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M T Cushion

Publications and source records attributed to M T Cushion.

At least 73 records · Page 4Linked to original sources
PubMed1984

Growth and serial passage of Pneumocystis carinii in the A549 cell line.

Pneumocystis carinii obtained from infected rats and patients was cultured in the A549 cell line, a presumptive alveolar type 2 cell line derived from a human lung carcinoma. Standard criteria were established for organism sampling, quantitation, and growth. The trophozoite form of P. carinii was a more sensitive indicator of growth than was the cyst. Rat P. carinii increased 10-fold in primary culture and could be serially passed three additional times to new cultures; success in growing human P. carinii was limited and appeared to be related to the quality of the specimen received for culture. Growth pattern experiments suggested that close interaction of P. carinii with the cell monolayer is an important step in the life cycle of the organism. Thus, the A549 culture system should be useful for in vitro studies of the immunobiology of P. carinii.

Animals↗
PubMed1984

Predisposing factors in Pneumocystis carinii pneumonia: effects of tetracycline, protein malnutrition, and corticosteroids on hosts.

Components of the immunosuppressive regimen used to reactivate latent Pneumocystis carinii infection were analyzed for their effects on the growth, nutrition, and lymphoid system of hosts. Rats that were administered either tetracycline or a low-protein (8%) diet alone for 7 weeks developed few abnormalities, but animals on the combined regimen developed lower body and lymphoid organ weights, lower serum albumin levels, and fewer circulating lymphocytes. Rats that were administered corticosteroids and tetracycline experienced severe wasting, debilitation, and generalized lymphocyte depletion; the low-protein diet increased the magnitude of these changes. Alterations in the frequency of occurrence of specific lymphocyte subsets occurred only in rats given corticosteroids and consisted mainly of a greater decline in peripheral blood T helper cells than in T suppressor cells. The data suggest that long-term tetracycline administration and a low-protein diet have a variety of adverse effects on the host which enhance the immunosuppressive properties of corticosteroids.

Adrenal Cortex Hormones↗
PubMed1984

Lymphocyte changes during chronic administration of and withdrawal from corticosteroids: relation to Pneumocystis carinii pneumonia.

Corticosteroids were administered for up to 8 wk in adult Lewis rats to provoke Pneumocystis carinii pneumonia, and lymphocyte subsets were analyzed at different body sites with monoclonal antibodies by flow microfluorometry in a fluorescence activated cell sorter. The rats became chronically ill, debilitated, and exhibited marked involution of all lymphoid tissues. The lymphocytopenia was characterized in peripheral blood by a large fall in the frequency of T helper cells, and in the lungs by a fall in T helper (Th) cells and a rise in T suppressor (Ts) cells; at both sites there was reversal of the Th to Ts ratio. These changes were not found in the thymus, spleen, or bone marrow. When corticosteroids were withdrawn, the rats gained weight, cleared P. carinii from the lungs, and regenerated their lymphoid tissues. The lymphocyte subpopulations exhibited variation in their frequencies at different body sites, but gradually returned to baseline levels. Thus, in this model chronic corticosteroid administration results in profound generalized lymphocyte depletion and changes in the proportions of circulating and pulmonary T cell subsets. These abnormalities may be an important immunologic mechanism in the development of P. carinii pneumonia.

Adrenal Cortex Hormones↗
PubMedDate not supplied

A method for isolation of RNA from Pneumocystis carinii.

Total RNA from Pneumocystis carinii obtained directly from the rat lung and from short term culture on A549 cells was evaluated for size and purity. An isolation procedure using guanidine isothiocyanate and lithium chloride was preferable to a hot phenol method. Host cells were eliminated by hypotonic lysis and a series of microfiltrations. Pneumocystis carinii were pretreated with Zymolyase for increased susceptibility to chaotropic agents. The major ribosomal species of P. carinii RNA migrated similarly to Saccharomyces cerevisiae rRNA. The 28s-like species migrated well ahead of rat and A549 cell rRNA and well behind the prokaryotic large rRNA species.

Animals↗
PubMedDate not supplied

Ultrastructural observations on life cycle stages of Pneumocystis carinii.

An ultrastructural study of life cycle stages of Pneumocystis carinii in infected rat lungs in situ was undertaken utilizing 8 different modes of fixation. Three of the fixatives employed gave good fixation of cysts and intracystic bodies, but for the trophic forms fixation was only fair. Both the trophic forms and intracystic bodies have nuclear pores. The mitochondria of the organism have cristae that appear lamellar. One of the fixation modes revealed a thin, electron-dense layer on the outer surface of the cell wall, a "fuzzy coat" that had not been described previously. This material appears to mediate tight adhesion of trophic forms with other trophic forms, cysts, and with pneumocytes of the lung alveolus.

Animals↗
PubMedDate not supplied

Lectins as probes to Pneumocystis carinii surface glycocomplexes.

The binding characteristics of a panel of commercially available FITC-conjugated lectins to Pneumocystis carinii (Pc) were assessed by fluorescence microscopy and flow cytometry. Rat Pc obtained from infected lung homogenates were incubated with FITC-conjugated lectins in a series of concentrations, counterstained with propidium iodide, and analyzed for percent fluorescence and fluorescence intensity. All organisms bound concanavalin A and Wisteria floribunda agglutinin, 2 representatives of the glucose/mannose-binding group. From the lectin group specific for N-acetylglucosamine, Pc reacted more strongly with wheat germ agglutinin than with Solanum tuberosum agglutinin or Griffonia simplicifolia II lectin. Pneumocystis treated with lectins specific for N-acetyl-D-galactosamine and galactose exhibited much variation; the cells reacted moderately well to soybean agglutinin and less to Bauhinia purpurea, Maclura pomifera and Dolichos biflorus agglutinins and Griffonia simplicifolia I lectin. Arachis hypogaea agglutinin, Viscum album agglutinin and Griffonia simplicifolia I-beta 4 lectin had not effect. The organisms reacted weakly with Ulex europeus I agglutinin which is specific for fucose and did not react with Limax flavus lectin, which is specific for sialic acid. Competitive inhibition studies using relevant carbohydrates were performed to indicate that the positive reactions were specific. These studies should help to elucidate the mechanisms of attachment and pathogenesis of this organism.

Animals↗
PubMedDate not supplied

Analysis of Pneumocystis carinii cyst wall. I. Evidence for an outer surface membrane.

It has long been thought that the cyst form of Pneumocystis carinii, which can resist host defenses and antimicrobial drugs, is responsible for relapses of P. carinii pneumonia. The thick wall of the cyst is immunogenic and rich in glucosyl/mannosyl and N-acetyl-D-glucosamine residues. In this study we have demonstrated the presence of a hitherto unreported outer membrane in the cyst wall of P. carinii. This membrane was detected by a combination of techniques, including transmission electron microscopy, freeze-fracture electron microscopy, and membrane labeling with fluorescent lipid analogs following treatment of P. carinii cysts from infected rats for 30 min with Zymolyase, a beta-1-3 glucanase. As in gram-negative bacteria and blue-green algae, this 2nd membrane may have an important role in osmoregulation and nutrient utilization; it may also mediate the interaction of P. carinii with its host and serve as a target for drug therapy.

Animals↗
PubMedDate not supplied

Analysis of Pneumocystis carinii cyst wall. II. Sugar composition.

Pneumocystis carinii cysts are capable of resisting host defenses and antimicrobial drugs and are therefore thought to be responsible for relapses of P. carinii pneumonia in AIDS and other immunocompromised patients. The interaction of P. carinii with its host, and other P. carinii, might be mediated by molecules which form the outer surfaces of this organism. Carbohydrates are known to play many roles in cell-cell adhesion, and have been detected on the surface of P. carinii by lectin labeling experiments. In this study P. carinii cyst wall material was obtained from Zymolyase treatment. Alditol acetate derivatives of neutral and amino sugars or trimethylsilyl derivatives of methyl glycosides were prepared from the monosaccharides released from the sample by acid hydrolysis. Analyses were done by a combination of gas chromatography and mass spectrometry. Glucose was found to be the major sugar constituent. Mannose and galactose were present in equal ratios. A lesser amount of N-acetyl-D-glucosamine, and trace amounts of ribose and sialic acid were present in the cyst wall samples analyzed. These sugars may mediate P. carinii-host interaction and play an important protective role by creating a permeability barrier around the cyst.

Acetates↗
PubMedDate not supplied

Molecular genetic distinction of Pneumocystis carinii from rats and humans.

Pneumocystis carinii from rats and from humans were compared with respect to electrophoretic karyotype, presence of DNA sequences known to be repeated in rat-derived P. carinii, overall DNA sequence homology, and the sequences at two genetic loci. The organisms from each host species were different in each respect. Neither of two repeated DNAs from rat-derived P. carinii was found in the genome of human-derived organisms, and total DNA from rat-derived P. carinii failed to hybridize to human-derived P. carinii DNA. The sequences of the alpha-tubulin genes from the two P. carinii were strikingly different and the base composition of the alpha-tubulin gene from rat-derived P. carinii was rich in adenine and thymine, while the base composition of this gene from human-derived P. carinii was rich in guanine and cytosine. The sequence from the 18S rRNA gene of human-derived P. carinii was twice as divergent from that of rat-derived P. carinii as the sequence from the corresponding region of Candida albicans was from that of Candida tropicalis. These data show that rats and humans can harbor distinct types of P. carinii that are sufficiently different to suggest that P. carinii from the two hosts could be different species.

Amino Acid Sequence↗
PubMedDate not supplied

Kinetics of 2 genetically distinct Pneumocystis carinii populations in rat colonies.

The natural history of prototype and variant Pneumocystis carinii populations in several colonies of rats were monitored over time periods ranging from 1 to 4 years. Karyotypic profiles of organism populations from individual rats were evaluated for the proportion of prototype:variant P. carinii and the number of animals harboring co-infections were enumerated. Throughout the observation periods: (1) each P. carinii population retained its distinctive karyotype; (2) the proportions of prototype:variant within the lungs fluctuated; and (3) the number of rats co-infected within a colony varied. These surveys suggest a competition between 2 similarly adapted populations.

Animals↗