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Biomedical subjects

M Cohn

Publications and source records attributed to M Cohn.

At least 271 records · Page 15Linked to original sources
PubMed1970

A theory of self-nonself discrimination.

1) Induction of humoral antibody formation involves the obligatory recognition of two determinants on an antigen, one by the receptor antibody of the antigen-sensitive cell and the other by carrier antibody (associative interaction). 2) Paralysis of antibody formation involves the obligatory recognition of only one determinant by the receptor antibody of the antigen-sensitive cell; that is, a nonimmunogenic molecule (a hapten) can paralyze antigen-sensitive cells. 3) There is competition between paralysis and induction at the level of the antigen-sensitive cell. 4) The mechanisms of low- and high-zone paralysis, and maintenance of the unresponsive state, are identical. 5) High-zone paralysis occurs when both the carrier antibody and the receptor antibody are saturated, so that associated interactions cannot take place. 6) The mechanisms of paralysis and induction for the carrier-antigen-sensitive cell are identical to those for the humoral-antigen-sensitive cell. 7) The formation of carrier-antigen-sensitive cells is thymus-dependent, whereas humoral-antigen-sensitive cells are derived from bone marrow. Since carrier antibody is required for induction, all antigens are thymus-dependent. 8) The interaction of antigen with the receptor antibody on an antigen-sensitive cell results in a conformational change in an invariant region of the receptor and consequently paralyzes the cell. As the receptor is probably identical to the induced antibody, all antibody molecules are expected to be able to undergo a conformational change on binding a hapten. The obligatory associated recognition by way of carrier antibody (inductive signal) involves a conformational change in the carrier antibody, leading to a second signal to the antigen-sensitive cell. 9) The foregoing requirements provide an explanation for self-nonself discrimination. Tolerance to self-antigens involves a specific deletion in the activity of both the humoral- and the carrier-antigen-sensitive cells.

Antibody Formation↗
PubMed1970

Leukemia viruses associated with mouse myeloma cells.

Myeloma cells derived from BALB/c and C3H mice show evidence of infection by a murine leumemia virus. The immunoglobulin-producing myelomas secrete an RNA-containing virus with a density of 1.20 to 1.22 gm/cm(3). RNA with a sedimentation coefficient of 74 S in 0.1 M sodium sodium chloride has been isolated from secreted virus particles and has a base composition similar to that found for other murine leukemia virus RNA. An intracellular virus particle has been partially purified and has a density of 1.29 to 1.32 gm/cm(3). Both extracellular and intracellular virus particles contain the leukemia virus group-specific antigen.

Animals↗
PubMed1969

Magnetic resonance studies of spin-labeled creatine kinase system and interaction of two paramagnetic probes.

Creatine kinase from rabbit muscle has been specifically labeled with a derivative of a nitroxide free radical on the two essential sulfhydryl groups, one per active site. The conformation in the environment of the enzyme-bound free radical and the change in conformation induced upon binding of the substrate, metal adenosine diphosphate, has been monitored by two parameters of the bound spin label, its electron paramagnetic resonance spectrum and its contribution to the proton relaxation rate of water. The specificity in activation of the enzymic reaction of the series of alkaline earth ions, Mg, Ca, Sr, Ba, was not reflected by differences in conformation of the ternary enzyme metal substrate complexes observable with the spin probe. However, with the inhibitory zinc ion, the conformation of ternary complex was distinctly different. The electron paramagnetic resonance spectra of complexes with two paramagnetic probes, namely, spin-labeled enzyme with paramagnetic metal adenosine diphosphate complexes (Mn(II), Ni(II), and Co(II)) revealed a spin-spin interaction between the protein-bound free radical and the paramagnetic metal ions. From the magnitude of the interaction, the distance between the manganous ion and the electron spin of the nitroxide moiety in the MnADP-spin-labeled creatine kinase was estimated to be in the range of 7-10 A.

Adenine Nucleotides↗
PubMed1969

In vitro differentiation of a mouse neuroblastoma.

Mouse tumor C1300 has been established in tissue culture. The cells have a round cell morphology in both the subcutaneous tumor and in suspension culture. However, when given a surface on which to attach, they send out processes up to 3 mm in length and assume the morphology of mature neurons. The attached cells are stained by the Bodian silver procedure for neurons, whereas the cells grown in suspension are not. Electron microscopy reveals that the attached cells contain neurofilaments, neurotubules, and densecore vesicles indicative of nerve fibers. Both free-floating and attached cells have tyrosine hydroxylase activity characteristic of sympathetic nervous tissue. Apparently cell attachment can induce morphological differentiation from an anaplastic round cell to a cell which has many properties of a mature neuron.

Animals↗