Functional and structural characterization of two populations of human monocyte-derived dendritic cells

Identification and Characterization of Two Human Monocyte-Derived Dendritic Cell Subpopulations with Different Functions in Dying Cell Clearance and Different Patterns of Cell Death

Human monocyte-derived dendritic cells (mdDCs) are versatile cells that are used widely for research and experimental therapies. Although different culture conditions can affect their characteristics, there are no known subpopulations. Since monocytes differentiate into dendritic cells (DCs) in a variety of tissues and contexts, we asked whether they can give rise to different subpopulations. In this work we set out to characterize two human mdDC subpopulations that we identified and termed small (DC-S) and large (DC-L). Morphologically, DC-L are larger, more granular and have a more complex cell membrane. Phenotypically, DC-L show higher expression of a wide panel of surface molecules and stronger responses to maturation stimuli. Transcriptomic analysis confirmed their separate identities and findings were consistent with the phenotypes observed. Although they show similar apoptotic cell uptake, DC-L have different capabilities for phagocytosis, demonstrate better antigen processing, and have significantly better necrotic cell uptake. These subpopulations also have different patterns of cell death, with DC-L presenting an inflammatory, "dangerous" phenotype while DC-S mostly downregulate their surface markers upon cell death. Apoptotic cells induce an immune-suppressed phenotype, which becomes more pronounced among DC-L, especially after the addition of lipopolysaccharide. We propose that these two subpopulations correspond to inflammatory (DC-L) and steady-state (DC-S) DC classes that have been previously described in mice and humans.

Functional Dissociation of the Basolateral Transcytotic Compartment from the Apical Phago-lysosomal Compartment in Human Osteoclasts

Tartrate-resistant acid phosphatase (TRAP) is essential for elimination of Staphylococcus aureus, the main infectious agent responsible for osteomyelitis. This in vitro study investigated uptake and processing of fluorescence-labeled S. aureus by human osteoclasts and dendritic cells. The cells were stained for TRAP and the acidic compartment using a fluorescence-based protocol. In dendritic cells, TRAP and bacteria were colocalized. In osteoclasts, there was no colocalization of bacteria, TRAP, or the acidic compartment, indicating that there are three distinct vesicular compartments: the apical phago-lysosomal compartment, the basal secretory compartment, and the basolateral transcytotic compartment. Dissociation of the TRAP-containing transcytotic vesicles from the apical phago-lysosomal compartment may restrain osteoclasts from eliminating S. aureus.

Tumor-derived TGFbeta-1 induces dendritic cell apoptosis in the sentinel lymph node

Lymphatic flux from a primary tumor initially flows into a tumor-draining lymph node (LN), the so-called sentinel LN (SLN). Carried by the lymph fluid are a variety of mediators produced by the tumor that can influence immune responses within the SLN, making it a good model with which to investigate tumor-related immunology. For instance, dendritic cell (DC) numbers are reduced in SLNs from melanoma and breast cancer patients. In the present study, we investigated the mechanism by which DC numbers were reduced within SLNs from patients with non-small cell lung cancer. We found that the incidence of apoptosis among DCs was higher in SLNs than in non-SLNs, as were levels of TGFbeta-1. In contrast, levels of TGFbeta-1 mRNA did not differ between SLNs and non-SLNs, but were 30 times higher in tumors than in either LN type. In vitro, incubation for 2 days with TGFbeta-1 induced apoptosis among both cultured DCs and DCs acutely isolated from normal thoracic LNs, effects that were blocked by the TGFbeta-1 inhibitor DAN/Fc chimera. Taken together, these results suggest that tumor-derived TGFbeta-1 induces immunosuppression within SLNs before the movement of tumor cells into the SLNs, thereby facilitating metastasis within those nodes.

Primary human alveolar type II epithelial cell CCL20 (macrophage inflammatory protein-3alpha)-induced dendritic cell migration

Inhalation of antigenic matter stimulates rapid recruitment of dendritic cells (DCs) into the lung. Recent studies propose that the chemokine CCL20 (macrophage inflammatory protein-3alpha) may play an important role in DC recruitment. We previously showed that primary human alveolar type II epithelial (ATII) cells are a rich source of chemokines and so hypothesized that the ATII cell produces CCL20 and might therefore be a key regulator of DC recruitment into the lung. Here, we show that primary human ATII cells, but not human alveolar macrophages, produce CCL20 both constitutively (403.5 +/- 85.4 pg/ml; 24 h) and in response to endotoxin (lipopolysaccharide) exposure (1,525.0 +/- 169.4 pg/ml; 1 mug/ml lipopolysaccharide; 24 h) in a time- and dose-dependent manner. In addition, we show that peripheral blood monocyte-derived CD1a+ DCs migrate in response to conditioned media from ATII cells but not those from alveolar macrophages; DC migration was significantly correlated with the amount of CCL20 (r(2) > 0.9; P < 0.05) detected in the media but not with any other chemokine measured. We therefore conclude that the alveolar epithelium is an important source of CCL20 in the lung and that the ATII cell may play a critical role in controlling the movement of DCs through the lung both under normal and inflammatory conditions.