Probing single jumps of surface atoms.

Jumps of single atoms can be followed on their time and space scale (nanoseconds and Angstroms) by applying nuclear resonance scattering of synchrotron radiation. Here we develop the theory for jump diffusion in two-dimensional systems. Two types of phenomena are noteworthy: apparent acceleration of the nuclear decay and relaxation of hyperfine interactions, in particular, electric quadrupole interactions. The latter effect becomes for the first time one of significance and well measurable due to the inherent anisotropy of the surface. We show how, by way of motional narrowing, to distinguish between the motion of the probe atom itself and the motion of adatoms.

Phonons in iron: from the bulk to an epitaxial monolayer.

The confinement of materials in low-dimensional structures has significant impact on propagating excitations like phonons. Using the isotope-specific 57Fe nuclear resonant vibrational spectroscopy we were able to determine elastic and thermodynamic properties of ultrathin Fe films on W(110). With decreasing thickness one observes a significant increase of the mean atomic displacement that goes along with an enhancement of vibrational modes at low energies as compared to the bulk. The analysis reveals that these deviations result from atomic vibrations of the single atomic layers at the two boundaries of the film, while the atoms inside the films vibrate almost bulklike.

Monoclonal antibodies to Escherichia coli beta-galactosidase and their use for detection and purification of recombinant expression products.

A panel of seven mouse monoclonal antibodies (BG-01-BG-07) was prepared against beta-galactosidase derived from E. coli. The antibodies are beta-galactosidase specific, show no cross-reactivity with other E. coli proteins and can be used for identification and characterization of beta-galactosidase fusion proteins expressed in lambda expression vectors. One of the antibodies allows a simple, one-step isolation of the fusion proteins directly from the crude bacterial lysates using immunoaffinity chromatography.

Tolerance of skin allografts incompatible at the entire H-2 complex induced in adult mice by the post-transplant treatment.

Permanent tolerance of the entire H-2 complex incompatible B10 skin allografts was induced in adult B10.A mice by post-transplant treatment. Recipient mice were treated with heterologous antithymocyte serum (ATS) and specific tissue extracts or monoclonal antibodies anti-Thy-1.2. Combination of treatments with the specific tissue extracts and monoclonal antibodies leads to a high degree of tolerance in the majority of ATS-treated animals. Results thus show that it is possible to induce long-term tolerance of the entire H-2 complex incompatible skin allografts in mice using specific and non-specific immunosuppression given in the post-transplant period.

Prolongation of skin allograft survival in ATS-treated mice by post-transplant injections of species antigenic extracts.

B10.A male mice were grafted with H-2-incompatible murine B10.A(2R) skin allografts and treated with antithymocyte serum on days 2, 4, and 7 after transplantation. Repeated injections of cell-free tissue extracts from livers or spleens of B10.A(2R) mice were given in the standard doses, starting on the day of transplantation or on day 14 or day 28 after transplantation. The standard doses were the equivalents of material extracted from 40 mg or 80 mg of wet weight of liver or spleen tissue. Almost all of the regimens used in which antigen injections were begun on day 14 or day 28 after transplantation were successful and led to a marked prolongation in skin allograft survival. In some experimental groups most of the grafts survived 100 days after grafting and 8--33% grafts showed long-term survival in individual groups. The mechanism of this tolerance is mediated by suppressor cells which were characterized by means of anti-Thy 1.2 antibodies as T lymphocytes. the in vitro experiments have shown that cytotoxic cell precursors may be present in long-term tolerant mice and that they may be reactive to the tolerated antigens after sensitization.

Induction of specific transplantation tolerance with blood serum in newborn and adult rats.

Histocompatibility (H) antigens present in the serum of rats induce a relatively high degree of neonatal transplantation tolerance in the absence of cellular chimerism. With the non-H-1 difference, which is relatively strong in the rat strain combination used, skin grafts survive permanently in some animals. With the H-1 plus non-H-1 difference, only some animals show a slight prolongation of skin graft survival, but cytotoxic antibody production is inhibited for long periods of time. In adult animals, at least with the non-H-1 difference, allograft survival is very significantly prolonged after treatment with serum alone, or in combination with hydrocortisone. The nonspecific component(s) of the serum also contributes to a prolongation of graft survival. The data suggest that blood serum is a good source of H antigens which seem to be present in a tolerogenic active form.

Transplantation immunity in the brain.

The resistance of animals to allogeneic tumor cells injected into the brain increases with age. The second-set reaction in the brain of rats appears to be equally effective after preimmunization into the brain and preimmunization into the leg. Also, the presence of cytotoxic antibodies is demonstrable after preimmunization into the brain. These findings suggest that both arcs of the transplantation reaction, the afferent and efferent, are involved in tumor-cell allotransplantation in the brain.

Attempts to compare the effectiveness of blocking factors and enhancing antibodies in vivo and in vitro.

Sera from rats carrying tolerated skin allografts were tested for the presence of blocking activity in vitro. Sera with blocking activity had no effect on transplantation tolerance induction in newborn animals. Immunological enhancement of tumor growth was procured by passive transfer of serum from tolerant animals bearing skin allografts. It made no difference whether or not the serum contained blocking activity in vitro. These results suggest that there is no relationship between blocking factors and enhancing activity in vivo.