Suppressive B-cell factor (SBF) produced by FcR-bearing B cells; suppression of B, but not non-B-cell proliferation

B cells that have receptors for the Fc portion of IgG (FcR gamma + B cell) elaborate an immunoregulatory lymphokine termed suppressive B-cell factor (SBF) after binding immune complexes, such as sheep erythrocytes sensitized with IgG anti-sheep erythrocyte antibody (EA). For producing SBF, de novo protein is required, but not DNA or DNA-dependent RNA synthesis. This mediator is released into the culture supernatant of FcR gamma + B cells during 6 to 48 hr after stimulation by EA. SBF suppresses the proliferation of B, but not non-B cells. Thus, it suppressed (i) plaque-forming cell responses in the induction phase in an antigen-non-specific manner, (ii) DNA synthesis of lipopolysaccharide-activated B cells, but neither concanavalin A nor phytohaemagglutinin-activated T cells, and (iii) the proliferation of B but not non-B tumour-cell lines by acting at the G1-S junction in the cell cycle. Concordance of H-2 haplotype between SBF-producing mice and target B cells is necessary for the suppression. Thus, the action of SBF is B-cell specific and antigen-non-specific. Immune complex-mediated negative feedback regulation seems to be operated by lymphokines such as SBF which may be also involved in the surveillance for B-cell tumours.     

Early stage of human adenovirus type 12-inoculated retinal tissue of F344 newborn rat

To elucidate the pathogenesis of adenovlrus type 12 (Ad12)-induced rat retinal tumor, an experimental animal model of human retinobiastoma (RB), DNA analysis, in situ hybridizatlon and immunohistochemlstry were performed. The adenovirus oncogene EIA was detected in the host genome by Southern blot hybridization. Examined retinal tlssues did not show any histological changes, but the number of retinal cells lmmunoreactive with an antibody to proliferating cell nuclear antigen (PCNA) increased with the course of study. In in situ hybridization, E1A gene expression was recognized at the Inner granular layer of the retina at an early stage arer virus inoculation, and subsequently, N-myc gene expression was recognized at the same region. No alteration was found in the retinoblastoma susceptibility gene ( Rb gene) expression. The product of the virus oncogene integrated into the host genome could induce an Increase in N-myc expression, without any abnormality of the Rb gene itself. Results from the present study could be useful in clarifying the tumorige-nesis of this experimental model.     

Properties and localization of the anterior semicircular canal-activated vestibulocollic neurons in the cat

Summary Unit activites of secondary vestibular neurons that selectively responded to stimulation of the anterior semicircular canal nerve (ACN) were recorded extracellularly in the anesthetized cat. Axonal pathways and projections in the spinal cord of the ACN-activated neurons were examined by recording their antidromic responses to stimulation of the lateral and medial vestibulospinal tracts (LVST and MVST), and the bilateral neck extensor motoneuron pools in the C₁segment (C₁dorsal rami [DR] motoneuron pools). In order to determine whether the neurons had ascending axon collaterals to the extraocular motoneurons, the contralateral (c-) inferior oblique (IO) motoneuron pool was also stimulated. Twenty-seven neurons sent their axons to the ipsilateral (i-) C₁DR motoneuron pool via the LVST without any projection to the extraocular motoneuron pool. All the cells except one were located in the ventral part of the lateral vestibular nucleus. This pathway produced monosynaptic EPSPs with short time-to-peak and short half-width in C₁DR motoneurons (16/16 motoneurons). Eight neurons sent axons to the i-C₁DR motoneuron pool via the MVST without any to the extraocular motoneuron pool. Cell somata were located in the descending nucleus or in the ventral part of the lateral nucleus. These neurons did not produce postsynaptic potentials (PSPs) in any C₁DR motoneurons. All thirty-five neurons sending axons to the c-C₁DR motoneuron pool have ascending axon collaterals to the c-IO motoneuron pool.     

Lysosome is a primary organelle in B cell receptor-mediated apoptosis: an indispensable role of Syk in lysosomal function

To investigate the mechanism of B cell receptor (BCR)-mediated apoptosis, we utilized immature B cell lines, DT40 and WEHI-231. In both cell lines, BCR-crosslinking caused the increase in lysosomal pH with early apoptotic changes characterized by chromatin condensation and phosphatidylserine exposure. This increase was detected in c-Abl-deficient DT40 cells but not in Syk-deficient cells, which corresponded to the fact that the former cells but not the latter revealed BCR-induced apoptosis. In contrast, BCR-crosslinking caused no apparent change in mitochondrial transmembrane potential. Therefore, the lysosomal change might be a primary event in BCR-induced apoptosis in DT40 cells. The increased activity of cathepsin B and apoptosis-preventing effect of a cathepsin inhibitor suggested a significant role of lysosomal enzymes in this apoptosis. By microscopic studies, lysosomes of wild-type DT40 cells fused to BCR-carrying endosomes became enlarged and accumulated one another. In contrast, these changes of lysosomal dynamics did not occur in Syk-deficient cells but transfer of wild-type Syk restored the lysosomal changes and apoptosis. These results demonstrated that the lysosomal change accompanied with the activation of lysosomal enzymes is a primary step in BCR-crosslinking-mediated apoptosis and Syk is responsible for this step through the fusion of BCR-carrying endosomes to lysosomes.     

Role of protein-tyrosine kinase syk in oxidative stress signaling in B cells

Oxidative stress induces the activation of multiple signaling pathways related to various cellular responses. In B cells, Syk has a crucial role in intracellular signal transduction induced by oxidative stress as well as antigen receptor engagement. Treatment of B cells with hydrogen peroxide (H(2)O(2)) induces enzymatic activation of Syk. Syk is essential for Ca(2+) release from intracellular pools through phospholipase C-gamma2 and the activation of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol 3-kinase-Akt survival pathway following H(2)O(2) stimulation. Oxidative stress-induced cellular responses in B cells follow different patterns, such as necrosis, apoptosis, and mitotic arrest, according to the intensity of H(2)O(2) stimulation. Syk is involved in the protection of cells from apoptosis and induction of G2/M arrest. Syk leads to the activation of the phosphatidylinositol 3-kinase-Akt survival pathway, thereby enhancing cellular resistance to oxidative stress-induced apoptosis. On the other hand, Syk-dependent phospholipase C-gamma2 activation is required for acceleration toward apoptosis following oxidative stress. These findings suggest that oxidative stress-induced Syk activation triggers the activation of several pathways, such as proapoptotic and survival pathways, and the balance among these various pathways is a key factor in determining the fate of a cell exposed to oxidative stress.     

Raft.1, a monoclonal antibody raised against the raft microdomain,recognizes G-protein beta1 and 2, which assemble near nucleus after shiga toxin binding to human renal cell line

SUMMARY: Raft microdomains are glycolipid-enriched microdomain scaffolding molecules involved in signal transduction. The binding of Shiga toxin to globotriaosyl ceramide in raft microdomains of the human renal tubular cell line ACHN causes temporal activation of Src-kinase Yes. To study the downstream signaling mechanism proceeding to the activation of Yes, we raised monoclonal antibodies (MAbs) against raft microdomains. The MAbs were screened on the basis of, first, binding to raft microdomains with dot-blot immunostaining, second, intracellular localization of the epitope by flowcytometry after permeabilization, and third, translocation of the antigen molecules after Stx treatment by immunohistochemical staining. Raft.1 MAb bound to the molecules that accumulated to the particular region near the nucleus after Stx treatment. Two-dimensional Western blotting and matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis revealed that the antigen molecule is GTP binding protein beta subunits 1 and 2 (Gbeta1 and 2). That Raft.1 recognized Gbeta1 and 2 was further confirmed by the reactivity to recombinant Gbeta1 and 2 proteins. To our knowledge, this is the first report of production of a MAb recognizing Gbeta1 and 2. Because Gbeta1 and 2 are highly conserved all through organisms and are deeply involved in signal transduction, Raft.1 is expected to be utilized frequently in research.     

The architecture of variant surface glycoprotein gene expression sites in Trypanosoma brucei

Trypanosoma brucei evades the immune system by switching between Variant Surface Glycoprotein (VSG) genes. The active VSG gene is transcribed in one of approximately 20 telomeric expression sites (ESs). It has been postulated that ES polymorphism plays a role in host adaptation. To gain more insight into ES architecture, we have determined the complete sequence of Bacterial Artificial Chromosomes (BACs) containing DNA from three ESs and their flanking regions. There was variation in the order and number of ES-associated genes (ESAGs). ESAGs 6 and 7, encoding transferrin receptor subunits, are the only ESAGs with functional copies in every ES that has been sequenced until now. A BAC clone containing the VO2 ES sequences comprised approximately half of a 330 kb 'intermediate' chromosome. The extensive similarity between this intermediate chromosome and the left telomere of T. brucei 927 chromosome I, suggests that this previously uncharacterised intermediate size class of chromosomes could have arisen from breakage of megabase chromosomes. Unexpected conservation of sequences, including pseudogenes, indicates that the multiple ESs could have arisen through a relatively recent amplification of a single ES.     

Differences in the abilities of individual fingers during the performance of fast,repetitive tapping movements

Using 12 healthy male subjects, the dynamic motor ability of individual fingers was investigated under four different finger tapping conditions. These were: maximum speed tapping with one finger (single-finger tapping), alternate movement of two fingers (double-finger tapping), double-finger tapping in an unsupported condition, and submaximum constant speed tapping with one finger in a passive manner. Key-contact forces for all fingers and the movement velocity of the tapping finger were monitored. With the exception of the unsupported condition, non-tapping fingers were maintained in contact with designated keys during the tapping tasks. It was found that the index finger attained the fastest cadence and greatest movement velocity, followed by the middle, little and ring fingers, respectively. Subjective assessment of rank order of "difficulty" of tapping by the subjects was highly correlated with tapping cadence. Thus dynamic motor function, as indicated by rapid, repetitive movement, differs among the individual fingers. Parallel changes were observed in the key-contact force of the neighboring non-tapping fingers during tapping. The range of the non-tapping finger forces was largest during tapping by the ring finger. A similar trend was found for passive tapping, during which the magnitude of key-contact force was less than one-third of that observed during active tapping. The lower cadence achieved by the ring finger may be attributed more to a lack of independence at the level of voluntary neuromuscular control, than to innate mechanical interaction with the other fingers. Tapping cadence of each finger was lower for the double-finger mode than for the single-finger mode. The magnitude of the observed decrease in cadence during double-finger tapping was, on the other hand, strongly dependent on finger-combination. The decrease was smallest for the index-middle finger-combination, and greatest for the ring-little finger-combination. Compatibilities with other fingers can play an essential role in the dynamic motor function of individual fingers. During the unsupported task, in which interactions were diminished by allowing all fingers to move freely, tapping cadence increased markedly. Therefore, the lower cadences observed in specific finger-combinations may be partly attributed to anatomical and neural interdigit interactions.