Dendritic cells and the regulation of a granulomatous immune response in the lung

Osteopontin Is Upregulated in Human and Murine Acute Schistosomiasis Mansoni

BACKGROUND

Symptomatic acute schistosomiasis mansoni is a systemic hypersensitivity reaction against the migrating schistosomula and mature eggs after a primary infection. The mechanisms involved in the pathogenesis of acute schistosomiasis are not fully elucidated. Osteopontin has been implicated in granulomatous reactions and in acute hepatic injury. Our aims were to evaluate if osteopontin plays a role in acute Schistosoma mansoni infection in both human and experimentally infected mice and if circulating OPN levels could be a novel biomarker of this infection.

METHODOLOGY/PRINCIPAL FINDINGS

Serum/plasma osteopontin levels were measured by ELISA in patients with acute (n = 28), hepatointestinal (n = 26), hepatosplenic (n = 39) schistosomiasis and in uninfected controls (n = 21). Liver osteopontin was assessed by immunohistochemistry in needle biopsies of 5 patients. Sera and hepatic osteopontin were quantified in the murine model of schistosomiasis mansoni during acute (7 and 8 weeks post infection, n = 10) and chronic (30 weeks post infection, n = 8) phase. Circulating osteopontin levels are increased in patients with acute schistosomiasis (p = 0.0001). The highest levels of OPN were observed during the peak of clinical symptoms (7-11 weeks post infection), returning to baseline level once the granulomas were modulated (>12 weeks post infection). The plasma levels in acute schistosomiasis were even higher than in hepatosplenic patients. The murine model mirrored the human disease. Macrophages were the major source of OPN in human and murine acute schistosomiasis, while the ductular reaction maintains OPN production in hepatosplenic disease. Soluble egg antigens from S. mansoni induced OPN expression in primary human kupffer cells.

CONCLUSIONS/SIGNIFICANCE

S. mansoni egg antigens induce the production of OPN by macrophages in the necrotic-exudative granulomas characteristic of acute schistosomiasis mansoni. Circulating OPN levels are upregulated in human and murine acute schistosomiasis and could be a non-invasive biomarker of this form of disease.

Evidence for local dendritic cell activation in pulmonary sarcoidosis

Background

Sarcoidosis is a granulomatous disease characterized by a seemingly exaggerated immune response against a difficult to discern antigen. Dendritic cells (DCs) are pivotal antigen presenting cells thought to play an important role in the pathogenesis. Paradoxically, decreased DC immune reactivity was reported in blood samples from pulmonary sarcoidosis patients. However, functional data on lung DCs in sarcoidosis are lacking. We hypothesized that at the site of disease DCs are mature, immunocompetent and involved in granuloma formation.

Methods

We analyzed myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) in broncho-alveolar lavage (BAL) and blood from newly diagnosed, untreated pulmonary sarcoidosis patients and healthy controls using 9-color flowcytometry. DCs, isolated from BAL using flowcytometric sorting (mDCs) or cultured from monocytes (mo-DCs), were functionally assessed in a mixed leukocyte reaction with naïve allogeneic CD4+ T cells. Using Immunohistochemistry, location and activation status of CD11c⁺DCs was assessed in mucosal airway biopsies.

Results

mDCs in BAL, but not in blood, from sarcoidosis patients were increased in number when compared with mDCs from healthy controls. mDCs purified from BAL of sarcoidosis patients induced T cell proliferation and differentiation and did not show diminished immune reactivity. Mo-DCs from patients induced increased TNFα release in co-cultures with naïve allogeneic CD4⁺ T cells. Finally, immunohistochemical analyses revealed increased numbers of mature CD86⁺ DCs in granuloma-containing airway mucosal biopsies from sarcoidosis patients.

Conclusion

Taken together, these finding implicate increased local DC activation in granuloma formation or maintenance in pulmonary sarcoidosis.

Dendritic cells in muscle lesions of sarcoidosis

Sarcoidosis is a chronic systemic granulomatous disorder of unknown etiology. The precise mechanism by which granulomatous lesions form is still obscure. Dendritic cells (DCs) are the most efficient antigen presenting cells; however, pathologic investigations of dendritic cells in the affected lesions of sarcoidosis are quite limited. We immunohistochemically examined the localization and phenotypes of dendritic cells and the expressions of CD40 and CD40L (CD154), which are key molecules in dendritic cell activation, in the muscles of 5 patients with muscular sarcoidosis, 8 patients with muscular disorders without inflammation, and 4 patients with histologically normal muscles as controls. In muscular sarcoidosis, CD1c-positive myeloid dendritic cells were scattered mainly in the lymphocyte layers of granulomas and the endomysium around the granulomas. Double immunostaining revealed that some CD1c-positive cells expressed the mature dendritic cell marker CD83, but immature dendritic cell marker CD1a-positive cells were not found. Smaller numbers of Blood dendritic cell antigen (BDCA)-2-positive plasmacytoid dendritic cells were found in the lymphocyte layers of granulomas. In the controls, small numbers of CD1c-positive cells were seen in the endomysium, whereas BDCA-2-positive cells were not observed except in 1 case. In muscular sarcoidosis, CD40 was expressed on mononuclear cells, on the interstitium around the muscle fibers and granulomas, and on the endothelium of vessels. CD40L was positive on mononuclear cells scattered within and around granulomas in 3 of 5 patients. In the controls, CD40 was expressed on the endothelium of the vessels and sparse mononuclear cells in the lesions of muscle fiber necrosis, whereas CD40L was not seen in any. In muscular sarcoidosis, recruitment of myeloid dendritic cells and less plasmacytoid dendritic cells and up-regulation of the CD40/CD40L system in affected muscles suggest that myeloid dendritic cells may be mainly involved in granulomatous inflammation through antigen presentation in a Th1 immune milieu.

The role of dendritic cells in mycobacterium-induced granulomas

The presence of dendritic cells (DCs) in mycobacterium-containing granulomas, as well as in other granuloma-inducing diseases, is beginning to be appreciated. This review will summarize what is known about DCs with regards to the granuloma and discuss the potential roles DCs may be playing during mycobacterial infection. Potential functions may include mycobacterial dissemination from lesions or sampling of granuloma-containing mycobacterial antigens and migration to the draining lymph nodes to maintain continuous T cell priming. Additionally, the review will discuss the potential outcomes of DC-T cell cross-talk within the granuloma and whether it results in boosting the effector functions of newly arrived T cells or anergizing systemic T cells locally. Understanding the DCs complex and changing role during this critical stage may help explain how latency is achieved and maintained. Such knowledge might also lead to improved vaccination strategies.

The lung vascular filter as a site of immune induction for T cell responses to large embolic antigen

The bloodstream is an important route of dissemination of invading pathogens. Most of the small bloodborne pathogens, like bacteria or viruses, are filtered by the spleen or liver sinusoids and presented to the immune system by dendritic cells (DCs) that probe these filters for the presence of foreign antigen (Ag). However, larger pathogens, like helminths or infectious emboli, that exceed 20 µm are mostly trapped in the vasculature of the lung. To determine if Ag trapped here can be presented to cells of the immune system, we used a model of venous embolism of large particulate Ag (in the form of ovalbumin [OVA]-coated Sepharose beads) in the lung vascular bed. We found that large Ags were presented and cross-presented to CD4 and CD8 T cells in the mediastinal lymph nodes (LNs) but not in the spleen or liver-draining LNs. Dividing T cells returned to the lungs, and a short-lived infiltrate consisting of T cells and DCs formed around trapped Ag. This infiltrate was increased when the Toll-like receptor 4 was stimulated and full DC maturation was induced by CD40 triggering. Under these conditions, OVA-specific cytotoxic T lymphocyte responses, as well as humoral immunity, were induced. The T cell response to embolic Ag was severely reduced in mice depleted of CD11c^hi cells or Ly6C/G⁺ cells but restored upon adoptive transfer of Ly6C^hi monocytes. We conclude that the lung vascular filter represents a largely unexplored site of immune induction that traps large bloodborne Ags for presentation by monocyte-derived DCs.

Mononuclear phagocyte-derived IL-10 suppresses the innate IL-12/IFN-gamma axis in lung-challenged aged mice

Previously, we reported that IL-10-producing mononuclear phagocytes increase in lungs of aged mice, causing impaired innate cytokine expression. Since dendritic cells (DCs) contribute to innate NK cell and adaptive T cell immunity, we tested the hypothesis that age-related IL-10 might influence DC function with effects on NK and T cell activation. The results showed that DC recruitment to sites of lung inflammation was normal in aged mice (>20 mo). However, IFN-gamma-producing NK cells in LPS-challenged lungs were decreased in aged as compared with young mice, which was associated with increased IL-10(+)CD11b(+)Gr-1(low)CD11c(-) cells consistent with mononuclear phagocytes. In vivo or in vitro blockade of IL-10 signaling restored IFN-gamma-producing NK cells. This restoration was reversed by IL-12 neutralization, indicating that IL-10 suppressed sources of IL-12 in aged mice. To probe DC function in adaptive immunity, we transferred young naive OVA-specific TCR transgenic T cells to old mice. Following challenge with OVA plus LPS, Ag presentation in the context of MHC-I and MHC-II occurred with similar kinetics and intensity in draining lymph nodes of young and old recipients as measured by proliferation. Despite this, aged hosts displayed impaired induction of IFN-gamma(+)CD4(+), but not IFN-gamma(+)CD8(+), effector T cells. Blockade of IL-10 signaling reversed age-associated defects. These studies indicate that the innate IL-12/IFN-gamma axis is not intrinsically defective in lungs of aged mice, but is rather suppressed by enhanced production of mononuclear phagocyte-derived IL-10. Our data identify a novel mechanism of age-associated immune deficiency.

Live Mycobacterium avium subsp. paratuberculosis and a killed-bacterium vaccine induce distinct subcutaneous granulomas, with unique cellular and cytokine profiles

Type II (lepromatous) granulomas are characterized by a lack of organization, with large numbers of macrophages heavily burdened with bacilli and disorganized lymphocyte infiltrations. Type II granulomas are a characteristic feature of the enteric lesions that develop during clinical Mycobacterium avium subsp. paratuberculosis infection in the bovine. Considering the poor organization and function of these granulomas, it is our hypothesis that dendritic cell (DC) function within the granuloma is impaired during initial infection. In order to test our hypothesis, we used a subcutaneous M. avium subsp. paratuberculosis infection model to examine early DC function within M. avium subsp. paratuberculosis-induced granulomas. In this model, we first characterized the morphology, cellular composition, and cytokine profiles of subcutaneous granulomas that develop 7 days after subcutaneous inoculation with either vaccine or live M. avium subsp. paratuberculosis. Second, we isolated CD11c(+) cells from within granulomas and measured their maturation status and ability to induce T-cell responses. Our results demonstrate that M. avium subsp. paratuberculosis or vaccine administration resulted in the formation of distinct granulomas with unique cellular and cytokine profiles. These distinct profiles corresponded to significant differences in the phenotypes and functional responses of DCs from within the granulomas. Specifically, the DCs from the M. avium subsp. paratuberculosis-induced granulomas had lower levels of expression of costimulatory and chemokine receptors, suggesting limited maturation. This DC phenotype was associated with weaker induction of T-cell proliferation. Taken together, these findings suggest that M. avium subsp. paratuberculosis infection in vivo influences DC function, which may shape the developing granuloma and initial local protection.

Limited phenotypic and functional maturation of bovine monocyte-derived dendritic cells following Mycobacterium avium subspecies paratuberculosis infection in vitro

After encountering antigen, dendritic cells (DC) must differentiate into a fully mature phenotype to induce a protective, lasting T cell immunity. Paratuberculosis is a disease caused by the intracellular pathogen Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) and is characterized by a transient cell mediated immune response, that when dissipates correlates to the onset of clinical disease. In order to study the mechanism of early cellular immunity associated with M. paratuberculosis infection, we tested the hypothesis that M. paratuberculosis infected bovine DC have impaired activation and maturation thus are defective in the initiation of a sustainable and protective Th1 immune response locally. Our results demonstrate that M. paratuberculosis infected DC showed decreased endocytosis of ovalbumin, indicating some functional maturation. Co-stimulatory molecules CD40 and CD80 mRNA expression from M. paratuberculosis infected DC was increased over untreated immature DC. M. paratuberculosis infection induced chemokine receptor CCR7 increase in DC, yet CCR5 remained high. MHC II surface expression remained low on M. paratuberculosis infected DC. M. paratuberculosis infection inhibited pro-inflammatory cytokine IL-12 production and promoted IL-10 secretion by bovine DC. Together, our findings showed evidence of phenotypic and functional maturation of DC. However, we did not see the expected antigen presentation via MHC II and cytokine responses as a fully mature DC. This may suggest semi-mature DC phenotype induced by M. paratuberculosis infection.

Severe sepsis exacerbates cell-mediated immunity in the lung due to an altered dendritic cell cytokine profile

Severe sepsis leads to long-term alterations in the immune response of surviving individuals. We have modeled this alteration in host immunity by studying the survivors of severe experimental sepsis (murine cecal ligation and puncture), which were subsequently challenged with lung granuloma-inducing Schistosoma mansoni eggs. This granulomatous response is a well-studied cell-mediated immune reaction characterized by elevated levels of type-2 cytokines. Pulmonary granulomas induced by S. mansoni eggs in cecal ligation and puncture survivors were significantly larger and contained more eosinophils than granulomas in sham-operated mice. Significantly lower interleukin (IL)-12p40 mRNA and IL-12p70 protein levels were observed in the lungs of postseptic mice with developing granulomas, compared with controls. Postseptic mice had significantly fewer dendritic cells in the lungs during the granulomatous response. Isolated lung dendritic cells from postseptic mice at days 8 and 16 after S. mansoni egg challenge exhibited defective IL-12 synthesis but enhanced IL-10 synthesis after Toll-like receptor agonist challenge. Pulmonary transfection with an IL-12-expressing adenovirus in postseptic mice reversed the skewing of the pulmonary cytokine profile and normalized the lung granulomatous response. Our data indicate that severe sepsis shifts the pulmonary cytokine environment, presumably via effects on pulmonary dendritic cells, which in turn alters the lung cell-mediated immune response.

Foamy macrophages within lung granulomas of mice infected with Mycobacterium tuberculosis express molecules characteristic of dendritic cells and antiapoptotic markers of the TNF receptor-associated factor family

Highly vacuolated or foamy macrophages are a distinct characteristic of granulomas in the lungs of animals infected with Mycobacterium tuberculosis. To date these have usually been considered to represent activated macrophages derived from monocytes entering the lesions from the blood. However, we demonstrate in this study that foamy macrophages express high levels of DEC-205, a marker characteristic of dendritic cells (DCs). In addition to high expression of the DEC-205 marker, these cells were characterized as CD11b(+)CD11c(high)MHC class II(high), and CD40(high), which are additional markers typically expressed by DCs. Up-regulation of CD40 was seen only during the early chronic stage of the lung disease, and both the expression of CD40 and MHC class II markers were down-regulated as the disease progressed into the late chronic phase. Foamy cells positive for the DEC-205 marker also expressed high levels of TNFR-associated factor-1 (TRAF-1), TRAF-2, and TRAF-3, markers associated with resistance to apoptosis. These data indicate that in addition to the central role of DCs in initiating the acquired immune response against M. tuberculosis infection, they also participate in the granulomatous response.

The cytosolic pattern-recognition receptor Nod2 and inflammatory granulomatous disorders

Pattern-recognition receptors are a first line of defense against invading pathogens. Recent advances in the understanding of innate immunity have revealed a novel family of cytosolic pattern-recognition receptors called Nods, which contain an amino-terminal effector-binding domain, a centrally located nucleotide-binding oligomerization domain (NOD) and a carboxy-terminal ligand recognition domain. Hereditary mutations of Nods have been reported in patients with certain inflammatory diseases; for example, Nod2 mutations are associated with the inflammatory granulomatous disorders, Crohn's disease and Blau syndrome. Missense mutations of Nod2 are also associated with early-onset sarcoidosis, a rare but sporadic disease. Because Nod2 is predominantly expressed in monocytes and recognizes a component of bacterial peptidoglycan, analysis of its function may help in understanding the role of the immune system in granuloma formation.

Differentiation, maturation, and survival of dendritic cells by osteopontin regulation

Dendritic cells (DCs) are antigen-presenting cells with the ability to induce primary immune responses necessary in innate immunity and adaptive immunity. Osteopontin (OPN) is a secreted acidic phosphoprotein containing an arginine-glycine-aspartate sequence and has been suggested to play an important role in early cellular immune responses. The interaction between DCs and OPN has not been clarified. We hypothesized that there is an important interaction between DCs and OPN, which is an indispensable extracellular matrix component in early cellular immune responses. Human monocyte-derived DCs synthesized OPN especially during the differentiation from monocytes to immature DCs. By blocking of OPN with anti-OPN antibody, cultured DCs became smaller and expressed lower levels of costimulatory molecules and major histocompatibility complex class II antigens than untreated DCs. Furthermore, DCs treated with anti-OPN antibody easily underwent apoptosis. These results suggest that human DCs can produce OPN and that OPN may play a role in the differentiation, maturation, and survival of DCs by autocrine and/or paracrine pathways.

Indigenous pulmonary Propionibacterium acnes primes the host in the development of sarcoid-like pulmonary granulomatosis in mice

Although many cases of sarcoidosis are self-limiting with spontaneous remission, uncontrolled pulmonary granulomatosis with fibrosis produces intolerable long-term respiratory symptoms in a minority of patients. Individuals with chronic pulmonary sarcoidosis require an alternative therapy to corticosteroidal treatment because of its insufficient effectiveness. Although many researchers have considered infection as the triggering factor for this disease, the mechanisms by which the candidate causative organisms induce this disorder remain unclear. We report here that extrapulmonary sensitization to Propionibacterium acnes, which is one of the candidates to date, induced pulmonary Th-1 granulomas mainly in the subpleural and peribronchovascular regions often observed in sarcoidosis. These granulomas appear to be caused by indigenous P. acnes pre-existing in the lower respiratory tract of the normal lung, which is believed to be germ-free, and by an influx of P. acnes-sensitized CD4(+) T cells from the circulation. Importantly, the eradication of indigenous P. acnes with antibiotics alleviated the granulomatous lung disease. This is the first report to present clear evidence of the contribution of an indigenous pulmonary bacterium to the formation of granulomatous lesions in the lung. We propose that treatment targeting indigenous P. acnes in the lung may be a possible remedy for pulmonary sarcoidosis.

The innate pulmonary granuloma: characterization and demonstration of dendritic cell recruitment and function

Granulomas are innate sequestration responses that can be modified by superimposed acquired immune mechanisms. The present study examined the innate stage of pulmonary granuloma responses to bead-immobilized Th1- and Th2-inducing pathogen antigens (Ags), Mycobacteria bovis purified protein derivative (PPD) and Schistosoma mansoni soluble egg Ags (SEA). Compared to a nonpathogen Ag, PPD and SEA bead elicited larger lesions with the former showing accelerated inflammation. Temporal analyses of cytokine and chemokine transcripts showed all Ag beads induced tumor necrosis factor-alpha mRNA but indicated biased interleukin (IL)-1, IL-6, and IL-12 expression with PPD challenge. All beads elicited comparable levels of CXCL9, CXL10, CCL2, CCL17, and CCL22 mRNA, but PPD beads caused biased CXCL2 CXCL5, CCL3, and CCL4 expression whereas both pathogen Ags induced CCL7. Immunohistochemical, electron microscopic, and flow cytometric analyses showed that Ag beads mobilized CD11c+ dendritic cells (DCs) of comparable maturation. Transfer of DCs from PPD Ag-challenged lungs conferred a Th1 anamnestic cytokine response in recipients. Surprisingly, transfer of DCs from the helminth SEA-challenged lungs did not confer the expected Th2 response, but instead rendered recipients incapable of Ag-elicited IL-4 production. These results provide in vivo evidence that lung DCs recruited under inflammatory conditions favor Th1 responses and alternative mechanisms are required for Th2 commitment.