Plasma electron acceleration driven by a long-wave-infrared laser.

Laser-driven plasma accelerators provide tabletop sources of relativistic electron bunches and femtosecond x-ray pulses, but usually require petawatt-class solid-state-laser pulses of wavelength λL ~ 1 µm. Longer-λL lasers can potentially accelerate higher-quality bunches, since they require less power to drive larger wakes in less dense plasma. Here, we report on a self-injecting plasma accelerator driven by a long-wave-infrared laser: a chirped-pulse-amplified CO2 laser (λL ≈ 10 µm). Through optical scattering experiments, we observed wakes that 4-ps CO2 pulses with < 1/2 terawatt (TW) peak power drove in hydrogen plasma of electron density down to 4 × 1017 cm-3 (1/100 atmospheric density) via a self-modulation (SM) instability. Shorter, more powerful CO2 pulses drove wakes in plasma down to 3 × 1016 cm-3 that captured and accelerated plasma electrons to relativistic energy. Collimated quasi-monoenergetic features in the electron output marked the onset of a transition from SM to bubble-regime acceleration, portending future higher-quality accelerators driven by yet shorter, more powerful pulses.

Long lifetime of bialkali photocathodes operating in high gradient superconducting radio frequency gun.

High brightness, high charge electron beams are critical for a number of advanced accelerator applications. The initial emittance of the electron beam, which is determined by the mean transverse energy (MTE) and laser spot size, is one of the most important parameters determining the beam quality. The bialkali photocathodes illuminated by a visible laser have the advantages of high quantum efficiency (QE) and low MTE. Furthermore, Superconducting Radio Frequency (SRF) guns can operate in the continuous wave (CW) mode at high accelerating gradients, e.g. with significant reduction of the laser spot size at the photocathode. Combining the bialkali photocathode with the SRF gun enables generation of high charge, high brightness, and possibly high average current electron beams. However, integrating the high QE semiconductor photocathode into the SRF guns has been challenging. In this article, we report on the development of bialkali photocathodes for successful operation in the SRF gun with months-long lifetime while delivering CW beams with nano-coulomb charge per bunch. This achievement opens a new era for high charge, high brightness CW electron beams.

High-Brightness Continuous-Wave Electron Beams from Superconducting Radio-Frequency Photoemission Gun.

Continuous-wave photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic x-ray free electron lasers, high-brightness hadron beams, or a new generation of microchip production. In this Letter we report on the record-performing superconducting rf electron gun with CsK_{2}Sb photocathode. The gun is generating high charge electron bunches (up to 10 nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement opens a new era in generating high-power beams with a very high average brightness.

DNA prime-protein boost increased the titer, avidity and persistence of anti-Abeta antibodies in wild-type mice.

Recently, we reported that a DNA vaccine, composed of three copies of a self B cell epitope of amyloid-beta (Abeta(42)) and the foreign T-cell epitope, Pan DR epitope (PADRE), generated strong anti-Abeta immune responses in wild-type and amyloid precursor protein transgenic animals. Although DNA vaccines have several advantages over peptide-protein vaccines, they induce lower immune responses in large animals and humans compared with those in mice. The focus of this study was to further enhance anti-Abeta(11) immune responses by developing an improved DNA vaccination protocol of the prime-boost regimen, in which the priming step would use DNA and the boosting step would use recombinant protein. Accordingly, we generated DNA and recombinant protein-based epitope vaccines and showed that priming with DNA followed by boosting with a homologous recombinant protein vaccine significantly increases the anti-Abeta antibody responses and do not change the immunoglobulin G1 (IgG1) profile of humoral immune responses. Furthermore, the antibodies generated by this prime-boost regimen were long-lasting and possessed a higher avidity for binding with an Abeta(42) peptide. Thus, we showed that a heterologous prime-boost regimen could be an effective protocol for developing a potent Alzheimer's disease (AD) vaccine.

Promoter regulatory elements and DNase I-hypersensitive sites involved in serglycin proteoglycan gene expression in human erythroleukemia, CHRF 288-11, and HL-60 cells.

We have compared regulation of the serglycin gene in human erythroleukemia (HEL) and CHRF 288-11 cells, which have megakaryocytic characteristics, with promyelocytic HL-60 cells. Deletion constructs were prepared from the region -1123/+42 to -20/+42, and putative regulatory sites were mutated. In all three cell lines, the two major regulatory elements for constitutive expression were the (-80)ets site and the cyclic AMP response element (CRE) half-site at -70. A protein from HEL and CHRF, but not HL60, nuclear extracts bound to the (-80)ets site. Another protein from all three cell lines bound to the (-70)CRE. Phorbol 12-myristate 13-acetate (PMA) and dibutyryl cyclic AMP (dbcAMP) increased expression of the reporter in HEL cells 2.5-3- and 4.5-fold, respectively, from all constructs except those with (-70)CRE mutations. PMA virtually eliminated expression of serglycin mRNA and promoter constructs, but dbcAMP increased expression in HL-60 cells. The effects of PMA and dbcAMP on promoter expression correlated with mRNA expression. The strengths of two DNase I-hypersensitive sites in the 5'-flanking region and the first intron in all three cells correlated with relative endogenous serglycin mRNA expression. An additional DNase I-hypersensitive site in HL60 DNA in the first intron may be related to the high serglycin expression in HL60 relative to HEL or CHRF cells.

Monoclonal antibodies define a cellular antigen involved in HTLV-I infection.

The exact mechanism by which the human T cell leukemia viruses (HTLV) infects target cells remains unclear; although some molecules have been identified to be important in viral infection and entry. To investigate these phenomena, we generated a panel of monoclonal antibodies (MAb) against a B cell line (BJAB-WH) which is highly permissive for infection with HTLV. These MAb have been used to further characterize the membrane molecules important for HTLV infection. Three of these MAb designated 4.2.3, 3.3.10, and 11.2.3 were capable of inhibiting syncytium formation induced in human B and T cell lines (i.e., BJAB-WH and SupT-1, respectively) by co-culture with HTLV-I infected MT-2 cells. All of these MAbs immunoprecipitated a 80-85 kDa antigen from the lysates of metabolically labeled BJAB-WH but not from BJAB-CC/84, a noninfectible target cell. The binding of these MAb with different HTLV target cells was analyzed and compared with binding of polyclonal monospecific antisera to the same cell lines. A 80-85 kDa membrane glycoprotein was isolated with an immunoaffinity chromatographic column constructed with MAbs 4.2.3 and 3.3.10. This cellular antigen was capable of inhibiting HTLV I/MT-2 induced fusion. This is the first direct demonstration that a 80-85 kDa cellular glycoprotein is directly involved in HTLV I/II infection and syncytium formation.