Norikatsu Mizumoto

CD39 is the dominant Langerhans cell–associated ecto-NTPDase: Modulatory roles in inflammation and immune responsiveness

CD39, the endothelial ecto-nucleoside triphosphate diphosphohydrolase (NTPDase), regulates vascular inflammation and thrombosis by hydrolyzing ATP and ADP. Although ecto-NTPDase activities have been used as a marker of epidermal dendritic cells (DCs) known as Langerhans cells, the identity and function of these activities remain unknown. Here we report that Langerhans cells in CD39−/− mice express no detectable ecto-NTPDase activity. Irritant chemicals triggered rapid ATP and ADP release from keratinocytes and caused exacerbated skin inflammation in CD39−/− mice. Paradoxically, T cell–mediated allergic contact hypersensitivity was severely attenuated in CD39−/− mice. As to mechanisms, T cells increased pericellular ATP concentrations upon activation, and CD39−/− DCs showed ATP unresponsiveness (secondary to P2-receptor desensitization) and impaired antigen-presenting capacity. Our results show opposing outcomes of CD39 deficiency in irritant versus allergic contact dermatitis, reflecting its diverse roles in regulating extracellular nucleotide-mediated signaling in inflammatory responses to environmental insults and DC–T cell communication in antigen presentation.

Generation and Function of Reactive Oxygen Species in Dendritic Cells During Antigen Presentation

Although reactive oxygen species (ROS) have long been considered to play pathogenic roles in various disorders, this classic view is now being challenged by the recent discovery of their physiological roles in cellular signaling. To determine the immunological consequence of pharmacological disruption of endogenous redox regulation, we used a selenium-containing antioxidant compound ebselen known to modulate both thioredoxin and glutaredoxin pathways. Ebselen at 5–20 μM inhibited Con A-induced proliferation and cytokine production by the HDK-1 T cell line as well as the LPS-triggered cytokine production by XS52 dendritic cell (DC) line. Working with the in vitro-reconstituted Ag presentation system composed of bone marrow-derived DC, CD4+ T cells purified from DO11.10 TCR-transgenic mice and OVA peptide (serving as Ag), we observed that 1) both T cells and DC elevate intracellular oxidation states upon Ag-specific interaction; 2) ebselen significantly inhibits ROS production in both populations; and 3) ebselen at 5–20 μM inhibits DC-induced proliferation and cytokine production by T cells as well as T cell-induced cytokine production by DC. Thus, Ag-specific, bidirectional DC-T cell communication can be blocked by interfering with the redox regulation pathways. Allergic contact hypersensitivity responses in BALB/c mice to oxazolone, but not irritant contact hypersensitivity responses to croton oil, were suppressed significantly by postchallenge treatment with oral administrations of ebselen (100 mg/kg per day). These results provide both conceptual and technical frameworks for studying ROS-dependent regulation of DC-T cell communication during Ag presentation and for testing the potential utility of antioxidants for the treatment of immunological disease.

CD1a and langerin: acting as more than Langerhans cell markers

Langerhans cells (LCs) represent a unique DC subset populating the outermost body surface, i.e., the epidermis. Although CD1a and langerin (CD207) are used as specific markers to distinguish LCs from other DC subsets, their immunological functions have remained mostly unknown. A new paper (see the related article beginning on page 701) demonstrates that LCs utilize these markers to induce cellular immune responses to Mycobacterium leprae: CD1a mediates the presentation of nonpeptide antigens to T cells, while langerin facilitates uptake of microbial fragments and perhaps their delivery to a specialized subcellular compartment.

Identification of crassin acetate as a new immunosuppressant triggering heme oxygenase-1 expression in dendritic cells

By screening 720 natural compounds in a standard 2-way allogeneic mixed leukocyte reaction assay, we identified a potent immunosuppressive capacity of crassin acetate (CRA), a coral-derived cembrane diterpenoid. CRA efficiently inhibited allogeneic mixed leukocyte reaction as well as antigen-specific activation of CD4 T cells by bone marrow-derived dendritic cells (DCs). With regard to cellular targets, CRA suppressed not only mitogen-triggered T-cell activation, but also lipopolysaccharide-induced DC maturation, indicating dual functionality. Treatment with CRA at nontoxic doses induced heme oxygenase-1 (HO-1) mRNA/protein expression and HO-1 enzymatic activity in DCs, suggesting a unique mechanism of action. In fact, lipopolysaccharide-induced DC maturation was also inhibited by structurally unrelated compounds known to induce HO-1 expression or carbon monoxide (CO) release. Allergic contact hypersensitivity response to oxazolone and oxazolone-induced Langerhans cell migration from epidermis were both prevented almost completely by systemic administration of CRA. Not only do our results support the recent concept that HO-1/CO system negatively regulates immune responses, they also form both conceptual and technical frameworks for a more systematic, large-scale drug discovery effort to identify HO-1/CO-targeted immunosuppressants with dual target specificity.