Gangliosides shed by tumor cells enhance tumor formation in mice. (65/181)

The role of tumor cell membrane gangliosides in tumor formation was probed using a series of cloned murine AKR lymphoma cell lines. Tumor formation was directly related to high expression and shedding of membrane gangliosides. In vivo, as little as 1 pmol of purified total gangliosides of highly tumorigenic cells, injected intradermally with poorly tumorigenic cells (which lacked and did not shed gangliosides), markedly increased the tumorigenicity of these cells in syngeneic normal mice. Thus, gangliosides shed by tumor cells are a previously unrecognized, extremely potent enhancer of tumor formation in vivo.  (+info)

Isolation of a retroviruslike sequence from the TL locus of the C57BL/10 murine major histocompatibility complex. (66/181)

Two retroviruslike sequences have been isolated from the TL locus of the major histocompatibility complex of C57BL/10 mice. One sequence (TLev2) hybridizes only with probes derived from the pol region of the murine leukemia provirus AKR; the other sequence (TLev1) hybridizes with gag, pol, and env AKR region probes. This 9-kilobase endogenous, TL region-associated virus (TLev1) has been further characterized. The TLev1 genome has been shown to contain murine leukemia virus-related sequences bounded by retroviruslike, VL30 long terminal repeats. Hybridization of TLev1-derived probes to mouse genomic digests reveals multiple copies which show distinct patterns compared with those observed with murine leukemia virus probes. The study of TLev1 may prove significant with respect to the interaction of retroviral sequences within the genome, expression of genes within the TL locus, and polymorphisms within the major histocompatibility complex.  (+info)

High incidence of B cell lymphomas derived from thymectomized AKR mice expressing TL.4 antigen. (67/181)

AKR mice, 6-12 mo after birth, display a high incidence of spontaneous T cell lymphomas that can be prevented by thymus removal at the age of 1-3 mo. We report here the presence of dormant preleukemic cells among bone marrow cells of 8-12-mo-old AKR mice that have been thymectomized when 40-60 d old. Transplantation of bone marrow cells from these thymectomized AKR donors into syngeneic or hybrid (AKR X DBA/2)F1 intact or thymectomized recipients resulted in lymphoma development of AKR origin in 80-100% of the recipients. Analysis, by flow microfluorometry, of the antigenic cell surface phenotypes of the developing lymphomas revealed that all tumors were B cell lymphomas, since the cells stained with class-specific anti-IgM reagents and other reagents specific for B cells (RA3-2C2, RA3-6B2, anti-I-A, and anti-Fc receptor), and were Thy-1-. All these B cell tumors also expressed two T cell differentiation antigens, TL.4, found exclusively on T cell lymphomas, and Lyt-1 antigen, previously shown (11) to be expressed on some B cell neoplasms. The surface markers mu, I-A, RA3-2C2, and TL.4 identified by immunofluorescence, were shown to be integral membrane components synthesized by the tumor cells, rather than passively acquired proteins.  (+info)

Presentation of an MuLV-related tumour antigen in liposomes as a potent tertiary immunogen after adoptive transfer. (68/181)

The immunogenicity of Gross virus cell surface antigen (GCSAa) extracted from rat lymphoma cells can be dramatically increased by its presentation into liposomes, probably by mimicking the cell membrane presentation. Induction of an anti-GCSAa secondary antibody response has been found to require the use of liposomes as GCSAa vehicle for both the priming and the boosting immunizations. In order to investigate the sensitivity of highly immune cells to the liposome presentation, immune spleen cells were stimulated in vitro with either soluble GCSAa or GCSAa-liposomes and transferred together with the immunogen into syngeneic animals. Only spleen cells from high responders, which have been immunized twice with GCSAa-liposomes, were able to generate an antibody response in naive recipients after their restimulation with the GCSAa-liposome preparation. Their restimulation with soluble antigen was ineffective unless 10% peritoneal exudate cells (PEC) from naive rats were added during the in vitro incubation. Stimulation with GCSAa-liposomes was further improved by the addition of 10% PEC. Macrophages were found to play a central role in the induction of antibody response in the recipients after stimulation with GCSAa-liposomes. Treatment of immune spleen cells with the macrophage-killing agent leucine methyl ester prior their restimulation in vitro with GCSA-liposomes in the absence of PEC, or depletion of macrophage after their in vitro incubation with this immunogen, completely abolished the induction of anti-GCSAa antibodies in the recipients.  (+info)

5.9-S RNA, a new RNA characterized in several mammalian cell lines. (69/181)

A new species of RNA has been isolated from several different cell lines, both oncornavirus producing and non-producing. This RNA, which we designate 5.9-S RNA is present in the cellular cytoplasmic fraction at very low concentration (approximately 1% of the quantity of 4-S RNA), but it accumulates to much higher levels in two murine oncornaviruses, Moloney murine sarcoma leukemia virus complex and Gross leukemia virus, where it represents as much as 10% of the low-molecular-weight RNA fraction associated with the 70-S RNA genome. The electrophoretic mobility and fingerprint analysis of T1 RNase digest products show that this species of RNA is approximately 160-165-residues long, and can be unequivocally distinguished from all previously described species of RNA in this size range.  (+info)

Semi-micro XC cell assay technique for murine leukemia virus. (70/181)

The XC cell assay employed in in vitro titration of murine leukemia viruses was modified for use as a semi-micro procedure.  (+info)

Structural proteins of mammalian oncogenic RNA viruses: multiple antigenic determinants of the major internal protein and envelope glycoprotein. (71/181)

The antigenic determinants of two purified protein constituents of mammalian C-type RNA viruses, the major structural protein of about 30,000 daltons, and the membrane glycopeptides of about 70,000 daltons were examined by competition radioimmunoassay. By the appropriate choice of antiserum and competing proteins, it was possible to distinguish type-specific, group-specific, and interspecies determinants. Both of the viral constituents were found to contain each of these three classes of antigens. The results suggested that the majority of the determinants of the major structural protein were group specific, 5% to 30% were interspecies, and a small fraction were type specific. In the case of the envelope glycopeptides, the chief determinants were type and group specific, and a small fraction were interspecies.  (+info)

Structural proteins of mammalian oncogenic RNA viruses: murine leukemia virus neutralization by antisera prepared against purified envelope glycoprotein. (72/181)

Goat and rabbit antisera prepared against a purified Rauscher murine leukemia virus glycoprotein (gp69/71) rapidly neutralized spleen focus-forming virus in Rauscher and Friend virus preparations. Absorption studies revealed that most of the neutralizing activity of goat anti-Rauscher virus gp69/71 serum was directed against type- and group-specific determinants.  (+info)