Therapeutic induction of regulatory, cytotoxic CD8+ T cells in multiple sclerosis

In the setting of autoimmunity, one of the goals of successful therapeutic immune modulation is the induction of peripheral tolerance, a large part of which is mediated by regulatory/suppressor T cells. In this report, we demonstrate a novel immunomodulatory mechanism by an FDA-approved, exogenous peptide-based therapy that incites an HLA class I-restricted, cytotoxic suppressor CD8+ T cell response. We have shown previously that treatment of multiple sclerosis (MS) with glatiramer acetate (GA; Copaxone) induces differential up-regulation of GA-reactive CD8+ T cell responses. We now show that these GA-induced CD8+ T cells are regulatory/suppressor in nature. Untreated patients show overall deficit in CD8+ T cell-mediated suppression, compared with healthy subjects. GA therapy significantly enhances this suppressive ability, which is mediated by cell contact-dependent mechanisms. CD8+ T cells from GA-treated patients and healthy subjects, but not those from untreated patients with MS, exhibit potent, HLA class I-restricted, GA-specific cytotoxicity. We further show that these GA-induced cytotoxic CD8+ T cells can directly kill CD4+ T cells in a GA-specific manner. Killing is enhanced by preactivation of target CD4+ T cells and may depend on presentation of GA through HLA-E. Thus, we demonstrate that GA therapy induces a suppressor/cytotoxic CD8+ T cell response, which is capable of modulating in vivo immune responses during ongoing therapy. These studies not only explain several prior observations relating to the mechanism of this drug but also provide important insights into the natural immune interplay underlying this human immune-mediated disease.     

The paroxysm of Plasmodium vivax malaria

The paroxysms of Plasmodium vivax malaria are antiparasite responses that, although distressing to the human host, almost never impart serious acute pathology. Using plasma and blood cells from P. vivax patients, the cellular and noncellular mediators of these events have been studied ex vivo. The host response during a P. vivax paroxysm was found to involve T cells, monocytes and neutrophils, and the activity, among others, of the pyrogenic cytokines tumor necrosis factor alpha and interleukin 2 in addition to granulocyte macrophage-colony stimulating factor. However, interferon gamma activity, associated with serious acute pathogenesis in other studies on malaria, was absent. Induction of the cytokines active during a P. vivax paroxysm depends upon the presence of parasite products, which are released into the plasma before the paroxysm. Chemical identification of these natural parasite products will be important for our understanding of pathogenesis and protection in malaria.     

Ontogeny of salinity tolerance and hyper-osmoregulation by embryos of the intertidal crabs Hemigrapsus edwardsii and Hemigrapsus crenulatus (Decapoda, Grapsidae): survival of acute hyposaline exposure

The adults of Hemigrapsus edwardsii and Hemigrapsus crenulatus are euryhaline crabs and strong hyper-osmoregulators. Their embryos are carried externally attached to the abdominal pleopods of female crabs, where they are exposed to temporal and spatial changes in salinity associated with their intertidal and estuarine habitats. Although embryos lack the branchial and excretory organs responsible for adult osmoregulation, post-gastrula embryos were highly tolerant of exposure to hypo-osmotic sea water. Detached eggs (embryos+envelopes), of both species, at all developmental stages between gastrulation and hatching, exhibited 80-100% survival for periods up to 96 h in sea water (osmolality, 1050 mmol kg(-1)) and in dilutions to 50%, 10%, and 1%. Cleavage stages were less tolerant of dilution; H. edwardsii, <50% survived 24 h in 10% sea water; H. crenulatus <50% survived 6 h in 10% sea water. Post-gastrulation stages strongly hyper-osmoregulated but cleavage stages were hyper-osmoconformers (maintaining internal osmolality approximately 150 mmol kg(-1) above external). Osmoregulatory capacity was reduced just prior hatching, particularly in H. crenulatus, although salinity tolerance remained high. Gastrulation therefore marks a critical stage in the ontogeny of osmoregulation and salinity tolerance. Total Na+/K(+)-ATPase activity increased greatly during embryogenesis of H. crenulatus (undetectable in blastulae; gastrulae 0.31+/-0.05 pmol P(i) embryo(-1) min(-1); pre-hatching 16.4+/-1.0 pmol P(i) embryo(-1) min(-1)). Na+/K(+)-ATPase activity increased in embryos exposed to dilute sea water for 24 h implicating regulation of this transporter in a short-term acclimation response.     

A unique group of scabies mite pseudoproteases promotes cutaneous blood coagulation and delays plasmin-induced fibrinolysis

BackgroundScabies, a highly contagious skin disease affecting more than 200 million people worldwide at any time, is caused by the parasitic mite Sarcoptes scabiei. In the absence of molecular markers, diagnosis requires experience making surveillance and control challenging. Superficial microthrombi in the absence of vasculitis in scabies-affected skin are a recognised, yet unexplained histopathological differential of scabies infection. This study demonstrates that a family of Scabies Mite Inactivated Cysteine Protease Paralogues (SMIPP-Cs) excreted by the mites plays a role in formation of scabies-induced superficial microthrombi.Methodology/Principal findingsA series of in vitro and ex vivo experiments involving two representative recombinant SMIPP-Cs was carried out. In the presence of SMIPP-Cs, the thrombin clotting time (TCT), fibrin formation and plasmin induced fibrinolysis were monitored in vitro. The ultrastructure of the SMIPP-C—modulated fibrin was analysed by Scanning Electron Microscopy (SEM). Immuno-histological analyses were performed ex vivo, to localise the SMIPP-C proteins within scabies infected skin biopsies. SMIPP-Cs displayed pro-coagulant properties. They bound calcium ions, reduced the thrombin clotting time, enhanced the fibrin formation rate and delayed plasmin-induced fibrinolysis. The SMIPP-Cs associated with fibrin clots during fibrinogen polymerisation and did not bind to preformed fibrin. Scanning electron microscopy revealed that the fibrin clots formed in the presence of SMIPP-Cs were aberrant and denser than normal fibrin clots. SMIPP-Cs were detected in microthrombi which are commonly seen in scabietic skin.Conclusions/SignificanceThe SMIPP-Cs are the first scabies mite proteins found in sub-epidermal skin layers and their pro-coagulant properties promote superficial microthrombi formation in scabetic skin. Further research is needed to evaluate their potential as diagnostic or therapeutic target.     

Cloning and characterization of a sialidase from the filamentous fungus, <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis>

A gene encoding a putative sialidase was identified in the genome of the opportunistic fungal pathogen, Aspergillus fumigatus. Computational analysis showed that this protein has Asp box and FRIP domains, it was predicted to have an extracellular localization, and a mass of 42 kDa, all of which are characteristics of sialidases. Structural modeling predicted a canonical 6-bladed β-propeller structure with the model’s highly conserved catalytic residues aligning well with those of an experimentally determined sialidase structure. The gene encoding the putative Af sialidase was cloned and expressed in Escherichia coli. Enzymatic characterization found that the enzyme was able to cleave the synthetic sialic acid substrate, 4-methylumbelliferyl α-D-N-acetylneuraminic acid (MUN), and had a pH optimum of 3.5. Further kinetic characterization using 4-methylumbelliferyl α-D-N-acetylneuraminylgalactopyranoside revealed that Af sialidase preferred α2-3-linked sialic acids over the α2-6 isomers. No trans-sialidase activity was detected. qPCR studies showed that exposure to MEM plus human serum induced expression. Purified Af sialidase released sialic acid from diverse substrates such as mucin, fetuin, epithelial cell glycans and colominic acid, though A. fumigatus was unable to use either sialic acid or colominic acid as a sole source of carbon. Phylogenetic analysis revealed that the fungal sialidases were more closely related to those of bacteria than to sialidases from other eukaryotes.     

The hydrolase and transferase activity of an inverting mutant sialidase using non-natural beta-sialoside substrates

The Y370G inverting mutant sialidase from Micromonospora viridifaciens possesses beta-sialidase activity with phenyl beta-sialoside (Ph-betaNeuAc) to give alpha-sialic acid as the first formed product. The derived catalytic rate constants for k(cat) and k(cat)/K(m) are 13.3 +/- 0.3 and (2.9 +/- 0.3) x 10(5) M(-)(1) s(-)(1), respectively. This enzyme is highly specific for the phenyl substrate, with substituted phenyl and thiophenyl leaving groups having k(cat) values that are at least 1000-fold lower. In addition, the Y370G mutant can transfer the sialic acid moiety from Ph-betaNeuAc to lactose in yields of up to 13%. Greater than 90% of the sialyl-lactose product formed in the coupling reactions is the alpha-2,6-isomer. A library encoding 6 x 10(5) different sialidases was constructed by mutating Y370, E260, T309, N310, and N311, residues that include and are proximal the catalytic tyrosine residue. A total of 2628 individuals were screened for hydrolytic activity against 4-nitrophenyl 2-thio-beta-sialoside and 4-methylumbelliferyl beta-sialoside. However, none of the mutants screened possessed a significant activity against either of the beta-sialosides.