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It is well known that both neuromuscular and perceptual properties are affected during spaceflight. These modificaitons can therefore induce dramatic alterations in the mechanical basis of movements and locomotion disturbances. The main objectives of this study were: 1) to examine whether the nervous control of muscular activity in the upper limbs of the rhesus monkey (Macaca mulatta) was modified in a microgravity environment; and 2) to quantify the electromyographic (EMG) pattern of biceps (BI) and triceps (TRI) muscles pre-, in-, and postflight during performance of goal-directed movements and locomotion.

Bifunctional antibodies specific for a determinant within the T cell receptor (TcR) complex of cytotoxic T lymphocytes (CTL) and a determinant expressed on the surface of the target cell will effectively mediate cytolysis. In such a lytic system anti-Lyt-2 antibody can block cytolysis. We have observed that the amount of inhibition varies considerably from clone to clone and surprisingly correlates well with inhibition of conjugate formation as mediated by bifunctional antibody. This implies that inhibition of antibody-mediated killing occurs as the result of reduction of the avidity of the effector cell for its target, the same mechanism responsible for inhibition of receptor-mediated lysis by anti-Lyt-2. In light of the similarity between the mechanism of inhibition by anti-Lyt-2 of receptor-mediated and antibody-mediated cytolysis, we compared the ability of anti-Lyt-2 to inhibit cytolysis in these two different assay systems by using a number of different CTL clones. Whereas the majority of secondary CTL clones (presumed to have high affinity TcR) are inhibited equally in both assay systems, most primary CTL (presumed to have low affinity TcR) are more susceptible to inhibition by anti-Lyt-2 in their receptor-specific than their antibody-directed cytolysis. These results, taken together with an apparent correlation between the amount of Lyt-2 expressed on the cell surface and susceptibility to inhibition, suggest anti-Lyt-2 may block CTL function by sterically inhibiting mobility of the TcR complex.

Since the last 25 years, the cortex is considered as a dynamic entity, susceptible of changes. Various types of modifications in stimuli may lead to the plasticity of the target neurons. These include immobilisation, denervation, amputation, deafferentation... In the somatosensory system, the most important changes are a substantial reorganisation of the cortical somatotopic representation, and an enlargement of the receptive fields (RF) of cortical neurons. Hindlimb suspension (HS) is characterized by the absence of weight-bearing and a reduced motor activity. In these conditions, the cutaneous receptors located on the foot sole are deactivated. Our hypothesis is that this condition of HS can produce a reorganisation of the somatosensory cortex (SmI) and a modification in the size of the cutaneous RF.

The present studies have made use of in vitro derived H-2Kb mutants to analyze the fine specificity of alloreactive cytotoxic T lymphocytes (CTL). The variants were derived by negatively selecting mutagenized tumor cells with a monoclonal anti-H-2Kb antibody and positively selecting for residual cells expressing serologically altered H-2Kb molecules. Details of this procedure are described in the companion paper. Selected populations of bulk alloreactive and cloned CTL were examined for recognition of the variants. In contrast to the serologic findings presented in the companion paper, there does not appear to be a correlation between the monoclonal antibody used to select the R8 variant and the CTL specificities recognized. In several instances, CTL clones could discriminate between variants having identical serologic profiles. Therefore, it would appear that the CTL have a large repertoire of allorecognition, even when generated across a mutant anti-Kb combination reflecting only a few amino acid differences. In addition, a diverse set of epitopes can be recognized on the Kb molecule. Finally, in some instances a change in what would appear to be a single amino acid resulted in a profound alteration of CTL recognition even though the Kb mutant molecule expressed limited serologic changes. These results support the idea that small changes in the H-2Kb molecule can have dramatic effects on CTL even though there are relatively little effects on serologic recognition of the target molecule.

Ag receptor triggering in B cells stimulates the activity of receptor-associated tyrosine protein kinases (TPK), leading to tyrosine phosphorylation of several cellular substrates, one of which is the Vav proto-oncogene product. We have recently determined that Vav is a TPK-regulated guanine nucleotide exchange factor for Ras in T cells. Here, we show that B cell extracts or Vav immunoprecipitates contain a Ras GDP/GTP exchange activity that is stimulated upon surface Ig (slg) triggering. The receptor-mediated stimulation of Vav exchange activity was blocked by the TPK antagonist, herbimycin A. Furthermore, immunodepletion of Vav from the B cell extracts removed approximately 80% of the Ras GDP/GTP exchange activity. These findings indicate, first, that B cell-derived Vav possesses GDP/GTP exchange activity for Ras; second, that the exchange activity of Vav is accelerated by a slg-triggered, herbimycin A-sensitive TPK and, third, that Vav accounts for most of the receptor-stimulated Ras GDP/GTP exchange activity. Thus, Vav may serve as a critical component in slg-mediated signal transduction pathways by coupling receptor-associated TPK to the activation of Ras proteins.

Le débat sur les nouvelles formes de critique et de recherche, universitaires ou non, se polarise à la fois sur les fonctions du numérique, à savoir son action de deep remixability, qui selon Lev Manovich identifie la spécificité des logiciels de rendre tout type de langage, et sur la prédominance conservée, même dans un contexte médiatique, par les stratégies expressives et argumentatives de l’écriture. Notre objectif est d’étudier l’apparition du numérique et les possibilités critiques et pédagogiques qu’il apporte à un genre qui a développé, au cours de l’histoire, la fonction de la critique et de la recherche. Tout en considérant la collaboration entre le visuel et l’écriture, nous voulons montrer que le vidéo-essai – cette typologie d’essai médiatique – ne se base ni sur la prédominance du visuel, ni sur la simple présence d’une argumentation, mais plutôt sur la relation critique entre les sources commentées (aussi bien visuelles qu’écrites) et une voix de commentaire qui est, elle aussi, technologisée par les logiciels.