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Biomedical subjects

E Yefenof

Publications and source records attributed to E Yefenof.

At least 91 records · Page 5Linked to original sources
PubMed1980

In vitro generation of cytotoxic lymphocytes against radiation- and radiation leukemia virus-induced tumors. III. Suppression of anti-tumor immunity in vitro by lymphocytes of mice undergoing radiation leukemia virus-induced leukemogenesis.

Adult C57BL/6 mice exposed to fractionated irradiation or inoculated with the radiation leukemia virus (RadLV), develop high incidence (80-100%) of lymphatic leukemias within 3-6 mo. RadLV-induced lymphomas can elicit cytotoxic responses in vitro in lymphocytes of preimmunized syngeneic mice, a reaction that is dependent on the expression of membrane-associated viral antigenicity. As soon as 5 d after RadLV inoculation, and during the entire leukemogenic process, suppressor T cells are detectable in the spleen that are capable of specifically abrogating generation of syngeneic anti-tumor cytotoxic cells in vitro. Mice exposed to fractionated x irradiation do not develop suppressor cells and their splenocytes may be stimulated in vitro to generate cytotoxicity toward RadLV-induced leukemias. These findings suggest that although RadLV has been isolated from radiation-induced leukemias, x-ray- and RadLV-induced leukemogenesis do not seem to involve a common viral etiology, and that induction of suppressor cells during RadLV leukemogenesis may be essential for tumor progression.

Animals↗
PubMed1980

In vitro generation of cytotoxic lymphocytes against radiation and radiation leukaemia virus-induced tumours. II. A radiation-induced thymoma generates cytyotoxic response in syngeneic but not in allogeneic lymphocytes.

A thymoma cell line (PXT), originally induced by X-irradiation in a C57Bl/6 mouse, was found capable of generating cytotoxic T lymphocytes (CTL) in a syngeneic mixed lymphocyte tumour culture (MLTC), but failed to stimulate allogeneic lymphocytes. Serologically defined H-2 antigens could readily be detected on PXT cells, which were also susceptible to lysis by alloreactive CTL generated against C57Bl/6 lymphoblasts or other thymomas of C57Bl/6 origin. These observations suggest that the PXT line lacks lymphocyte-activating determinants (LAD) essential for allosensitization but possesses other determinants enabling stimulation of syngeneic CTL, and that the cellular events leading to generation of anti-H-2 and anti-'modified self' CTL proceed along distinct T-cell differentiation pathways.

Animals↗
PubMed1979

Moloney lymphoma cells express a polyprotein containing the GAG gene-coded p15 and the Moloney leukemia virus-induced cell surface antigen (MCSA).

The relationship between MCSA and the viral structural proteins in YAC Moloney lymphoma cells was further investigated by using membrane immunofluorescence and immunoadsorbent columns. As previously observed, MCSA showed only minimal capping and thereby differed in behaviour from gp70, p30 and p12 virion antigens. Whereas antibody-induced capping of gp70 did not change the membrane distribution of MCSA, co-capping was observed between MCSA and p30 and p12 gag protein antigens. This indicated that, whereas MCSA is distinct from gp70, it is linked to p30 and p12 on the membrane of living cells. It was then attempted to isolate MCSA on anti-p30 and anti-p15 immunoadsorbent columns from solubilized YAC cells. Contrary to what was expected, no MCSA was found to the anti-p30 column. On the other hand, a part (10-15%) of the MCSA was bound to the anti-p15 column, indicating that MCSA is linked to the gag p15.

Animals↗
PubMed1979

Detection of proteolytic (C 3-cleaving) activity on mouse mastocytoma (P 815) cells and other mouse cell lines by formation of cell contact with C 3-carrying mouse lymphocytes.

Mouse mastocytoma cells (P 815) formed rosettes with normal mouse spleen lymphocytes which had been coated with uncleaved human C 3; this interaction was clearly dependent on the amount of C 3. Lymphocytes treated with C 3 b or buffer alone were ineffective. Formation of cell contact could be inhibited by the presence of protease inhibitors such as diisopropyl fluorophosphate, phenyl methyl sulfonyl fluoride and tosyllysyl chloromethyl ketone. Seve n out of 13 different cell lines behaved like P 815 cells. The results strongly suggested that a proteolytic activity on mouse tumor cells led to a cooperation with uncleaved C 3 on a carrier cell to connect these two cells. We interpreted these data in analogy to the complement-dependent bridge formation mechanism (M. P. Dierich and B. Landen, J. Exp. Med. 1977. 146: 1484): uncleaved C 3, attached to mouse spleen lymphocytes as carriers, becomes cleaved by enzymes associated with the tumor cells tested; by this cleavage, the labile binding site is released on C 3 (nascent C 3 b) and anchors the C 3-carrying cell to the protease-carrying cell; since this labile binding site is short-lived, this process can be induced by membrane-associated proteases only. The nature of the proteases and the biological implications of this process are as yet uncertain.

Animals↗
PubMed1978

Relationship between Epstein-Barr virus (EBV)-production and the loss of the EBV receptor/complement receptor complex in a series of sublines derived from the same original Burkitt's lymphoma.

Virus production, EBV (P3HR-1 substrain) superinfectability, IdUrd inducibility, EBV receptor and complement (C3) receptor expression were assessed in two independently maintained jijoye lines, the derived P3HR-1 clone that releases a growth inhibitory and cytopathic, non-transforming viral mutant, and in non-producer sublines derived from the P3HR-1 line by the spontaneous cessation of virus production. Both jijoye lines were superinfectable, inducible, and carried EBV and C3 receptors. Virus-producing P3HR-1 cells and recently derived non-producer sublines lacked EBV-receptors and C3 receptors, could not be superinfected, but were IdUrd inducible. Two long-passaged, non-producer sublines of P3HR-1 reexpressed EBV and C3 receptors to an equal degree (different in the two sublines). EBV-superinfectability became partially reestablished in the subline with the higher expression of EBV and C3 receptors. These findings support the hypothesis that the EBV-receptor/C3 receptor negativity of the producer P3HR-1 sublines and their recent non-producer derivatives is due to negative selection by the growth-inhibitory, cytopathic P3HR-1 virus variant. The closely linked disappearance and reappearance of EBV-receptors and complement receptors gives further support to the idea that these two receptors are either identical or closely linked constituents of the cell membrane.

Antigens, Viral↗
PubMed1978

Shedding of anti-IgM from antibody-coated human lymphoma lines: differences between Epstein-Barr virus-negative lines and their virus-converted sublines.

In vitro converted, Epstein-Barr (EBV) genome-carrying cell lines showed a reduced ability to shed surface-bound antibodies, compared to their EBV-free parental B lymphoma lines. On the other hand, antibody degradation was higher with EBV-positive cells. Analysis of antibody-coated single cells revealed that cells which failed to redistribute or cap their ligand-bound surface components at 37 degrees C, were also capable of shedding bound antibody. This suggests that capping and shedding are essentially independent phenomena, although both may be influenced by the same virally induced change in the lateral mobility of membrane constituents.

Antibodies, Anti-Idiotypic↗
PubMed1978

Inhibition of DNA metabolism in human B lymphocytes by a substrain of Epstein-Barr virus (P3HR-1): a method for virus quantitation.

Pretreatment with the P3HR-1 substrain of Epstein-Barr virus (EBV) inhibited approximately 85% of the DNA stimulation induced by Staphylococcus aureus in human B lymphocytes. In parallel experiments, the DNA stimulation induced by the transforming B95-8 substrain of EBV was almost completely inhibited by prior exposure to P3HR-1 virus. Phytohemagglutinin stimulation was only slightly inhibited, whereas the DNA synthesis of continuously growing Raji cells was inhibited to a considerable extent. The degree of DNA inhibition was correlated with the induction of the EBV-determined antigens (membrane, early, and nuclear antigens) in sensitive indicator cells.

B-Lymphocytes↗
PubMed1978

Human blood lymphocyte fractionation with special attention to their cytotoxic potential.

In studies concerning the natural cytotoxic activity of human blood lymphocytes we have found that: 1. T cell, which rosette with sheep erythrocytes can be separated by centrifuging on Ficoll the lymphocyte and erythrocyte mixture without previously pelleting and incubating in the cold. 2. Lysis of marker erythrocytes with ammonium chloride impairs the cytotoxic activity of lymphocytes. Incubation at 37 degrees C for 12 hr prior to the test restores the activity to some extent. 3. A high proportion of the so call "null" fraction i.e. cells remaining in the interface after removal of B cells (passage on nylon column) and sedimentation of E rosettes, sediments as rosettes with sheep EAC'indicating that these cells carry low density E and C3 receptors. Rosetting with SRBC or ox EAC' gave significantly lowr values. On a per cell basis the "null" fraction was the most efficient one in natural cytotoxicity. Depletion of cells with low affinity E or E and C3 receptors left highly active subfractions.

Ammonium Chloride↗
PubMed1977

Immunization of mice with syngeneic Moloney lymphoma cells induces separate antibodies against virion envelope glycoprotein and virus-induced cell surface antigens.

Immunization of mice with heavily irradiated syngeneic Moloney lymphoma cells evokes antibodies against the major viral envelope antigen, gp71, and the Moloney virus-induced cell surface antigen (MCSA). A9HT cells, an L-cell subline, react with the antibodies against the viral envelope antigen only; this reaction can be completely inhibited by virus or purified gp71. Reactivity to Moloney lymphoma cells (YAC) was only partially inhibited (maximum 30%) or not at all. This can be attributed to the reaction of the YAC cells with antibodies directed against MCSA, a nonvirion cell surface component according to both biological and biochemical evidence. Antibody-induced capping of gp71 or p15(E) did not change the membrane distribution of MCSA or H-2, indicating that these antigens represent distinct entities on the cell surface. MCSA showed only minimal capping and thereby differed in behavior from both H-2 and virion antigens. gp71 could be capped by the mouse antiserum as revealed by subsequent staining with monospecific anti-gp71 antiserum. Under ordinary test conditions this reactivity is overshadowed by the reaction against MCSA. The lack of MCSA capping reflects a difference in anchorage of this antigen.

Antibodies, Viral↗
PubMed1977

Membrane receptor stripping confirms the association between EBV receptors and complement receptors on the surface of human B lymphoma lines.

Complement (C3) receptors, EBV receptors, Fc receptors, membrane IgM and beta2microglobulin (beta 2m) were individually stripped from the surface of human B lymphoma lines. The cells were subsequently tested for their ability to absorb infectious EB virus. Stripping of Fc receptors, IgM and beta2m did not reduce EBV absorption. Stripping of either EBV receptors or C3 receptors eliminated or drastically reduced EBV-absorptive capacity. The results confirm the distinctive association between EBV receptors and C3 receptors on human lymphoma cells.

Burkitt Lymphoma↗