Clonal abortion of bone marrow T cell precursors: T cells acquire specific antigen reactivity prethymically

Lethally irradiated (900 R) mice were reconstituted with bone marrow cells from syngeneic donors that had been tolerized 2 to 3 wk earlier to either DNP or TNP compounds. Five weeks after reconstitution, these animals were tested for their ability to mount a delayed hypersensitivity (DH) response to the tolerizing haptens. Recipient mice were specifically tolerant to the hapten that was used to induce tolerance in the marrow donor. Mixing experiments in which mice were reconstituted with marrow from DNP-tolerant and TNP-tolerant donors showed no indication of active suppression or effective antigen carry-over in this system. This observation held true even in experiments in which mice were reconstituted with a mixture of marrow from tolerant and normal donors at a ratio of 5:1. Thus the reduced responsiveness in recipient mice seemed to be due to the functional elimination of hapten-responsive T cell precursor (pre-T) clones. Recipient unresponsiveness was also shown to be MHC restricted. Maintenance of unresponsiveness appeared to be due to the restricted access of regenerating pre-T cell clones to the maturational influence of the recipient's thymus.     

Significance of partial pre-acidification of glucose for methanogenesis in an anaerobic digestion process

Summary The effect of partial pre-acidification of carbohydrate containing wastewaters on anaerobic digester performance was investigated. The influent was a 1% (w/v) glucose solution in a mineral salts medium imposing carbon-limited growth conditions. Up to 13% of the Chemical Oxygen Demand (COD) was added as volatile fatty acids (VFA).In all cases, addition of VFA to the glucose medium resulted in significant increases in the maximum specific COD-conversion rates of the sludge (both with respect to continuous feeding and following a shock loading), as compared with values found on digestion of glucose media alone.     

Capsular contracture and steroid-related complications after augmentation mammaplasty. A preliminary study.

Ninety-one patients who had had augmentation mammaplasties were evaluated retrospectively. The intra-implant use of steroids appeared to reduce the incidence of breast firmness--at least over the short follow-up period--but there were complications from this which appear to be dose related (mg of Solu-Medrol/100 cc saline). A long-term evaluation of such patients is desirable. Meanwhile, our limited data strongly suggest that the intra-implant use of steroids should be used only with caution as to the dose and with a careful follow-up.     

Regulation of meiotic recombination and prophase I progression in mammals.

Meiosis is the process by which diploid germ cells divide to produce haploid gametes for sexual reproduction. The process is highly conserved in eukaryotes, however the recent availability of mouse models for meiotic recombination has revealed surprising regulatory differences between simple unicellular organisms and those with increasingly complex genomes. Moreover, in these higher eukaryotes, the intervention of physiological and sex-specific factors may also influence how meiotic recombination and progression are monitored and regulated. This review will focus on the recent studies involving mouse mutants for meiosis, and will highlight important differences between traditional model systems for meiosis (such as yeast) and those involving more complex cellular, physiological and genetic criteria.     

Regulation of Apterous activity in Drosophila wing development.

Apterous is a LIM-homeodomain protein that confers dorsal compartment identity in Drosophila wing development. Apterous activity requires formation of a complex with a co-factor, Chip/dLDB. Apterous activity is regulated during wing development by dLMO, which competes with Apterous for complex formation. Here, we present evidence that complex formation between Apterous, Chip and DNA stabilizes Apterous protein in vivo. We also report that a difference in the ability of Chip to bind the LIM domains of Apterous and dLMO contributes to regulation of activity levels in vivo.     

Models of the Na-K pump in cardiac muscle predict the wrong intracellular Na+ activity

The Na-K pump in cardiac Purkinje strands has been carefully studied with voltage clamp and Na+-selective microelectrodes. In three of these studies both the rate of change of intracellular Na+ activity, a(Nai), after pump blockade, and the time constant of reduction of a(Nai) after an Na+ load were measured. These two parameters can be employed with a formalism relating pump activity to a(Nai) in order to predict the a(Nai) in the steady state. Several formalisms were tested: (a) a first-order dependence on a(Nai); (b) a model based on the assumption of a single, saturable, Na+-binding site that must be occupied for transport to occur; (c) a model based on n equivalent, saturable, Na+ binding sites per pump molecule all of which must be occupied for transport to occur. The first two models predicted an a(Nai) that is far below the value of about 6 mM that is experimentally obtained. The third model would work for n greater than or equal to 4. These results suggest that either the cardiac Na-K pump is not well described by available Na-K pump models for n less than 4 or that the measured Na+ influx rate, extrusion rate or a(Nai) are in error.