Viruses and mycoplasma (PPLO) in human leukemia

Electron Microscopic Study of the Graffi Virus in Bone Marrow of Leukemic Mice

Bone marrow from C57BL mice with myeloid leukemia induced by Graffi virus has been studied with the electron microscope by ultrathin section and negative stain techniques. Virus particles were usually found in different types of bone marrow cells as well as in extracellular spaces. However, the highest number of particles in various stages of maturation was observed in the cytoplasm of megakaryocytes. Two main types of virus particle were found: the immature Al particle and the mature C particle. They were morphologically indistinguishable from other murine leukemogenic viruses. In partially purified preparations studied by negative staining, some of the particles which were not penetrated by PTA, frequently showed a tail-like structure of variable length. In ultrathin sections, particles were found to originate by budding from the cell membranes. Budding of particles was particularly evident in megakaryocytes and especially within the granules and cytoplasmic vesicles or in connection with the platelet demarcating membranes. The findings of a high number of virus particles in all stages of maturation in megakaryocytes together with a certain degree of megakaryocytosis observed in the bone marrow suggest that this type of cell is possibly one of the main source of production of the virus. A few particles resembling morphologically mycoplasma were detected within the cytoplasm of some immature bone marrow cells.

Do mycoplasmas cause human cancer?

A linkage between mycoplasmas and malignancy was mainly proposed in the 1960s when human-associated mycoplasmas were becoming of interest given the novel characterization of the human respiratory pathogen Mycoplasma pneumoniae. Associations with leukemia and other malignancies, however, were largely ascribed to tissue-culture contamination, which is now recognized as a significant potential problem in molecular biology circles. A few epidemiological studies, however, continue to raise concern over such a linkage. As well, in vitro data have demonstrated the potential for some mycoplasmas to induce karyotypic changes and malignant transformation during chronic tissue-culture infestation. As cellular and molecular mechanisms for such transformation become studied, a resurgence of interest in this area is inevitable. A role for mycoplasmas in malignancy of any sort is conjectural, but there remains a need to continue with focussed epidemiological and laboratory investigations.Key words: mycoplasma, cancer, oncogenesis, leukemia.

Cytoplasmic inclusions and virus-like particles in blast cells in acute lymphoblastic leukemia

Cytoplasmic inclusions and virus-like particles are described in blast cells of peripheral blood from a 16-year-old female with acute lymphoblastic leukemia. Three kinds of inclusions were identified on electron microscopy. The first type of inclusion was single membrane-bounded vacuoles, some of which contained virus-like particles, the second was lysosome-like structures, and the third appeared to be of mitochondrial origin. Virus-like particles were round in shape and had a diameter of 26 to 58 nm. They consisted of an electron-dense outer membrane and an electron-lucent core. At the present time the exact nature and significance of these virus-like particles still remain unclear.

Virus-like particles in leukaemia

Hitherto intracytoplasmic virus-like particles have not been observed simultaneously in nucleus and cytoplasm in human lymphoblasts. We analysed 20 cases of lymphoblastic leukaemia in children and found some virus-like particles in cytoplasm (12 cases) and both in nucleus and cytoplasm (4 cases).

Donor to host transmission of disease via corneal transplantation

A literature search was conducted to report all cases of documented transmission of infectious diseases from donors to recipients of corneal transplants. Fourteen such cases have been reported. There is no experimental or clinical evidence to suggest the transmissions of either hepatitis or syphilis via corneal grafting. Available evidence regarding a number of neurologic and other disorders in which a slow virus etiology has been implicated were reviewed. On the basis of this review, we are able to draw certain conclusions and guidelines for selection or rejection of donor material for transplant surgery.

Electron microscopical and biochemical investigations on retra viruses in spleen tissue in malignancy

Simultaneous biochemical and electron microscopical investigations on surgically removed spleens yielded evidence for the presence of reverse transcriptase containing (Retra) virus in two patients with hematological malignancies with spleen involvement. In three other patients with hematological diseases and in one control patient, the spleens were negative in both assays. The results of these combined studies support the view, that retraviruses are present in human malignancies.

Corneal donor material selection

Histologic study of eyes used as donor material for corneal transplant revealed one instance of massive leukemic infiltration with leukemic keratic precipitates on the fellow eye. In another eye, microabscesses composed of acute and chronic inflammatory cells containing Crytococcus neoformans were present. In a third patient metastatic anaplastic cells were present in the choroid. We think donor eyes are absolutely unacceptable if death was caused by any chronic neurologic disorder, unless clearly secondary to trauma. Eyes from patients with septecimia, hepatitis, jaundice and any evidence of any active viral infection, syphilis, and positive serology are also unacceptable. Extreme caution should be used in selecting eyes of patients with ocular or systemic malignancy, long-term diseases, particularly if immunosuppressive agents were used, where a history of eye disease exists, including corneal disease or dystrophy, iritis, absolute glaucoma or acute glaucoma, and eyes with a history of previous intraocular surgery.

Growing human sarcomas in culture

Efforts to establish human soft tissue and bone sarcomas in long-term cultures are described. Of 49 attempts 22 (45%) were successful, yielding cells that proliferated in vitro for 6 months or longer. Infrequent medium changes, maintenance of pH in physiologic range and avoidance of early trypsinization all appear to be important for survival of explanted cells and their initial growth under culture conditions. Cytologic criteria can be used to confirm that cells in established lines derive from malignant mesenchymal cells present in the tumors of origin.

A comparative evaluation of methods for isolation of RNA-directed DNA polymerase from cells in a reconstituted system

We have compared the relative merits of several procedures for the isolation of RNA-directed DNA polymerase (EC 2.7.7.7.) from cells using a reconsituted model system consisting of a mixture of woolly monkey (simian) sarcoma virus and a cultured human lymphoblastoid cell line, NC-37. When the cell-virus mixture was gently disrupted and fractionated by differential centrifugation, most of the added polymerase was recovered associated with a particulate fraction obtained from the post-mitochondrial supernatant. Purification of the polymerase was best achieved starting from this fraction. The particulate fraction itself can be purified by gel filtration through a Sepharose 2 B column. This procedure did not significantly alter the composition of viral and cellular DNA polymerases. Whereas as little as 7.5 - 10(5) viral particles were sufficient for the detection of RNA-directed DNA polymerase activity, a minimum of about 10(11) particles were necessary for the isolation and unequivocal characterization of the enzyme from the cell-virus mixture by subcellular fractionation and chromatographic separation from cellular DNA polymerases. Purified RNA-directed DNA polymerase had the same primer-template characteristics, sedimentation properties, and immunological cross reactivity as the enzyme purified from density gradient-banded virions of simian sarcoma virus. Methods involving total extraction of the cell-virus mixture either by repeated freezing and thawing followed by detergent treatment or by Dounce homogenization and treatment with high salt and detergent failed to provide RNA-directed DNA polymerase free of cellular DNA polymerases. Because of this, low levels of cellular RNA-directed DNA polymerase may be missed when these approaches are used.

Morphologic study of virus-like particles in a case of acute leukemia

Virus-like particles, grouped in clusters not bound by a membraine, were seen in electron micrographs of fresh leucoblasts of an acute leukemic patient. They consisted of large (100-nm diameter), round particles apparently composed of subunits. Tubular structures (30-50-nm diameter) were also seen in leucoblasts of the same patient. The two types of structures were never seen simultaneously in the same cell. The authors review the literature pertaining to the morphology of virus-like particles associated with malignant hematologic disease.

RNA processing and RNA tumor virus origin and evolution

The results of molecular hybridization experiments with high-molecular-weight RNA isolated from RNA tumor viruses and DNA from normal cells suggest that RNA tumor virus genomes originate from cell genes. Some RNA tumor viruses (here called class 1) appear to have been generated in recent times in that their RNA is closely related in nucleotide sequence to certain cell genes (class 1 genes). A second class of RNA tumor viruses (here called class 2) is more distantly related to genomic information of normal cells. Structural properties of the RNA of RNA tumor viruses lead us to propose that the tumor virus RNA is originated when RNA transcripts of class 1 genes are processed by a mechanism we call "paraprocessing." We postulate that RNA paraprocessing is normally used only at particular times during differentiation and is characterized by the cytoplasmic appearance of high-molecular-weight RNA chains containing terminal polyadenylic acid (200 residues). Paraprocessing of class 1 gene transcripts in committed or differentiated cells is considered to be aberrant in transcription that can lead to the generation of an RNA tumor virus genome. If the paraprocessed class 1 gene transcript codes for a reverse transcriptase, replication of the RNA becomes possible. Transfer of the replicating RNA to a new cell can result in genetic change such that the virus genome mutates, differing from the original progenitor genes. We propose that this genetic change causes class 1 viruses to become class 2. These ideas are applied to evidence concerning the biology of infection of RNA tumor viruses and concerning the involvement of RNA tumor viruses in human cancer. Genetic change can also occur during the origination of an RNA tumor virus genome by repeated reverse transcription and recombination (45) or by genetic alteration of particularly changeable cell genes ("hot spots") (43).