Biomedical subjects

N T Gross

Publications and source records attributed to N T Gross.

7 recordsLinked to original sources

PubMed2000

Treatment of experimental Cryptococcus neoformans infection in newborn rabbits by airway instillation of specific antibody and surfactant.

Cryptococcosis in AIDS patients has a slow response to antifungal chemotherapy, and passive antibody treatment has thus been considered as an adjunct. Polyclonal anticryptococcal IgG dissolved in a suspension of modified natural surfactant was given intratracheally to near-term rabbits. Killing of Cryptococcus neoformans within the lungs was determined by counting the colony forming units (cfu). After 5 h a significant decrease in cfu was observed in rabbits treated with the IgG-surfactant mixture compared with control animals receiving saline. In conjunction with conventional therapy, the combined treatment of IgG-surfactant given by bronchoscopy might be used in high-risk patients to enhance killing of the yeast within the lungs.

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PubMed2000

Lipid peroxidation by alveolar macrophages challenged with Cryptococcus neoformans, Candida albicans or Aspergillus fumigatus.

Increased formation of oxygen radicals has previously been shown for alveolar macrophages (AM) challenged with Cryptococcus neoformans cells opsonized with fresh serum or polyclonal immunoglobulin G. AM show similar responses to Candida albicans or Aspergillus fumigatus. Oxygen radicals are capable of damaging various macromolecules, including lipids. In the present study, lipid peroxidation (LPO) caused by AM incubated with the fungi was examined in the presence and absence of lung surfactant. The level of malonaldehyde was used as an indicator of LPO. AM damage was examined by electron microscopy (EM), by trypan blue exclusion and by counting the AM loss from culture dish to supernatant. Stimulation of AM by each fungus increased cellular LPO but did not affect AM viability. A slight surfactant LPO induced by AM alone was shown with significantly increased values after addition of each fungus. EM studies showed that dense lipid droplets, presumably consisting of oxidized lipids, were ingested in high amounts together with C. neoformans cells that had been opsonized in fresh serum, and in low amounts in combination with C. albicans. These processes were accompanied by increased numbers of AM in the supernatants. LPO and detachment of AM were counteracted by vitamin E. In the lungs, AM exposed to one of these fungal pathogens might promote peroxidation of surfactant lipids.

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PubMed1999

Production of nitric oxide by rat alveolar macrophages stimulated by Cryptococcus neoformans or Aspergillus fumigatus.

Cryptococcus neoformans and Aspergillus fumigatus are airborne fungi and the alveolar macrophages (AM) constitute a first line of host defence against both pathogens. We investigated the ability of rat AM to produce nitric oxide (NO) when challenged in vitro with C. neoformans, A. fumigatus conidia or inert silica particles alone and together with interferon gamma (IFN-Gamma). The role of NO in the killing of C. neoformans as well as the relationship between phagocytosis of the yeast or A. fumigatus conidia and NO production by AM were studied. Both fungi, but not the inert particles induced a small but significant increase in NO production by AM. A synergistically enhanced NO production by AM was observed when each fungus, but not silica particles, were incubated together with IFN-Gamma. AM treated with IFN-Gamma and challenged with C. neoformans showed higher killing activity than untreated AM, a finding that correlated with increased NO production by AM. Both effects were reduced by an inhibitor of NO synthesis. Increased NO production by IFN-Gamma activated AM was found together with an increased accumulated attachment of A. fumigatus conidia and serum opsonized, but not unopsonized C. neoformans. The IFN-Gamma dependent increase in accumulated attachment of the fungi might be responsible for the synergistic effect of the fungi and IFN-Gamma on the NO production. Our data suggest that activated rat AM might efficiently use the antimicrobial nitric oxide system in the defence against these pathogens in the normal host.

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PubMed1997

In vivo interaction between alveolar macrophages and Cryptococcus neoformans.

In vivo interactions of rabbit alveolar macrophages (AM) and Cryptococcus neoformans, a yeast pathogenic for humans, were studied. As a control, inert silica particles of a similar diameter (5-6 microns) were used. Of 16 rabbits, 6 were instilled intratracheally with fluorescein-labelled heat-killed C. neoformans, 6 with fluorescein-labelled silica particles and 4 with saline only. After 24 h, the AM were collected by lung lavage, and phagocytosis, oxidative metabolism, phagolysosomal pH and morphology were studied. The accumulated number of yeasts attached to the AM was almost the same for C. neoformans as for the silica particles. The ingested fraction of C. neoformans was even higher than that of the silica particles. Quantitative NBT reduction by the AM, reflecting their oxidative metabolism, was markedly increased by exposure to C. neoformans for 24 h. The phagolysosomal pH was on the average lower in phagolysosomes with C. neoformans than with the silica particles, although approximately 2% of the phagolysosomes with C. neoformans had neutral pH. Phagolysosomes with neutral pH was not observed for silica particles. Electron microscopy showed presence of C. neoformans in phagolysosomes of AM. The conclusion of this study is that the phagocytic activity, oxidative metabolism and phagolysosomal pH AM against C. neoformans are significant 24 h after the exposure.

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PubMed1996

Anticryptococcal activity by alveolar macrophages from rats treated with cortisone acetate during different periods of time.

The effect of cortisone acetate (CA) treatment on the anticryptococcal activity by rat alveolar macrophages (AM) was investigated. The animals received a weekly dose of 5 mg CA during 1, 2, 3 or 4 weeks. Following the final dose the AM were collected by lung lavage and challenged with Cryptococcus neoformans. Parallel experiments with silica particles of a similar size were performed. The phagocytic function was assessed using a fluorescence method that distinguishes between attached and ingested particles. The oxidative metabolism was studied by the nitroblue tetrazolium (NBT) reduction test. The accumulated attachment (a measure of the attachment process) of cryptococci and silica particles per AM was significantly depressed after the third and fourth week of CA treatment. The ingested fraction (a measure of the ingestion process) of cryptococci but not of silica particles showed a small but significant decrease after the fourth week. The NBT reduction of the unstimulated AM and those stimulated with either the cryptococci or silica particles for 24 h was significantly reduced after the fourth week of treatment. In conclusion, these results demonstrate that high dose CA treatment primarily affects the attachment of the cryptococci to the AM and to a lesser extent also the ingestion process. In addition, it decreases the NBT reduction by AM in response to the yeast. The impairment of the AM anticryptococcal activity by high doses of CA constitutes a risk of dissemination of C. neoformans from the lungs.

Animals↗

PubMedDate not supplied

In vitro effect of lung surfactant on alveolar macrophage defence mechanisms against Cryptococcus neoformans.

The effects of a modified natural porcine surfactant (Curosurf) on phagocytosis and killing of Cryptococcus neoformans by alveolar macrophages and on the production of superoxide anions were investigated in vitro. Attachment and ingestion were evaluated separately by a fluorescent quenching technique. The nitroblue tetrazolium reduction test was used as an indirect measurement of superoxide anion production. Killing was assessed by a colony-forming assay. Surfactant induced increased ingestion of C. neoformans, unopsonized as well as opsonized with fresh serum or anticryptococcal polyclonal IgG. Surfactant had, however, no effect on the attachment or killing of unopsonized or opsonized C. neoformans by the alveolar macrophages. In addition, the enhancement of the oxidative metabolism of the macrophages after stimulation with opsonized yeast was impaired, although the killing was not affected. This study indicates that in vitro Curosurf can influence the alveolar macrophage defence against C. neoformans by enhancing its ingestion and by interacting with the superoxide anions release from alveolar macrophages stimulated with fresh serum or anticryptococcal polyclonal IgG opsonized yeast cells.

Animals↗

PubMedDate not supplied

Interaction between Cryptococcus neoformans and alveolar macrophages.

Phagocytosis, oxidative metabolism and phagolysosomal pH of rat alveolar macrophages (AM) were studied at different points of time after challenge with Cryptococcus neoformans. Phagocytosis was evaluated using a fluorescent quenching technique which distinguishes between attached and ingested organisms. The nitroblue tetrazolium (NBT) test was used as an indirect measurement of the oxidative metabolism of the phagocytes. The pH of the phagolysosomes was measured using a cytofluorometric technique. Both the attachment and ingestion of serum opsonized C. neoformans by AM were slow during the first hours of incubation, but were considerable after 24 h. The oxidative metabolism of Am challenged with the yeast was insignificant during the first hour, but reached high levels after 24 h. Most phagolysosomes in AM with ingested cryptococci had a pH < 5.5. Our results indicate that these AM defence mechanisms, although poor during the first hours after exposure to the yeast, are of significance after 24 h. Thus, in the immunocompetent host the AM should prevent the dissemination of C. neoformans from the lungs.

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