No abstract

Antibodies are an effective line of defense in preventing infectious diseases. Highly potent neutralizing antibodies can intercept a virus before it attaches to its target cell and, thus, inactivate it. This ability is based on the antibodies' specific recognition of epitopes, the sites of the antigen to which antibodies bind. Thus, understanding the antibody/epitope interaction provides a basis for the rational design of preventive vaccines. It is assumed that immunization with the precise epitope, corresponding to an effective neutralizing antibody, would elicit the generation of similarly potent antibodies in the vaccinee. Such a vaccine would be a 'B-cell epitope-based vaccine', the implementation of which requires the ability to backtrack from a desired antibody to its corresponding epitope. In this article we discuss a range of methods that enable epitope discovery based on a specific antibody. Such a reversed immunological approach is the first step in the rational design of an epitope-based vaccine. Undoubtedly, the gold standard for epitope definition is x-ray analyses of crystals of antigen:antibody complexes. This method provides atomic resolution of the epitope; however, it is not readily applicable to many antigens and antibodies, and requires a very high degree of sophistication and expertise. Most other methods rely on the ability to monitor the binding of the antibody to antigen fragments or mutated variations. In mutagenesis of the antigen, loss of binding due to point modification of an amino acid residue is often considered an indication of an epitope component. In addition, computational combinatorial methods for epitope mapping are also useful. These methods rely on the ability of the antibody of interest to affinity isolate specific short peptides from combinatorial phage display peptide libraries. The peptides are then regarded as leads for the definition of the epitope corresponding to the antibody used to screen the peptide library. For epitope mapping, computational algorithms have been developed, such as Mapitope, which has recently been found to be effective in mapping conformational discontinuous epitopes. The pros and cons of various approaches towards epitope mapping are also discussed.

Color Doppler imaging helps differentiate placental chorioangioma from other placental lesions and may be useful in the prenatal follow-up of chorioangioma.

The human liver-type subunit of the key glycolytic enzyme, phosphofructokinase (PFKL), is encoded by a gene residing on chromosome 21. This chromosome, when triplicated, causes the phenotypic expression of Down's syndrome (trisomy 21). Increased phosphofructokinase activity, a result of gene dosage, is commonly found in erythrocytes and fibroblasts from Down's syndrome patients. We describe the construction of transgenic mice overexpressing PFKL for use as a well-defined model system, in which the effects of PFKL overexpression in various tissues, and throughout development, can be studied. Mice transgenic for a murine PFKL 'gene cDNA' hybrid construct were found to overexpress PFKL in a tissue-specific manner resembling that of the endogenous enzyme. Although unchanged in adult brain, PFK specific activity was found to have been almost doubled in brains of embryonic transgenic-PFKL mice, suggesting that the extra copies of the PFKL gene are expressed during the developmental period. This pattern of overexpression of PFKL in brains of transgenic-PFKL mice suggests that gene-dosage effects may be temporally separated from some of their consequences, adding an additional layer of complexity to the analysis of gene dosage in trisomy 21.