Internalization of titanium dioxide nanoparticles by glial cells is given at short times and is mainly mediated by actin reorganization-dependent endocytosis

Many nanoparticles (NPs) have toxic effects on multiple cell lines. This toxicity is assumed to be related to their accumulation within cells. However, the process of internalization of NPs has not yet been fully characterized. In this study, the cellular uptake, accumulation, and localization of titanium dioxide nanoparticles (TiO₂ NPs) in rat (C6) and human (U373) glial cells were analyzed using time-lapse microscopy (TLM) and transmission electron microscopy (TEM). Cytochalasin D (Cyt-D) was used to evaluate whether the internalization process depends of actin reorganization. To determine whether the NP uptake is mediated by phagocytosis or macropinocytosis, nitroblue tetrazolium (NBT) reduction was measured and the 5-(N-ethyl-N-isopropyl)-amiloride was used. Expression of proteins involved with endocytosis and exocytosis such as caveolin-1 (Cav-1) and cysteine string proteins (CSPs) was also determined using flow cytometry.TiO₂ NPs were taken up by both cell types, were bound to cellular membranes and were internalized at very short times after exposure (C6, 30 min; U373, 2 h). During the uptake process, the formation of pseudopodia and intracellular vesicles was observed, indicating that this process was mediated by endocytosis. No specific localization of TiO₂ NPs into particular organelles was found: in contrast, they were primarily localized into large vesicles in the cytoplasm. Internalization of TiO₂ NPs was strongly inhibited by Cyt-D in both cells and by amiloride in U373 cells; besides, the observed endocytosis was not associated with NBT reduction in either cell type, indicating that macropinocytosis is the main process of internalization in U373 cells. In addition, increases in the expression of Cav-1 protein and CSPs were observed.In conclusion, glial cells are able to internalize TiO₂ NPs by a constitutive endocytic mechanism which may be associated with their strong cytotoxic effect in these cells; therefore, TiO₂ NPs internalization and their accumulation in brain cells could be dangerous to human health.     

Inhibitory effect of phospholipase A2 isolated from Crotalus durissus terrificus venom on macrophage function

Recent work demonstrated that crotoxin, the main toxin of Crotalus durissus terrificus venom, inhibits macrophage spreading and phagocytic activities. The crotoxin molecule is composed of two subunits, an acidic non-toxic and non-enzymatic polypeptide named crotapotin and a weakly toxic basic phospholipase A₂ (PLA₂). In the present work, the active subunit responsible for the inhibitory effect of crotoxin on macrophage function was investigated. Peritoneal macrophages harvested from naive rats were used. Crotapotin (2.12, 3.75, or 8.37 nM/ml), added for 2 h to the medium of peritoneal cell incubation, did not modify the spreading and phagocytic activities of these cells. On the other hand, the PLA₂ (1.43, 2.86, or 6.43 nM/ml) subunit caused a significant reduction (30, 33, and 35%, respectively) of the spreading activity. The PLA₂ also inhibited the phagocytosis of opsonised zymosan, opsonised sheep erythrocytes, and Candida albicans, indicating that this inhibitory effect is not dependent on the type of receptor involved in the phagocytosis process. The inhibitory effect of PLA₂ was not due to loss of cell membrane integrity, since macrophage viability was higher than 95%. These findings indicate that the inhibitory effect of crotoxin on macrophage spreading and phagocytic activities is caused by the phospholipase A₂ subunit.     

The influence of synovial fibroblasts on the phagocytosis of Staphylococcus by polymorphonuclear cells

Summary It has been suggested that the reduced resistance of patients with rheumatoid arthritis (RA) to bacterial joint infections may be due in part to polymorphonuclear cell (PMN) function. To obtain further insight into the mechanis that contribute to the increased susceptiblity of RA patients to such infections we investigated the influence of different solid surfaces on the ingestion of various bacterial strains by PMN. Both in the presence and absence of serum, phagocytosis of bacteria by PMN was significantly lower on monolayers of synovial fibroblasts as compared to monolayers of endothelial cells and embryonic fibroblasts. It could be shown that the relative influence of the solid surfac on the results of the phagocytosis assay increased when decreasing concentrations of purified IgG were used. The results of this study sugpurified IgG were used. The results of this study suggested that the effect of synovial fibroblasts on PMB may lead to reduced clearance of bacteria from the joint.     

HIV GP120对人和无脊椎动物免疫细胞的抑制作用

通过人工合成了人类免疫缺陷性病毒（Ｈｕｍａｎｉｍｍｕｎｏｄｅｆｉｃｉｅｎｃｙｖｉｒｕｓ，ＨＩＶ）糖蛋白肽ＧＰ１２０对人和无脊椎动物（Ｍｙｔｉｌｕｓｅｄｕｌｉｓ）免疫细胞的抑制作用的研究。人单核细胞和Ｍｙｔｉｌｕｓｅｄｕｌｉｓ免疫细胞分别与ＧＰ１２０保温后，均抑制细胞的吞噬细菌（Ｐｓｕｄｏｍｏｎａｓｓｔｒｅｔｚｉ）作用。应用计算机显微图像术（Ｃｏｍｐｕｔｅｒ－ａｓｓｉｓｔｅｄｍｉｃｒｏｓｃｏｐｙ）直     

纤维胶原素

纤维胶原素是一组含纤维蛋白原样区和胶原样区的蛋白质,其结构与甘露聚糖结合凝集素(BML)相似,但其糖结合区不同,前者是纤维蛋白原样区,后者是糖识别域。纤维胶原素识别病原体表面的糖结构后,通过结合MBL相关丝氨酸蛋白酶而激活补体凝集素途径,还能介导调理吞噬作用。     

Insulin inhibits phagocytosis in normal human neutrophils via PKCα/β-dependent priming of F-actin assembly

Objective: This study investigated the effects of insulin on the phagocytosis of C3bi – and IgG-opsonized yeast particles in normal human neutrophils. Methods: Neutrophils were incubated in different insulin concentrations for 30 minutes and stimulated by C3bi – or IgG-opsonized yeast particles. Phagocytosis was quantified by both light microscopy and FACscan flow cytometry. Laser confocal microscopy was used for quantification of F-actin levels. Results: Elevated insulin concentrations decreased neutrophil phagocytosis of both types of targets. This defect was shown to be in part due to a delayed phagocytosis in the presence of insulin. Following a 30 minute incubation, insulin was found to increase the accumulation of cortical F-actin, without affecting the total cellular F-actin content. The specific PKCα/β inhibitor, Go6976, abolished the insulin-mediated increase in cortical F-actin content and both Go6976 and the PKCα/β/δ/ε-specific inhibitor GF109203X reversed the inhibitory effects of insulin on phagocytosis. Conclusion: Hyperinsulinemia in vitro can inhibit phagocytosis of opsonized targets in normal human neutrophils. This effect of insulin is dependent on activation of PKCα and/or PKCβ, and these insulin signals may interfere with the dynamic assembly/disassembly and/or distribution of F-actin, which is required for the phagocytosis process. Received 8 July 2005; accepted 13 October 2005 without revision I. Ahnfelt-R?nne     

Phagocytosis in the colonial ascidian Botryllus schlosseri

Phagocytosis by Botryllus schlosseri hemocytes in influenced by temperature, pH, concentration, and physicochemical properties of the test particles and requires Ca²⁺ or Mg²⁺ ions to occur. Phagocytes recognized glucosyl or mannosyl residues on the surface of yeast cells, and a respiratory burst is associated with phagocytosis, as indicated by increased superoxide production. Factors that enhance phagocytosis of yeast, sheep red blood cells, and latex beads and reduce the uptake of yeast and sheep erythrocytes are present in the plasma.     

Effects of L-carnitine on neutrophil functions in aged rats

Several age-related alterations occur at the cellular level in the immune system leading to a decrease in the immune response. The present study was designed to determine the effect of L-carnitine on impaired neutrophil functions of aged rats. For this reason, superoxide anion radical production, chemotaxis and phagocytic activity were studied in the neutrophils obtained from the peripheral blood of young and old rats. We orally gavaged L-carnitine (50 mg/kg b.w. per day) or control vehicle into young (2 months) and aged (24 months) rats for 30 consecutive days. The neutrophils of aged rats exhibited an increase in superoxide anion production and decline in phagocytosis and chemotaxis when compared with that in young rat neutrophils. Superoxide anion production in aged rats was significantly decreased by L-carnitine treatment which was accompanied with a significant enhancement of chemotactic and phagocytic activity being restored to control levels. These findings demonstrated that L-carnitine is capable of restoring the age-related changes of neutrophil functions.