Loss of Phagocytic and Antigen Cross-Presenting Capacity in Aging Dendritic Cells Is Associated with Mitochondrial Dysfunction.

Impaired functionality of dendritic cells (DCs) significantly contributes to decreased adaptive immune responses in aged hosts. The expression of MHC-peptide on the DC surface is the critical first step in T cell priming, but few studies have addressed the effect of aging on Ag acquisition, processing, and presentation by DCs. In this study, we show that aged murine DCs were less efficient in the cross-presentation of cell-associated Ag and subsequently in the cross-priming of CD8(+) T cells than were their young counterparts. The decreased cross-presentation was associated with a reduction in the frequency of CD8α DCs and merocytic (CD8α(-)CD11b(-))DCs that could endocytose cell-associated Ag, as well as the number and the size of the endocytosed particles in the DC that did internalize cell-associated materials. Mechanistically, phagocytic capacity has been associated with mitochondrial activity and membrane potential (Δψm). Aged DCs exhibited profound signs of mitochondrial dysfunction, illustrated by lower Δψm, reduced ATP turnover and coupling efficiency, decreased baseline oxidative phosphorylation, and greater proton leak and reactive oxygen species (ROS) production. Mimicking the aged metabolic phenotype in young DCs by pharmacologic manipulation indicated that the reductions in Δψm and ATP impeded the phagocytic capacity whereas ROS interfered with a later step in the cross-presentation process. Conversely, in vitro scavenging of ROS partially restored cross-presentation by aged DCs. Taken together, these data suggest that improvement of aged DC functionality might be feasible in the elderly by targeting metabolic dysfunction or its downstream sequelae, thereby opening new avenues for enhancing vaccine efficiency in this population.

Exploring the activated adipogenic niche: interactions of macrophages and adipocyte progenitors.

Adult adipose tissue contains a large supply of progenitors that can renew fat cells for homeostatic tissue maintenance and adaptive growth or regeneration in response to external challenges. However, the in vivo mechanisms that control adipocyte progenitor behavior are poorly characterized. We recently demonstrated that recruitment of adipocyte progenitors by macrophages is a central feature of adipose tissue remodeling under various adipogenic conditions. Catabolic remodeling of white adipose tissue by ß3-adrenergic receptor stimulation requires anti-inflammatory M2-polarized macrophages to clear dying adipocytes and to recruit new brown adipocytes from progenitors. In this Extra Views article, we discuss in greater detail the cellular elements of adipogenic niches and report a strategy to isolate and characterize the subpopulations of macrophages and adipocyte progenitors that actively participate in adrenergic tissue remodeling. Further characterization of these subpopulations may facilitate identification of new cellular targets to improve metabolic and immune function of adipose tissue.

Extracellular transport of cell-size particles and tumor cells by dendritic cells in culture.

Many particulate materials of sizes approximating that of a cell disseminate after being introduced into the body. While some move about within phagocytic inflammatory cells, others appear to move about outside of, but in contact with, such cells. In this report, we provide unequivocal photomicroscopic evidence that cultured, mature, human dendritic cells can transport in extracellular fashion over significant distances both polymeric beads and tumor cells. At least in the case of polymeric beads, both fibrinogen and the ß2-integrin subunit, CD18, appear to play important roles in the transport process. These discoveries may yield insight into a host of disease-related phenomena, including and especially tumor cell invasion and metastasis.

Cross-presentation of cell-associated antigens by mouse splenic dendritic cell populations.

Cross-presentation of cell-associated antigens (Ag) plays an important role in the induction of anti-tumor responses, autoimmune diseases, and transplant rejection. While several dendritic cell (DC) populations can induce pro-inflammatory CD8(+) T cell responses to cell-associated Ag during infection, in the absence of infection, cross-priming of naïve CD8(+) T cells is highly restricted. Comparison of the main splenic DC populations in mice - including the classic, cross-presenting CD8α DC and the recently described merocytic DC (mcDC) - reveals that cross-priming DCs display a distinct phenotype in cell-associated Ag uptake, endosomal/lysosomal trafficking, lysosomal acidification, and Ag persistence compared to non-cross-priming DC populations. Although the CD8α DC and mcDC subsets utilize similar processing pathways to cross-present cell-associated Ag, cross-priming by CD8α DCs is associated with IL-12 production, while the superior priming of the mcDC is critically dependent on type I IFN production. This discussion illustrates how subtle differences in internal processing pathways and their signaling sequelae significantly affect the duration of Ag cross-presentation and cytokine production by DCs, thereby shaping the ensuing CD8(+) T cell response.

Adsorbed fibrinogen regulates the behavior of human dendritic cells in a CD18-dependent manner.

The involvement of fibrinogen in inflammation has been considered by many, but the roles of the protein in that process have yet to be fully elucidated. The protein readily coats surfaces and is deposited at sites of inflammation. Furthermore, adsorbed fibrinogen influences many cells of the immune system, likely a result of increased receptor recognition upon ligand immobilization. To better understand adsorbed fibrinogen's role in inflammation, we studied the effects of the protein, adsorbed to the surface of microscopic beads, on human dendritic cells. Adsorbed fibrinogen increased dendritic cell expression of IL-6, IL-8, MIP-1beta and MCP-1. In contrast, solution phase fibrinogen had no effect. Importantly, dendritic cells formed complexes with, and subsequently accumulated around, beads in fibrinogen-dependent fashion. Antibodies directed against CD18 significantly decreased cytokine/chemokine expression and bead-cell complexation. Epsilon-aminocaproic acid limited bead-cell complexation, suggesting fibrinogen degradation products modulate dendritic cell activity. In support of this proposal, fibrinogen fragment D also increased MCP-1 expression by human dendritic cells. Taken together our data indicate adsorbed fibrinogen and its degradation products directly influence human dendritic cell operation. We propose a model whereby adsorbed fibrinogen plays a distinct causatory role in inflammation through its beta(2) integrin-mediated interaction with dendritic cells.

Corticortophin releasing factor 2 receptor agonist treatment significantly slows disease progression in mdx mice.

BACKGROUND: Duchenne muscular dystrophy results from mutation of the dystrophin gene, causing skeletal and cardiac muscle loss of function. The mdx mouse model of Duchenne muscular dystrophy is widely utilized to evaluate the potential of therapeutic regimens to modulate the loss of skeletal muscle function associated with dystrophin mutation. Importantly, progressive loss of diaphragm function is the most consistent striated muscle effect observed in the mdx mouse model, which is the same as in patients suffering from Duchenne muscular dystrophy. METHODS: Using the mdx mouse model, we have evaluated the effect that corticotrophin releasing factor 2 receptor (CRF2R) agonist treatment has on diaphragm function, morphology and gene expression. RESULTS: We have observed that treatment with the potent CRF2R-selective agonist PG-873637 prevents the progressive loss of diaphragm specific force observed during aging of mdx mice. In addition, the combination of PG-873637 with glucocorticoids not only prevents the loss of diaphragm specific force over time, but also results in recovery of specific force. Pathological analysis of CRF2R agonist-treated diaphragm muscle demonstrates that treatment reduces fibrosis, immune cell infiltration, and muscle architectural disruption. Gene expression analysis of CRF2R-treated diaphragm muscle showed multiple gene expression changes including globally decreased immune cell-related gene expression, decreased extracellular matrix gene expression, increased metabolism-related gene expression, and, surprisingly, modulation of circadian rhythm gene expression. CONCLUSION: Together, these data demonstrate that CRF2R activation can prevent the progressive degeneration of diaphragm muscle associated with dystrophin gene mutation.