Effect of glass composition on the degradation properties and ion release characteristics of phosphate glass--polycaprolactone composites

A series of polycaprolactone and ternary-based (Na(2)O)(0.55-x)(CaO)(x)(P(2)O(5))(0.45) glass composites were created, each containing 20% volume percentage of glass with various calcium compositions. A short-term degradation study was carried out to investigate the physical and ion release behaviour of these composites, utilising analytical techniques such as dynamical mechanical analysis, and ion chromatography. All the composites experienced significant loss of weight and stiffness throughout the study, with the 24 mol% calcium composites losing the greatest amount of weight and stiffness. The pH profile of the aqueous solutions in which the composites were placed were initially acidic, but began to neutralise mid-way through the study, with the 36 mol% solution achieving the most acidic conditions. The ion release behaviour mirrored the mass loss behaviour of the glass component of the composites. The cations (sodium and calcium ions) release was comparable with the initial stages of composite mass degradation, both of which exhibited almost immediate release when placed into solution. The 24 mol% composites underwent rapid rates of cation release, while the 36 mol% experienced the slowest rates of release. By contrast, anion (phosphates and polyphosphates) release showed a dissimilar trend, with rapid release of the P(2)O(7) and P(3)O(10) occurring during the first few hours in solution, whilst the P(3)O(9) structure released steadily during the first 48 h in solution. Finally, PO(4) release was at a constant rate over the duration of the study, releasing up to 300 ppm from the 32 and 36 mol% samples by the end of 200 h. To summarise, these results show that by combining phosphate glasses with biodegradable polymer, it is possible to create composites whose rate of degradation can be controlled to meet the needs of their end application.     

Role of a conserved amino-terminal sequence in the ecotropic MLV receptor mCAT1

The amino-terminus of mCAT1 and homologous proteins is predicted to form a positively charged, amphipathic alpha helix on the cytoplasmic side of the plasma membrane. Peptides with similar sequence motifs often provide membrane anchors, protein-protein interaction domains, or intracellular transport-targeting signals. Deleting most of the cytoplasmic N-terminal sequence of mCAT1 led to reduced expression on the cell surface and accumulation in the endoplasmic reticulum but did not abrogate receptor function. Surprisingly, when the N-terminal 36 or 18 amino acids of mCAT1 were fused to green fluorescent protein (gfp), gfp accumulated almost exclusively in mitochondria. Mitochondrial targeting depended on arginines at positions 15 and 16 and was inhibitable by downstream transmembrane sequences. Although the full-length mCAT1 was not detected in mitochondria, the mitochondrial-targeting property of the N-terminal sequence fused to gfp is conserved in orthologous and paralogous proteins that diverged approximately 80 million years ago, suggesting a conserved biological function. We propose that the conserved N-terminal motif of CAT proteins provides a regulatable signal for transport to, or retention in, different cell membrane compartments.     

Leishmania mexicana promastigotes induce cytotoxic T lymphocytes in vivo that do not recognize infected macrophages

The question is addressed whether antigens of Leishmania, a parasite residing in the endosomal compartment of macrophages, can be presented in the context of major histocompatibility complex class I molecules. We used E. coli β-galactosidase as a model antigen which can be expressed in high levels in L. mexicana promastigotes (L. mexicana-gal). Infection of BALB/c mice with L. mexicanagal induces β-galactosidase-specific cytotoxic T cells (CTL), which can be isolated using a β-galactosidase-expressing mastocytoma line as an antigen-presenting cell. These CTL recognize epitopes of β-galactosidase in the context of H-2K^d; however, they do not recognize L. mexicanagal-infected macrophages even after killing of the intracellular amastigotes by drug treatment or macrophage activation by lymphokines, although class I-peptide interaction and the presentation of endogenously produced antigens is normal. It is concluded that parasite antigens can induce a CTL response in vivo but that these CTL cannot recognize infected macrophages because the relevant epitopes cannot gain access to class I molecules. The effect of priming in vivo may be explained by the well-known but ill-understood phenomenon of cross-priming.     

P2X receptors in trigeminal subnucleus caudalis modulate central sensitization in trigeminal subnucleus oralis

This study investigated the role of trigeminal subnucleus caudalis (Vc) P2X receptors in the mediation of central sensitization induced in nociceptive neurons in subnucleus oralis (Vo) by mustard oil (MO) application to the tooth pulp in anesthetized rats. MO application produced a long-lasting central sensitization reflected in neuroplastic changes (i.e., increases in neuronal mechanoreceptive field size and responses to innocuous and noxious mechanical stimuli) in Vo nociceptive neurons. Twenty minutes after MO application, the intrathecal (i.t.) administration to the rostral Vc of the selective P2X(1), P2X(3), and P2X(2/3) receptor antagonist, 2'-(or 3'-)O-trinitrophenyl-ATP (TNP-ATP), significantly and reversibly attenuated the MO-induced central sensitization for more than 15 min; saline administration had no effect. Administration to the rostral Vc of the selective P2X(1), P2X(3), and P2X(2/3) receptor agonist, alpha,beta-methylene ATP (alpha,beta-meATP, i.t.) produced abrupt and significant neuroplastic changes in Vo nociceptive neurons, followed by neuronal desensitization as evidenced by the ineffectiveness of a second i.t. application of alpha,beta-meATP and subsequent MO application to the pulp. Administration to the rostral Vc of the selective P2X(1) receptor agonist beta,gamma-methylene ATP (beta,gamma-meATP, i.t.) produced no significant neuroplastic changes per se and did not affect the subsequent MO-induced neuroplastic changes in Vo nociceptive neurons. These results suggest that P2X(3) and possibly also the P2X(2/3) receptor subtypes in Vc may play a role in the initiation and maintenance of central sensitization in Vo nociceptive neurons induced by MO application to the pulp.     

Delineation of an estimated 6.7 MB candidate interval for an anophthalmia gene at 3q26.33-q28 and description of the syndrome associated with visible chromosome deletions of this region

Anophthalmia or microphthalmia occur in approximately one in 10 children who have severe visual impairment. These eye malformations are often of unknown aetiology, but can be inherited in autosomal dominant, recessive or X-linked forms, and can also occur in association with specific chromosome abnormalities. Four children are described in the medical literature with microphthalmia or anophthalmia in association with chromosome rearrangements involving distal 3q, suggesting the presence of a micro/anophthalmia gene in this region. We have identified two further patients with micro/anophthalmia and chromosome rearrangements involving 3q26-->3q27 and identified a 6.7 MB common deleted region. Patient 1 had multiple abnormalities including bilateral anophthalmia, abnormalities of the first and second cranial nerves and partial absence of the corpus callosum. His karyotype was 46,XY,del(3)(q26.33q28). Patient 2 had right anophthalmia and left extreme microphthalmia. Her karyotype was 46,XX,del(3)(q26.33q28)t(3;7)(q28;q21.1). Both patients had intrauterine growth retardation (IUGR) and strikingly similar dysmorphic facies consisting of bossed forehead, downward-slanting palpebral fissures, grooved bridge of the nose, prominent low-set ears, small down-turned mouth and small mandible. We identified BAC clones mapping to distal 3q from the ENSEMBL and NCBI Entrez databases. These BAC clones were used as fluorescence in situ hybridisation (FISH) probes to identify the minimum deleted region common to both patients. This interval, between clones RPC11-134F2 and RPC11-132N15, was estimated to be 6.7 MB. We conclude that there is an anophthalmia locus within this interval. Candidate genes mapping to this region include Chordin and DVL3, a homologue of the Drosophila Dishevelled gene.     

T cell immunodominance and maintenance of memory regulated by unexpectedly cross-reactive pathogens

We show here that T cell cross-reactivity between heterologous viruses influences the immunodominance of virus-specific CD8(+) T cells by two mechanisms. First, T cells specific for cross-reactive epitopes dominate acute responses to viral infections; second, within the memory pool, T cells specific for cross-reactive epitopes are maintained while those specific for non-cross-reactive epitopes are selectively lost. These findings suggest an immunological paradigm in which viral infections shape the available T cell repertoire, causing alterations in the hierarchies of both the primary and memory CD8(+) T cell responses elicited by subsequent viral infections. Thus, immunodominance is a function of the host's previous exposure to unrelated pathogens, and this may have an impact on protective immunity and immunopathology.