Cloned mouse cells with natural killer function and cloned suppressor T cells express ultrastructural and biochemical features not shared by cloned inducer T cells.

We have examined the morphology, cytochemistry, and biochemistry of mouse leukocyte subsets by analyzing cloned leukocyte populations specialized to perform different immunologic functions. Cloned cells expressing high-affinity plasma membrane receptors for IgE and mediating natural killer (NK) lysis and cloned antigen-specific suppressor T cells contained prominent osmiophilic cytoplasmic granules similar by ultrastructure to those of mouse basophils. Both clones also incorporated 35SO4 into granule-associated sulfated glycosaminoglycans, expressed a characteristic ultrastructural pattern of nonspecific esterase activity, incorporated exogenous [3H]5-hydroxytryptamine, and contained cytoplasmic deposits of particulate glycogen. By contrast, cloned inducer T cells lacked cytoplasmic granules and glycogen, incorporated neither 35SO4 nor [3H]5-hydroxytryptamine, and differed from the other clones in pattern of nonspecific esterase activity. These findings establish that certain cloned cells with NK activity and cloned suppressor T cells express morphologic and biochemical characteristics heretofore associated with basophilic granulocytes. However, these clones differ in surface glycoprotein expression and immunologic function, and the full extent of the similarities and differences among these populations and basophils remains to be determined

Mast cell clones: a model for the analysis of cellular maturation.

Cloned mouse mast cells resemble, by ultrastructure, immature mast cells observed in vivo. These mast cell clones can be grown in the absence of any other cells, facilitating direct investigations of their biochemistry and function. We find that cloned mast cells express plasma membrane receptors (Fc epsilon R) that bind mouse IgE with an equilibrium constant (KA) similar to that of normal mouse peritoneal mast cells. In addition, cloned mast cells do not display detectable la antigens and cannot enhance lg secretion when added to lymphocyte cultures or mediate natural killer lysis. In the presence of 1 mM sodium butyrate, cloned mast cells stop dividing and acquire abundant electron-dense cytoplasmic granules similar to those of mature mast cells. Their histamine content increases concomitant with cytoplasmic granule maturation and may exceed that of untreated mast cells by 50-fold. Unlike peritoneal mast cells, cloned mast cells incorporate 35SO4 into chondroitin sulfates rather than heparin. These findings demonstrate that, unlike fully differentiated mouse peritoneal mast cells, cloned immature mouse mast cells contain no heparin and low levels of histamine. In addition, they establish that high-affinity Fc epsilon R are expressed early in mast cell maturation, well before completion of cytoplasmic granule synthesis and mediator storage

Spin Degree of Freedom in a Two-Dimensional Electron Liquid

We have investigated correlation between spin polarization and magnetotransport in a high mobility silicon inversion layer which shows the metal-insulator transition. Increase in the resistivity in a parallel magnetic field reaches saturation at the critical field for the full polarization evaluated from an analysis of low-field Shubnikov-de Haas oscillations. By rotating the sample at various total strength of the magnetic field, we found that the normal component of the magnetic field at minima in the diagonal resistivity increases linearly with the concentration of ``spin-up'' electrons.Comment: 4 pages, RevTeX, 6 eps-figures, to appear in PR

Parallel magnetic field induced giant magnetoresistance in low density {\it quasi}-two dimensional layers

We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density {\it quasi}-two dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the {\it orbital} motion arising from the {\it finite} layer thickness and the large Fermi wavelength of the {\it quasi}-two dimensional system at low carrier densities.Comment: 4 pages with 4 figures. Accepted for Publication in Physical Review Letter

Possible triplet superconductivity in MOSFETs

A theory that predicts a spin-triplet, even-parity superconducting ground state in two-dimensional electron systems is re-analyzed in the light of recent experiments showing a possible insulator-to-conductor transition in such systems. It is shown that the observations are consistent with such an exotic superconductivity mechanism, and predictions are made for experiments that would further corroborate or refute this proposal.Comment: 4 pp., REVTeX, psfig, 1 eps fig, final version as publishe

Metal-insulator transition at B=0 in a dilute two dimensional GaAs-AlGaAs hole gas

We report the observation of a metal insulator transition at B=0 in a high mobility two dimensional hole gas in a GaAs-AlGaAs heterostructure. A clear critical point separates the insulating phase from the metallic phase, demonstrating the existence of a well defined minimum metallic conductivity sigma(min)=2e/h. The sigma(T) data either side of the transition can be `scaled' on to one curve with a single parameter (To). The application of a parallel magnetic field increases sigma(min) and broadens the transition. We argue that strong electron-electron interactions (rs = 10) destroy phase coherence, removing quantum intereference corrections to the conductivity.Comment: 4 pages RevTex + 4 figures. Submitted to PRL. Originally posted 22 September 1997. Revised 12 October 1997 - minor changes to referencing, figure cations and figure

Universality in an integer Quantum Hall transition

An integer Quantum Hall effect transition is studied in a modulation doped p-SiGe sample. In contrast to most examples of such transitions the longitudinal and Hall conductivities at the critical point are close to 0.5 and 1.5 (e^2/h), the theoretically expected values. This allows the extraction of a scattering parameter, describing both conductivity components, which depends exponentially on filling factor. The strong similarity of this functional form to those observed for transitions into the Hall insulating state and for the B=0 metal- insulator transition implies a universal quantum critical behaviour for the transitions. The observation of this behaviour in the integer Quantum Hall effect, for this particular sample, is attributed to the short-ranged character of the potential associated with the dominant scatterers

Symmetry in the insulator - quantum Hall - insulator transitions observed in a Ge/SiGe quantum well

We examine the magnetic field driven insulator-quantum Hall-insulator transitions of the two dimensional hole gas in a Ge/SiGe quantum well. We observe direct transitions between low and high magnetic field insulators and the $\nu=1$ quantum Hall state. With increasing magnetic field, the transitions from insulating to quantum Hall and quantum Hall to insulating are very similar with respect to their transport properties. We address the temperature dependence around the transitions and show that the characteristic energy scale for the high field transition is larger.Comment: 4 page