Biomedical subjects

L Viña

Publications and source records attributed to L Viña.

10 recordsLinked to original sources

PubMed2002

Polarization control of the nonlinear emission of semiconductor microcavities.

The degree of circular polarization ( Weierstrass p ) of the nonlinear emission in semiconductor microcavities is controlled by changing the exciton-cavity detuning. The polariton relaxation towards K approximately 0 cavitylike states is governed by final-state stimulated scattering. The helicity of the emission is selected due to the lifting of the degeneracy of the +/-1 spin levels at K approximately 0. At short times after a pulsed excitation Weierstrass p reaches very large values, either positive or negative, as a result of stimulated scattering to the spin level of lowest energy (+1/-1 spin for positive/negative detuning).

Journal Article↗

PubMed2000

B-cell epitope mapping of the Neisseria meningitidis P64k protein using overlapping peptides.

A common meningococcal antigen designated P64k has been identified, cloned and expressed in Escherichia coli. The recombinant antigen is highly immunogenic in several animal species and its immunogenicity in healthy human volunteers is under investigation. Recently, P64k has been used as an immunological carrier for weak immunogens. To characterize the B-cell epitopes on P64k, recognized by immune sera obtained from mice, rabbits and monkeys, multiple overlapping peptides were synthesized and screened for antibody binding. Peptides covering the complete sequence of the P64k protein, 59 in all, of 20 amino acids each (overlapped by 10 residues), were synthesized. A number of continuous epitopes were detected with all sera, when immune and pre-immune bleeds were compared. For mouse and monkey sera, a few major antigenic peptides were identified, while the recognition of the rabbit serum was much more heterogeneous. Despite variation in the exact location of continuous epitopes defined by different anti-P64k sera, we found an immunogenic core region within the molecule, composed of amino acids Asp(524)-Gly(533). Consistently, in this protein segment there was an amino acid stretch located in a beta-hairpin loop, which is exposed to the solvent in the previously determined three-dimensional structure of the protein. This region is protruding and accessible to a sphere with a radius of 9 A.

Amino Acid Sequence↗

PubMed2000

P64k meningococcal protein as immunological carrier for weak immunogens.

Previously, the P64k meningococcal protein, an antigen of 64 kDa expressed in Escherichia coli, has been extensively characterized. We have successfully conjugated several synthetic peptides and meningococcal group C polysaccharide to P64k. In three out of four model peptides, the murine humoral immune response against the homologous peptide, evaluated after three doses of conjugate, was higher in the animals immunized with the coupled peptide than in those that received free peptide. The fourth and largest was immunogenic by itself. Similarly, the antigroup C polysaccharide levels reached by conjugated polysaccharide were significantly higher than those produced against unconjugated polysaccharide. As a carrier for one of the peptides, P64k was compared with bovine serum albumin (BSA) and tetanus toxoid (TT), being able to induce slightly higher or similar antipeptide antibody levels than these well-establish protein carriers. Our results suggest that recombinant P64k protein could be a readily available immunological carrier, as efficient as other commonly used large carrier molecules.

Amino Acid Sequence↗

PubMed1998

Influence of several adjuvants on the immune response against a recombinant meningococcal high molecular weight antigen.

Studying outer membrane proteins as vaccine candidates, our group has previously isolated, cloned, and expressed in Escherichia coli the gene encoding for a high molecular weight protein (P64k), common to many meningococcal strains. To continue the characterisation of this meningococcal antigen, we have evaluated its immunogenicity in mice alone or combined with several commercially-available adjuvants. We used as an adjuvant aluminium hydroxide (Alhydrogel and Rehydragel), aluminium phosphate, Algammulin, crude saponin, the saponin Quil A, dimethyl-dioctadecyl ammonium bromide (DDA), Freund's adjuvant, and Montanide 888. The antibody titres against the recombinant protein and whole meningococci elicited with these adjuvants were compared. We found that Quil A produced the highest titres against the recombinant P64k. Algammulin and the quaternary ammonium compound DDA induced the highest levels of antibodies against meningococci. We analysed the recognition of a set of linear peptides by antisera prepared against the protein combined with some of the adjuvants. The responses depended on the adjuvant used and the results have been confirmed by epitope mapping using overlapping peptides synthesised on pins.

Adjuvants, Immunologic↗

PubMed1996