Induction of self-tolerance in T cells but not B cells of transgenic mice expressing little self antigen

Self-tolerance to a transgene-encoded protein, hen egg lysozyme, was examined in the T and B cell repertoires of a series of lines of transgenic mice that expressed different serum concentrations of soluble lysozyme. T cells were tolerant in all lines in which lysozyme was expressed irrespective of the antigen concentration, whereas B cell tolerance did not occur when the serum lysozyme concentration was less than 1.5 nanograms per milliliter (0.1 nM). Induction of elevated transgene expression could restore B cell tolerance. These findings support the hypothesis that autoimmune disease may in some instances arise through a bypass of T cell tolerance.     

Activation of 2-aminofluorene by cultured plant cells

Cultured tobacco plant cells activated 2-aminofluorene to an agent mutagenic to Salmonella typhimurium strain TA98. The plant activation of 2-aminofluorene is heat-inactivated and may not involve solely cytochrome P-450. The kinetics of activation demonstrated both time- and concentration-dependent responses.     

Epidermal viral immunity induced by CD8alpha+ dendritic cells but not by Langerhans cells

The classical paradigm for dendritic cell function derives from the study of Langerhans cells, which predominate within skin epidermis. After an encounter with foreign agents, Langerhans cells are thought to migrate to draining lymph nodes, where they initiate T cell priming. Contrary to this, we show here that infection of murine epidermis by herpes simplex virus did not result in the priming of virus-specific cytotoxic T lymphocytes by Langerhans cells. Rather, the priming response required a distinct CD8alpha+ dendritic cell subset. Thus, the traditional view of Langerhans cells in epidermal immunity needs to be revisited to accommodate a requirement for other dendritic cells in this response.     

DNA methylation decreases in aging but not in immortal cells

When normal diploid fibroblasts from mice, hamsters, and humans were grown in culture, the 5-methylcytosine content of their DNA's markedly decreased. The greatest rate of loss of 5-methylcytosine residues was observed in mouse cells, which survived the least number of division. Immortal mouse cell lines had more stable rates of methylation.     

Mouse B-type lamins are required for proper organogenesis but not by embryonic stem cells

B-type lamins, the major components of the nuclear lamina, are believed to be essential for cell proliferation and survival. We found that mouse embryonic stem cells (ESCs) do not need any lamins for self-renewal and pluripotency. Although genome-wide lamin-B binding profiles correlate with reduced gene expression, such binding is not directly required for gene silencing in ESCs or trophectoderm cells. However, B-type lamins are required for proper organogenesis. Defects in spindle orientation in neural progenitor cells and migration of neurons probably cause brain disorganizations found in lamin-B null mice. Thus, our studies not only disprove several prevailing views of lamin-Bs but also establish a foundation for redefining the function of the nuclear lamina in the context of tissue building and homeostasis.     

Fibronectin binds to some bacteria but does not promote their uptake by phagocytic cells

The involvement of plasma fibronectin in phagocytosis of bacteria was investigated by testing the binding of fibronectin to several species of bacteria and by evaluating the ability of fibronectin to promote binding and endocytosis of two species of these bacteria by phagocytic cells. Fibronectin binds non-covalently to Gram-positive and Gram-negative bacteria and to yeast but did not appear to be necessary or sufficient for uptake of Staphylococcus aureus and Salmonella typhimurium by several different phagocytic cell types.     

Activation of gamma delta T cells in the primary immune response to Mycobacterium tuberculosis

Although the immunologic role of T cells bearing the conventional alpha beta T cell receptor (TCR) has been well characterized, little is known about the function of the population of T cells bearing the gamma delta TCR. Therefore, the role of gamma delta T cells in the immune response to Mycobacterium tuberculosis (MT) was investigated. The number of TCR gamma delta cells in the draining lymph nodes of mice immunized with MT was greatly increased in comparison with the number of TCR alpha beta cells. Three biochemically distinct gamma delta TCRs were detected. Analyses of cell cycle, of interleukin-2 receptor expression, and of interleukin-2 responsiveness showed that a large proportion of the gamma delta T cells were activated in vivo. TCR gamma delta cells responded to solubilized MT antigens in vitro but, in contrast to MT-specific alpha beta T cells, the response of gamma delta T cells to MT did not require major histocompatability complex class II recognition. These results provide an example of antigen-specific activation of gamma delta T cells in vivo and indicate that gamma delta T cells may have a distinct role in generating a primary immune response to certain microorganisms.     

Control of experimental autoimmune encephalomyelitis by T cells responding to activated T cells

T cell vaccination against experimental autoimmune disease is herein shown to be mediated in part by anti-ergotypic T cells, T cells that recognize and respond to the state of activation of other T cells. The anti-ergotypic response thus combines with the previously shown anti-idiotypic T cell response to regulate autoimmunity.     

Replacements of Pro86 in phage T4 lysozyme extend an alpha-helix but do not alter protein stability

To investigate the relation between protein stability and the predicted stabilities of individual secondary structural elements, residue Pro86 in an alpha-helix in phage T4 lysozyme was replaced by ten different amino acids. The x-ray crystal structures of seven of the mutant lysozymes were determined at high resolution. In each case, replacement of the proline resulted in the formation of an extended alpha-helix. This involves a large conformational change in residues 81 to 83 and smaller shifts that extend 20 angstroms across the protein surface. Unexpectedly, all ten amino acid substitutions marginally reduce protein thermostability. This insensitivity of stability to the amino acid at position 86 is not simply explained by statistical and thermodynamic criteria for helical propensity. The observed conformational changes illustrate a general mechanism by which proteins can tolerate mutations.     

Disrupted timing of discontinuous but not continuous movements by cerebellar lesions

Patients with cerebellar damage are known to exhibit deficits in the temporal control of movements. We report that these deficits are restricted to discontinuous movements. Cerebellar patients exhibited no deficit in temporal variability when producing continuous, rhythmic movements. We hypothesize that the temporal properties of continuous movements are emergent and reflect the operation of other control parameters not associated with the cerebellum. In contrast, discontinuous movements require an explicit representation of the temporal goal, a function of the cerebellum. The requirement for explicit temporal representation provides a parsimonious account of cerebellar involvement in a range of tasks.     

Activation of muscarinic potassium currents by ATP gamma S in atrial cells

Intracellular perfusion of atrial myocytes with adenosine 5'-(gamma-thio) triphosphate (ATP gamma S), an ATP analog, elicits a progressive increase of the muscarinic potassium channel current, IK(M), in the absence of agonists. In this respect, ATP gamma S mimics the actions of guanosine triphosphate (GTP) analogs, which produce direct, persistent activation of the guanyl nucleotide-binding (G) protein controlling the K+(M) channel. The effect of ATP gamma S on IK(M), however, differs from that produced by GTP analogs in two aspects: it requires relatively large ATP gamma S concentrations, and it appears after a considerable delay, suggesting a rate-limiting step not present in similar experiments performed with guanosine 5'-(gamma-thio) triphosphate (GTP gamma S). Incubation of atrial homogenates with [35S]ATP gamma S leads to formation of significant amounts of [35S]GTP gamma S, suggesting that activation of IK(M) by ATP gamma S arises indirectly through its conversion into GTP gamma S by cellular enzymes. ATP gamma S is often used to demonstrate the involvement of protein phosphorylation in the control of various cellular processes. The finding that cytosolic application of ATP gamma S can also lead to G-protein activation implies that experiments with ATP gamma S must be interpreted with caution.     

Male-specific antigen: modification of potency by the H-2 locus in mice

Skin grafts from C57BL/10 (B10) male mice survive significantly longer than do B10.BR male skin grafts on (B10 x X B10.BR)F(1) females. This indicates that the H-2 locus influences the potency of the male-specific antigen in mice.     

Inhibition of leishmanias but not host macrophages by the antitubulin herbicide trifluralin

The dinitroaniline herbicide trifluralin (alpha, alpha, alpha-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine), at micromolar concentrations, selectively inhibited both proliferation and differentiation of the parasitic protozoan Leishmania mexicana amazonensis. In vitro, radioactive trifluralin showed specific binding to leishmania tubulin but not to mammalian tubulin. Because herbicides such as trifluralin are economical and are considered safe for man and domesticated animals, they may serve as useful sources of potential antiparasitic agents.     

Prevention of allogeneic bone marrow graft rejection by H-2 transgene in donor mice

Rejection of bone marrow grafts in irradiated mice is mediated by natural killer (NK) cells and is controlled by genes linked to the major histocompatibility complex (MHC). It has, however, not been possible to identify the genes or their products. An MHC class I (Dd) transgene introduced in C57BL donors prevented the rejection of their bone marrow by NK cells in irradiated allogeneic and F1 hybrid mice expressing the Dd gene. Conversely, H-2Dd transgenic C57BL recipients acquired the ability to reject bone marrow from C57BL donors but not from H-2Dd transgenic C57BL donors. These results provide formal evidence that NK cells are part of a system capable of rejecting cells because they lack normal genes of the host type, in contrast to T cells, which recognize cells that contain abnormal or novel sequences of non-host type.     

Detection of alpha-transducin in retinal rods but not cones

The distribution in chicken retina of the alpha subunit of transducin, the guanine nucleotide--binding protein that couples light-dependent activation of rhodopsin with activation of guanosine 3',5'-monophosphate phosphodiesterase, was determined with the aid of a specific antiserum. alpha-Transducin was found in rod photoreceptor cells but was not detected in cones. These results show that rods and cones differ with respect to alpha-transducin content and suggest that the processes of phototransduction may differ correspondingly in rods and cones.     

Regulation of cutaneous malignancy by gammadelta T cells

The localization of gammadelta T cells within epithelia suggests that these cells may contribute to the down-regulation of epithelial malignancies. We report that mice lacking gammadelta cells are highly susceptible to multiple regimens of cutaneous carcinogenesis. After exposure to carcinogens, skin cells expressed Rae-1 and H60, major histocompatibility complex-related molecules structurally resembling human MICA. Each of these is a ligand for NKG2d, a receptor expressed by cytolytic T cells and natural killer (NK) cells. In vitro, skin-associated NKG2d+ gammadelta cells killed skin carcinoma cells by a mechanism that was sensitive to blocking NKG2d engagement. Thus, local T cells may use evolutionarily conserved proteins to negatively regulate malignancy.