Failure of carcinogen-altered dendritic cells to initiate T cell proliferation is associated with reduced IL-1 beta secretion

Polycyclic aromatic hydrocarbons affect functional differentiation and maturation of human monocyte-derived dendritic cells

Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BP) are environmental carcinogens exhibiting potent immunosuppressive properties. To determine the cellular bases of this immunotoxicity, we have studied the effects of PAHs on differentiation, maturation, and function of monocyte-derived dendritic cells (DC). Exposure to BP during monocyte differentiation into DC upon the action of GM-CSF and IL-4 markedly inhibited the up-regulation of markers found in DC such as CD1a, CD80, and CD40, without altering cell viability. Besides BP, PAHs such as dimethylbenz(a)anthracene and benzanthracene also strongly altered CD1a levels. Moreover, DC generated in the presence of BP displayed decreased endocytic activity. Features of LPS-mediated maturation of DC, such as CD83 up-regulation and IL-12 secretion, were also impaired in response to BP treatment. BP-exposed DC poorly stimulated T cell proliferation in mixed leukocyte reactions compared with their untreated counterparts. In contrast to BP, the halogenated arylhydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin, which shares some features with PAHs, including interaction with the arylhydrocarbon receptor, failed to phenotypically alter differentiation of monocytes into DC, suggesting that binding to the arylhydrocarbon receptor cannot mimic PAH effects on DC. Overall, these data demonstrate that exposure to PAHs inhibits in vitro functional differentiation and maturation of blood monocyte-derived DC. Such an effect may contribute to the immunotoxicity of these environmental contaminants due to the major role that DC play as potent APC in the development of the immune response.

Mouse Dendritic Cells Express the P2X7 Purinergic Receptor: Characterization and Possible Participation in Antigen Presentation

Immune cells express P2 purinoceptors of the P2Y and P2X subtypes. In the present work, we show that three dendritic cell (DC) lines, D2SC/1, CB1, and FSDC, representative of immature DCs, express the P2X7 (formerly P2Z) receptor, as judged from RT-PCR amplification, reactivity to a specific antiserum, and pharmacological and functional evidence. Receptor expression is higher in FSDC cells, a cell line that is functionally more mature than D2SC/1 and CB1. From the wild-type DC population, we selected cell clones lacking the P2X7R (P2X7less). We also used a P2XR blocker, oxidized ATP, to irreversibly inhibit the P2X7R. Ability of P2X7less FSDCs or of oxidized ATP-inhibited FSDCs to stimulate Ag-specific TH lymphocytes was severely decreased although Ag endocytosis was minimally affected. During coculture with TH lymphocytes, wild-type FSDC secreted large amounts of IL-1β. Release of this cytokine was reduced in P2X7less DCs. These data show that DCs express the P2X7 purinoceptor and suggest a correlation between P2X7R expression and Ag-presenting activity.

Effects of UV on the migration and function of epidermal antigen presenting cells

Depletion of epidermal Langerhans cells (LC) and the concomitant depression of the skin immune system after excessive exposure to ultraviolet B light (UVB) has been established in the international literature for some time. Our investigations were intended to determine whether or not these phenomena occurred as a direct result of increased LC migration being triggered by the UVB exposure. To test this hypothesis, a sheep model was established in which the lymphatic vessels draining a defined region of skin were cannulated and the cells migrating towards the regional lymph node continuously collected. Cell populations in these collections were identified and enumerated by indirect immunofluorescence and flow cytometry. These experiments showed there was a significant, dose-dependent increase in the rate of LC migration from sheep skin after exposure to doses of UVB light exceeding 1 minimal erythemal dose (MED). In a series of parallel experiments, the functional characteristics of dendritic cells (DC) migrating from normal or UVB irradiated sheep were studied. To assay them, enriched preparations of DC were collected via cannulated afferent lymphatic vessels and pulsed with antigen prior to incubation with autologous peripheral blood lymphocytes. The relative efficiency of antigen presentation was determined by the ability of DC to induce T cell proliferation. Our data clearly demonstrate that there is a profound loss of normal antigen-presenting cell function after exposure to UVB light. Various experiments were undertaken to determine the mechanism(s) associated with these changes in migration kinetics and cellular function. Electron microscopic examinations of LC migrating from normal or UVB irradiated skin have demonstrated a profound loss of dendritic processes after UVB exposure. This provides a possible explanation for the changes in skin immunity after UVB exposure.