Upregulation of TGF-beta, FOXP3, and CD4+CD25+ regulatory T cells correlates with more rapid parasite growth in human malaria infection

Understanding the regulation of immune responses is central for control of autoimmune and infectious disease. In murine models of autoimmunity and chronic inflammatory disease, potent regulatory T lymphocytes have recently been characterized. Despite an explosion of interest in these cells, their relevance to human disease has been uncertain. In a longitudinal study of malaria sporozoite infection via the natural route, we provide evidence that regulatory T cells have modifying effects on blood-stage infection in vivo in humans. Cells with the characteristics of regulatory T cells are rapidly induced following blood-stage infection and are associated with a burst of TGF-beta production, decreased proinflammatory cytokine production, and decreased antigen-specific immune responses. Both the production of TGF-beta and the presence of CD4+CD25+FOXP3+ regulatory T cells are associated with higher rates of parasite growth in vivo. P. falciparum-mediated induction of regulatory T cells may represent a parasite-specific virulence factor.     

CTLA-4 expression on antigen-specific cells but not IL-10 secretion is required for oral tolerance

CD4(+) T cells play a vital role in mediating the tolerance induced at mucosal sites following exposure to non-pathogenic stimuli, and further understanding of the precise mechanisms by which these cells prevent aberrant responses is required. We have developed a model using transfer of DO11.10 TCR-transgenic bone marrow into irradiated recipients in which it has been possible to track antigen-specific CD4(+) cells in mesenteric lymph nodes (mLN), Peyer's patches (PP) and lamina propria following primary exposure to antigen. Using this model we have demonstrated initial activation in all three gut-associated lymphoid tissue compartments characterized by increases in the frequency of transgenic cells expressing CD69 and CD25. These cells subsequently enter a state of hyporesponsiveness both locally in the mLN and PP and in the periphery following feeding and challenge. Investigating the role of CTLA-4 either using anti-CTLA-4 mAb or by generating chimeras using DO11.10xCTLA-4(-/-) mice as donors we have clearly shown that antigen-specific cells require the expression of this regulatory molecule for oral tolerance. In contrast, oral tolerance was intact in chimeras generated using DO11.10xIL-10(-/-) cells, indicating that secretion of this cytokine by antigen-specific cells is not required.     

Fast network oscillations in the rat dentate gyrus in vitro

The dentate gyrus is a prominent source of gamma frequency activity in the hippocampal formation in vivo. Here we show that transient epochs of gamma frequency network activity (67 +/- 12 Hz) can be generated in the dentate gyrus of rat hippocampal slices, following brief pressure ejections of a high-molarity potassium solution onto the molecular layer. Oscillatory activity remains synchronized over distances >300 microm and is accompanied by a modest rise in [K(+)](o). Gamma frequency oscillations were abolished by a GABA(A) receptor antagonist demonstrating their dependence on rhythmic inhibition. However, in many cases, higher frequency oscillations (>80 Hz) remained in the absence of synaptic transmission, thus demonstrating that nonsynaptic factors may underlie fast oscillatory activity.     

Single-column thalamocortical network model exhibiting gamma oscillations, sleep spindles, and epileptogenic bursts

To better understand population phenomena in thalamocortical neuronal ensembles, we have constructed a preliminary network model with 3,560 multicompartment neurons (containing soma, branching dendrites, and a portion of axon). Types of neurons included superficial pyramids (with regular spiking [RS] and fast rhythmic bursting [FRB] firing behaviors); RS spiny stellates; fast spiking (FS) interneurons, with basket-type and axoaxonic types of connectivity, and located in superficial and deep cortical layers; low threshold spiking (LTS) interneurons, which contacted principal cell dendrites; deep pyramids, which could have RS or intrinsic bursting (IB) firing behaviors, and endowed either with nontufted apical dendrites or with long tufted apical dendrites; thalamocortical relay (TCR) cells; and nucleus reticularis (nRT) cells. To the extent possible, both electrophysiology and synaptic connectivity were based on published data, although many arbitrary choices were necessary. In addition to synaptic connectivity (by AMPA/kainate, NMDA, and GABA(A) receptors), we also included electrical coupling between dendrites of interneurons, nRT cells, and TCR cells, and--in various combinations--electrical coupling between the proximal axons of certain cortical principal neurons. Our network model replicates several observed population phenomena, including 1) persistent gamma oscillations; 2) thalamocortical sleep spindles; 3) series of synchronized population bursts, resembling electrographic seizures; 4) isolated double population bursts with superimposed very fast oscillations (>100 Hz, "VFO"); 5) spike-wave, polyspike-wave, and fast runs (about 10 Hz). We show that epileptiform bursts, including double and multiple bursts, containing VFO occur in rat auditory cortex in vitro, in the presence of kainate, when both GABA(A) and GABA(B) receptors are blocked. Electrical coupling between axons appears necessary (as reported previously) for persistent gamma and additionally plays a role in the detailed shaping of epileptogenic events. The degree of recurrent synaptic excitation between spiny stellate cells, and their tendency to fire throughout multiple bursts, also appears critical in shaping epileptogenic events.     

Oligomerization and polymerization of the filovirus matrix protein VP40

The matrix protein VP40 from Ebola virus plays an important role in the assembly process of virus particles by interacting with cellular factors, cellular membranes, and the ribonuclearprotein particle complex. Here we show that the N-terminal domain of VP40 folds into a mixture of two different oligomeric states in vitro, namely hexameric and octameric ringlike structures, as detected by gel filtration chromatography, chemical cross-linking, and electron microscopy. Octamer formation depends largely on the interaction with nucleic acids, which in turn confers in vitro SDS resistance. Refolding experiments with a nucleic acid free N-terminal domain preparation reveal a mostly dimeric form of VP40, which is transformed into an SDS resistant octamer upon incubation with E. coli nucleic acids. In addition, we demonstrate that the N-terminal domain of Marburg virus VP40 also folds into ringlike structures, similar to Ebola virus VP40. Interestingly, Marburg virus VP40 rings reveal a high tendency to polymerize into rods composed of stacked rings. These results may suggest distinct roles for different oligomeric forms of VP40 in the filovirus life cycle.     

Hand involvement in Schmid metaphyseal chondrodysplasia

Schmid metaphyseal chondrodysplasia (Schmid MCD, MIM 156500) is caused by mutations in the COL10A1 gene and is clinically characterized by short stature, bowed legs, and a waddling gait. Radiographic findings include anterior cupping, sclerosis and splaying of the ribs, diffuse metaphyseal flaring, and irregularity that is most pronounced at the knees, coxa vara, and femoral bowing. We reviewed the radiographs of Schmid MCD patients at the International Skeletal Dysplasia Registry in Los Angeles for evidence of hand involvement. We found hand involvement in 47% (7/15) of cases included in our analysis. These changes were subtle and consisted of shortening of the tubular bones and metaphyseal cupping of the proximal phalanges and metacarpals. Mild hand involvement is a common feature of Schmid MCD.     

Role of O2-sensitive K and Ca channels in the regulation of the pulmonary circulation: Potential role of caveolae and implications for high altitude pulmonary edema

High altitude pulmonary edema (HAPE) is a potentially fatal complication in response to exposure to low O₂ at high altitudes. Hypoxia, by causing pulmonary vasoconstriction, increases pulmonary vascular resistance and pulmonary arterial pressure, both of which are features in the pathogenesis of HAPE. Uneven hypoxic pulmonary vasoconstriction is thought to be responsible for increased capillary pressure and leakage, resulting in edema. O₂-sensitive ion channels are known to play pivotal roles in determining vascular tone in response to hypoxia. K⁺, Ca²⁺ and Na⁺ channels are ubiquitously expressed in both endothelial and smooth muscle cells of the pulmonary microvasculature, subfamilies of which are regulated by local changes in P_O2. Hypoxia reduces activity of voltage-gated K⁺ channels and down-regulates their expression leading to membrane depolarization, Ca²⁺ influx in pulmonary artery smooth muscle cells (by activating voltage-dependent Ca²⁺ channels) and vasoconstriction. Hypoxia up-regulates transient receptor potential channels (TRPC) leading to enhanced Ca²⁺ entry through receptor- and store-operated Ca²⁺ channels. Altered enrichment of ion channels in membrane microdomains, in particular in caveolae, may play a role in excitation–contraction coupling and perhaps in O₂-sensing in the pulmonary circulation and thereby may contribute to the development of HAPE. We review the role of ion channels, in particular those outlined above, in response to low O₂ on vascular tone and pulmonary edema. Advances in the understanding of ion channels involved in the physiological response to hypoxia should lead to a greater understanding of the pathogenesis of HAPE and perhaps in the identification of new therapies.     

The impact of telomere erosion on memory CD8+ T cells in patients with X-linked lymphoproliferative syndrome

Patients with X-linked lymphoproliferative syndrome (XLP) experience excessive T cell proliferation after primary Epstein-Barr virus (EBV) infection, due to mutations in the signalling lymphocyte activation molecule (SLAM) associated protein (SAP) molecule. We examined the impact of dysfunctional proliferative control on the extent of CD8+ T cell differentiation in XLP patients who recovered from primary EBV infection. Although these young patients have normal numbers of lytic and latent EBV-epitope-specific CD8+ T cells, they were extremely differentiated as defined by loss of CCR7 and CD27, low telomerase activity and very short telomeres. This was not a direct effect arising from the loss of SAP, but was due to excessive T cell stimulation due to this defect. Thus, transduction of XLP CD8+ T cells with the catalytic component of telomerase (hTERT), but not SAP, prevented telomere loss and considerably extended proliferative lifespan in vitro. These results indicate that excessive proliferation in CD8+ T cells in XLP patients may lead to end-stage differentiation and loss of functional EBV-specific CD8+ T cells through replicative senescence. This may contribute to the defective immunity found in XLP patients who survive acute EBV infection who develop EBV-related B cell lymphomas before the fourth decade of life.     

The Schizosaccharomyces pomberfc3 + gene encodes a homologue of the human hRFC36 and Saccharomyces cerevisiae Rfc3 subunits of replication factor C

In the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe replication factor C (RF-C) plays key roles both in chromosomal DNA replication and in DNA replication checkpoint function. At the replication fork, the five-subunit RF-C complex functions to load the trimeric polymerase accessory factor PCNA onto DNA. PCNA then acts as a sliding clamp, tethering Pol δ to the DNA to maximise its processivity. Here we describe the cloning of the S. pomberfc3 ⁺ gene, encoding a homologue of the S. cerevisiae Rfc3 and human hRFC36 proteins. The 1026 bp rfc3 ⁺ ORF is interrupted by five introns, ranging in size from 49 to 165 bp. The spliced ORF is predicted to encode a 342 amino-acid protein that is approximately 50% identical at the amino acid sequence level to the S. cerevisiae Rfc3 and human hRFC36 proteins. As expected, S. pomberfc3 ⁺ is an essential gene, with rfc3Δ cells being defective for DNA replication. Loss of rfc3 ⁺ function can be rescued by heterologous expression of either the S. cerevisiae Rfc3 or human hRFC36 proteins in S. pombe. Received: 15 October 1999