Iron oxide-based nanoparticles with different mean sizes obtained by the laser pyrolysis: structural and magnetic properties.

Nano-sized iron oxide-based particles have been directly synthesized by the laser induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). In this paper we further demonstrate the possibility to vary the chemical composition and the nanoparticle dimensions of the iron oxide-based materials by handling the oxidation procedure in the frame of the laser pyrolysis process. Thus, nanoparticles with major maghemite/magnetite content may change composition into mixtures with variable amounts of three components: major gamma-Fe2O3/Fe3O4 iron oxide, metallic Fe and cementite Fe3C. By X-ray diffraction (XRD) it is found that the relative proportion of these phases differs in function of the reaction temperature (laser power). As revealed by transmission electron microscopy (TEM), mean particle sizes between about 4 nm and 6 nm and between about 9 and 11 nm may be prepared by varying the oxidation procedure and the laser power, respectively. By the controlled heating of samples (maximum temperature 185 degrees C), increased crystallinity for the gamma-Fe2O3/Fe3O4 oxide phase was found as well as an increase of the mean particle diameters. The examination of the magnetization curves for samples obtained for different laser powers indicates notable differences in the magnetic behavior and parameters. The temperature dependent Mossbauer measurements confirm the formation of larger particles at higher laser power densities as well as the presence of inter-particle magnetic interactions. On this basis, the estimation of phase composition for the different representative samples is given.

Staphylococcal protein A enhances natural killing activity against lymphoid tumor cell lines.

Protein A (pA), was found to augment the natural killing (NK) activity of peripheral blood lymphocytes against Burkitt's lymphoma-derived Raji and Daudi cells. This pA-enhanced NK activity was determined using the 51Chromium release microcytotoxicity assay. It was found that the increased NK activity was dependent on the concentration of pA used. In addition, the pA-enhanced NK activity was dependent on the time of incubation of pA with the effector and target cell mixture. Pretreatment of effectors for 16 h or more dramatically increased the NK activity against a wide range of tumor targets of different origin and possessing either B, T or null cell surface characteristics. The presence of the Epstein-Barr virus (EBV)-genome in the target cells did not influence the pA-enhanced NK activity. Nylon-wool column-fractionated, non-adherent lymphocytes (enriched in NK cells) showed an increased NK activity in the presence of pA than unfractionated lymphocytes. Pretreatment of certain targets with pA rendered them more sensitive to NK lysis. Interferon production was readily detected in supernatants from cultures of pA-treated effectors or effector-target mixtures, but not in supernatants from pA-treated target cultures tested. Results of different physicochemical treatments indicate that the pA-induced interferon is of gamma type (type II). Thus, the data presented suggest that the pA-induced enhancement of NK activity is most likely mediated by the pA-induced interferon.

Serological survey for congenital toxoplasmosis among 4,136 pregnant women.

A prospective seroepidemiological survey for latent congenital toxoplasmosis was carried out among 4,136 women and 3,787 of their offspring in and around Montreal. The indirect immunofluorescent antibody test was used to titrate specific IgG and IgM antibodies and results were standardized in international units. The prevalence of antibodies was 40-8% for the mothers and 36-4% for the babies. Mean annual seroconversion rate was 0-95%. Thus, 30 women would have been expected to acquire toxoplasmosis during pregnancy: two cases only were observed and the reasons for it are discussed. Four cases of congenital toxoplasmosis were diagnosed serologically (0-1%), none of them showed any signs of illness. Preventive treatment was administered to 12 of 52 pregnant women suspected of a recently acquired infection.