Phagocytosis of agarose beads by receptors for C3b (CR1) and iC3b (CR3) on alveolar macrophages from patients with sarcoidosis

Purified complement C3b triggers phagocytosis and activation of human neutrophils via complement receptor 1

The complement system provides vital immune protection against infectious agents by labeling them with complement fragments that enhance phagocytosis by immune cells. Many details of complement-mediated phagocytosis remain elusive, partly because it is difficult to study the role of individual complement proteins on target surfaces. Here, we employ serum-free methods to couple purified complement C3b onto E. coli bacteria and beads and then expose human neutrophils to these C3b-coated targets. We examine the neutrophil response using a combination of flow cytometry, confocal microscopy, luminometry, single-live-cell/single-target manipulation, and dynamic analysis of neutrophil spreading on opsonin-coated surfaces. We show that purified C3b can potently trigger phagocytosis and killing of bacterial cells via Complement receptor 1. Comparison of neutrophil phagocytosis of C3b- versus antibody-coated beads with single-bead/single-target analysis exposes a similar cell morphology during engulfment. However, bulk phagocytosis assays of C3b-beads combined with DNA-based quenching reveal that these are poorly internalized compared to their IgG1 counterparts. Similarly, neutrophils spread slower on C3b-coated compared to IgG-coated surfaces. These observations support the requirement of multiple stimulations for efficient C3b-mediated uptake. Together, our results establish the existence of a direct pathway of phagocytic uptake of C3b-coated targets and present methodologies to study this process.

Hypoxia Promotes a Mixed Inflammatory-Fibrotic Macrophages Phenotype in Active Sarcoidosis

Background

Macrophages are pivotal cells in sarcoidosis. Monocytes-derived (MD) macrophages have recently been demonstrated to play a major role especially in pulmonary sarcoidosis. From inflammatory tissues to granulomas, they may be exposed to low oxygen tension environments. As hypoxia impact on sarcoidosis immune cells has never been addressed, we designed the present study to investigate MD-macrophages from sarcoidosis patients in this context. We hypothesized that hypoxia may induce functional changes on MD-macrophages which could have a potential impact on the course of sarcoidosis.

Methods

We studied MD-macrophages, from high active sarcoidosis (AS) (n=26), low active or inactive sarcoidosis (IS) (n=24) and healthy controls (n=34) exposed 24 hours to normoxia (21% O2) or hypoxia (1.5% O2). Different macrophage functions were explored: hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-kappa B (NF-κB) activation, cytokines secretion, phagocytosis, CD80/CD86/HLA-DR expression, profibrotic response.

Results

We observed that hypoxia, with a significantly more pronounced effect in AS compared with controls and IS, increased the HIF-1α trans-activity, promoted a proinflammatory response (TNFα, IL1ß) without activating NF-κB pathway and a profibrotic response (TGFß1, PDGF-BB) with PAI-1 secretion associated with human lung fibroblast migration inhibition. These results were confirmed by immunodetection of HIF-1α and PAI-1 in granulomas observed in pulmonary biopsies from patients with sarcoidosis. Hypoxia also decreased the expression of CD80/CD86 and HLA-DR on MD-macrophages in the three groups while it did not impair phagocytosis and the expression of CD36 expression on cells in AS and IS at variance with controls.

Conclusions

Hypoxia had a significant impact on MD-macrophages from sarcoidosis patients, with the strongest effect seen in patients with high active disease. Therefore, hypoxia could play a significant role in sarcoidosis pathogenesis by increasing the macrophage proinflammatory response, maintaining phagocytosis and reducing antigen presentation, leading to a deficient T cell response. In addition, hypoxia could favor fibrosis by promoting profibrotic cytokines response and by sequestering fibroblasts in the vicinity of granulomas.

Alterations in gene expression of complement components in chronic rhinosinusitis

BACKGROUND

The complement cascade forms part of the initial innate response to pathogens in the airway. Complement activation is important in the maintenance of host homeostasis, but excessive and uncontrolled activation may lead to inflammation and disease. The role of the complement pathway in the innate response in chronic rhinosinusitis (CRS) is poorly characterized Methods: Sinus mucosa biopsy specimens from the anterior ethmoid or uncinate process of patients with allergic fungal rhinosinusitis (AFRS), CRS without NPs (CRS-NPs), and controls were harvested and gene and protein expression of C3, factor B (fB), C5, and C7 complement proteins were analyzed using quantitative polymerase chain reaction and immunohistochemical techniques.

RESULTS

fB, C3, and C5 gene expression were increased in both AFRS and CRS-NPs compared with controls (p < 0.05). Transcriptional activity for the terminal pathway protein C7 was not significantly increased when compared with controls, with C7 levels actually reduced in AFRS patients when compared with controls. Immunohistochemistry studies showed the presence of C3 and fB on the mucosal surface and in submucosa of both AFRS and CRS-NPs, but not normal controls. Terminal pathway protein C9 was not found in our specimens.

CONCLUSION

Both AFRS and CRS-NPs display up-regulation of the complement pathway, in particular, the alternative pathway (fB) and common pathways (C3 and C5). Enhanced innate responses as shown by alterations in complement components may play a pivotal role in the inflammatory response noted in CRS and provide potential therapeutic targets in the future.

Increased production of hydrogen peroxide and expression of CD11b/CD18 on alveolar macrophages in patients with active pulmonary tuberculosis

SETTING

Alveolar macrophages (AM) are important in host defense against Mycobacterium tuberculosis (TB). beta 2-integrins, especially CD11a/CD18 and CD11b/CD18, are implicated in leukocyte migration, antigen presentation, phagocytosis, and production of reactive oxygen species.

OBJECTIVE

To explore the functional relevance of beta 2-integrin expression to intracellular H2O2 capacity of AM in TB patients.

DESIGN

In a prospective study, AM retrieved from 18 active pulmonary TB patients and 18 normal subjects were assessed for beta 2-integrin expression and intracellular H2O2 metabolism capacity by loading with anti-CD11a/CD18, anti-CD11b/CD18 monoclonal antibodies and 2',7' dichlorofluorescein diacetate (DCFH-DA) respectively, and analyzed by flow cytometry. AM from 8 normal subjects were stimulated with tumor necrosis factor-alpha (TNF-alpha, 10(5) units/ml) to examine the relationship between H2O2 production and CD11b/CD18 expression.

RESULTS

The magnitude of DCFH oxidation and CD11b/CD18 expression of AM was higher in TB patients than in normal subjects. The CD11b/CD18 expression was related to the magnitude of DCFH oxidation, but not to lymphocyte numbers or subpopulations (CD4, CD8, CD25). Stimulation of AM with TNF-alpha increased H2O2 production and CD11b/CD18 expression. Pretreatment with CD11b/CD18 monoclonal antibodies inhibited TNF-alpha-induced H2O2.

CONCLUSION

AM in TB patients possessed a higher capacity of oxidant metabolism. The increased CD11b/CD18 expression may be related to the increased respiratory burst response in AM against mycobacterial invasion.

Adhesion molecules in lung diseases

The human body possesses highly specialized cellular defense mechanisms that, when activated pathologically, can induce a number of immunologic disorders. For a normal cellular immune response, the following conditions must be fulfilled: (1) accumulation of white blood cells, (2) their diapedesis through the vessel walls of the inflammatory area affected by an injurious agent, and (3) normal cellular effector functions in the tissue. This cascade of inflammatory processes has recently been shown to be regulated by a group of molecules that are termed adhesion molecules and consist of three subfamilies: selectins, the immunoglobulin supergene family, and integrins. The cellular functions influenced by adhesion molecules include, among others, cytotoxic T-cell responses, CD4-dependent activation of B lymphocytes by T lymphocytes, activation of granulocytes and macrophages, phagocytosis of opsonized particles by monocytes, macrophages, and granulocytes, antigen-presenting function of macrophages, their antibody-dependent cytotoxicity, initiation of a respiratory burst by white blood cells, and activation of fibroblasts. Studies performed in recent years have shown that pathogenetically relevant changes in the expression and function of adhesion molecules are involved in a variety of pulmonary diseases. These changes include the accumulation and activation of alveolar macrophages in smokers, experimentally induced bronchial hyperreactivity in bronchial asthma, accumulation of eosinophils in allergic rhinitis, bleomycin-induced pulmonary fibrosis, binding of viruses and bacteria to respiratory mucosa, and various mechanisms of acute damage to pulmonary parenchyma. Though their role in tumor development is still unclear, adhesion molecules are obviously involved in determining the route and organotropism of metastases. Further studies of the function of adhesion molecules in pulmonary diseases will contribute to our understanding of the pathomechanisms of these diseases and, through the development of specific antibodies, may provide attractive new therapeutic approaches to problems for which treatment is not yet available.

Associated complement C3b. Towards an understanding of its intracellular modifications

Covalent Superose microspheres-bound C3b was used as a model system to simplify the analysis of antigen-bound C3b modifications during antigen processing. The model was set up using purified C3 and Superose-bound trypsin. C3b was covalently bound to Superose through an ester link, as indicated by lability to hydroxylamine treatment at alkaline pH. C3b-Superose was incubated with L subcellular fraction, enriched in endosomes/lysosomes, purified from U937 cell line. Two types of limited activities on the C3b-Superose model system were detected: (i) a proteolytic activity cleaving C3b into mainly a C3c-like fragment which was released and a C3d-like fragment of apparent M(r) 32 kDa which remained bound to Superose through the original ester link; (ii) an esterolytic activity cleaving the ester bond and releasing C3b. Inhibition experiments pointed to the involvement of serine, aspartyl and cysteine proteases. Cathepsin B appeared most probably as one of the major proteases of L fraction catalysing the proteolysis of the C3b-bound. Kinetic studies were in favour of a good stability on the ester bond, supporting an effective role of C3b as a chaperone during the extracellular and intracellular travel of C3b-bound antigen.

Expression of alveolar macrophage adhesion molecules in pulmonary sarcoidosis

Beta-2-integrins belong to a family of leukocyte surface glycoproteins that are essential for immune functions of bronchoalveolar cells. The expression of three alpha chains designed as CD11a, CD11b, CD11c, a common beta chain CD18, and of a ligand for several integrins CD54 (ICAM-1) was studied on alveolar macrophages of patients with active and inactive sarcoidosis and in control subjects. The percentage of macrophages expressing CD11b (CR3) was significantly increased in patients with active sarcoidosis compared with patients who had inactive disease and control subjects. The adhesion molecule CD54 (ICAM-1) was detected on a higher percentage of alveolar macrophages in patients with active rather than inactive sarcoidosis and in control subjects. Since integrin-mediated adhesion seems to be important in macrophage-lymphocyte interactions during the immune response, higher expression of both CD11b and CD54 on sarcoid alveolar macrophages may be related to several immune abnormalities reported in pulmonary sarcoidosis.