Human antibody-Fc receptor interactions illuminated by crystal structures

Immunoglobulins couple the recognition of invading pathogens with the triggering of potent effector mechanisms for pathogen elimination. Different immunoglobulin classes trigger different effector mechanisms through interaction of immunoglobulin Fc regions with specific Fc receptors (FcRs) on immune cells. Here, we review the structural information that is emerging on three human immunoglobulin classes and their FcRs. New insights are provided, including an understanding of the antibody conformational adjustments that are required to bring effector cell and target cell membranes sufficiently close for efficient killing and signal transduction to occur. The results might also open up new possibilities for the design of therapeutic antibodies.     

Biodegradable films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer: modulation of phase morphology, plasticization properties and thermal depolymerization

We report on the modulation of phase morphology, plasticization properties, and thermal stability of films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer (PLLA-co-PCL) with additions of low molecular weight compounds, namely, triethyl citrate ester, diethyl phthalate, diepoxy polyether (poly(propylene glycol) diglycidyl ether), and with epoxidized soybean oil (ESO). The PLLA-co-PCL/polyether films showed significant stability against thermal depolymerization, high film flexibility, and good plasticizing properties, probably due to cross-linking and chain branching formation between diepoxy groups with both the end carboxyl and hydroxyl groups of the PLLA copolymer (initially present or generated during the degradation process) to produce primary ester and ether bonds, respectively. Diethyl phthalate and triethyl citrate ester were found to be efficient plasticizers for PLLA copolymer in terms of glass transition and mechanical properties, but the more water-soluble plasticizer triethyl citrate induced a dramatic loss in the molecular weight of the copolymer. Although ESO cannot play the role of a plasticizer, it substantially stabilizes and retards thermal depolymerization of the PLLA copolymer matrix, possibly because of a reaction between epoxy groups with the end carboxyl and hydroxyl groups of the PLLA copolymer. The presence of ESO in PLLA-co-PCL/ESO/triethyl citrate blends enhanced the compatibility and miscibility of the plasticizer with the PLLA copolymer matrix, considerably improved the mechanical properties (elongation at break), and substantially stabilized the copolymer against thermal depolymerization. It seems likely that the epoxy groups interact not only with the end hydroxyl and carboxyl group of the copolymer but as well with the hydroxyl group of triethyl citrate plasticizer to produce a new ether bond (C-O-C) as the cross-linking unit. On the other hand, for PLLA-co-PCL/ESO/polyether blends, (80/10/10) epoxidized oil distorts the compactness of the blend by diminishing the proposed entanglements between carboxyl, hydroxyl, and diepoxy groups of polyether and reduces the high elongation properties otherwise observed in the PLLA-co-PCL/polyether films. The multicomponent approach toward modulating poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer films using epoxy compounds and plasticizers and the insight into the nature of various PLLA matrixes presented here offer advantages to a broad engineering of PLLA copolymer films having desirable physical properties and multiphase behavior for efficient uses in future technical applications.     

Antigens up the nose: identification of putative biomarkers for nasal tolerance induction functional studies combined with proteomics

Intranasal autoantigen delivery is the most effective means of inducing mucosal tolerance and suppression of autoimmune disease. In an effort to identify markers of the "tolerant state", we employed proteomics technology at the level of the cervical lymph node. The analysis revealed that nasal antigen administration (without adiuvant) led to modulation of various proteins among which the most prominent were haptoglobin, nonintegrin 67 kDa laminin receptor, and MRP8. The immunoregulatory haptoglobin may qualify as (bio)marker for effective immunotherapy.     

Divergence in gene expression related to variation in host specificity of an ectomycorrhizal fungus

Ectomycorrhizae are formed by mutualistic interactions between fungi and the roots of woody plants. During symbiosis the two organisms exchange carbon and nutrients in a specific tissue that is formed at the contact between a compatible fungus and plant. There is considerable variation in the degree of host specificity among species and strains of ectomycorrhizal fungi. In this study, we have for the first time shown that this variation is associated with quantitative differences in gene expression, and with divergence in nucleotide sequences of symbiosis-regulated genes. Gene expression and sequence evolution were compared in different strains of the ectomycorrhizal fungus Paxillus involutus; the strains included Nau, which is not compatible with birch and poplar, and the two compatible strains Maj and ATCC200175. On a genomic level, Nau and Maj were very similar. The sequence identity was 98.9% in the 16 loci analysed, and only three out of 1075 genes analysed by microarray-based hybridizations had signals indicating differences in gene copy numbers. In contrast, 66 out of the 1075 genes were differentially expressed in Maj compared to Nau after contact with birch roots. Thirty-seven of these symbiosis-regulated genes were also differentially expressed in the ATCC strain. Comparative analysis of DNA sequences of the symbiosis-regulated genes in different strains showed that two of them have evolved at an enhanced rate in Nau. The sequence divergence can be explained by a decreased selection pressure, which in turn is determined by lower functional constraints on these proteins in Nau as compared to the compatible strains.     

The capacity to form H-DNA cannot substitute for GAGA factor binding to a (CT)n*(GA)n regulatory site

Previous studies of the Drosophila melanogaster hsp26 gene promoter have demonstrated the importance of a homopurine·homopyrimidine segment [primarily (CT)_n·(GA)_n] for chromatin structure formation and gene activation. (CT)_n regions are known to bind GAGA factor, a dominant enhancer of PEV thought to play a role in generating an accessible chromatin structure. The (CT)_n region can also form an H-DNA structure in vitro under acidic pH and negative supercoiling; a detailed map of that structure is reported here. To test whether the (CT)_n sequence can function through H-DNA in vivo, we have analyzed a series of hsp26-lacZ transgenes with altered sequences in this region. The results indicate that a 25 bp mirror repeat within the homopurine·homopyrimidine region, while adequate for H-DNA formation, is neither necessary nor sufficient for positive regulation of hsp26 when GAGA factor-binding sites have been eliminated. The ability to form H-DNA cannot substitute for GAGA factor binding to the (CT)_n sequence.     

(E)-beta-ocimene and myrcene synthase genes of floral scent biosynthesis in snapdragon: function and expression of three terpene synthase genes of a new terpene synthase subfamily

Snapdragon flowers emit two monoterpene olefins, myrcene and (E)-beta-ocimene, derived from geranyl diphosphate, in addition to a major phenylpropanoid floral scent component, methylbenzoate. Emission of these monoterpenes is regulated developmentally and follows diurnal rhythms controlled by a circadian clock. Using a functional genomics approach, we have isolated and characterized three closely related cDNAs from a snapdragon petal-specific library that encode two myrcene synthases (ama1e20 and ama0c15) and an (E)-beta-ocimene synthase (ama0a23). Although the two myrcene synthases are almost identical (98%), except for the N-terminal 13 amino acids, and are catalytically active, yielding a single monoterpene product, myrcene, only ama0c15 is expressed at a high level in flowers and contributes to floral myrcene emission. (E)-beta-Ocimene synthase is highly similar to snapdragon myrcene synthases (92% amino acid identity) and produces predominantly (E)-beta-ocimene (97% of total monoterpene olefin product) with small amounts of (Z)-beta-ocimene and myrcene. These newly isolated snapdragon monoterpene synthases, together with Arabidopsis AtTPS14 (At1g61680), define a new subfamily of the terpene synthase (TPS) family designated the Tps-g group. Members of this new Tps-g group lack the RRx(8)W motif, which is a characteristic feature of the Tps-d and Tps-b monoterpene synthases, suggesting that the reaction mechanism of Tps-g monoterpene synthase product formation does not proceed via an RR-dependent isomerization of geranyl diphosphate to 3S-linalyl diphosphate, as shown previously for limonene cyclase. Analyses of tissue-specific, developmental, and rhythmic expression of these monoterpene synthase genes in snapdragon flowers revealed coordinated regulation of phenylpropanoid and isoprenoid scent production.     

Infections that induce autoimmune diabetes in BBDR rats modulate CD4+CD25+ T cell populations

Viruses are believed to contribute to the pathogenesis of autoimmune type 1A diabetes in humans. This pathogenic process can be modeled in the BBDR rat, which develops pancreatic insulitis and type 1A-like diabetes after infection with Kilham's rat virus (RV). The mechanism is unknown, but does not involve infection of the pancreatic islets. We first documented that RV infection of BBDR rats induces diabetes, whereas infection with its close homologue H-1 does not. Both viruses induced similar humoral and cellular immune responses in the host, but only RV also caused a decrease in splenic CD4(+)CD25(+) T cells in both BBDR rats and normal WF rats. Surprisingly, RV infection increased CD4(+)CD25(+) T cells in pancreatic lymph nodes of BBDR but not WF rats. This increase appeared to be due to the accumulation of nonproliferating CD4(+)CD25(+) T cells. The results imply that the reduction in splenic CD4(+)CD25(+) cells observed in RV-infected animals is virus specific, whereas the increase in pancreatic lymph node CD4(+)CD25(+) cells is both virus and rat strain specific. The data suggest that RV but not H-1 infection alters T cell regulation in BBDR rats and permits the expression of autoimmune diabetes. More generally, the results suggest a mechanism that could link an underlying genetic predisposition to environmental perturbation and transform a "regulated predisposition" into autoimmune diabetes, namely, failure to maintain regulatory CD4(+)CD25(+) T cell function.     

CD1d-restricted NKT cells express a chemokine receptor profile indicative of Th1-type inflammatory homing cells

CD1d-restricted T cells (NKT cells) are innate memory cells activated by lipid Ags and play important roles in the initiation and regulation of the immune response. However, little is known about the trafficking patterns of these cells or the tissue compartment in which they exert their regulatory activity. In this study, we determined the chemokine receptor profile expressed by CD1d-restricted T cells found in the peripheral blood of healthy volunteers as well as CD1d-restricted T cell clones. CD1d-restricted T cells were identified by Abs recognizing the invariant Valpha24 TCR rearrangement or by binding to CD1d-Fc fusion tetramers loaded with alpha-GalCer. CD1d-restricted T cells in the peripheral blood and CD1d-restricted T cell clones expressed high levels of CXCR3, CCR5, and CCR6; intermediate levels of CXCR4 and CXCR6; and low levels of CXCR1, CCR1, CCR2, and CX(3)CR1, a receptor pattern often associated with tissue-infiltrating effector Th1 cells and CD8+ T cells. Very few of these cells expressed the lymphoid-homing receptors CCR7 or CXCR5. CCR4 was expressed predominantly on CD4+, but not on double-negative CD1d-restricted T cells, which may indicate differential trafficking patterns for these two functionally distinct subsets. CD1d-restricted T cell clones responded to chemokine ligands for CXCR1/2, CXCR3, CXCR4, CXCR6, CCR4, and CCR5 in calcium flux and/or chemotaxis assays. These data indicate that CD1d-restricted T cells express a chemokine receptor profile most similar to Th1 inflammatory homing cells and suggest that these cells perform their function in peripheral tissue sites rather than in secondary lymphoid organs.