Biomedical subjects

Gordon D Brown

Publications and source records attributed to Gordon D Brown.

48 records · Page 3Linked to original sources

PubMed2004

The role of Dectin-1 in antifungal immunity.

beta-Glucans are structural components of fungal cell walls, which have a stimulatory effect on the immune system. Although a number of receptors for these carbohydrates have been proposed, the recently identified C-type lectin-like receptor, Dectin-1, appears to play a central role. Dectin-1 is expressed on phagocytic cells, including macrophages and neutrophils, and mediates both the internalization and cellular responses to beta-glucan, through unique mechanisms. Dectin-1 can recognize and respond to live fungal pathogens and is being increasingly appreciated as having a key role in the innate responses to these pathogens. In addition to its exogenous ligands, Dectin-1 can recognize an unidentified endogenous ligand on T cells and may act as a co-stimulatory molecule, although its function in these responses is less clear. This review will highlight the current knowledge of Dectin-1 and its potential role in antifungal immunity, as well as deficiencies in our understanding.

Animals↗

PubMed2003

Alveolar macrophage-mediated killing of Pneumocystis carinii f. sp. muris involves molecular recognition by the Dectin-1 beta-glucan receptor.

Innate immune mechanisms against Pneumocystis carinii, a frequent cause of pneumonia in immunocompromised individuals, are not well understood. Using both real time polymerase chain reaction as a measure of organism viability and fluorescent deconvolution microscopy, we show that nonopsonic phagocytosis of P. carinii by alveolar macrophages is mediated by the Dectin-1 beta-glucan receptor and that the subsequent generation of hydrogen peroxide is involved in alveolar macrophage-mediated killing of P. carinii. The macrophage Dectin-1 beta-glucan receptor colocalized with the P. carinii cyst wall. However, blockage of Dectin-1 with high concentrations of anti-Dectin-1 antibody inhibited binding and concomitant killing of P. carinii by alveolar macrophages. Furthermore, RAW 264.7 macrophages overexpressing Dectin-1 bound P. carinii at a higher level than control RAW cells. In the presence of Dectin-1 blockage, killing of opsonized P. carinii could be restored through FcgammaRII/III receptors. Opsonized P. carinii could also be efficiently killed in the presence of FcgammaRII/III receptor blockage through Dectin-1-mediated phagocytosis. We further show that Dectin-1 is required for P. carinii-induced macrophage inflammatory protein 2 production by alveolar macrophages. Taken together, these results show that nonopsonic phagocytosis and subsequent killing of P. carinii by alveolar macrophages is dependent upon recognition by the Dectin-1 beta-glucan receptor.

Animals↗

PubMed2003

Dectin-1 expression and function are enhanced on alternatively activated and GM-CSF-treated macrophages and are negatively regulated by IL-10, dexamethasone, and lipopolysaccharide.

Dectin-1 is the major macrophage receptor for beta-glucans and generates a proinflammatory response through the recognition of these carbohydrates on fungal pathogens. We have examined the effects of cytokines and other agents on the expression and functions of dectin-1 in both resident and elicited murine peritoneal macrophages (Mphi). Dectin-1 expression was found to be highly up-regulated by GM-CSF and by the cytokines that induce alternative macrophage activation, IL-4 and IL-13. In contrast, IL-10, LPS, and dexamethasone, but not IFN-gamma, down-regulated the expression of this receptor. Modulation of dectin-1 receptor levels correlated with the ability of these macrophages to bind zymosan and significantly affected the contribution of this receptor to the resultant proinflammatory response, as measured by the production of TNF-alpha, although some Mphi-specific differences were observed. These results correlate with the known effects of these cytokines and other agents on the ability of the immune system to recognize and respond to fungal pathogens.

Adjuvants, Immunologic↗

PubMed2003

Dectin-1 mediates the biological effects of beta-glucans.

The ability of fungal-derived beta-glucan particles to induce leukocyte activation and the production of inflammatory mediators, such as tumor necrosis factor (TNF)-alpha, is a well characterized phenomenon. Although efforts have been made to understand how these carbohydrate polymers exert their immunomodulatory effects, the receptors involved in generating these responses are unknown. Here we show that Dectin-1 mediates the production of TNF-alpha in response to zymosan and live fungal pathogens, an activity that occurs at the cell surface and requires the cytoplasmic tail and immunoreceptor tyrosine activation motif of Dectin-1 as well as Toll-like receptor (TLR)-2 and Myd88. This is the first demonstration that the inflammatory response to pathogens requires recognition by a specific receptor in addition to the TLRs. Furthermore, these studies implicate Dectin-1 in the production of TNF-alpha in response to fungi, a critical step required for the successful control of these pathogens.

Animals↗

PubMed2003

Pattern recognition receptors and differentiation antigens define murine myeloid cell heterogeneity ex vivo.

Recruitment of myeloid cells during inflammatory reactions plays an important role in the propagation and resolution of inflammation. However, the identification and characterization of these cells in mice has been hampered by cellular heterogeneity at the functional and phenotypic level. We have defined criteria for the rapid flow-cytometric identification of monocytes (M(o)), macrophages (MPhi), neutrophils (N(eu)) and eosinophils (E(os)) in murine tissues using novel and established myeloid markers. These criteria were applied to the study of naive mice and mice with experimentally induced inflammation, both local and systemic, and also to a murine model of tumor progression. We show that the murine 7/4 antigen and the beta-glucan receptor, Dectin-1, are particularly useful for the sub-division of myeloid cells into individual populations, even when inflammatory conditions modulate their surface expression. Furthermore, 7/4 expression allows distinction between M(o) recently recruited to a site and the resident cells already present. These studies highlight the heterogeneity of the murine M(o)/MPhi-lineage, define an extended phenotype for murine myeloid cells and greatly facilitate the ex vivo characterization of these cells during very different models of inflammation.

Animals↗

PubMed2003

Fungal beta-glucans and mammalian immunity.

Beta-glucans are structural cell wall polymers of many fungi which possess immunomodulatory activities. Although the therapeutic benefits associated with these compounds, particularly as anti-infective and antitumorigenic agents, have led to a large body of published research over the last five decades, it is still unclear how these carbohydrates mediate their effects. Recent studies, however, are starting to shed some light on the cellular receptors and molecular mechanisms involved, which also have direct relevance on the innate immune response to fungal pathogens.

Animals↗

PubMed2003

Analysis of mannose receptor regulation by IL-4, IL-10, and proteolytic processing using novel monoclonal antibodies.

The study of the murine macrophage mannose receptor (MR) has been hampered by the lack of specific reagents. We have generated and characterized novel anti-MR monoclonal antibodies and used them to analyze MR expression in primary mouse macrophages (M(phi)). In BioGel- and thioglycollate-elicited M(phi), interleukin (IL)-4 up-regulated total cell-associated MR (cMR), correlating with enhanced surface expression. We investigated the influence of IL-10, a well-characterized deactivator of M(phi) function, on MR levels and observed that it had a similar effect to IL-4. In both cases, enhanced cMR levels translated into increased production of the soluble form of the receptor (sMR). We have demonstrated the presence of sMR in cultures of stable non-M(phi) transductants expressing full-length MR, indicating that the proteolytic activity responsible for cMR cleavage is not M(phi)-restricted. These data support a role for the MR in T helper cell type 2 cytokine-driven, immune responses and suggest a non-M(phi) contribution to sMR production in vivo.

3T3 Cells↗

PubMed2003

A rationale and training agenda for rehabilitation informatics: roadmap for an emerging discipline.

Decreased length of inpatient rehabilitation stay, greater long-term injury survival rates, broader access to information technologies, and the growing role of the Internet create potential for new models of rehabilitation that are more community- and person-centered rather than historically hospital- and provider-centered services. In recent years, information-based rehabilitation technologies have grown rapidly, expanding the possibilities for numerous interventions to promote independent living. These programs have centered primarily on providing rehabilitation health services over a distance ("telerehabilitation"). Telerehabilitation can be conceived as part of a broader approach that includes elements of direct rehabilitation services, service coordination, community resources, and information relay between numerous individuals, service providers, and community members ("rehabilitation informatics"). Because of the complexity of these information types and sectors, this broader conceptual approach of rehabilitation informatics borrows heavily from fields such as adaptive computing, robotics, computer networking, and high-level systems programming. As such, innovation in rehabilitation informatics will require new models of training that span these domains. This paper proposes a rationale for the new field of rehabilitation informatics, and offers a multidisciplinary training model for the next generation of rehabilitation informaticians.

Curriculum↗

PubMed2003

Application of peer-to-peer networking to health care.

People with chronic illness or disability share similar information needs that are not routinely handled by a system designed for traditional health services. Recent historical initiatives to provide alternate information systems for sharing information or coordinating services have been highly centralized, were expensive to set up and were not sustainable. We propose a novel application of peer-to-peer networking to provide an infrastructure for information exchange and service coordination. The peer-to-peer model empowers the user (citizen with disabilities) with control over the type and extent of information about themselves that is communicated and to whom. Further, the peer-to-peer model leads to a decentralized resource that grows incrementally, supported by the users, and is potentially more sustainable.

Chronic Disease↗

PubMed2002

Mycosin-1, a subtilisin-like serine protease of Mycobacterium tuberculosis, is cell wall-associated and expressed during infection of macrophages.

BACKGROUND: Exported proteases are commonly associated with virulence in bacterial pathogens, yet there is a paucity of information regarding their role in Mycobacterium tuberculosis. There are five genes (mycP1-5) present within the genome of Mycobacterium tuberculosis H37Rv that encode a family of secreted, subtilisin-like serine proteases (the mycosins). The gene mycP1 (encoding mycosin-1) was found to be situated 3700 bp (four ORF's) from the RD1 deletion region in the genome of the attenuated vaccine strain M. bovis BCG (bacille de Calmette et Guérin) and was selected for further analyses due to the absence of expression in this organism. RESULTS: Full-length, 50 kDa mycosin-1 was observed in M. tuberculosis cellular lysates, whereas lower-molecular-weight species were detected in culture filtrates. A similar lower-molecular-weight species was also observed during growth in macrophages. Mycosin-1 was localized to the membrane and cell wall fractions in M. tuberculosis by Western blotting, and to the cell envelope by electron microscopy. Furthermore, M. tuberculosis culture filtrates were shown to contain a proteolytic activity inhibited by mixed serine/cysteine protease inhibitors and activated by Ca2+, features typical of the subtilisins. CONCLUSIONS: Mycosin-1 is an extracellular protein that is membrane- and cell wall-associated, and is shed into the culture supernatant. The protein is expressed after infection of macrophages and is subjected to proteolytic processing. Although proteolytically active mycosin-1 could not be generated recombinantly, serine protease activity containing features typical of the subtilisins was detected in M. tuberculosis culture filtrates.

Animals↗

PubMed2002

The beta-glucan receptor, dectin-1, is predominantly expressed on the surface of cells of the monocyte/macrophage and neutrophil lineages.

We recently identified dectin-1 (betaGR) as a major beta-glucan receptor on leukocytes and demonstrated that it played a significant role in the non-opsonic recognition of soluble and particulate beta-glucans. Using a novel mAb (2A11) raised against betaGR, we show here that the receptor is not dendritic cell-restricted as first reported, but is broadly expressed, with highest surface expression on populations of myeloid cells (monocyte/macrophage (Mphi) and neutrophil lineages). Dendritic cells and a subpopulation of T cells also expressed the betaGR, but at lower levels. Alveolar Mphi, like inflammatory Mphi, exhibited the highest surface expression of betaGR, indicative of a role for this receptor in immune surveillance. In contrast, resident peritoneal Mphi expressed much lower levels of betaGR on the cell surface. Characterization of the nonopsonic recognition of zymosan by resident peritoneal Mphi suggested the existence of an additional beta-glucan-independent mechanism of zymosan binding that was not observed on elicited or bone marrow-derived Mphi. Although this recognition could be inhibited by mannan, we were able to exclude involvement of the Mphi mannose receptor and complement receptor 3 in this process. These observations imply the existence of an additional mannan-dependent receptor involved in the recognition of zymosan by resident peritoneal Mphi.

3T3 Cells↗

PubMed2002

Dectin-1 is a major beta-glucan receptor on macrophages.

Zymosan is a beta-glucan- and mannan-rich particle that is widely used as a cellular activator for examining the numerous responses effected by phagocytes. The macrophage mannose receptor (MR) and complement receptor 3 (CR3) have historically been considered the major macrophage lectins involved in the nonopsonic recognition of these yeast-derived particles. Using specific carbohydrate inhibitors, we show that a beta-glucan receptor, but not the MR, is a predominant receptor involved in this process. Furthermore, nonopsonic zymosan binding was unaffected by genetic CD11b deficiency or a blocking monoclonal antibody (mAb) against CR3, demonstrating that CR3 was not the beta-glucan receptor mediating this activity. To address the role of the recently described beta-glucan receptor, Dectin-1, we generated a novel anti-Dectin-1 mAb, 2A11. Using this mAb, we show here that Dectin-1 was almost exclusively responsible for the beta-glucan-dependent, nonopsonic recognition of zymosan by primary macro-phages. These findings define Dectin-1 as the leukocyte beta-glucan receptor, first described over 50 years ago, and resolves the long-standing controversy regarding the identity of this important molecule. Furthermore, these results identify Dectin-1 as a new target for examining the immunomodulatory properties of beta-glucans for therapeutic drug design.

Animals↗