Construction of Naive and Immune Human Fab Phage-Display Library.

This protocol describes the processes involved in the generation of human antibody libraries in Fab format. The antibody repertoire is derived from peripheral blood mononucleocytes focusing on different immunoglobulin isotypes. A two-step cloning process was used to generate a diverse human Fab library for subsequent selection by phage display. The method can be applied for the generation of both naive and immune antibody libraries. The naive repertoire allows for the library to be applied for the generation of human monoclonal antibodies against a broad range of target antigens making it a useful resource for antibody generation. However, the immune repertoire will be focused against target antigens from a particular disease. The protocol will focus on the generation of the library including the panning process.

Generation and selection of naïve Fab library for parasitic antigen: Anti-BmSXP antibodies for lymphatic filariasis.

Phage display has been applied successfully as a tool for the generation of monoclonal antibodies (mAbs). Naive antibody libraries are unique as they are able to overcome several limitations associated with conventional mAb generation methods like the hybridoma technology. Here, we performed an in vitro selection and generation of Fab antibodies against Brugia malayi SXP protein (BmSXP), a recombinant antigen for the detection of lymphatic filariasis. We developed a naïve multi ethnic Fab antibody library with an estimated diversity of 2.99 × 109 . The antibody library was used to screen for mAbs against BmSXP recombinant antigen. Soluble monoclonal Fab antibodies against BmSXP were successfully isolated from the naïve library. The Fab antibodies obtained were expressed and analyzed to show its binding capability. The diversity obtained from a pool of donors from various ethnic groups allowed for a diverse antibody library to be generated. The mAbs obtained were also functional in soluble form, which makes it useful for further downstream applications. We believe that the Fab mAbs are valuable for further studies and could also contribute to improvements in the diagnosis of filariasis.

IQPA: isothermal nucleic acid amplification-based immunoassay using DNAzyme as the reporter system.

Immunoassays are often coupled to peroxidase activity for antigen detection. Sensitivity and speed of detection has been increased by the advent of hybrid methods such as immuno-PCR (polymerase chain reaction). However, a more simplified immunoassay that retains both colorimetric peroxidase detection and effective DNA amplification in a setting closer to field application conditions has been nonexistent. Here we describe a method that successfully combines a competitive immunoassay with the new isothermal quadruplex-primed amplification (QPA) to generate excess quadruplex reporter molecules with intrinsic peroxidase DNAzyme activity.

Development of an antigen-DNAzyme based probe for a direct antibody-antigen assay using the intrinsic DNAzyme activity of a daunomycin aptamer.

G-Quadruplex (G-4) structures are formed when G-rich DNA sequences fold into intra- or intermolecular four-stranded structures in the presence of metal ions. G-4-hemin complexes are often effective peroxidase-mimicking DNAzymes that are applied in many detection systems. This work reports the application of a G-rich daunomycin-specific aptamer for the development of an antibody-antigen detection assay. We investigated the ability of the daunomycin aptamer to efficiently catalyze the hemin-dependent peroxidase activity independent of daunomycin. A reporter probe consisting of biotinylated antigen and daunomycin aptamer coupled to streptavidin gold nanoparticles was successfully used to generate a colorimetric readout. In conclusion, the daunomycin aptamer can function as a robust alternative DNAzyme for the development of colorimetric assays.