A terrestrial planet candidate in a temperate orbit around Proxima Centauri.

At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun's closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.

Raft localisation of FcgammaRIIa and efficient signaling are dependent on palmitoylation of cysteine 208.

Ligand-dependent aggregation of FcgammaRIIa initiates multiple biochemical processes including the translocation to detergent resistant membrane domains (DRMs) and receptor tyrosine phosphorylation. Palmitoylation of cysteine residues is considered to be one process that assists in the localisation of proteins to DRMs. Within the juxtamembrane region of FcgammaRIIa there is cysteine residue (C208) that we show to be palmitoylated. Mutation of this cysteine residue results in the disruption of FcgammaRIIa translocation to DRMs as empirically defined by insolubility at high Triton X-100 concentrations. This study also demonstrates that the lack of lipid raft association diminishes FcgammaRIIa signaling as measured by receptor phosphorylation and calcium mobilisation functions suggesting that FcgammaRIIa signaling is partially dependent on lipid rafts.

Mouse FcgammaRI: identification and functional characterization of five new alleles.

The mouse Fcgr1 gene encoding the high-affinity IgG receptor (FcgammaRI) exists as two known alleles, FcgammaRI-BALB and FcgammaRI-NOD, and these alleles exhibit functional differences. To determine whether other alleles exist in mouse strains, Fcgr1 coding regions from 35 strains of mice were sequenced and a further five alleles were identified. The FcgammaRI-BALB and NOD alleles are now designated the "a" and "d" alleles, respectively. Analysis of the five new alleles revealed that although no polymorphisms were observed in the two leader exons, nucleotide and subsequent amino acid changes were observed in the exons encoding the extracellular domains, and transmembrane and cytoplasmic tail. The cDNA of the seven alleles (a-g) were isolated and transiently transfected into COS cells, and IgG-binding studies were performed. Receptors encoded by four of the five new alleles (b, c, f, g) bound IgG2a with high affinity, displaying IgG binding characteristics similar to the a allele (previously FcgammaRI-BALB). The d allele (previously FcgammaRI-NOD) and the e allele [derived from Mus spretus (SPRET/Ei)] encoded receptors which showed broader specificity by binding monomeric IgG2a, IgG2b, and IgG3.

Genotypic and phenotypic characterization of six new recombinant congenic strains derived from NOD/Shi and CBA/J genomes.

Recombinant Congenic Strains (RCS) are useful for dissecting complex polygenic traits. Here, we describe genetic and phenotypic characterization of six new RCS generated from outcrosses between NOD/Shi and CBA/LsLt, followed by sib mating of first backcross progeny (to CBA) for 20 generations, whereupon genetic and phenotypic analysis commenced. Four of the RCS were selected on the basis of residual heterozygosity present at F20 in one of the three original RCS. Contrary to expectations for RCS developed at first backcross, all derived at least 50% of the polymorphic markers typed from the NOD parental strain. Development of autoimmune insulin-dependent diabetes mellitus (IDDM) in NOD is a strain-specific characteristic. The major genetic component predisposing NOD mice to IDDM, their H2(g7) haplotype, was present in all RCS. Nevertheless, the presence of variable amounts of CBA genome at non-MHC loci conferred complete resistance in all RCS to spontaneous IDDM development, and rendered them strongly resistant to cyclophosphamide-induced IDDM. Although the RCS more resemble NOD in regard to certain strain-specific characteristics, such as prolificacy, an immunologic phenotype that was significantly reduced when compared to both parental strains was the number of peripheral CD8(+) T cells. Given the genetic characterization presented, these new RCS should prove valuable to investigators interested in studying genes controlling differential susceptibilities distinguishing the NOD and CBA inbred strain backgrounds.

Gain-of-function mutations in FcgammaRI of NOD mice: implications for the evolution of the Ig superfamily.

It has been postulated that, during evolution of the Ig superfamily, modifications of the function of individual receptors might occur by acquisition of exons and their subsequent modification, though evidence of this is lacking. Here we have analysed the interaction of mouse IgG subclasses with high-affinity FcgammaRI (CD64) which contains three Ig-like domains and is important in innate and adaptive immunity. This analysis has identified a mechanism by which the postulated modification of newly acquired exons provides gains in function. Thus, the most widely distributed FcgammaRI allele in mice (e.g. BALB/c), bound only a single IgG subclass, IgG2a, with high affinity. However, non-obese diabetic (NOD) mice expressed a unique allele that exhibits broader specificity and, in addition to binding IgG2a, FcgammaRI-NOD bound monomeric IgG3 and bound IgG2b with high affinity, an IgG subclass not bound by FcgammaRI of other mouse strains, either as monomer or multivalent immune complexes. Analysis of mutants of FcgammaRI wherein segments of the interdomain junctions were exchanged between FcgammaRI-BALB and FcgammaRI-NOD identified these regions as having major influence in 'gain-of-function' by the NOD form of FcgammaRI. Nucleotide sequence analysis of intron/exon boundaries encoding the interdomain junctions of the FcgammaRI alleles showed these to have arisen by mutation to alter existing or create new mRNA splice donor/acceptor sites, resulting in generation of modified junctions.

Identification of the mouse IgG3 receptor: implications for antibody effector function at the interface between innate and adaptive immunity.

Mouse IgG3 appears early in immune responses independently of T cell help and, as such, is an early effector molecule of the immune system. Yet, a specific IgG3 cellular receptor remains undefined. In transfection experiments, mouse Fc gammaRI was clearly able to bind immune complexes of IgG3, whereas mouse Fc gammaRII could not. Furthermore, macrophages from mice expressing Fc gammaRII and Fc gammaRIII but lacking Fc gammaRI were unable to phagocytose IgG3 immune complexes, thus identifying mouse Fc gammaRI as the sole receptor for IgG3 immune complexes. Competition studies demonstrated that monomeric mouse IgG3 could inhibit IgG2a binding to mouse Fc gammaRI with an ID50 approximately 10(-7) M (fivefold lower than IgG2a). The identification of mouse Fc gammaRI as the IgG3 receptor establishes Fc gammaRI as a participant in events at the interface between innate and adaptive immunity, implying a greater role for this receptor in the development of normal and pathologic immune responses than previously recognized.

Extracellular mutations of non-obese diabetic mouse FcgammaRI modify surface expression and ligand binding.

The non-obese diabetic mouse (NOD) expresses a unique form of the high affinity receptor for IgG (FcgammaRI), containing multiple mutations that result in substitutions and insertions of amino acids and a truncated cytoplasmic tail. As a result of these major changes, receptor affinity for IgG increases 10-fold over that of wild-type FcgammaRI from BALB/c mice, while the specificity for ligand is retained. Kinetic analysis revealed that while the association rate of IgG with FcgammaRI from NOD mice (FcgammaRI-NOD) and FcgammaRI from BALB/c mice (FcgammaRI-BALB) is similar, IgG bound much more tightly to FcgammaRI-NOD as revealed by a profoundly diminished dissociation rate. Transfection studies demonstrated that FcgammaRI-NOD was expressed at one-tenth of the level of FcgammaRI-BALB. Although mouse FcgammaRI was previously not known to associate with the FcepsilonRI gamma-subunit, transfection of COS-7 cells demonstrates that like human FcgammaRI, mouse FcgammaRI is also able to associate with this signaling subunit. Furthermore, expression levels of FcgammaRI-NOD were not restored by the presence of the FcepsilonRI gamma-subunit. The difference in the levels of expression was mapped to mutations in the extracellular region of FcgammaRI-NOD as replacement of the extracellular domains with those of human FcgammaRI or FcgammaRI-BALB restored expression to that of human FcgammaRI or FcgammaRI-BALB.

Recombinant soluble Fc gamma RII inhibits immune complex precipitation.

Control of IgG immune complex formation and deposition is important in determining the nature and extent of subsequent immune effector responses, and appears to be aberrant in some autoimmune diseases. In this study we demonstrate that recombinant soluble Fc gamma RII (rsFc gamma RII) is an effective modulator of immune complex formation, delaying immune precipitation in a manner which is dose-dependent, and can be specifically inhibited by anti-Fc gamma RII MoAb Fab' fragments. This inhibitory role in immune precipitation also provides a possible mechanistic explanation for our previous demonstration of the efficacy of rsFc gamma RII as an inhibitor of immune complex-induced inflammation in the Arthus reaction in vivo. RsFc gamma RII inhibited immune complex precipitation in two different experimental systems. First, rsFc gamma RII inhibited the precipitation of 125I-bovine serum albumin (BSA)-anti-BSA complexes in a dose-dependent manner, while an irrelevant protein (soybean trypsin inhibitor) had no effect on the precipitation of the immune complexes. Moreover, rsFc gamma RII inhibited the precipitation of ovalbumin (OVA)-anti-OVA complexes as determined by turbidimetric analysis, where the inhibition of immune complex precipitation by rsFc gamma RII was dose-dependent and was specifically blocked by prior incubation with Fab' fragments of a blocking MoAb to Fc gamma RII. RsFc gamma RII could inhibit the precipitation of BSA-anti-BSA complexes in the presence of excess bystander IgG and did not inhibit complement-mediated prevention of immune precipitation, demonstrating that rsFc gamma RII did not block C1 binding to the BSA-anti-BSA complex. Unlike complement, rsFc gamma RII could not cause re-solubilization of pre-formed precipitated BSA-anti-BSA complexes. Soluble Fc gamma Rs have been detected in biological fluids of normal and inflammatory disease patients, yet the role of sFc gamma R is still unclear. However, they now play a potential role in the modulation of immune complex solubility.

Expression of recombinant soluble Fc epsilon RI: function and tissue distribution studies.

Recombinant soluble IgE Fc receptors (rsFc epsilon RI) are potent inhibitors of type I hypersensitivity reactions tested in a local inflammatory setting. However, the fate of these receptors in vivo is dependent on the cellular source of the rsFc epsilon RI. We have produced these by transiently transfecting Cos-7 cells with a cDNA encoding the extracellular domains of human Fc epsilon RI alpha-chain. Following affinity purification, the rsFc epsilon RI was characterized as 58,000 MW, which was reduced to 23,000 MW following endoglycosidase F treatment. The purified rsFc epsilon RI could inhibit mouse IgE binding to Fc epsilon RI+ transfected CHO-K1 cells in vitro, bind sIgE+ B lymphoma cells in vitro, and inhibit the passive cutaneous anaphylaxis model in vivo in Sprague-Dawley rats. Pharmacokinetic studies in vivo involving intravenous injection of radiolabelled rsFc epsilon RI in mice revealed the receptor to have a rapid initial blood clearance (t1/2 early phase of 15 min) and to accumulate in the liver before being detected in urine. The localization of rsFc epsilon RI in the liver could be blocked by administration of mannose glycosylated ovalbumin and mannan, demonstrating that liver uptake involved the mannose receptor that is expressed on liver sinusoid cells and Kupffer cells. The production of rsFc epsilon RI using a stable expression system in CHO-K1 cells produced functional receptor of the same molecular weight as the Cos-7 system by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). However, biodistribution studies demonstrated differences; the CHO-K1 cell-produced material did not localize to the liver in comparison to the Cos-7-produced rsFc epsilon RI.