Regulatory mechanisms in cell-mediated immune responses. V. H-2 homology requirements for the production of a minor locus-induced suppressor factor

A mixed leukocyte reaction suppressor factor is produced by spleen cells sensitized in vivo and restimulated in vitro across non-H-2 antigenic barriers. Cells capable of producing this factor appear in the spleens of minor locus-immunized animals later than in animals sensitized to major histocompatibility complex-encoded antigens. However, both H-2 and non H-2-induced factors suppress proliferative responses to any alloantigen. Splenocytes from animals immunized with H-2-identical, minor locus-disparate cells produce suppressor factor in vitro only when restimulated with cells sharing both H-2 and non-H-2 antigens with the in vivo stimulators.

Sidedness of (sodium, potassium)-adenosine triphosphate of inside-out red cell membrane vesicles. Interactions with potassium

Inside-out membrane vesicles of human red cells, prepared according to the method of Steck et al. (1970) Science 168, 255-257) have sufficiently low cation permeability to allow the examination of the side-specific interactions of ligands with the asymmetric sodium pump complex. In accordance with the known properties of the pump in intact cells the following results were observed: (a) ATP-dependent sodium influx and (b) maximal (sodium, potassium)-ATPase with K+ present inside the vesicles with larger than or equal to 20 micronM ATP. With much lower [ATP], K+ inhibited sodium-activated ATPase. K+ was inhibitory at either surface. Inhibition was different on the two sides since cytoplasmic (extravesicular) Na+ counteracted inhibition by cytoplasmic (extravesicular) K+ but not inhibition by K+ at the plasma or external membrane surface, i.e. intravesicular K+. A decrease in the steady state level of the phosphenzyme intermediate of sodium-activated ATPase was caused also by K+ at either surface. The effect of cytoplasmic K+ is compatible with its competitive inhibition of activation of phosphorylation of the enzyme by cytoplasmic Na+. At 37 degrees, the inhibitory effect of external K+ is due to interaction with the phosphoenzyme to form a stable complex of K+ with the dephosphenzyme resulting in a decreased overall reaction rate but increased turnover of the phosphoenzyme (E-P + K leads to EK + Pi). At 0 degree, external K+ inhibits by interacting with the unphosphorylated enzyme to form an occluded enzyme-K complex. This results in a decreased overall rate but relatively small change in apparent turnover of the phosphoenzyme. At 0 degree, but not at 37 degrees, external Na+ counteracted the inhibitory effects of external K+.

Fractionation of lymphocyte subpopulations which regulate mixed lymphocyte reactions

Four days after injection of allogeneic lymphocytes BALB/c splenic T cells suppress proliferation of syngeneic cells in mixed lymphocyte reactions (MLR). Conversely, lymph node cells from the same mice amplify MLR responses. To further characterize these functional subpopulations, alloantigen-primed lymphocyte suspensions from both organs were fractionated by velocity sedimentation at unit-gravity. After fractionation MLR suppressor cells from spleens localized exclusively in rapidlly sedimenting fractions of large cells. MLR suppressor activity of cells from these fractions, as well as that of unfractionated spleen cell suspensions, was abolished by treatment with anti-Thy-1.2 serum and complement. Spleen cell fractions of similar sedimentation velocity also secreted a soluble MLR suppressor into culture supernatants. Although inhibitory of MLR, spleen cells of rapid sedimentation velocity did not suppress responses to T cell mitogens. In marked contrast with the effects of spleen cells, large 4-day-alloantigen-primed lymph node cells had no suppressive activity in MLR. MLR amplifier cells of uncertain derivation were found in fractions of medium sedimentation velocity from both spleens and lymph nodes. Fractionation of alloantigen-primed lymph node cell suspensions did reveal, however, a subpopulation of small cells with MLR suppressor acitivty which was unaffected by treatment with anti-Thy-1 serum and complement. The data thus indicate that large alloantigen-activated lymphocytes are not intrinsically suppressive nor are cells which suppress MLR necessarily large. We consequently conclude that regulation of MLR responses by alloantigen-primed lymphocytes involves a complex interaction between distinct functional subpopulations of cells which are separable both by physical and biologic properties.

Modifications of mammalian cell surfaces induced by sugars: scanning electron microscopy

Substitution of galactose, xylose, or mannose for glucose in the growth medium of L cells or the addition of equal concentrations of the alternate sugars to glucose-containing medium results in marked morphologic changes. The changes are revealed by conventional staining for light microscopy and by scanning electron microscopy. L cells grow indefinitely on combinations of equal concentrations of glucose and galactose, xylose, or mannose. There appear to be no significant differences in growth rate on glucose compared to the combinations of sugars cited. Cells subcultured from glucose to the combinations while undergoing rapid multiplication show marked morphologic changes by light and scanning electron microscopy within 36 hr. Of particular note are the loss of microvilli; flattening of the cells; assumption of polygonal shape; prominence of nuclei and nucleoli; and changes in the structure and distribution of filopodia. Virtually all cells in the population exhibit the changes noted.

Growth of pseudotypes of vesicular stomatitis virus with N-tropic murine leukemia virus coats in cells resistant to N-tropic viruses

Formation of pseudotypes between murine RNA tumor viruses and vesicular stomatitis virus (VSV) has been confirmed. Pseudotypes of VSV genomes coated by the surface envelope from an N-tropic tumor virus grew equally well in cells homozygous for either the Fv-1(n) or Fv-1(b) alleles. Therefore, the product of the Fv-1 locus, which restricts growth of murine RNA tumor viruses, must act on an intracellular aspect of tumor virus replication, a step after attachment and penetration.