Leukemogenesis in vitro induced by thymus epithelial reticulum cells transmitting murine leukemia viruses

The role of the thymus in induction of leukemia was studied in vitro. Curltivation of normal thymus cells on thymus epithelial reticulum cell monolayers that had been grown from radiation leukemia virus-induced leukemic thymuses rendered the thymocytes leukemic. C57BL/6 thymocytes were cultivated for 3 days on leukemic thymus reticulum monolayers, and 106 thymocytes were injected i.p. into young adult C57BL/6 mice. After 3 to 4 weeks all mice died of disseminated lymphatic leukemia. Mice given thymocytes that had been cultivated on thymus epithelial reticulum monolayers from normal mice did not develop lymphomas. The leukemic thymus epithelial reticulum cells were shown to produce thymotropic as well as ecotropic and xenotropic radiation leukemia virus. (Thymotropic virus has affinity for thymus lymphocytes but noes not infect fibroblasts.) The cells were brightly positive for murine leukemia virus group-specific antigen in immunofluorescence tests. Leukemic thymus epithelial reticulum cells produced ample infectious exotropic virus in the culture supernatant, although the cells were negative in the XC syncytia test. Upon infection of mouse fibroblasts with ecotropic virus produced by the leukemic reticulum cells, XC syncytia were readily obtained. Thymocytes that were cultivated on leukemic thymus reticulum cells became positive for murine leukemia virus group-specific antigen and produced syncytia in the XC test. Thus, in vitro lymphomagenesis of the thymocytes that were cultured on leukemic thymus reticulum cells was associated with their infection with thymotropic and ecotropic radiation leukemia virus.

Medical student education in psychiatry

The authors interpret data obtained from 99 medical schools which submitted grant applications for support of either undergraduate psychiatric education programs or human behavior programs. They tentatively conclude that high-quality programs for teaching medical students psychiatry are characterized by a well-rounded faculty, a psychodynamic orientation, a greater commitment to medical student education than to resident training, varied teaching methods, enthusiastic student response, and systematic evaluation that produces change in subsequent years.

Transient virus expression during murine leukemia induction by X-irradiation

Most X-irradiation-induced thymomas in C57BL/6 mice are virus-free when assayed by immunofluorescence for the gs antigen (gsa) of murine leukemia virus (MuLV). Virus was induced transiently in bone marrow cells and later appeared in thymus cells. Six to 7 weeks post irradiation, thymocytes and bone marrow cells were MuLV gsa-negative and remained negative for the lifetime of most animals, whether or not they contracted overt leukemia. During the period when MuLV gsa-positive bone marrow cells were found, XC-positive syncytia-producing bone marrow cells were also found. Virus information was expressed, therefore, for a limited duration, long before any signs of leukemia in the animals were evident. MuLV gsa-positive thymocytes taken from mice 4 weeks after X-irradiation were cocultivated with a series of indicator cells. B-tropic virus, in addition to a xenotropic virus, was isolated from these cells. Ecotropic virus was not found in normal mouse thymocytes, in irradiated thymocytes a few days after termination of the X-irradiation sequence, or in most primary thymomas. All thymocytes produced only xenotropic virus in the cocultivation assays. Expression of the ecotropic virus was, therefore, transient, as assayed by immunofluorescence, XC syncytia formation, and virus isolation from MuLV gsa-positive thymus cells.

[Comparative studies on the teaching of oral pathology]

This is a self-assessment of teaching effectiveness for teacher, students and teaching-material as well. A curriculum of oral patholology was created and prepared as syllabus, lectures and audiovisual aids. In order to estimate and compare the eductional achievements of different systems, a series of written multiple choice questions were prepared. Only items with an index of discrimination of more than 0,25 were used. The average index was 0,5. The results of a short-term experimetn (1 hour) shows that a teaching sequence in the conventional lecture style was most effective in transmitting knowledge (72% of maximum), audiovisual aids rating second (63%), followed by individual homework study using printed material (48%). The differences were statistically significant in most experiments. In the second type of experiment (long-term-experiment) we registered the time the students spent with lectures over a period of six months. When permitted to chose between the different systems the students preferred the audiovisual method to the lectures. Individual testing of these students shows a positive correlation between knowledge acquired and time spent with the audiovisual machines.

Pulsed nuclear magnetic resonance study of 17O from H217O in rat lymphocytes

Lymphocytes obtained from thymus glands of normal rats and culture lines of malignant rat thymocytes were enriched with H217O. The longitudinal and transverse relaxations of the 17O were determined separately in samples of packed cells and supernatant solutions. The longitudinal relaxation of intracellular 17O of fresh viable lymphocytes was nonexponential, becoming simply exponential with eventual necrosis. The rate of spin-lattice relaxation (1/T1) was fitted by a sum of two exponentials. The average mole fraction of the molecules subject to the slower relaxation rate (1/T1s) was two-thirds of the total water. Lowering the Larmor frequency (omega) from 7.72 to 4.36 MHZ increased the faster component (1/T1f) by 12% without altering (1/T1s). The value of the single exponential decay of the nonviable cells was not appreciably different from the initial rate of relaxation of the fresh cells. Similar results were obtained in studies of the transverse relaxation rates. The simplest interpretation is that two-thirds of the cell water is located within the nucelus and is characterized by a slower rate of relaxation than the one-third of the cell water in the cytoplasm because of the different macromolecular compositions of the two-subcellular compartments. The malignant lymphocytes were characterized by prolonged values for the slow and fast components of both the longitudinal and transverse relaxations of 17O.

Enzymatic modification of aminoglycoside antibiotics: a new 6'-N-acetylating enzyme from a Pseudomonas aeruginosa isolate

We describe an aminoglycoside 6'-N-acetyltransferase, isolated from Pseudomonas aeruginosa, that exhibits a novel substrate profile characterized by markedly reduced activity towards butirosin and amikacin.

Enzymatic modification of aminoglycoside antibiotics: a new 3-N-acetylating enzyme from a Pseudomonas aeruginosa isolate

A new 3-N-aminoglycoside acetyltransferase is described, which possesses a wider substrate range than any such enzyme so far discovered in clinical isolates of antibiotic-resistant bacteria.

In vitro infection of lymphoid cells by thymotropic radiation leukemia virus grown in vitro

Murine lymphoid cells were infected in vitro with purified leukemogenic radiation leukemia virus (RadLV) produced by virus-induced lymphoblast cell lines. Thymocytes were shown to be highly susceptible to infection by the virus, whereas murine or other fibroblasts were refractory to it. Murine bone marrow and spleen cells were shown to be much less sensitive to infection by this thymotropic RadLV. By comparison, a B-tropic RadLV isolate (RadLV), propagated on a mouse fibroblast cell line, was noninfectious for lymphoid cells but infected fibroblasts. A correlation was shown to exist between in vitro infection of thymocytes, as assayed by immunofluorescence, and in vivo leukemogenicity of the thymotropic RadLV. This constitutes a rapid in vitro test for in vivo leukemogenicity of a natural lymphatic leukemia virus.

Loss of simian virus 40 DNA-RNA hybrids from nitrocellulose membranes; implications for the study of virus--host DNA interactions

Complete hybrids of simian virus 40 (SV40)DNA and its complementary RNA (cRNA) are not retained on nitrocellulose membranes. At saturating cRNA concentrations, retention of the hybrids indicates incomplete homology between DNA and RNA, probably due to incorporation of host DNA in the viral DNA; this effect is most pronounced when DNA is produced in cells infected at high multiplicity. Hybrids between DNA of Chinese hamster cells transformed by SV40 and cRNA are retained if the DNA fragments are long, but they are lost if the DNA is sheared to less than the length of an SV40 DNA molecule. Hence, in cells examined with about six SV40 genomes per cell, each genome is individually integrated. The results may explain previous discrepancies in the estimation of the number of viral genomes in transformed cells.

Defective bacteriophage PBSH in Bacillus subtilis. I. Induction, purification, and physical properties of the bacteriophage and its deoxyribonucleic acid

PBSH, a defective phage of Bacillus subtilis strain 168, is described. Conditions are given for optimal induction of the prophage with mitomycin C. After a latent period of 90 min, cells were lysed and phage-like particles were released with a burst size of approximately 100 to 400 phage per bacterium. Since no known host supports phage replication after infection, burst size was determined by electron microscope count. Purification procedures and criteria for purity are described. The molecular weight of deoxyribonucleic acid (DNA) extracted from PBSH was estimated by length measurement and sedimentation. No circular DNA molecules were found by either technique. PBSH DNA molecules are linear, double-stranded, and of homogeneous molecular weight, about 12 x 10(6) daltons. There is no evidence for single-strand breaks. The majority of PBSH DNA molecules show a sedimentation behavior dependent on ionic strength. It is inferred that most of the DNA molecules are less hydrodynamically rigid than native DNA having a similar average base composition and molecular weight. Possible reasons for the sedimentation behavior are discussed.

Defective bacteriophage PBSH in Bacillus subtilis. II. Intracellular development of the induced prophage

Treatment of Bacillus subtilis strain 168 with mitomycin C caused induction of a defective prophage, PBSH. During induction, extensive deoxyribonucleic acid (DNA) synthesis took place. Concurrently, a change in marker frequency of the bacterial DNA was noticed. The frequency of only one marker, ade-16, the marker closest to the origin of the bacterial chromosome, was enhanced manyfold. DNA from whole phage particles transformed all bacterial markers at a frequency equal to that of DNA in the noninduced culture, except ade-16, the frequency of which was enhanced 30 to 100 times. Analysis of a double isotope experiment demonstrated that 14% of the phage DNA was derived from preinduction bacterial DNA. The other 86% of DNA in phage particles was DNA replicated after induction. Density label experiments with 5-bromodeoxyuridine showed that postinduction DNA synthesis took place preferentially at the origin region of the bacterial chromosome. Measurement of the molecular weight of DNA replicated after induction clearly showed that postinduction DNA replication is chromosomal. No evidence for prophage detachment and autonomous phage DNA replication was found. The data indicated that, after mitomycin C action, the bacterial chromosome under-went multiple reinitiation at the origin, while normal sequential DNA replication was stopped. The pool of replicated bacterial DNA was fragmented randomly. This DNA was packaged into PBSH particles which were released after cell lysis.