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M Cohn

Publications and source records attributed to M Cohn.

At least 109 records · Page 6Linked to original sources
PubMed1983

The WI-L2-729-HF2 human hybridoma system. Stable hybrids at high frequency.

A new system for the rapid production at high frequency (greater than 10(-5] of stable human hybridomas is described. This system is based on a high efficiency fusion variant human lymphoblastoid cell line designated WI-L2-729-HF2 and is comparable in many ways to commonly used murine hybridoma systems. WI-L2-729-HF2 cells fuse at high frequency with mitogen-stimulated human b cells resulting in the rapid appearance (within 2 weeks) of stable hybridomas in hypoxanthine/aminopterin/thymidine (HAT) medium. Whereas the WI-L2-729-HF2 cell line secretes only trace levels (50 to 100 ng/ml) of an IgG,kappa and has surface IgM,kappa, HAT-resistant hybridomas secrete high levels (10 to 20 micrograms/ml) of new human immunoglobulins, including immunoglobulins containing alpha or lambda chains not found in the tumor parental cell line. These hybridomas have remained stable for over four months in continuous culture, secreting high levels of new immunoglobulins in both conventional and serum-free medium, a feature which makes possible large-scale production and purification of human antibodies. This system has the potential to provide tools and reagents for investigations involving, for example, the diagnosis and treatment of human autoimmune disease and cancer.

B-Lymphocytes↗
PubMed1983

An analysis of the sensitivity of somatic cell hybrids to natural killer cell- and natural cytotoxic cell-mediated lysis.

The analysis of the NK and NC sensitivity of somatic cell hybrids formed between parental cell lines that differ in their NK and NC sensitivity has shown the following. 1) The dominant expression of both NK and NC recognition determinants on target cells; 2) the dominant expression of two post-recognitive NC resistance mechanisms, one requiring protein synthesis and one being protein synthesis independent; and 3) the dominant expression of a post-recognitive NK resistance mechanism, which is protein synthesis independent. The post-recognitive protein synthesis-independent NC resistance mechanism confers no NK resistance and the post-recognitive NK resistance mechanism confers no NC resistance. Whether the post-recognitive protein synthesis-dependent NC resistance mechanism confers NK resistance remains open to question. The analysis of the hybrids indicates that transformed cells become sensitive to either NK- or NC-mediated lysis by losing their resistance to the lytic activity of these effector cells, and it appears that differentiation plays a role in determining whether NK or NC resistance will be lost upon transformation. A model is proposed in which the differentiation into a fibroblast associates the loss of NC resistance with transformation, whereas the differentiation into a lymphocyte associates the loss of NK resistance with transformation. Because the loss of NK resistance is not associated with the transformation of fibroblasts, they remain NK resistant, and because the transformation of lymphocytes is not associated with the loss of NC resistance, they remain NC resistant. This provides the basis for the target specificity exhibited by NK and NC effectors.

Animals↗
PubMed1982

In vivo surveillance of tumorigenic cells transformed in vitro.

Any theory of surveillance against cancer requires that cells susceptible to host protective mechanisms exist as intermediates on the pathway from normal to cancer. The failure to demonstrate a significant frequency of such intermediates as a result of chemical carcinogenesis has cast serious doubt on the validity of the surveillance hypothesis. Here we report the conditions in which such intermediates can be identified as the major class of transformed cells resulting from in vitro chemical carcinogenesis of a cloned fibroblastic cell line.

Benzopyrenes↗
PubMed1982

Immunological identification of cerebellar cell lines.

Spleen cells from BALB/c mice, previously immunized with rat cerebellar tissue, were fused to the mouse myeloma cell line SP2/0-Ag14 and the cerebellar cell type specificity of the resultant hybridomas determined. In this report we describe the specificity of one hybridoma, C4/12. Monoclonal antibodies secreted by this hybridoma recognize granule cell neurons in adult cerebellar frozen sections, and in primary cultures started from 3 to 5-day-old newborn rats. In addition, C4/12 recognizes a subclass of astrocytes when screened on primary cultures but not adult cerebellar tissue. Two temperature sensitive Rous sarcoma virus transformed cerebellar cell lines, previously shown to be either neuronal or glial, were screened for the presence of the antigen. Both cell lines are positive at the temperature permissive for transformation, whereas the glial line but not the neuronal line exhibits the antigen at the nonpermissive temperature. These results are discussed in light of the cell lines being representative of precursor cells.

Animals↗
PubMed1981

31P NMR of enzyme-bound substrates of rabbit muscle creatine kinase. Equilibrium constants, interconversion rates, and NMR parameters of enzyme-bound complexes.

The reaction catalyzed by rabbit muscle creatine kinase ATP + creatine in equilibrium ADP + P-creatine has been investigated by 31P NMR. At pH 8.0 and 4 degrees C, the equilibrium constant of the overall reaction [P1][P2]/[S1] [S2] is found to be 0.08, while that for the interconversion step between enzyme-bound substrates and products [E.P1. P2]/[E.S1.S2] is estimated to be approximately 1; the latter value is the same for all other kinases investigated. The rate of interconversion of enzyme-bound substrates and products is approximately 90 s-1 and is not the rate-limiting step of the overall reaction. Of the phosphate groups in enzyme complexes of reactants or products, the 31P chemical shifts of beta-P(ADP) and beta-P[MgADP) change by approximately 2 ppm downfield while all others change by less than 0.8 ppm. In the transition state analog complexes E.MgADP.NO3-.creatine and E.MgADP.HCOO-.creatine, the beta-P(MgADP) signal shows a substantial upfield shift in the direction of the beta-P(MgATP) resonance. The pattern of chemical shifts and line shapes of nucleotide complexes of creatine kinase parallel those for the corresponding complexes of arginine kinase, indicating structural and/or conformational similarity of the phosphate chains of nucleotides bound to the two enzymes. However, a difference in active sites is indicated by the pH independence (pH 6.0 to 9.0) of the chemical shift of the beta-P of MgADP bound to creatine kinase, whereas with arginine kinase this resonance showed a pKa approximately 7.5.

Adenosine Diphosphate↗
PubMed1981

Tumorigenicity and lysis by natural killers.

Detailed analysis of the natural killer (NK) activity directed at nontumorigenic cell lines and their transformed tumorigenic derivatives has revealed a paradox. On the one hand, a correlation has been found between the tumorigenic potential of chemically transformed fibroblast cell lines and their sensitivity to NK cells in vitro. Nontransformed cells (N-type cell lines) and cells tumorigenic in normal mice (C-type cell lines) are resistant to NK-mediated lysis. In contrast, cell lines that are tumorigenic in ATxFL mice (these mice are very low in NK activity), but not in normal mice (I-type cell lines) are sensitive to NK-mediated lysis. These findings support the concept that NK activity is involved in host surveillance against tumors. On the other hand, NK-resistant fibroblasts, whether taken directly form animals or derived as tumorigenic or nontumorigenic cell lines, compete with NK-sensitive target cells to inhibit their lysis by NK effectors. Not only are both NK-sensitive and -resistant cells recognized by NK effectors but both receive lytic signals from NK effector cells. Target cell resistance is a result of a protein synthesis-dependent mechanism that prevents lysis such that in the presence of inhibitors of protein synthesis all fibroblasts tested are NK sensitive. Those fibroblasts that are normally sensitive to NK-mediated lysis must be deficient in their ability to produce or respond to this counterlytic mechanism. These findings are in contrast with the general findings when lymphoid cells are studied as NK targets where sensitivity appears to be a result of recognition by NK effectors. Because our findings show that transformed and normal cells express the same recognition determinants, in order for NK activity to play an important in vivo role in tumor surveillance, a mechanism must operate to permit NK effectors to find their targets in vivo. In the absence of a special discrimination mechanism, the killing of NK-sensitive transformants that arise autochronously would be less than optimal as a consequence of competition by the normal, NK-resistant, cells.

Animals↗
PubMed1981

The expression of glial fibrillary acidic protein in a rat cerebellar cell line.

A rat cerebellar cell line, WC5, derived by transformation with Rous sarcoma virus, which is temperature-sensitive for transformation (ts-RSV), can be induced to express glial fibrillary acidic protein (GFAP). Immunofluorescence, radioimmune assay, and electron microscopy studies show that GFAP is expressed in WC5 cells grown at the nonpermissive temperature (NPT), but not at the permissive temperature (PT) for transformation. GFAP is first detectable about 3 days after incubating cells at the NPT, and reaches an apparent plateau by the seventh or eighth day. The expression of GFAP is reversible; shifting cells from the NPT to the PT causes a dramatic decrease in GFAP after 96 hr. In order to determine if the expression of GFAP is linked to the temperature-sensitive transforming activity of the viral src gene product, phenotype revertants of WC5 were established. By the criteria of morphology and growth in agar, the revertant lines, in contrast to the parent cell line WC5, were shown to exhibit a transformed phenotype at both the NPT and PT. Immunofluorescence studies on several of the revertant cell lines show that they do not express GFAP at either the PT or NPT. These findings suggest that the expression of GFAP in WC5 is linked to the expression of the src gene product. The advantage of using ts-RSV to derive neural cell lines which exhibit differentiated properties is discussed.

Animals↗