Peroxisome proliferator-activated receptor gamma inhibits the migration of dendritic cells: consequences for the immune response

The migration of dendritic cells (DCs) from the epithelia to the lymphoid organs represents a tightly regulated multistep event involved in the induction of the immune response. In this process fatty acid derivatives positively and negatively regulate DC emigration. In the present study we investigated whether activation of peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors activated by naturally occurring derivatives of arachidonic acid, could control DC migration from the peripheral sites of Ag capture to the draining lymph nodes (DLNs). First, we show that murine epidermal Langerhans cells (LCs) express PPAR gamma, but not PPAR alpha, mRNA, and protein. Using an experimental murine model of LC migration induced by TNF-alpha, we show that the highly potent PPAR gamma agonist rosiglitazone specifically impairs the departure of LCs from the epidermis. In a model of contact allergen-induced LC migration, PPAR gamma activation not only impedes LC emigration, and their subsequent accumulation as DCs in the DLNs, but also dramatically prevents the contact hypersensitivity responses after challenge. Finally, after intratracheal sensitization with an FITC-conjugated Ag, PPAR gamma activation inhibits the migration of DCs from the airway mucosa to the thoracic LNs and also profoundly reduces the priming of Ag-specific T lymphocytes in the DLNs. Our results suggest a novel regulatory pathway via PPAR gamma for DC migration from epithelia that could contribute to the initiation of immune responses.     

The effect of low dose gamma irradiation on the differentiation and maturation of monocyte derived dendritic cells

The effects of gamma-irradiation on the differentiation of peripheral blood monocytes (PBM) into monocyte derived dendritic cells (MDC), their maturation, and subsequent ability to present antigen to T cells was studied. Undifferentiated MDC were more sensitive to gamma-irradiation induced apoptosis than mature MDC. Irradiation of immature MDC with 5 Gy of gamma-rays down regulated the expression of the costimulatory receptors CD80/CD86 and may compromise their ability to capture and present antigen. By contrast, gamma-Irradiation of mature MDC did not affect the expression of CD86/CD80, and HLA-DR. Gamma-irradiation increased the apoptosis of MDC; but did not affect the ability of mMDC to stimulate autologous MLR. T cell proliferative response in the MLR and in response to tetanus antigen was reduced when gamma-irradiated primary DC1 were used to either stimulate or present antigen to T cells.     

Fractionated low-level gamma irradiation of Chinese hamster cells: Cellular and biochemical effects

Summary Chinese hamster V79 cells in log-phase were exposed daily to 0.6 Gy of radiation for 3–6 months. After such an exposure the population doubling time increased from 10 to 15 h. When irradiation was discontinued doubling time gradually decreased. Cell survival following acute radiation dose of the low-level irradiated cells remained the same as that of untreated cells. The fractionated irradiation did not affect the capacity of the cells to perform DNA repair synthesis. Likewise, the sensitivity to inhibition by acute radiation exposure of the ability to induce ornithine decarboxylase activity was similar in cells exposed to fractionated irradiation and in untreated cells. It is concluded that there is no apparent effect of sublethal radiation dose received in one generation on the radiation sensitivity of the succeeding generations during the log-phase of growth.     

A comparison of gamma and neutron irradiation on Raji cells: effects on DNA damage, repair, cell cycle distribution and lethality.

The Comet assay (microgel electrophoresis) was used to study DNA damage in Raji cells, a B-lymphoblastoid cell line, after treatment with different doses of neutrons (0.5 to 16 Gy) or gamma rays (1.4 to 44.8 Gy). A better growth recovery was observed in cells after gamma-ray treatments compared with neutron treatments. The relative biological effectiveness (RBE) of neutron in cell killing was determined to be 2.5. Initially, the number of damaged cells per unit dose was approximately the same after neutron and gamma-ray irradiation. One hour after treatment, however, the number of normal cells per unit dose was much lower for neutrons than for gamma rays, suggesting a more efficient initial repair for gamma rays. Twenty-four hours after treatment, the numbers of damaged cells per unit dose of neutrons or gamma rays were again at comparable level. Cell cycle kinetic studies showed a strong G2/M arrest at equivalent unit dose (neutrons up to 8 Gy; gamma rays up to 5.6 Gy), suggesting a period in cell cycle for DNA repair. However, only cells treated with low doses (up to 2 Gy) seemed to be capable of returning into normal cell cycle within 4 days. For the highest dose of neutrons, decline in the number of normal cells seen at already 3 days after treatment was deeper compared with equivalent unit doses of gamma rays. Our present results support different mechanisms of action by these two irradiations and suggest the generation of locally multiply damaged sites (LMDS) for high linear energy transfer (LET) radiation which are known to be repaired at lower efficiency.     

Some effects of enhanced UV-B irradiation on the growth and composition of plants

Barley (Hordeum vulgare), corn (Zea mays), bean (Phaseolus vulgaris), and radish (Raphanus sativus) seedlings were continuously irradiated under a lighting device for 5–10 d at an increased ultraviolet (UV)-B fluence rate. In their growth parameters, composition, and leaf surface, these four species responded differently to the increased UV-B exposure. Bean seedlings suffered the most serious effects, radish and barley less, and corn was hardly influenced at all. In all plant species, the fresh weight, the leaf area, the amounts of chlorophylls, carotenoids and the galactolipids of the chloroplasts were reduced. The lipid content of the corn and bean seedlings also diminished. But all the irradiated plants showed a rise in their protein content compared to the control plants. The content of flavonoids increased in barley and radish seedlings by about 50%. The effects on growth parameters and composition were more extensive with increasing UV-B fluence rates, at least as shown in the case of barley seedlings. The fresh weights fell proportionally with the chlorophylls and carotenoids. In contrast, the flavonoid content of barley leaves rose parallel to the increasing UV-B fluence rates and reached 180% of the value in the control plants with the highest UV-B fluence rate. Scorching appeared regularly in the form of bronze leaf discoloration at the highest UV-B fluence rates. Scanning electron micrographs of the leaf surface of UV-B irradiated plants showed deformed epidermal structures.Abbreviations MGDG monogalactosyldiglyceride - DGDG digalactosyldiglyceride - SL sulfoquinovosyldiglyceride - PG phosphatidylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - LA leaf are - FW fresh weight - DW dry weight - SEM scanning electron microscopy - C total carotenoids - Chl total chlorophyll     

Migration and maturation of human colonic dendritic cells

Dendritic cells (DC) in the colon may regulate intestinal immunity but remain poorly characterized. In this study a CD11c(+)HLA-DR(+)lin(-) (CD3(-)CD14(-)CD16(-)CD19(-)CD34(-)) population has been identified by flow cytometry in cells obtained by rapid collagenase digestion of human colonic and rectal biopsies. These day 0 (d0) CD11c(+)HLA-DR(+)lin(-) cells comprised approximately 0.6% of the mononuclear cells obtained from the lamina propria, were endocytically active, and had the phenotype of immature DC; they were CD40(+) and expressed low levels of CD83 and CD86, but little or no CD80 or CD25. Similar d0 DC populations were isolated from the colonic mucosa of healthy controls and from both inflamed and noninflamed tissue from patients with Crohn's disease. The lamina propria also contained a population of cells capable of migrating out of biopsies during an overnight culture and differentiating into mature DC with lower levels of endocytic activity and high cell surface expression of CD40, CD80, CD86, CD83, and CD25. This mature DC population was a potent stimulator of an allogeneic mixed leukocyte (MLR). Overnight culture of cells isolated by enzymatic digestion on d0 yielded DC with a phenotype intermediate between that of the d0 cells and that of the cells migrating out overnight. Overnight culture of colonic cells in which DC and HLA-DR(+)lin(+) cells were differentially labeled with FITC-dextran suggested that some of the maturing DC might differentiate from HLA-DR(+)lin(+) progenitors. This study presents the first analysis of the phenotype, maturational status, and migratory activity of human gut DC.     

Prevention of GVHD by modulation of rat bone marrow with UV-B irradiation: II. Kinetics of migration of UV-B-irradiated bone marrow cells in naive and lethally irradiated rats

UV-B irradiation (700 J/m2) of bone marrow (BM) cells prior to transplantation into lethally gamma-irradiated (1050 rad) allogeneic rats prevents the development of GVHD and results in a stable mixed lymphohematopoietic chimerism. To better understand the underlying mechanisms of the development of stable radiation chimeras in this model, this study was designed to examine whether the dose (700 J/m2) of UV-B irradiation used for the modulation of the BM inoculum would affect the homing pattern of radiolabeled BM cells compared to that of thoracic duct lymphocytes (TDL) in the naive and lethally irradiated recipients. The results showed that intravenously administered, 111Indium-oxine-labeled, unmodified TDL home specifically to the spleen, lymph nodes, and BM compartments with a subsequent recirculation of a large number of cells from the spleen to the lymph nodes. In contrast, radiolabeled, unmodified BM cells migrate specifically to the spleen, liver, and BM with the lymph nodes, thymus, and nonlymphoid organs containing very little amounts of radioactivity. The stable concentrations of radioactivity in the lymphoid and nonlymphoid compartments between 3 and 72 hr after injection suggest that BM cells, unlike TDL, do not recirculate. The migration pattern of BM cells in the naive recipient was not significantly different from that seen in lethally irradiated animals except for the higher concentration of radioactivity in the spleen and BM of irradiated animals compared to that seen in naive recipients. The similarity of tissue localization of BM cells in naive or in irradiated syngeneic recipients to that of allogeneic recipients suggests that the homing of BM cells is not MHC restricted. Our findings of similarity between tissue localization of UV-B-irradiated labeled BM cells and unmodified BM cells in naive and lethally irradiated recipients suggest that a dose of 700 J/m2 of UV-B irradiation is not capable of impairing BM cell migration although it is sufficient to abolish the homing of TDL to the HEV-bearing organs. Thus, our results show that BM cells are less susceptible to cell damage by UV-B irradiation than lymphocytes thereby providing the rationale for ex vivo modulation (rather than elimination) of mature T-lymphocytes in the donor BM inoculum with UV-B irradiation. This relatively simple and effective approach to modulation of T-cells in donor BM inoculum may be potentially useful in preventing GVHD without endangering successful engraftment in larger animals and in man.     

Effect of gamma irradiation on brain enkephalin hydrolase activity in the rat

A study was made of the effect of different radiation doses on the brain enzymes degrading enkephalins. Enkephalin aminopeptidase activity decreased during the first 60 min following irradiation with a dose of 774 X 10(-4) C/kg and increased after a dose of 3096 X X 10(-4) C/kg; enkephalinase A exhibited opposite changes. 48 hr after irradiation, enkephalin aminopeptidase activity exceeded the normal level, and no significant changes occurred in encephaliase A activity irrespective of the radiation dose.     

Characterization of altered absorptive and secretory functions in the rat colon after abdominal irradiation: comparison with the effects of total-body irradiation.

The aim of this work was to determine the alterations in the absorptive and secretory functions of the rat colon after abdominal irradiation and to compare the effects of abdominal and whole-body irradiation. Rats received an abdominal irradiation with 8 to 12 Gy and were studied at 1, 4 and 7 days after exposure. Water and electrolyte absorption was measured in vivo by insertion of an agarose cylinder into the colons of anesthetized rats. In vitro measurements of potential difference, short-circuit current and tissue conductance were performed in Ussing chambers under basal and agonist-stimulated conditions. Most of the changes appeared at 4 days after abdominal irradiation. At this time, a decrease in water and electrolyte absorption in the colon was observed for radiation doses > or = 9 Gy. The response to secretagogues (VIP, 5-HT and forskolin) was attenuated after 10 and 12 Gy. Epithelial integrity, estimated by potential difference and tissue conductance, was altered from 1 to 7 days after 12 Gy abdominal irradiation. These results show that the function of the colon was affected by abdominal irradiation. Comparison with earlier results for total-body irradiation demonstrated a difference of 2 Gy in the radiation dose needed to induce changes in the function of the colon.     

Migration of epithelial cells on laminins: RhoA antagonizes directionally persistent migration

Spatial and temporal expression of laminin isoforms is assumed to provide specific local information to neighboring cells. Here, we report the remarkably selective presence of LM-111 at the very tip of hair follicles where LM-332 is absent, suggesting that epithelial cells lining the dermal-epidermal junction at this location may receive different signals from the two laminins. This hypothesis was tested in vitro by characterizing with functional and molecular assays the comportment of keratinocytes exposed to LM-111 and LM-332. The two laminins induced morphologically distinct focal adhesions, and LM-332, but not LM-111, elicited persistent migration of keratinocytes. The different impact on cellular behavior was associated with distinct activation patterns of Rho GTPases and other signaling intermediates. In particular, while LM-111 triggered a robust activation of Cdc42, LM-332 provoked a strong and sustained activation of FAK. Interestingly, activation of Rac1 was necessary but not sufficient to promote migration because there was no directed migration on LM-111 despite Rac1 activation. In contrast, RhoA antagonized directional migration, since silencing of RhoA by RNA interference boosted unidirectional migration on LM-332. Molecular analysis of the role of RhoA strongly suggested that the mechanisms involve disassembly of cell-cell contacts, loss of the cortical actin network, mobilization of α6β4 integrin out of stable adhesions, and displacement of the integrin from its association with the insoluble pool of intermediate filaments.     

Prolonged effects of acute gamma irradiation on acetylcholine-induced potassium currents in human umbilical vein endothelial cells

Bourlier, V., Diserbo, M., Gourmelon, P. and Verdetti, J. Prolonged Effects of Acute Gamma Irradiation on Acetylcholine-Induced Potassium Currents in Human Umbilical Vein Endothelial Cells. Radiat. Res. 155, 748-752 (2001). We have recently reported an acute effect of gamma irradiation (15 Gy, 1 Gy/min) on acetylcholine-mediated endothelium-dependent relaxation in rat aortic rings. Given the importance of permeability to K+ to endothelium-dependent relaxation, we have evaluated the effect of the same radiation on K+ currents in human endothelial cells in culture using the patch-clamp technique in the whole-cell recording configuration. Our results indicate that, in resting cells, gamma irradiation has no effect on endothelial permeability to K+. However, irradiation during stimulation of endothelial cells with acetylcholine reduces the sustained increase in permeability to K+ observed in the acetylcholine-stimulated, nonirradiated cells. Additional experiments using K+ channel inhibitors (TEA, charybdotoxin, apamin) suggest that irradiation may in part decrease the prolonged activation of Ca2+-activated K+ channels by acetylcholine. Taken together with our previous finding that irradiation inhibits the acute relaxing effects of acetylcholine, these results show that gamma irradiation also affects the delayed effects of acetylcholine on permeability to K+.     

Effect of gamma irradiation on insulin receptor interaction in rat erythrocytes

An insulin receptor interaction has been studied in rat erythrocytes after whole-body gamma irradiation (1 Gy). Specific binding of insulin was found to increase 30 days following irradiation against the background of a decreased immunoreactive insulin concentration in the blood. A change in the postirradiation activity of insulin receptors is considered as a manifestation of the homeostatic mechanism of "up" regulation in exposed animals.     

Sterilization of allograft bone: effects of gamma irradiation on allograft biology and biomechanics

Gamma irradiation from Cobalt 60 sources has been used to terminally sterilize bone allografts for many years. Gamma radiation adversely affects the mechanical and biological properties of bone allografts by degrading the collagen in bone matrix. Specifically, gamma rays split polypeptide chains. In wet specimens irradiation causes release of free radicals via radiolysis of water molecules that induces cross-linking reactions in collagen molecules. These effects are dose dependent and give rise to a dose-dependent decrease in mechanical properties of allograft bone when gamma dose is increased above 25 kGy for cortical bone or 60 kGy for cancellous bone. But at doses between 0 and 25 kGy (standard dose), a clear relationship between gamma dose and mechanical properties has yet to be established. In addition, the effects of gamma radiation on graft remodelling have not been intensively investigated. There is evidence that the activity of osteoclasts is reduced when they are cultured onto irradiated bone slices, that peroxidation of marrow fat increases apoptosis of osteoblasts; and that bacterial products remain after irradiation and induce inflammatory bone resorption following macrophage activation. These effects need considerably more investigation to establish their relevance to clinical outcomes. International consensus on an optimum dose of radiation has not been achieved due to a wide range of confounding variables and individual decisions by tissue banks. This has resulted in the application of doses ranging from 15 to 35 kGy. Here, we provide a critical review on the effects of gamma irradiation on the mechanical and biological properties of allograft bone.     

Interactive effects of UV-B irradiation and triadimefon on nodulation and nitrogen metabolism in Vigna radiata plants

Supply of aqueous solution of triadimefon (20 mg dm⁻³) to unstressed green gram plants increased the contents of soluble proteins, amino acids, nitrate and nitrite, and the activity of nitrate reductase in the leaves and nitrate reductase in nodules. The nitrogenase activity in nodules and roots was also increased. Number and fresh mass of nodules and their nitrate and nitrite contents were also higher than those of the controls. In contrast, the UV-B stress (12.2 kJ m⁻² d⁻¹) suppressed nodulation and nitrogen metabolism in leaves and roots compared to plants under natural UV-B (10 kJ m⁻² d⁻¹). Triadimefon-treated plants did not show such severe inhibitions after exposure to elevated UV-B. Thus triadimefon increased their tolerance to UV-B stress.     

Karyometric characteristics of the rat sensorimotor cortex in non-uniform gamma irradiation

Neurocyte nuclei increase in volume without structural changes in karyoplasm at early times after gamma-irradiation of rat head with doses of 50 to 100 Gy. Irradiation of 200 Gy causes a diminution of the nuclei volume while at a dose of 400 Gy the nuclei do not change their volume. A dose as high as 1000 Gy causes severe changes in the karyoplasm leading to nucleus swelling. At later times (24-72 h), the increase in the nuclei volume is associated with the changes in the karyoplasm structure. At one and the same dose, radiation causes either a decrease (irradiation of the head) or increase (exposure of the body) in the neurocyte nuclei volume. At early times after wholebody uniform irradiation no karyometric changes are detected. The nucleus swelling is more pronounced at lower dose-rates.     

Migration of Langerhans cells and gammadelta dendritic cells from UV-B-irradiated sheep skin

Depletion of dendritic cells from UV-B-irradiated sheep skin was investigated by monitoring migration of these cells towards regional lymph nodes. By creating and cannulating pseudoafferent lymphatic vessels draining a defined region of skin, migrating cells were collected and enumerated throughout the response to UV-B irradiation. In the present study, the effects of exposing sheep flank skin to UV-B radiation clearly demonstrated a dose-dependent increase in the migration of Langerhans cells (LC) from the UV-B-exposed area to the draining lymph node. The range of UV-B doses assessed in this study included 2.7 kJ/m2, a suberythemal dose; 8 kJ/m2, 1 minimal erythemal dose (MED); 20.1 kJ/m2; 40.2 kJ/m2; and 80.4 kJ/m2, 10 MED. The LC were the cells most sensitive to UV-B treatment, with exposure to 8 kJ/m2 or greater reproducibly causing a significant increase in migration. Migration of gammadelta+ dendritic cells (gammadelta+ DC) from irradiated skin was also triggered by exposure to UV-B radiation, but dose dependency was not evident within the range of UV-B doses examined. This, in conjunction with the lack of any consistent correlation between either the timing or magnitude of migration peaks of these two cell types, suggests that different mechanisms govern the egress of LC and gammadelta+ DC from the skin. It is concluded that the depression of normal immune function in the skin after exposure to erythemal doses of UV-B radiation is associated with changes in the migration patterns of epidermal dendritic cells to local lymph nodes.