Regulatory effect of IFN-kappa,a novel type I IFN,on cytokine production by cells of the innate immune system

IFN-kappa is a recently identified type I IFN that exhibits both structural and functional homology with the other type I IFN subclasses. In this study, we have investigated the effect of IFN-kappa on cells of the innate immune system by comparing cytokine release following treatment of human cells with either IFN-kappa or two recombinant IFN subtypes, IFN-beta and IFN-alpha2a. Although IFN-alpha2a failed to stimulate monocyte cytokine secretion, IFN-kappa, like IFN-beta, induced the release of several cytokines from both monocytes and dendritic cells, without the requirement of a costimulatory signal. IFN-kappa was particularly effective in inhibiting inducible IL-12 release from monocytes. Unlike IFN-beta, IFN-kappa did not induce release of IFN-gamma by PBL. Expression of the IFN-kappa mRNA was observed in resting dendritic cells and monocytes, and it was up-regulated by IFN-gamma stimulation in monocytes, while IFN-beta mRNA was minimally detectable under the same conditions. Monocyte and dendritic cell expression of IFN-kappa was also confirmed in vivo in chronic lesions of psoriasis vulgaris and atopic dermatitis. Finally, biosensor-based binding kinetic analysis revealed that IFN-kappa, like IFN-beta, binds strongly to heparin (K(d): 2.1 nM), suggesting that the cytokine can be retained close to the local site of production. The pattern of cytokines induced by IFN-kappa in monocytes, coupled with the unique induction of IFN-kappa mRNA by IFN-gamma, indicates a potential role for IFN-kappa in the regulation of immune cell functions.     

Functional activity of natural antibody is altered in Cr2-deficient mice

The major source of natural IgM Abs are B-1 cells, which differ from conventional B cells in their anatomic location, cell surface phenotype, restricted usage of particular V(H) genes and limited use of N-region addition during V-D-J rearrangement. The origin of B-1 cells is unclear. However, they are capable of self-renewal and their development is sensitive to signaling via the B cell receptor, as genetic defects that impair the strength of the signal often result in limited development. These findings suggest that B-1 cells require either an intrinsic signal, or contact with Ag, for positive selection and expansion and/or maintenance in the periphery. In support of interaction with cognate Ag, deficiency in the complement receptors CD21/CD35 results in a 30-40% decrease in the CD5(+) B-1 population. To determine whether this reduction reflects a loss of certain specificities or simply a proportional decline in the repertoire, we examined peritoneal B cells isolated from Cr2(+) and Cr2(def) mice for recognition of a B-1 cell Ag, i.e., phosphatidylcholine, and assayed for injury in an IgM natural Ab-dependent model of reperfusion injury. We found a similar frequency of phosphatidylcholine-specific CD5(+) B-1 cells in the two strains of mice. By contrast, the Cr2(def) mice have reduced injury in the IgM-dependent model of reperfusion injury. Reconstitution of the deficient mice with pooled IgM or adoptive transfer of Cr2(+) peritoneal B cells restored injury. These results suggest that complement receptors CD21/CD35 are important in maintenance of the B-1 cell repertoire to some, but not all, specificities.     

Schistosoma mansoni sporocysts in culture: host plasma hemoglobin contributes to in vitro oxidative stress

The initiation and promotion of sporocyst propagation and subsequent production of cercariae by intramolluscan larval stages of digenic trematodes are thought to depend on mollusc-derived factors. The ability to investigate this using in vitro cultures of Schistosoma mansoni sporocysts has been impeded by the fact that plasma from the host, Biomphalaria glabrata, becomes toxic to the parasite in long-term cultures. The present study identifies hemoglobin as the plasma component responsible for this toxicity. The addition of the enzyme catalase to sporocyst cultures neutralized the toxic effects of both purified hemoglobin and whole plasma, suggesting that the generation of H2O2 as a consequence of hemoglobin oxidation is the mechanism of plasma toxicity. Furthermore, cultures incubated in unconditioned schistosome medium with plasma plus catalase yielded significantly higher numbers of daughter sporocysts than cultures with media or plasma alone, but not higher than cultures with catalase alone. These latter results suggest that the oxidative environment and the antioxidant capacity of the media are critical factors for in vitro propagation of S. mansoni sporocysts.     

Predicting out-of-sequence reassembly in DNA shuffling

We present an analysis for calculating the frequency of out-of-sequence reassembly in DNA shuffling experiments. Out-of-sequence annealing events are undesirable since they typically encode non-functional proteins with missing or repetitive regions. The approach builds on the e Shuffle framework for the prediction of crossover formation using equilibrium thermodynamics and complete sequence information to model the reassembly process. An in silico case study of a set of subtilases reveals that, as expected, the presence of significant sequence identity between distant portions of the parental sequences gives rise to out-of-sequence annealing events that upon reassembly generate sequences with missing or repetitive DNA segments. The frequency of these events increases as the fragment length decreases. Interestingly, out-of-sequence annealing events are at a minimum near the annealing temperature of 55 degrees C used in the original DNA shuffling protocol. Neither parental sequence identity nor number of shuffled parents significantly alter the extent of out-of-sequence reassembly     

A P22 scaffold protein mutation increases the robustness of head assembly in the presence of excess portal protein

Bacteriophage with linear, double-stranded DNA genomes package DNA into preassembled protein shells called procapsids. Located at one vertex in the procapsid is a portal complex composed of a ring of 12 subunits of portal protein. The portal complex serves as a docking site for the DNA packaging enzymes, a conduit for the passage of DNA, and a binding site for the phage tail. An excess of the P22 portal protein alters the assembly pathway of the procapsid, giving rise to defective procapsid-like particles and aberrant heads. In the present study, we report the isolation of escape mutant phage that are able to replicate more efficiently than wild-type phage in the presence of excess portal protein. The escape mutations all mapped to the same phage genome segment spanning the portal, scaffold, coat, and open reading frame 69 genes. The mutations present in five of the escape mutants were determined by DNA sequencing. Interestingly, each mutant contained the same mutation in the scaffold gene, which changes the glycine at position 287 to glutamate. This mutation alone conferred an escape phenotype, and the heads assembled by phage harboring only this mutation had reduced levels of portal protein and exhibited increased head assembly fidelity in the presence of excess portal protein. Because this mutation resides in a region of scaffold protein necessary for coat protein binding, these findings suggest that the P22 scaffold protein may define the portal vertices in an indirect manner, possibly by regulating the fidelity of coat protein polymerization.     

Stabilization of the soluble,cleaved, trimeric form of the envelope glycoprotein complex of human immunodeficiency virus type 1

The envelope glycoprotein (Env) complex of human immunodeficiency virus type 1 has evolved a structure that is minimally immunogenic while retaining its natural function of receptor-mediated virus-cell fusion. The Env complex is trimeric; its six individual subunits (three gp120 and three gp41 subunits) are associated by relatively weak, noncovalent interactions. The induction of neutralizing antibodies after vaccination with individual Env subunits has proven very difficult, probably because they are inadequate mimics of the native complex. Our hypothesis is that a stable form of the Env complex, perhaps with additional modifications to rationally alter its antigenic structure, may be a better immunogen than the individual subunits. A soluble form of Env, SOS gp140, can be made that has gp120 stably linked to the gp41 ectodomain by an intermolecular disulfide bond. This protein is fully cleaved at the proteolysis site between gp120 and gp41. However, the gp41-gp41 interactions in SOS gp140 are too weak to maintain the protein in a trimeric configuration. Consequently, purified SOS gp140 is a monomer (N. Schülke, M. S. Vesanen, R. W. Sanders, P. Zhu, D. J. Anselma, A. R. Villa, P. W. H. I. Parren, J. M. Binley, K. H. Roux, P. J. Maddon, J. P. Moore, and W. C. Olson, J. Virol. 76:7760-7776, 2002). Here we describe modifications of SOS gp140 that increase its trimer stability. A variant SOS gp140, designated SOSIP gp140, contains an isoleucine-to-proline substitution at position 559 in the N-terminal heptad repeat region of gp41. This protein is fully cleaved, has favorable antigenic properties, and is predominantly trimeric. SOSIP gp140 trimers are noncovalently associated and can be partially purified by gel filtration chromatography. These gp140 trimers are dissociated into monomers by anionic detergents or heat but are relatively resistant to nonionic detergents, high salt concentrations, or exposure to a mildly acidic pH. SOSIP gp140 should be a useful reagent for structural and immunogenicity studies.     

Enhancing the proteolytic maturation of human immunodeficiency virus type 1 envelope glycoproteins

In virus-infected cells, the envelope glycoprotein (Env) precursor, gp160, of human immunodeficiency virus type 1 is cleaved by cellular proteases into a fusion-competent gp120-gp41 heterodimer in which the two subunits are noncovalently associated. However, cleavage can be inefficient when recombinant Env is expressed at high levels, either as a full-length gp160 or as a soluble gp140 truncated immediately N-terminal to the transmembrane domain. We have explored several methods for obtaining fully cleaved Env for use as a vaccine antigen. We tested whether purified Env could be enzymatically digested with purified protease in vitro. Plasmin efficiently cleaved the Env precursor but also cut at a second site in gp120, most probably the V3 loop. In contrast, a soluble form of furin was specific for the gp120-gp41 cleavage site but cleaved inefficiently. Coexpression of Env with the full-length or soluble form of furin enhanced Env cleavage but also reduced Env expression. When the Env cleavage site (REKR) was mutated in order to see if its use by cellular proteases could be enhanced, several mutants were found to be processed more efficiently than the wild-type protein. The optimal cleavage site sequences were RRRRRR, RRRRKR, and RRRKKR. These mutations did not significantly alter the capacity of the Env protein to mediate fusion, so they have not radically perturbed Env structure. Furthermore, unlike that of wild-type Env, expression of the cleavage site mutants was not significantly reduced by furin coexpression. Coexpression of Env cleavage site mutants and furin is therefore a useful method for obtaining high-level expression of processed Env.