exon 1 and exon 2 were separated by 6 kb of non-translated genomic sequence containing two pseudoexons that are not expressed although they feature intact exon/intron boundaries and complete open reading frames. In order to allow a detailed analysis, a 2.7-kb fragment containing the promoter region and the first exon of AMAC-1 gene was cloned into a reporter gene construct. In the AMAC-1 promoter, two possible transcription start points were identified. In addition, several putative regulatory sequences for IL-4- and IFN-gamma-dependent transcriptional pathways were found including STAT6 and STAT1 binding sites as well as several AP-1 and C/EBP elements. Interestingly, a combined STAT6/STAT1 binding element is located in the direct vicinity of the first putative transcription start point. Competitive binding of IL-4-induced STAT6 versus IFN-gamma-induced STAT1 to this site may explain the antagonistic effects these cytokines exert on AMAC-1 expression.

Macrophages from inflamed but not normal glomeruli are unresponsive to anti-inflammatory cytokines

This study examined the properties and responsiveness to cytokines of macrophages purified from normal and nephritic glomeruli to ascertain whether macrophages activated in vivo develop programmed unresponsiveness to cytokines as do bone marrow-derived macrophages in vitro when activated by interferon-gamma (IFN-gamma), tumor necrosis factor (TNF), interleukin-4 (IL-4), or transforming growth factor-beta (TGF-beta). Macrophages from normal glomeruli did not generate nitric oxide (NO) spontaneously but only after treatment with IFN-gamma and TNF-alpha. NO generation by these macrophages was abrogated by administering IL-4, TGF-beta, or TNF-alpha before but not after IFN-gamma treatment. Glomerular macrophages also expressed beta-glucuronidase, which was increased by TGF-beta and decreased by IFN-gamma and TNF. By contrast, glomerular macrophages from rats with nephrotoxic nephritis did not express beta-glucuronidase even after exposure to TGF-beta. Furthermore, they generated NO spontaneously, and this spontaneous generation of NO was not suppressed by IL-4, TGF-beta, or TNF-alpha. Systemic treatment of nephritic rats with IL-4 reduced NO generation by 40% but did not prevent activation, which is similar to the effect of IL-4 on bone marrow-derived macrophages in vitro when given simultaneously with IFN-gamma. We conclude that macrophages infiltrating inflamed glomeruli have developed programmed unresponsiveness to activating cytokines. This may enable them to function appropriately in the complex conditions within an inflammatory focus.

Cytokine production by rabbit alveolar macrophages: differences between activated and suppressor cell phenotypes

The differences between cytokine-producing profiles of activated macrophages (A-M phi) and suppressor macrophages (S-M phi) were examined. A-M phi, which exhibited cytotoxicity against RK-13 cells, were generated from resident rabbit alveolar M phi by treatment with lymphokine solution (culture fluids of rabbit spleen cells stimulated with concanavalin A [Con A]). S-M phi, which were able to inhibit cellular proliferations of rabbit spleen cells stimulated with Con A, were generated from resident alveolar M phi by treatment with 1-methyladenosine (an immunosuppressive molecule in tumourous ascites fluids). When A-M phi were stimulated with lipopolysaccharide (LPS) in vitro, the cells produced significantly more interleukin (IL)-1 (approximately 1.4 times), IL-6 (approximately 2.1 times), IL-12 (approximately 60 times), and tumour necrosis factor-alpha (TNF-alpha) (approximately 37 times) than did resting macrophages (R-M phi) stimulated with LPS as control cells. After the stimulation with LPS, both A-M phi and R-M phi did not produce transforming growth factor-beta (TGF-beta). In contrast, when S-M phi were stimulated with LPS in vitro, the cells produced significantly more TGF-beta (approximately 1.6 times) and significantly less IL-6 (approximately 1.8 times) than did control cells. Also, S-M phi did not produce IL-1, IL-12, and TNF-alpha into their culture fluids after the stimulation with LPS. These results show the differences between cytokine-producing profiles of A-M phi and S-M phi, and characteristics of their cytokine-producing profiles are analogous to T cell subsets. Differences displayed in the cytokine profiles may contribute to the effector (A-M phi) or the suppressor (S-M phi) functions of alveolar M phi.

Cultured murine parenchymal liver cells induce differentiation of bone marrow cells to macrophage-like cells which present antigen to Th1 clones but inhibit their proliferation by nitric oxide and prostaglandins

Suppressor cells were developed from nylon wool nonadherent CD4(-)8(-)TCRbeta(-) bone marrow cells cocultured with parenchymal liver cells for 2.5 days. The major suppressor cell population consisted of nylon wool/plastic dish-adherent, phagocytic Mac-1(+) CD3(-)4(-)8(-) cells (Ad cells), with 34% of the Ad cells being F4/80(+). These Ad cells suppressed the antigen-specific proliferation of Th1 clones in an MHC-nonrestricted manner. They showed a dose-dependent increase in suppressive activity, with both NO and PGE(2) levels in the culture supernatant rising with Ad cell concentration. OVA-pulsed Ad cells (OVA-Ad cells) were found to stimulate IFN-gamma production, resulting in an elevation of the NO and PGE(2) levels in wells containing OVA-specific Th1 clones. No DNA synthesis by these clones was detected in the absence of N(G)-monomethyl-l-arginine and indomethacin, yet the proliferation of the clone was induced in the presence of these chemicals. As proliferation is inhibited by NO and PGE(2) the Ad cells give the impression that they have no antigen-presenting function. This function is MHC-class-II-restricted. If cells such as Ad cells did actually exist in the hepatic sinusoid, they could by their nature play a major role in inducing the early emerging unresponsiveness of T cells in the liver which we reported in a previous paper.

Modulation of inflammation and immunity by arginine supplements

Arginine holds a key position in the cellular functions and interactions that occur during inflammation and immune responses. The competition for arginine as a substrate between nitric oxide synthase and arginase appears to be at the core of the regulation of the inflammatory process. This review examines some of the recently defined effects of arginine on various inflammatory processes and immune cell functions.

Langerhans cells do not express alternative macrophage activation-associated CC chemokine (AMAC)-1

We have cloned a novel human CC chemokine, alternative macrophage activation-associated CC chemokine (AMAC)-1 that is highly homologous to macrophage inflammatory protein (MIP)-1alpha. In contrast to MIP-1alpha, AMAC-1 is induced in macrophages by Th2-associated cytokines IL4, IL13, and IL10 in vitro; in addition, AMAC-1 is expressed by Th1-suppressive alveolar macrophages in vivo. Surprisingly, however, AMAC-1 is also expressed by GM-CSF-induced, in vitro monocyte-derived dendritic cells when treated by IL4. Here, we present a detailed analysis of AMAC-1 expression in monocyte-derived dendritic cells in vitro and show that the prime dendritic cells in vivo, i.e. epidermal Langerhans cells, do not express AMAC-1 mRNA. In conclusion, AMAC-1 is a novel CC chemokine whose Th2-associated expression pattern in alternatively activated suppressor macrophages in vivo and in vitro and its absence from epidermal Langerhans cells in vivo suggest that it may be involved in inhibition of Th1 reactions and in tolerance induction.

Identification of the Integral Membrane Protein RM3/1 on Human Monocytes as a Glucocorticoid-Inducible Member of the Scavenger Receptor Cysteine-Rich Family (CD163)

The RM3/1 Ag is a membrane glycoprotein restricted to human monocytes and macrophages that evolve in the late phase of inflammation. Peptide sequence analysis of the RM3/1 protein revealed similarity to CD163, a member of the scavenger receptor cysteine-rich family. Using specific Abs (RM3/1, Ki-M8), we demonstrate an identical cellular regulation for the RM3/1 and the CD163 protein. Most notably, we show for the first time that CD163 is significantly up-regulated by glucocorticoids. In contrast, the protein is down-regulated by the immunosuppressant cyclosporin A and by phorbol esters, while the inflammatory mediator LPS has no significant influence on the expression. We describe the first isolation of a full-length cDNA of CD163 and expression of the corresponding protein. Several splice variants of CD163 exist, and we elucidated the kinetics of induction of three major mRNA splice variants by fluticasone propionate; another splice variant was proved to be unresponsive to this glucocorticoid. Taken together with a previous result showing an involvement of RM3/1 in adhesion of monocytes to the activated endothelium, we discuss that CD163 might play an important role in inflammatory processes.

Alternative Macrophage Activation-Associated CC-Chemokine-1, a Novel Structural Homologue of Macrophage Inflammatory Protein-1α with a Th2-Associated Expression Pattern

We have cloned a novel human CC-chemokine, alternative macrophage activation-associated CC-chemokine (AMAC)-1. The isolated cDNA clone (803 bp) shows a single open reading frame of 267-bp coding for 89 amino acid residues; mature AMAC-1 protein is predicted to consist of 69 amino acids with a m.w. of 7855. Sequence alignment and 3D-modeling show the typical structural characteristics of CC-chemokines with special features in the receptor-activating domain. AMAC-1 is most closely related to MIP-1α with a cDNA and protein sequence homology of 55% and 59%, respectively. However, the expression pattern of AMAC-1 is directly opposite to that of MIP-1α. While MIP-1α is induced by classical macrophage mediators such as LPS and is inhibited by IL-4 and glucocorticoids, AMAC-1 is specifically induced in macrophages by alternative macrophage mediators such as IL-4, IL-13, and IL-10. Expression of AMAC-1 is inhibited by IFN-γ while glucocorticoids exert a slightly positive synergistic effect in combination with IL-4. Peripheral blood monocytes do not express AMAC-1; time course experiments show that monocyte-to-macrophage differentiation is a prerequisite for AMAC-1 expression. Expression of AMAC-1 by granulocyte--macrophage CSF/IL-4-induced, monocyte-derived dendritic cells is complex; in mature adherent dendritic cells, however, only minor AMAC-1 mRNA expression was found. In vivo, AMAC-1 is expressed by alveolar macrophages from healthy persons, smokers, and asthmatic patients. In conclusion, AMAC-1 is a novel CC-chemokine whose expression is induced in alternatively activated macrophages by Th2-associated cytokines; thus, AMAC-1 may be involved in the APC-dependent T cell development in inflammatory and immune reactions.