Plasma membrane-focused proteomics: dramatic changes in surface expression during the maturation of human dendritic cells.

The differential expression of surface molecules on dendritic cells (DC) reflects their functional differences as immature and mature subsets. It is difficult, however, to characterize differences in surface expression by standard proteomic approaches, due mainly to the hydrophobic nature and low abundance of the individual proteins in question. We have established a method for obtaining high-yield plasmalemma preparations which contain surface molecules enriched more than 200-fold by coating cells with beads conjugated with antibody against a cell type-specific cell-surface molecule, followed by nitrogen cavitated disruption, magnetic separation, and density gradient ultracentrifugation. We identified and quantified 339 human monocyte-derived DC transmembrane proteins, including 33 previously uncharacterized molecules. Whereas 106 proteins were selectively expressed in immature cells or down-regulated after maturation, 191 proteins were selectively expressed in mature cells or up-regulated after maturation.

Plasmacytoid dendritic cells: from specific surface markers to specific cellular functions.

We have recently described a panel of monoclonal antibodies (mAb), that recognize two novel leukocyte surface antigens, BDCA-2 and BDCA-4. BDCA-2 is a novel type II C-type lectin specifically expressed by plasmacytoid dendritic cells (PDCs) that can internalize antigen for presentation to T cells. Furthermore, signaling via BDCA-2 may play a role in switching from interferon (IFN)-alpha/beta-controlled to interleukin (IL)-12-controlled immune response pathways, as triggering of BDCA-2 potently inhibits secretion of IFN-alpha/beta by PDCs and thereby promotes IL-12 p70 production in PDCs and other cells. Viruses may exploit this switch to escape innate antiviral immunity, but it may be beneficial for patients with systemic lupus erythematosus (SLE) if induced, for instance by anti BDCA-2 mAb treatment. BDCA-4 is shown here to be identical to neuropilin-1 (NP-1), a neuronal receptor for the axon guidance factors belonging to the class-3 semaphorin subfamily, and a receptor on endothelial and tumor cells for vascular endothelial growth factor (VEGF-A). In blood and bone marrow, BDCA-4/NP-1 is exclusively expressed on PDCs, but in tonsils also on a few other cells, primarily follicular B helper memory T cells (T(FH)).

Difference between kidney and liver in decreased manganese superoxide dismutase activity caused by exposure of mice to mercuric chloride.

Dysfunction of antioxidant enzymes caused by mercuric compounds is partially associated with substantial induction of oxidative stress. In the present study, changes in renal and hepatic enzyme activity of an antioxidant protein manganese superoxide dismutase (Mn-SOD) after exposure to mercuric chloride (HgCl(2)) were examined in ICR mice. Subcutaneous administration of HgCl(2) (0.25-3 mg/kg) resulted in a decrease in renal Mn-SOD activity in a dose-dependent manner, whereas the hepatic enzyme activity was unaffected following injection of HgCl(2). Mercury accumulation in the kidney was drastically higher (34-75 times) than that in the liver after HgCl(2) administration. Examining interactions of purified Mn-SOD with HgCl(2) indicated that mercury ions suppressed Mn-SOD activity by reduction of the native form. These results suggest that inorganic mercury can directly interact with murine Mn-SOD, resulting in decrease of the enzyme activity and that the HgCl(2)-mediated significant reduction of renal, but not hepatic, Mn-SOD activity in vivo appears to be associated with the tissue specificity for mercury accumulation.